Rapid Rate Sintering of Yttria Transparent Ceramics

This paper reports on the influence of rapid rate sintering (RRS) on densification and microstructure evolution of yttria transparent ceramics by using vacuum sintering. The presence of temperature gradient has been confirmed during the RRS process. The higher the heating rate (HR), the larger the temperature gradient in the samples would be. By using RRS, e.g., HR = 40 degrees C/min, the samples could be densified very fast to a relative density of 99.6%. However, these samples could not be further densified, due to the presence of difference in densification caused by a heating rate-induced temperature gradient. By using a two-step RRS with an intermediate-temperature thermal treatment, this problem has been successfully addressed. The intermediate-temperature treatment allowed for the particle neck growth, so that effective thermal conductivity of the compacts was increased greatly. Therefore, the temperature gradient and differentiate densification were effectively prevented. Samples sintered using the two-step RRS process could be fully densified and excellent in-line optical transmittance was achieved. It is believed this strategy is applicable to other transparent ceramics, as well as other engineering ceramics.