Sarah H. Tolbert
UCLA, Los Angeles, CA
Synopsis of the presentation
In this presentation we explore the unique structural properties
of periodic surfactant-templated silicas and ordered mesoporous
silicas. Our results indicate that under hydrostatic compression,
these composites can be as stiff as bulk silica, but that deformations
are more elastic. At modest pressures (up to ~4 GPa), small angle
X-ray scattering is used to determine the volume compressibility.
In the composites, this compressibility is found to be essentially
identical to that of bulk vitreous silica despite the high organic
fraction (> 60 volume%), suggesting that nanometer scale architecture
can produce materials that are stiffer than the predictions of continuum
theories. At higher pressures, deformations of the nanometer scale
periodicity are observed, but unlike the pressure-induced distortions
seen in bulk silica, these distortions are reversible upon release
of pressure. Luminescence from probe molecules located within the
pores indicates that the silica framework supports the applied load
and that a more fluid environment exists within the pores, even
at very high pressures. These results are unified by the results
of high-pressure infrared spectroscopy. Modeling the peak shifts
shows that at modest pressure, the local silica bonding distorts
in much the same way that bulk silica distorts under pressure. At
higher pressures (above 4 GPa), atomic scale distortions cease and
are replaced by distortions on the nanometer length scale. These
nanometer scale distortions appear to be more reversible than the
atomic scale distortions that occur in bulk silica, thus explaining
the unique combination of high stiffness at moderate pressures and
good elasticity at high pressures. Tensile measurements on films
of these composites support the conclusions stated above - remarkable
elasticity is observed in these composities with measured strain-to-break
values that are over 10 fold higher than those observed in bulk
vitreous silica.
Key outstanding areas relevant to this presentation:
How does nanometer scale architecture combine with finite size
effects to control the mechanical properties of periodic nanoscale
ceramics? How do atomic scale deformations couple to deformations
on longer periodic lengthscales, particularly in materials that
are amorphous on the atomic scale?
Selected publications for background information
- Junjun Wu, Xiaoyang Liu, and Sarah H. Tolbert, "High-Pressure
Stability in Ordered Mesoporous Silicas: Rigidity and Elasticity
through Nanometer Scale Arches" , J. Phys. Chem. B,
104, 11837-11841, 2000.
- Junjun Wu, Liang Zhao, Eric L. Chronister and Sarah H. Tolbert,
"Elasticity through Nanoscale Distortions in Periodic Surfactant-Templated
Porous Silica under High Pressure", J. Phy. Chem.
B, 106, 5613-5621, 2002.
- Junjun Wu, Mehdi M. Abu-Omar, and Sarah H. Tolbert, "Fluorescent
Probes of the Molecular Environment within Mesostructured Silica/Surfactant
Composites under High Pressure", Nano Letters, 1,
27-311, 2001.
Contact information of the
speaker
Sarah Tolbert
Asst. Professor of Chemistry
Dept. of Chemistry and Biochemistry
UCLA
Los Angeles, CA 90095-1569
Phone: (310) 206-4767
FAX: (310) 206-4038
Email: tolbert@chem.ucla.edu
URL: http://www.chem.ucla.edu/dept/Faculty/tolbert/
Session Chair Contact Info
Ivar E. Reimanis
Associate Professor
Metallurgical and Materials Engineering Department
Colorado School of Mines
Golden, CO 80401
USA
Phone: 303-273-3549
Fax: 303-273-3057
email: reimanis@mines.edu
Web: www.mines.edu/academic/met/pe/faculty/reimanis.html
Poster Session
NASIM ALEM
Materials Science & Engineering
Northwestern University
Nanoscale Deformation and Fracture Behavior in Interfacial Microcomposites
Luke Brewer, Nasim Alem, Vinayak P. Dravid
Abstract: Directionally solidified eutectics (DSEs) present
an excellent model system for probing the hierarchical influence
of various microstructural elements on crack propagation and fracture
properties of microcomposites. The well-defined aligned microstructure
coupled with low-index high-symmetry crystallography of the phases
allows for experimental analysis and modeling with consistency and
with due consideration to various length-scales involved in the
DSE system. 1-3 In addition, the excellent high temperature strength
to weight ratio and the reasonably high creep resistance of DSEs
of oxide systems lends itself to potential applications in aerospace
technology and power generation systems. However, the low fracture
toughness of these materials at room temperature has limited their
widespread use as structural materials. To investigate the prevailing
mechanisms associated with interfacial fracture and deformation
behavior of DSEs, NixCo1-xO/ZrO2
has been chosen as a DSE model system. Diverse electron, x-ray and
neutron analytical tools are used to determine the interface structure,
chemistry, bonding, and residual stresses associated with the NixCo1-xO/ZrO2
system. Micro- and spatially resolved nano-indentation experiments
are also performed to monitor changes in local mechanical behavior
across DSE interfaces. NixCo1-xO/ZrO2
system shows no plastic deformation for x > 0.3, i.e. NiO-rich
compositions. However addition of CoO in solid solution changes
the interfacial fracture behavior of NixCo1-x/ZrO2
system towards enhanced plastic deformation within CoO, unidirectional
interfacial delamination, and secondary cracking ahead of the crack-tip.
This poster will present a working model describing all crack propagation
behavior in this system. The model is derived from extensive experimental
and analytical studies involving: interfacial structure, bonding
and "toughness", residual stress tensor distribution,
microstructural and crystallographic anisotropy, plasticity factors
and strain hardening coefficients of the phases. The model adequately,
albeit qualitatively, explains practically all experimental observations
of complex crack propagation behavior and provides significant general
clues about crack and deformation front propagation in microcomposite
system
AMIR AVISHAI
Materials Engineering
Technion - Israel Institute of Technology
The Influence of Si-Ca Additions on Interface Structure and
Chemistry in Cu-Al203 Composites
Amir Avishai and Wayne D. Kaplan
Abstract: Intergranular amorphous films are observed in
many ceramic systems. Recently, such films were observed at metal
ceramic interfaces (Cu-A1203).
In this work the microstructure of Cu-A1203
composites was investigated using analytical and High Resolution
TEM. Two different samples were prepared, with and without glass-forming
additives. The samples containing glass additives formed glass pockets
at the triple junctions as well as amorphous films at the Cu-A1203
interfaces. No amorphous phase was observed in the undoped sample,
neither at the triple junctions nor at the interfaces although an
excess of Ca and Si was measured at the A1203
grain boundaries. In the doped sample the Cu was found at triple
junctions, grain boundaries, and as occluded particles within the
alumina grains. No occluded particles were found in the glass-free
sample. The results indicate a specific role of Ca and Si during
Cu occlusion.
KAVAIPATTI R. BALASUBRAMANIAN
Materials Science & Engineering
Carnegie Mellon University
Hexagonal GdMn03 as a Thin Film
via Pulsed Laser Deposition
K.R. Balasubramanian and Paul Salvador
Abstract: The rare-earth manganates, RE Mn03,
crystallize in 2 different structures: the stable form for the larger
rare-earth manganates (RE = La, Ce, Pr, Nd, Sm, Gd, Tb) is orthorhombic
( Space Group: Pnma). while the stable form for the smaller rare-earth
manganates (RE = Ho, Er, Tin, Yb, Lu, Y and Dy) is hexagonal (Space
Group: P63cm). The emphasis of this poster will be on the stabilization
of metastable hexagonal GdMn03 as a thin film, and these results
will be compared to those obtained for YMn03. All the films were
synthesized via Pulsed Laser Deposition (PI.D) on different substrates,
while the remaining deposition conditions were held at fixed values.
The choice and orientation of the substrate determines the strain
and interfacial energies of the growing film. thus affecting the
phase selection. To differentiate the effects of interfacial energy
and strain energy, we deposited YMn03
on SrTi03(l 11) and Pt(l 11) - a
ceramic and a metal with similar lattice parameters. YMn03
grew in it's metastable orthorhombic form on SrTi03(l
11) and in it's stable hexagonal form on Pt(l 11). On Mg0(l 11)
crystals, which have been used to grow (OOl)-oriented hexagonal
YMn03, a mixture of orthorhombic and (001)-oriented hexagonal GdMn03
was obtained. The best films of phase-pure (OOl)-oriented hexagonal
GdMn03 were obtained on those substrates
with a buffer layer of YMn03 (Pt(l
11) and Mg0(l 11)). Finally, to demonstrate that interfacial energy
also predominates the phase selection of these metastable hexagonal
compounds, we developed polycrystalline substrates of YMn03
using normal ceramic processing techniques. Phase-pure hexagonal
GdMn03 films grew on these polycrystalline
substrates. We will discuss the use of these polycrystalline substrates
for the growth of other new materials.
CATHERINE M. BISHOP
Materials Science & Engineering
Massachusetts Institute of Technology
A Phase Field Model of Intergranular Glassy Films
C.M. Bishop and W.C. Carter
Abstract: The morphology of intergranular glassy films in
ceramics is determined by the thermo-dynamic boundary conditions
on the material and by the geometry of the boundary. A phase field
model that allows the exploration of these relationships is presented.
The equilibrium fields that solve the one-dimensional variational
problem are calculated and these results are confirmed by computer
simulation..
MANUEL E. BRITO
Ceramics Research Institute
Natl' Inst. AIST, Nagoya, JAPAN
Porous Alumina: A Different Story Via TEM
Manuel E. Brito, M. C. Valecillos* and N. Kondo*
* Synergy Materials Research Center, Natl' Inst. AIST, Nagoya, JAPAN
Abstract: Detailed studies "ad-hoc" of porous ceramics
by transmission electron microscopy (TEM) are hardly found in the
available literature. Among porous ceramics, those produced by partial
sintering are of technological and economic importance. Early stages
of sintering, where neck growth occurs, should be understood in
detail to take maximum advantage of it in the processing of porous
materials. Here, the microstructural evolution of alumina is analyzed
by TEM and related analytical techniques to clarify the role of
localized plastic deformation (a role till now completely ignored)
in the evolution of necks. For such a purpose, alumina powders were
cold isostatic pressed under different conditions followed by firing
under "mild" heating schedules.
KRISTEN BROSNAN
Penn State University
Microwave Sintering of Alumina Parts
Kristen Brosnan, Gary L. Messing, and Dinesh K. Agrawal
Abstract: Commercial green tubes of alumina (~17 mm length,
~9 mm inner diameter, and ~11 mm outer diameter) were used to study
the sintering kinetics and microstructural evolution under conventional
and microwave heating (at 2.45 GHz). Temperature during microwave
heating was measured with an infrared pyrometer and was calibrated
to +/- 10°C. With no hold at sintering temperature, microwave
sintered samples reached 98% TD at 1400°C, ~200°C lower
than conventionally sintered samples to the same density. Tube samples
microwave sintered to 98% TD at 1200°C in 120 minutes, however
the conventionally sintered sample were only 49% TD after 1000 minutes.
The activation energy for microwave sintering was 85 kJ/mol, whereas
conventionally sintered samples activation energy was 520 kJ/mol.
The exact mechanism for the lower activation energy for microwave
sintering can not be determined from the results of this study,
but enhanced diffusion may not be solely responsible. Grain growth
in both conventional and microwave sintered tubes was found to be
similar. It is concluded that microwave sintering can be used to
uniformly sinter commercial alumina parts.
JUN CAI
Department of Chemistry
University of Connecticut
Syntheses and Applications of Nanosize Perovskite Ceramics for
High Temperature Hydrogen Purification
Jun Cai1, Francis S. Galasso1,
H. Russell Kunz2, James M. Fenton2
1. Chemistry, University of Connecticut, 2. Chemical Engineering,
University of Connecticut
Abstract: Perovskite ceramic membranes have been successfully
fabricated by a variety of preparation methods to study their electronic
and ionic conductivities for high temperature hydrogen purification
in fuel cell applications. Solid state reaction, co-precipitation,
sol-gel, and microemulsion methods were used to prepare pure-phase
and transition-metal-doped perovskite BaCeO3
powders to study their effects on the particle size of powders and
the electronic and ionic conductivities of membranes. Perovskite
powders were ground and pressed to form ceramic pellets. The pellets
were sintered at 1500 oC to form dense ceramic membranes, which
were used for electronic and ionic conductivity studies. Various
transition metal dopants such as Gd3+,
Nd3+, and Mn2+/3+/4+
have been used to increase the oxygen vacancies in perovskite membranes
in order to increase the electronic and ionic conductivities. Because
all the reactant materials were homogeneously mixed in solutions
in co-precipitation, sol-gel, and microemulsion syntheses, perovskites
were formed at 900 oC, at least 200 oC lower than the calcination
temperature required for solid state preparations. The pH of the
reactant solutions has shown to greatly affect the phase transformation
and particle size of perovskites. Microemulsion syntheses produced
perovskite powders with the smallest particle size among these methods.
