Macor

Macor is the trademark for a machineable glass-ceramic developed and sold by Corning Inc. It is a white material that looks somewhat like porcelain. Macor is a good thermal insulator, and is stable up to temperatures of 1000 °C, with very little thermal expansion or outgassing. It can be machined into any shape using standard metalworking bits and tools.

Macor is made up of fluorphlogopite mica in a borosilicate glass matrix. Its composition is roughly: 46% silica (SiO₂), 17% magnesium oxide (MgO), 16% aluminium oxide (Al₂O₃), 10% potassium oxide (K₂O), 7% boron trioxide (B₂O₃). 4% fluorine (F).

Macor has a density of 2.52 g/cm³, a Young's modulus of 66.9 GPa at 25 °C, a specific stiffness of 26.55x10⁶ m²s⁻², a Poisson’s Ratio of 0.29 and a thermal conductivity of 1.46 W/(m·K). It has a low-temperature (25 to 300 °C) thermal expansion of 9.3×10⁻⁶ m/(m·K). Its compressive strength is 50×10³ lb/in² (~350 MPa). Nominal engineering properties are comparable to borosilicate glass.

Extremely machinable, Macor offers tight tolerances capabilities, allowing complicated shape design (optimal performances up to +/- 0.013 mm for dimensions, < 0.5 μm for finished surface and up to 0.013 μm for polished surface). Macor remains continuously stable at 800 °C, with a maximum peak at 1000 °C under no load, and unlike ductile materials, doesn’t creep or deform. Its coefficient of thermal expansion readily matches most metals and sealing glasses. As an electric insulator, particularly at high temperatures, it is excellent at high voltages and a broad spectrum of frequencies.

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