Porous ceramics with a duplex pore structure by compression molding of alumina-NaCl paste in molten sucrose

Abstract

Abstract Alumina-NaCl pastes in molten sucrose were prepared by hot blending of alumina-NaCl-sucrose mixtures at a fixed alumina powder to sucrose weight ratio of 1:1 and NaCl to alumina powder weight ratios in the range of 0.6–1. The pastes compression molded at 160 °C for 2 h set due to the caramelization of the molten sucrose. The NaCl and alumina catalyzed the caramelization of molten sucrose as evidenced from the torque-time measurements. The compression molded bodies on carbonization followed by salt removal by leaching with water, carbon burnout and sintering produced porous alumina ceramics with a duplex pore structure. The carbon produced from the sucrose effectively bound the alumina particles which prevented the disintegration of the green body during NaCl removal. Macropores (48–71 µm) were created by the water vapour produced by –OH condensation during setting by caramelization and the microcells (0.7–8 µm) were formed by the removal of NaCl templates. The porosity of the alumina ceramics increased from 59 to 71 vol% whereas the compressive strength decreased from 59.2 to 11.7 MPa when the NaCl to alumina powder weight ratio increased from 0.6 to 1.