Kinetics and mechanism of the thermal decomposition of barium titanyl oxalate

Thermal analysis of barium titanyl oxalate reveals that the decomposition proceeds through four distinct rate processes. Among them, the decomposition of oxalate occurs in the temperature range 230–350°C, and has been studied by TG and gas pressure measurements, supplemented by IR spectroscopy, electron microscopy and chemical analysis. Oxalate decomposition proceeds differently in vacuum and in flowing gas atmospheres. Analytical results indicate the formation of a complex carbonate together with CO, CO₂ and water vapour below 400°C. Schemes for each type of decomposition are proposed and discussed. For decomposition in vacuum, kinetic observations fitted the three-dimensional, diffusion controlled, rate equation for almost the entire α-range (0.028≤α≤0.92). The activation energy is calculated to be3 189±6 kJ mol⁻¹. In celebration of the 60^th birthday of Dr. Andrew K. Galwey     

Characterisation and thermal analysis of vanadium(II) oxalate

The synthesis, compositional formula and mode of thermal decomposition of a compound for which there existed only a single literature reference [1] have been investigated in this work.The product of the aqueous phase reaction between vanadium(II) ions and oxalate ions at lowpH has been identified: vanadium(II) oxalate dihydrate, VC₂O₄·2H₂O, has been characterised by thermal methods of analysis supported by a range of complementary analytical techniques.The findings of a previous author [1] have been confirmed and extended in this work. In addition, a synthetic procedure for the preparation of gram quantities of vanadium(II) oxalate dihydrate, VC₂O₄·2H₂O, is reported here for the first time.The oxalate compound prepared was found to be remarkably stable in relation to aerial oxidation, unlike other representative solid state compounds of the vanadium(II) oxidation state. Vanadium(II) oxalate dihydrate may, therefore, serve as an important intermediate in the future synthesis of other vanadium(II) compounds.We would wish to thank Mr. S. Sutcliffe, University College Salford, for providing the Thermal Analysis data and also Mr. S. Unsworth, Magnesium Electron, Clifton, Manchester, for providing the XRD data.     

Kinetics of thermal decomposition of nickel sulfate hexahydrate

The paper describes the kinetics of all the recorded steps of thermal decomposition of nickel sulfate hexahydrate in air. The thermal decomposition of the salt in air led to NiO at about 1060 K. The kinetic parameters, the activation energyE and the preexponential factorA, and the thermodynamic parameters, the entropy, enthalpy and free energy of activation were evaluated for the dehydration and decomposition reactions. Tentative reaction mechanisms are suggested for each step of the thermal decomposition.     

Kinetics of thermal decomposition of barium zirconyl oxalate

Kinetics of the thermal decomposition of anhydrous barium zirconyl oxalate and a carbonate intermediate have been studied. Decomposition of the anhydrous oxalate, though it could be explained based on a contracting-cube model, is quite complex. Kinetics of decomposition of the intermediate carbonate Ba₂Zr₂O₅CO₃ is greatly influenced by thermal effects during its formation. (-t) curves are sigmoidal and obey a power law equation followed by first order decay. Presence of carbon in the vacuum-prepared carbonate has a strong deactivating effect. Decomposition of the carbonate is accompanied by growth in particle size of the product barium zirconate.

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Die Kinetik der thermischen Zersetzung von Barium-zirkonyl-oxalat

Zusammenfassung Es wurde die thermische Zersetzung von wasserfreiem Barium-zirkonyl-oxalat und dem intermediären Karbonat untersucht. Die Zersetzung des wasserfreien Oxalates ist — obwohl über das contracting-cube-Modell erklärbar — sehr komplex. Die Kinetik der Zersetzung des intermediären Karbonates Ba₂Zr₂O₅CO₃ ist stark von den thermischen Effekten während seiner Bildung abhängig. Die (-t)-Kurven gehorchen einem exponentiellen Gesetz, gefolgt von einem Zerfall erster Ordnung. Die Gegenwart von Kohlenstoff im Karbonat hat einen starken desaktivierenden Effekt. Die Zersetzung des Karbonats wird von einem Wachstum der Partikelgröße des Produktes (Bariumzirkonat) begleitet.

     

Mechanism and kinetics of thermal decomposition of nickel(II) sulfate(VI) hexahydrate

This work presents results of research on thermal decomposition of nickel(II) sulfate(VI) hexahydrate in air and in helium atmosphere. On the base of TG and XRD results a mechanism of thermal decomposition of NiSO₄ hydrate was established. For calculations of kinetic parameters of the Arrhenius equation, the Coats-Redfern approximation was applied. Choice of g(a) function and thus of a mechanism best describing given stage of decomposition was performed by testing 12 kinetic models. This revised version was published online in July 2006 with corrections to the Cover Date.     

