Authors:A. Duran, L. Perez-Maqueda, J. Poyato, and J. Perez-Rodriguez
Roman ancient mortars have been widely studied, in connection with both diagnosis and application required for restoring.
Thermoanalytical experiments performed on mortars from Pompeii and Herculaneum provided a very good understanding of the technology
employed. The mortars from Pompeii were obtained by the proper mixing of lime and marble grains while mortars of Herculaneum
by lime and silicates compounds. The position of the endothermic peak of calcite decomposition showed important variations
in the different samples studied, which was assigned to the different crystallinity and particle sizes. Experiments under
CO2 flow confirmed the presence of magnesium calcium carbonates.
A thermogravimetry-microchromatography assembling has been developed and tested for solvent vaporization studies. Cyclodextrine
and calcium sulfate dehydrations as well as cobalt carbonate decomposition were studied.
The thermal decomposition behavior of hard coal fly ash (HCA2), obtained from the combustion of an Australian hard coal in
thermoelectric power plants, in different atmospheres (air, N2 and N2-H2 mixture), was studied using thermogravimetry (TG), infrared-evolved gas analysis (IR-EGA), differential scanning calorimetry
(DSC) and thermodilatometry (DIL) techniques. It was found that changing of the applied atmosphere affects the carbon content
of the ash which results in different thermal decomposition behaviors. In air, the carbon content was oxidized to carbon dioxide
before the decomposition of carbonate. In N2 or in N2-H2 atmospheres, the carbon content acts as a spacer causing a fewer points of contact between calcium carbonate particles, thus
increasing the interface area which results in a decrease of the carbonate decomposition temperature. Following the carbonate
decomposition, the iron oxide content of the ash undergoes a reductive decomposition reaction with the unburned carbon. This
oxidation-reduction reaction was found to be fast and go to completion in presence of the N2-H2 mixture than in the pure nitrogen atmosphere due to the reducing effect of the hydrogen.
The kinetics of the carbonate decomposition step, in air and N2-H2 mixture was performed under non-isothermal conditions using different integral methods of analysis. The dynamic TG curves
obeyed the Avrami-Erofeev equation (A2) in air, and phase boundary controlled reaction equation (R2) in N2-H2 mixture. The change in the reaction mechanism and the difference in the calculated values of activation parameters with the
change of the atmosphere were discussed in view of effect of the atmosphere on the carbon content of the ash.
Kinetics of mechanically induced CO2 extensive sorption by silicate minerals (labradorite, diopside, okermanite, ghelenite and wollastonite) was considered. Mechanical
activation of the silicates was carried out in a planetary mill in CO2 at atmospheric pressure. Carbon dioxide was consumed by the silicates in the form of carbonate ions and its content in the
samples after 30 min of mechanical treatment reached 3–12 mass% CO2 depending on mineral composition. Equations that reasonably good represent kinetics of CO2 mechanosorption by silicates were proposed. These equations enable to calculate mechanosorption coefficients that characterize
the diffusivity of CO2 into disordered silicate matrix under intensive mechanical impact. Thermal analysis of the mechanically activated silicates
showed that there was positive correlation between temperature of complete carbonate decomposition and mechanosorption coefficient.
Authors:Mary Alves, Soraia Souza, Márcia Silva, Elaine Paris, S. Lima, R. Gomes, E. Longo, A. de Souza, and Iêda Garcia dos Santos
SrSnO3 was synthesized by the polymeric precursor method with elimination of carbon in oxygen atmosphere at 250 °C for 24 h. The
powder precursors were characterized by TG/DTA and high temperature X-ray diffraction (HTXRD). After calcination at 500, 600
and 700 °C for 2 h, samples were evaluated by X-ray diffraction (XRD), infrared spectroscopy (IR) and Rietveld refinement
of the XRD patterns for samples calcined at 900, 1,000 and 1,100 °C. During thermal treatment of the powder precursor ester
combustion was followed by carbonate decomposition and perovskite crystallization. No phase transition was observed as usually
presented in literature for SrSnO3 that had only a rearrangement of SnO6 polyhedra.
The thermal decomposition of cadmium acetate dihydrate in helium and in air atmosphere has been investigated by means of a
coupled TG-DTA-MS method combined with X-ray diffraction analysis. Dehydration of Cd(CH3COO)2·2H2O is a two-stage process with Cd(CH3COO)2·H2O as intermediate. The way of Cd(CH3COO)2 decomposition strongly depends on the surrounding gas atmosphere and the rate of heating. CdO, acetone and CO2 are the primary products of decomposition in air. In helium decomposition goes by two parallel and consecutive reactions
in which intermediates, Cd and CdCO3, are formed. Metallic cadmium oxidizes and cadmium carbonate decomposes giving CdO. Some of the metallic cadmium, depending
on the heating rate and the concentration of oxygen, evaporates. Acetone is partially oxidized in secondary reactions with
Iron(II) sulphate heptahydrate undergoes decomposition in the presence of basic beryllium carbonate without any interaction with the carbonate. The components of the mixture decompose individually. Iron(II) sulphate decomposes with the formation of tetrahydrate, monohydrate, anhydrous salt, oxysulphate and ferric sulphate as intermediate phases. The basic beryllium carbonate decomposes to the oxide with BeO·BeCO3 as the intermediate compound.
The thermal decompositions of pure and mixed manganese carbonate and ammonium molybdate tetrahydrate in molar ratios of 3:1,
1:1 and1:3 were studied by DTA and TG techniques. The prepared mixed solid samples were calcined in air at 500, 750 or 1000C
and then investigated by means of an XRD technique. The results revealed that manganese carbonate decomposed in the range
300–1000C, within termediate formation of MnO2, Mn2O3 andMn3O4. Ammonium molybdate tetrahydrate first lost its water of crystallization on heating, and then decomposed, yielding water
and ammonia. At 340C,MoO3 was the final product, which melts at 790C. The thermal treatment of the mixed solids at 500, 750 or 1000C led to solid-solid
interactions between the produced oxides, with the formation of manganese molybdate. At 1000C, Mn2O3 and MoO3 were detected, due to the mutual stabilization effect of these oxides at this temperature.
In addition to calcite, other carbonate minerals in coal all undergo endothermic reactions on heating, i.e. dolomite, ankerite, siderite, aragonite, magnesite, rhodochrosite, witherite and strontianite. Of these, when determined in air, siderite and rhodochrosite give small exothermic resultants, while the amount of Fe in ankerites affects the actual endothermic values obtained. The magnitude of these carbonate decomposition reactions can be shown by DTA to be different and will need to be allowed for individually in calorific value corrections of coals containing them.
Authors:Denis A. Brosnan, John P. Sanders, and Stephanie A. Hart
. 1 . The mortar is comprised of calcium carbonate and silica sand, based, respectively, on observation of the decomposition of the carbonate (801.9 °C) and the alpha to beta quartz inversion (575.5 °C). The mass loss on carbonatedecomposition of 12