The material eroded by a high voltage spark discharge in a point-to-plane configuration was investigated. Glass microscope slides were used to collect material close to the spark discharge and material which had traveled away from the spark. The effluent was also directed into a microwave discharge, and material from the spark which had traveled through this discharge was collected and inspected. The collected material was visually inspected with a light microscope and with a Scanning Electron Microscope (SEM). Using these microscopes, it was found that the material collected near the spark discharge consisted mainly of very small particles, although some larger droplets were also observed. As the material was collected farther from the spark, larger particles were observed. These were apparently aggregations of the smaller particles observed close to the spark. When these large particles passed through the microwave plasma, some were melted.
Deborah J. C. Helmer and J. P. Walters, "Microscopic Investigations of the Material Eroded by a High Voltage Spark Discharge," Appl. Spectrosc. 38, 399-405 (1984)