The effect of the water vapor pressure on the kinetics of thermal dehydration of manganese(II) formate dihydrate

The effect of the water vapor pressure on the thermal dehydration of manganese(II) formate dihydrate was studied by means of isothermal gravimetry under various water vapor pressure, ranging from 4.6 to 24.4 torr. The kinetics of dehydration was described by a two-dimensional phase-boundary model,R ₂. The rate of dehydration decreased with increasing atmospheric water vapor pressure, but the Smith-Topley phenomenon was not observed for the present dehydration. The activation energy and the frequency factor for the dehydration were 110–170 kJ·mol⁻¹ and 10¹⁰–10¹⁶ cm·s⁻¹, respectively. These values increased with increasing water vapor pressure, and were much larger than those reported for the dehydration in vacuum.     

Kinetics of thermal decomposition of iron(III) dicarboxylate complexes

Summary Tris(dicarboxylate) complexes of iron(III) with oxalate, maleate, malonate and phthalate viz. K₃[Fe(C₂O₄)₃]×3H₂O (1), K₃[Fe(OOCCH₂COO)₃]×3H₂O (2), K₃[Fe(OOCCH=CHCOO)₃]×3H₂O (3), K₃[Fe(OOC-1,2-(C₆H₄)-COO)₃]×3H₂O (4) have been synthesized and characterized using a combination of physicochemical techniques. The thermal decomposition behaviour of these complexes have been investigated under dynamic air atmosphere upto 800 K. All these complexes undergo a three-step dehydration/decomposition process for which the kinetic parameters have been calculated using Freeman-Carrol model as well as using different mechanistic models of the solid-state reactions. The trisoxalato and trismalonato ferrate(III) complexes undergo rapid dehydration at lower temperature below 470 K. At moderately higher temperatures (i.e. >600 and 500 K, respectively) they formed bis chelate iron(III) complexes. The trismalonato and trismaleato complexes dehydrate with almost equal ease but the latter is much less stable to decomposition and yields FeCO₃ below 760 K. The cis-dicarboxylate complexes particularly with maleate(2-) and phthalate(2-) ligands are highly prone to the loss of cyclic anhydrides at moderately raised temperatures. The thermal decomposition of the tris(dicarboxylato)iron(II) to iron oxide was not observed in the investigated temperature range up to 800 K. The dehydration processes generally followed the first or second order mechanism while the third decomposition steps followed either three-dimensional diffusion or contracting volume mechanism.     

A thermal decomposition study on cobalt(II) complexes of 1,2-bis(IMINO-4'-antipyrinyl)ethane

The phenomenological, kinetic and mechanistic aspects of thermal decomposition of perchlorate, nitrate, chloride, bromide and iodide complexes of cobalt(II) with the Schiff base 1,2-bis(imino-4'-antipyrinyl)ethane (GA) have been studied by TG and DTG analyses. The kinetic parameters like the activation energy, pre-exponential factor and entropy of activation were calculated. The decomposition reactions follow 'random nucleation with one nucleus on each particle - Mampel model'. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetics of thermal decomposition of dinitramide

Kinetic regularities of thermal decomposition of dinitramide in aqueous and sulfuric acid solutions were studied in a wide temperature range. The rate of the thermal decomposition of dinitramide was established to be determined by the rates of decomposition of different forms of dinitramide as the acidity of the medium increases: first, N(NO₂)⁻ anions, then HN(NO₂)₂ molecules, and finally, protonated H₂N(NO₂)₂ ⁺ cations. The temperature dependences of the rate constants of the decomposition of N(NO₂)⁻ (k _an) and HN(NO₂)₂ (k′_ac) and the equilibrium constant of dissociation of HN(NO₂)₂ (K _a) were determined:k _an=1.7·10¹⁷ exp(−20.5·10³/T), s⁻¹,k′_ac=7.9·10¹⁶ exp(−16.1·10³/T), s⁻¹, andK _a=1.4·10 exp(−2.6·10³/T). The temperature dependences of the decomposition rate constant of H₂N(NO₂)₂ ⁺ (k _d) and the equilibrium constant of the dissociation of H₂N(NO₂)₂ ⁺ (K _d) were estimated:k _d=10¹² exp(−7.9·10³/T), s⁻¹ andK _d=1.1 exp(6.4·10³/T). The kinetic and thermodynamic constants obtained make it possible to calculate the decomposition rate of dinitramide solutions in a wide range of temperatures and acidities of the medium. In this series of articles, we report the results of studies of the thermal decomposition of dinitramide performed in 1974–1978 and not published previously. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2129–2133, December, 1997.     

