Effect of boehmite and organic binders on extrusion of alumina

The extrusion of alumina pastes processed by sol gel assisted colloidal processing involving nano particulate boehmite gel as binder phase was studied. Submicron alumina was dispersed in aqueous boehmite sol at pH 3 followed by gelation and centrifugal filtration to form alumina–boehmite pastes and further subjected to single screw ceramic extrusion. Alumina–15 wt.% boehmite pastes exerted a peak pressure of 1.6 MPa at the die exit at a screw speed of 20 rpm. The pressure analysis of alumina–boehmite paste was compared with the conventional water-soluble HPMC polymer system. The exit pressure for alumina–HPMC system was only 0.2 MPa. The addition of processing aids such as 0.25 wt.% of PVA, 3.0 wt.% of either PEG or glycerin with alumina–15 wt.% boehmite paste exhibit very low exit pressure as equal to that of the HPMC binder. A green density of 65% theoretical was achieved for extruded alumina. The alumina rods attained 98% theoretical sintered density at 1500 °C. The study shows the use of nano particulate boehmite gel as binder for alumina ceramics as well as the influence of conventional ceramic processing additives on extrusion characteristics of alumina–boehmite pastes.