Background

Macor is a tradename for a machinable glass ceramic grade from Corning. Glass Ceramics Glass ceramics are formed by the careful heat treatment of glasses to induce crystallisation. Glass ceramics are fully dense materials which can contain up to 98 vol% crystals, where the crystals are typically less than 1µm in diameter. The remainder of the material will be residual glassy phase. Composition Macor is composed of approximately 55% fluorophlogopite and 45% borosilicate glass. Its composition is given in table 1. Table 1. Composition of Macor. Material Approx wt% SiO2 46 MgO 17 Al2O3 16 K2O 10 B2O3 7 F 4

Key Properties

· Key properties include: · Macor is white in appearance and looks very similar to porcelain · Continuous usage temperature limit of 800°C · Peak usage temperature of 1000°C · Has a similar co-efficient of thermal expansion to most sealing metals and glasses · It is non-wetting · It is non-porous · Excellent insulator at high voltages, various frequencies and high temperatures · Properly heat treated materials will not outgas in vacuum environments · It can be machined with high speed steel and carbide tools · Can be machined into complex shapes · Can be machined to tight tolerances (up to 0.005”) · Can be machined to a surface finish of 20µin · It can be joined and sealed to itself and other materials using processes such as metallising, sputtering, soldering and brazing, as well as adhesives such as epoxies. · It has no known toxicological effects, but exposure to dust should be avoided as much as possible as it can be an irritant

Applications

Macor has been used in the following areas: · Vacuum seals and in vacuum environments · Aerospace · Nuclear and radiation environments · Welding nozzles · Engineering components · Medical equipment.