THERMAL-DIFFUSIVITY, HEAT-CAPACITY AND THERMAL-CONDUCTIVITY IN AL2O3-NI COMPOSITE

Thermal diffusivity, heat capacity, and thermal conductivity of Al2O3-Ni composite with 5 vol.% of Ni particulate were investigated. The thermal conductivity of the composite increases monotonically with increase of Ni particle size, and approaches a limiting value for Ni particles of 2 mu m or larger. The reduced conductivity at smaller particle sizes is due primarily to the increased interfacial resistance related to the increase of Al2O3/Ni contact area, even though metal Ni has higher value of thermal conductivity than that of Al2O3. The mode of heat conduction in the composite with the smallest Ni particulate, i.e. D=0.1 mu m, is a result of both phonons and interfacial defects, and this leads to the composite characterizing with a lower temperature-dependent thermal conductivity. The Kapitza radius of the composite was experimentally determined as approximately 0.6-0.7 mu m, at which the Ni conductivity is balanced by interfacial resistance, resulting in composite conductivity=matrix conductivity. This suggests that a minimum Ni particle size of similar to 1.4 mu m is essentially required for the improvement of the overall thermal conductivity in Al2O3-Ni composite.