Thermal and optical properties of transparent magnesium oxide ceramics fabricated by post hot-isostatic pressing

The transparent magnesium-oxide (MgO) ceramic could be fabricated by a hot-isostatic press (HIP) technique of pressureless-sintered MgO compact, using non-agglomerated MgO powder with the average primary particle size of 57 nm. The relative density and average grain size of MgO compact pressureless-sintered at 1600 °C for 5 h were 96.7% and 10.7 μm, respectively. Owing to the HIPing operation (0.5 h) of pressureless-sintered compact at a temperature between 1500 and 1600 °C, relative densities of the MgO ceramics attained 99.9% or more with light transmission. The average grain size increased from 132 to 199 μm with HIPing temperature from 1500 to 1600 °C. The in-line transmission of the MgO specimen HIPed at 1600 °C for 0.5 h increased from 52 to 55% with increasing wavelength from 500 to 900 nm and corresponded to approximately 65%, compared to that of the MgO single crystal. The thermal conductivity of this MgO specimen attained 53.5 W m^-1 K^-1, whereas the thermal diffusivity decreased gradually to reach 0.0416 cm² s^-1 with increasing test temperature up to 873 K.