Kinetic studies on the thermal decomposition of phosphate-doped sodium oxalate

The thermal decomposition kinetics of sodium oxalate (Na₂C₂O₄) has been studied as a function of concentration of dopant, phosphate, at five different temperatures in the range 783–803 K under isothermal conditions by thermogravimetry (TG). The TG data were subjected to both model-fitting and model-free kinetic methods of analysis. The model-fitting analysis of the TG data of all the samples shows that no single kinetic model describes the whole α versus t curve with a single rate constant throughout the decomposition reaction. Separate kinetic analysis shows that Prout–Tompkins model best describes the acceleratory stage of the decomposition, while the decay region is best fitted with the contracting cylinder model. Activation energy values were evaluated by both model-fitting and model-free kinetic methods. The observed results favour a diffusion-controlled mechanism for the thermal decomposition of sodium oxalate.     

Stability Fields in the System Mn?Mo?O and Thermochemical Data of Mn2Mo3O8 and MnMoO4

The decomposition of MnMoO₄ and Mn₂Mo₃O₈ has been investigated by modified TG measurements in a controlled oxygen atmosphere. From the results the μ-x phase diagram of the system Mn? Mo? O in an isothermal representation has been obtained. The following thermochemical data have been evaluated: .     

Gefriergetrocknete Acetate von Sr und Fe als reaktive Vorläufer für komplexe Eisen-Strontium-Oxide

The thermal decomposition of reactive freeze-dried acetate precursors for Sr-Fe-oxides was investigated by means of DTA, TG, mass spectroscopy and X-ray powder diffractometry. In the case of decomposition of Fe(III)-m-oxo-acetate four superimposed main steps are characterized as release of (a) H₂O, (b) acetic acid and ketene (c) methane, ketene and CO₂ and (d) acetone and CO₂. On careful decomposition, single phase γ-Fe₂O₃ can be formed. The decomposition of freeze-dried mixed Fe-Sr-acetates reflects some aspects of the single acetates, but also an interaction between the components. The interactions result in a lower decomposition temperature of Sr-acetate (release of acetone and formation of SrCO₃). The decomposition temperature of SrCO₃ in the reactive mixture is also lowered. The simultaneous decomposition of SrCO₃ and its reaction with the Fe-component results directly in the formation of the expected complex Sr-Fe-oxide. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal decomposition of barium(II) tetraphenylborate

Barium(II) tetraphenylborate, Ba(Bph₄))₂·4H₂O was prepared, and its decomposition mechanism was studied by means of TG and DTA. The products of thermal decomposition were examined by means of gas chromatography and chemical methods. A kinetic analysis of the first stage of thermal decomposition was made on the basis of TG and DTG curves and kinetic parameters were obtained from an analysis of the TG and DTG curves using integral and differential methods. The most probable kinetic function was suggested by comparison of kinetic parameters. A mathematical expression was derived for the kinetic compensation effect.     

Thermoanalytical investigations of 4-methylpiperazine-1-carbodithioic acid ligand and its iron(III), cobalt(II), copper(II) and zinc(II) complexes

The thermal decomposition studies on 4-methylpiperazine-1-carbodithioic acid ligand (4-MPipzcdtH) and its complexes, viz. [M(4-MPipzcdtH)_n](ClO4)_n (M=Fe(III) when n=3; M=Co(II), Cu(II) when n=2) and [Zn(4-MPipzcdtH)₂]Cl₂ have been carried out using non-isothermal techniques (TG and DTA). Initial decomposition temperatures (IDT), indicate that thermal stability is influenced by the change of central metal ion. Free acid ligand exhibits single stage decomposition with a sharp DTA endotherm. Complexes, [M(4-MPipzcdtH)_n](ClO₄)_n undergo single stage decomposition with detonation and give rise to very sharp exothermic DTA curves while the complex [Zn(4-MPipzcdtH)₂]Cl₂ shows three-stage decomposition patterns. The kinetic and thermodynamic parameters, viz. the energy of activation E, the frequency factor A, entropy of activation S and specific rate constant k, etc. have been evaluated from TG data using Coats and Redfern equation. Based upon the results of the differential thermal analysis study, the [M(4-MPipzcdtH)_n](ClO₄)_n complexes have been found to possess characteristic of high energy materials.     

