Exploring the evolution of pores in HIPed Y2O3 transparent ceramics

Y2O3 transparent ceramics were fabricated by using vacuum sintering followed by hot isostatic pressing (HIPing). After HIP, large pores were eliminated, but a certain amount of nano-sized pores survived. Air annealing is required to bleach the as-HIPed ceramics. However, the annealing temperatures affected the transparency by affecting the evolution of the residual nano-pores. A high annealing temperature of >= 1600 degrees C resulted in obvious pore growth and loss of transparency of the samples. Pressure-less thermal expansion and shrinkage behaviors of the as-HIPed Y2O3 ceramics were studied in detail. The high annealing temperature (1600 degrees C) could lead to obvious swelling of both the pore sizes and the dimensions of the samples. It implies that the swelling of pores is not only from the diffusion and aggregation of the existing smaller pores, but may also from the thermal expansion of the high-pressure precipitated insoluble gas.