Kinetics of thermal decomposition of metal acetates

The acetates of magnesium, nickel, copper, manganese, sodium and barium were subjected to thermal decomposition by means of thermogravimetric techniques (TG) under a constant flow of nitrogen. The decompositions occurred in steps and the kinetics of every set of reactions was determined by the Coats and Redfern method. These results were analysed to establish the decomposition kinetics and hence to calculate activation energies. The activation energies were also determined by applying the Horowitz-Hugh method, which yielded similar results.

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Zusammenfassung Mittels TG in konstantem Stickstoffstrom wurde die thermische Zersetzung von Magnesium-, Nickel-, Kupfer-, Mangan-, Natrium- und Bariumazetat untersucht. Es erfolgte eine schrittweise Zersetzung, die Kinetik für jede der Reaktionen wurde mit Hilfe der Methode von Coats und Redfern bestimmt. Diese Ergebnisse wurden genutzt, um die Kinetik der Zersetzung und anschlie\end die Aktivierungsenergien festzustellen. Ähnliche Werte für die Aktivierungsenergien erhielt man auch mit Hilfe der Methode von Horowitz Hugh.

     

Thermogravimetric analysis of peat decomposition under different oxygen concentrations

Smoldering combustion of peat is of global concern as a natural hazard to consume sequestered carbon and form wide-area haze. It is affected by thermal decomposition kinetics of peat and the diffusion and availability of oxygen. In this work, thermal decomposition behavior of peat was investigated using thermogravimetric analysis under the atmosphere with different oxygen concentrations. The results showed that thermal decomposition process of peat could be divided into three stages: dehydration, oxidative pyrolysis of organic matters into volatiles and char, and oxidation of the generated char. The apparent activation energies of peat decomposition under different oxygen concentrations were calculated by model-free methods of Kissinger, FWO, Starink, Gyulai, and Friedman. A two-step reaction model was proposed to describe thermal decomposition kinetics of peat (excluding dehydration stage) and the effect of oxygen concentration on the kinetic parameters was discussed. These results provide basic data for smoldering modeling of peat.     

Preparation and thermal decomposition of certain. Substituted bis-(thenoyl) peroxides

The effect of various substituents on the rates of thermal decomposition of substituted bis-(thenoyl) peroxides has been investigated. Nine unreported peroxides were prepared, including derivatives of 2- and 3-thenoic acids. The thermal decomposition rates of these peroxides were examined, in the presence of styrene as a free radical scavenger. First order kinetics were observed in all cases studied. In general it was found that electron releasing substituents increase, while electron withdrawing groups decrease, the decomposition rate; the only exception being bis-(5-nitro-3-thenoyl) peroxide. Entropies and energies of activation were determined and found to be linearly related for the peroxides studied.     

Thermal and kinetic analysis of uranium salts

The thermal decomposition kinetics of UO₂C₂O₄·3H₂O were studied by TG method in a flowing nitrogen, air, and oxygen atmospheres. It is found that UO₂C₂O₄·3H₂O decomposes to uranium oxides in four stages in all atmosphere. The first two stages are the same in the whole atmosphere that correspond to dehydration reactions. The last two stages correspond to decomposition reactions. Final decomposition products are determined with X-Ray powder diffraction method. Decomposition mechanisms are different in nitrogen atmosphere from air and oxygen atmosphere. The activation energies of all reactions were calculated by model-free (KAS and FWO) methods. For investigation of reaction models, 13 kinetic model equations were tested and correct models, giving the highest linear regression, lowest standard deviation, and agreement of activation energy value to those obtained from KAS and FWO equations were found. The optimized value of activation energy and Arrhenius factor were calculated with the best model equation. Using these values, thermodynamic functions (??H ^*, ??S ^*, and ??G ^*) were calculated.     

