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 the rmal conductivity of the composite increases monotonically with increa se of Ni particle size, and approaches a limiting value for Ni particl es of 2 mu m or larger. The reduced conductivity at smaller particle s izes is due primarily to the increased interfacial resistance related to the increase of Al2O3/Ni contact area, even though metal Ni has hig her 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 thi s leads to the composite characterizing with a lower temperature-depen dent thermal conductivity. The Kapitza radius of the composite was exp erimentally determined as approximately 0.6-0.7 mu m, at which the Ni conductivity is balanced by interfacial resistance, resulting in compo site 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.