Preparation of transparent MgO·1.8Al2O3 spinel ceramics by aqueous gelcasting, presintering and hot isostatic pressing

Non-stoichiometric MgO·1.8Al 2 O 3 spinel transparent ceramic was prepared from synthesized single phase powder through an aqueous gel-casting forming technique. In order to prevent hydrolysis, the powder was specially treated in toluene with stearic acid and then dispersed in an aqueous solution with the help of amphoteric compound Tween 80 and dispersant TMAH. The surface modification process was confirmed by various techniques such as Fourier transmission infrared absorption spectroscopy (FT-IR), pH value, zeta potentials and rheological properties. Afterwards, gel-casted green compacts were debinded, pressureless-sintered (PS) and hot-isostatic-pressed (HIP). Highly transparent MgO·1.8Al 2 O 3 ceramics (3.6 mm in thickness) with in-line transmittance values of 77–82 % in visible region and higher than 85% in near infrared region were obtained. The samples exhibited Knoop hardness of 12.2 ± 0.2 GPa, Young’s modulus of 302 GPa, refractive index of 1.7046, and Abbe's number of 75.8.