Studies on Sintering Y₂O₃

Abstract

Y₂O₃ is chemically stable and one of the hopeful refractory materials. It is, however, difficult to obtain the dense Y₂O₃ pieces using an ordinary sintering method without any additives. A few kinds of powders were sintered by the ordinary method. The effect of sintering conditions such as sintering temperature, sintering time and atmosphere on sinterability of Y₂O₃ were investigated.
Total impurity of every Y₂O₃ was less than 0.1% and the average grain size of the powder was 4-6μm. The compacting pressure was 0.17-17t/cm². The green compacts were heated at 1, 700-2, 120°C for 30-100 min in a H₂ (d. p. -36 or 20°C) atmosphere or an Ar atmosphere. When the density of green compacts was 2.0-2.7g/cm³, the density of sintered pieces in a H₂(d. p. -36°C) atmosphere increased with that of green compacts. The sintered pieces became black from the inside. In-line transmittance of the sintered pieces in a H₂(d. p. 20°C) atmosphere increased with the grain size. Grain size was observed and described by D=(1.33-3.15)×10⁹t^1/2 exp (-9×10⁴/RT). Activation energy for the grain growth was approximately 90kcal/mol. The pieces sintered in an Ar atmosphere had the brown or dark surface layer where Mo was detected.
A translucent Y₂O₃ piece was obtained, which has in-line transmittance of 70% at 0.76mm thickness in the visible range.