Thermal and Electrical Conductivity of Porous Metals made by Powder Metallurgy Methods

Abstract

Measurements are reported of the thermal conductivity and electrical resistivity over the range of 20° c to 200° c on several specimens of a sintered porous bronze material (89% Cu, 11% Sn). The constituent powder particles were substantially spherical in shape and the specimens studied covered particle diameters ranging from 0.00133 to 0.040 cm and had densities from 5.27 to 7 01 g/cm3 The modified Lorenz relationship between the thermal conductivity K the electrical resistivity ρ and the absolute temperature T was found to apply, the experimental results satisfying the straight line K = 0.58 × 10-8 T/ρ+0.005 Existing data for solid bronzes of similar composition also conformed to this line. It is shown that, to a first approximation, the conductivities are independent of the particle size of the powder from which the specimen has been made, but can be correlated to a density basis, the values falling along a straigth line drawn from the point for the solid material to cut the abscissa at a density corresponding to the maximum porosity which can be attained on packing equal sized spheres. This method of correlation is also confirmed by data from the literature for the electrical conductivity of copper, nickel and iron Suggestions are made for estimating the thermal conductivities of similar porous materials.