Dielectrics forsterite

In forsterite ceramics the mineral forsterite (Mg2Si04) crystallizes. They have excellent low-dielectric-loss characteristics but a high thermal expansion coefficient which imparts poor thermal shock resistance. During the 1960s they were manufactured for parts of rather specialized high-power devices constructed from titanium and forsterite and for which the operating temperature precluded the use of a glass-metal construction. The close match between the thermal expansion coefficients of titanium and forsterite made this possible. Today alumina-metal constructions have completely replaced those based on titanium-forsterite and the ceramic is now manufactured only to meet the occasional special request. 

Cordierite and forsterite, which possess low dielectric constants and may act as high-temperature electrical insulators, have also been formed into fibers by the sol-gel route (Boulton et al., 1989 Tsai, 2002a, 2002b, 2002c, 2002d). 

Forsterite, 2MgO Si02, ceramics are easier to fire than steatite or cordierite and have low dielectric losses, even to microwave frequencies. Their high thermal expansion limits their use as substrate materials and results in poor thermal shock resistance. Forsterite ceramics are used in high-power applications such as ceramic vacuum tube envelopes. 

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