The particle size of perovskites formed has been as small as 40
nm even after calcination. The electronic conductivity of perovskite
membranes has been greatly enhanced by doping and it increased with
the increasing temperature. A high temperature electronic and protonic
conductivity measurement system has been built to study the effect
of doping and particle size on the high temperature hydrogen purification
ability of perovskite membranes in a hydrogen atmosphere.
JIANGLONG CHEN
Department of Materials Science and Engineering, Massachusetts
Institute of Technology
Influence of Microstructure on the Response ofBi2Mo3012
to Alcohols
Jianglong Chen, Richard L. Smith
Abstract: Bismuth molybdate are widely used as catalysts
for the partial oxidation of hydrocarbons, for example the oxidation
of propene to acrolien, and have also been proposed for conductance-type
gas sensor applications. Because the sensory response of phases
in the Bi203-Mo03
system are generally based on bulk conductance changes, their response
is virtually insensitive to humidity, unlike more traditional semiconducting
gas sensors, such as Sn02 and ZnO.
Very little is known, however, about the influence of microstructure
on the electrical or sensory behavior of the bismuth molybdates.
In this poster, we will present the results of experiments designed
to probe the influence of both surface and bulk microstructure (including
grain size, porosity, and surface morphology) on the sensory properties
ofBi2Mo3012.
TAMMY P. CHOU
Materials Science and Engineering
University of Washington
Nanorods Of Various Oxides And Hierarchically-Structured Mesoporous
Silica By Sol Electrophoresis
Tammy P. Chou, Steven J. Limmer, and Guozhong Cao
Abstract: Ceramic oxide materials at the nano-scale have
recently gained considerable attention for use in optical applications.
Much interest into the tunable functionality of these small-scale
optical materials has been the focus for possible use in lasers,
light filters, sensors, detectors, solar cells, and photocatalysis.
We present a study of the formation of nanorods of various oxide
ceramics and hierarchically-structured mesoporous silica by means
of template-based growth involving the combination of sol-gel processing
and electrophoretic deposition. Both single metal oxide (TiO2,
SiO2) and complex oxide (BaTiO3,
Sr2Nb2O7,
Pb(Zr0.52Ti0.48)O3)
nanorods, as well as mesoporous silica nanorods with ordered pore
structure, have been grown using this method. Various oxide nanorods,
approximately 100-200 nanometers in diameter and 10 microns in length,
with uniform size and near unidirectional alignment was grown. Desired
stoichiometric chemical composition and crystal structure of the
oxide nanorods was readily achieved through appropriate sol preparation
and heat treatment for crystallization and densification. By tuning
the surfaces of these nanomaterials, through self-assembly of dye
molecules or metal particles, the functionality of these nanorod
structures could be tailored accordingly.
CHRISTOPHER W. DEEB
Materials Science and Engineering
Case Western Reserve University
Solid-State Formation of Ni Silicide Contacts to SiC at Low
Temperatures
C. Deeb and A. H. Heuer
Abstract: Low resistance, ohmic contacts to n-type 6H-SiC
are formed using the solid-state reaction between a sacrificial
silicon layer and a sputter deposited Ni layer. The reaction temperature
used in this work is 300 C. Comparison of the reaction between Ni
and both sputter deposited Si and low pressure chemical vapor deposited
(LPCVD) Si has been performed using transmission electron microscopy.
Contact resistivity has been measured to be in the 10-4 ?cm2 range
using circular TLM structures. This compares well with standard
Ni contacts which require annealing at temperatures in excess of
800 C for practical operation.
R. PETER DILLON
Materials Science and Engineering
University of California, Irvine
Superplasticity in 8 mol% Y2O3
Cubic Stabilized ZrO2 with Intergranular
Silica
R. Peter Dillon and Martha Mecartney
Abstract: The potential to net shape form components using
superplastic forming in ceramic materials has gained interest since
superplasticity was reported in yttria tetragonal zirconia polycrystals
(Y-TZP) in 1986. The primary requirements for high temperature superplasticity
in ceramics are a stable fine grain size and grain boundary sliding
with limited grain separation (cavitation) during high temperature
deformation. Research in our group has shown that incorporating
a viscous second phase, such as silica, allows superplastic behavior
in a ceramic that has not traditionally exhibited superplasticity.
This poster will demonstrate that significant deformation in 8 mol%
Y203 cubic stabilized ZrO2 (8Y-CSZ)
can be achieved by the addition of a silica intergranular phase.
This material can exhibit deformation over 500% in compression and
over 500% elongation in tension at temperatures from 1400 to 1500C.
The role of the intergranular phase limiting grain growth during
deformation and how the intergranular phase assists in grain boundary
sliding will be discussed.
VADIM A DROZD
Kiev Taras Shevchenko University
Kiev, Ukraine
Synthesis and Resistivity of Polycrystalline Srl-x Kx Pb03-y
Solid Solutions
Vadim Drozd, Alexander Gabovich, Marek Pekala, Valery Boychuk,
Dmitry P. Moiseev, Sergey Nediiko
Abstract: New ceramics of Srl-xKxPb03-y
with x = 0, 0.05, 0.1, 0.15 and 0.2 were synthesized and analyzed.
Temperature (T) variations of resistivity (R) and thermopower (S)
were measured for 20 K < T < 300 K. For low T thermal resistivity
coefficients dR/dT for all compositions were found to be negative,
which suggests localization of current carriers or the appearance
of the dielectric gap in the electron spectrum. The analysis of
the dependences R(T) shows that the electrical conduction has at
least a substantial contribution from the tunneling processes at
grain boundaries. The thermoelectric power S is negative for all
compositions and for all T, thus indicating the electron-like conduction.
The collection of data demonstrates that the parent substance SrPb03/nis
on the verge of the metal-insulator transition and different kinds
of doping may substantially change transport properties and a degree
of current carrier degeneracy. The system seems to be promising
as a building block for new superconducting families.
JENS EICHLER
Materials Science
Technische Universitat Darmstadt
Mechanical Properties Of Nanocrystalline Zirconia
J. Eichler, U. Eisele, J. Rodel
Abstract: The influences of grain size and yttria dopant
content on the crack tip toughness and R-curve behavior of nanocrystalline
zirconia were studied. No relevant literature is available on how
the mechanical properties will change down to lOOnm and if the models
for microcrystalline materials are still applicable. R-curves were
obtained by measuring 0.8mm thick CT-samples in order to investigate
the effect of transformation toughening. The onset of the R-curves
were compared with KO-values obtained by CTOD measurements on cracks
caused by vickers indentation. For nanocrystalline zirconia both
measurements gave a KO of 2.2 MPa.ml/2 independent of the dopant
content. X-ray measurements and investigations in order to get the
height of the process zone complement the other studies.
GEOFF E. FAIR
Materials Department
University of California, Santa Barbara
Processing of Ceramic Composites with Three-Dimensional Architectures
Designed to Produce a Threshold Strength
Geoff E. Fair and Fred F. Lange
Abstract: Threshold strength behavior has recently been
observed in ceramic laminates utilizing thin compressive layers.
Our work focuses on developing 3D architectures of thin compressive
layers to produce composites with isotropic mechanical properties.
Ceramic microspheres are produced by drying aqueous slurry droplets
with an immiscible hygroscopic liquid while carefully controlling
the interparticle pair potential. Microspheres are coated using
spouted bed technology in which the coating is applied by atomizing
the coating slurry into an air stream suspending the particles.
The coated spheres are reconstituted with water to a plastic state
and consolidated into composite bodies using both uniaxial and isotatic
pressing techniques.
ROGER FRENCH
DuPont Co. Central Research
Wilmington, Delaware
London Dispersion Forces and Full Spectral Hamaker Coefficients
for Nanostructured Amorphous Films with Multilayer or Graded Structures
Roger H. French1, Lin K. Denoyer2, V. Adrian Parsegian3, Rudolf
Podgornik3
1. DuPont Co. Central Research, E356-384 Exp. Sta. Wilmington DE
19880
2. Deconvolution and Entropy Consulting, 755 Snyder Hill Rd, Ithaca
NY 14856
3. National Institute of Health Laboratory of Physical and Structural
Biology, Section on Molecular Biophysics. Bethesda MD 20892.
Abstract: London dispersion forces1 play a role in interface
and surface energies, wetting, surficial and interfacial films,
flocculation of colloidal systems, force microscopy and other physical
phenomena. These forces are represented by the Hamaker coefficient
(A), which is calculated directly from the optical properties and
electronic structure using the London dispersion spectra and Lifshitz
theory. Previously Hamaker coefficients were calculated for simple
multilayer structures of 3 or 5 materials in configurations such
as 1|2|1, 1|2|3 or 1|2|3|2|1. We have now been able to generalize
the Lifshitz calculations, using full spectral data and spatially
varying data, for multilayer configurations with arbitrary numbers
of layers. These calculations fully account for the role of retardation
and the speed of light which can become important when layer thickness
increases, as for example in surficial films. The variational pathway
for the thermodynamic free energy calculation is then defined by
designating the thickness of one of the layers as variable. This
approach allows one to consider, from the point of view of the London
dispersion interaction, the relative stability to variation of a
multilayer interface in which some layers may want to thicken (wet)
while other layers might want to thin (dewet) if allowed to proceed
to thermodynamic equilibrium. This work was partially funded by
NSF Award DMR-0010062 in cooperation with EU Commission Contract
G5RD-CT-2001-00586
SUSAN GALAL YOUSEF
Darmstadt University of Technology
Microcracking in alumina due to anisotropic thermal expansion
in experiment and simulation
S. Gala! Yousef, J. Roedel, A. Zimmermann
Abstract: The effect of microcracking upon cooling was studied
in alumina as a function of grain size experimentally and by FEM
simulation. MgO-doped alumina samples in a grain size range between
10 micrometer and 99 micrometer were prepared. The onset of microcracking
was experimentally analysed by measuring the temperature dependent
Young's modulus, thermal diffusivity and dilatometric measurements.
Studies of temperature dependent acoustic emission are in preparation.
With an object-oriented finite element code (OOF, NIST) the accumulated
stress after cooling from the fabrication temperature was simulated,
the microcrack initiation was calculated using a Griffith like fracture
criterion. This work presents a first attempt of a comparison between
simulation and experimental results.
EDWIN GARCIA
Massachusetts Institute of Technology
Microstructural Design of Rechargeable Batteries
Edwin Garcia, Catherine M. Bishop, W. Craig Carter, Stephen
A. Langer, D Pimpa LImthongkul, Yet-Ming Chiang
Abstract: The properties of rechargeable lithium ion batteries
are determined by the electrochemical and kinetic properties of
their constituent materials as well as their underlying microstructure.
For instance, microstructural parameters such as lithium manganese
oxide particle volume fraction and particle size distribution affect
the macroscopic power and energy density of the system. Prediction
of macroscopic response requires a model that incorporates the details
of the microscopic arrangement of materials and treats pertinent
spatial and crystallographic aspects of microstructure. Furthermore,
models should account for coupled material effects such as stress
development and local concentration changes. We have developed a
method that uses microscopic information and constitutive material
properties to calculate the macroscopic response of rechargeable
lithium ion batteries. Previous attempts of incorporating microstructural
effects on the properties of batteries have used mean-field approaches;
such calculations will not capture potentially important effects
such as localized electric shielding, stress development, or heat
dissipation. The technique is demonstrated for a typical lithium
ion battery microstructure and demonstrates the beneficial effect
of microstructural design on the compromise between power density
and capacity.
EDWIN GARCIA
Massachusetts Institute of Technology
The Effect of Crystallographic Texture on Piezoelectric Ceramics
Edwin Garcia, W. Craig Carter, Stephen A. Langer
Abstract: The effect of Crystallographic texture on the
macroscopic piezoelectric response of ceramic PZN-PT and Barium
Titanate is modeled and calculated for polycrystalline microstructures.
