Toward Oxidation-Resistant ZrB2-SiC Ultra High Temperature Ceramics

Ultra high temperature ceramics (UHTCs), including ZrB2-SiC, are designed for extreme environment applications in which temperatures exceed 2273 K (2000 A degrees C). A key material property of UHTCs in many applications is their resistance to oxidation. Recent research into UHTCs is described, revealing a variety of different methods for improving the oxidation performance, which include control of starting powders, composition and size distribution, mixing, and densification techniques. The use of additives has also been researched widely, for example, to increase the viscosity of any liquid phase formed or provide protective refractory phases at high temperatures. SiC additions are effective in forming protective silica but only in static environments and to similar to 1873 K (1600 A degrees C). For higher temperature applications, additions of La lead to the formation of a dense ZrO2 scale probably via liquid phase sintering. Such ceramic systems, which produce self-generating refractory oxidation barriers or dense ZrO2 scales, show the greatest promise in providing oxidation-resistant UHTCs.