A method for a routine, direct analysis for fluoride in electroslag refining (ESR) fluxes, using potentiometry, is described that is faster, more economical, and less operator-dependent than previously known methods of fluoride analysis in these materials. Flux samples were prepared using a rapid sodium carbonate/borate fusion with subsequent digestion in dilute nitric acid prior to chelant addition and analysis by fluoride ion-selective electrode (FISE). Disodium ethylenediaminetetraacetate (EDTA), ethylenediamine, ammonium citrate, ammonium tartrate, and citric acid were used to chelate metal cations in solutions of flux containing calcium fluoride (fluorspar) as a major constituent. It was found that, for optimal recovery of fluoride, pH of the chelant/flux solution must be controlled between 8.0 and 9.0. High concentrations of calcium reduced the ability of the fluoride ion-selective electrode to detect fluoride. It is suspected that high concentrations of magnesium would also contribute to this reduced sensitivity, but such fluxes were not tested. The technique is well-suited for analysis of fluxes when the sample CaF 2 content is ≤63% by mass. Analysis of several flux formulations showed that the new FISE method is more practical and produces results that are as accurate and precise as conventional methodology.
All Science Journal Classification (ASJC) codes
- Chemical Engineering(all)
- Industrial and Manufacturing Engineering