Properties of polymer-derived ceramics

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Narisawa, H.P., K. Nakoshiba, and K. Okamara. 1995. Effect of rapid heat treatments on electrical properties of polymer derived ceramic fibers. Pp. 287 292 in High-Temperature Ceramic-Matrix Composites II Manufacturing and Materials Development Vol. 58 in Ceramic Transactions, A.G. Evans and R. Naslain (eds.). Westerville, Ohio American Ceramic Society. 

Torrey, J. D., Bordia, R. K. (2008b). Mechanical properties of polymer-derived ceramic composite coatings on steel. Journal cf the European Ceramic Society, 2S(1), 253-257. doi 10.1016/j.jeurceramsoc.2007.05.013. 

Summary Precursor-derived quaternary Si-B-C-N ceramics frequently possess an enhanced thermal stability compared to SiC, SisN4 or Si-C-N ceramics. The stability of the materials towards crystallization and/or decomposition is directly coimected to the molecular structure and the elemental composition of the polymeric precursors. This paper highlights recent investigations on the synthesis of boron-modified polysilazanes and polysilylcarbodiimides. Hydroboration of polyvinylsilazanes and dehydrocoupling reactions of boron-modified silanes with ammonia or amines as well as cyanamide are described. It is shown that simple organosilicon chemistry provides a means to efficiently optimize ceramic yields and tune elemental composition as well as thermal properties of the polymer-derived ceramics. 

Hitherto we have discussed the formation of amorphous covalent ceramics only on the basis of polymer derived materials. In Sects. 2.2 and 4.2.2.2, thin amorphous, hydrogen stabilized SiC layers (a-SiC H) are also considered which are formed, first of all, by gas phase processes (CVD, PVD). They represent another type of amorphous covalent ceramics. And though it is not expected that properties of such layers agree completely with those of the polymer derived ACC, the basic ideas of stability and transformability of the ACC state discussed above should be transferable to this type of amorphous covalent ceramics, too. 

In Chapter 1, we observed that plastics have experienced a phenomenal growth since World War n, when they assumed enhanced commercial importance. This explosive growth in polymer applications derives from their competitive costs and versatile properties. Polymers vary from liquids and soft rubbers to hard and rigid solids. The unique properties of polymers coupled with their light weight make them preferable alternatives to metallic and ceramic materials in many applications. In the selection of a polymer for a specific end use, careful consideration must be given to its mechanical properties. This consideration is important not only in those applications where the mechanical properties play a primary role, but also in other applications where other characteristics of the polymer sueh as eleetrical, optical, or thermal properties are of crucial importance. In the latter cases, mechanical stability and durability of the polymer may be required for the part to perform its function satisfactorily. 

In 19 6 the principle means of measuring mechanical properties of polymers were the test methods derived from older technologies such as metals and ceramics. They had to be revised for these relatively new materials but little atttention had been payed to the question of whether or not these materials were so different that a new approach should be taken. We asked ourselves what does one really need to know about polymers to apply them properly. 

Polymer-derived ceramics (PDCs) represent a rather novel class of ceramics which can be synthesized via cross-linking and pyrolysis of suitable polymeric precursors. In the last decades, PDCs have been attaining increased attention due to their outstanding ultrahigh-temperature properties, such as stability with respect to decomposition and crystallization processes as well as resistance in oxidative and corrosive environments. Moreover, their creep resistance is excellent at temperatures far beyond 1000 °C. The properties of PDCs were shown to be strongly related to their microstructure (network topology) and phase composition, which are determined by the chemistry and molecular structure of the polymeric precursor used and by the conditions of the polymer-to-ceramic transformation. 

Polymer derived ceramics have been known for the last four decades and are prepared via solid-state thermolysis of preceramic polymers. They exhibit a unique combination of remarkable properties due to their covalent bonding and amorphous nature. Thus, silicon oxycarbide (SiOC) and silicon carbonitride (SiCN) based ternary PDCs have been shown to possess outstanding high-temperature properties such as stability with respect to crystallization and decomposition, oxidation and corrosion resistance as well as excellent thermomechanical properties (e.g., near zero steady state creep resistance up to temperatures far beyond 1000 °C). Their properties are directly influenced by the chemistry and the architecture of the preceramic precursors, thus there is an enormous potential in tuning the microstructure and properties of the PDCs by using tailored polymers. Furthermore, suitable chemical modification of the preceramic precursors leads to quaternary and multinary ceramics, as it has been shown for instance for silicon boron carbonitride ceramics in the last 25 years, which in some cases exhibit improved properties as compared to those of the ternary materials. 

Martinez-Crespiera, S., Mera, G., Riedel, R. (2012). Polymer derived-ceramic micro electro mechanical systems (PDC-MEMS). In Bernard, S. (Ed), Design, Processing and Properties of Ceramic Materials from Preceramic Precursors (pp. 37-72). Nova Science Publishers, Inc.. 

Riedel, R., Mera, G., Hauser, R., Klonczynski, A. (2006). Silicon-based polymer-derived ceramics S3mthesis properties and applications - A review. Journal of the Ceramic Society of Japan, 774(1330), 425 144. doi 10.2109/jcersj.l 14.425. 

The production of boron containing Si-C-N-ceramics provides an efficient system for materials with high thermal stability. Previously, the preparation of quaternary systems such as Si-B-C-N was realized by blending boron-containing compounds with polysilazanes This processing route leads to an inhomogenous elemental distribution in the finally received ceramic. In the last few years several investigations of ceramics derived from different polymers have been performed [1-3]. Therefore, the stoichiometry and basic structure units determine the properties of the final non-oxide ceramic materials [4-5]. 

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