Estudos em materiais vitreos e/ou ceramicos de SiCxOy e/ou SiC enriquecidos com fase dispersa de carbono / Studies in vitreous and/or ceramic materials based on SiCxOy and/or SiC enriched with dispersed carbon

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

In this study, vitreous and/or ceramic materials based on SiCxOy and/or SiC enriched with carbon were obtained by pyrolysis of hybrid polymeric precursors, in the presence or not of nickel acetate (NiAc). The polymeric precursors with and without NiAc were prepared by hydrosilylation reaction between poly(methylsiloxane) (PMS) and divinylbenzene (DVB), in different compositions. Apart from these precursors, carbon nanotubes (CNT) were added to the PMS/DVB precursor and submitted to thermal treatment at 1500°C in different times. The thermal stability and the ceramic yield of the precursors were analyzed by TGA and the polymer to ceramic conversion was monitored by XRD and IR, C and Si NMR and Raman spectra, elemental analysis and density measurements. The porosity and morphology of these materials were also evaluated. The polymeric precursor composition influenced the total carbon amount in the resulting ceramics, increasing with the DVB amount added to precursor. The effect of composition was more pronounced in the Ni-containing ceramics. In addition, the presence of Ni in the polymeric precursors promoted remarkable changes in the structure and morphology of the ceramics, particularly in relation to the crystallization and carboreduction, resulting in denser materials due to contribution of b-SiC crystalline phase. The introduction of Ni also contributed to the formation of straight and curved nanowires, mainly on the surface of the ceramic bodies, which presented different compositions according to their shapes. The increase of temperature from 950 to 1500°C promoted continuous structural transformations, leading to ordering process of Cfree phase dispersed in the ceramic matrix. The presence of CNT, used as an extra carbon source, in the polymeric precursor promoted the formation of cristobalite and b-SiC phases and the increase of defects in the Cfree phase presents in the ceramics. In the CNT-containing ceramics, the increase of the annealing time at 1500°C resulted in an ordering process of carbon nanodomains and a different morphology of the corresponding ceramics obtained without CNT.

ASSUNTO(S)

acetato de niquel nickel acetate polymeric pyrolysis hybrid polymer pirolise de polimeros polimeros hibridos silicon oxycarbide oxicarbeto de silicio

ACESSO AO ARTIGO

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