Experiments on thermal decomposition of nano-sized calcium carbonate were carried out in a thermo-gravimetric analyzer under non-isothermal condition of different heating rates (5 to 20K·min-1). The Coats and Red...Experiments on thermal decomposition of nano-sized calcium carbonate were carried out in a thermo-gravimetric analyzer under non-isothermal condition of different heating rates (5 to 20K·min-1). The Coats and Redfern's equation was used to determine the apparent activation energy and the pre-exponential factors. The mechanism of thermal decomposition was evaluated using the master plots, Coats and Redfern's equation and the kinetic compensation law. It was found that the thermal decomposition property of nano-sized calcium carbonate was different from that of bulk calcite. Nano-sized calcium carbonate began to decompose at 640℃, which was 180℃lower than the reported value for calcite. The experimental results of kinetics were compatible with the mechanism of one-dimensional phase boundary movement. The apparent activation energy of nano-sized calcium carbonate was estimated to be 151kJ·mol-1 while the literature value for normal calcite was approximately 200kJ·mol-1. The order of magnitude of pre-exponential factors was estimated to be 10~9 s-1.展开更多
A constant-composition technique has been used to study thekinetic of dissolution of barium fluoride in which the activities of the latticeions were maintained constant during the experiments. The method enableskineti...A constant-composition technique has been used to study thekinetic of dissolution of barium fluoride in which the activities of the latticeions were maintained constant during the experiments. The method enableskinetic data to be obtained at very low undersaturation. A striking change inthe mechanism of dissolution is observed as the driving force is changed. Athigher driving forces (relative undersaturation 0.15--0.20) the process appearsto follow normal diffusion-controlled dissolution, while at very low undersatu-ration (0.04--0.12) a surface controlled reaction predominates. The tworegions of undersaturation a show marked difference in reactions.展开更多
基金Supported by the Key Research of Science & Technology of Education(No.0202)and the Fundamental Research Plan of HuoYingdong(No.81063).
文摘Experiments on thermal decomposition of nano-sized calcium carbonate were carried out in a thermo-gravimetric analyzer under non-isothermal condition of different heating rates (5 to 20K·min-1). The Coats and Redfern's equation was used to determine the apparent activation energy and the pre-exponential factors. The mechanism of thermal decomposition was evaluated using the master plots, Coats and Redfern's equation and the kinetic compensation law. It was found that the thermal decomposition property of nano-sized calcium carbonate was different from that of bulk calcite. Nano-sized calcium carbonate began to decompose at 640℃, which was 180℃lower than the reported value for calcite. The experimental results of kinetics were compatible with the mechanism of one-dimensional phase boundary movement. The apparent activation energy of nano-sized calcium carbonate was estimated to be 151kJ·mol-1 while the literature value for normal calcite was approximately 200kJ·mol-1. The order of magnitude of pre-exponential factors was estimated to be 10~9 s-1.
文摘A constant-composition technique has been used to study thekinetic of dissolution of barium fluoride in which the activities of the latticeions were maintained constant during the experiments. The method enableskinetic data to be obtained at very low undersaturation. A striking change inthe mechanism of dissolution is observed as the driving force is changed. Athigher driving forces (relative undersaturation 0.15--0.20) the process appearsto follow normal diffusion-controlled dissolution, while at very low undersatu-ration (0.04--0.12) a surface controlled reaction predominates. The tworegions of undersaturation a show marked difference in reactions.
