Surface modification of alumina powder for LPIM

To utilise all the advantages of the low-pressure powder injection moulding (LPIM) technique in the production of complex-shaped high-performance ceramics, a stable suspension with a high solids loading and appropriate rheological propel ties is needed. In this investigation different surface active agents were either physisorbed or chemisorbed to modify the surface of alumina powder. To introduce the proper amount of the surfactants homogeneously into the powder-paraffin system, different techniques were applied including direct admixing into the melted paraffin, as well as coating of the alumina particles during milling in a solution of the surfactant in an organic liquid. The efficiency of the physisorbed or chemisorbed surfactants was examined in terms of the apparent viscosity of highly loaded powder-paraffin suspensions. Moreover, the hydrophobicity, of the powders as well as the sensitivity of alumina-paraffin suspensions and of moulded green parts to destabilisation with water were estimated. (C) 1996 Elsevier Science Limited.