As precursors for ceramic materials

We have described new routes to useful preceramic organosilicon polymers and have demonstrated that their design is an exercise in functional group chemistry. Furthermore, we have shown that an organosilicon polymer which seemed quite unpromising as far as application is concerned could, through further chemistry, be incorporated into new polymers whose properties in terms of ceramic yield and elemental composition were quite acceptable for use as precursors for ceramic materials. It is obvious that the chemist can make a significant impact on this area of ceramics. However, it should be stressed that the useful applications of this chemistry can only be developed by close collaboration between the chemist and the ceramist. 

Di-t-butyl phosphate complexes of zinc were synthesized as precursors for ceramic material formation. A tetrameric zinc complex was characterized from the treatment of zinc acetate with the phosphate resulting in a compound with a bridging oxo at the center, [Zn4(/i4-0)(di-t-butyl phosphate)6]. In the presence of auxiliary donor ligands such as imidazole or ethylenediamine, monomeric complexes are formed, [Zn(di-t-butyl phosphate)2(imidazole)4]. It is also possible to convert the tetramer into the monomer by treating with a large excess of imidazole.41... 

The last chapter includes the numerous biochemical applications of carbodiimides, and the chapters on silicon substituted carbodiimides and metal substituted carbodiimides include their role as precursors for ceramic materials. 

Because of the growing importance of homo- and heterometallic alkoxides (3, 24) as precursors for ceramic materials by the MOCVD technique (cf. Section VIII), their mass spectroscopic studies should be very useful in ascertaining their applicability. 

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. 

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... 

Silicate and Hybrid Materials through Molecular Siloxanes. Renewed interest in monosilanols and si-lanediols is primarily because compounds obtained from [(ffiuO)3SiOH] and (fBuO)2Si(OH)2] serve as better singlesource precursors for ceramic materials. A number of metallasiloxanes have been synthesized starting from [(fBuO)3SiOH, and a selection of these compounds is... 

Besides polysilazanes, PSCs are intensively investigated preceramic polymers for ternary Si-C-N materials. Their polymer backbone is composed of alternating Si-N=C=N nnits. Bis(silyl)carbodiimides, R3Si-N=C=N-SiR3 (R = alkyl) have been known since the early 1960s.Flowever, similar to low-molecular weight silazanes, they evaporate with heat treatment and are therefore not suitable as precursors for ceramics. PSCs were first obtained by Pump and Rochow ° in 1964 by metathesis reactions of dichlorosilanes and disilvercyanamide. 

Although organoaluminum-oxygen derivatives (alumoxanes) are extremely important compounds in Ziegler-Natta polymerization of olefins and molecular precursors for ceramic materials [70, 71], their structure was considered an enigma as recently as 1994 [72] although considerable experimental data indicating association... 

S. Szafert, J.L. Utko and Sobota, Well-defined polynuclear heterometallic complexes as precursors for ceramic and magnetic materials, Dalton Trans., vol. 46, pp. 6509-6520, 2008. 

Yajima s trendsetting work has not only renewed interest in polysilanes but also in other polymeric materials that can function as precursors for ceramics such as silicon nitride, Si3N4 and boron nitride, BN [6]. 

The interest in transition metal-containing polymers stems from the optical, biological, thermal, catalytic, electrical, and magnetic properties of these materials. They are candidates as essential materials for a wide variety of applications for the 21st century because of these properties. They are used in the coatings, colorants, pharmaceutical, aerospace, and communications industries. They can serve as precursors for ceramics. 

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) ... 

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