Effect of Calcium Diphosphate Addition on Sintering of Magnesium Oxide
1982 Volume 90 Issue 1044 Pages 463-469
Details
1982 Volume 90 Issue 1044 Pages 463-469
The sintering of MgO with γ-Ca2P2O7 addition in the concentrations of 0.1, 0.5, 1.0 and 3.0mol% has been studied at increasing temperatures up to 1400°C (heating rate: 10°C⋅min-1) and at a constant temperature of 1400°C in air. The shrinkage coefficient of specimens (5mmφ×3mm) was measured dilatometrically at increasing temperatures and the bulk density of fired specimens (originally 8mmφ×3mm) was evaluated. The microstructure of resultant specimens was examined. The results of sintering at increasing temperatures were nearly in accord with those at constant temperature. At increasing temperatures, the shrinkage process of MgO specimens was markedly different for various contents of γ-Ca2P2O7. The shrinkage was promoted in the initial stage (950°-1150°C) and delayed in the final stage (1200°-1400°C) by the addition of 0.5mol% or more γ-Ca2P2O7. At constant temperature, the densification of MgO specimens was inhibited by the addition of γ-Ca2P2O7 in all the concentrations used and was most inhibited by that of 1.0mol%. However, a liquid phase formed at 1200°C, which retarded the growth of periclase grains. The reaction products in the sintering process were β-Ca3(PO4)2, Ca3Mg3(PO4)4, and Mg3(PO4)2 at increasing temperature. The final reaction product was (Ca, Mg)3(PO4)2, at a constant temperature of 1400°C for 5h. The above products had little effects on the lattice parameter of periclase.
