碱式碳酸锌非等温热分解动力学研究

采用TG-DTA曲线分析研究了碱式碳酸锌在氮气气氛中的热分解反应动力学,利用Doyle-Ozawa法和Kissinger法对碱式碳酸锌非等温热分解动力学数据进行了分析,同时运用Satava-Sestak法研究了碱式碳酸锌的热分解机理.结果表明,碱式碳酸锌的热分解反应服从随机成核和随后生长机理.     

In situ thermo-TOF-SIMS study of thermal decomposition of zinc acetate dihydrate

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used for an in situ thermal decomposition study of Zn(CH₃COO)₂·2H₂O forming ZnO nanoparticles. TOF-SIMS spectra were recorded at regular temperature intervals of 25 °C in positive and negative detection modes in a dynamic thermal process. Controlled heating (5 °C min⁻¹) of Zn(CH₃COO)₂·2H₂O was also carried out using thermogravimetric analysis (TGA) in an oxygen atmosphere (20 ml min⁻¹). Nearly spherical ZnO nanoparticles with no agglomeration and a narrow size distribution (diameter ∼50 nm) were observed, which were characterized using scanning electron microscopy, transmission electron microscopy and x-ray diffraction. In situ thermo-TOF-SIMS was used to monitor the ⁶⁴Zn⁺ and ⁶⁶Zn⁺ ion abundances as a function of temperature, which showed a similar profile to that observed for weight loss in TGA during decomposition. Based on the experimental results, a possible decomposition mechanism for the formation of ZnO is proposed. Copyright © 2004 John Wiley & Sons, Ltd.     

Kinetics and mechanism of thermal decomposition of hydroxylammonium nitrate

The kinetics of thermal decomposition of melted hydroxylammonium nitrate have been investigated by the rate of heat production in the temperature range 84.8–120.9°C. The decomposition proceeds with autocatalysis and up to 60 % of conversion the rate of the process increases proportionally to the square of the degree of decomposition. The initial rate is proportional to the square of the concentration of HNO₃ formed due to dissociation of the salt. The activation energy of this process is 15.3±1.8 kcal/mol. It is suggested that the initial stage the process proceeds via interaction between N₂O₃ and NH₃OH⁺, whereas the subsequent acceleration is due to oxidation of NH₃OH⁺ by nitrogen oxides formed as well as by nitrous acid.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1897–1901, November, 1993.     

Synthesis and thermal decomposition of antimony(III) oxide hydroxide nitrate

The thermal decomposition of the only known antimony nitrate antimony(III) oxide hydroxide nitrate Sb₄O₄(OH)₂(NO₃)₂, whose synthesis routes were reviewed and optimized was followed by TG-DTA under an argon flow, from room temperature up to 750°C. Chemical analysis (for hydrogen and nitrogen) performed on samples treated at different temperatures showed that an amorphous oxide hydroxide nitrate appeared first at 175°C, and decomposed into an amorphous oxide nitrate above 500°C. Above 700°C, Sb₆O₁₃ and traces of -Sb₂O₄ crystallized.Author to whom all correspondence should be addressed     

Kinetic and thermodynamic parameters of the thermal decomposition of zinc(ii) dialkyldithiocarbamate complexes

The thermodynamic and kinetic parameters of the thermal decomposition of Zn(S₂CNR₂)₂ complexes (R=CH₃, C₂H₅ and n-C₃H₇) were determined with the dynamic thermogravimetric method. Superimposed TG/DTG/DSC curves show that thermal decomposition reactions for chelates with R=C₂H₅ and n-C₃H₇ occur in the liquid phase, at temperatures far away from their melting points, whereas for the complex with R=CH₃ the thermal decomposition begins at a temperature closer to its melting point, suggesting a rather complex decomposition mechanism. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis and characterization of ZnO nanoparticles by thermal decomposition of a curcumin zinc complex

ZnO nanoparticles were generated by thermal decomposition of a binuclear zinc (II) curcumin complex as single source precursor. Thermal behavior of the precursor showed a considerable weight loss at about 374 °C by an exothermic reaction with a maximum weight loss rate of 14%/min. Complete decomposition of precursor was observed within 49 min with a heating rate of 10 °C/min. Synthesized nanoparticles have been characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy and selected area electron diffraction microscopy. Results revealed monodispersed hexagonal zincite structure with an average size of 117 ± 4 nm.     

