GELCASTING OF ALUMINA SLURRY DISPERSED IN SILICA SOL WITHOUT DE-AIRING PROCESS

A novel gelcasting technique without a de-airing step was developed to prepare mullite green body based on the mechanism of stabilization of bubbles entrapped in the slurry.Utilizing the scattering action of alumina particles in a silica sol at a pH value of about 9.5,an alumina slurry dispersed in the silica sol with a chemical composition of stoichiometric pure mullite,with a solid volume loading of 50 % and with viscosity as low as 953 mPa·s was prepared.In situ consolidation of the slurry was accomplished by adjusting the concentration of NH_(4)Cl to control the gelation time of the slurry.The results show that the de-airing time of the slurry has little effect on the porosity of the green body,because no surfactant is introduced into the slurry.A defect-free dried green body with a bending strength of 4.83 MPa can be obtained by this gelcasting technique without de-airing.