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.^[1]

Composition

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)

Properties

Macor has a density of 2.52 g/cm³,^[2] a Young's modulus of 66.9 GPa at 25 °C,^[3] a specific stiffness of 26.55x10⁶ m²s⁻², a Poisson’s Ratio of 0.29^[4] and a thermal conductivity of 1.46 W/(m·K).^[5] It has a low-temperature (25 to 300 °C) thermal expansion of 9.3×10⁻⁶ m/(m·K).^[6] Its compressive strength is 50×10³ lb/in² (~350 MPa).^[7] Nominal engineering properties are comparable to borosilicate glass.^[8]

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.

Macor comes in a standard size maxi slab (36cm x 36cm x 6cm approx.) Corning Macor Maxi-Slab.^[9] Components, bars, rods and plates can be machined within the size of this slab (hand tools can be used).

Applications

Macor is used in the following applications: Constant and ultra-high vacuum environments • Laser technology • Semiconductor / Electronic • Aerospace / Space • Medical/ Laboratory equipment • Fixtures • Chemical • Automobile • Military • Nuclear

Safety

There are no major safety concerns or toxic effects associated with Macor. The dust created when machining it can be an irritant and inhalation should be avoided.^[10]

Machining Guidelines

Key factors for successful machining are proper machining speeds and coolant. • Macor can be machined with high speed steel tools, but carbide tools are recommended for longer wear. • Best results achieved by using a watersoluble coolant(such as Cimstar 40 - Pink) especially formulated for cutting and grinding glass or ceramics. Note: No post firing is required after machining.

References

Corning Macor® Technical Brochure 2014'
Macor® Machining Guidelines 2014'
Corning Authorized Macor® Distributor