Pyrolytic boron nitride coated graphite as a container of reference electrodes for molten fluorides

Abstract

A one-end-open graphite cylinder which was coated externally with pyrolytic boron nitride, except the bottom, was used successfully as the container of a reference electrode for use in fluoride melts. The electrode consists of a nickel wire or silver wire immersed in a solution of nickel or silver fluoride in LiF-NaF-KF (FLINAK) eutectic. It was tested by using both the Ni-Ni(II) and the Ag-Ag(I) redox couples at temperatures between 650 and 800 °C. The emf between two identical electrodes was stabilized within 3 h after the immersion in the bath and a Nernstian response with temperature was observed. The electrode was found to be stable for more than 50 h and could be reused with reproducible results. No potential shift was observed in cyclic voltammograms which were obtained, with a lapse of 12 h, from FLINAK with 0.1 mol% K 2NbF 7.