Analysis of electrical resistance measurements as a potential determination method for coating thickness on powders

Abstract

The electrical resistance of conductive and non-conductive coatings on non-conductive and conductive powders, respectively, is investigated under increasing external load. A specially designed equipment was used to deposit coatings on small and light as well as heavy powdery substances by DC magnetron sputtering. Several reference methods to predict or measure the absolute film thickness on powders are discussed. When measuring the electrical resistance of insulating powders coated with a metal, in this case hollow glass microspheres (HGMs) coated with copper, under increasing load, a typical resistance curve is found. This resistance curve is discussed in terms of percolation theory and the Heckel equation for powder compaction. The influence of coating thickness of the conductive coating is then evaluated and other factors like inhomogeneity of the coating are discussed. To reduce the influence of measurement parameters, selected experiments are interpreted under the concept of a force per grain, which is introduced and explained. To further substantiate the typical electrical resistance curve, stabilized and non-stabilized NMC811 powder is coated with aluminium and zirconium oxides of different thicknesses, corresponding to a conductive powder with an insulating coating. When comparing measurements for stabilized and non-stabilized powder, the perspective for electrical resistance measurements under increasing load becomes apparent, as it is possible to even detect surface modifications which are not known a priori.