Kinetics of the thermal decomposition of bis(2,2-dinitropropyl)-N-fluoroamine

The kinetics of the thermal decomposition of bis(2,2-dinitropropyl)-N-fluoroamine are studied in the liquid phase. The reaction is autocatalytic in a melt. In dilute solution, the reaction rate is described by the first-order law. It is tens of times faster in polar sulfolan than in weakly polar dimethyl phthalate. A mechanism of the decomposition involving the formation of a cyclic transition state at the first, limiting stage of the process is suggested.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 874–877, May, 1995.This work was financially supported by the Russian Foundation for Basic Research (Project No. 94-03-08103).     

Synthesis,structure, and thermal decomposition of a novel one-dimensional chain complex of manganese(II) with 2,2-diphenic acid and 1,10-phenanthroline

A novel one-dimensional (1D) chain coordination polymer [Mn₂(2,2′-dipha)₂(phen)]_n has been synthesized by hydrothermal reaction, and characterized by elemental analysis, IR spectroscopy, TGA, and X-ray diffraction. Orange crystals crystallized in the monoclinic system, space group C2/c with a = 19.393(7) Å, b = 19.183(7) Å, c = 19.729(7) Å, β = 90.826(6)°, V = 7338(5) ų, Z = 8. In the crystal structure, one manganese atom is six-coordinated with four carboxylate oxygen atoms from one pentadentate 2,2′-dipha ligand and two tetradentate 2,2′-dipha ligands, and with two nitrogen atoms of one phen ligand, giving a slightly distorted octahedral geometry. The other manganese atom is five-coordinated with five oxygen atoms from two tetradentate 2,2′-dipha ligands and two pentadentate 2,2′-dipha ligands and has a trigonal bipyramidal environment. The TGA curve shows that the compound is stable below 310°.     

Co(II)Schiff碱配合物的合成、氧合反应热力学及热分解动力学的研究

合成了两种新的钴(II)schiff碱配合物水杨醛L-甲硫氨酸-水合钴(II)(1), 邻香兰素L-甲硫氨酸-水合钴(II)(2)。通过元素分析、红外光谱、热分析等测试手段研究了配合物的性质, 并确定了配合物的组成。用气体吸收装置测定配合物在乙腈溶液中不同温度下的饱和吸氧量, 求得氧合反应的平衡常数及热力学参数, 同时探讨了温度和配体结构对配合物氧合性能的影响。用TG-DTG法研究了配合物的热稳定性及非等温热分解动力学, 并采用积分法和微分法相结合的方法,推断了两种配合物的第一步热分解反应机理, 得到了热分解反应动力学参数及其动力学方程。     

Effect of atmosphericwater vapor on the kinetics of thermal decomposition of copper(II) carbonate hydroxide

The effect of atmospheric water vapor on the kinetic rate behavior of the thermal decomposition of copper(II) carbonate hydroxide, Cu₂CO₃(OH)₂, was investigated by means of TG-DTA coupled with a programmable humidity controller. With increasing water vapor pressure p(H₂O) from 0.8 to 10.6 kPa, a systematic reduction of the reaction temperature of the thermal decomposition was observed as the continuous trend from the previous works at the lower p(H₂O). Through a comparative kinetic analysis of the reaction at different p(H₂O), a catalytic action of the atmospheric water vapor on the nucleation process at the first half of the reaction was identified as the possible origin of the reduction of the reaction temperature.     

Effect of type and position of the anions on the thermal decomposition of some copper(II) complexes

A number of copper(II) complexes of some aromatic diamines have been prepared and characterized. The thermal stabilities of the complexes were studied and discussed in terms of covalent bond character, chelate ring size and angle strain. On the other hand, the effective role of the anions on the decomposition pathways was also considered. Moreover, the nature of interaction of the solvent of crystallization has also been investigated.

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Zusammenfassung Es wurde eine Anzahl von Kupfer(II)-komplexen einiger aromatischer Diamine hergestellt und beschrieben. Die thermische Stabilität der Komplexe wurde als Funktion des kovalenten Bindungscharakters, der Chelatringgröße und der Winkelspannung untersucht und diskutiert. Andererseits wurde auch der Einfluß der Anionen auf den Zersetzungsweg in Erwägung gezogen. Außerdem wurde auch die Wechselwirkung zwischen Lösungsmittel und Kristallisierung untersucht.

     

Studies of thermal decomposition of palladium(II) complexes with olefin ligands

Thermal decomposition kinetics of ML₂ (M = Ni(II) and Co(II); L = 5-(2-(1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)hydrazono)-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione) complexes were investigated by thermogravimetric analysis (TGA). The first decomposition process of the NiL₂ and CoL₂ complexes occurs in the temperature range of 320–350 °C. Kinetics parameters corresponding to this step, such as activation energy, E_α, and apparent pre-exponential factor, ln A_aap, were calculated from the thermogravimetric data at the heating rates of 5, 10, 15 and 20 K min⁻¹ by differential (Friedman's equation) and integral (Flynn–Wall–Ozawa's equation) methods. The results show that the activation energy evidently depends on the extent of conversion. As far as their activation energy is concerned, NiL₂ complex shows a higher thermal stability than the CoL₂ complex.     

