Tensi-Volumetric Studies of the CaCO sub 3 -CaO-CO sub 2 System

摘要

A tensi-volumetric apparatus was developed and used to study two aspects of the CaO-CO sub 2 -CaCO sub 3 system, namely the thermodynamics of the CaCO sub 3 (calcite) phase viewed as a pseudo-binary solid solution of CaO and CO sub 2 , and the kinetics of decomposition of CaCO sub 3 (calcite). The solubility of CO sub 2 in the calcite (CaCO sub 3 ) phase was studied as a function of pressure and temperature. It is shown that it is possible to obtain calcite of substoichiometric compositions expressed by (CaO x (CO sub 2 )/sub 1-delta), where at the temperatures of measurement, 773 exp 0 K to 1000 exp 0 K, delta is a small, but measurable quantity. The composition limits of this phase increase rapidly with temperature. Calcite decomposition rates were measured in the range of P//sub Peq/ from 0.05 to about 0.8 and in the temperature range of 853 exp 0 to 933 exp 0 K. The decomposition rate changed by about three orders of magnitude in this range of P//sub Peq/ at every temperature of study. Decomposition rates of calcite powder depend on particle size, powder bed depth and compactness of samples. Measurements with single crystals of calcite suggest that at least two different processes limit the decomposition rate in different P//sub Peq/ regimes. The apparent activation enthalpy, delta H/sup */, for decomposition at P//sub Peq/ less than or equal to 0.1, calculated in terms of decomposition fluxes, is about 49.2 +- 1.2 K cals mole exp -1 . At values of P//sub Peq/ near unity, the value of delta H/sup */ rose to about 61.8 +- 1.8 K cals mole exp -1 . Decomposition rates for powders did not show a consistent apparent activation enthalpy over the range of P//sub Peq/ studied; they varied between 65 and 80 K cals mole exp -1 . (ERA citation 05:013981)