Thermal insulators with macroscopic and microscopic pore anisotropy created by gelation–freezing with alumina platelets

Abstract

Thermal insulators were fabricated by freezing and drying gelatin gels containing calcined kaolinite with various amounts of hexagonal alumina platelets, followed by sintering. Unidirectional macroscopic porosity was created via the freezing process, with accompanying pore walls composed of the platelet grains microscopically longitudinally oriented. The relationship among different platelet contents, microstructure, compressive strength, and thermal conductivity was examined. Varying the platelet content in the initial gels enabled effective control of the porosity and properties of the resultant insulators. The use of a gel with a high content of platelets led to a larger porosity because of reduced shrinkage during sintering, resulting in decreased thermal conductivity and strength. The overall morphology and properties of the insulators prepared by gelation–freezing were investigated.