EFFECTS OF MIXING SEQUENCE ON ALUMINA PREPARED BY INJECTION-MOLDING

Two mixing sequences of binder system were used to prepare the feedsto cks containing high purity alumina (A-16SG) powder. The properties of the feedstocks were analyzed by various techniques, including FT/IR, c apillary rheometry, and TGA. Besides, the green density and pore size distribution of injection molded Al2O3 parts, and the sintered densiti es, the fracture strength and Weibull distribution of the densified te st bars were measured. The results indicated that the sequence of bind er addition is better adding polypropylene (PP) into preheated alumina powder, then stearic acid (SA), followed by paraffin wax (PW). This m ixing step was found effective for the preparation of a good mixture o f plastics/powder system to produce feedstocks with a lower viscosity and better homogeneity for injection molding. The statistics of fractu re strength and the results of fractography reveal that the sintered t est bars made by the better feedstocks have a uniform microstructure w hich is free from large cracks and pore clusters. They result in a hig her fracture strength (375 MPa) and Weibull modulus (up to 20.9) than those produced by the other process. (C) 1998 Elsevier Science Limited . All rights reserved.