In this project, magnesia-alumina composite granules were prepared via the spray drying method. Next, the synthesized powder was sintered at 1400 degrees C-1500 degrees C by the spark plasma sintering method under the pressure of 100 MPa without using any sintering aids. The effects of two sintering temperatures (1400 degrees C and 1500 degrees C) on the phase evolution, density, fracture toughness, and light transmission of the samples in the visible and IR range were investigated. SEM results indicated that the magnesia-alumina composite granules had spherical morphology with a mean particle size of 7-8 mu m. The XRD pattern showed that after spark plasma sintering at 1400 degrees C and 1500 degrees C, magnesium aluminate phase spinel was obtained from the penetration and reaction of alumina and magnesia nanoparticles. The disc sintered at 1400 degrees C had more transparency than the sample sintered at 1500 degrees C within the UV-Vis and middle IR region because of the lower porosity of the sample. The magnesium aluminate spinel sintered at 1400 degrees C had a density of 99.98% theoretical density, hardness of 18 GPa, and fracture toughness of 1.6 MPam(1/)(2).
