Estimation of isothermal values of activation energy for aluminothermic reduction
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Table I. Nonisothermal Activation Energy Values of Aluminothermic Reduction of MnO2, Fe2O3, and Cr2O3 Activation Energy Activation Energy (kJ/mole) Heating (kJ/mole) Dixit and Ray System/Molar Rate Coats and Redfern Approach[6] Ratio (K/min) Approach[5] MnO2-Al 1:5
B. SARANGI, H.S. RAY, and R.R. DASH In several publications, the authors have previously shown that aluminothermic reduction of oxides can be studied using a calibrated differential thermal analyzer (DTA) unit. They have determined heat of reduction for aluminothermic reduction of Fe2O3, MnO2, V2O5, Cr2O3, WO3, and TiO2 and also reported analysis of data from a kinetic point of view. Reaction rates have been analyzed on the basis of rates of heat generation. They have thus reported kinetic parameters for different rates of heating for aluminothermic reduction of Fe2O3, MnO2, and Cr2O3. The so-called activation energy is basically an experimentally determined parameter to describe the effect of temperature on reaction rate. During most metallurgical reactions, it does not have any well-defined physical significance. Traditionally, the parameter is determined by conducting a series of isothermal experiments, determining the rate constant and then applying the Arrhenius expression. The parameter, the so-called isothermal activation energy, is well accepted and is easy to use to estimate temperature effect. On the other hand, the so-called nonisothermal activation energy is a more complicated parameter and is difficult to comprehend. For any system, one should be able to obtain isothermal kinetic data, if the data for different rates of heating are extrapolated to zero rate of heating. This communication presents some data obtained by using this extrapolation technique. Experiments have been carried out in a Shimadzu DT40 thermal analyzer consisting of a simultaneous DTA-TG modular unit. The DTA unit was calibrated using a reagent grade chemical compound for its successful use as a heat flux differential scanning calorimeter.[1] Suitable thermite mixtures for the systems Fe2O3-Al, MnO2-Al, and Cr2O3-Al were selected on the basis of some elementary trial runs. A considerable body of literature giving details of the experimental procedure and on the various aspects of the aluminothermic reduction of several transition metal oxides has been published by the authors.[2–5] In a DTA-TG setup, aluminothermic reduction, which is in fact a redox type of reaction, is triggered by the exothermic heat made available by oxidation of excess aluminum, which necessarily requires oxygen gas. The nonisothermal values of activation energy for aluminothermic reduction of the following oxides have been reported by the authors:[2,3,4] (1) MnO2, (2) Fe2O3, and (3) Cr2O3.
B. SARANGI, Lecturer, Metallurgical and Materials Engineering Department, and R.R. DASH, Lecturer, Mechanical Engineering Department, are with the Indira Gandhi Institute of Technology, Sarang759 146, Orissa, India. H.S. RAY, Director, is with the Regional Research Laboratory, Council of Scientific and Industria
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