Thermal and spectroscopic studies of solid oxamate of light trivalent lanthanides

Solid-state LnL₃·1.25H₂O compounds, where L is oxamate and Ln is light trivalent lanthanides, have been synthesized. Simultaneous thermogravimetry and differential scanning calorimetry (TG–DSC), experimental and theoretical infrared spectroscopy, TG–DSC coupled to FTIR, elemental analysis, complexometry, and X-ray powder diffractometry were used to characterize and to study the thermal behavior of these compounds. The results led to information about the composition, dehydration, thermal stability, thermal decomposition, and gaseous products evolved during the thermal decomposition of these compounds in dynamic air atmosphere. The dehydration occurs in a single step and through a slow process. The thermal decomposition of the anhydrous compounds occur in a single (Ce), two (Pr), and three (La, Nd to Gd) steps with the formation of the respective oxides, CeO₂, Pr₆O₁₁, and Ln₂O₃ (Ln = La, Nd to Gd). The theoretical and experimental spectroscopic study suggests that the carboxylate group and amide carbonyl group of oxamate are coordinate to the metals in a bidentate chelating mode.     

Kinetic analysis of complex decomposition reactions using evolved gas analysis

For complex decomposition reactions, traditional methods, such as TG and DSC cannot fully resolve all of the steps in the reaction. Evolved gas analysis (EGA) offers another tool to provide more information about the decomposition mechanism. The decomposition of sodium bicarbonate was studied by TG, DSC and EGA using a simultaneous thermal analysis unit coupled to a FTIR. The decomposition of sodium bicarbonate involves two reaction products H₂O and CO₂, which are not evident from either TG or DSC measurements alone. A comparison of the reaction kinetics from TG, DTG and EGA data were compared.     

On the thermal decomposition of K2PdCl4 in a hydrogen atmosphere

The decomposition of single crystals and powders of K₂PdCl₄ in a hydrogen atmosphere was investigated by means of thermogravimetry (TG) at temperatures between 85 and 170°C, and by optical microscopy. The rate of decomposition is controlled by a combined process of nucleation and growth. The activation energy was calculated to be 15.2 ± 0.5 kcal mol^?1 for single crystals and 13.5 ± 0.4 kcal mol^?1 for powders. The results are compared with those obtained for K₂PtCl₄.An attempt was made to explain the differences in the orientation relationships, previously determined by X-ray diffraction, between K₂PtCl₄ and K₂PdCl₄, Rb₂PdCl₄ and K₂PdBr₄ and their decomposition products with a different kinetic behaviour.     

LaCoO3 formation from precursors obtained by water-based sol–gel method with citric acid

In the present work the LaCoO₃ formation from gel precursors obtained by water-based sol–gel method with citric acid was studied. As precursors La and Co nitrates were used. The obtained gels were analyzed by TG/DTA and TG/AGE. The decomposition of the gels takes place in two main steps with the evolution of the same volatile compounds (H₂O, CO₂ si NO₂) leading to the conclusion that two types of bonding of the components in the gels occurred. The decomposition of the gels takes place up to 400 °C. The gels thermally treated at 600 °C lead to single pure perovskite rhombohedral phase of lanthanum cobalt oxide (LaCoO₃).     

Thermoanalytical investigation of calcium chromate

Thermoanalytical methods have been used to study calcium chromate (CaCrO₄) samples. Thermal decomposition temperatures determined by TG in vacuum and by DTA in air could not be successfully used for screening purposes. Other thermogravimetry studies in air indicate that TG can be an effective quality control tool in screening out samples which have an assay value below 97.0% CaCrO₄. More complete analyses using TG in an argon atmosphere gave good results for CaCO₃ and H₂O content as well as for total CaCrO₄. Reliable measurement of Ca(OH)₂ was not achieved. Effluent gas analysis—mass spectrometry was used to identify gaseous products as a function of temperature, in order to verify interpretation of TG curves.Thermogravimetry, differential scanning calorimetry, nuclear magnetic resonance, and mass spectrometry have been used in an effort to explain the unusual weight loss observed between 400 and 600°C for many CaCrCO₄ samples. Ca(OH)₂ decomposition is not the primary cause of this weight loss, as originally suspected, but instead the loss appears to be due to volatization of H₂O trapped in the CaCrO₄ crystal.     