The model consists of an assembly of grains, each poled in one its
crystallographically equivalent "soft" directions. The
orientation of each grain is randomly chosen from a texture orientation
distribution-a modified March-Dollase distribution of the c-axis
of PZN-PT and Barium Titanate. The March-Dollase parameters are
varied and are used to generate a set of microstructural instances.
The macroscopic response of each set is used to develop statistical
inferences about microstructural behaviour as a function of texture.
In both PZN-PT and Barium Titanate, the maximum macroscopic piezoelectric
response in a specific sample orientation is observed for a slightly
untextured polycrystal. The optimal texture is determined by comparing
the coefficients against the corresponding single crystal piezoelectric
coefficient. The effect of grain size versus sample size is also
considered as a statistical sampling of the variation of response
within a polycrystalline microstructure; results show that variations
of the macroscopic response is a decreasing function of the ratio
(sample size)/(grain size). The microscopic distribution of polarization
and elastic energy density are calculated and their correlated effects
on macroscopic response is discussed.
ROSARIO A. GERHARDT
Materials Science and Engineering
Georgia Institute of Technology
Frequency Dependence And Percolation Behavior Of Multiphase
Materials
Rosario Gerhardt
Abstract: Ceramic materials can be considered to be multiphase
as the presence of porosity and grain boundary layers is common
and can result in electrical responses, which are different from
the response of the bulk grains. To detect electrical inhomogeneities,
it is desirable to use ac measurements because dc measurements are
usually dominated by the electrical response of the most interconnected
path, which is not necessarily the path of least resistance. On
the other hand, too high a frequency or too high a voltage can also
result in tunneling effects. Composites containing mixtures of insulating
and conducting phases will be used as examples. At low volume fractions
of the added second phase, the behavior is found to be dominated
by the matrix material while interconnectivity dominates in the
cross-over (percolation) region. Transformation of the impedance
data into other dielectric formalisms is extremely useful for identifying
differences between similar samples with different microstructures,
especially in the cross-over region. This type of analysis can be
extended to include many ceramic materials such as solid electrolytes
for fuel cells and ferroelectric materials for various applications.
Developing an understanding of these effects in a given material
system will permit characterization of their microstructure in a
non-destructive way.
* Funded in part by NSF under DMR-0076153
EDWARD P GORZKOWSKI
Materials Science and Engineering
Lehigh University
Effects of lnterfacial Chemistry on Single Crystal Growth of
PMN-PT
Edward P Gorzkowski, P.T. King, A. M. Scotch, D.J. Rockosi,
M. P. Harmer, and H. M. Chan
Abstract: Single crystals ofPb(Mgl/3
Nb2/3)03
- 35 mol % PbTi03 [PMN-35PT] have
been grown using the Seeded Polycrystal Conversion (SPC) process.
Prior work has shown that chemistry and volume fraction of second
phase additions are two factors that can control the single crystal
growth rate in this process. The current work focuses on characterizing
the liquid film composition at key interfaces (e.g. single crystal/matrix
interface) during the firing/growth cycle. Analysis of these interfaces
is expected to provide an understanding of the underlying mechanisms
controlling single crystal and matrix grain growth. Specific boundaries
were selected for characterization and prepared for STEM analysis
using a dual-beam focused ion beam (FIB) instrument. The interfacial
chemistry was characterized using high-resolution analytical electron
microscopy (AEM). The viability and application of measuring oxygen
content directly in the presence of heavy elements using the Zeta
factor approach will be presented.
GREGORY M. GRATSON
Materials Science and Engineering
University of Illinois, Urbana
Directed Assembly of Three Dimensional Periodic Ceramics
Gregory M. Gratson, Robert F. Shepherd, James E. Smay, and Jennifer
A. Lewis
Abstract: Mesoscale periodic structures were fabricated
via robotic deposition of concentrated colloidal gels. During this
directed assembly process, a concentrated colloidal gel-based "ink"
(Phi ~ 0.5) is extruded through a cylindrical nozzle (diameter ~
100 to 1000 micron) to architect complex, 3-D structures in a layer-by-layer
build sequence. We have studied the rheological properties (e.g.,
G' and ty) of inks with varying gel strength, colloid volume fraction,
and particle size and investigated these effects on this directed
assembly process. Currently, we are exploring new ink designs in
order to fabricate structures at smaller length scales (~ 10 micron
or less). Such structures may find application as functional ceramics,
composites, tissue engineering scaffolds, or photonic band gap materials.
YAMATO HAYASHI
ISIR, Osaka University
Fabrication Of Metal Nano-Particles Supported Materials By Ultrasonic
Shock Wave
Yamato Hayashi*, Tohru Sekino, Koichi Niihara
Abstract: In general, the properties of specific energy
source determine the course of a chemical reaction. The ultrasonic
irradiation differs from traditional energy sources in duration,
pressure, and energy per molecule, and it is a unique means on the
interaction between energy and matter. It is well known that the
chemical reactions which take place under conventional conditions
can be accelerated by ultrasonic irradiation. In this study, the
process of nano-sized metal deposition on various kinds of materials
were investigated for ultrasonic shock wave system at room temperature.
By choosing suitable conditions, it is reasonable to expect that
these simple nanochemical processes can be extended to obtain nano-sized
metal particles from metal oxide. Thus applications by using these
reactions were investigated to prepare the nano-sized metal particles
on various materials at ecology, and mechanisms were investigated.
PHILIP M. HUSEMAN
Materials Science & Engineering
Ohio State University
Fabrication Of Homogeneous, Dense, Near Net-Shaped Mgo/Fe-Si
Composites By The Displacive Compensation Of Porosity Within Colloidal
Filtration Compacts
Philip M. Huseman, Kenneth H. Sandhage, and Henk Verweij
Abstract: Fe3Si/MgO composites
are expected to exhibit an attractive combination of properties
(e.g., excellent resistance to high temperature corrosion, thermal
cycling, and creep). Of particular interest for thermal cycling
applications is the close match in the coefficients of thermal expansion
between Fe3Si and MgO. Furthermore,
the fabrication of such composites with sub-micron phases is expected
to result in improved mechanical performance. In order to produce
dense Fe3Si/MgO composites with the
desired (fine, uniform) phase distributions and in complex shapes,
a hybrid preparation route has been developed that merges the attractive
features of colloidal processing with those of near net-shape reaction
processing. Porous, shaped compacts comprised of well-dispersed,
homogeneous, isometric SiO2 and Fe2O3
precursor particles were first prepared. Monodispersed Fe2O3
and SiO2 particles were mixed to
yield colloidally stable dispersions. The dispersions were then
filtered and lightly sintered at 1100°C. Magnesium gas was then
allowed to infiltrate and react with the rigid compacts at 900°C
to produce near net-shaped Fe3Si/MgO
composites. The conversion of a mixture of SiO2
and Fe2O3
into a mixture of MgO and Fe3Si results in a volume expansion that
can fill the pores within the porous compacts (i.e., reaction-induced
densification without sintering). Because the preforms remain rigid
during such reaction, the final, dense composites retain the shape
of the starting preforms.
JACOB L. JONES
Materials Engineering
Purdue University
Quantifying Texture in Piezoelectric Bismuth Titanate
Jacob L. Jones, Keith J. Bowman, and Elliott B. Slamovich
Abstract: Quantifying orientation in strongly anisotropic
bismuth titanate processed via tape casting is critical to understanding
properties. Prior methods concentrating on conventional diffraction
pattern peak intensity comparison are insufficient for complete
description of non-axisymmetric symmetries. When poled in the most
efficient poling direction for these devices, the symmetry is truly
orthorhombic and orientation analysis in this poling direction has
not been considered. Methods displayed in this poster include the
use of an area detector to generate pole figures and the calculation
of a complete orientation distribution function. Comparison with
traditional powder diffractometry methods are given.
EVA JUD
ETH Zurich
Zurich, Switzerland
What is "Activated" Sintering?
Eva Jud*, Christoph Huwiler and Ludwig J. Gauckler
Abstract: The term "activated sintering" is used
when a material sinters at unusual low temperature with unusual
high sintering rates to full density due to the aid of a second
minor phase. Many results of examples exist in literature for this
phenomenon including metallic and ceramic two phase systems. We
report the sintering characteristics and grain growth of CeO2
solid solutions (ss) with minor amounts of transition metal oxides
at temperatures as low as 900°C arising in fully dense material
with a grain size of <100nm. The grain boundaries consist of
1-3 nm thick amorphous material when sintered at low temperatures
for short time. The analysis of the sintering process using Herring's
scaling-law reveals that densification occurs predominantly via
grain boundary diffusion whereas the densification of undoped CeO2
ss is governed by both, grain boundary as well as volume diffusion.
Grain growth in the later stage of sintering at low sintering temperatures
is extremely slow in doped materials whereas normal third stage
grain growth prevails in undoped material. We used models proposed
by Johnson for "activated" sintering and Luo for the stability
of amorphous grain boundary films to explain our observations
SERGEI V. KALININ
University of Pennsylvania
Scanning Impedance Microscopy/Nanoimpedance Spectroscopy: Frequency
Dependent Transport At Interfaces
Sergei V. Kalinin, Rui Shao, and Dawn A. Bonnell
Abstract: The progress in micro- and nanoelectronics necessitates
an understanding of the structure and properties of materials on
the local level. In recent years, scanning probe techniques have
been used to measure local dc or ac transport down to the nanometer
scale. The paradigms for the current and potential sensitive SPM
measurements of local ac and dc transport properties are described,
including Scanning Impedance Microscopy - a novel microscopic technique
for the measurement of local electronic properties. The frequency
dependence of transport across bicrystal grain boundaries and metal/silicon
diode interfaces yields local resistance, capacitance, and relaxation
times associated with interfacial processes. The tip/surface response
functions in the limits of high and low frequency are derived, from
which measurement independent properties can be obtained. To access
the local properties of heterogeneous systems, the AFM tip is used
as a moving probe of conventional impedance spectroscopy. This technique,
referred to as nanoimpedance spectroscopy, is applied to the characterization
of the local properties of several model nanostructures.
Field Induced Dielectric Constant Variation At Interfaces
S.V. Kalinin, G. Duscher* and D.A. Bonnell
(*North Carolina State University)
Abstract: In order to investigate fundamental processes
involved in transport across interfaces in transition metal oxides,
we have examined a series of SrTiO3
bicrystals with controlled misorientation. High-resolution transmission
electron microscopy and energy loss near edge structure have confirmed
the atomic structures of the interfaces and provided some information
about local electronic structures at the interfaces. A variety of
Scanning Probe based measurements of local transport characterizes
room temperature properties. Temperature dependent electronic transport
measurements have been made in the range of 100 to 400 K. Specifically,
four probe resistance measurements and impedance spectroscopy were
performed in this temperature range. These results, particularly
those from the low temperature measurements, suggest that the dielectric
constant in the vicinity of the grain boundary differs from that
of the bulk. This phenomenon has not previously been observed and
is unexpected in the context of current models. The basis of this
behavior will be speculated.
Defect Mediated Transport In Molecular Devices
Sergei V. Kalinin, Marcus Freitag, A.T. Johnson, and Dawn A.
Bonnell
Abstract: Defects and proximity effects will play a crucial
and perhaps limiting role in the behavior of nanoscale functional
devices. An understanding of these issues requires knowledge of
the local electronic structures of individual defects. We have developed
Scanning Impedance Microscopy (SIM) in which a probe tip acts simultaneously
as a local gate and an electrostatic probe of local potential to
yield frequency dependent transport properties. When used in conjunction
with Scanning Gate Microscopy (SGM), electronic structural information
about individual defects is obtained. This will be illustrated for
1-D transport along a wire, specifically through organic nanowires
and semiconducting single-wall carbon nanotubes. In the latter case,
the perturbation of the valence band edge at the defect is quantified
from a defect 'turn on' voltage. A relation between the magnitude
of the local perturbation and the strength of the defect in terms
of transport resistance is derived. Ultimately nanosized wires will
need to be integrated into complex systems through electrical contacts.
The potential impact of proximity effects will be illustrated with
measurements of size dependent contact potential of metallic clusters
on substrates.
WAYNE D. KAPLAN
Materials Engineering
Technion - Israel Institute of Technology
Atomistic Study of Structural Correlations and Wetting Behavior
at a Model Metal-Ceramic Interface
Wayne D. Kaplan
Abstract: The wetting properties of liquid metals on solid
ceramics are important in a variety of applications. The microscopic
correlations between the structure in the solid and the structure
in the liquid near the interface, and how they may affect the macroscopic
phenomenon of wetting, have not been fully addressed. Historically,
this stems from the technical difficulties in experimentally accessing
the structure of an interface between a solid and a liquid. Atomistic
simulations offer direct access to the local structure at the interface.