Energy of activation for the decomposition of the alkaline-earth carbonates from thermogravimetric data

Activation energies for the vacuum thermal decomposition of calcium, strontium and barium carbonates have been determined from thermogravimetric data, using the Coats and Redfern equation. A computer program, written in 4100 Algol, was used to process the data and to obtain the order (n) of the decomposition reactions. In all three cases, a value ofn=2/3 was in closest agreement with the experimental results, suggesting that decomposition occurs at a progressively shrinking spherical interface. The energies of activation obtained were in close agreement with the corresponding values of the enthalpy of decomposition, calculated at the temperature at which half of the sample had decomposed.     

Preparation and characterization of microcapsulated red phosphorus and its multi-step thermal oxidation processes based on kinetic approach

Aluminium hydroxide/melamine–formaldehyde resin microcapsulated red phosphorus (MRP) was successfully prepared by two-step processes. The microcapsulated red phosphorus was characterized with Fouriertransform infrared spectroscopy (FTIR) and scanning electron microscope (SEM). Meanwhile its water absorption, thermostability were also determined. The results show that the MRP exhibited lower water absorption and higher thermostability compared with red phosphorus (RP) itself. Moreover, the thermal oxidative decomposition kinetics of MRP was investigated by TG/DTG and DTA in air atmosphere using non-isothermal experiments. The results show that the MRP’s decomposition consisted of two steps. And the apparent activation energies E_α was determined by applying both the Ozawa–Flynn–Wall (OFW) and Kissinger, Akahira and Sunose (KAS) methods. It was found that the dependence of E_α on α is complex. Both of the steps in this study fitted Sestak–Berggren (SB) model in overall reaction controlled kinetics and the corresponding model parameters, n, m, A were obtained. The simulated curves were fitted to experimental curves by plotting dα/dt vs. temperature at different heating rates.     

新型阻燃聚丙烯腈共聚物在空气中的非等温热分解动力学

用O,O-二乙基-O-烯丙基硫代磷酸酯(DATP)与丙烯腈共聚合成了新型阻燃聚丙烯腈共聚物(FR-PAN), 对其在空气中的非等温动力学通过TG-DTG技术进行了研究, 并通过极限氧指数法(LOI)考查了FR-PAN的阻燃性能; 利用Kissinger方法和Flynn-Wall-Ozawa (FWO)方法计算出了FR-PAN热降解过程中的表观活化能; 采用Satava-Sestak方法通过对不同机理模型的选取, 确定了FR-PAN的热降解机理. 结果表明, 由Kissinger法和FWO法所计算得到的FR-PAN的表观活化能分别为119.62和123.99 kJ•mol－1; FR-PAN的热降解反应属于随机成核和随后增长机理, 其机理函数为G(α)＝－ln(1－α), 反应级数n＝1.     

NEW POLY(METHACRYLATE)S CONTAINING OXIME ESTERS MOIETIES BASED ON CYCLOHEXANON AND CYCLOPENTANON

The synthesis of two new methacrylates such as 2-[(cyclohexylideneamino)oxy]-2-oxoethyl methylacrylate (CHOEMA)and 2-[(cyclopentylideneamino)oxy]-2-oxoethyl methylacrylate(CPOEMA)are described.The monomers produced from the reaction of corresponding cyclohexanone O-(2-chloroacetyl)oxime and cyclopentanone O-(2- chloroacetyl)oxime with sodium methacrylate was polymerized in 1,4-dioxane solution at 65℃using AIBN as an initiator. The monomers and their polymers were characterized by IR,~1H- and ~(13)C-NMR s...     

Thermal Kinetics and Decomposition Mechanism of Methylphenylphosphinic Acid and Diphenylphosphinic Acid

Thermal degradation and degradation kinetics of methylphenylphosphinic acid（MPPA） and diphenyl- phosphinic acid（DPPA） were investigated via thermogravimetric analysis（TGA） technique under non-isothermal conditions. The activation energies of the decomposition process for the two compounds were calculated through the Friedman and Kissinger-Akahira-Sunose（KAS） methods. The thermal decomposition mechanism was investigated by the Criado method based on a set of TGA data obtained at different heating rates. It was shown that the activation energies calculated from the decomposition reaction by different methods were consistent with each other. The results show that the probable model for the degradation of MPPA and DPPA agreed with the two-dimensional（D2） and three-dimensional（D4） diffusion models, respectively. Moreover, the thermodynamic functions（△H, △S, △G） of the two decomnosition reactions were also calculated.     

