Adhesion of carbonyl iron powder particles studied by atomic force microscopy

Adhesion forces between individual micrometer-sized carbonyl iron powder (CIP) particles were measured with an atomic force microscope (AFM) using the colloid probe technique. The effective normalized adhesion force F-adh/R was 14 +/- 10 mN/m (R is the reduced radius of two particles), which is much smaller than expected from the surface energy of iron oxide. This is mainly due to the pronounced surface roughness of the particles. The spatial variation of adhesion and the influence of surface contamination could be visualized from the adhesion maps of the particle surface using the force volume AFM mode. Adhesion between CIP particles and a silicon surface increased by 160% when increasing the external load from 21 to 204 mu N and remained high afterwards, indicating plastic deformation of the particles. Residual magnetization after exposure of the particles to a magnetic field of 0.8 T did not influence the adhesion force.