Comparative Study of Spots and Craters Formed during Spark Discharge in Air on Electrodes Made of Different Metals

We described the procedure for processing images of electrode spots of an oscillatory spark discharge on a flat polished surface of electrodes made of various metals (Fe, Ti, Cu, Al, Sn) in an air atmosphere. The amplitude of the discharge current was from 3.6 to 7 kA, the period was 1.6 μs, the discharge energy was from 5 to 18 J. The aim of the work is to clarify the effect of thermophysical properties of the metal on the characteristics of the crater system that appears on the electrode spot under conditions of obtaining nanopowders by the spark discharge method. The images were taken using a NewView 5010 interference surface analyzer. Crater diameters were measured from the images. A comparative statistical analysis of diameter samples was performed. It was found that the diameter distribution is satisfactorily described by a logarithmic normal law. The properties of the metal determine both qualitative differences in the type of electrode spot (the presence of a melt pool, the density of crater layout) and the parameters of diameter samples (median, geometric standard deviation). The median diameters of craters and their maximum depths correlate with each other and increase in the sequence: Cu, Fe, Ti, Al, Sn. They also decrease with the growth of the specific volume enthalpy of the molten metal. The area of electrode spots increases with the growth of the amplitude of the discharge current, and so that the average current density through the spot remains constant. Copper deviates from these regularities; for it, the diameters and depths of the craters turned out to be smaller than expected.