Pyrolytic characteristics and kinetics of pistachio shell by thermogravimetric analysis

Pyrolytic characteristics and kinetics of pistachio shell were studied using a thermogravimetric analyzer in 50?C800?°C temperature range under nitrogen atmosphere at 2, 10, and 15?°C?min^?1 heating rates. Pyrolysis process was accomplished at four distinct stages which can mainly be attributed to removal of water, decomposition of hemicellulose, decomposition of cellulose, and decomposition of lignin, respectively. The activation energies, pre-exponential factors, and reaction orders of active pyrolysis stages were calculated by Arrhenius, Coats?CRedfern, and Horowitz?CMetzger model-fitting methods, while activation energies were additionaly determined by Flynn?CWall?COzawa model-free method. Average activation energies of the second and third stages calculated from model-fitting methods were in the range of 121?C187 and 320?C353?kJ?mol^?1, respectively. The FWO method yielded a compatible result (153?kJ?mol^?1) for the second stage but a lower result (187?kJ?mol^?1) for the third stage. The existence of kinetic compensation effect was evident.     

Thermal and kinetic analysis of uranium salts

In this study the thermal decomposition kinetics of uranyl acetate dehydrate [UO₂(CH₃COO)₂·2H₂O] were studied by thermogravimetry method in flowing nitrogen, air, and oxygen atmospheres. Decomposition process involved two stages for completion in all atmosphere conditions. The first stage corresponded to the removal of two?moles of crystal water. The decomposition reaction mechanism of the second stage in nitrogen atmosphere was different from that in air and oxygen atmospheres. Final decomposition products were determined with X-ray powder diffraction method. According to these data, UO₂ is the final product in nitrogen atmosphere, whereas U₃O₈ is the final product in air and oxygen atmospheres. The calculations of activation energies of all reactions were realized by means of model-free and modeling methods. Kissinger?CAkahira?CSunose (KAS) and Flynn?CWall?COzawa (FWO) methods were selected for model-free calculations. For investigation of reaction models, 13 kinetic model equations were tested. The model, which gave the highest linear regression, the lowest standard deviation, and an activation energy value which was close to those obtained from KAS and FWO equations, was selected as the appropriate model. The optimized value of activation energy and Arrhenius factor were calculated using the selected model equation. Using these values, thermodynamic functions (??H*, ??S*, and ??G*) were calculated.     

Kinetics of Thermal Decomposition of Solid Propellant Based on Aluminum and Ammonium Perchlorate

Kinetic regularities of the mass loss and heat and-gas release were studied in the thermal decomposition of a solid propellant composed of aluminum, ammonium perchlorate, and a polymer binder. It was shown that, under heating from 40 to 340°C under permanent vacuum conditions, propellant samples decompose without ignition, with the limiting mass loss in the decomposition being 48%. When experiments were performed in air, the propellant formulation decomposes with sharp ignition, with the inflammation temperature (270–287°C) and amount of volatiles released by this instant of time (10–16 wt %) dependent on the heating rate. The kinetic regularities of the mass loss in the decomposition of a solid propellant were described in terms of the polychromatic kinetics model that assumes that the reaction system has ensembles of particles differing in reactivity. The distribution functions of the mass fractions of the propellant by activation energies of decomposition were calculated. The heat release kinetics in the decomposition of a propellant formulation in the temperature range 153–270°C in a closed evacuated system is described by a sum of equations for two parallel reactions: 1st-order reaction with a heat effect Q₁ = 200 ± 5 kJ kg^–1 and 1st-order autocatalysis with heat effect Q₂ = 1900 ± 50 kJ kg–1. The rate constants and the activation parameters of the process were determined.

