The effect of chemically bonded organic surface layers on the behaviour of fine powders

We have examined the effects of chemically bonded organic surface layers on the behaviour of a ceramic and a metal powder. The thin monomolecular layers were found to improve the corrosion resistance of the sensitive Nd–Fe–B powder and make the fine alumina powder hydrophobic and, as a result, making both coated powders significantly less sensitive to environmental humidity. Our analysis of the flowability of the noncoated and coated powders revealed that the alumina powder can be classified as very cohesive—the addition of the coating even increased its cohesivity. The Nd–Fe–B powder was determined to be easy flowing, and the effect of the coating changed with the applied normal stress. The coating does, however, improve the powder-compaction properties of both powders. In addition, the beneficial effect of the coating in terms of viscosity as well as in resistance to destabilization was also observed for suspensions in organic solvents.