Lanthanum nitrate decomposition by both temperature programmed heating and citrate gel combustion

Thermal decomposition of lanthanum nitrate to lanthanum oxide was carried out by both temperature programmed heating (TPH) and citrate-gel combustion. The temperature programmed heating was carried out under flow of oxidizing (air), neutral (nitrogen) and reducing (25 vol.% hydrogen+argone mixture) gases, and the processes were controlled by simultaneous thermogravimetry and differential thermal analysis. It was shown that hydrogen atmosphere helps to reduce temperatures of all decomposition steps. The results of TPH were utilized to check the nature of residues in the products of lanthanum nitrate-to-oxide conversion performed via citrate-gel combustion technique.     

The influence of chemical structure of sulfonamides on the course of their thermal decomposition

The thermal decomposition of several sulfonamides and potassium salts of sulfonamides was investigated. The analyses were performed using a derivatograph in an air atmosphere, sample sizes were from 50 to 200 mg and heating rate from 2.5 to 20 K min^-1. It has been established, that the thermal destruction of studied compounds occurs via three stages with formation of potassium carbonate as a final product of the complete combustion of potassium salts of sulfonamides. The temperature ranges, in which the analyzed compounds undergo thermal transformations were established. For evaluation of the results the principal component analysis (PCA) was applied. By this method the influence of the specific functional groups on the thermal decomposition of sulfonamides and potassium salts of sulfonamides was determined. It has also been recognized, that better discrimination among the analyzed compounds is obtained for the data set of the DTA. This revised version was published online in July 2006 with corrections to the Cover Date.     

Preparation of nano-Co3O4-coated Albizia procera-derived carbon by direct thermal decomposition method for electrochemical water oxidation

It is obtained that nano-Co₃O₄-coated carbon prepared by thermal decomposition of Co(NO₃)₂·6H₂O at 300 °C on home-made Albizia procera (Roxb.) leaves derived carbon is an efficient electrocatalyst for electrochemical water oxidation in 0.1 M NaOH (aq.) solution. The loading of nano-Co₃O₄ on the carbon was changed by varying the amount of precursor of cobalt (100–1000 mg) and using a constant amount of the carbon (200 mg) during thermal decomposition. The prepared samples were characterized by physical techniques, including X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), thermo-gravimetric analysis (TGA), fourier transform infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HRTEM), diffuse reflectance spectroscopy (DRS), Brunauer-Emmett-Teller (BET) and X-ray photoelectron spectroscopy (XPS). XRD, TEM, FESEM, and EDS confirmed the formation of uniformly distributed nanoparticles of single-phase Co₃O₄ on the surface of carbon. The XRD data reveals formation of nano-Co₃O₄ with average particle sizes in the range of 9–17 nm. The FESEM micrographs demonstrate that Co₃O₄ nanoparticles, having irregular morphology, are uniformly and densely covered on the surface of supporting carbon.. The prepared samples were immobilized on the filter paper derived carbon electrode (FPCE) to study their electrocatalytic properties toward water oxidation. The cyclic voltammetric studies showed that the nano-Co₃O₄-C prepared using 400 mg of Co(NO₃)₂·6H₂O (nano-Co₃O₄-C-400), which possesses meso- and macropores with BET surface area of 192.4 m²/g, reaches a current density of 28 mAcm⁻² at 1.5 V and electrochemical water oxidation starting potential of 0.7 V. In this work, it is also shown that the current densities, at 1.5 V, increase by increasing the amount of cobalt oxide in the prepared samples though. The nano-Co₃O₄-C-400 catalyst shows optimum performance for electrochemical water oxidation in terms of starting water oxidation potential, reasonable amount of Co₃O₄ and moderate level of current density at 1.5 V.     

