Use of the Langmuir method for kinetic studies of decomposition reactions: calcite (CaCO3)

Abstract

The Langmuir method for measurement of vapour pressures has been tested for use in studies of decomposition reactions. The isothermal weight loss in vacuum from cleavage (1011) planes of calcite (CaC03) single crystals was measured continuously at temperatures from 934 to 1013 K. The rate was constant until approximately 80 % of a 1 mm slice had decomposed. The apparent activation enthalpy was 205 kJ (49 kcal) mol-'. Micrographic examination showed an approximately 30 pm thick layer, probably a metastable form of calcium oxide, separating the calcite from the growing layer of oriented stable calcium oxide. The 30 pm layer yielded a single X-ray diffraction peak which was displaced slightly from the strongest (220) peak of the oriented normal calcium oxide. Lower apparent activation enthalpies measured in previous studies of calcite decomposition in inert atmospheres are suggested to result either from partial diffusion control of the process or from catalysis of the direct formation of normal calcium oxide by carbon dioxide or a component of the system atmosphere. The ratio of the measured decomposition rate in vacuum to the maximum rate, which can be calculated from the Hertz-Knudsen-Langmuir equation, is suggested to be a useful parameter in correlating and predicting decomposition reaction rates.

The influence of mass transfer phenomena on the kinetic analysis for the thermal decomposition of calcium carbonate by constant rate thermal analysis (CRTA) under vacuum

“…Two different experimental approaches under high vacuum can be selected from numerous experimental studies of the kinetics of the thermal decomposition of calcium carbonate, as a possible solution for the kinetic analysis of reversible solid-state decompositions. One is the Langmuir method employed by Beruto and Searcy [12], in which the rate of linear advance of the reaction interface along a selected direction of a single crystalline or shaped sample is subjected to kinetic study at constant temperatures under high vacuum. The Langmuir method has several advantages [12], compared with the conventional thermogravimetry (TG) for measuring the decomposition rates for powdered or granular samples in flowing inert gas.…”

Rearrangement of Porous CaO Aggregates During Calcite Decomposition in Vacuum

“…Calcite crystals with a spectrographic analysis given in a previous paper [1] were cut along (lOll) planes to obtain slices 2 ~o. 75 mm thick, with areas of ~ 20 mm and rv40 mg weight.…”

“…distinguishable CaO layers [1,2]. Beruto and Searcy [3] suggested that the intermediate CaO layer transforms to the second CaO layer as a consequence of accumulated strain.…”

Stop Smoking—Tube-In-Tube Helical System for Flameless Calcination of Minerals

“…Wang and Thompson [44], as well as Beruto and Searcy [45], determined the activation energy of calcite to be as high as 197 kJ/mol and 205 kJ/mol. Sceats et al [17] subsequently estimated the power that was required for the calcination reaction to being 2.6 MW for 1.45 kg mineral feed per second per calcination unit employed.…”