Transparent Al2O3 is the most widely used transparent ceramic. The main factors affecting the transparency of Al2O3 are porosity and impurities. It was found that increasing the sintering temperature or extending the holding time can increase the grain size and reduce the porosity. Holding at 1800°C for more than 1 h is critical for grain growth and elimination of porosity. The increase in light transmittance mainly depends on the decrease in porosity, and the increase in grain size also helps. The increase in bending strength is inversely proportional to the increase in grain size. In a comprehensive comparison, the sample held at 1800°C for 2 h can achieve 87% light transmittance based on the bending strength of 322 MPa.
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