Thermal decomposition of copper(II) and zinc carbonate hydroxides by means of TG-MS

Summary For the quantitative analyses of evolved CO₂and H₂O during the thermal decomposition of solids, calibration curves, i.e. the amounts of evolved gases vs. the corresponding peak areas of mass chromatograms measured by TG-MS, were plotted as referenced by the reaction stoichiometry of the thermal decomposition of sodium hydrogencarbonate NaHCO₃. The accuracy and reliability of the quantitative analyses of the evolved CO₂and H₂O based on the calibration curves were evaluated by applying the calibration curves to the mass chromatograms for the thermal decompositions of copper(II) and zinc carbonate hydroxides. It was indicated from the observed ratio of evolved CO₂and H₂O that the compositions of copper(II) and zinc carbonate hydroxides examined in this study correspond to mineral malachite, Cu₂CO₃(OH)₂, and hydrozincate, Zn₅(CO₃)₂(OH)₆, respectively. Reliability of the present analytical procedure was confirmed by the fairly good agreement of the mass fraction of the evolved gases calculated from the analytical values with the total mass-loss during the thermal decompositions measured by TG.     

Influences of evolved gases on the thermal decomposition of zinc carbonate hydroxide evaluated by controlled rate evolved gas analysis coupled With TG

The influences of atmospheric CO₂ and H₂O on the kinetics of the thermal decomposition of zinc carbonate hydroxide, Zn₅(CO₃)₂(OH)₆, were investigated by means of controlled rate evolved gas analysis (CREGA) coupled with TG. Although CO₂ and H₂O were evolved simultaneously in a single mass-loss step of the thermal decomposition, different effects of those evolved gases on the kinetic rate behavior were observed. No distinguished effect of atmospheric CO₂ was detected within the possible range of self-generated CO₂ concentration. On the other hand, apparent acceleration effect by the increase in the concentration of atmospheric H₂O was observed as the reduction of reaction temperature during the course of constant rate thermal decomposition. The catalytic effect was characterized by the decrease in the apparent activation energy for the established reaction with increasing the concentration of atmospheric H₂O, accompanied by the partially compensating decrease in the pre-exponential factor.     

Thermal decomposition of chromium(III) nitrate(V) nanohydrate

Thermal decomposition of Cr(NO₃)₃·9H₂O in helium and in synthetic air was studied by means of TG, DTA, EGA and XRD analysis. The dehydration occurs together with decomposition of nitrate(V) groups. Eight distinct stages of reaction were found. Intermediate products of decomposition are hydroxy- and oxynitrates containing chromium in hexa- and trivalent states. The process carried out in helium leads to at about 260°C and in air is formed at about 200°C. The final product of decomposition (>450°C) is Cr₂O₃, both in helium and in air. This revised version was published online in July 2006 with corrections to the Cover Date.     

The thermal decomposition of zirconium oxyhydroxide

The thermal decomposition of zirconium oxyhydroxides prepared by the mixture of aqueous zirconium oxychloride solutions and aqueous solutions of sodium hydroxide or ammonium hydroxide under various conditions has been examined by thermogravimetry, differential thermal analysis, X-ray diffraction study and infrared spectrophotometry. As a result, it is seen that the thermal decomposition of zirconium oxyhydroxide, in which the composition is ZrO_2-x(OH)_2xyH₂O where x2 and 1y<2, proceeds according to the following process:

The role of anhydrous zinc nitrate in the thermal decomposition of the zinc hydroxy nitrates Zn5(OH)8(NO3)2·2H2O and ZnOHNO3·H2O

The steps associated with the thermal decomposition of Zn₅(OH)₈(NO₃)₂·2H₂O and ZnOHNO₃·H₂O are re-examined. Previous reports have suggested that Zn₅(OH)₈(NO₃)₂·2H₂O decomposes to ZnO via two intermediates, Zn₅(OH)₈(NO₃)₂ and Zn₃(OH)₄(NO₃)₂ whereas ZnOHNO₃·H₂O has been reported to decompose to ZnO via a Zn₃(OH)₄(NO₃)₂ intermediate. In this study, we demonstrate using TG, mass spectral analysis of evolved gases and in situ variable temperature powder X-ray diffraction analysis that, in fact, in the decomposition of Zn₅(OH)₈(NO₃)₂·2H₂O an anhydrous zinc nitrate intermediate is also involved. We, additionally, show that the decomposition of ZnOHNO₃·H₂O to ZnO also involves the formation of an anhydrous zinc nitrate intermediate. The anhydrous zinc nitrate formed in both cases is poorly crystallised and this observation may explain why this phase could not be observed by PXRD analysis in the previous studies.     