Influences of product gases on the kinetics of thermal decomposition of synthetic malachite evaluated by controlled rate evolved gas analysis coupled with thermogravimetry

An instrument of controlled rate evolved gas analysis (CREGA) coupled with TG‐DTA was constructed for analyzing the influences of product gases on the kinetics and mechanism of the thermal decomposition of solids that produce more than one gaseous products at the same stage of reaction. The thermal decomposition of synthetic malachite, Cu₂(OH)₂CO₃, was subjected to the measurements of CREGA‐TG under controlled concentrations of H₂O and CO₂ in the reaction atmosphere with taking account of self‐generated H₂O and CO₂ during the course of reaction. By a series of CREGA‐TG measurements carried out under various atmospheric conditions, it was reconfirmed that the reaction is accelerated and decelerated by the effects of atmospheric H₂O and CO₂, respectively. From the kinetic analysis of the CREGA‐TG curves and results of high temperature X‐ray diffraction measurements under various reaction atmospheres, it was revealed that the anomalous effects of atmospheric H₂O on the reactivity and on the reaction rate of the thermal decomposition of synthetic malachite appear at the early stage of the reaction. Usefulness of the CREGA‐TG technique for measuring the kinetic rate data for the thermal decomposition of solids was demonstrated in the present study, by emphasizing the importance of quantitative control of self‐generated reaction atmosphere. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 346–354, 2005     

Synthesis, crystal structure and thermal decomposition of a new copper propionate [Cu(CH3CH2COO)2]·2H2O

A new copper propionate complex was synthesised and characterized for application as precursor for CuO based oxide thin films deposition. The FT-IR and X-ray diffraction analyses have revealed the formation of a cooper propionate complex [Cu(CH₃CH₂COO)₂]·2H₂O. The crystal and molecular structure of a new copper propionate complex was determined by XRD on the copper propionate single crystal. The copper propionate complex has a binuclear structure, connected by bridging bidentate carboxylates groups and a Cu?Cu bond of 2.6 Å. The thermal decomposition of copper propionate has been investigated by thermal analysis using thermogravimetric (TG) and differential thermal analysis (DTA), differential thermal analysis coupled with quadrupole mass spectrometry-QMS, X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR) techniques. TG and XRD data indicate the reduction of Cu(II)-Cu(I,0) during the decomposition of copper propionate.     

Physicochemical study on selenites of the three-component system Yb2O3-SeO2-H2O

The solubility isotherm of the three-component system Yb₂O₃-SeO₂-H₂O at 100°C was studied. There are two fields of crystallization in the solubility diagram at this temperature - a small one of Yb₂(SeO₃)₃·4H₂O and a large one of YbH(SeO₃)₂·2H₂O. These compounds were identified by the Schreinemakers' method, and by chemical and X-ray analyses as well. Simultaneous TG and DTA curves of the two compounds obtained were made and the mechanism of the thermal decomposition was described. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the thermal decomposition of K2PtCl4 in a hydrogen atmosphere

The reaction of single crystals and powders of K₂PtCl₄ with hydrogen is studied by means of thermogravimetry (TG) at temperatures between 175 and 225°C and by optical microscopy. Two different mechanisms are observed. The rate of decomposition of single crystals is determined by the displacement of the reaction interface, which is similar in every crystallographic direction.The rate of decomposition of the powders is limited by the rate of nucleation in the powder particles. For both mechanisms the kinetic parameters are calculated. The activation energy for the displacement of the interface is much higher than the one necessary for nucleation.     

Studies on energetic compounds part 37: kinetics of thermal decomposition of perchlorate complexes of some transition metals with ethylenediamine

Five bis(ethylenediamine)metal perchlorate (BEMP) complexes like [M(en)₂](ClO₄)₂ (where M=Mn, Co, Ni, Cu, Zn and en=ethylenediamine) have been prepared and characterized by gravimetric methods, infrared spectroscopy (IR) and elemental analysis. Thermal decomposition studies have been undertaken using simultaneous thermogravimetry (TG) and differential thermal analysis (DTA) in nitrogen atmosphere. Non-isothermal TG and DTA studies have also been carried out separately in air to examine the effect of atmosphere on thermolysis of these complexes. Thermal stability of the complexes was found to decrease in the order: [Zn(en)₂](ClO₄)₂>[Mn(en)₂](ClO₄)₂>[Ni(en)₂](ClO₄)₂>[Cu(en)₂](ClO₄)₂>[Co(en)₂](ClO₄)₂.Isothermal TG over the temperature range of decomposition of all these complexes, has been done to evaluate the kinetics of decomposition. Both model fitting and model free isoconversional methods have been used to analyse the kinetics. Isoconversional method has been found to be superior over the conventional model fitting method and is able to describe the complex decomposition of these complexes. It indicates that the values of activation energy vary with the extent of conversion (α) while model fitting method results in a single value of E for overall decomposition process which cannot be attributed to any process under such a complex decomposition reaction. Explosion delay (D_E) measurement has been carried out to investigate the response of these complexes under the condition of rapid heating.     

