THERMODYNAMICS OF CACO3 PHASE-TRANSITIONS

Thermodynamic quantities of the aragonite --> calcite transition, were evaluated using results of calorimetric investigations. (1) Dissoluti on enthalpies of the CaCO3 polymorphs aragonite and calcite measured n ear room temperature with different calorimeter, (2) the enthalpy of t he spontaneous phase transformation obtained by differential scanning calorimetry, (3) heat capacities and heat capacity differences determi ned with a heat flux calorimeter as well as previously determined, (4) e.m.f. data on Gibbs-energies of the phase transition were processed simultaneously with an optimization routine developed recently. The op timized data set (25 degrees C) given below corresponds reasonably wit h CODATA recommendations, however, the precision has markedly improved . [GRAPHICS] 631,632,633,634,CP2,CP3,CP4,NIL_0006,COVER3,COVER4