Microtribology of alumina particles on metal-coated surfaces

Abstract

The friction of alumina micro-size particles with radii between 0.5 and 30 µm on Co, Cr and Au — coated Si(100) surfaces is presented and analyzed in terms of classical mechanical and unconventional components relevant to these scales. Friction parameters related to the rolling and the sliding friction (K 1 and y 0), the van der Walls forces (K 2) and the depth of electromagnetic penetration (t) are estimated from the experimental results. The development of the friction parameters when the surfaces are coated is described and discussed. The measurements are based on optical observation of the motion of a single micro-particle on a surface under ambient conditions. The motion is initiated by using a mechanical vibration with a micrometer amplitude at frequencies in the acoustic range. The long-range van der Waals forces and the short-range adhesive forces are found to become dominant with contributions of up to 80% for particle sizes below 7 µm and 9 µm for the coated and the bare surfaces, respectively.