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|Type:||Artigo de periódico|
|Title:||Novel poly(borosiloxane) precursors to amorphous SiBCO ceramics|
|Abstract:||Novel poly(borosiloxanes), with a B/Si molar ratio of 0.2, were synthesized by a dehydrogen coupling reaction of 1,3,5,7-tetramethyl-1,3,5,7-tetracyclotetrasiloxane (D(4)H) oligomer and boric acid, B(OH)(3), and by hydrolysis/condensation reactions of vinyltriethoxysilane and B(OH)(3), followed by a hydrosilylation reaction with D(4)H, which gave rise to boron and silicon oxycarbide glasses (SiBCO), by pyrolysis. The polymers as well as the polymer-to-ceramic transformation resulting in SiBCO glasses, at 1000 degrees C, were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier-transform infrared (FTIR), (29)Si and (11)B MAS NMR spectroscopies. FTIR spectra of the poly(borosiloxanes) obtained showed an absorption at similar to 880 cm(-1), assigned to the stretching of Si-O-B=bonds, which is an evidence for the connectivity between the silicon oligomers and BO(3) units. The pyrolysis of these polymers at 1000 degrees C, in argon atmosphere, produced black and amorphous SiBCO materials. (29)Si NMR analyses of these glasses showed different distributions of Si sites, similar to those observed for silicon oxycarbide glasses. (C) 2008 Elsevier B.V. All rights reserved.|
|Editor:||Elsevier Science Sa|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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