Preparation of .BETA.-FeSi2 by liquid phase sintering and its thermoelectric properties.

Abstract

Effects of Al or Cu addition on sintering behavior, phase transformation during sintering and thermoelectric properties of β-FeSi2 were investigated. Al addition narrowed down the temperature range where the β phase was stable. In the sintering of the samples with Al addition before mechanically ground (MG), liquid phase of Al was not formed. In the case of Al addition after MG, Al-Si eutectic liquid was formed around 850K. However, the liquid phase formation caused remarkable swelling of the compacts. When Cu was added to FeSi2 powder, Cu-Si eutectic liquid was formed around 1075K during heating. The liquid phase formation was quite effective for the compound densification. Cu addition caused a rapid transformation to the β phase around 1100K during cooling. From these results, it is evident that Cu addition enables a densely sintered β-FeSi2 compound to be synthesized through the sintering only, without a conventional heat treatment for the β phase formation. The thermoelectric power and electrical resistivity of the samples with Cu addition were improved with increasing Cu content. The maximum value of the figure of merit, which is almost same as the hot-pressed samples, was obtained for the sample with 4 mass% Cu addition.