Stability and electrical properties of MoSi2‐ and WSi2‐oxide electroconductive composites

Abstract

AbstractMoSi2‐ and WSi2‐based electroconductive ceramic composites were fabricated using 40‐80 vol% fine‐ and coarse‐Al2O3, and ZrO2 particles (refractory oxides) after sintering in argon. Their chemical and thermal stability was tested between 1400°C‐1600°C for up to 48 hours. X‐ray diffraction analysis showed the formation of secondary 5‐3 metal silicide (Mo5Si3, W5Si3) and silica phases on the grain boundaries and surface. The fraction of the W5Si3 (11.4‐38.8 vol%) was significantly higher than that of the Mo5Si3 (3.3‐7.3 vol%) in the composites after annealing at 1400°C for 48 hours. The rates of grain growth in the composites (0.013‐0.023 μm/h) were highly decreased by a grain‐boundary pinning effect. This effect was relatively better with the addition of the coarse‐grained oxides due to their more homogeneous distribution throughout the microstructure. The 20–80 vol% MoSi2‐Al2O3 (fine‐grained) composite exhibited an electrical conductivity of 8.8 S/cm at 900°C. At the 60 vol% silicide content, MoSi2–Al2O3 (coarse‐grained) and WSi2–Al2O3 (fine‐grained) showed higher electrical conductivity (126‐128 S/cm) at 900°C. The density, porosity level, particle distribution, intrinsic conductivity of silicide phase, particle size, and fraction of the secondary 5‐3 silicide phase highly influenced their electrical properties.