Thermal decomposition of gamma-irradiated potassium bromate by dynamic thermogravimetry

The thermal decomposition of γ-irradiated KBrO₃studied by dynamic thermogravimetry. The reaction order, activation energy, frequency factor and entropy of activation were computed by means of the Coats-Redfern, Freeman-Carroll and modified Horowitz-Metzger methods and were compared with those for the unirradiated salt. Irradiation enhances the decomposition and the effect increases with the irradiation dose. The activation energy is decreased on irradiation. The mechanism for the decomposition of unirradiated and irradiated KBrO₃ follows the Avrami model equation, [1-(1-α)^1/3] = kt, and the rate-controlling process is a phase boundary reaction assuming spherical symmetry.     

Effect of γ-irradiation on the thermal decomposition of strontium bromate

The effect of irradiation on the thermal decomposition of strontium bromate has been studied by dynamic thermogravimetry. Irradiaton enhances the decomposition and decreases the energy of activation but does not change the mechanism of decomposition.     

Effect of radiation dose on the thermal decomposition of sodium bromate

Influence of radiation dose in the range of 0.5–2.0 MGy of⁶⁰Co -rays on the isothermal decomposition of sodium bromate at 633.0 K shows that irradiation increases the initial gas evolution {ie37-1}, shortens the induction period (I), enhances the rate of reaction in the accelerating and decay stages. The data fit well the Prout-Tompkins relationship, indicating that nucleation occurs in a chain branching manner during the process. The fraction decomposed, , increases with increasing radiation dose.     

Effect of metal oxide catalysts on thermal decomposition of potassium bromate

Kinetic studies on the effect of metal oxide catalysts, (25% w/w) such as Cr₂O₃, CuO, MnO₂, Al₂O₃ and TiO₂, on the thermal decomposition of KBrO₃ have been carried out. The kinetic parameters of the catalysed and uncatalysed decompositions were calculated by the Freeman-Carroll, Coats-Redfern and Horowitz-Metzger methods. It has been found that Al₂O₃ is almost as good a catalyst as any other oxide used unlike in the thermal decomposition of KClO₃. In the case of TiO₂ there was an increase in the activation energy of decomposition. Of the other oxides Cr₂O₃ underwent reaction and was converted to dichromate and so the parameters of the reaction were not calculated. The effect of varying amounts of Al₂O₃ on the thermal decomposition was also studied.

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Zusammenfassung Kinetische Untersuchungen bezüglich der Wirkung von Metalloxid-katalysatoren z. B. 25 Gew. %, Cr₂O₃, CuO, MnO₂, Al₂O₃ und TiO₂ auf die thermische Hersetzung von KBrO₃ wurden durchgeführt. Die kinetischen Parameter der katalysierten und nichtkatalysierten Zersetzungen wurden mit den Methoden von Freeman-Carroll, Coats-Redfern und Horowitz-Metzger errechnet. Es wurde festgestellt, dass — im Gegensatz zur thermischen Zersetzung von KClO₃-Al₂O₃ ein beinahe so guter Katalysator ist wie jedes andere angewandte Oxyd. Im Falle von TiO₂ trat eine Erhöhung der Aktivierungsenergie der Zersetzung auf. Von den anderen Oxiden trat Cr₂O₃ in Reaktion und wurde zu Dichromat umgesetzt, deswegen wurden diese Reaktionsparameter nicht berechnet. Die Wirkung verschiedener Mengen von Al₂O₃ auf die thermische Zersetzung wurde ebenfalls untersucht.

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Résumé Des études cinétiques sur l'influence d'oxydes métalliques tels que Cr₂O₃, CuO, MnO₂, Al₂O₃ et TiO₂ comme catalyseurs (25 % en poids) de la décomposition thermique de KBrO₃ ont été effectuées. Les paramÊtres cinétiques des réactions de décomposition catalysé es ou non ont été calculés par les méthodes de Freeman-Carroll, Coats-Redfern et Horowitz-Metzger. On a établi que — contrairement à la décomposition thermique de KClO₃-l'oxyde Al₂O₃ était un catalyseur presque aussi bon que n'importe quel autre oxyde utilisé. Dans le cas de TiO₂ l'énergie d'activation de la décomposition se trouve augmentée. Parmi les autres oxydes, Cr₂O₃ entre en réaction et se transforme en bichromate; c'est pourquoi les paramÊtres de la réaction n'ont pas été calculés. L'effet de quantités variables en Al₂O₃ sur la décomposition thermique a également été étudié.

