| Transparent polycrystalline magnesia-alumina spinel (MgAl2O4 spinel) has superior mechanical properties and optical properties similar to single crystal, such as high hardness, high strength ,high abrasion and erosion resistance as well as high transmission in ultraviolet band, visible band and infrared band. Compared with sapphire single crystalline material, it is possible to produce MgAl2O4 transparent polycrystalline material with relatively large size at relatively low cost, making it become promising substitutive material for sapphire single crystal in many technical applications therefore, the development of transparent polycrystalline MgAL2O4 spinel with high strength and large size, and it's application as transparent armor material, window material and dome material in 0.3~0.5um have been extensively investigated.Transparent polycrystalline MgAl2O4 spinel was initially fabricated by a hot pressing method followed by a hot isostatic pressing (HIP) to increase the transmission of electromagnetic radiation at shorter wavelength. Normal pressure sintering/HIP method was a subsequently developed method based on rate control sintering method has also been reported. In this research, MgAl2O4 fine powder with high purity synthesized by a sol-gel method was used as starting powder, and transparent polycrystalline MgAl2O4 spinel with the size of 100mmX 130mm x 6mm was fabricated by a vacuum sintering/HIP method. The transmission and mechanical properties of the products, including transmitivity, hardness, flexural strength and thermal expansion coefficient, were measured. The preferred processing conditions were ascertained to yield desired strength, hardness and transparency. It was confirmed that the MgAl2O4 spinel fabricated by the vacuum sintering/HIP method exhibit advantages of high performance and low cost, benefiting the wide application of the material. The results of bulletproof experiment demonstrate excellent performance of the material in practical application.
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