Gordon Research Conference

Rishi Raj
University of Colorado at Boulder, Boulder CO

Synopsis of the presentation:

PDCs represent a new direction in the science of ceramic materials for the following reasons: (i) they are made directly from molecular organics into highly refractory ceramics by casting, polymerization and pyrolysis, (ii) the resulting materials are highly refractory, having much greater resistance to creep and far greater micro/nanostructural stability than conventional ceramics, (iii) their creep resistance is contrary to conventional wisdom since are essentially glasses, or at least appear to be so in x-ray diffraction, and (iv) the polymer route offers unlimited opportunity to create nanophases that impart functional properties to the ceramic material.

The talk will highlight the above issues, emphasizing the scientific issues that must be addressed for this sub-field of ceramics to move forward; these are summarized below.

Key outstanding areas relevant to this presentation:

The most critical issue is clarification of the nanostructure of PDCs. This is a challenge because new spectroscopic techniques must be used to elucidate the molecular bondings and environments that give rise to such unusual properties as described above.

Selected publications for background information:

1. "Newtonian Viscosity of Amorphous Silicon Carbonitride at High Temperatures", L. An, R. Riedel, C. Konetschny, H. -J. Kleebe and R. Raj, J. Amer. Ceram. Soc., 81, 5, 1349-52 (1998).
   
   
2. "Amorphous Silicoboron Carbonitride Ceramic with very high Viscosity at Temperatures above 1500 °C ", R. Riedel, L. M. Ruswisch, L. An and R. Raj, J. Amer. Ceram. Soc., 81, 12, 3341-44 (1998).
   
   
3. "Oxidation Kinetics of an Amorphous Silicon Carbonitride Ceramic", R. Raj, L. An, S. Shah, R. Riedel, C. Fasel and H.-J. Kleebe, J. Am. Cer. Soc., Vol 84 [8], 1803-10 (2001).
   
   
4. "Pyrolysis Kinetics for the Conversion of a Polymer into an Amorphous Ceramic", L. Pederiva, G.D. Soraru, J. Latournerie and R. Raj, submitted to J. Amer. Ceram. Soc., November 2001.
   
   
5. "Nanoscale Densification Creep in Amorphous Silicon Carbonitride", S. Shah and R. Raj, J.Amer. Ceram. Soc.,Vol. 84 [10], 2208-12 (2001).

Contact information of the speaker:

Rishi Raj
Professor
Department of Mechanical Engineering
University of Colorado at Boulder
Boulder CO 80309-0427

Phone: (303)492-1029
Fax: (303)492-3498

Email: rishi.raj@colorado.edu
URL: http://me-www.colorado.edu/~rajr/ultratemp/

Peter Greil
University of Erlangen, Erlangen, GERMANY

Synopsis of the presentation:

Hierarchically structured biopolymers such as proteines, nucleic acids, etc. have become of particular interest to serve as a template for nanoscaled organization of inorganic as well as organic and metallic materials structures. For example, biomineralization of hydroxyapatite on skleroproteines like collagene and of iron oxide in spheroproteine compartements like ferritine or precipitation of metal clusters on DNA nanowires are well known. While most of the research efforts were directed on the physico-chemical understanding of the fundamental molecular interaction mechanisms which govern the local material synthesis reaction, less work was devoted to the question of how to scale up nanostructures by templating processing into macro devices to be used in materials engineering applications.

This work reports on the use of polysaccharides as a microstructure template for ceramic processing covering various hierarchical levels. Ceramic fibers and cellular ceramics with anisotropic pore architecture were prepared from native as well as chemically modified cellulose template structures. The formation of threedimensional cellulose templates with special cell geometries based on surface-tension driven Bénard-Marangoni convection at a liquid interface offers the possibility for producing micropatterned ceramic structures. Fundamental questions to be addressed with respect to the potential of polysaccharide templates for ceramic processing will be:

• effect of chemical and molecular structure on self assembling behavior;
• modification of cellulose by coupling with functional and linker molecules;
• structural rearrangement during thermal or enzymatic degradation;
• mechanisms and kinetics of ceramic formation at the biorganic-inorganic interface.

Polysaccharides are produced on a large scale by the photosynthesis process in nature. A wide range of chemical and structural varieties are available which can further be extended by chemical modification. The cristalline and chiral molecular structure of fibrillar polysaccharides offers the possibility for designing one as well as two and even three dimensional template structures. Compared to many other biopolymers the polysaccharides exhibit an improved thermal and chemical stability which should facilitate their implementation into advanced ceramic manufacutring technologies.

Key outstanding areas relevant to this presentation:

Structure hierarchy and preservation of symmetry and anisotropy in macroscopic materials and components will be the subject of advanced ceramics processing science in the future. Transfer of nanoscale microstructure and properties to macroscale material without loss of structural information has yet to be achieved. Coupling of properties at different microstructure levels in brittle ceramics is still a matter of basic consideration. Following the concept of mircoshaped materials (Ashby) three dimensional cellular templates will be of particular interest for macro- as well as micro-shaping of ceramic materials over a wide range of length scales.

Polysaccarides and its derivatives as well as biocarbon derived from those biopolymers are supposed to have an interesting potential for serving as hierarchically structured templates in the processing of ceramics. Their availability in nature (annual production rate by photosynthesis 1010- 1011 tons), chemical versatilit, and crystallinity are of particular interest for tailoring of hierarchically structured template substrates. Naturally grown plant tissue as well as chemically processed three dimensional arrays of cellulose are accessible for gaseous or liquid precursors which subsequently may react at the functionalized surface to form cellular ceramic structures. Thus, structure, properties, and templating behavior of polysaccaride substrates will be a matter of future research activities in bioinspired ceramics processing science.

Selected publications for background information:

1. P. Greil, "Biomorphous Ceramics from Lignocellulosics", J.Europ.Ceram.Soc. 21 (2001) 105-118 P. Greil, T. Lifka, A. Kaindl, "Biomorphic Cellular Silicon Carbide Caeramics from Wood: I. + II", J.Europ.Ceram.Soc. 18 (1998) 1961-1983
   
   
2. D. Klemm, B. Philipp, T: Heinze, U. Heinze, W. Wagenknect, "Comprehensive Cellulose Chemistry", Wiley-VCH, Weinheim, (2001)
   
   
3. T. Boek, A. Thess, "Inertial Bénard-Marangoni Convection", J.Fluid Mech. 350 (1997) 149-175
   
   
4. L.J. Gibson, M.F. Ashby, Cellular Solids, Cambridge Univ.Press, (1999)
   
   
5. C.M. Niemeyer, "Nanoparticles, Proteines and Nucleic Acids: Biotechnology meets Material Science", Angew. Chemie 113 (2001) 4254-4287 (in German)

Contact information of the speaker:

Peter Greil
Professor, Department of Materials Science (III)
University of Erlangen
Martensstr. 5
D-91058 Erlangen, Germany

Phone: 0049 (9131) 8527543
Fax: 0049 (9131) 8528311
Email: greil@ww.uni-erlangen.de
URL: www.glass-ceramics.uni-erlangen.de

Session Chair Contact Info

Rowland M. Cannon
Evans Hall (MC 1760)
Lawrence Berkeley National Laboratory
Berkeley, CA 94720

Phone: 510-642-9338
Fax: 510-486-6086

Email: cannon@socrates.berkeley.edu