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.     

Mechanism of thermal decomposition of thiourea derivatives

The thermal decomposition of a series of compounds has been studied by thermogravimetry, mass spectrometry, nuclear magnetic resonance and elemental analysis. The combined use of mass spectrometry and thermogravimetry (MS and TG) in the analysis of these compounds has allowed characterization of the fragmentation pattern which was the objective of this research. The gaseous products, volatile condensed products and solid residues were identified by NMR and MS. Based on the product of thermal decomposition, the mechanism of thermal decomposition has been derived.     

A comparative study of the effects of decomposition rate control and mechanical grinding on the thermal decomposition of aluminum hydroxide

Summary Two different processes of the thermal decomposition of synthetic bayerite, i.e., the non-isothermal decomposition of mechanically ground sample in flowing N₂ and the controlled rate thermal decomposition of crystalline bayerite under vacuum, were investigated comparatively. In comparison with the conventional non-isothermal decomposition of crystalline bayerite in flowing N₂, the reaction temperature of the thermal decomposition was lowered by the individual effects of mechanical grinding of the sample and the reaction rate control. These decomposition processes indicated similar behavior characterized by the restricted changes of the specific surface area during the course of decomposition reaction and the formation of an amorphous alumina as the decomposition product. Different thermal behaviors were observed for those amorphous Al₂O₃ produced by the respective decomposition processes.     

Investigation of thermal decomposition of CrOx (x≥2.4)

The phase transitions and thermal effects occurring during annealing in air of material with general formula CrO_x (x≥2.4) have been investigated. The investigations were performed with TG, DTA, DSC, EGA, XRD and other spectral techniques. The formation of an amorphous phase with average composition Cr₅O₁₂ in the range 300-400°C has been observed. Further heating leads to partial loss of oxygen, simultaneous decay of Cr₂O₅ and CrO₂ phases and formation of nonstoichiometric Cr₂O_3+x. The distinct loss of mass is observed in the range 415-428°C, connected with evolving oxygen and small amount of nitric oxides. Thermal effects accompanying the mass changes depend on the mass of the sample. When the mass decreases, the transition from exothermic to endothermic effects is observed. This phenomenon can be explained as the competition between two processes: reconstruction of the crystalline lattice (endothermic effect) and recombination of the evolved atomic oxygen (exothermic effect). This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal decomposition of zinc hydroxy azide

The isothermal decomposition of zinc hydroxy azides, Zn(OH)_2-x(N₃)_x: follows deceleratory kinetics throughout the temperature range studied. The initial part of the decomposition fits into unimolecular decay law, log (1-a) = -kt. The contracting volume law satisfactorily describes the data at higher degrees of decomposition. The maximum value ofa upto which the slow decomposition could be recorded was 0.75. The aged form of zinc hydroxy azide decomposes with much lower rates and slightly different topochemical characteristics. The decrease in the rate of decomposition on ageing has been attributed to the formation of carbonate on the surface of the compound during storage. The change in topochemical behaviour is traced to the reported layer structure of zinc hydroxy azide. The effect of pre-heating on subsequent thermal decomposition has also been discussed.     

Preparation and thermal decomposition of indium hydroxide

Summary Indium hydroxides were prepared by the mixing of aqueous indium nitrate solution with sodium or ammonium hydroxide solutions under various conditions. The thermal decomposition of the resulting materials was examined by thermogravimetry, differential thermal analysis, X-ray diffraction study and infrared spectroscopy. It has been found that sodium hydroxide solution is more suitable than the addition of ammonium hydroxide solution to prepare indium hydroxide in well crystallization; the thermal decomposition of indium hydroxide, in which the composition is In(OH)₃·xH₂O where x￡2, proceeds according to the following process: In(OH)₃·xH₂O?cubic In(OH)₃?cubic In₂O₃