Solid state reactions in the potassium iodate and molybdenum(VI) oxide system
01 Jul 1989-Journal of Thermal Analysis and Calorimetry (Akadémiai Kiadó, co-published with Springer Science+Business Media B.V., Formerly Kluwer Academic Publishers B.V.)-Vol. 35, Iss: 4, pp 1191-1195
TL;DR: In this paper, the reaction between potassium iodate and molybdenum(VI) oxide in mixtures of different mole ratios has been investigated employing TG and DTA techniques in static air atmosphere.
Abstract: The reaction between potassium iodate and molybdenum(VI) oxide in mixtures of different mole ratios has been investigated employing TG and DTA techniques in static air atmosphere. The products are characterised by infrared spectroscopy, chemical analysis and X-ray diffraction studies. The studies indicate the formation of mono-, di-, tri- and tetramolybdates of potassium from mixtures with 2∶1, 1∶1, 2∶3 and 1∶2 mole ratios of KlO3∶MoO3. The kinetics of the reaction was followed and the energy of activation values were computed.
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TL;DR: In this paper, the effect of gamma ray irradiation on the rate and kinetics of thermal decomposition of potassium iodate (KIO3) has been studied by thermogravimetry (TG) under non-isothermal conditions at different heating rates (3, 5, 7, and 10 Kmin−1).
Abstract: The effect of gamma ray irradiation on the rate and kinetics of thermal decomposition of potassium iodate (KIO3) has been studied by thermogravimetry (TG) under non-isothermal conditions at different heating rates (3, 5, 7, and 10 K min−1). The thermal decomposition data were analyzed using isoconversional methods of Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, and Friedman. Irradiation with gamma rays increases the rate of the decomposition and is dependent on the irradiation dose. The activation energy decreases on irradiation. The enhancement of the rate of the thermal decomposition of KIO3 upon irradiation is due to the combined effect of the production of displacements and extended lattice defects and chemical damage in KIO3. Non-isothermal model fitting method of analysis showed that the thermal decomposition of irradiated KIO3 is best described by the contracting sphere model equation, with an activation energy value of ~340 kJ mol−1.
31 citations
Cites background or methods from "Solid state reactions in the potass..."
...Suba and Udupa [32] studied the reaction between potassium iodate and molybdenum (VI) oxide in mixtures of different mole ratios employing TG, derivative thermogravimetry (DTG) and DTA techniques in static air atmosphere; followed the kinetics of the reaction and computed the values of E....
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...Even though a vast number of publications are available in the literature on KIO3 [21–36], studies on the thermal decomposition and kinetics are not available....
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TL;DR: In this article, the hydrogen absorption characteristics of V4Cr4Ti alloy have been evaluated by measuring the pressure composition isotherm (PCIT) at 57°C temperature.
Abstract: V4Cr4Ti alloy is synthesized by aluminothermy process followed by electron beam refining. Hydrogen absorption characteristics of the alloy have been evaluated by measuring the pressure composition isotherm (PCIT) at 57 °C temperature. Two plateau pressures are observed in the PCIT curve. Substantial decrease in the hydrogen absorption capacity of the alloy as compared to vanadium has been recorded. Hydrogen absorption kinetics of the alloy was investigated in the temperature range of 200–500 °C. Three-dimensional diffusion appears to be the rate controlling step of the hydrogen absorption. The apparent activation energy was calculated as 0.16 eV/atom-hydrogen.
25 citations
TL;DR: In this article, the vanadium-aluminum alloy has been prepared by aluminothermy process and the alloy ingot obtained was refined by electron beam melting and homogenized by vacuum arc melting technique.
Abstract: The vanadium–aluminum alloy has been prepared by aluminothermy process. The alloy ingot obtained was refined by electron beam melting and homogenized by vacuum arc melting technique. The refined alloy was crushed into small pieces. These pieces were kept isothermally in a thermobalance attached to the Sieverts apparatus for the hydrogen charging. Reacted fraction α was calculated using isothermal thermo-gravimetry method. The reacted fraction α–t data thus obtained have been linearly fitted over a suitable reaction mechanism function. Rate constants at different temperatures are determined using slope of these linearly fitted curves. Activation energy of hydrogen charging has been calculated using Arrhenius equation.