In this study a model system for a generic solid-liquid metal heterophase
interface is introduced. The solid is assumed to be composed of
static atoms positioned in an ideal lattice, and the liquid metal
is introduced adjacent to several different terminating planes of
the solid. Molecular dynamics is applied to study the structure
in the liquid at the interface and wetting behavior as a function
of different crystallographic orientations and at different temperatures
above the melting point of the metal. It is found that the liquid
exhibits ordering both perpendicular and parallel to the interface.
In the perpendicular direction, the order is characterized by density
oscillations, which decay with distance from the interface. The
decay distance is dependent on the structure of the solid and the
properties of the liquid. If good wetting exists between the liquid
and the solid, layering is found to exist even when no in-plane
order is present in the liquid. Correlations between the simulated
model system and wetting of alumina by liquid Al will be presented.
MAXIM KELMAN
Materials Science & Engineering
Stanford University
Effect Of Thin Film Stress On Structural And Electrical Properties
Of PZT Thin Films
Maxim B. Kelman, Paul C. McIntyre, Bryan C. Hendrix, Steven
M. Bilodeau, Jeffrey F. Roeder, Sean Brennan, Alexei Gruverman
Abstract: We have investigated the structural and electrical
properties of Pb(Zr0.35Ti0.65)O3
thin films of thickness from 700Å to 4000Å. Using
high-resolution x-ray diffraction, electron backscatter diffraction
and electrical measurements, we have observed that the thinnest
as-deposited PZT films of 1000Å and less are rhombohedral,
while the thicker films are partially tetragonal and partially rhombohedral.
X-ray depth profiling was used to show that thicker as-deposited
PZT films are tetragonal at the surface and rhombohedral at the
substrate interface. Piezoresponse imaging was used to show that
in the as-deposited PZT films, each grain contains a single ferroelastic
domain. Relative volume fractions of the tetragonal and rhombohedral
phases change as a result of post-deposition annealing treatment.
The volume fraction of the rhombohedral phase increases for intermediate
temperature (~400ºC) anneals and decreases for high temperature
anneals (T>500ºC). The changes in relative volume fractions
of the tetragonal and rhombohedral phases affect the coercive field,
which increases with intermediate temperature anneals and decreases
for high temperature anneals. Wafer curvature and x-ray diffraction
stress measurements showed that the observed structure of the PZT
is consistent with the theoretically predicted stress-induced phase
transformation from the equilibrium tetragonal into the rhombohedral
phase.
RYAN KERSHNER
Department of Materials Science and Engineering
Massachusetts Institute of Technology
Electrophoretic Assembly of Micron Scale Silica Particles Using
Patterned Microelectrodes
Ryan J. Kershner and Michael J. Cima
Abstract: A system of noble metal microelectrodes was prepared
by lithographic patterning on a sapphire substrate. The electrodes
were used to manipulate micron scale ceramic particles in-plane.
The particles were imaged in transmission using an inverted metallurgical
microscope focused on the plane of interest. The use of a digital
video system allowed the real time motion and packing of particles
at the electrodes to be observed directly during application of
a DC field. The particle motion was characterized as a function
of field strength, pH, and ionic strength of the background electrolyte.
Particles were also seen to adhere to the sapphire substrate near
the electrodes during application of the field. A technique for
tracking the two dimensional stochastic motion of particles settled
on the substrate was developed and used to characterize the adhesion
as a function of pH and ionic strength. Electrokinetic measurements
for the particles and substrate were used as inputs to a dissimilar
surface charge interaction model. These experiments are compared
with a similar assembly process of silica particles using electrodes
patterned on a quartz substrate.
JOHN KIEFFER
Materials Science and Engineering
University of Michigan
Phase Transformation and Structural Disorder in Cristobalite
Silica
L. Huang and J. Kieffer
Abstract: still to come
UNGSOO KIM
Whiteware Research Center
NYSCC at Alfred University
PVA Binder Migration via Polymeric Interactions
Ungsoo Kim and William Carty
Abstract: Interactions between polymeric additives used
for spray drying process substantially influence the properties
of polymers and can adversely affect the properties of dry pressed
body. Flory-Huggins calculations predict that the interaction between
polymers in aqueous solution results in either a homogeneous or
phase-separated solution depending on the functional groups and
chain length of polymers. Light scattering and optical microscopy
studies for polymer mixtures confirm these results. PVA can be stained
to determine its location within the spray dried granule to ascertain
the effect of other polymers (dispersants and plasticizers) on binder
migration. Polymer systems have been identified that reduce binder
migration, potentially eliminating case-hardening in spray dried
granules and the subsequent problems observed during compaction.
MAKSIM V. KIREITSEU
Institute of Machine Reliability
Minsk, Belarus
Modeling The Kinetic Of Micro Plasmic Oxidizing Technology Under
Pulse Current Regimes
Sergey Yerakhavets, Dr. Maksim Kireitseu, V. Basenuk
Abstract: A model is presented for the micro plasmic oxidizing
of aluminum or its alloy. The model is based on the space-charge-limited
drift of negative oxygen ions through the growing oxide film to
react at the aluminum dioxide interface. In the initial linear growth
region, the supply of ions from the plasma determines the growth,
whilst for longer periods the drift of ions through the oxide gives
rise to parabolic growth kinetics. The theory is consistent with
the lack of orientation dependence observed for the plasma oxidation
of AI. It is applicable over the whole of the growth kinetics, for
oxidizing in both pulse and periodic alternating current modes.
The dependence of current and voltage with time during the process
may also be predicted. The theory is found to be applicable to oxide
growth occurring in micro arc plasmic oxidizing. The relevant validity
of the model is grounded through mechanical characterization of
obtained alumina-coated samples.
DMITRI O. KLENOV
Materials Department
University of California, Santa Barbara
Studies Of Oxygen Vacancies In Epitaxial La0.5Sr0.5CoO3-D
Thin Films
D.O. Klenov*, W. Donner**, A.J. Jacobson***, S. Stemmer*
* Dept of Materials, University of California, Santa Barbara; **
Dept of Physics, University of Houston; *** Dept of Chemistry, University
of Houston
Abstract: Mixed ionic-electronic
conductors with the perovskite structure, such as La0.5Sr0.5CoO3-d
(LSCO) are of interest for oxygen transport membranes, electrode
for solid oxide fuel cells and as oxygen sensor because of their
high electronic and oxygen ionic conductivity. Thin films of these
materials have several potential technological advantages such as
lower device operating temperatures, which would reduce costs and
materials degradation problems. Thin films are also of scientific
interest because they can be used to study the electronic and oxygen
transport properties of materials, interfaces and surfaces along
controlled orientations and in structurally highly perfect materials.
The excellent oxygen transport properties of these oxides are based
on a high concentration of oxygen vacancies, that tend to form ordered
superstructures at low temperatures. In this study we have optimized
an rf sputtering deposition process to produce epitaxial cation
stoichiometric LSCO thin films from a single target. Film microstructures
were studied using high-resolution transmission electron microscopy
and X-ray diffraction and related to the films electrical resistivity.
We have also investigated the nature of oxygen vacancy ordering
as a function of film stoichiometry, post-deposition annealing treatment,
and stresses arising from the thermal and lattice mismatch with
the substrate. We will discuss the implications of the transport
properties of the films.
YOUNG-HAG KOH
Materials Science & Engineering
University of Michigan
New Fabrication Method for Strong and Bioactive Porous Bioceramics
Young-Hag Koh and John W. Halloran
Materials Science and Engineering Department,
University of Michigan-Ann Arbor, USA
Hyoun-Ee Kim
School of Materials Science and Engineering,
Seoul National University, Seoul, Korea)
Abstract: A New fabrication method for fabricating porous
bioceramics was developed using coextrusion process in order to
improve the control of the pore geometry and the compressive strength.
This porous body showed a uniform array of macrochannels on the
sintered bioceramic body, such as calcium phosphate and tetragonal
zirconia polycrystal (TZP). Specially, the macrochannels on sintered
strong TZP body were clad on the inside with bioactive calcium phosphate
to ensure the osteoconductivity, while maintaining the high compressive
strength. Furthermore, 3-directionally macro channeled bioceramics
were also fabricated in order to improve the osteoconductivity.
SAKI KRISHNAMURTHY
Department of Metallurgical and Materials Engineering
Colorado School of Mines
Determination of Toughness of Compressively Stressed Cr2N Films
on Brass Substrates
Saki Krishnamurthy and Ivar E. Reimanis
Abstract: Cracking in chromium nitride films of different
compositions (CrN and Cr2N) is examined
by conducting controlled fracture experiments in which the brass
substrate is loaded in uniaxial tension. The fracture toughness
of the film is estimated using a model developed by Klingbeil et
al. in which the stress required to initiate cracks is used. These
results are compared with direct measurements of fracture toughness
determined by measuring the displacement fields ahead of the crack
tip using electron beam moire. It is shown that residual stress
measured via glancing angle x-ray diffraction, film composition
and microstructure affect the fracture toughness.
ZDRAVKO KUTNJAK
Jozef Stefan Institute
Ljubljana, Slovenia
Nonlinear Dielectric Properties Of Relaxor Ceramics
Zdravko Kutnjak
Abstract: The quasistatic and the third harmonic third order
nonlinear dielectric response was measured in incipient ferroelectric
6/65/35 PLZT ceramics and in relaxor 9/65/35 PLZT ceramics. The
results are discussed within the frame of the newly obtained E-T
phase diagram of relaxor PLZT ceramics and the spherical random
bond random field model.
WEI LAI
Materials Science
California Institute of Technology
Preparation And Characterization Of La2Zr2-XMgXO7-Î
Pyrochlores By Sol-Gel Method
W. Lai, ZP. Shao, S. M. Haile
Abstract: Pyrochlores La2Zr2-xMgxO7-Î
(x=0, 0.1, 0.2, 0.3, 0.4) were prepared by a sol-gel method using
both EDTA and citric acid as the chelants. The particle size of
La2Zr2O7
was found to increase with the calcination temperature and time.
The sintering ability of as-synthesized powders was studied using
isostatic cool pressing and uniaxial pressing respectively. Electrical
conductivies under wet nitrogen were measured by AC complex impedance.
It was shown that the conductivity reached its maxima at an optimal
doping level.
XIAOJUN LEI
Materials Science & Engineering
University of Pennsylvania
Atomic Polarization On Ferroelectric Surfaces: A New Route Toward
Complex Nanostructures
S.V. Kalinin, T. Alvarez, X. Lei, Z. Hu, J.H. Ferris, D.A. Bonnell
Abstract: The potential to assemble dissimilar molecular
or nanostructural elements into structures with complex functionality
has motivated considerable activity in several scientific disciplines.
In recent advances in assembling nanostructures complex functionality
has been achieved in a few select systems. In order to realize the
potential inherent in nanodevices, methods of assembling a range
of dissimilar elements and integrating them into systems must be
developed by controlling structural elements with diverse properties,
locating them in pre defined positions. This poster will describe
a novel approach that controls local reactivity of ferroelectric
surfaces due to variations in atomic polarization. We will show
that atomic polarization can be controlled with an electron beam,
as well as the local field from a probe tip, and demonstrate that
chemical reactivity is domain specific based on control of local
electronic structure. When combined with processes associated with
chemical self-assembly, it is possible to selectively position multiple
types of metal clusters in complex patterns on substrates and attach
different organic molecules. The properties of individual clusters
and molecules are measured and local size dependent variations and
defect related properties will be described. Potential device applications
will be outlined.
DAN MAIDENBERG
Materials Science and Engineering
Stanford University
Adhesion Of Porous Organosilicate Dielectric Films
Dan Maidenberga, Willi Volksenb, Robert Millerb, and Reinhold
Dauskardta
Dept of Materials Science and Engineering, Stanford University;
bIBM-Almaden Research Center, San Jose, CA
Abstract: Methylsilsesquioxane (MSSQ) films are primary
candidates to replace silica as the interlayer dielectric in future
generations of microelectronic devices. More importantly, the dielectric
constant of MSSQ is continuously tunable with the incorporation
of porosity at the nanometer length scale. However, before integration
is possible it is necessary to understand and quantify the mechanical
and fracture behavior of these thin films. Specifically, the addition
of porosity may have detrimental effects on many of the required
mechanical properties, which will reduce survivability during CMP
and lower the resistance to electromigration back stresses during
operation. The effect of porosity on a range of salient mechanical
properties including inherent fracture resistance, adhesion, and
elastic modulus will be addressed for several resin formulations.
