Iron oxide layer effects on the sedimentation behavior of carbonyl iron powder suspension
Heebo Ha, Russ Thompson, Byungil Hwang
Abstract
Understanding the sedimentation behavior of carbonyl iron powder (CIP) in ethanol or water is important for fabricating a highly stable magnetorheological polishing suspension. Thermal annealing in ambient air is typically adopted to enhance the sedimentation stability of nano/micro metal powder-based suspension. However, the change in sedimentation behavior due to the oxide layer on CIP formed by annealing has not been sufficiently studied; thus, the sedimentation behavior of thermally annealed CIP in ethanol is systematically studied here. The iron oxide layer formed by annealing accelerates the sedimentation of CIP in ethanol. Contact angle analysis indicates that thermal annealing modified the surface characteristics of CIP as hydrophobic states due to dehydration and oxide-layer formation on the surface. The decreased solvent wettability due to the hydrophobicity resulted in the agglomeration of CIPs, thereby accelerating the sedimentation.