| 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 IJm. 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. |