Various other factors, including surface modification with UV-ozone,
will be presented. The implications of different matrix microstructures
and pore architectures are discussed.
CARLOS J. MARTINEZ
Materials Science
University of Illinois
Real Space Imaging of Structure Evolution in Microsphere-Nanoparticle
Mixtures
Carlos J. Martinez, Angel T. Chan, Mike Bevan*, and Jennifer
Lewis
Abstract: We are studying the phase behavior and structure
of binary mixtures consisting of negligibly charged colloidal microspheres
and highly charged nanoparticles using confocal microscopy. This
technique permits direct visualization of colloidal assemblies during
sedimentation on patterned and non-patterned surfaces. We have shown
that such systems undergo a remarkable phase transition from a colloidal
gel to a homogeneous fluid with increasing nanoparticle volume fraction.
Our aim is to use the homogeneous fluid phase as a precursor for
assembling colloidal crystals with controlled orientation and defect
density. Confocal images were acquired through the cross-section
of sedimented assemblies in both the wet and dry states, and the
positions of each particle center were obtained through image analysis.
New computer algorithms have been created to quantify global and
local structure , e.g., six-fold and four-fold order parameters,
and the interparticle separation distance. The poster will highlight
our recent efforts in this area.
GARRY R. MASKALY
Materials Science & Engineering Department
Massachusetts Institute of Technology
Ionic Colloidal Crystals Produced Via Controlled Heterocoagulation
Garry R. Maskaly, R.E. Garcia, W.C. Carter, and Y.-M. Chiang
Abstract: Ionic colloidal crystals (ICCs) are here defined
as ordered multicomponent colloids formed through heterocoagulation
(electrostatic interactions). The conditions under which ICCs are
stable have been analyzed. A model is presented in which two dimensionless
parameters are found to fully characterize an ICC system. We calculate
the Madelung constant of several ICC structures as a function of
these two parameters, and discuss the parallels between the ICC
Madelung constants and those for classical ionic crystals. Experimentally
accessible regions of surface charge, salt concentration, and temperature
where ionic crystallization should be possible are identified.
CLAUDIA B. MILZ
Materials Science and Engineering
University of Florida
Sol-Gel Processing Of Ceramics Utilizing Spinodal Phase Separation
Claudia B. Milz, Huiyan Huang, Charles M. Lofton, Wolfgang M.
Sigmund
Abstract: Spinodal phase separation of inorganic sol-gel
and an organic polymer yield bioactive glasses with defined porosity.
Due to the addition of polymer to a gelling sol and their separation
at specific equilibrium temperature, both a ceramic phase and polymer-rich
phase are formed. The evaporation of the solvent and the burnout
of the polymer produce a microstructure of interconnected and nearly-uniform
porosity, which can be controlled by various processing parameters.
The dependency on said parameters, best predicted by a comparison
to polymer phase separation rather than glass melt separation, is
discussed. This type of phase separation will be useful for manufacturing
other ceramics with a defined porous structure.
ARAVIND MOHANRAM
Materials Science and Engineering
Penn State University
Prediction of Shrinkage and Distortion During LTCC Device Production
- Modeling Co-fired Systems
Aravind Mohanram, Gary L. Messing, David J. Green
Abstract: LTCC technology promises new applications in the
wireless age. Advances in LTCC technology include improved characterization
and precise modeling of the co-sintering process. In the present
work, industrial LTCC systems such as DuPont 951, Heraeus CT2000,
Ferro A6-S and silver have been evaluated for their thermo-mechanical
properties, such as viscosity using cyclic loading dilatometry.
The viscosities are used in Newtonian constitutive laws commonly
used to simulate sintering. The viscosity decreases with temperature
and increases with relative density and ranges from 0.1-100 GPa.s.
Under isothermal conditions, the increase in viscosity is exponential
as relative density increased to > 92%. Glass crystallisation
has a significant influence on the viscosity. Camber (warpage) evolution
in LTCC/Ag systems was examined in real-time and correlated to viscosities
of individual components. It was found that the rate of camber depends
on: differential strain rate, relative viscosity and relative thickness
of the co-fired components. For a given thickness ratio, the amount
of camber can be kept to a minimum by optimizing the values of relative
viscosity and matching the strain rates. Experimental observations
show good agreement with previous theoretical models.
ANAND MURUGAIAH
Materials Engineering
Drexel University
Effect Of Anisotropy On The Mechanical Behavior Of Titanium
Silicon Carbide
Anand Murugaiah, Michel W. Barsoum, Surya R. Kalidindi, and
Tiejun Zhen
Abstract: Titanium Silicon Carbide has shown to combine
some of the best attributes of ceramics and metals. Its thermal
and elastic properties are quite similar to stoichiometric TiC.
It has the same density as Ti. but is roughly three times as stiff
(30 times stiffer than ice!) and yet is readily machinable. Above
1100 °C it is plastic with quite respectable strengths. In air
it is creep, oxidation, fatigue and thermal shock resistant, as
well as. damage tolerant. The mechanical behavior of Titanium Silicon
Carbide is very anisotropic and its excellent damage tolerance is
attributed to local confinement of the damage initiated during deformation.
The objective of this work is to understand the effect of anisotropy
and the physical origins of the damage mechanisms in Titanium Silicon
Carbide and to develop physical mechanisms/micro scale models to
explain the experimental observations of deformation. Experimental
work involving nano-indentations to obtain grain-scale properties
such as crystal elastic constants, fracture toughness, etc... and
in-situ loading in electron microscope using orientation imaging
microscopy to observe deformation/damage behavior at the grain scale
(R.T and elevated temp.) are presented. The results from these experiments
are used in finite element simulations to predict the behavior of
Titanium Silicon Carbide with different microstructures.
TADACHIKA NAKAYAMA
ISIR Osaka University
Osaka, Japan
Nano To Cluster Level Design Of Ceramic Materials
Tadachika Nakayama and Koichi Niihara
Abstract: Materials with grain sizes less than 10 nm defined
as "nanocluster" have attracted much attention due to
the physical and chemical properties which are significantly different
from those of bulk materials and the production of nanoclusters
becomes one of the most important subjects of the new technologies
[1]. The reduction in size of the materials and components plays
an important role in the development of the miniaturization technology,
and causes new applications such as catalysts due to the great value
of the surface to volume ratio. Therefore, it is very important
to have general methods for obtaining nanoclusters by simple and
reproducible methods. Cerium dioxide, ceria is a promising material
in several distinctly different application areas. It has commonly
been used as an additive or support oxygen storage media, and as
a noble metal dispersion aid, as well as its capability to dissolve
a large number of divalent and trivalent rare earth metals into
the lattice and the high temperature stability [2]. In this study,
the Active gas condensation (AGC) method combined with a co-evaporation
process and uneven bar system is employed to synthesize the ceria
based nanocluster composites (NCC). The microstructure of the NCC
have been studied by SEM and TEM. A copper content around 10 at%
with a morphology that favours high-energy surfaces of ceria is
shown to be beneficial for a high catalytic activity.
FUMIO OHUCHI
Materials Science and Engineering
University of Washington
Evolution of Cation Oxidation State Distribution in Mixed-Valency
Transition-Metal Oxide Thin Films Prepared by Solution Deposition
Fumio S. Ohuchi , Dmitry A. Kukuruznyak, Jerome G. Moyer, and
Mike. S. Prowse
Abstract: Multi-component oxides are normally prepared from
a mixture of elemental oxides by solid-state reactions at high temperatures.
In this process, oxidation state of the elements are varied within
a very narrow range through adjusting the level of dopants, This
is because the material characteristics are controlled by the thermodynamic
equilibrium that determines the oxidation states. Other oxidation
states stable at lower temperatures are not achieved. We have recently
developed a technique controlling the oxidation states with much
wider intervals in complex mixed-valence oxide systems. This was
realized during the synthesis of materials decomposition of organo-metallic
solutions followed by a two-step pyrolysis-annealing. This solution-based
methods allow mixing of precursors at the molecular level, thereby
reducing the need for high temperature infer-diffusion in the solid
state synthesis. We apply this technique to synthesize complex mixed-valency
transition metal oxides of compositions, Ni0.48+z
Co0.24+yCux-y-zMn2.28-xO4,
in thin film form. Various analytical techniques, including XRD,
electrical conductivity, Seebeck measurements, XPS, EXAFS, TEM and
ELS, have been used to characterize the material properties. As
annealing temperatures are decisive factors in controlling the electrical
properties and electronic structure, we were able to change the
oxidation state from Cu1+ to Cu2+
, which was accompanied by the reduction of manganese cations from
Mn4+ to Mn3+
in the spinel crystal. We also discovered a very unusual phenomenon,
'negative binding energy shift' of the electron binding energy associated
with Cu+1 oxidation states. As
this negative chemical shift is caused by similar shifts of the
Cu-3d valence bands, we modeled the experimental valence band photoemission
spectra by theoretical DOS of the d-levels using an ab-initio FEFF8
code. We have determined that the negative shift of the d-levels
was not caused by a long-range electrostatic interaction (Madelung
potential). The amount of the total charge on the Cu1+
cation in the spinel structure was similar to that of copper in
Cu2O, thus charging is not the cause
of negative shift either. It was found that only Cu-4s and 4p electrons
participated in the chemical bonding, but the filled d10 shells
of the copper in spinel structure did not form a band, but were
localized, thereby an atomic-like character. The 3d-level therefore
appeared as a false valence band edge in the spectrum. We claim
that this negative chemical shift is not due to charging or splitting
effects, but occurs when a completely occupied non-bonding d10 shell
appears on the XPS spectra as a false valence band edge.
HYOUNGJOON PARK
Lehigh University
Oxidation And Solid State Conversion Of Al Thin Films On A Sapphire
Substrate
Hyoungjoon Park and Helen M. Chan
Abstract: At present, sapphire substrates for blue LED and
laser diode applications are prepared by a combination of mechanical
and chemical polishing. The ensuing device performance is highly
dependent on the quality of the surface finish, and degree of subsurface
damage. Results will be presented on a new approach capable of generating
a pristine surface layer, starting with a sapphire substrate mechanically
polished to a 3 micron diamond finish. The process consists of oxidation
of a thin surface film of Al, followed by solid phase epitaxy of
the underlying substrate. Development of the surface layer was studied
using XRD. SEM, OIM (orientation image microscopy), AFM and TEM.
Thin foil samples were prepared using FIB (focused ion beam) instrumentation.
The influence of coating temperature and heat treatment time/temperature
on the final surface finish will be discussed. The mechanism of
solid state conversion from polycrystalline alumina to sapphire
single crystal will be also discussed. The proposed method has the
potential to be more cost-effective than conventional techniques,
and would be compatible with current device manufacturing procedures.
CHRISTOPHER PERREY
Chemical Engineering & Materials Science
University of Minnesota
Challenges And Techniques Of Nanoparticle Preparation And Characterization
For Electron Microscopy
Christopher R. Perrey and C. Barry Carter
Abstract: Nanoparticles and nanoparticle films have been
shown to have unique properties. In order to harness the potential
of these materials, a fundamental understanding of their structure
and properties is needed. Because of their inherently small size,
the preparation of these samples for analysis is problematic. Ceramic
particles and particulate films may not adhere well to substrates,
and traditional preparation techniques can lead to chemical and
structural information being lost. Furthermore, the ability to "find"
a single nanoparticle is becoming more important in device manufacturing.
Using novel particle collection and preparation techniques, such
as the use of the focused ion beam (FIB) tool, nanoparticles and
nanoparticle films have been examined by scanning electron microscopy
(SEM) and transmission electron microscopy (TEM). Applications and
results of these techniques will be discussed.
BRIAN M. PINTO
Whiteware Research Center
Alfred University
Effect of Filler Particle Size on Porcelain Strength
Brian Pinto and William Carty
Abstract: The objective of this study was to investigate
the stress and strain levels present in quartz and alumina-bearing
porcelains, and correlate these values to mechanical strength. Data
indicated that residual strain increased as filler particle size
increased, but only to a critical value, after which strain decreased,
indicating a relaxation caused by spontaneous microcracking of quartz
grains. The maximum strain was observed for samples containing 87µm
quartz grains. Analysis of stresses and strains generated between
quartz grains and the surrounding glass phase demonstrate that cracking
must first occur in the weaker filler grains, not the glass phase,
as is commonly reported. Mechanical strength was maximum in samples
containing 26µm quartz grains, decreasing rapidly upon increase
of quartz size. Acoustic emission was used to attribute this trend
to the generation of microcracks upon induced loading.
