Densification and grain growth behaviour of high-purity MgO ceramics by hot-pressing

High-purity MgO ceramics with a relative density higher than 99.60% and a mean grain size of 8.1 mu m were prepared by hot-pressing at 1450 degrees C and 35 MPa for 120 min. The MgO ceramic was 130 mm in diameter and 10 mm in height. The densification mechanism and grain growth of MgO powder during the sintering process were investigated based on the principles of general deformation and classical phenomenological kinetic theory. The threshold pressure of plastic deformation at the initial sintering stage was also analysed. The results suggest that plastic deformation is the dominant densification mechanism during the initial period and that an applied pressure of 20 MPa is sufficient for the deformation. During the final period, Mg2+ diffusion along the grain boundaries controls the densification process, and the grain growth activation energy at the final stage is estimated as 336.38 +/- 2.35 kJ mol(-1).