Gelcasting of alumina using urea-formaldehyde - I. Preparation of concentrated aqueous slurries by particle treatment with hydrolysed aluminium

A treatment of alpha-alumina with hydrolysed aluminium (Hh), generated in s itu by homogenous hydrolysis of aqueous aluminium nitrate solution using he xamethylene tetramine (HMTA), has been evolved to enhance the surface activ ity of the powder towards complexation with H+ and thus to promote dispersi on of its aqueous concentrated (>50 vol%) slurries using a mineral acid (ni tric acid) with a view to prepare slurries having high solids loading and l ow viscosity for gelcasting. Viscosity minimum of the slurries was obtained at HA minimum (Al3+ added in the system)similar to 6 x 10(-6) mol/m(2) (BE T surface area) of the powder. Slurries of solids loading >60 vol% having v iscosity <1 Pa a at 93 s(-1) could be prepared by HA treatment of alpha-alu minas of median particle size 0.3-0.8 mu m to obtain green bodies with rela tive density of 65-71% by evaporational drying. (C) 1999 Elsevier Science L td and Techna S.r.l. All rights reserved.