Jan 6 2004
Background
Mica is a naturally occurring mineral and as such its exact composition varies between grades, as will its properties. Ruby Mica or Pottassium Aluminosilicate is the highest grade of Muscovite Mica. The name comes from the latin ‘micare’, to shine or glitter. It can be split into thin uniform layers, down to 0.05 mm.
The high skill involved in such splitting results in a high cost. Mica is transparent, and resistant to heat, as well as being one of the best electrical insulators known. Potassium Aluminosilicate is resistant to high temperatures and chemically inert to most substances.
Key Properties
The key properties of Potassium Aluminosilicate are tabulated below.
Table 1. Key properties
| Chemical Resistance |
| Acids - concentrated |
Fair |
| Acids - dilute |
Good |
| Alkalis |
Good |
| Electrical Properties |
| Dielectric constant |
6.0-6.6 |
| Dielectric strength ( kV.mm-1 ) |
40-200 |
| Volume resistivity ( Ohm.cm ) |
1012 @ 25 °C |
| Mechanical Properties |
| Compressive strength ( MPa ) |
190-280 |
| Hardness - Vickers ( kgf.mm-2 ) |
2-3 Mohs |
| Shear strength ( MPa ) |
215-265 |
| Tensile strength ( MPa ) |
170-300 |
| Physical Properties |
| Density ( g.cm-3 ) |
2.6-3.2 |
| Refractive index |
1.5-1.6 |
| Useful optical transmission range |
450-700 nm |
| Water absorption - saturation ( % ) |
Very Low |
| Thermal Properties |
| Coefficient of thermal expansion ( x10-6 K-1 ) |
9-36 @ 20-1000 °C |
| Specific heat ( J.K-1.kg-1 ) |
50 @ 25 °C |
| Thermal conductivity ( W.m-1.K-1 ) |
0.5-7 @ 20 °C |
| Upper continuous use temperature ( °C ) |
500-600 |
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