Thermal decomposition kinetics of strontium oxalate

The thermal decomposition behavior in air of SrC₂O₄ · 1.25H₂O was studied up to the formation of SrO using DTA-TG-DTG techniques. The decomposition proceeds through four well-defined steps. The first two steps are attributed to the dehydration of the salt, while the third and fourth ones are assigned to the decomposition of the anhydrous strontium oxalate into SrCO₃ and the decomposition of SrCO₃ to SrO, respectively. The exothermic DTA peak found at around 300°C is ascribed to the recrystallization of the anhydrous strontium oxalate. On the other hand, the endothermic DTA peak observed at 910°C can be attributed to the transition of orthorhombic-hexagonal phase of SrCO₃. The kinetics of the thermal decomposition of anhydrous strontium oxalate and strontium carbonate, which are formed as stable intermediates, have been studied using non-isothermal TG technique. Analysis of kinetic data was carried out assuming various solid-state reaction models and applying three different computational methods. The data analysis according to the composite method showed that the anhydrous oxalate decomposition is best described by the two-dimensional diffusion-controlled mechanism (D₂), while the decomposition of strontium carbonate is best fitted by means of the three-dimensional phase boundary-controlled mechanism (R₃). The values of activation parameters obtained using different methods were compared and discussed.     

Kinetics of thermal decomposition of hexanitrohexaazaisowurtzitane

Thermal decomposition of hexanitrohexaazaisowurtzitane (HNIW) in the solid state and in solution was studied by thermogravimetry, manometry, optical microscopy, and IR spectroscopy. The kinetics of the reaction in the solid state is described by the first-order equation of autocatalysis. The rate constants and activation parameters of HNIW thermal decomposition in the solid state and solution were determined. The content of N₂ amounts to approximately half of the gaseous products of HNIW thermolysis. The thermolysis of HNIW and its burning are accompanied by the formation of a condensed residue. During these processes, five of six nitro groups of the HNIW molecule are removed, and one NO₂ group remains in the residue, which contains amino groups and no C−H bonds. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 815–821, May, 2000.     

硫化氢热分解制氢过程的化学动力学研究

采用化学热平衡分析方法研究了硫化氢热分解制氢过程,研究了硫化氢在不同温度和体积分数下的分解过程,并与试验数据进行了比较。结果表明,基元反应机理能较好地模拟硫化氢热分解制氢过程。硫化氢的热分解率依赖于反应温度,高温下能获得较好的分解制氢效果;温度较低时,时间是硫化氢趋于平衡的主要影响因素,随着温度的提高,温度成为影响硫化氢趋于平衡的主要影响因素。硫化氢初始体积分数对热分解制氢反应具有较大的影响,采用较低体积分数的硫化氢混合气有利于获得高的硫化氢热分解制氢率。     

Kinetics of the thermal decomposition of dinitramide

The kinetic regularities of the thermal decomposition of dinitramide in aqueous solutions of HNO₃, in anhydrous acetic acid, and in several other organic solvents were studied. The rate of the decomposition of dinitramide in aqueous HNO₃ is determined by the decomposition of mixed anhydride of dinitramide and nitric acid (N₄O₆) formed in the solution in the reversible reaction. The decomposition of the anhydride is a reason for an increase in the decomposition rates of dinitramide in solutions of HNO₃ as compared to those in solutions in H₂SO₄ and the self-acceleration of the process in concentrated aqueous solutions of dinitramide. The increase in the decomposition rate of nondissociated dinitramide compared to the decomposition rate of the N(NO₂)₂ ⁻ anion is explained by a decrease in the order of the N−NO₂ bond. The increase in the rate constant of the decomposition of the protonated form of dinitramide compared to the corresponding value for neutral molecules is due to the dehydration mechanism of the reaction. For Part 1, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 41–47, January, 1998.     

Dehydration Reaction of Manganese(II) Oxalate Dihydrate in the Solid State New Method in the Study of Non-isothermal Kinetics

A new method was proposed for determining the most probable mechanism function of a solid phase reaction. According to Coats-Redfern's integral equation E_β→0 was calculated by extrapolating β to zero using a series of TG curves with different heating rates. Similarly, E_α→0 was calculated according to Ozawa's equation. The most probable mechanism function of the solid phase dehydration of manganese(II) oxalate dihydrate was confirmed to be G(α)=(1-α)^1/2 by comparing E_α→0 with E_β→0. This revised version was published online in July 2006 with corrections to the Cover Date.