A new aqueous gelcasting system for alumina was investigated. Concentrated
(55 vol%) aqueous ceramic slurries dispersed using a mineral acid was gelle
d by pH controlled condensation polymerisation of methylolurea monomers der
ived from urea and formaldehyde. Gelation of the slurry occurred at ambient
conditions during 30-80 min at pH 2.5-3. Humidity controlled drying of gel
led bodies prepared using alumina of average particle size of 0.34 mu m yie
lded green bodies with density of 57% (corrected for organic content) of th
eoretical density and strength (by diametrical compression test) of 0.35 MP
a at polymer content similar to 6% by weight of alumina. Debinderization of
the green bodies was accomplished by pyrolysis in air below 350 degrees C.
The relative density of the bodies sintered at 1550 degrees C for 2 h was
97% TD and the shrinkage during sintering was isotropic and averaged 14 to
16%. (C) 1999 Elsevier Science Ltd and Techna S.r.l. All rights reserved.