Physical and Mechanical Properties of Sapphire by Insaco

For more than 60 years, Insaco has been synonymous with excellence in the development and production of high precision machined parts. As a custom fabricator of ceramic, glass, sapphire, and other hard materials, Insaco specialize in machining parts that often require tolerances measured in millionths of an inch, and wear properties that satisfy even the most demanding applications.

Crystal Structure of Sapphire

Sapphire is an anisotropic, rhombohedral crystal form of Aluminum Oxide.

Anisotropic single crystal materials exhibit some properties such as thermal expansion and hardness which vary significantly by orientation. For most applications this is unimportant, however it should be considered. Insaco has more than 60 years of experience with this material and we can provide considerable insight as to how orientation might affect your application.

Sapphire is also "birefringent" which is an optical refractive property that offsets wave transmission up to 0.8% at right angles to the optic axis. Birefringence is eliminated along the optic or C-axis of the crystal. Therefore, for certain optical applications, C-axis sapphire should be specified to avoid this effect.

Crystal Structure of Sapphire

Industrial Sapphire

Industrial sapphire is created by melting aluminum oxide (Al2O3) at 2040°C and then encouraging crystal growth with a seed and careful control of the environment. Growers have developed several unique methods for growth, with varying levels of resultant quality, size, and cost. The EFG or Stephanov methods allow the directed growth of shapes like ribbon, or even tubes, however there are many limitations to what can be done. The Czochralski, HEM, or Kiropolous methods allow the highest optical quality sapphire, but the result is a rod like "blob" of crystal called a boule, that must be entirely machined into useable shapes and sizes.

Sapphire and Ruby are actually the same material with small amounts of chromium (typically = 0.05% by weight) added which affects color and optical properties, while not affecting mechanical, thermal and electrical properties significantly.

Physical and Mechanical Properties of Sapphire

Property

Value

General

Chemical Formula

?-Al2O3

Mechanical

Density

3.97 gm/cc

Hardness

2200 Knoop perpendicular to the c-axis

1900 Knoop parallel to the c-Axis

Tensile Strength

58 kpsi

Modulus of Elasticity

68 x 106 psi

Flexural Strength

100 kpsi

Compressive Strength

425 kpsi

Poisson's Ratio

~ 0.28 (Varies with orientation)

Electrical

Dielectric Strength

1200 ac V/mil

Dielectric Constant

9.3 - 11.5 (@ 1 MHz) (parallel to the c-axis)

Volume Resistivity

> 1014 ohm-cm2

Thermal

Coefficient of Thermal Expansion

4.3 x 10-6/°C (perpendicular to the c-axis)

5.4 x 10-6/°C (parallel to the c-axis)

Thermal Conductivity

46.0 W/mK

Specific Heat

0.16 cal/g °C

Maximum Working Temperature

2000 °C

Optical

Index of Refraction

1.768 (Ordinary ray, No, c-axis)

1.760 (Extraordinary ray, Ne, c-axis)

Birefringence

0.008 (No-Ne)

Transmission Band

0.3 - 5.0 Wavelength (microns)

> 80% transmission

All properties are at room temperature unless otherwise noted.

Engineering data are representative, and are not intended as absolute nor warrantable. Manufacturer's Data shown is blended from multiple sources and therefore illustrates the marketplace.

This information has been sourced, reviewed and adapted from materials provided by INSACO Inc.

For more information on this source, please visit INSACO Inc.

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Comments

  1. Chad Bedford Chad Bedford United States says:

    I have searched the net and cannot find a good understanding of how, where, and why a sapphire is used in non-liquid filled compasses.  Can someone explain this to me or tell me where to look for this SPECIFIC information?  Wikipedia glosses over the matter on their "Compass" page, and is slightly more enlightening with its "jewel bearing" entry.  But I just cannot figure out how such a non-liquid system would work.  I'm not stupid, just very curious.  Any help would be greatly appreciated.    Chad Bedford

  2. Chad Bedford Chad Bedford United States says:

    I have searched the net and cannot find a good understanding of how, where, and why a sapphire is used in non-liquid filled compasses.  Can someone explain this to me or tell me where to look for this SPECIFIC information?  Wikipedia glosses over the matter on their "Compass" page, and is slightly more enlightening with its "jewel bearing" entry.  But I just cannot figure out how such a non-liquid system would work.  I'm not stupid, just very curious.  Any help would be greatly appreciated.    Chad Bedford

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of AZoOptics.com.

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