the United States Air Force, the idea being that they are a combination of two materials, a metal and a ceramic. Basic physical properties of metals include ductility, high strength, and high thermal conductivity. Ceramics possess basic physical properties such as a high melting point, chemical stability, and especially oxidation resistance. The first ceramic metal material developed used magnesium oxide (MgO), beryllium oxide (BeO), and aluminum oxide (Al2O3) for the ceramic part. Emphasis on high stress rupture strengths was around 980 °C. Ohio State University was the first to develop Al2O3 based cermets with high stress rupture strengths around 1200 °C. Kennametal, a metal-working and tool company based in Latrobe, PA, USA, developed the first titanium carbide cermet with a and 100-hour stress-to-rupture strength at 980 °C. Jet engines operate at this temperature and further research was invested on using these materials for components. Quality control in manufacturing these ceramic metal composites was hard to standardize. Production had to be kept to small batches and within these batches, the properties varied greatly. Failure of the material was usually a result of undetected flaws usually nucleated during processing. The existing technology in the 1950s reached a limit for jet engines where little more could be improved. Subsequently, engine manufactures were reluctant to develop ceramic metal engines. Interest was renewed in the 1960s when silicon nitride and silicon carbide were looked at more closely. Both materials possessed better thermal shock resistance, high strength, and moderate thermal conductivity. Cermet production, Helipot Division of Beckman Instruments, 1966 Applications Ceramic-to-metal joints and seals Cermets were first used extensively in ceramic-to-metal joint applications. Construction of vacuum tubes was one of the first critical systems, with the electronics industry employing and developing such seals. German scientists recognized that vacuum tubes with improved performance and reliability could be produced by substituting ceramics for glass. Ceramic tubes can be outgassed at higher temperatures. Because of the high-temperature seal, ceramic tubes withstand higher temperatures than glass tubes. Ceramic tubes are also mechanically stronger and less sensitive to thermal shock than glass tubes. Today, cermet vacuum tube coatings have proved to be key to solar hot water systems. Ceramic-to-metal mechanical seals have also been used. Traditionally they have been used in fuel cells and other devices that convert chemical, nuclear, or thermionic energy to electricity. The ceramic-to-metal seal is required to isolate the electrical sections of turbine-driven generators designed to operate