, Volume 26, Issue 20, pp 5495-5501

Thermal properties of chemical vapour-deposition SiC-C nanocomposites

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Abstract

The relationship between the thermal properties and the microstructure of chemical vapour-deposition (CVD) SiC-C nanocomposites, covering the entire composition range from SiC to C, was investigated after measuring thermal conductivity and thermal expansion. The samples were prepared under deposition temperatures (T dep) of 1673 and 1773 K and total gas pressure (Ptot) of 40 kPa. The thermal conductivity of CVD SiC-C nanocomposites decreased as C content increased. For the deposits containing 24.3 to 71 mol % C prepared atT dep = 1773 K, some parts of the C phase formed a layered structure having its plane parallel to the deposition surface. This arrangement reduced the thermal conductivity in the direction perpendicular to the deposition surface to a much lower value. The CVD C and CVD C-SiC containing < 1.5 mol % SiC showed strong anisotropic thermal expansion. However, the thermal expansion of CVD SiC-C nanocomposites having a C content up to about 70 mol % was isotropic and nearly equal to that of CVD SiC. The low preferred orientation and the low modulus of elasticity of the C phase may be reasons for these results.