Rokor | About sapphire

General information

Sapphire is a single crystal of aluminum oxide Al2O3. Sapphire has exceptional physical (optical, mechanical, dielectric and thermal) and chemical properties compared to other optical materials. For this reason, sapphire is in high demand for many scientific, industrial and military applications. Sapphire is the second hardest material in nature after diamond. It has high hardness, resistance to abrasion and corrosion, durability under extreme pressure and temperature conditions, biocompatibility and chemical inertness.

Sapphire is a material that is an ideal dielectric substrate material for making electronic devices. Its ability to be fabricated in various shapes and sizes and its unique crystalline and physical properties make it the predominant material for LED fabrication. Sapphire is transparent from 180 nm to over 5500 nm. This wide transparency window makes sapphire one of the best materials in optics.

comparison table

Physical properties of single crystal Sapphire

Chemical Formula

To the₂THE₃

Structure

hexagonal-rhombohedral

Molecular weight

101.96

Lattice Constants Å

a=4.765, c=13,000

Density (g/cm³)

3.98

Hardness

9 Mohs

1800 knoop parallel to C-axis

2200 knoop perpendicular to C-axis

Water Absorption

nil

Young Modulus (Gpa)

379 at 30° to C-axis

352 at 45° to C-axis

345 at 60° to C-axis

386 at 75° to C-axis

Shear Modulus (Gpa)

145

Bulk Modulus (Gpa)

240

Bending Modulus/

Modulus of Rupture (MPa)

350 to 690

Tensile strength (MPa)

400 at 25°C

275 at 500°C

345 at 1000°C

Elastic Coefficients

C11=496, C12=164, C13=115, C33=498, C44=148

Apparent Elastic Limit (MPa)

448 to 689

Flexural Strength (GPa)

2.5 — 4.0

Poisson ratio

0.25 — 0.30

Friction Coefficient

0.15 on steel

0.10 on sapphire

Abrasion resistance

8 times higher than steel

Thermal properties

Melting Point (°C)

2040

Maximum use temperature (°C)

1800

Specific Heat J/(kg × K)

105 at 91 K

761 at 291 K

Thermal coefficient of linear expansion at 323 K (K^-1)

6.66 × 10^-6 parallel to optical axis

5 × 10^-6 perpendicular to optical axis

Thermal conductivity (W/m °K) at 20° C

41.9

Thermal Expansion (20 — 1000°C)

Parallel to C-axis: 9.03 × 10^-6°C

Perpendicular to C-axis: 8.31 × 10^-6°C

60° to C-axis: 8.4 × 10^-6°C

Optical properties

Transmission Range

0.2 — 5.5 microns

Transmission (thickness of disc 1mm)
Visible light		>85%
Infrared	0.75 to 5 µm	85%
	5.5 µm	70%
Ultraviolet	400 — 300 nm	80%
	280 nm	60%
	200 nm	50%

Reflection loss

14% at 1 micron (2 surfaces)

Restrahlen Peak

13.5 microns

dN/dT

+13 × 10^-6°C

Electrical properties

Resistivity, Ohm·cm at 20-500° C

10¹¹ — 10¹⁶

Dielectric Constant

11.5 parallel to C axis

9.4 perpendicular to C axis

Dielectric strength (V/cm)

4 × 10⁵

Loss Tangent

10^-4

Stability parameters

Solubility
In water	insoluble
In HNO₃, H₂SO₄, HCl, HF	insoluble up to 300° C
In alkalis	insoluble up to 800° C
In melts of metals: Mg, Al, Cr, Co, Ni, Na, K, Bi, Zn, Cs	insoluble up to 800 — 1000° C

Radiation stability

No change in transmission above 2.5 micron after exposure to 10⁷ Rads.

No visible coloration after exposure to 10⁸ Rads/hr for 60 minutes at -195° C

Proton radiation stability

No change in transmission below 0.3 micron after exposure 10¹² proton/cm² total dose.

Properties of sapphire 82 KB

Light scatter grading

Grade	Application (reference)	Bubbles / Dispersion Centers				Accumulations of Bubbles
Grade	Application (reference)	Size, µm	Min distance between each, mm	Σ size, µm/cm³	Admissible quantity, 1/ cm³	Size, µm	Min distance between each, mm	Admissible quantity, 1/ cm³
Optical Grade
1	High power laser	No Bubbles / Dispersion Centers
2	Laser	< 10	10	50	2	No
3	Premium optical	< 20	10	100	2	No
4	Standard optical	20-50 < 20	10 2	200 No limit	2 No limit	No
4 a	LED & Semiconductor	< 200 20-50 < 20	50 10 2	200 No limit	4 No limit	300	20	1
4 b	View ports & Large size parts (>150mm)	Bubbles must be not visible to the naked eye under normal day light.
Mechanical Grade
5	Wafer carriers	< 200 20-50 < 30	20 10 2	200 No limit	2 No limit	500	10	1
5 a	Mechanical & Isolator	< 200 20-50 < 30	20 10 2	200 No limit	2 No limit	1000	5	5
5 b	Test of equipment & cutting tools	< 500 < 200 20-50 < 30	20 20 10 2	200 No limit	2 No limit	2000	2.5	10

Rokor’s Grading System for Kyropulos Sapphire78 KB