Sintering in the Binary System MoSi2-WSi2

Abstract

Molybdenum disilicide has recently been developed as an excellent heating element of high refractoriness and of high oxidation resistivity. The binary system of MoSi2-ZrO2 was studied for the purpose of improving the too low electrical resistivity of MoSi2 without changing the other favorable characteristics.ZrO2 used was previously stabilized by dissolving 10 mol % of Y2O3 at 1600°C. Samples of six different chemical compositions differing from each other by 20% in ZrO2 content, were formed under the pressure of 6ton/cm2 and sintered at five different temperatures between 1300° and 1650°C in H2 gas.The electrical resistivity, density and modulus of rupture were measured on sintered specimens and expressed as functions of sintering temperature, chemical composition and sintering time.The density becomes minimum at about 60% of ZrO2 content and the modulus of rupture varies approximately with the density.The electrical resistivity at a room temperature increases rapidly with the amount of ZrO2 above 60%. The change of the electrical resistivity was also investigated up to the surface temperature of 1700°C. The resistivity increases with temperature on the MoSi2 side, while decreases on the ZrO2 side.The thermal shock test by repeated rapid heating and cooling between a room temperature and 1400°C, showed that the samples of the medium composition had the least thermal shock resistance.