Spinel

Spinel is a mineral called magnesium aluminum oxide, which exists in natural rocks and is also artificially synthesized as a gemstone for appreciation. Spinel crystals for optical purposes are formed by hot pressing and sintering of magnesium aluminum raw material powder.

In the fields of bulletproof transparent armor and ultra-high hardness optical windows, there has been significant controversy over the performance and suitability of Sapphire, Nitrogen Alumina ceramics, and Magnesium Aluminum spinel.

Sapphire:
Advantages: The comprehensive mechanical properties are optimal, the commercial development is extensive, the preparation technology is relatively mature, and currently the most widely used.
Disadvantages: high preparation cost, small size of finished products obtained by Kyro Poulos method or direct drawing method, and low utilization rate of materials; The finished product obtained by the guide mold method has a larger size, but the process is unstable.

Nitrogen alumina（ALON）:
Advantages: Balanced mechanical and optical properties, capable of preparing large and complex shapes
Disadvantages: High preparation cost, complex and unstable process

Spinel:
Advantages: The most outstanding optical performance, low preparation cost, and the ability to achieve large-scale and complex shape preparation
Disadvantages: It is difficult to obtain high-quality raw material powder, and the sintering process is not perfect enough

At present, from the perspective of market applications, sapphire has the largest market share as bulletproof armor and super hard optical window. Due to the difficulties in preparation technology, nitrogen alumina and spinel have been continuously researching and breaking through for decades. 

Anticipation Photonics has participated in the research and development projects of spinel preparation and processing technology both domestically and internationally and has already applied small batches of finished products to foreign customers in the military field.

Spinel window

Composition:   MgAl2O4 Structure: Polycrystalline                 Cubic, Spinel Density:  3.58 g/cm3 Melting Point: 2135°C Thermal Expansion：6.7210-6（20~300℃） Young's Modulus:   275GPa Poisson's Ratio: 0.26 Vickers Hardness：1.26104 N/mm2 Flexure Strength: 160 MPa Thermal Conductivity: 17.0W/m.k @ 20℃ Transmission Conductivity: 0.25 to 6.5 microns Typical Transmission:  >76%@0.4~0.8μm  (@4mm thickness)     80~86%@ 3~5μm

Index of refractive   λ（μm）      n 0.546         1.718 0.60          1.714 0.70          1.709 0.80          1.707 3.0           1.698 4.0           1.675 5.0           1.659

Spinel optical ceramic

Substitute for sapphire

The infrared optical performance of spinel optical ceramic is better than that of sapphire, and spinel has excellent mechanical properties, suitable for used as window materials.