Direct coagulation casting of alumina using magnesium citrate as coagulating agent with glycerol diacetate as pH regulator

Direct coagulation casting of alumina suspension via high valence counter ions (DCC-HVCI) using magnesium citrate as coagulating agent with glycerol diacetate as pH regulator was investigated. Influence of concentrations of glycerol diacetate and magnesium citrate on pH and rheological properties of alumina suspension was investigated. High viscosity enough to coagulate the suspension is achieved by adding magnesium citrate and glycerol diacetate. Hydrolysis of glycerol diacetate shifts the suspension to lower pH which promotes the decomposition of magnesium citrate and contributes enough magnesium ions to coagulate the suspension. Coagulated samples with different shapes can be demolded without deformation by treating 55 vol% alumina suspension with 2 vol% glycerol diacetate and 0.5–1.2 wt% magnesium citrate at room temperature for 2.5–6 h. Dense alumina ceramics with relative density above 99.5 % can be prepared by DCC-HVCI using magnesium citrate as coagulating agent with glycerol diacetate as pH regulator sintered at 1550 °C for 2 h.