Glass-to-metal seal formation of lithium tungstate. Due to its low thermal expansion coefficient, matched to glass, tungsten is frequently used for glass-metal bonds. Tungsten forms satisfying bonds with glasses with similar thermal expansion coefficient such as high-borosilicate glass. The surface of both the metal and glass should be smooth, without scratches. Tungsten has the lowest expansion coefficient of metals and the highest melting point. 304 Stainless steel forms bonds with glass via an intermediate layer of chromium(III) oxide and iron(III) oxide. Further reactions of chromium, forming chromium silicide dendrites, are possible. The thermal expansion coefficient of steel is however fairly different from
Melting point a liquid phase only exists above pressures of and estimated (see ). Tantalum hafnium carbide (TaHfC) is a refractory compound with a very high melting point of 4215 K (3942 °C, 7128 °F). At the other end of the scale, helium does not freeze at all at normal pressure even at temperatures close to absolute zero; a pressure of more than twenty times normal atmospheric pressure is necessary. Many laboratory techniques exist for the determination of melting points. A Kofler bench is a metal strip with a temperature gradient (range from room temperature to 300 °C). Any substance can be