Gel-Assisted Extrusion of Alumina

Abstract

Fabrication of alumina shapes through paste extrusion using boehmite gel, a monohydroxy aluminium oxide (AIOOH), as a reactive binder was studied and reported. The rheological characteristics of alumina with and without boehmite binder were studied at different shear rates. The critical quantity of boehmite binder was optimized from the results on effective solid loading, influence of medium pH, development of torque and viscosity. The alumina paste containing 15% (wt) boehmite binder resulted in 53.4% (vol) of total solids at pH 6.7 with extrudable consistency. The system exhibits a low torque value of 51.85 Pa at shear rate 28.5 S⁻¹ and showed a plastic behaviour. The apparent viscosity of the system showed a shear dependent flow behaviour. Alumina-15 wt% boehmite resulted in higher particle packing, and 60.4% theoretical green density was achieved. The extruded alumina has sintered density of >98% of theoretical density after firing at 1500°C. The microstructure of sintered alumina showed average grain size <2 μm. The boehmite binder has several advantages, e.g. matrix compatibility, good workability, imparting higher green strength and also as a ‘sintering aid’ and can be successfully used for alumina ceramics.