Effect of Additives on Thermal Decomposition of Basic Magnesium Carbonate

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The effect of eleven halides on the thermal decomposition of basic magnesium carbonate (4MgCO3·Mg(OH)2·4H2O) has been studied by means of thermogravimetry (TG), differential thermal analysis (DTA) and gas chromatography. The size of crystallite of magnesium oxide prepared by heating the carbonate containing halide was determined by X-ray diffractometry, the oxides being studied by transmission electron microscopy. The thermal decomposition of basic magnesium carbonate was influenced by the addition of beryllium chloride tetrahydrate, magnesium chloride hexahydrate, calcium chloride hexahydrate and magnesium bromide hexahydrate. The DTA curve was changed with the amount of additive, i.e., three endothermic peaks (at about 300, 430, and 530 °C) and an exothermic peak (at 490 °C) turned to only two endo-thermic peaks in the case where the molar ratio of an additive to the carbonate exceeded 0.005, the peak at higher temperature becoming sharp with shift toward lower temperature. The results of TG of basic magnesium carbonate corresponded to those of DTA. Gas chromatographic data showed that the composition of evolved gas varied with temperature. The activation energies of decarbonation and dehydration were obtained by gas chromatography by use of Freeman-Carroll's technique. Increase in the amount of additive caused a decrease in the activation energy of decarbonation, but not in that of dehydration except for magnesium bromide hexahydrate. The size of crystallite of magnesium oxide prepared by calcination at 600 °C for 2 hr, increased with the increase in the amount of additive.
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Effect of Additives on Thermal Decomposition of Basic Magnesium Carbonate

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