In situ coagulation moulding: a new route for high quality, net-shape ceramics

A fast, near-net shape route for the production of advanced ceramic components has been developed that uses carboxylic acid derivatives as coagulants for electrosterically dispersed, high solids content ceramic suspensions. The time dependent in situ hydrolysis of the coagulant D-gulonic-gamma-lactone progressively destabilises the suspension to form a viscoelastic solid within which the homogeneity of the initial dispersion is maintained. Constraining this hydrolysis reaction within a non-porous mould leads to the formation of green bodies. After drying, the ceramic components can be sintered without special debinding operations since only a small amount of organic additive, less than 1 wt.% of the total batch mass, is needed. Since the forming process takes place without pressure and at temperatures around ambient conditions, inexpensive moulds and tools can be used. As applied to A16-SG grade alpha-alumina, this new forming technology, called in situ coagulation moulding, produces components that possess high sintered densities, similar to 99% theoretical, high average mechanical strengths, sigma(3pt)approximate to 450 MPa, good reliability, Weibull modulus, m=10, and uniform microstructures. (C) 2005 Elsevier Ltd and Techna Group S.r.l. All rights reserved.