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(25 .%), ₂₃, u, n₂, l₂₃ i_{2 3}. - , - . , l₂₃ , , , ClO₃. iO₂ . ₂₃ , . l₂₃ .

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The authors are thankful to Dr. S. S. Moosath, Professor of Chemistry, University of Calicut, for encouragement and to Dr. K. H. Stern, Naval Research Laboratory, Washington (DC) for graciously providind reprints from High Temperature Properties of Inorganic Salts.     

Effect of gamma/neutron irradiation and permanganate additives on thermal decomposition of ammonium perchlorate

When mixed with 2% by weight of either KMnO₄, Ba(MnO₄)₂ or NH₄MnO₄, an enhanced thermal decomposition of cubic ammonium perchlorate, AP, was observed over the temperature range 255–300?. A still more pronounced effect was observed when AP was subjected to a radiation dose of 10 Mrad. The activation energy involved over the acceleratory stage was found to be 46 kJ mol^?1 for the irradiated AP, as against the normal value of 85 kJ mol^?1. The value remained unaltered in the case of the first two additives, while in the presence of NH₄MnO₄ it decreased to 55 kJ mol^?1. Neutron bombardment did not change the decomposition characteristics of AP; the³⁸Cl activity produced following the (n, γ) reaction showed highly damaged centres with the activity distribution ratio 0∶8.5∶20∶71.5 for ClO ₄ ^? ∶ ClO ₃ ^? ∶ (ClO^? + ClO ₂ ^? ) ∶ Cl^?. Heating above 220? created further disorder through complete reduction of the recoil oxyanions.     

On the use of electron paramagnetic resonance to implement thermogravimetry data: the thermal decomposition of zinc oxalate dihydrate

The complementary use of thermogravimetric analysis and electron paramagnetic resonance spectroscopy enables the identification on interrelated and successive steps in the vacuum decomposition of ZnC₂O₄ · 2H₂O. After completion of the oxalate dehydration, CO adsorbed species (analogous to those previously reported on MgO) are observed by EPR, starting at a temperature of 250°C. In the temperature range 250–350°C, the CO ad-species disappear while paramagnetic ZnO_1?x and possibly CO^?₄ entities are formed. It is proposed that the latter stems from the reaction of oxygen released by the decomposition of ZnO with CO₂ produced during the oxalate decomposition. Above 300°C, ZnO_1?x and CO^?₄ disappear, leading to the formation of O^3?₃ centers. The latter are gradually decomposed between 350 and 575°C, releasing O₂ observed in EPR as O^?₂ molecular anions and trapped electrons which are again detected as ZnO_1?x. A partially reduced ZnO phase is most probably the end-product of the decomposition.     

The effect of γ-irradiation on the thermal decomposition of magnesium bromate

The thermal decomposition of -irradiated magnesium bromate was studied by dynamic thermogravimetry. The reaction order, activation energy, frequency factor and entropy of activation were calculated by the Coats-Redfern equation and were compared with those of the unirradiated salt. Irradiation enhances the decomposition and the effect increases with irradiation dose. The activation energy decreases on irradiation. The mechanism for the decomposition of unirradiated and irradiated magnesium bromate follows the Avrami model equation, 1-/1-/1/3=kt, and the rate-controlling, process is a phase boundary reaction assuming spherical symmetry.     

The effect of particle size on the thermal decomposition kinetics of potassium bromate

The thermal decomposition of potassium bromate (KBrO₃) has been studied as a function of particle size, in the range 53?C150???m, by isothermal thermogravimetry at different temperatures, viz. 668, 673, 678, and 683?K in static air atmosphere. The theoretical and experimental mass loss data are in good agreement for the thermal decomposition of all samples of KBrO₃ at all temperatures studied. The isothermal decomposition of all samples of KBrO₃ was subjected to both model fitting and model-free (isoconversional) kinetic methods of analysis. Isothermal model fitting analysis shows that the thermal decomposition kinetics of all the samples of KBrO₃ studied can be best described by the contracting square equation. Contrary to the expected increase in rate followed by a decrease with decrease in particle size, KBrO₃ shows a regular increase in rate with reduction in particle size, which, we suggest, is an impact of melting of this solid during decomposition.     

