A reference electrode for electrochemical studies in fused alkali chlorides at high temperatures

Electrode potentials in fused systems X. Measurement of cation concentration in molten salts using glass membrane electrodes

“…Combined with the data of previous studies [4,5], these re s ults show that the method prese nted in this paper is capable of measuring the silver ion concentration in Ag+ -Na+ melts over a range of 10 4 • The valu es of t' and its standard de viation for the syste ms studied are t' is independent of temperature betwee n 800 and 900 °C [4]. A previous comparison between Vycor and Supremax [2,4], two glasses of quite different composition , indicates that t' is n early independent of the particular glass used .…”

“…A number of membran e elec trode designs, all based on the Ag-Ag+ equilibrium, have been published [1,2,3,4).1 In contrast to aqueous systems in which the glass electrode functions as indicator electrode, primarily for pH measurements, in molten salts it serves as a reference electrode with respect to which potential changes at other electrodes can be observed. For this appli cation the primary requirement is stability and reproducibility, i.e., several electrodes of identical design s hould vary as little as possible in potential be havior.…”

“…For sys te ms co ntainin g a sin gle ani on only catio n term s ar e in c lude d in th e s umm ati on. S in ce It ; = L e q ( 1) beco mes Equation (2) is use ful for th e meas ure me nt of a n unkn own co mpositi on onl y if (a) tM t is r e ally inde· pe nd e nt of compos iti on ove r til e e ntire c on centration ra nge, (b) no chan ges occ ur in th e refe re nce electrode , e.g. co mpos iti o n c h anges by va pori za ti on , a nd (c) th e th erm od yna mi c be havi or of th e melt , i. e. , th e ac tivit y coefficients of the components , are known.…”

“…Co nditi on (b) can be sati s fi e d fairly well by usin g sm all di a me ter tubin g. For th e purpose of meas urin g melt co mposition co n· dition (c) imposes a grea t in c onve ni e nce . In th at case it is proba bly prefe ra ble to writ e e q (2) in ter ms of th e mole frac tio ns and to le t t Mt a bs orb the non· idealit y ot th e syste m. Alth ough thi S treatme nt c an give mi sleadin g res ults if precise info rmati on on io n tra nsport in glass is des ire d [7], it is jus tifi e d wh e n th e purpose of th e meas ure me nt is th e de te rmin ati on of me lt co mpositio n. In th a t case it is more co nve ni e nt to write eq (2) in term s of th e mole frac ti o n, viz…”

Electrochemistry—I

“…The noble metals that behave in this way may of course be used to monitor the redox potentials of melts. 56 In this mode they act as inert electron sinks for the various oxidation-reduction reactions which interact to determine the redox level of the melt.…”