Spray Drying Technique as a Method for Improving Rheology of Alumina Feedstocks for Powder Injection Moulding

摘要

Rheological behaviour of three feedstock formulations with different surface powder treatment was studied. Spray dried process was able to break all hard particle agglomerates conducting to a monomodal particle size distribution with spherical morphology. In contrast, coating alumina powder with SA did not produce important morphology changes. Bimodal particle size distribution of as received powder was also observed in coated powder. However, when the powder is previously treated with SA in a high-performance dispersing instrument, some big agglomerates are disintegrated into primary particles. Feedstock prepared with these three kinds of powders exhibited a pseudoplastic behaviour with suitable viscosity values in the shear rate range recommended for CIM. Besides treating the powder is effective to improve flow behaviour of mixtures showing lower viscosities in comparison with untreated powder. This could allow to increase powder loading in alumina feedstocks permitting higher densities, lower shrinkages and therefore better properties of final parts.