Effect of gamma-irradiation on the thermal decomposition of pure and doped (Ba2+ caesium bromate

Effect of γ-irradiation on the isothermal decomposition of pure and doped (Ba²⁺, 0.50 mol%) caesium bromate has been studied in the temperature range 633–673 K. It is indicated that though the pure and pure irradiated crystals are immune to decomposition, doped and doped irradiated crystals undergo decomposition rapidly. There is initial rapid gas evolution representing 1–2% reaction, which is completely eleminated in doped irradiated crystals. The other stages exhibited by the crystals are, (1) acceleratory and (2) decay stages. Presence of two decay stages (one short and one long) is indicated in the doped substance, and the short decay diminishes with increase in temperature and virtually remains absent at 673 K. The acceleratory as well as decay periods of doped and doped irradiated crystals are analysed according to Prout-Tompkins, Avrami-Erofeev and Contracting square models. The rate constants in all the stages increase with increase in temperature. The energy of activation for the acceleratory periods of both the substances are almost same (± 10 kJ/mol) irrespective of the kinetic equation employed. Similar is the case with decay stages. But the energy of activation of the decay stages are higher than those of the acceleratory stages. Microscopic observation reveals that the reaction begins essentially on surfaces by the rapid formation of an interface and is followed by the penetration of the interface into the crystallite. The melting of a eutectic formed between the product CsBr and the parent material causes a marked increase in the rate.     

Effects of admixtures of potassium bromide on the thermal decomposition of potassium bromate

The effects of admixtures of potassium bromide (2.5% and 5%) on the thermal decomposition of potassium bromate were studied within the temperature range 653–683 K. The fraction decomposed() vs. time (t) relations revealed (i) initial gas evolution, (ii) acceleratory and (iii) decay steps. The data were analysed on the basis of the first-order law with two rate constantsk ₁ andk ₂,k ₁ being the rate constant for the initial, slow first-order process (0.02, 0.26), andk ₂ being the rate constant for the subsequent faster process, holding within the range 0.21 to 0.98. Upon increase of the concentration of added potassium bromide to 5%, the range for the slow and faster processes became 0.01 to 0.16 and 0.1 to 0.98, respectively. At a given temperature,k ₁ increased with increasing bromide concentration, whereask ₂ almost identical for pure potassium bromate and its mixtures (2.5% and 5% bromide).

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Zusammenfassung Im Temperaturbereich von 653–683 K wurde der Einfluß von Beimengen von Kaliumbromid (2,5% und 5%) auf die thermische Zersetzung von Kaliumbromat untersucht. Die Funktion der zersetzten Menge () in Abhängigkeit von der Zeit (t) weist eine anfängliche Gasentwicklung(i), eine beschleunigte(ii) und eine abklingende Stufe(iii) auf. Die Daten wurden auf der Grundlage einer Kinetik erster Ordnung mit den zwei Geschwindigkeitskonstantenk ₁ undk ₂ durchgeführt, wobeik ₁ die Geschwindigkeitskonstante für den einleitenden, langsameren Schritt erster Ordnung ist (0,02, 0,26) undk ₂ die Geschwindigkeitskonstante für den darauffolgenden schnelleren Vorgang mit Werten zwischen 0,21 und 0,98. Bei Erhöhung der Konzentration von Kaliumbromid auf 5% betrug der Bereich für den langsameren und den schnelleren Vorgang 0,01 bis 0,16 bzw. 0,10 bis 0,98. Bei gegebener Temperatur steigtk ₁ mit zunehmender Kaliumbromidkonzentration an, währendk ₂ für reines Kaliumbromat und seine Mischungen mit 2,5% und 5% Kaliumbromid fast identisch bleibt.

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653–683 (2,5 5%) . , . k ₁ k ₂, ( 0,02 0,26), - 0,21–0,98. 5% k ₁ k ₂ , , 0,01–0,16 0,1–0,98. k ₁, , k ₂ , (2,5 5%) .

