Advanced isoconversional and master plot analyses on solid-state degradation kinetics of a novel nanocomposite

The decomposition kinetics of glycerol diglycidyl ether (GDE)/3,3-dimethylglutaric anhydride/nanoalumina composite have been investigated by thermogravimetry analysis under nonisothermal mode. The activation energy, E _a, of the solid-state decomposition process was evaluated using the advanced isoconversional method. From the experimental data, the dependence of conversion on temperature and activation energy was constructed allowing calculating the master plots. Our results showed that the decomposition mechanism at temperatures below 400 °C could be fitted by R2 kinetic model with E _a = 143 kJ mol^?1. The information about the kinetic parameters based only on thermal degradation data has been used for quick lifetime estimation at different temperatures. The Vyazovkin method was also employed to predict the times to reach α = 0.5 at isothermal mode using the activation energy calculated by the advanced isoconversional approaches. Scanning electron microscopy (SEM) analysis was carried out to investigate the fracture surface morphology. It was revealed from the SEM images that the presence of nanoalumina results in reinforcement of GDE matrix.     

Kinetics of thermal decomposition of Co3O4 powder and single crystals

Kinetics of thermal decomposition in vacuum of Co₃O₄ powder as well as single crystals has been investigated. Discrepancies with the results of previous authors have been discussed. Decomposition of Co₃O₄ proceeds through formation of a compact layer of CoO and hence diffusion is the rate-limiting factor. The experimental curves α(t) be described for 0.05 < α < 0.85 using a modified Ginstling-Brounshtein equation: 1 ? 2α/3 ? (1 ? α)^2/3 = ktⁿ where the activation energy varies with the degree of decomposition.     

Thermal decomposition of [Co(NH3)5Cl]Cl2

The thermal decomposition of [Co(NH₃)₅Cl]Cl₂ was studied under non-isothermal conditions, in dynamic air and argon atmospheres. The kinetics of the particular stages of [Co(NH₃)₅Cl]Cl₂ thermal decomposition were evaluated from the dynamic weight loss data by means of the modified Coats-Redfern method. TheD _n andR _n models were selected as the models best fitting the experimental TG curves. These models suggest that the kinetics and macromechanism of [Co(NH₃)₅Cl]Cl₂ decomposition can be governed by diffusive and/or phase boundary processes. The values of the activation energy,E _a, and the pre-exponencial factor,A, of the particular stages of the thermal decomposition were calculated.     

The thermal decomposition of (NH4)4V2O11 in a nitrogen atmosphere and the kinetics of the first decomposition step

Although the reaction products are unstable at the reaction temperatures, at a heating rate of 2 deg·min^?1 ammonium peroxo vanadate, (NH₄)₄V₂O₁₁, decomposes to (NH₄)[VO (O₂)₂ (NH₃)] (above 93°C); this in turn decomposes to (NH₄) [VO₃ (NH₃)] (above 106°C) and then to ammonium metavanadate (above 145°C). On further heating vanadium pentoxide is formed above 320°C. The first decomposition reaction occurs in a single step and the Avrami-Erofeev equation withn=2 fits the decomposition data best. An activation energy of 148.8 kJ·mol^?1 and a ln(A) value of 42.2 are calculated for this reaction by the isothermal analysis method. An average value of 144 kJ·mol^?1 is calculated for the first decomposition reaction using the dynamic heating data and the transformation-degree dependence of temperature at different heating rates.     

A new method of assessing solid state reactivity illustrated by reference to the change in oxidation rate of alkaline and acid washed carbons

