The thermal conductivity of a 40 vol% silicon carbide-particulate-reinforced aluminum matrix composite was determined as a function of silicon carbide mean particle size ranging from 0.7 to 28 pm. A size dependence was found consisting of a decrease in thermal conductivity with decreasing Sic particle size. This effect is in accordance with theoretical expectations for composites with an interfacial thermal barrier at the dispersion-matrix interface. At the finest particle size of the silicon carbide, the composite thermal conductivity approached the value for the matrix with pores, as expected from theory. Only at the largest SIC particle size did the composite thermal conductivity exceed the value for the matrix. These results suggest that in maximizing the thermal conductivity of composites with an interfacial thermal barrier, the reinforcement particle size should be as large as practically possible.

Experimental thermal diffusivity data transverse to the fiber direction for composites composed of ;a reaction bonded silicon nitride matrix reinforced with uniaxially aligned carbon-coated silicon carbide fibers indicate the existence of a significant thermal barrier at the matrix-fiber interface. Calculations of the interfacial thermal conductances indicate that at 300°C and 1-atm N2, more than 90% of the heat conduction across the interface occurs by gaseous conduction. The magnitude of the interfacial cainductance is decreased significantly under vacuum or by removal of the carbon surface layer from the fibers by selective oxidation. Good agreement is obtained between thermal conductance values for the oxidized composite at 1 atmi calculated from the thermal conductivity of the N3 gas and those inferred from the data for the effective composite thermal conductivity. [

The effect of 15 vol% particulate diamond reinforcement on the thermal conductivity of a cordierite matrix was studied as a function of diamond particle size from room temperature to 700°C. The thermal conductivity was found to increase with increasing particle size to a maximum increase of about 75% for a mean particle size of 50 pm. The particle size effect was found to be more pronounced at the lower temperatures than at the higher temperatures. The observed effect of particle size and temperature was attributed to the existence of an interfacial thermal barrier, possibly resulting from interfacial phonon scattering, with a positive temperature dependence of the interfacial thermal conductance. The magnitude of this conductance suggested strong adhesion between the diamond and cordierite.