William B. Hillig

Prospects for Ultra-High-Temperature Ceramic Composites

In the search to improve the efficiency and performance of existing devices and systems, there is a constant demand for structural materials that are stronger, more reliable, and have higher temperature capability. Other attributes are also often sought such as low cost and a lesser dependence on scarce elements. This paper is concerned with the question of how far can this search continue before nature finally intervenes.

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

Abstract The feasibility of producing high temperature non-silicate all-oxide composites by melt infiltration was investigated in the CaO-MgO-Al 2 O 3 system. Both non-reactive and reactive melt infiltration approaches were explored. Molten CaO.Al 2 O 3 and the CaO.2Al 2 O 3 -MgO.Al 2 O 3 (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.Al 2 O 3 was used to impregnate preforms comprised of CaO.6Al 2 O 3 or Al 2 O 3 , 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.