In this study gasification in air of activated carbons and carbon blacks is investigated using a simultaneous TG-DTA unit. It is found that a final acid or alkaline treatment can substantially alter their reactivity in the gasification reaction in air. To make a proper assessment of their solid state reactivity with respect to their gasification in air a simple method is advanced which has been used recently in assessing solid state reactivity of other materials. In this method a thermogravimetric (TG) plot is obtained on a reference carbon and then similar TG plots are obtained on the other samples of carbon using identical experimental conditions and the same TG unit. The solid state reactivity is assessed from plots of the α_R (the value of α_R, the extent of the gasification of the reference carbon) against the sample carbons values of the α_S (labeled α_S to denote the value of the various carbon samples). The values of appropriate couples of α_R and α_S at temperaturesT ₁,T ₂,T ₃,...T_n allow an α_R-α_S plot to be constructed. If the solid state reactivity of the carbon samples matches exactly that of the reference carbon the result will be a linear plot, showing coincidence of α_S and α_R at all values of α_R. If the solid state reactivity of a carbon sample exceeds that of the reference carbon then the lines plotted will be on one side of the coincidence plot, while if they are less than the carbon reference they will lie on the other side. The results show that treatment of a carbon with alkaline or acid may have a significant effect on the reactivity of the carbon sample which is only partly explained by observable differences in surface area.     

Effect of rare earth oxides on the thermal decomposition of barium oxalate

Catalytic activity of rare earth oxides (REO); La₂O₃, Sm₂O₃, Gd₂O₃ and Ce₂O₃ on the isothermal decomposition of barium oxalate has been studied at 723 K. The α?t plots for pure salt as well as mixtures indicate that the process follows: initial gas evolution, a short acceleratory and a long decay stages. The results of the kinetic analysis show that Prout-Tompkins relationship and two-dimensional phase boundary reaction give best fit of the data for both pure salt as well as mixtures. The rate constants of acceleratory and decay periods are enhanced remarkably by adding REO admixtures and their catalytical activity is in the order La₂O₃>Sm₂O₃>Gd₂O₃ >Ce₂O₃. The plausible mechanism of decomposition and the role of admixture there on has been discussed in the light of electron transfer process.     

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.     

Ab initio calculation of the dipole polarizabilities of unsaturated hydrocarbons

Finite-field SCF MO calculations of polarizability are reported for ethene, benzene and naphthalene using three good gaussian basis sets Double-zeta wavefunctions yield values of α_LL and α_MM in agreement with experiment but the calculated α_NN is half the experimental value. Polarization functions when present preferentially improve α_NN. (L,M) and N refer to the molecular long, medium and normal axes, respectively.) STO-4G results are given for benzene, naphthalene, azulene, anthracene and phenanthrene, and the agreement with the experiment is reasonable after scaling the calculated α_LL and α_MM by a constant factor. The calculated α_MM are an order of magnitude too low.     

Kinetics of the thermal decomposition of cadmium carbonate (CdCO3)

Cadmium carbonate used in the study was prepared from cadmium chloride, ammonium carbonate and ammonia. The X-ray powder diffraction, infrared spectral and chemical analysis conducted on the product show that the sample is of analytically acceptable purity. The thermal decomposition kinetics of cadmium carbonate was then studied by using the isothermal thermogravimetric method under a flow of dry nitrogen gas. The decomposition kinetics is best described by a two-dimensional phase boundary reaction mechanism (R ₂). An activation energy (E _a) of 135.006 kJ·mol^?1 and natural logarithm of the frequency factor (lnZ) of 16.754 were obtained in the range of 9 temperatures (400, 390, 380, 370, 360, 350, 340, 330 and 320°C).     

Thermal and FTIR spectral studies of N,N′-diphenylguanidine

Thermal decomposition of N,N??-diphenylguanidine (DPG) was investigated by simultaneous TG/DSC-FTIR techniques under nonisothermal conditions. Online FTIR measurements illustrate that aniline is a major product of DPG decomposition. The observation that the activation energy depends on the extent of conversion indicates that the DPG decomposition kinetics features multiple processes. The initial elimination of aniline from DPG involves two pathways because of the isomerization of DPG. Mass spectrometry and thin film chromatography suggest that there are two major intermediate products with the major one of C₂₁N₃H₁₇. The most probable kinetic model deduced through multivariate nonlinear regression method agrees well with the experimental data with a correlation coefficient of 0.9998. The temperature-independent function of conversion f(??), activation energy E and the pre-exponential factor A of DPG decomposition was also established through model-fitting method in this research.     