MICHAEL PROWSE
Materials Science and Engineering
University of Washington
Compositional Effects on Thermoelectric Properties of Mn-Cu-Co-Ni
Oxide Thin films.
Michael S. Prowse, Jerome G. Moyer, Dmitry A. Kukuruznyak, and
Fumio S. Ohuchi
Abstract: For decades, complex Ni-Co-Cu-Mn oxides have been
utilized in industrial thermistor applications, as they exhibit
strong negative temperature coefficient (NTC) properties. As our
understanding of the science governing these materials has evolved,
their capacity to provide a novel approach to thermoelectric technologies
has also emerged. We therefore look at these complex multi-component
oxide systems from the thermoelectric perspective. Our research
utilizes a fabrication technique, referred to as Organo Metallic
Decomposition (MOD) that can offer enhanced control over material
properties. From this basis, we are learning how compositional variations
and processing procedures may allow for the tailoring of electronic,
structural and thermal properties. Our thermoelectric characterization
measurements display how these materials provide new possibilities
for thermoelectric applications. One of the unique features in MOD
is that the oxidation states of the cations are thermally equilibrated
at each step of the annealing process, thereby exhibiting unique
properties that are not normally obtained by conventional solid-state
reactions. For example, the Seebeck coefficients measured from the
composition, Ni0.48Co0.24Cu0.60Mn1.68O4,
change from "negative" to "positive" when the
annealing temperature is raised from 600°C to 800°C. This
implies that the material changes from n- to p-type due to the change
in relative concentrations of Mn3+
and Mn4+ ions in the structure
at different equilibrium temperatures. The change of the oxidation
state in Mn is compensated by the change in Cu states: Cu1+
+ Mn4+? Cu2+
+ Mn3+. The electrical conduction
seems to occur via hopping of small polarons between Mn3+
and Mn4+ sites as evidenced by
the fact that the Seebeck coefficient has basically no temperature
dependence. Compositional variation thus alters the activation energy
for polaron hopping, leading to different electrical conductivity
values. What has been seldom realized is that this unique electrical
conduction mechanism, paired with the high thermopower values obtained
in these materials, provides us with the opportunity to approach
the usual constraints of thermoelectric materials from a completely
new direction. In this paper, we describe the effect that chemical
composition has on thermoelectric properties of Ni0.48-zCo0.24Cux+y+zMn2.28-x-yO4
thin films.
RANJEET B. RAO
Materials Science
University of Illinois, Urbana
Directly Assembly of 3-D Interpenetrating Ceramic Composites
Ranjeet B. Rao*. Jennifer A. Lewis*, and Frederick F. Lange^
*Department of Materials Science and Engineering, University of
Illinois
^Materials Department, University of California, Santa Barbara.
Abstract: 3-D periodic ceramic composites were directly
assembled via robotic deposition of colloidal inks. These concentrated
gel-based inks are engineered to have moduli and yield stresses
large enough to create self-supporting structures. Face-centered
lattices (or scaffolds) were assembled from an alumina ink with
varying lattice constants (~ 250 microns). 3-3 interpenetrating
composites were also created that consisted of an alumina lattice
embedded in an alumina-mullite matrix. Preliminary results of mechanical
property measurements carried out using Moire interferometry will
be presented.
SUMMER K. RHODES
Advanced Materials Laboratory
Sandia National Laboratories
Reaction and Bonding of Hf and Zr Containing Alloys to Alumina
Summer K. Rhodes, Bryan D. Gauntt, Ping Lu, Ronald E. Loehman
Abstract: Adhesion of metals to ceramics typically involves
a bond created, in part, by a reaction of the two materials at the
interface. Such a bond can be promoted by inclusion of a reactive
metal to the alloy composition. Ag alloys containing different amounts
of the reactive metals, Hf or Zr, were reacted in a controlled atmosphere
with sapphire, 99.6% and 96% alumina, and fused silica. Samples
were examined with scanning electron microscopy, transmission electron
microscopy and energy dispersive spectroscopy to identify the phases
present and their microstructure. Wetting was observed by taking
wetting angles during reaction. Comparisons between those ceramics
with varying amounts of alumina and between alloys with different
amounts of reactive metal have allowed for a better understanding
of the reaction. Wetting and bonding was attained for all alloys
on all substrates. Analysis identified Zr and Hf oxide phases bonded
with the substrate surfaces. Differences in microstructures are
found between the respective additive reactive metals, and their
concentrations, in an otherwise constant system. Sandia is a multiprogram
laboratory operated by Sandia Corporation, a Lockheed Martin Company,
for the U.S. Dept. of Energy under Contract DE-AC04-94AL85000
DERRICK J. ROCKOSI
Lehigh University
Growth From Twinned And Untwinned Abnormal Grains Of PMN-35PT
In A Matrix Containing PbO Additions
D. J. Rockosi*, H.M. Chan, M.P. Harmer, S. Wu, A. M. Scotch,
E. P. Gorzkowski, and P. T. King
Abstract: Previous studies observed the presence of exaggerated
grains of Lead Magnesium Niobate - Lead Titanate in samples with
high liquid fraction. Orientation Image Microscopy (OIM) showed
these abnormal grains to contain 60: <111> twin
boundaries which possibly gave them a growth advantage over untwinned
grains. The present study will compare the growth and growth rates
of twinned and untwinned crystals embedded in PMN-35PT with 0-5
vol% PbO additions. Attention will also be given to the microstructure
of the matrix and its effect on abnormal grain growth. Microstructures
and OIM analysis of abnormal grains will be presented.
ROBERT C. ROGAN
Materials Science
California Institute of Technology
Multiscale Characterization of Ceramics using Diffraction
Robert C. Rogan, Ersan Üstündag, Geoffrey A. Swift,
Bjørn Clausen, Mark Daymond, Nobumichi Tamura
Abstract: Recent developments in X-ray (synchrotron) and
neutron diffraction facilities have provided a unique opportunity
to study materials in situ at length scales ranging from sub- m
to cm. For the first time, material behavior in the sub-grain to
bulk levels can be studied under a wide range of conditions. Several
examples from our recent work on ceramics will be exhibited: Structure
and strain fields of individual domains in BaTiO3:
X-ray microdiffraction with a 0.7x0.7 m beam was used to study the
local structure and strain tensors of domains. Ferroelastic behavior
of Pb(Zr,Ti)O3: Domain switching
and elastic strain evolution under applied compressive load was
studied using neutron diffraction. High temperature elastic properties
of Si3N4:
Tensile stress was applied to a monolithic Si3N4
and its composite with SiC at temperatures reaching 1400 C while
the specimens were sampled with a neutron beam. The diffraction
data yielded elastic stiffness and thermal expansion tensors and
provided information about the mechanical behavior of both materials.
ATANU SAHA
Mechanical Engineering
University of Colorado at Boulder
Alkoxide Modified Silazane for Polymer Derived Ultrahigh Temperature
Fibers and NanoComposites*
Atanu Saha and Rishi Raj
Abstract: Silicon carbonitride is a ceramic which is made
directly from an inorganic polymer. The precursor, which is a liquid,
is first cross-linked into a rigid shape. When this object is pyrolyzed
under controlled conditions it yields a ceramic with an amorphous
structure which exhibits unusual resistance to creep and crystallization
up to very high temperatures. It is postulated that the genesis
of this amorphous structure lies in the highly cross-linked structure
of the polymer before it is pyrolyzed.
The cross-linking step also has a profound influence on the change
in rheology of the inorganic precursor. Commercial polysilazane
based precursors, such as CerasetTM, appear to form a stiff, three-dimensional
network rapidly, precluding the possibility of drawing fibers in
the preceramic state.
In this poster we report on modification of CerasetTM by combining
it with an alkoxide. The alkoxide apparently linearizes the polymer
chains (presumably through the divalent oxygen bonds). This modified
precursor is highly amenable to fiber drawing. The resulting fiber
has a maximum tensile strength of 2.8 GPa. It is also oxidation
resistant. The parabolic rate constant of 16 x 10-18 m2/s at 1350oC
is comparable to the rates of oxidation which have been achieved
only in ultrapure silicon carbide.
In this poster we will present the processing science of the polymer
derived silicon carbonitride fibers. The polymer reactions were
characterized by infrared spectroscopy. The study is based upon
modification of polysilazane with zirconium alkoxide. The role of
oxygen based polymerization reactions, and zirconium based cross-linking
reactions will be discussed. The poster will also describe the mechanical
and oxidation behavior of the fibers. The high temperature chemical
and nanostructural stability of the oxide/nonoxide composite will
be discussed and compared to the high temperature properties of
Nicalon-SiC fibers.. The polymer derived process offers the possibility
of incorporating molecular-clusters with functional properties into
the amorphous nanostructure. Results demonstrating the potential
of multifunctional fibers will be discussed.
_____________________________________________
*Supported by the Air Force Office of Scientific Research.
OLGA SCHNEIDER
California Institute of Technology
Quasicontinuum And Its Applications To Ferroelectrics
Olga Schneider, Jarek Knap, Michael Ortiz
Abstract: The poster presents a streamlined and fully three-dimensional
version of the quasicontinuum (QC) theory and analyzes its accuracy
and convergence characteristics. QC is a method which seamlessly
bridges modeling at the atomistic and continuum levels. It systematically
coarsens the atomistic description by introduction of kinematic
constraints and retains an atomistic description only where required.
Work in progress is an application of QC to complex lattices, and
ferroelectrics in particular. Applications will be the simulation
of extended defects occurring in ferroelectrics, steps in domain
walls, interaction between domain walls and obstacles, and electrostatic
interactions.
JUNWU SHEN
Materials Science and Engineering
Penn State University
Variable Temperature Ion-exchanged ESP Glass
Junwu Shen and David J. Green
Abstract: A two-step ion exchange using different bath compositions
can decrease the strength variability of ion exchanged glasses while
still maintaining significant strengthening (ESP glasses). However,
the use of two exchanges to produce ESP glass can be considered
an economic disadvantage. By introducing a high temperature step
into the normal ion exchange process, the strength variability can
be greatly decreased (~60%) with only about 10% loss in the average
strength. The surface damage resistance was also studied by indentation
strength tests and there was, again, a significant improvement compared
to the traditional isothermal ion exchange. As only one salt bath
is involved in this process and the temperature change can be easily
controlled, this new variable temperature exchange process can produce
ESP glasses in a more economic way.
JINGYU SHI
Materials Science and Engineering
Ohio State University
Nanostructured ZrO2 Coating Via Modified Emulsion
Jingyu Shi and Henk Verweij
Abstract: Porous and dense nanostructured ceramic materials
can be used as wear-resistant and insulating coatings, fuel cell
electrodes and electrolytes and dense and mesoporous membranes.
In these applications the nanostructured materials are present as
thin supported layers. Such layers can be made by depositing nanoparticle
suspensions directly on the substrates followed by a rigidizing
or densifying thermal processing treatment. The ceramic nanoparticles
in the suspension must be in a state of dispersion and agglomeration
that enables a packing resulting in the desired properties and processing
conditions. In this study we consider the special case of random
dense packing of non-agglomerated ~10 nm O zirconia particles, followed
by full densification with a near-room temperature process. The
particles are made by modified emulsion precipitation [1]. This
method starts with the preparation of two thermally stable water-in-oil
emulsions: one with water-soluble zirconium salt in the water phase
and the other with the precipitation reagent hexamethylenetetramine
(HMTA) in the water phase. The emulsion is stabilized by nonylphenoltetraethyleneglycolether
(Arcopal-40) non-ionic surfactant and didodecyldimethylammonium
bromide (DIDAB) ionic co-surfactant. The emulsions are mixed and
HMTA is decomposed so that the PH of the water droplets is increased
and the formation of zirconium hydroxide induced. Water is then
removed by azeotropic distillation, leaving a transparent dispersion
of the ZrO2 nanoparticles in the
oil phase. A polymeric stabilizer poly(octadecyl methacrylate) (PODMA)
is added prior to water removal. It is thought that a synergistic
complex of PODMA and DIDAB covers the particle surface and ensures
an excellent dispersion after water removal due to steric stabilization.
