Adhesion of Small Metal Spheres to Plane Metal Substrates

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Abstract
Small metal spheres (gold and silver, diameter 5–60 μ) dusted on plane metal substrates (gold, silver, nickel, stainless steel) were removed by application of centrifugal forces or electrostatic fields. For forces applied perpendicularly outward from the substrate, the force for removal by centrifuging was found to be much larger than that for removal by electrostatic fields. Analysis of these results shows that the spheres are not to be treated as particles, but rather as elastic or plastic bodies whose adhesion to a substrate is controlled by tangential as well as normal components of the applied force. To investigate the mechanism of removal, centrifuge runs were made with the removal force applied at varying angles with the normal to the plane. The dependence of force on angle is affected by the hardness of the substrate. For relatively soft substrates, the adhesion force reaches its minimum at angles greater than 90°, that is, when the sphere is actually pushed into the substrate. This surprising result can be interpreted on the basis of a plastic‐deformation model.

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