Differential scanning calorimetry study of the thermal decomposition of peroxides in the absence of a solvent

The thermal decompositions of benzoyl peroxide (Bz₂O₂), dicumyl peroxide (DICUP) and α, α′-bis (t-butylperoxy)m/p-diisopropylbenzene (Peroximon F) in the absence of solvents have been studied by means ofDSC alone. The DSC curves allowed calculation of the half-lifetime (t _1/2) and the time (t ₁) required to decompose the whole of the peroxides. Thet ₁, andt _1/2 values found for the pure peroxides are lower than those in the literature for decomposition in solution. The heat of decomposition and the activation energy for each peroxide are reported.     

Investigation of the differentiation of kinetic models

The differentiation of known kinetic models in appropriately chosen coordinate systems has been investigated. A new method of defining the control of chemical reaction rate has been presented, the suggested method being based on the use of known kinetic model equations. It consists in comparing the respective model courses with the experimental. For isothermal conditions, the model curves, f(α) vs. α, are compared with the experimental DTG vs. TG. For conditions of linear temperature increase, however, model courses of the type (1/f(α) (df(α)/dα) vs. α and corresponding experimental curves {[(DDTG/DTG²)—(Eγ/RT²)](1/DTG)} vs. TG are used for comparison: such visual comparison allows a rapid estimation of the closeness of experimental results and predicted models. This method was verified with positive results with experimental material under isothermal conditions (for the thermal decomposition of PbSO₄ and for the oxidation of copper in air) and for conditions of linear temperature increase (for the oxidation of copper in air).     

Development of master curves for discriminating the mechanism of solid state reactions from experimental data obtained by using the cyclic and controlled rate thermal analysis

The cyclic and Controlled Rate Thermal Analysis method (CRTA) has been used. The two rates automatically selected in the cyclic curve are small enough to allow the two states of the sample to be compared have nearly the same reacted fraction. Thus, the activation energy can be calculated without previous knowledge of the actual reaction mechanism. Provided that the activation energy,E, is known, a procedure has been developed for determining the kinetic law obeyed by the reaction by means of master curves that represent the values of the reacted fraction, α, as a function of?E/R(1/T-1/T _0.5),T _0.5 being the temperature at which α=0.5. This procedure has been tested by studying the thermal decomposition reaction of BaCO₃.     

The particle dimension controlling synthesis of α-MnO2 nanowires with enhanced catalytic activity on the thermal decomposition of ammonium perchlorate

Hydrothermal method synthesis of α-MnO₂ nanowires has been achieved at different temperatures in this work. X-ray diffraction and transmission electron microscopy confirmed the pure phase of the α-MnO₂ nanowires. All of the samples crystallized in a single-phase nanowires shape. The α-MnO₂ nanowires diameter increased from 11 nm to 21 nm with the increase in hydrothermal temperature from 120 °C to 200 °C. The α-MnO₂ catalytic activity on the decomposition of ammonium perchlorate (AP) was characterized through thermogravimetric analysis. The decomposition rate of AP with the addition of α-MnO₂ was size relative. The 11 nm MnO₂ nanowires exhibited the best catalytic activity, which lowered the high-temperature peak of AP by 130 °C.     

Kinetic analysis for non-isothermal decomposition of un-irradiated and gamma-irradiated potassium bromate

The thermal decomposition of un-irradiated and gamma-irradiated potassium bromate (KBrO₃) was performed under non-isothermal conditions at different heating rates (5, 10, 15 and 20 K min^?1). The data was analysed using isoconversional and non-isoconversional methods. The kinetic parameters of thermal decomposition process were obtained by three model-free isoconversional methods: Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose and Friedman. Irradiation enhances the decomposition and the effect increases with the irradiation dose. The activation energy decreases on irradiation. Kinetic analysis of data in view of various solid-state reaction models showed that the decomposition of un-irradiated and irradiated anhydrous KBrO₃ is best described by the Avrami–Erofeev model equation, [?ln(l?α)]^1/2 = kt.     