Light laser scattering results show that the average (ZrO2)
particle size in dispersion is about 12 nm. NMR and RAMAN experiments
are used to clarify the detailed stabilization mechanism. Dense
nanostructured ZrO2 coatings can
be made by spin-coating on a substrate, followed by drying and activation
with an oxygen plasma near room-temperature to remove the organic
particle stabilization. The ZrO2 layer
can be crystallized to show a dense tetragonal ZrO2
10 nm O grain structure by heating at 600oC [2]. The characteristics
of the coatings are investigated by XRD, SEM, HRTEM and AFM.
WEI-HENG SHIH
Materials Engineering
Drexel University
Nanoeoating of Paniculate Surface in Colloidal Ceramic Processing
Wei-Heng Shih
Abstract: Colloidal processing offers the advantage of controlling
the interactions between particles. Nanometer is the critical length
scalefor interparticle interactions. Modification of interparticle
separation in the nanometer range plays a cr,t,cal role in thepropertesofpart^u
late suspensions. We have developed a nanocoating method that modifies
the surface chemistry of ceramic powders. The nanocoat.ng erves
multiple purposes. It enhances the chemical and thermal stability
of the powders, improves the consolidation andgeological properties
of slurries, increases the homogeneous distribution of processing
additives, and lowers the sintering temperatures of he green -".P^,^
example we showed that boehmite (AlOOH)-coated silicon nitride and
silicon carbide powders have a significantly higher sohds oadmg
than the uncoated powders in water. Coated suspensions have lower
viscosity and wider linear viscoelastic region, and lower shear
SIs than that of uncoated suspensions. With an increasing coating
thickness, the shear modulus of coated suspensions decreases indicating
the coating prevents close contact of core panicles thereby reducing
the van der Waals attraction interaction between the core particles.
Boehmite coating is shown to enhance the thermal stability of catalytic
oxide Zr02. Coating of Mg(OH)2
layer on Nb205
particles facilitates the synthesis ofpyrochlore-free perovskite
lead manganese niobate (PMN) powders by a single heat-treatment
step. Normally this must be done in two heat-treatment steps as
in the columbite process. More recently, the coating technique has
been used to fabricate piezoelectric PMN-PT thick-film sensors.
JOHN N STUECKER
Sandia National Laboratories
Robocasting Periodic Lattice Filters for Catalytic Methane Combustion
and Diesel Particulate Traps
John N Stuecker, Joseph Cesarano III, James E. Miller
Abstract: Robust catalytic supports and particulate filters
can play an important role in the development of electric-power
generators utilizing the combustion of methane and regenerating-diesel-particulate-trapping
systems. With an estimated 1900 gas-turbine electric power plants
needed within the next 20 years, increased NOx
emissions are becoming a growing environmental concern. Additionally,
there are increased restrictions on diesel soot emissions for the
U.S. and Europe for 2005 which cannot be met by current technologies.
These problems can both be solved by appropriate structural support
design and catalytic functionality. In order to address this problem,
periodic lattices of rods with controlled porosity in three dimensions
were created using the robocasting process, keeping in mind that
low pressure drops and high surface areas are important for both
systems being investigated. Robocasting allows for the deposition
of a wide range of ceramics and metals, with the capability of multiple
material deposition, as well as controlled placement of these materials.
Periodic lattice filters with very high surface area to volume ratios
were compared to current catalyst support and particulate trapping
technologies (extruded honeycomb and ceramic foam monoliths). This
project is funded by the Laboratory Directed Research and Development
(LDRD) program at Sandia National Laboratories. Sandia is supported
by the United States Department of Energy under Contract DE-AC04-94AL850000.
Sandia is a multiprogram laboratory operated by Sandia Corporation,
a Lockheed Martin Company, for the United States Department of Energy.
ENDER SUVACI
Penn State University
Tailoring Microstructure Of Advanced Ceramics Via Templated
Grain Growth (TGG)
Ender Suvaci* And Gary L. Messing**
* Department of Ceramic Engineering, Anadolu University, Turkey.
** Department of Materials Science and Engineering, Pennsylvania
State University.
Abstract: The microstructure and, subsequently, the physical
properties of advanced ceramics can be tailored by Templated Grain
Growth (TGG); a technique for developing crystallographic texture
in ceramic bodies via the grain growth of aligned anisometric particles
(i.e.. templates) in a dense and fine grain size matrix. It has
been shown that significant template growth is only observed after
density reaches to -90% TD and the degree of texture development
in TGG systems is directly related to template growth. Thus. template
growth can be analyzed to understand the kinetics and thermodynamics
of the process and their influences on texture development. Thermodynamically.
template to matrix grain size ratio is important in determining
the final microstructure. Higher the ratio results in the higher
volume fraction of textured material. In alpha alumina (with some
calcium aluminosilicate liquid phase former) system, template growth
is anisotropic. In radial directions faster grain growth kinetics
are observed than that of thickness direction
GUOLONG TAN
Physics Department
Hampton University
#1: Synthesis And Optical Properties Of CdTe Nanocrystals Fabricated
By Mechanical Alloying Process
G. L. Tan a), U. Hommerich a), D. Temple a), Ei Ei a), J. T.
Seo a),, G. Loutts b), N.Q.Wu c),, S. B. Trivedi d)
a) Physics Department, Hampton University; b) Center for photonic
Materials Research, Norfolk State University;
c) Chemistry Department, Northwestern University; d) Brimrose Corp.
of America
Abstract: CdTe nanocrystals had been synthesized by a physical
method, ball mill process. The potential advantage of the physical
approach is the possibility of achieving the intrinsic quantum confinement
effect of the uncapped CdTe nanocrystals excluding the influence
of the organic surface effect, i.e. the interaction between the
surfaces of the nanocrystals and capped organic ligand, as well
as the batch production of the nanocrystals in larger scale compared
with chemical method. The influence of the surface on QD properties
is complicated and remains controversial. So reducing this influence
can be valuable in determining intrinsic QD's physical properties.
Experimentally, the stoichiometric amount of reagents of Cd and
Te elemental powders were sealed in the hardened alloy vials on
a Spex 8000D miller machine. The mass ratio of reagents to balls
was 1:20. Small amounts of as-milled powders were taken out of the
vial within different intervals for structural and optical measurement.
XRD measurement results revealed that CdTe nanocrystals were successfully
fabricated upon the alloyed samples during ball milling process
for only 10 minutes, remaining some amounts of Cd and Te elemental
powders being unreacted. The intensity of the diffraction peaks
from elemental Cd and Te powders decreases with ball milling time.
After 20 hours mechnochemical reaction of the elemental powders
during the ball milling process, single phase CdTe nanocrystals
were successfully fabricated. The mean particle size of this product
was estimated to be around 13.04 nm calculated by Scherer equation.
Further ball milling for up to 50 hours gave rise to very fine nanoparticles
with average size of around 3nm, with serious contamination from
the vial. The as-milled powders dispersed in non-polarization organic
ligand did not exhibit any colorization, with its absorption peak
lying within the ultraviolet wavelength range. After capped with
polarization organic ligand, the CdTe nanocrystals dispersion solution
turned into red colorization. The UV visible spectrum exhibits an
absorption peak locating at 527 nm for the red colloid dispersion.
While the raw elemental powders were milled with certain organic
agents, the powders exhibit red colorization. The colloid dispersion
of these nanoparticles in hexane show brown color under visible
lamp lightening. The absorption spectrum and the surface state studied
by XPS will be presented.
YIN TANG
Materials Science & Engineering
Case Western Reserve University
Interactions between Self-Assembled Monolayers and Zirconia
Particles in Aqueous Solution
Yin Tang and Mark R. De Guire
Abstract: The interaction forces between a ZrO2 sphere and
different self-assembled monolayers (SAMs) were measured using AFM
in aqueous KNO3 solutions of varying pH and concentration. The trends
of the attractive force, adhesion force, and jump-in distance versus
pH, ionic strength and functional group were reported. Results for
sulfonate functionalized SAMs were qualitatively consistent with
Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. OTS surface exhibited
a long range attractive force that was not expected on the basis
of DLVO theory. The range of this force is about 40-60 nm, extending
with decreasing pH. The force decays exponentially with distance
and shows little dependence on solution concentration at pH 5. Forces
which are observed here may be responsible in part for the formation
of ceramic thin films on SAMs from aqueous media containing nano-scale
solid particles.
CHRISTIAN TURQUAT
Materials Research Center
Lehigh University
Doping Alumina In Order To Increase Its Creep Behavior
C.P. Turquat, M.D. Drahus, H.M. Chan, J.M. Rickman, and M.P.
Harmer
Abstract: Alumina is extensively used in industry for its
mechanical properties and its high chemical stability in a wide
range of temperatures, and in addition its relatively low cost of
production. This having been said, one can easily understand the
large number of scientific investigations completed in order to
enhance alumina properties. In this work. we concentrated our research
in the improvement of the creep behavior of alumina. In order to
achieve this objective, doping elements are added to ultra-pure
alumina in concentrations never exceeding few hundred of ppm. The
single and co-doped alumina bulk pallets are then bone-shaped before
performing the creep experiments. Additionally, the microstructure
of the doped aluminas has been investigated using a wide range of
electron microcopy techniques (SEM. CTEM. HRTEM, STEM) in conjunction
with their associated spectroscopic techniques (EDX. EELS), in order
to understand the correlation creep-microstructure. The latest advancements
with regard to synthesis, creep behavior and microstructure of these
materials will be summarized and compared to our previous investigations.
HONG-REN WANG
Materials Science and Engineering
Massachusetts Institute of Technology
Alumina-Doped Silica Gradient-Index (GRIN) Lenses by Slurry-Based
Three-Dimensional Printing (S-3DPTM)
Hong-Ren Wang and Michael J. Cima
Abstract: Traditional slurry-based three-dimensional printing
(S-3DPTM) process has been used to fabricate complex structure materials
by printing organic binders in selective positions of each printing
layer. This process is modified to fabricate functional graded materials,
such as gradient index (GRIN) lenses, by depositing different concentrations
of dopant into selective positions. The modified S-3DPTM process
offers advantages over conventional GRIN lens processes, including
reduced processing time, improved compositional flexibility, and
increased index profile dimensionality. Two different approximately
parabolic dopant concentration profiles, which have maximum alumina
concentrations of 1.63 mol% and 2.5 mol%, are printed into the silica
powder beds using S-3DPTM. The samples with maximum alumina concentration
of 1.63 mol% can be sintered into optical transparency at 1650 0C
for 30 minutes in a vacuum furnace (5x10-6 torr) while an additional
dehydration process before sintering is required for the samples
with maximum alumina concentration of 2.5 mol%. The magnifying effects
of GRIN lenses with profiles of 1.63 mol% and 2.5 mol% alumina are
observed and have effective focal lengths of 10 cm and 6.1 cm, respectively.
The S-3DPTM technology has been demonstrated to provide a more flexible
method to fabricate GRIN lenses
QINGLEI WANG
Materials Research Laboratory
Penn State University
Grain Boundary Segregation in Yttrium-doped TiO2
Q. Wang, G. Lian, E. C. Dickey
Abstract: Solute segregation to grain boundaries plays a
critical roll in the macroscopic dielectric behavior of electroceramics.
Due to its well-known defect chemistry and relatively simple crystal
structure, TiO2 has been studied
to understand the relationship between dopant concentration, grain
boundary segregation and grain boundary dielectric behavior. In
particular, we have studied the segregation of Y to TiO2
grain boundaries by complementary analytical transmission electron
microscopy and impedance spectroscopy. The quantitative segregation
and impedance results have been compared to analytical segregation
models that take into account both elastic and electrostatic driving
forces for segregation.
WENSHENG WANG
Materials Science and Engineering
University of Utah
Determination of Kinetic Parameters of H2O
Absorption by Oxygen-Deficient Oxide Perovskites
Wensheng Wang and Anil V. Virkar
Abstract: Many oxide perovskites of the structure ABO3
(A = Ba, Sr; B = Ce, Zr, Th) or AB'1/3B"2/3O3
(B' = Ca, B" = Nb, Ta) become oxygen-deficient when either
doped with a lower valent dopant (in the case of ABO3)
or when are made off-stoichiometric by increasing the concentration
of B' (in the case of AB'1/3B"2/3O3).
