Decompositions of two-component solid solutions

Many of the most detailed kinetic studies of the reactions of these solids have been concerned with mixtures containing a common ion, (A,B)X. 

There have been several kinetic studies of the calcination of dolomite [29], a reaction of considerable technological importance. As in many reversible reactions, the rate of carbon dioxide release is sensitive to the prevailing pressure of this product (.Pco2) in the vicinity of the reaction interfaces. At low pressures (PCo2 12 Torr), reaction proceeds to completion in a single stage between 900 and 950 K 

When Pco2 24 Torr, a higher decomposition temperature ( 960 K) is required and the reaction is 

Even higher temperatures are required for calcite dissociation. As f co2 is increased to 760 Torr, the reaction temperature rises to 1170 K and the extent of dissociation is diminished [29]. The rate of decomposition of dolomite in vacuum [734] was intermediate between those for magnesite and calcite. Ranges of study were magnesite 810—870 K, dolomite 910— 990 K, and calcite 990—1050 K. Values of E were in the different sequence, magnesite calcite dolomite. Magnesite, which would decompose very rapidly at the temperature of dolomite dissociation, is, therefore, relatively stabilized, whereas the reactivity of calcite is enhanced in the mixed crystal. 

It was concluded [734] from visual inspection and chemical analysis of partially decomposed dolomite, that reaction was initiated at the outer surfaces of the crystallites and the interface established advanced thereafter into the bulk. The deceleratory a—time curves obeyed the contracting volume equation [eqn. (7), n = 3] and the values of E determined were between 206 and 232 kJ mole-1. These values of E were generally greater than those reported for other studies ( 190 kJ mole-1) which are in the range mentioned [121] for CaC03 dissociation and slightly larger than the enthalpy of that reaction. On exposure of the residue from vacuum decomposition of dolomite to C02, the gas uptake at 1070 K was 

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