Variable temperature PXRD investigation of the phase changes during the dehydration of potassium Tutton salts

The thermal dehydration of the potassium Tutton salts K₂M(SO₄)₂·6H₂O (M = Mg, Co, Ni, Cu, Zn) was investigated using thermal gravimetric analysis (TG), differential scanning calorimetry (DSC), FTIR, and variable temperature powder X-ray diffraction. While each Tutton salts lost all six waters of hydration when heated to 500 K, the decomposition pathway depended on the divalent metal cation. K₂Ni(SO₄)₂·6H₂O lost all six waters in a single step, and K₂Cu(SO₄)₂·6H₂O consistently lost water in two steps in capped and uncapped cells. In contrast, multiple decomposition pathways were observed for the magnesium, cobalt, and zinc Tutton salts when capped and uncapped TG cells were used. K₂Zn(SO₄)₂·6H₂O lost the waters of hydration in a single step in an uncapped cell and in two steps in a capped cell. Both K₂Mg(SO₄)₂·6H₂O and K₂Co(SO₄)₂·6H₂O decomposed in a series of steps where the stability of the intermediates depended on the cell configuration. A greater number of phases were often observed in DSC and capped-cells TG experiments. A quasi-equilibrium model is presented that could explain this observation. These results highlight that experimental conditions play a critical role in the observed thermal decomposition pathway of Tutton salts.     

Thermoanalytical study of heavier trivalent lanthanides fumarates

Solid-state heavier lanthanides fumarates compounds have been synthesized, and the compounds were characterized by employing simultaneous thermogravimetry and differential thermal analysis (TG–DTA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), TG coupled to FTIR, elemental analysis, and complexometry. On heating, the dehydration occurs in a single and two consecutive steps and the thermal decomposition of the anhydrous compounds occurs in consecutive and/or overlapping steps, with formation of the respective oxides: Tb₄O₇ and Ln₂O₃ (Ln=Dy to Lu). The results also led to information about composition, thermal behavior, and the type of coordination of the isolated compounds.     

Characterization of light and heavy hydrated magnesium carbonates using thermal analysis

Upon heating, hydrated magnesium carbonates (HMCs) undergo a continuous sequence of decomposition reactions. This study aims to investigate the thermal decomposition of various commercially produced HMCs classified as light and heavy, highlight their differences, and provide an insight into their compositions in accordance with the results obtained from thermal analysis and microstructure studies. An understanding of the chemical compositions and microstructures, and a better knowledge of the reactions that take place during the decomposition of HMCs were achieved through the use of SEM, XRD, and TG/differential thermal analysis (DTA). The quantification of their CO₂ contents was provided by TG and dissolving the samples in HCl acid. Results show that variations exist within the microstructure and decomposition patterns of the two groups of HMCs, which do not exactly fit into the fixed stoichiometry of the known HMCs in the MgO–CO₂–H₂O system. The occurrence of an exothermic DTA peak was only observed for the heavy HMCs, which was attributed to their high CO₂ contents and the relatively delayed decomposition pattern.     

Thermal decomposition kinetics of palladium(II) 1‐allylimidazole complexes

Thermal dehydration and decomposition processes of a Pd(II) coordination compound, [PdL₄]Cl₂·3H₂O ( 1 ), (where L is 1‐allylimidazole) were studied by simultaneous TG/DSC techniques under constant heating rates condition. The released gas products were analyzed by online coupling a FTIR spectrometer to the TG equipment. The so obtained evolved gas analysis confirmed that only two ligand molecules were released and that a new 1‐allylimidazole Pd(II) complex, trans‐[PdL₂Cl₂] ( 2a ), was obtained. The same coordination compound was also prepared by heating 1 at 413.15 K in air atmosphere until a constant weight was reached 2b . Thermal decomposition mechanisms for the 2a and 2b complexes examined were proposed according to the three mass loss steps derived by TG data. Based on the model‐free isoconversional method described by Flynn–Wall–Ozawa (FWO), the dependencies of activation energy on the degree of conversion were determined. A model‐free “single point” method was also applied using the Kissinger equation, and derived results were compared to those of the former method. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 667–674, 2005     

Decomposition of Cyclohexyl-t-butyl-Dimethylammonium Tetraphenylborate: Synthesis and kinetics

A new compound cyclohexyl-t-butyldimethylammonium tetraphenylborate, [C₆H₁₁N(CH₃)₂(C(CH₃)₃)]BPh₄ has been prepared, and its decomposition mechanism was studied by TG. The IR spectra of the products of thermal decomposition were examined at every stage. Kinetic analysis for the first stage of thermal decomposition process was obtained by TG and DTG curves, and kinetic parameters were obtained from the analysis of the TG-DTG curves with integral and differential equations. The most probable kinetic function was suggested by comparison of kinetic parameters.This revised version was published online in November 2005 with corrections to the Cover Date.