COLLOIDAL PROCESSING AND FRACTURE STRENGTH OF ALUMINA PREPARED FROM PARTIALLY AGGLOMERATED THETA-PHASE POWDER

One highly pure theta-Al2O3 powder (APA-0.2) with large surface area, but with partial agglomeration, was colloidally processed to prepare s amples with uniform microstructure and high strength. a dispersant, se micarbazide hydrochloride (S-HCl) and two preparing methods, ball-mill ing and turbomixing, were utilized to disperse alumina agglomerates in aqueous solution. With an air-pressure-casting and step-sintering sch edule, fine-grain alumina of average grain size 2.5 mu m, average four -point bending strength of 506 MPa, and reproducible Weibull distribut ion (modulus=12) were obtained. The zeta-potential of APA-0.2 powder, the rheology of the slurries, green density, porosity and sintering pr operties of the powder were presented and discussed. Properties of gre en and sintered APA-0.2, including fracture strength, were compared wi th that of samples prepared from A-16SG powder.