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Abstract  

The effect of sample mass, heating rate and partial pressure of carbon dioxide on TG, DTG and DTA curves for the decomposition of some common carbonates has been investigated. These variables gave a marked effect, similar in magnitude for both DTG and DTA. The effect of sample mass, or depth of undiluted sample, is shown to be due to an increase in the partial pressure of carbon dioxide within the reacting powder. This effect is most pronounced in nitrogen but is much reduced in carbon dioxide. Inert diluents have little effect on the curves since they do not increase the partial pressure of CO2. The first stage of the decomposition of dolomite (CaMg(CO3)2) varies with increasing partial pressure of carbon dioxide in an anomalous manner and hence the effects of these procedural variables (except heating rate) are not similar to those observed for magnesite (MgCO3) and calcite (CaCO3). The second stage is, however, strongly dependent on these variables and behaves in a manner that would be predicted for a sample of calcite diluted with magnesite.

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Abstract  

In the present paper the thermal behaviour of Mg-carbonates and -silicates is reviewed and discussed, based on own DTA investigations and data from the literature. Mg-bearing minerals in soils and sediments offer informations about the palaeoenvironment and palaeoclimatology of sediments and soils and - thus - the study of their crystal chemical compositions by means of (differential) thermal analysis informs about environmental conditions of (sedimentary Mg-) mineral (trans-) formations. The paper stresses (1) the interrelations between decomposition temperatures of (Mg-) carbonates and substitution processes and is (2) concerned with the interdependence between the dehydroxylation behaviour of Mg-bearing sheet silicates and their crystal chemical composition.

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-added chemicals [ 1 ]. Among the chemicals derived from glycerol, glycerol carbonate, which can be used as the solvent or reaction intermediate, is a high value-added product with many potential applications [ 2 – 6 ]. Glycerol carbonate can be prepared

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vacancies both in anionic and cationic sites which make these materials as highly effective ion exchange matrixes [ 1 ]. Carbonate apatites are the main mineral components of human and animal hard tissues (bones and teeth) [ 2 – 4 ]. It has been established

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Introduction Apatites are a large class of mineral compounds with the general formula M 10 (PO 4 ) 6 X 2 , where M is generally a divalent cation and X can be a hydroxyl, carbonate or a halide. They crystallise in the hexagonal

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distributed solar thermal power. The melting point of mixed nitrate used in the current stations is about at range of 150–200 °C, which can not meet the requirement of high storage temperature. However, mixed carbonate, with high melting point and larger

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Abstract  

Pressureless sintering of CaCO3 was carried out, with Li2CO3 (from 0.5 to 8 wt%) as an additive, under different pressures of CO2. Densification occurs between 600 and 700°C. Sintering above the eutectic temperature (T>662°C) leads to the decomposition of calcium carbonate and the materials become expanded. At 620° under 1 kPa of CO2, a relative density of 96% is reached. Li2CO3 enhances the densification process and grain growth of calcium carbonate. CO2 pressure slows down densification and grain growth kinetics. These results are explained by the influence of carbonate and calcium ion vacancies on the sintering mechanisms.

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, Hess law, and several equations derived from basic thermodynamic equations. In this study, this method was applied for determination of temperature equilibrium of CaCO 3 dissociation. Calcium carbonate dissociation is represented by reaction ( 1 ): 1

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. T. Nakamori 2001 Global carbonate accumulation rates from Cretaceous to Present and their implications for the carbon cycle model Island Arc 10

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can occur. Among these substitutions, the partial replacement of the F − and PO 4 3− ions by the carbonate ions presents a special interest generated by the similarity of the carbonated compounds with the natural apatites. There are two possibilities

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