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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 has particular thermal characteristics, acting as efficient insulation, and 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. This combination of machineability and good thermal properties have made it the material of choice in many engineering contexts.
- 46% silica (SiO2)
- 17% magnesium (MgO)
- 16% aluminium oxide (Al2O3)
- 10% potassium (K2O)
- 7% boron (B2O3)
- 4% fluorine (F)
Macor has a density of 2.52 g/cm3, and a thermal conductivity of 1.46 W/(m·K). Its low-temperature (25 to 300 °C) thermal expansion is 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.
Macor is a very good insulator with excellent tolerance. Even with temperature changes, its low thermal expansion ensures that its shape changes very little.
There are no major safety concerns or toxic effects associated with Macor. Its excellent temperature stability makes it safe in most situations. The dust created when machining it can be an irritant and inhalation should be avoided.
Macor is used in a wide variety of industries, including aerospace, nuclear engineering, medicine, and fundamental research. It is often used in high-temperature and/or high-vacuum environments, where dimensional stability and low outgassing are critical.