Effect of Sintering Atmosphere on Isolated Pores During the Liquid‐Phase Sintering of MgO‐CaMgSiO4

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Abstract
The shrinkage behavior of isolated pores during the liquidphase sintering of MgO‐CaMgSiO4 at 1650°C in O2 and N2 atmospheres has been studied. When 90MgO‐ 10Ca MgSiO4 specimens containing artificially produced large spherical pores are sintered in O2, the liquid and grains flow into the pores as oxygen diffuses out. When sintered in N2 the pores remain intact even after a long time, because the N2 gas entrapped in them does not diffuse out. The effect of the sintering atmosphere has also been studied in a fine powder mixture of 80MgO 20CaMgSiO4 composition. Changing the atmosphere from O2 to N2 during the sintering treatment reduces the porosity, probably because of the enhanced oxygen diffusion from the pores. The pores grow when the sintering atmosphere is changed from N2 to O2, probably because of oxygen diffusion into the pores from the specimen surface. The practical implication of these results is that changing the atmosphere from O2 to air during the liquid‐phase sintering of oxide ceramics can greatly reduce the porosity.