Precursors to ceramics

West (p. 6), Miller (p. 43), Zeigler (10), and Sawan (p. 112) outline the synthesis of a wide variety of soluble, processable polydiorganosilanes, a class of polymers which not long ago was thought to be intractable. Matyjaszewski (p. 78) has found significant improvements in the synthetic method for polydiorganosilane synthesis as well as new synthetic routes to unusual substituted polydiorganosilanes. Seyferth (p. 21, 143) reports synthetic routes to a number of new polycarbosilanes and polysilazanes which may be used as precursors to ceramic materials. 

Inorganic polymers based on alternating main group element-nitrogen skeletons (e.g. I - IV) are of interest for their potential as elastomers, high-temperature oils, electrical conductors, biological molecule carriers, and precursors to ceramic materials (J - 6). 

Soluble polysilane derivatives (I) represent a new class of radiation sensitive materials for which a number of new applications have recently appeared. In this regard, they have been utilized as (i) thermal precursors to ceramic materials (2,3) ... 

A unique characteristic of polymers composed of extended chains of Group 14 elements is the delocalization of electrons through the cr-bond framework of the polymer backbone.7 These polymers are known to absorb in the ultraviolet, with absorption maxima dependent both on main chain substituents and on chain length. Several potential applications exist, such as photoconductors, photoresists in microelectronics, photoinitiators for radical reactions, and precursors to ceramic materials. 

All our preliminary CVD experiments were carried out under an atmosphere of N2 gas in order to determine the intrinsic ability of the studied molecules to serve as precursors to ceramic materials. Further studies could be run under a reactive medium such as H2 in order to reduce the C and O content of the films. This was done in the case of compound 19. Cold-wall CVD experiments on this molecule were performed at 973 K and normal pressure under H2 carrier gas. These experiments resulted in the formation of highly pure VC films.38 XPS and EPMA-WDS analyses of these films showed both the free carbon and oxygen contents to be lower than the limits of detection of the techniques. Various factors can account for these results diminution of the C content induced by H2, stabilization of the Cp ligand in the gas phase due to the presence of f-butyl groups, and decomposition mechanism involving a methyl activation leading to the formation of V = CH2 species.38... 

These last two points concern how precursor design and synthesis are influenced by the precursor-to-ceramic conversion process. The next set of criteria identify materials properties that drive precursor design and synthesis including product selectivity. 

Detailed investigations of metal complexes of monovalent CHdo-alcohols were initiated to find alternatives to the /S-diketonate complexes as precursors to ceramic materials. In particular, mononuclear and very volatile complexes of the elements Cu, Zn, Bi, Pb were pointing the way [94], Section 4 will put the main emphasis on the adaptation of this strategy to lanthanide elements. 

The focus here on self-organizing polymers, electrical and optical properties, and biosynthesis is not even close to comprehensive in the enumeration of avenues and opportunities in new polymeric materials. Degradable plastics that do not remain in our environment forever [24] and polymer precursors to ceramics [19] and inorganic fibers are two of many more areas in which new polymeric materials will provide new challenges to engineers in production and processing. 

Thermal treatment of the polymeric precursor (3P) and molecular precursors (4) result in an amorphous material (Scheme 2). After the precursor-to-ceramic conversion, a black, dense ceramic was obtained. The density of the material was determined to be 1.6 — 1.7 g/cm. One of our main interests was to reduce the accompanying formation of gaseous by-products during pyrolysis. As shown in Fig. 2, TG measurements up to 1500 °C reveal a weight loss of ca. 37% in the case of 3P... 

Carboranes - polyhedral boranes containing carbon in the framework - have been known for over 35 years, and their intrinsic stability, versatility, structural variety, and electronic properties have been put to use in a number of diverse areas, [1] for example in the synthesis of extraordinarily heat-stable polymers, in BNCT (boron neutron capture therapy), as ligands in metallacarborane catalysts, as com-plexing agents for extraction of metal ions, as precursors to ceramics, conducting polymers, and nonlinear optical materials, as anticancer... 

Hydroxide clusters [Gdi4( 4-0H)2(/i3-0H)l6(H20)s precursors to ceramic materials by solution processing techniques MRI contrast-enhancing agent Messerle et al. (2005)... 

Therefore PSE might be a useful model system for the study of the precursor-to-ceramic conversion, despite its relatively high costs. 

Polymer pyrolysis refers to the pyrolytic decomposition of metal-organic polymeric compounds to produce ceramics. The polymers used in this way are commonly referred to as preceramic polymers in that they form the precursors to ceramics. Unlike conventional organic polymers (e.g., polyethylene), which contain a chain of carbon atoms, the chain backbone in preceramic polymers contains elements other than carbon (e.g., Si, B, and N ) or in addition to carbon. The pyrolysis of the polymer produces a ceramic containing some of the elements present in the chain. Polymer pyrolysis is an extension of the well-known route for the production of carbon materials (e.g., fibers from pitch or polyacrylonitrile) by the pyrolysis of carbon-based polymers (54). It is also related to the solution sol-gel process described in the previous section where a metal-organic polymeric gel is synthesized and converted to an oxide. 

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