Abstract：The preferential discharge phenomenon existed in spark discharge atomic emission spectrometry. However, the formation mechanism has been not systemically and comprehensively discussed. The related researches revealed that the preferential discharge was related to the work function of components and surface roughness of samples. A group of experiments were designed to verify these influencing factors: two metal contact samples with different work functions, the samples with smooth surface with protrusions as well as rolling samples and casting samples were prepared. The morphology features and distribution of spark discharge spots in these samples were observed. The experiments proved that the preferential discharge occurred in phases with low work function and samples with surface protrusions. The tip protrusions formed by inclusions with low work function could easily cause protrusions discharge compared to the steel-based protrusions with same dimension. According to the experimental results and physical theory, the preliminary interpretation and judgment criterion for preferential discharge phenomenon were proposed. Moreover, some special phenomena in spark discharge were also observed in experiments: the discharge with two time sequences existed in one spark pulse process, indicating that one discharge may cause several “single sparks” with time sequence. In addition, the inclusion evaporation or fragment residue was also observed around the discharge pits.
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