ENERGETICS OF FORMATION OF KF-GDF3 BINARY-INTERMEDIATE COMPOUNDS

Enthalpies of formation were measured for KGdF4, K2GdF5 and KGd2F7 usi ng the transposed temperature drop calorimetry method. These compounds were synthesized by conventional solid state reaction methods using m ixtures of KF and GdF3. The measured enthalpies of formation from fluo rides for KGdF4, K2GdF5 and KGd2F7 were -22.3, -16.1 and -18.3 kJ mol( -1), respectively. From these measurements, enthalpies of formation fr om the elements were computed to be -2290.0, -2852.4 and -3985.2 kJ mo l(-1) for the respective compounds. These enthalpies were compared wit h estimated values calculated by two methods previously reported to be effective for multicomponent oxides. Estimated values compare favorab ly with measured data, with deviations ranging from 0.5 to 2.9%. The e rrors of 0.5-2.9% correspond to a 16-85 kJ mol(-1) uncertainty range f or Delta(f)H(0) of ternary fluorides from binary fluorides. One of the se methods, based on the summation of Delta(f)H(0) values for the cons tituent binary fluorides, is recommended for the K-Gd-F compounds.