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The work is dedicated to the memory of the late Prof. S. R. Mohanty.     

Effect of zinc chloride on thermal decomposition of polymethacrylic and polyacrylic esters

Zinc chloride reduces the rate of thermal and thermooxidative decompositions of polymethacrylic esters and increases the thermal decomposition rate of polyacrylic esters. Mechanisms of the thermal decompositions of polymethacrylates and polyacrylates in the presence of ZnCl₂ have been suggested.For thermal decomposition polymethacrylic esters, the rate of depolymerization decreases due to the formation of cycles in a polymer chain by reaction of Zinc chloride with neighbouring ester groups. For thermooxidative decomposition of polymethacrylates, ZnCl₂ decreases also the rate of initiation of depolymerization and causes decomposition of hydroperoxide groups by a heterolytic mechanism. The increase in thermal decomposition rate of polyacrylic esters results from the high activity of complexes of ester groups and ZnCl₂ in decomposition reactions with formation of alcohol and CO₂ through Cameron mechanism.     

Effect of gamma irradiation on the thermal and rheological properties of grain amaranth starch

Physical properties of starch from two cultivars of gamma-irradiated grain amaranth with different amylose content were investigated. Pasting viscosities decreased continuously with the increase in dosages of irradiation. Furthermore, different irradiation dosages resulted in modification of the thermal properties and crystallinity of starch. Dynamic oscillation on shear was also employed, temperature and frequency sweeps showed that changes in storage modulus and loss modulus were significant, with Tibet Yellow producing more elastic gels as compared to Hy030 at different irradiation dosages.     

The thermal decomposition of zinc hydroxocarbonate

Institute of Catalysis, Siberian Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 31, No. 5, pp. 8–13, September–October, 1990.     

Study of the induction period of the thermal decomposition of irradiated barium bromate

The influence of -irradiation upto 200 Mrad on the thermal decomposition of barium bromate has been studied in the temperature range 553–583 K. The fraction decomposed //-time /t/ characteristics for irradiated barium bromate exhibit stages, viz. initial gas and decay stages. Irradiation shortens the induction period conforming to the relation I=C₁–C₂ lg dose. All experimental data for induction period are tested against the values obtained from the theoretical calculations by making use of this induction-period dose relation. The topochemical aspect of the validity of the above relation has been considered to be due to the linear growth of nuclei during irradiation and subsequent exponential growth during the induction period.     

Effect of water vapor on the thermal decomposition process of zinc hydroxide chloride and crystal growth of zinc oxide

Thermal decomposition process of zinc hydroxide chloride (ZHC), Zn₅(OH)₈Cl₂·H₂O, prepared by a hydrothermal slow-cooling method has been investigated by simultaneous X-ray diffractometry and differential scanning calorimetry (XRD-DSC) and thermogravimetric-differential thermal analysis (TG-DTA) in a humidity-controlled atmosphere. ZHC was decomposed to ZnO through β-Zn(OH)Cl as the intermediate phase, leaving amorphous hydrated ZnCl₂. In humid N₂ with P_H2O=4.5 and 10 kPa, the hydrolysis of residual ZnCl₂ was accelerated and the theoretical amount of ZnO was obtained at lower temperatures than in dry N₂, whereas significant weight loss was caused by vaporization of residual ZnCl₂ in dry N₂. ZnO formed by calcinations in a stagnant air atmosphere had the same morphology of the original ZHC crystals and consisted of the c-axis oriented column-like particle arrays. On the other hand, preferred orientation of ZnO was inhibited in the case of calcinations in 100% water vapor. A detailed thermal decomposition process of ZHC and the effect of water vapor on the crystal growth of ZnO are discussed.     

Influence of SO 4 2− doping and Y-irradiation on the thermal decomposition of barium bromate

The effects of SO ₄ ^2– doping and Y-irradiation on the isothermal (563 K) decomposition of barium bromate have been investigated gasometrically with a vacuum apparatus. Plots of the fraction decomposed avs. timet for pure, doped and irradiated crystals exhibited characteristic stages: initial gas evolution (initial puff), an induction period, linear reaction, an acceleratory period and decay. The data are considered in the light of various kinetic models, e.g. linear rate equation, Prout-Tompkins and Avrami-Erofeev. The plausible mechanism of the reaction and the effects on this of anion vacancies and Y-irradiation are discussed briefly.

