Preceramic polymers characterization

Characterization of Preceramic Polymers. The study of the pyrolysis products of preceramic polymers is not always straightforward. If crystalline species are produced (e.g., SiC and Si3N4 in the case of polysilazanes), then their identification by X-ray diffraction presents no problems. 

Research in the preceramic polymer area, if it is to come to fruition, must be an interdisciplinary endeavor. After the chemistry has been developed, there are important ceramics issues to be addressed. Good chemistry does not guarantee good ceramics However, there is the possibility that the chemistry can still be modified to give good ceramics. Either the chemist must learn a good bit about ceramics characterization and processing... 

Silicon-containing preceramic polymers are useful precursors for the preparation of ceramic powders and fibers and for ceramic binder applications (i). Ceramic fibers are increasingly important for the reinforcement of ceramic, plastic, and metal matrix composites (2, 3). This chapter will emphasize those polymer systems that have been used to prepare ceramic fibers. An overview of polymer and fiber processing, as well as polymer and fiber characterization, will be described to illustrate the current status of this field. Finally, some key issues will be presented that must be addressed if this area is to continue to advance. 

The preceding brief discussion, shows that a wide variety of characterization techniques have been used to characterize preceramic polymers and the derived ceramic fibers. Although some structural details remain elusive, the structural understanding of these fibers has advanced dramatically during the past 5 years. 

Characterization serves as an indispensable adjunct to synthesis and processing activities. To this end, the preceramic polymers must be intensively characterized and the cure kinetics of the pyrolytic processing studied extensively. The characterization portion is therefore generally composed of studies pertaining to (1) thermal processing and (2) materials properties. Table 1 is a summary of the pertinent instrumental techniques. 

In general, all preceramic polymers are susceptible to further crosslinking due to ongoing polycondensation, even at ambient conditions. Thus, this kind of polymer can be denoted living polymers. This issue is crucial to all aspects related to storage, handling, and processing as well as to analytical characterizations. 

The Polymer Data Handbook offers, in a standardized and readily accessible tabular format, concise information on the syntheses, structures, properties, and applications of the most important polymeric materials. Those included are currently in industrial use or they are under study for potential new applications in industry and in academic laboratories. Considerable thought was given to the criteria for selecting the polymers included in this volume. The first criterion was current commercial importance—the use of the polymer in conunercial materials—for example, as a thermoplastic, a thermoset, or an elastomer. The second criterion was novel applications—a polymer that is promising for one or more purposes but not yet of conunercial importance—for example, because of its electrical conductivities, its nonlinear optical properties, or its suitability as a preceramic polymer. The hope is that some readers wiU become interested enough in these newer materials to contribute to their further development and characterization. Finally, the handbook includes some polymers simply because they are unusually interesting—for example, those utilized in fundamental studies of the effects of chain stiffness, self-assembly, or biochemical processes. 

DAVID WILSON is a research specialist with 3M and has more than 10 years of research and development experience in the synthesis of new ceramic fibers using sol-gel techniques and is the inventor of the Nextel 610 and Nextel 720 ceramic fibers. His experience includes the development of novel fiber precursor formulations, continuous fiber processing, and characterization of ceramic fibers at room and elevated temperatures. Current research activities include preceramic polymer-derived SiC fibers and MOCVD coating and composite fabrication for the Mullite Matrix Composite Consortium Program. Mr. Wilson holds four patents and is the author of several publications. 

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