Preparation and thermoelectric properties of joint of chromel/alumel porous sintered compacts for thermoelectric transducer

The miniaturization of a thermoelectric generator of gas combustion type requires a sharp temperature gradient between hot and cold junctions. It has been proposed by R. Echigo that this could be achieved by flowing a mixture of inflammable gas and air through the continuous coarse pores of a porous thermoelectric transducer and burning it at the outlet. The present article describes the preparation and thermoelectric properties of chromel/alumel porous sintered compact for the thermoelectric transducer. The average particle sizes of both chromel and alumel coarse powders were about 300 mu m. Under the conditions of the relative density of green compact of 70%, sintering atmosphere of vacuum (10(-3) Pa), sintering temperature of 1623 K and sintering time of 3.6 similar to 14.4 ks, porous chromel and alumel sintered compacts having the following properties were obtained; continuous pores (porosity, 30%; relative density, 70%), appropriate mechanical property (bending strength at room temperature, above 90 MPa), specific electrical conductivity of about 2.5 similar to 3.6 x 10(5) S . m(-1) (ratios to the value of dense compact are about 17 similar to 24%) and 10 similar to 15 x 10(5) S . m(-1) (23 similar to 35%), respectively, and thermal conductivity of 7.1 similar to 10 Wm(-1) K-1 (23 similar to 32%) and 13 similar to 16 Wm(-1) K-1 (32 similar to 39%). And the porous thermoelectric transducer, i.e., joint of the two kinds of the sintered compacts having thermoelectric power of 4.2 similar to 4.3 x 10(-2) mV . K-1 (100%) and figure of merit of 2.2 similar to 2.6 x 10(-5) K-1 (76 similar to 90%) were obtained under the same conditions.