21 citations
Cites background from "Solid state reactions in the potass..."
...The rate constant k(T) and the activation energy (E) are related by Arrhenius equation [28]....
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References
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TL;DR: In this article, a thermocouple is used to measure the sample temperature in a Stanton HT-D thermobalance, the bead of which is positioned in or near the sample, depending on crucible design.
Abstract: THE use of thermogravimetric data to evaluate kinetic parameters of solid-state reactions involving weight loss (or gain) has been investigated by a number of workers1–4. Freeman and Carroll2 have stated some of the advantages of this method over conventional isothermal studies. To these reasons may be added the advantage of using one single sample for investigation. However, the importance of procedural details, such as crucible geometry, heating rate, pre-history of sample, and particle size, on the parameters has yet to be fully investigated. It is also necessary to ensure accurate temperature measurement, both for precision and also to detect any departure from a linear heating rate due to endo- or exo-thermic reactions. (The effect of these may be largely eliminated by the use of small samples.) In our present work (using a Stanton HT–D thermobalance) the sample temperature is measured directly by means of a thermocouple the bead of which is positioned in or near the sample, depending on crucible design, the wires of which run down a twin-bore rise rod. The connexion between the end of the thermocouple wires on the balance arm and the terminal block is made by 0.001 in. platinum and platinum/rhodium wires5. It has been shown that these wires do not affect the performance of the balance but act merely as a subsidiary damping. From the terminal block compensated cable leads to the cold junction and a potentiometric arrangement for direct measurement of the thermocouple output.
5,770 citations
TL;DR: In this article, the site symmetry of the anionic group is discussed in terms of the site-symmetry of the X-ray powder diffraction of 19 molybdates and 18 tungstates.
Abstract: The infra-red spectra of 19 molybdates and 18 tungstates have been measured from 4000 to 250 cm−1. The identity of the samples was confirmed by X-ray powder diffraction. The spectra are generally sufficiently individual in detail to permit identification of the particular substance. The results are discussed in terms of the site symmetry of the anionic group.
202 citations
TL;DR: In this article, the authors determine les spectres infrarouges, entre 4000 and 200 cm −1, of polymolybdates and polywolframates alcalins, M m M' n O x (M = alcalin, M' = Mo ou W).
Abstract: Resume On a determine les spectres infrarouges, entre 4000 et 200 cm −1 , de polymolybdates et polywolframates alcalins, M m M' n O x (M = alcalin, M' = Mo ou W). On propose une interpretation des spectres observes, en accord avec une structure construite d'octaedres M'O 6 deformes et de tetraedres irreguliers M'O 4 , joints par les sommets. On trouve, en outre, une isotypie entre les tetramolybdates de K, Rb et Cs, et, d'un autre cote, entre les triwolframates de Rb et Cs.
31 citations
25 citations
TL;DR: In this paper, a study of the thermal decomposition of intimate mixtures of different molar ratios of KClO4 and chromium(III) oxide was conducted employing thermogravimetry, differential thermal analysis, chemical analysis, infrared spectroscopy and X-ray diffraction analysis.
Abstract: A study of the thermal decomposition of intimate mixtures of different molar ratios of potassium perchlorate and chromium(III) oxide, and potassium perchlorate and nickel(II) chromite(III) was conducted employing thermogravimetry, differential thermal analysis, chemical analysis, infrared spectroscopy and X-ray diffraction analysis. Upon heating to 400°C Cr(III), in 2:1 molar ratios, is oxidized to potassium dichromate. Only a stoichiometric amount of Cr(III) was oxidized from molar ratios less than 2:1, leaving behind excess Cr2O3 and NiCr2O4 whereas from molar ratios greater than 2:1, Cr(III) was completely oxidized and the excess KClO4 started decomposing around 410°C which is much below the decomposition temperature of pure KClO4.
22 citations