Magnesium aluminate spinel (MgAl 2 O 4 ) is an optical ceramic with high light traarency (87 percent) and suitable mechanical properties (370MPa fracture strength). Porosity is the most important parameter that affects the light scattering. Therefore, for good traarency the bulk density must be close to the theoretical density. For example, porosity content higher than 0.5 percent in the magnesium aluminate spinel samples remarkably decreases the traarency. In general, when the pore size is approaching to the light wavelength, the traarency reduces more. Therefore it is necessary to produce bulk samples with minimum porosity and suitable pore distribution. Recently application of colloidal shaping methods (e.g. slip cast) for production of traarent ceramics has been considered. In this study the effect of slip casting parameters on traarency of bulk MgAl 2 O 4 ceramics was investigated. Rheological properties of spinel powders with different particle sizes were studied at different amounts of dispersal Dollapix CE 64 .It was found that there is an optimum amount of dispersant at which the viscosity becomes minimum. This optimum amount of dispersant depends on particle size. In fact by increasing the particle size from 90 nm to 500 nm, due to the reduced surface area, optimum percentage of dispersant are decreases from 2.5 to 0.5 wt% solid load. Green samples were casted with optimal amount of dispersant and various solid loads using different powders. It was observed that green density increases by increasing solid load. For slurry of 500 nm powder with 65 percent solid load and 0.5 wt% dispersant, 65 percent green density was obtained. In addition by increasing the particle size (under the 150 nm) green density decreases because the powder agglomeration. For sample produced at optimal conditions (solid load of 65wt%, 0.5wt% dispersant and green density of 65%) the porosity size and distribution was measured. It was observed that the pore size distribution has a single peak at the half of particle size. Moreover to evaluate, the effect of addition of LiF, as sintering aid, 1wt% powder was mixed with MgAl 2 O 4 powder and then consolidated by spark plasma sintering (). This sample showed less traarency compared to slip cast sample; 10% in the visible region and 15%in the infrared region. In addition, by reducing the sintering temperature from 1500 to 1400 °C the transmittance increased by 20 percent due to lower grain growth at lower temperatures. Keywords: Magnesium Aluminate Spinel, Slip Casting, Rheology, Particle Size, Spark Plasma Sintering ().