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Zusammenfassung Die Wirkung von Versetzen mit SO ₄ ^2} - und -Bestrahlung auf die isotherme (563 K) Zersetzung von Bariumbromat wurde gasometrisch untersucht. Es zeigte sich, daß die Zeitcharakteristiken für die reinen, die versetzten und bestrahlten Kristalle verschiedene Stufen durchlaufen, nämlich anfängliche Gasentwicklung (Aufblähen), Induktionsperiode, lineare Reaktion, Beschleunigung und Abklingen. Die Daten wurden unter dem Gesichtspunkt verschiedener kinetischer Modelle betrachtet, z. B. lineare Geschwindigkeitsgleichung, das Modell von Prout-Tompkins und Avrami-Erofeev. Es werden kurz ein einleuchtender Reaktionsmechanismus und der Einfluß von Anionengitterlücken und -Bestrahlung darauf diskutiert.

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- (563 ) . , ,-, «t» , , , , , . , - -. .

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The authors thank the Department of Atomic Energy, Government of India, for financial support. M.K.S. also gratefully acknowledges the award of a Research Fellowship by the same agency, which made the work possible.     

Exploration of the thermal decomposition of zinc oxalate by experimental and computational methods

Zinc oxalate dihydrate has been synthesized by precipitation method and characterized by FT-IR, XRD and SEM-EDAX. The kinetics of dehydration and decomposition were studied by non-isothermal DSC technique in the N₂ atmosphere at different heating rates: 4, 6, 8 and 10 K min^?1. The product of thermal decomposition, ZnO has been characterized by UV, TEM, SEM-EDAX and XRD and found that the particles are in nanometer range. The activation energy for thermal dehydration and decomposition was calculated by various isoconversional methods. Furthermore, structure and reactivity of zinc oxalate have also been investigated using B3LYP/631+g (d, p) level of theory with the help of Gaussian 09W software. The theoretical investigation indicates that most probably the compound decomposes to ZnO along with the evolution of CO₂ and CO.

     

Influence of preliminary UV irradiation on the thermal decomposition of copper hypophosphite

The effect of the influence of preliminary UV irradiation on the kinetics of the thermal decomposition of crystalline copper hypophosphite has been discovered, revealing a decrease in the induction period. Spectral dependence of the effect was determined by absorption of copper hypophosphite in the 255 nm charge transfer band. Comparison of the quantum efficiency of the disappearance of ions of bivalent copper 10^?1–10^?2 ions per quantum and the quantum output of hydrogen 10^?4–10^?5 mole per quantum as well as acid formation during photolysis shows that a proton (acid) as well as the univalent copper is the main primary product of photolysis. Formation of acid in the course of photolysis participating in the nucleation during the investigated topochemical process of thermal decomposition is the reason for the discovered effect.     

Effect of gamma irradiation on density and thermal expansion changes of uniaxially oriented linear low-density polyethylene

The density and thermal expansion behaviour of linear low density polyethylene, over the temperature range from −95° to +10°C, is measured. The influence of drawing on density and thermal expansion behaviour is related to the chain scission and crosslinking induced by the γ irradiation.     

Effect of precompression on isothermal decomposition kinetics of pure and doped potassium bromate

Pure and doped samples of potassium bromate (KBrO₃) were subjected to precompression and their thermal decomposition kinetics was studied by thermogravimetry at 668 K. The samples decomposed in two stages governed by the same rate law (contracting square equation), but with different rate constants, k ₁ (for a α ≤ 0.45) and k ₂ (for α ≥ 0.45), as in the case of uncompressed samples. The rate constants k ₁ and k ₂ decreased dramatically on precompression, the decrease being higher for doped samples. Cation dopants (Ba²⁺, Al³⁺) caused more desensitization effect than the anion dopants ( \textSO₄ ^2- {\text{SO}}_{4}{}^{ 2- } , PO₄ ³⁻) of the same magnitude of charge and concentration. The results favor ionic diffusion mechanism proposed earlier on the basis of doping studies.