The Effect of pH and Calcination on the Optical Transmittance of SPS Alumina Ceramics

In this research, transparent alumina ceramic was synthesized through the Spark Plasma Sintering (SPS) process. In this respect, its chemical deposition in the presence of Magnesium Nitrate and Lanthanum Nitrate, as the sintering agents, was surveyed. For this purpose, two types of alpha alumina powders (200 and 1000 nm) were used to prepare samples containing 100 ppm Magnesium Oxide and 100 ppm Lanthanum Oxide. In the chemical deposition process, the pH factors were compared, and the absence of powder calcination was investigated. In order to evaluate the phases, the samples were compared before and after SPS using X-Ray Diffraction (XRD) analysis, and deliberation of the microstructure was done using Field Emission Scanning Electron Microscopy (FESEM) analysis. Further, SPS was performed at 1500 °C at the rate of 50 °C/min under the pressure of 70 MPa for 15 min. The results of the IR transmittance test showed that the pH was adjusted and calcination was performed in 65 % of the 200-nm sample. EDS-Line analysis was then done to determine the mechanism of the sintering aids. The obtained results revealed the placement of Lanthanum oxide along the Alumina grain boundaries and the exclusion of the growth of Alumina grains during the sintering process while Magnesium oxide formed a spinel lattice to increase the density of alpha Alumina. Of note, pH adjustment and calcination reaction had significant effects on the enhanced transparency of the samples produced through the chemical deposition process.