THE STANDARD GIBBS ENERGIES OF FORMATION OF ACRO4 (A = CA, SR OR BA) FROM EMF-MEASUREMENTS

The thermodynamic stabilities of CaCrO4, BaCrO4 and SrCrO4 are of interest to materials scientists and also in nuclear technology because these are the possible compounds of fission product-cladding chemical interaction under conditions of accident in fast nuclear reactors. Though there are some reports on the thermodynamic stabilities of CaCrO4 and BaCrO4 obtained by the fluoride electrolyte EMF method, there is no reliable thermodynamic information on SrCRO4. Hence the EMF of the galvanic cells Pt,O2(g)/CaO,CaF2/CaF2/AF2,ACrO4,Cr2O3/Pt,O2(g) were studied under an atmosphere of pure oxygen at a pressure of 0.1 MPa over the ranges 788-1070, 851-1116 and 850-1168 K where A is Ca, Sr and Ba respectively. From the cell EMF data, the standard Gibbs energies of formation DELTA-G(f)O of the chromates, according to the reaction AO(s) + 1/2 Cr2O3(s) + 3/4 O2(g) --> ACrO4(s) were derived to be DELTA-G(f)O(CaCrO4) = -1356.6 + 0.31641T (+/- 0.63) kJ mol-1, DELTA-G(f)O(SrCrO4) = -1359.1 + 0.32998T (+/- 0.30) kJ mol-1, DELTA-G(f)O(BaCrO4) = -1323.7 + 0.31159T (+/- 0.34) kJ mol-1.