     

Thermal studies of some mixed complexes of Mn(II) with picrate and nitrogen donors

The thermal decompositions of nine mixed ligand complexes of Mn(II) containing picrate and mono- or bidentate nitrogen ligands were studied by thermogravimetry. The kinetics of decomposition were examined by using the Coats-Redfern and Horowitz-Metzger equations; the decomposition was in all cases of the first order. The activation energies and other kinetic parameters were computed. The decomposition mechanisms exhibited a similar character for all the studied compounds. It was observed from the TG curves that the complexes decomposed to give six-coordinate intermediates, formed from substitution of the picrate into the inner coordination sphere. These intermediates decomposed to Mn(II) picrate and finally to Mn₂O₃.     

Kinetics and mechanism of non-isothermal dehydration of nickel acetate tetrahydrate in air

The non-isothermal decomposition of nickel acetate tetrahydrate in air was studied using thermogravimetry (TG)–DTG, differential scanning calorimetry (DSC) and XRD techniques. The decomposition occurs in two major steps and the final product is NiO. The dependence of mass loss on heating rates in TG measurements imply that the dehydration and hydrolysis concur at temperature below 240 °C; the apparent activation energies calculated by Flynn, Wall and Ozawa (FWO) isoconversional method indicate the existence of a consecutive process. The kinetics of the first major decomposition step (below 240 °C) was obtained with multivariate non-linear regression of four measurements at different heating rates. According to the kinetics results from non-linear regression, the dehydration reaction (F1 type with an activation energy E of 167.7 kJ/mol) goes first. After the loss of almost half of water, the retained water and acetate are linked to each other by hydrogen bonding, so dehydration and hydrolysis concur. The pathway with a lower E is related to the hydrolysis process and the other is corresponding to the dehydration process. The simulations of reactants at different heating rates were used to verify the correctness of the reaction model. With the kinetics results, the dehydration mechanism was discussed for the first time.     

Comparative Thermogravimetric Studies of Poly(ether-ketone/sulfone) Imides and Their Parent Polymers: I. Poly(ether-ketone/sulfone) ethylimide

Thermogravimetry (TG) was employed to study the thermal degradation kinetics of poly(etherketone/sulfone)ethylimide (PEK-IE and PES-IE). The corresponding decomposition activation energies and reaction orders were obtained and the comparison was made with their parent polymerspoly(ether-ketone/sulfone) with Cardo group (PEK-C and PES-C). The results show that the degradation activation energies of PEK-IE and PES-IE were lower than that of PEK-C and PES-C; and two stages of the degradation process were found for all the four polymers. For PEK-IE and PES-IE, the activation energies in the first decomposition stage are much lower than that in the second stage and the two stages can be taken as slow induction and fast degradation, whereas for PEK-C and PES-C the activation energies in the first decomposition stage are larger than that in the second stage, and the two stages can both be taken as two fast degradation stages. The decomposition mechanism of the two stages was also speculated.This revised version was published online in November 2005 with corrections to the Cover Date.     

Decomposition kinetics of the AlH3 polymorphs

Aluminum hydride polymorphs (alpha-AlH3, beta-AlH3, and gamma-AlH3) were prepared by organometallic synthesis. Hydrogen capacities approaching 10 wt % at desorption temperatures less than 100 degrees C have been demonstrated with freshly prepared AlH3. The temperature-dependent rate constants were determined by measuring the isothermal hydrogen evolution between 60 degrees C and 140 degrees C. Fractional decomposition curves showed good fits using both the second and third-order Avrami-Erofeyev equations, indicating that the decomposition kinetics are controlled by nucleation and growth of the aluminum phase in two and three dimensions. The large activation energies measured for the AlH3 polymorphs suggest that the decomposition occurs via an activated complex mechanism with complexes consisting of approximately nine AlH3 molecules (1-2 unit cells for alpha-AlH3).     

