Grain Growth, Mechanical Strength and Light Transmission of Hot-pressed Alumina

Abstract

Hot-pressing of Linde C alumina was carried out at the temperature range from 1700° to 1900°C. Average grain size, bending strength and transmission of light were measured. The rate of grain growth for hot-pressed alumina was compared with that for ordinarily sintered alumina.Results obtained are as follows:(1) The rate of continuous grain growth of alumina during hot-pressing was smaller than that during ordinary sintering. In other words, continuous grain growth was hindered by pressing at high temperatures. This phenomenon might come from the concentration depression of lattice vacancies caused by compressive stress.(2) Continuous grain growth of alumina during hot-pressing was retarded by addition of 0.16wt% magnesia.(3) Alumina was subjected to discontinuous grain growth easily in carbon-monooxide and nitrogen atmosphere.(4) The bending strength of specimens was in the range from 20 to 67kg/mm2, and was inversely proportional to 0.6 power of the average grain diameter.(5) Hot-pressed alumina specimens showed good translucency. Transmission of light was about 55%/mm for a specimen hot-pressed at 1900°C for 60 min.