Halogenation with CCl 4 and CF 2Cl 2 vapours in arc emission spectrometry

Abstract

Halocarbon vapour diluted with air or nitrogen was applied during the arc excitation of carbide forming elements in solution form, of metal samples (copper, aluminium) and powder samples (alumina, glass, RU-powder) on graphite supporting electrodes. Means were developed for the carrier vaporization of CCl 4 and for the introduction of the halocarbon vapour into the arc discharge. The gaseous agent was supplied continuously during excitation. This possibility was also subjected to some theoretical predictions. On applying CCl 4 with samples introduced in solution form, the volatilization rates of the most refractory elements (e.g. W) were found to increase at least 50 times on the basis of line intensities. Fractional distillation could be attained on constituents and matrices similar to those reported with solid agents, but the gaseous agents could be applied more easily and without contamination problems. The overall effect of halogenation on excitation processes was evaluated from line intensities integrated over the total evaporation time of a complex powder sample, with and without graphite powder dilution. A high intensification (a factor of 3–12) was obtained for the u.v. lines of the refractory constituents with halogenation, which was attributed to the increased efficiency of these elements in entering the excitation zone. Decrease in the intensities of barium atom and ion lines in the VIS range and a decrease of self-absorption were found as a consequence of halide formation in the arc fringe.