2022 年 63 巻 5 号 p. 703-710
Improving the oxidation resistance and mechanical strength of Mg2Si is an especially critical issue for practical use in thermoelectric devices. To solve this problem, a sintered sample was prepared by adding 1.1 mol% to 11.0 mol% of TiB2 powder to Mg2Si (0.2 at% Sb) powder, and the oxidation resistance and mechanical strength were evaluated. The oxidation resistance was evaluated by raising the temperature from 300 K to 1023 K in a 200 Pa H2O atmosphere using an environmental scanning electron microscope and the sample surface condition was evaluated. In addition, the composition of the sample surface layer before and after oxidation was evaluated by energy dispersive X-ray spectroscopy (EDX). Mechanical strength was evaluated by a three-point bending test from 300 K to 823 K. Thermoelectric properties were measured from 300 K to 773 K.
According to EDX analysis, the oxygen concentration in the sample without TiB2 before and after thermal oxidation was 0.26 at% and 37.15 at%, respectively, while the concentration in the sample containing 3.3 mol% of TiB2 was 0.02 at% and 6.59 at%, respectively. The bending strength of the sample without TiB2 was 152.8 MPa at 773 K, and that of the sample with 3.3 mol% TiB2 was 207.7 MPa at 773 K. The dimensionless figure of merit of Mg2Si (0.2 at% Sb) with 3.3 mol% TiB2 was 0.49 at 773 K, which was the same as without addition of TiB2. It was found that the addition of up to 4.4 mol% of TiB2 to Mg2Si can suppress oxidation and improve high temperature bending strength without affecting thermoelectric properties.
