Polissiloxanos polissilazanos como precursores de materiais ceramicos e suas aplicacões na obtenção de compositos de matriz ceramica

AUTOR(ES)
DATA DE PUBLICAÇÃO

2002

RESUMO

In this work different preceramic polymers, as polysiloxane and polysilazane were prepared, and their conversions by controlled pyrolysis to silicon oxycarbide (SiOC) and silicon carbonitride (SiCN) glasses, respectively, were studied. The polysiloxane was prepared from 1,3,5,7-tetravinyl-1,3,5,7-tetramethylciclotetrasiloxane and 1,3,5,7-tetramethyl-1,3,5,7-ciclotetrasiloxane oligomers, by hydrosilylation reaction, and the polysilazane by radicalar polymerization of 1,3,5-trivinyl-1,3,5-trimethylciclotrisilazane oligomer. The polymer-to-ceramic conversion was monitored by techniques as IV, RMN Si-29 and C-13, and XRD. Ceramic matrix composites (CMC) as SiC/SiOC and Si3N4/SiOC were prepared using polysiloxane and SiC and Si3N4 inert fillers. The mixture of this polymer with CrSi2, as reactive filler, generated SiC/CrSi2 and Si3N4/Cr3C2 composites, under Ar and N2 atmospheres, respectively. In all these cases the polysiloxane not only acted as a binder of ceramic particles, but also as a precursor of the ceramic phase, making possible the control of the shrinkage and the porosity of the CMC s. The CMC s presented good mechanical properties when evaluated by three-point flexural and abrasion resistance tests. The introduction of boron in the polysiloxane, by the sol-gel process, and in the polysilazane, by hydroboration, was easily achieved, generating poly(borosiloxanes) and poly(borosilazanes) with different boron amounts. While the silicon-boron carbonitride presented low crystallization rate in higher temperatures, when compared to the correspondent glass without this element, the silicon-boron oxycarbide presented contrary effect.

ASSUNTO(S)

carboneto de silicio polimeros ceramica pirolise materiais compostos

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