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Sapphire

Impex HighTech offers a wide range of products of synthetic sapphire. This material is used among others to manufacture precision optics, domes, high pressure components, and other optics.

Some of our main products

  • Sapphire substrates
  • Sapphire domes (grounded and polished)
  • Sapphire windows for optical standard applications
  • Precision windows (laser, analytics, measurement technique)
  • Sapphire windows with very high aperture
  • High temperature windows
  • High pressure windows
  • Scanning windows
  • High pressure tubes
  • Sapphire tubes and crucibles (chemical industry)
  • Sapphire light guidance (Beauty Care / dermatology)
  • Sapphire tips / scalpels (laser surgery)
  • Bearing bricks
  • Sapphire components on specific request
  • Sapphire optics from stock

Synthetic single crystalline Sapphire (Al2O3)

is the most requested material for optical high-tech applications due to its unique combination of excellent physical and chemical properties. Sapphire is transparent over a large wavelength range from Vacuum-UV up to middle infrared (0.18µm up to nearly 6µm). Because of its rhombic, hexagonal crystal structure, sapphire shows anisotropic behavior in many of its optical and physical properties. Therefore, the exact behavior optical components made of sapphire is strongly dependent on the crystallographic alignment relative to the optical axis (c-axis, 0001). Sapphire shows slight birefringence in all crystal directions except parallel to the c-axis. As sapphire is the hardest material among the oxidic single crystals, sapphire can be processed by only a few materials (e.g., diamond or boron carbide) due to its extreme hardness. It therefor is "scratch resistant" to other materials. Thanks to its high strength, sapphire windows, for example, can be made much thinner than comparable windows made of other optical materials while maintaining the same performance. That is one more reason to use sapphire also at wavelengths close to the transmission limit. The resistivity towards most chemicals, its high temperature resistivity and biocompatibility open many other application possibilities besides optics in the fields of industry, medicine & Healthcare, aerospace etc.

We deliver preferably - but not only - sapphire materials produced via the following methods:

DSC00434-2a

Kyropoulos Method

This growth method results in very big crystal bulbs with nearly cylindric shape, diameters between 70mm and 300mm and a length up to 600mm. Kyropoulus crystals stand out in their high homogeneity and very low dislocation density (crystal defects) and can be cut in any orientation. This method is economically efficient to produce substrates for LED and SOS technology.

sapphire-chemical

Stepanov (EFG) Method

This method allows the crystal growth with geometries near the final product and minimizes the processing effort. This results in a significant cost reduction diversely. These include tubes, rods (also single- or multi-hole rods), plates or, e.g., unilaterally closed crucibles. Such plates can reach dimensions of 80mm width and over 1000mm length. Rods and tubes can be larger depending on the diameter. These crystals can grow according to different crystallographic orientations and can be applied wherever the optical requirements are not so high.

Optical and spectral properties
Transmission range in µm (minimum 10%)
0.14-6.4

0.15-5.4 (parallel to c-axis)

Transmission range in µm (minimum 50%)
0,16‐4
Refractive index @633nm
1.766 (no)

1.758 (neo)

Reflection losses in % at 1 surface
6.94 @2.9µm
Reflection losses, % for two surfaces
14 @0.06µm
dN/dT in 1/K
13.6 · 10-6
Physical properties
Density in g/cm3
3.97-3.99
Melting point in °C
2053
Specific heat capacity in J/(kg · K)
753
Thermal conductivity in W/(m · K)
32.5 (parallel to c-axis)

30.3 (perpendicular to c-axis)

Thermal expansion in 1/K
6.6 · 10-6 (parallel to c-axis)

5 · 10-6 (perpendicular to c-axis)

Dielectric constant
11.5 (parallel c-axis)

9.3 (perpendicular to c-axis)

Solubility in water in g/100g
insoluble
Mohs hardness
9
Knoop hardness in kg/mm²
2200 (parallel to c-axis)

1900 (perpendicular to c-axis)

Material type
single crystalline, synthetic
Crystal type
hexagonal
Crystal structure
R3c
Lattice constant in Å
a = 4.785

c = 12.991

Elastic coefficient in GPa
C11 = 497

C12 = 164

C33 = 498

C44 = 147

C13 = 111

C14 = 24

Young's Modulus (E) in Gpa
360-440
Shear Modulus (G) in GPa
145
Bulk Modulus (K) in GPa
145
Rupture Modulus in MPa
450‐900
Apparent elastic limit in MPa
480‐890
Poisson's ratio
0.27-0.3
Spectral properties
sample thickness: 2 mm

Main application areas of synthetic sapphire

Optics

Sapphire is the excellent material for most demanding optical applications due to its high transparency in the wavelength area of approximately 180nm to 6µm and, because it is harder than glass in order of magnitudes. The high optical transmission in combination with the nearly 100% chemical resistivity, mechanical friction resistance and high temperature tolerance makes sapphire to the leading material in the optical sensor technology, spectroscopy, interferometry etc.

Mechanics

Sapphire has a wide application area as scratch-resistant cover glass for high-quality watches, scanning applications (supermarket, logistics, chemical and pharmaceutical industry) and other areas where high mechanical resistivity is needed. From bearing stones to cell phone displays to water- / sand-blasting nozzles!

High temperature and high pressure

Due to the combination of its unique physical, chemical and optical properties, sapphire can withstand highest pressure or thermal shock. Because it has a melting point of more than 2000°C, it is the ideal material for high temperature applications but comes also into play in cryogenics. Customer specific high temperature tubes and oven windows or vacuum viewports are only a small part of our production range.

Chemistry

Sapphire is inert against most acids and alkalines up to a temperature of 1000°C. Therefore, it has different applications in the chemical industry. Tubes, crucibles and optics made of sapphire offer extremely long service lives compared to other materials or do not need to be changed at all. Sapphire replaces more and more quartz products due to its high lifetime and low contamination abilities with good UV transmission.

Electrical engineering

Due to the high and stable dielectric constants of sapphire, it is widely applied as electronic substrate material besides typical application as isolation and thermal conductivity. By exploiting the anisotropic properties, sapphire wafer are the bases for different products from the semiconductor industry and therefore, they are the most widely used substrate material for the epitaxial layer deposition for LEDs based on GaN.

Medicine

Sapphire is a common window material for medical (and also technical) endoscopes. In addition to biocompatibility, this is based on high resistance in contact with biological tissue and medical fluids and easy sterilizability in autoclaves. The use of scalpels or tips made of sapphire for the laser surgery is common today. In the field Beauty Care / dermatology, sapphire light guides form the contact between high energy sources and human skin, e.g., to treat pigment disorders, hair and tattoo removal etc.

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