Optically transparent polycrystalline Al2O3 produced by spark plasma sintering

The spark plasma sintering (SPS) technique was used to produce mid-infrared (IR) transparent alumina with the desired transmittance. An excellent transmittance of 85% has been obtained in a sample sintered at 1300 degrees C for 5 min. The heating rate, sintering time, and annealing have a significant influence on IR transmittance. The improvement in transmission may be attributed to the progressive elimination of residual porosity when applying a slower heating rate, longer sintering time during SPS, and postsinter annealing. It is suggested that localized residual strain/stress at grain boundaries and oxygen vacancy concentration are other factors influencing the optical properties of the SPS-sintered alumina.