These perovskites exhibit oxygen ion and electronic conduction in
a dry atmosphere, and additionally protonic conduction in H2O-containing
atmospheres. Transport of both protons and oxygen ions also implies
that such materials can transport molecular H2O under its chemical
potential gradient. The parameters, which determine the kinetics
of absorption of H2O by such perovskites
include the chemical diffusion coefficient, , and the surface exchange
parameter, . Both parameters, in principle, can be measured by techniques
such as TGA, dilatometry, and chemical analysis (depth profiling).
In this work we report a conductivity relaxation technique, which
can be used to determine both the and , by measuring the time dependence
of total conductivity upon change of atmosphere from dry to wet,
or from wet to dry. The total conductivity, in such cases, reflects
transport due to protons, oxygen ions, and possibly electronic defects.
Its time dependence upon change of atmosphere reflects the occurrence
of changes in defect or species concentrations by virtue of the
absorption (or desorption) of H2O.
The present study also reports on the measurement of transport properties
in both dense as well as porous samples. Measurements on porous
samples, provides an experimental approach for the measurement of
with possibly greater accuracy than is possible with dense samples.
In this poster presentation, we will report our recent results on
the determination of and by analyzing the time dependent conductivity
in Ba3Ca1.18Nb1.82O9-
(BCN18). The experimental approach
consists of conducting four-probe DC measurements on dense and porous
samples of BCN18, and using standard
transient solutions to appropriate diffusion equations. Experiments
show that most of the data can be readily analyzed assuming a concentration-independent
over the range of degree of hydration realized in typical experiments.
A study of time dependence of conductivity of porous samples suggests
a possible humidity sensor based on these materials.
XIAOPING WANG
Institute of Materials Science
The University of Connecticut
Synthesis and Characterization of Highly-Organized Metal/Ceramic
Nanocomposites
Xiaoping WANG, Tania Bhatia, Mark Aindow and Nitin P. Padture
Abstract: We describe a remarkable, highly-organized Cu/g-Al2O3
nanocomposite, which consists of monodisperse spherical Cu nanoparticles
uniformly embedded within a polycrystalline g-Al2O3
matrix. The formation of this nanocomposite was discovered serendipitously
during the examination of ion-beam milled ceramic specimens in TEM.
It is believed that this nanostructure was formed during ion-milling,
by the reactive co-sputtering of Cu and Al from ion-mill hardware
in the presence of O. An exploratory research project is established
to: (i) synthesize these type of metal/ceramic nanocomposites in
Cu/Al2O3,
Co/Al2O3,
and Cu/SiO2 systems using a diode-sputtering
device; (ii) characterize their microstructures; (iii) elucidate
the formation mechanisms; and (iv) evaluate appropriate optical/electrical
and magnetic properties of the resulting thin film nanocomposites.
XIAOTONG WANG
Institute of Materials Science
University of Connecticut
Processing and Mechanical Properties of Nanocrystalline Ceramics
Xiaotong Wang and Nitin P. Padture
Abstract: The objective of this work is to evaluate the
size effects in wear properties of nanocrystalline ceramics. To
that end, bulk nanocrystalline ceramics (Y2O3
and Al2O3/TiO2)
with a relative density >97% and the grain size in the range
100nm ~ 200nm have been pressureless sintered. Results from the
microstructure development study will be presented. Preliminary
wear results will also be presented and discussed.
KOJI WATARI
National Institute of Advanced Industrial Science & Technology
Nagoya, Japan
Centrifugal Sintering of Ceramics
K. Watari, T.Tsugoshi, K.Sato, Y.Kinemuchi (National Institute
of Advanced Industrial Science and Technology, Nagoya, Japan); K.Uchimura
(Sinto V-Cerax, Toyokawa, Aichi, Japan)
Abstract: Pressure sintering techniques such as hot-pressing
and HIP provide densification at low firing temperature, and are
applied to produce material components with orders of several cm
to several ten cm. Recently, ceramic film with thickness of several
ten µm to several thousand µm and small ceramic piece
with complicated shape have been interested because of highly integrated,
small electric devices. In this case, conventional pressure sintering
techniques are not used for the thick film and small piece, since
specimen surface is contaminated during sintering, and removal of
contaminated portion is usually required. In this presentation,
we introduce concept about centrifugal sintering method with high
pressure and without pressure medium for small ceramic piece and
thick ceramic film, and processing merit through its sintering method.
Furthermore, some experimental sintering data will be shown.
YOUCHANG XIE
Chemistry
Peking University
Title?
Youchang Xie
Abstract: Nano-oxides phase can be controlled by surface
additives. It is found that the phase of some nano oxides such as
ZrO2 and TiO2
can be influended by additives on their surface. For instance, when
a monolayer or submonolayer Y2O3
on the surface of nano ZrO2 can make
the ZrO2 phase change from monoclinic
to tetragonal. Phase changes of TiO2
can occur when CuO or WO3 was put
on the surface of nane TiO2 particles.
ZONGHAN XIE
School of Materials Science & Engineering
The University of New South Wales
Sydney 2052, Australia
Influence of Grain Length upon Surface Contact-Induced Deformation
and Fracture of -Sialon Ceramics
Zonghan Xie, Mark Hoffman, Robert J. Moon and Paul Munroe
Abstract: A key aspect of the machining of -sialon ceramic
components is the control of the surface/subsurface quality. In
this current study, three -sialon microstructures featured by fine
equiaxed (EQ), large elongated (EL) and mixed (E/E) grains were
prepared. Young's modulus, hardness and fracture toughness were
measured via indentation tests. All three microstructures exhibited
high hardness; EL shows a significant improvement in fracture toughness,
compared to the EQ and E/E, due to crack bridging by the elongated
grains. Static contact and scratch experiments were conducted to
investigate the plastic deformation and crack formation in the different
microstructures. The focused ion beam milling technique was used
to identify the interaction of the grain structure with surface
and subsurface cracks. Observations showed that the elongated grains
in EL could effectively restrict the propagation of cracks and subsequent
material removal. An analytical model was established to elucidate
the role of grain length in the determination of crack resistance
during sliding contact. Furthermore, the grinding tests were performed
and verified the results of the earlier experiments and predictions
of this model.
SVETLANA V. YANINA
Department of Materials Science and Engineering, Massachusetts
Institute of Technology
Structural Evolution Of The Bi2Mo3012(010)
Surface In Water-Air Mixtures
Svetlana V. Yanina and Richard L. Smith
Abstract: Bismuth molybdates are constituents of industrial
catalysts used for selective (amm)oxidation of alkenes. The objective
of this work has been to characterize the structure and morphological
evolution of the (010) cleavage surface
of a-bismuth molybdate (Bi2Mo3012)
during treatments in dry air and in air-H20 with Atomic Force Microscopy
(AFM), X-Ray Photoelectron Spectroscopy (XPS) and X-Ray Diffraction
(XRD). The cleavage Bi2Mo3012(010)
surfaces consisted of atomically flat terraces separated by steps
that were an integer multiple ofb/2 (5.75 A). The treatments in
excess of 100 h at 300-400 °C had no detectable effect on the
(010) surface morphology or chemical composition of Bi2Mo3012
crystals. Within 2 h at 500-600°C in dry air however,
crystal surfaces were etched through evaporation. Treatments at
600°C in dry air lead to preferential Mo loss from Bi2Mo3012
crystals, resulting in the nucleation and growth ofBi2Mo209
crystals on the (010) Bi2Mo3012
surfaces. Water vapor facilitated the volatilization of Mo. in particular
from steps and sites of extended crystal defects (dislocations,
pores, etc.) on the (010) Bi2Mo3012
surfaces. At 500°C in air-H20.
the loss of Mo lead to the growth of Bi2Mo06
precipitates, while at 600°C, it resulted in the formation of
Bi2Mo209
overlayers over the Bi2Mo3012(010)
surfaces.
SERGEY G. YERAKHAVETS
Institute of Machine Reliability
Minsk, Belarus
Modeling the Kinetic Of Micro Plasmic Oxidizing Technology Under
Pulse Current Regimes
Sergey Yerakhavets, Dr. Maksim Kireitseu, V. Basenuk
Abstract: A model is presented for the micro plasmic oxidizing
of aluminum or its alloy. The model is based on the space-charge-limited
drill of negative oxygen ions through the growing oxide film to
react at the aluminum dioxide interface. In the initial linear growth
region, the supply of ions from the plasma determines the growth,
whilst for longer periods the drift of ions through the oxide gives
rise to parabolic growth kinetics. The theory is consistent with
the lack of orientation dependence observed for the plasma oxidation
of Al. It is applicable over the whole of the growth kinetics, for
oxidizing in both pulse and periodic alternating current modes.
The dependence of current and voltage with time during the process
may also be predicted. The theory is found to be applicable to oxide
growth occurring in micro arc plasmic oxidizing. The relevant validity
of the model is grounded through mechanical characterization of
obtained alumina-coated samples.
DI YU
Materials Science and Engineering
Ohio State University
Quantitative Description Of Alpha-Alumina Compact Formation
From Dispersions
Di Yu and Henk Verweij
Abstract: Homogeneous porous ceramic compacts can be made
by colloidal filtration of panicles dispersions, followed by careful
drying and rigidifying by partial sintering. Such compacts can be
used as filters or substrates for mesoporous and dense inorganic
membranes or sintered to full density to a homogeneous fine-grained
microstructure. The objective of this study is to obtain accurate
experimental data for the relation between dispersion methods, the
amount and nature of colloidal stabilizers and compact microstructure.
To achieve this goal we consider colloidal filtration of commercially
available alpha-A1203
particles with a narrow size distribution around 400 nm. Those particles
are delivered as dry powder known to be fairly well dispersible
and to contain only minor concentrations of hard (multi-particle)
agglomerates. The as-delivered powder is dispersed in water with
either HN03 as charge-stabilizer
or Ammonium Poly-Methacrylate as electrosteric stabilizer. Dispersion
is promoted by either high shear mixing or focused ultra-sonic treatment.
The dispersions are filtered on a coarse filter to removed residual
agglomerates and the purified dispersion is subsequently filtered
on a macroporous membrane such that a disk-shaped filter cake is
formed. The wet disks are dried two-side and unconstrained under
a controlled atmosphere, followed by sintering (at low temperature)
in the surface-diffusion controlled regime such that necks are formed
between the particles but hardly any shrinkage occurs. The density
of the disks is measured by mercury pycnometry, followed by determination
of two-dimensional microstructural cross-sections and sintering
temperature. These results are used to obtain an unambiguous relation
between particle-solvent interfacial chemistry and mechanical agitation
and final compact density. Cast formation kinetics and microstructure
are compared with theoretical predictions from recent literature.
We expect that this will give us, amongst others, a better insight
into co-operative effects in the liquid-solid transition as occurs
during filtration at the interface between the dispersion and the
filtered compact.
TIEJUN ZHEN
Department of Materials Engineering
Drexel University
Time Independent Anelastic Behavior in Ti3SiC2:
A New Physical Phenomenon
T. Zhen, S.R. Kalidindi, M.W.Barsoum, T.El-Raghy
Abstract: Ti3SiC2
, one of ternary carbides, combines some of the best properties
of ceramics and metals. It is stable in inert atmospheres to temperature
2200 C. stiff and is readily machinable, oxidation, fatigue and
thermal shock resistant and damage tolerant. Thus, Ti3SiC2
is good candidate material for high temperature structural application.
The aim of this work is to characterize of mechanical behavior of
312 at macroscopic scale as a function of temperature, strain-rate,
microstructure and stress state. Polycrystalline Ti3SiC2
sample do not exhibit linear elastic behavior in compression even
at room temperature. Room temperature loading-unloading tests result
in closed hysteresis loops even the stress reach I Gpa. suggesting
that the mechanical response can be described as an elastic. Cyclic
loading-unloading tests at high temperature and low strain rates
demonstrate that the sample continue to deform even during unloading,
suggesting that behave viso-plastically at high temperature.
Session Leader
Jürgen Rödel
Professor
TU Darmstadt
FB 11, FG Nichtmetallisch-
Anorganische Werkstoffe
Petersenstr. 23, Geb. 73a
64287 Darmstadt, GERMANY
Phone: +49 6151 16-6315
Fax: +49 6151 16-6314
Email: roedel@ceramics.tu-darmstadt.de
URL: www.tu-darmstadt.de/fb/ms/fg/naw
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