Irreversible behaviour of an electrochemical device for the monitoring of carbon in liquid sodium

Galvanic Cell Studies on Ionic Carbide and Nitride Solutions in Molten Salts

“…Galvanic cells using CaC2 solutions in molten salts as electrolyte have been studied by previous authors (1-3) with unsatisfactory results as regards the possibility of determining accurately the carbon activity in iron electrodes. The reason for this lack of accuracy has been ascribed to the existence of electronic conductivity in the melt (3,4) as a consequence of the presence of calcium resulting from the establishment of the following equilibrium CaC2 (melt) ~ Ca (melt) -5 2C (s) [1] Most of the previous authors (1,3) have used pure synthetic CaC2 PrePared from the elements at a temperature near 1000~ and the physicochemical behavior of molten salt solutions prepared with the pure synthetic CaC2 seems to be quite different from that obtained with technical grade carbide. In fact, anodic voltametric curves (5) and chronopotentiometric studies (6) carried out in solutions prepared with synthetic CaC2 show, respectively, two waves and two transition times, the first attributed to the oxidation of calcium and the second to the oxidation of carbide ion.…”

Galvanic Cell Studies Involving Calcium Carbide Solutions

“…and the cell electromotive force to be given by RT EI -" --~ In ac [2] F However, possible problems with the cell were indicated by (i) cell voltages corresponding to carbon activities lower by 0-10% than those from gas equilibration studies using CO/CO2 and CH4/H2 gas mixtures (2), (ii) a need to introduce a nickel gauze partition between the electrodes to prevent carburization, and (iii) the possibility of less than equilibrium voltages because of electronic conduction in the melt as has been discussed for similar cells (3)(4)(5).…”

“…It is well known that calcium metal is soluble in its halides, possibly in the form of a molecule-ion Ca~ 2+ (14). The results of chemical analysis of calcium carbide-chloride solutions equilibrated in graphite crucibles have been interpreted using a thermodynamic argument based upon equilibrium [4] (6). Chronopotentiometric studies by White (11) and voltammetric studies by Dosaj (15) have been interpreted in terms of a dissociative equilibrium preceding the electrochemical step at low current densities.…”

“…A model is postulated for the galvanic cell in which calcium metal in solution is viewed as the electroactive species, and at the electrode-electrolyte phase boundary there exists the chemical equilibrium CaC2(soln) ~ Ca(soln) -]-2C(eleetro~e) [4] and the electrochemical equilibrium Ca(soln) .~ Ca 2+ (soln) -[-2e [5] Cell [I] is therefore more accurately represented by cell [II] in which the calcium metal activities at the two electrodes are determined by equilibrium [4]. It is thus similar to the bimetallic cells with alkali metal anodes in which Hesson et at.…”