Refractory Alkali‐Free Cristobalite Glass‐Ceramics: Activated Reaction Sinter‐Crystallization Synthesis and Properties

Abstract

A new approach for the synthesis of chemically stabilized β‐cristobalite‐like glass‐ceramic materials is developed. It is based on an activated reaction sinter‐crystallization process of compacted powder mixtures at relatively low temperatures (1400–1450°C) and short heat treatment times. To facilitate homogeneous dopant distribution and thus the formation of a high content of βx‐cristobalite‐like phases, possessing a very low thermal expansion coefficient, the batch components are introduced in a chemically, mechanically, or thermally preactivated form. In this way, the high‐temperature glass premelting usually employed in the “classical” synthesis of glass‐ceramics is avoided. Using different, mutually complementary techniques of analysis it is revealed that optimal refractory properties are achieved with glass‐ceramics containing αx‐ and βx‐cristobalite solid solutions with close values of the lattice parameters. In this case, the transformation between these two cristobalite‐like solid solutions proceeds instead by a first‐order displacive transition, by a process exhibiting features characteristic for both a suppressed first‐order phase change and a second‐order λ‐type phase transitions. The refractory properties of the glass‐ceramic materials thus synthesized and the possibility to use various forming techniques open many fields for their application.