An exploratory study of producing non-silicate all-oxide composites by melt infiltration

The feasibility of producing high temperature non-silicate all-oxide composites by melt infiltration was investigated in the CaO-MgO-Al2O3 system. Both non-reactive and reactive melt infiltration approaches were explored. Molten CaO.Al2O3 and the CaO.2Al2O3-MgO.Al2O3 (magnesium spinel) eutectic composition were the usual infiltrants. The melting temperatures are 1602 °C and 1700 °C respectively. Non-reactive infiltration involved infiltrating porous spinel bodies with a molten eutectic composition that was already substantially in equilbirium with the preform material. Reactive infiltration occurred, for example, when molten CaO.Al2O3 was used to impregnate preforms comprised of CaO.6Al2O3 or Al2O3, neither of which was in phase equilibrium with the melt. Accordingly the preform phase underwent chemical change as equilibrium became established. Sound composites could be obtained using both approaches. However, the infiltration behaviors were quite different; reactive infiltration was more difficult to control.