Effect of temperature difference on presintering behavior of gelcast thick alumina bodies

Alumina spherical green bodies (empty set approximate to 75 mm) prepared by gelcasting were presintered at 1000 degrees C. Green bodies' temperature difference between the center and surface as a function of solids loading, heating rate, and gel system were extensively investigated. Temperature in the center was lower than that on surface of the alumina spheres cast using PIBM gel system during presintering, and temperature difference (Delta T: T-center-T-surface) slightly decreased with increased solids loading but significantly increased with heating rate. Temperature difference (Delta T < 0) generated compressive stress near the surface and tensile stress in center, which led to a porosity difference between the center and the surface. Moreover, the porosity exponentially decreased with increased compressive stress. Tensile stress in the center of the green body cast using PIBM gel system was estimated as 0.3 MPa, which was less than the minimal strength. Therefore, the body was successfully presintered without cracking. However, cracking was found on the surface of the body cast by epoxy-amine gel system, which exhibited a more severe temperature difference fluctuation. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.