Effects of mixing sequence on alumina prepared by injection molding

Two mixing sequences of binder system were used to prepare the feestocks containing high purity alumina (A-16SG) powder. The properties of the feedstocks were analyzed by various techniques, including FT/IR, capillary rheometry, and TGA. Besides, the green density and pore size distribution of injection molded Al₂O₃ parts, and the sintered densities, the fracture strength and Weibull distribution of the densified test bars were measured. The results indicated that the sequence of binder addition is better adding polypropylene (PP) into preheated alumina powder, then stearic acid (SA), followed by a paraffin wax (PW). This mixing step was found effective for the preparation of a good mixture of plastics/powder system to prdouce feedstocks with a lower viscosity and better homogeneity for injection molding. The statistics of fracture strength and the results of fractography reveal that the sintered test bars made by the better feestocks have a uniform microstructure which is free from large cracks and pore clusters. They result in a higher fracture strength (375 MPa) and Weibull modulus (up to 20.9) than those produced by the other process.