In-situ Observation on the Explosion Process of Inclusions in Spark OES Analysis Using High Speed Camera

Abstract

The Spark electric discharge optical emission spectrometry has been widely applied to a rapid composition analysis of molten elements in the field of steel making processes. The advantage of this method is that the simultaneously composition analysis from light elements to heavy ones is possible and that the acid soluble elements and insoluble inclusions can be analyzed separately. In this study, spark phenomena in discharge and sample surface morphology were investigated using high-speed camera, SEM-EDS, and spark-OES methods. On the basis of detailed analyses of spark images between electrode and sample surfaces, it was found that the explosion process of inclusion consists of the following three stages. At first, a breakdown between sample surface and electrode occurs, and then inclusions are transformed to cathode points. Finally, vapor jet spouts out to electrode and collides with electrons, Ar⁺, and Ar* leading to strong plasma light. In this process plural inclusions are initially destroyed and dispersed finely into the matrix. These findings led us a new model for the selective discharge of inclusions in spark discharge.