The effect of interfacial decohesion, due to the thermal expansion mismatch, on the thermal diffusivity of a hot-pressed glass matrix with a dispersed phase of nickel was investigated by the laser-flash technique at 25" to 600°C. The interfacial gap formed on cooling acts as a barrier to heat flow and lowers the thermal diffusivity to values below those predicted from composite theory and also creates a strongly positive temperature dependence of the thermdl diffusivity. Preoxidation of the Ni spheres promotes interfacial bonding and yields values of thermal diffusivity higher than those for nonoxidized spheres and a thermal diffusivity which is relatively temperature-independent. The results of the present study also confirm the criteria for the effective thermal diffusivity of composites established by Lee and Taylor.
Data are presented for the thermal diffusivitylconductivity of hot-pressed mixtures of S i c and AIN. Results indicate that hot-pressing at higher temperatures, which permits solid-solution formation, results in significantly lower thermal diflusivityl conductivity than is obtained by hot-pressing at lower temperatures, at which discrete phases exist.
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