Effects of Al particles and thin layer on thermal expansion and conductivity of Al–Y₂Mo₃O₁₂ cermets

Low thermal expansion composites are difficult to obtain by using Al with larger positive thermal expansion coefficient (TEC) and the materials with smaller negative TECs. In this investigation, Y₂Mo₃O₁₂ with larger negative TEC is used to combine with Al to obtain a low thermal expansion composite with high conductivity. The TEC of Al is reduced by 19% for a ratio Al:Y₂Mo₃O₁₂ of 0.3118. When the mass ratio of Al:Y₂Mo₃O₁₂ increases to 2.0000, the conductivity of the composite increases so much that a transformation from capacitance to pure resistance appears. The results suggest that Y₂Mo₃O₁₂ plays a dominant role in the composite for low content of Al (presenting isolate particles), while the content of Al increases enough to contact each other, the composite presents mainly the property of Al. For the effect of high content Al, it is considered that Al is squeezed out of the cermets during the uniaxial pressure process to form a thin layer on the surface. (paper)