Hot Isostatic Pressing of MgAl2O4 Spinel Infrared Windows

Optically transparent MgAl₂O₂ spinels have been produced by hot isostatic pressing (HIP). The spinel samples were prepared by hot pressing and subjected to capsule-free HIPing. The hot-pressed samples were made at 1500°C with a pressure from 14 to 41 MPa for 2 to 4 hours. In the HIP process, the pressure ranged from 14 to 207 MPa at 1500°C. The effect of hot isostatic pressure on the bulk density, microstructure and optical properties of the spinel sample were investigated here. The bulk density of the sample increased with HIP pressure and the sample HIPed at 207 MPa resulted in a bulk density of 3·576 g/cm³, about 99·94% of the theoretical density. A bimodal grain size distribution exists in samples HIPed at pressures ≤ 138 MPa. The extent of the abnormal grain growth decreased with pressure. The transparent spinel with uniform and fine grain size of 2 μn was obtained at 207 MPa. The transmission at short wavelength increased significantly with HIPing pressure. The transmittance of the sample HIPed at 207 MPa at a wavelength of 0·7 μn was 72%.