Study of the mechanism of evaporation of impurity elements in arc atomic emission analysis of high-purity graphite powder in the presence of fluorine-containing additives

The effect of chemically active fluorine-containing additives AlF3, ZnF2, and SrF2 on the nature of evaporation of low- and medium-volatile impurity elements from the crater of a DC arc electrode during graphite powder analysis is studied. It is shown that the use of AlF3 and ZnF2 contributes to a significant increase in the intensity of the spectral lines of the elements being determined and a decrease in the time of their complete evaporation from the electrode crater. It is found that the most effective additive is zinc fluoride at a concentration of 5 wt. %. In this case, the maximum increase in intensity is observed in the case of low-volatile elements prone to carbide formation. The use of ZnF2 made it possible to reduce the limits of determination of low- and medium-volatile elements in graphite powder by direct arc atomic emission analysis by 2–3 orders of magnitude to n × 10–7–n × 10–5 wt. % and to improve the convergence of their determination results by two times compared to the analysis of graphite powder without the use of additives.