Apr 16 2003
Chemical Formula
The chemical formula of Ruby is Al2O3/Cr2O3/Si2O3
Background
Ruby exhibits identical properties to those of Sapphire. Small amounts of impurities give Ruby a red colouration.
Key Properties
The key properties of Ruby are tabulated below.
Table 1. Key properties
| Chemical Resistance |
| Acids – concentrated |
Good |
| Acids – dilute |
Good |
| Alkalis |
Good |
| Halogens |
Good |
| Metals |
Good |
| Electrical Properties |
| Dielectric constant |
7.5 - 11.5 |
| Dielectric strength ( kV.mm-1 ) |
15 - 50 |
| Volume resistivity @ 25 °C ( Ohm.cm ) |
1014 |
| Mechanical Properties |
| Compressive strength ( MPa ) |
2100 |
| Hardness - Knoop ( kgf.mm-2 ) |
2000 |
| Hardness - Vickers ( kgf.mm-2 ) |
2500 - 3000 |
| Tensile modulus ( GPa ) |
350 - 390 |
| Tensile strength ( MPa ) |
250 - 400 |
| Physical Properties |
| Apparent porosity ( % ) |
0 |
| Density ( g.cm-3 ) |
3.98 |
| Useful optical transmission range |
150 - 5500 nm |
| Water absorption - saturation ( % ) |
0 |
| Thermal Properties |
| Coefficient of thermal expansion, 20-1000 °C ( x10-6 K-1 ) |
5.8 |
| Melting point (°C ) |
2050 |
| Specific heat @ 25 °C ( J.K-1.kg-1 ) |
750 |
| Thermal conductivity @ 20 °C ( W.m-1.K-1 ) |
35 - 40 |
| Upper continuous use temperature ( °C ) |
1800 - 1950 |
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