Effect of Sodium Tripolyphosphate on The Morphology and Thermal Properties of Anorthite-Based Ceramic Foam Filters for Aluminum Alloy Castings

Aluminum is one of the most widely used materials for daily life and has a wide range of applications. However, the continuous use of aluminum makes Indonesia unable to meet its needs for aluminum, thus forcing Indonesia to import aluminum. Therefore, the use of secondary aluminum as a substitute for primary aluminum raw materials is one solution that can be offered. Despite the low cost of secondary aluminum as the raw material, there are many impurities contained in secondary aluminum that can reduce the properties of the resulting aluminum products. In this study, porous anorthite ceramic filters were fabricated to improve the purity of cast products with secondary aluminum. This filter is made by using polyurethane as a support that is dipped into a slurry consisting of a mixture of silica sand and limestone, accompanied by the addition of sodium tripolyphosphate (STPP) deflocculant with variations in composition (5, 10, and 15 grams). Based on the results of testing and characterization, it is found that the filter sample with the addition of 15 grams of STPP provides optimum performance, with an average pore area of 0.329 mm², viscosity of 1.54 cP, porosity level of 68%, density of 0.55 g/cm³, water absorption of 126%, permanent linear change (PLC) of -4.8%, and thermal expansion of 1.06%.