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Abstract  

High-temperature reactions were investigated in the MoO3-Ag2O system by means of X-ray, DTA and scanning microscopy methods, and a model was proposed according to which first an Ag2Mo4O13 phase was formed at the MoO3 and Ag2O (or metallic Ag) interface. Subsequently, at the Ag2Mo4O13-Ag2O contact area a layer of Ag2Mo2O7 appeared. If the amount of silver oxide is sufficiently high, a layer of Ag2MoO4 is formed between the Ag2O and Ag2Mo2O7 phases.

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Abstract  

Materials with high surface areas and small particle size (nanophases), metastable polymorphs, and hydrated oxides are increasingly important in both materials and environmental science. Using modifications of oxide melt solution calorimetry, we have developed techniques to study the energetics of such oxides and oxyhydroxides, and to separate the effects of polymorphism, chemical variation, high surface area, and hydration. Several generalizations begin to emerge from these studies. The energy differences among different polymorphs (e.g., various zeolite frameworks, the - and -alumina polymorphs, manganese and iron oxides and oxyhydroxides) tend to be small, often barely more than thermal energy under conditions of synthesis. Much larger contributions to the energetics come from oxidation-reduction reactions and charge-coupled substitutions involving the ions of basic oxides (e.g., K and Ba). The thermodynamics of hydration involve closely balanced negative enthalpies and negative entropies and are very dependent on the particular framework and cage or tunnel geometry.

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Abstract  

A new thermoanalytikal method, called electrothermal explosion (ETE) is described in which uniform heating of samples at extremely high rates (up to 105 deg. sec−1) is achieved. Heating is by direct passing of an electric current through the sample in the initial stages and by chemical heat release after the ignition conditions have been attained. ETE is the only direct method that allows the macrokinetics of heterogeneous reactions occurring in condensed systems to be studied at high temperature and at short conversion times, which are prohibitive for traditional thermoanalytical devices (up to 3500 K and 10−2 sec respectively). Kinetic data on high-temperature, high-speed interactions in powder mixtures of carbon with titanium, silicon and tantalum are presented. The rate of heat release in the Ti−C system depends only to a small extent on temperature after the metal has melted, being mainly determined by the solution rate of carbon particles. The interaction mechanism in the Si−C system is similar to that in Ti−C, but the high enthalpy of carbon solution in liquid silicon results in a bulk activation energy ofE=55 kcal. mol−1. Synthesis of tantalum carbide from the elements in the temperature range 1500–3000 K occurs by the mechanism of reaction diffusion and proceeds with strong self-retardation.

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Abstract  

A simple optical pyrometric method is described, based on a photocell with red and blue filters calibrated by the disappearing filament technique. The method, which is cheap, non-invasive and reproducible, is used for measurement of the rate of heating of solid materials such as coke, CuO or Fe3O4 in a microwave oven. All materials were heated under dinitrogen in a silica reaction vessel over 3 min in a 650 W oven. Coke (which contains graphitic phases) and magnetite heat smoothly to maximum temperatures of 1180 and 1050°C respectively. CuO heats erratically with plasma discharges from the surface, however when covered with a layer of coke the oxide heats smoothly achieving a maximum temperature of 1210°C. The observations are discussed.

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The paper presents the results of studies on thermal reduction and oxidation of the nonstoichiometric phases from the Y-Ba-Cu-O in air.

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The structural changes occurring during the dehydroxylation of kaolinite have been followed using flash calcination to produce kinetically frozen calcines. The percentage of dehydroxylation was varied by changing the furnace residence time or temperature and/or heating speed. These calcination conditions affected the reaction kinetics, but the products depended only on the extent of dehydroxylation.

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Introduction Knowing exact equilibrium temperatures of high temperature reactions are of extreme importance especially in industrial applications. This method offers simple, yet, if properly conducted, very accurate tool for

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Iron ore sintering

Characterization by calorimetry and thermal analysis

Journal of Thermal Analysis and Calorimetry
Authors: Riham Morcos and Alexandra Navrotsky

Abstract  

Differential scanning and high temperature reaction calorimetry have been used to characterize a series of natural iron ore and flux samples commonly used during iron ore sintering. Most iron ore samples were shown to contain measurable quantities of goethite, with a characteristic dehydration peak in DSC and TG between 200 and 400°C. At higher temperatures, all samples decomposed to produce magnetite with an accompanying mass loss in the TG profile due to the evolution of oxygen. High temperature reaction calorimetry has been used to measure the heat of solution of the ore in the melt formed during iron ore sintering. The dehydration and calcination of iron ore and flux samples was also examined using high-temperature reaction calorimetry. The results support the DSC/TG findings.

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Phase diagrams for cuprates of alkaline earth and rare earth elements are presented, covering binary to quintenary oxides and including selected solid solution series with other elements. Elementary crystal chemical data are included for identification of the occurring phases. Chemical stability is discussed with respect to the high-temperature reactions with Lewis acids like CO2, protons, etc. Particularly the occurrence of oxide carbonates is consistently pointed out as one of the possible reasons for contradictory results in phase diagrams which comprise oxides with high basicity.

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