Kinetics of free-surface decomposition of dolomite single crystals and powders analyzed thermogravimetrically by the third-law method

The results of our thermogravimetric experiments on the decompositions of dolomite crystals and powders and some data reported in the literature were used for the determination of the E parameter of the Arrhenius equation by the third-law method and estimation of the self-cooling effect on the results of these determinations. The experimental values of the E parameters, obtained under different conditions by the third-law method, are in excellent agreement with the theoretically predicted values based on the mechanism of congruent decomposition of CaMg(CO₃)₂ into gaseous CO₂, CaO and MgO with the simultaneous condensation of low-volatility CaO and MgO molecules. The second important result of this study is the first quantitative comparison of absolute rates of decomposition of powder samples and single crystals. Based on these results, a simple procedure was proposed for the determination of the E parameter by the third-law method from the data obtained for powder samples. It consists in the evaluation of the absolute decomposition rate of a powder sample (reduced to the unit of the outer surface area of a pellet formed by the powder sample in a cylindrical crucible). The value received is lowered by the empirical factor and then used for the calculation of the E parameter by the third-law method. The value of this factor (2.8±0.4) does not depend on the temperature, residual pressure of air in the reactor, grain size and mass of a powder sample. This procedure permits to expand the application of the third-law method to the determination of decomposition kinetics for many solids available only in the powder form.     

Catalytic effect investigation of α-Fe2O3 and α-Fe2O3-CMS nanocomposites on the thermal behavior of NC/DEGDN mixture: DSC measurements and kinetic modeling

In this work, the thermal behavior and kinetics of energetic systems containing α-Fe₂O₃ and iron oxide–carbon mesospheres (α-Fe₂O₃-CMS) with nitrocellulose (NC)/diethylene glycol dinitrate (DEGDN)-based composites have been investigated using differential scanning calorimetry DSC and four isoconversional kinetic methods, respectively. The obtained results indicate that NC/DEGDN show only one decomposition peak, corresponding to the decomposition of the nitrate esters. Furthermore, the introduction of α-Fe₂O₃ and α-Fe₂O₃-CMS have lowered the peak temperature by 3.1 °C and 4.7 °C, respectively. Besides, the activation energy of the thermal decomposition of NC/DEGDN was decreased by 11.9 kJ/mol and 27.97 kJ/mol, after the introduction of α-Fe₂O₃ NPs and α-Fe₂O₃ NPs supported on CMS. These results confirm the good catalytic effect of the added catalysts on the thermal decomposition of the NC/DEGDN mixtures. However, the best catalytic effect was provided by the α-Fe₂O₃-CMS. Furthermore, the three considered systems were found to decompose according to different integral models g(α).     

Metal triflate catalyzed highly regio- and stereoselective 1,2-bromoazidation of alkenes using NBS and TMSN3 as the bromine and azide sources

Metal triflate catalyzed 1,2-bromoazidation of alkenes was performed using N-bromosuccinimide (NBS) and trimethylsilyl azide (TMSN₃) as the bromine and azide sources, respectively. Among the metal triflates, Zn(OTf)₂ was found to be the best catalyst. This catalytic process represents a highly regioselective, stereoselective and high yielding method for the synthesis of anti-1,2-bromoazides from a variety of alkenes including α,β-unsaturated carbonyl compounds.     

Kinetic model of copper electrodeposition in sulfate solution containing trisodium citrate complexing agent

Simultaneous solution of two kinetic models of electrodeposition of copper in sulfate solution is studied in this paper. Bulk concentration of species involved in the numerical solution was calculated using MATLAB software. COMSOL Multiphysics software was used for the numerical solution of copper electrodeposition. Numerical results were evaluated using experimental data obtained by linear sweep voltammetry technique. The experimental data was almost fitted using COMSOL optimization physic module. It was found that kinetic parameters of Cu²⁺ (k^1Cu), Cu¹⁺ (k_2Cu), and CuCitH (k_1CuCitH) and diffusion coefficient and charge transfer coefficient of Cu²⁺ (\({D_{C{u^{2 + }}}}\), α_Cu1), Cu¹⁺ (α_Cu2) and CuCitH (D_CuCitH, α_CuCitH) affect the fitting of the experimental data with the computed ones. The variables such as concentration profiles and optimum kinetic parameters that cannot be experimentally measured were achieved by analysis of the model. The parameters, that not affect the fitting, were recognized and kept constant when using the optimization.