Influence of molecular weight and chemical structure of soft segment in reaction kinetics of polycarbonate diols with 4,4′-diphenylmethane diisocyanate

This third paper in this series regarding the mechanism and kinetics of urethane systems presents the results obtained in the study of the influence of molecular weight and chemical structure of several polycarbonate diols on the polycondensation reaction with 4,4′-diphenylmethane diisocyanate (MDI), comparing them with those obtained previously for condensation reaction with p-tolyl isocyanate (p-TI). The substitution effect induced in the second isocyanate group by the reaction of the first isocyanate group of a symmetric diisocyanate likes MDI has been studied by size exclusion chromatography (SEC) using a model monoalcohol. The condensation reaction kinetics is adequately described by an autocatalyzed third order rate equation. The values obtained for rate constants, using a Runge-Kutta mathematical model, suggest association phenomena by hydrogen bonding implying hydroxyl groups but also urethane groups. In bulk and in stoichiometric conditions, the association phenomena observed increase proportionally on one hand, to the decrease of molecular weight of macrodiol and on the other hand, to the tendency to form intramolecular hydrogen bonds. The activation energies were obtained from the evaluation of kinetic data at different temperatures in the range 45-65 °C. As association phenomena increase, activation energies decrease. The slightly higher activation energies obtained for polycondensation compared to condensation are explained because of the rapid increase of viscosity of the medium.     

TG studies of a composite solid rocket propellant based on HTPB-binder

Thermal decomposition kinetics of solid rocket propellants based on hydroxyl-terminated polybutadiene-HTPB binder was studied by applying the Arrhenius and Flynn-Wall-Ozawa's methods. The thermal decomposition data of the propellant samples were analyzed by thermogravimetric analysis (TG/DTG) at different heating rates in the temperature range of 300-1200 K. TG curves showed that the thermal degradation occurred in three main stages regardless of the plasticizer (DOA) raw material, the partial HTPB/IPDI binder and the total ammonium perchlorate decompositions. The kinetic parameters E _a (activation energy) and A (pre-exponential factor) and the compensation parameter (S _p) were determined. The apparent activation energies obtained from different methods showed a very good agreement. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermogravimetry study of pyrolytic characteristics and kinetics of the giant wetland plant Phragmites australis

The pyrolytic characteristics and kinetics of wetland plant Phragmites australis was investigated using thermogravimetric method from 50 to 800?°C in an inert argon atmosphere at different heating rates of 5, 10, 25, 30, and 50?°C?min^?1. The kinetic parameters of activation energy and frequency factor were deduced by appropriate methods. The results showed that three stages appeared in the thermal degradation process. The most probable mechanism functions were described, and the average apparent activation energy was deduced as 291.8?kJ?mol^?1, and corresponding pre-exponential factors were determined as well. The results suggested that the most probable reaction mechanisms could be described by different models within different temperature ranges. It showed that the apparent activation energies and the corresponding pre-exponential factors could be obtained at different conversion rates. The results suggested that the experimental results and kinetic parameters provided useful information for the design of pyrolytic processing system using P. australis as feedstock.     

Curing kinetics and thermal stability of epoxy blends containing phosphorous-oxirane with aromatic amide-amine as curing agents

This article describes the synthesis of a series of aromatic amide-amines and their potential use as epoxy hardeners. These amines were synthesized by the reaction of L-phenylalanine（PA） with diamines of different structures i.e.1,4- phenylene diamine（PD）,1,5-diamino naphthalene（N）,4,4’-（9-fluorenyllidene）-dianiline（F）,4,4’-diaminodiphenyl sulphide （DS） and 3,4’-oxydianiline（O） in a stoichiometric ratio（1:1）.Structural characterization of synthesized amide-amines was done with the help of elemental analysis and spectroscopic techniques viz.FT-IR,¹H-NMR and ¹³C-NMR.An epoxy blend was prepared by mixing tris（glycidyloxy） phosphine oxide（TGPO） with conventional epoxy i.e.diglycidyl ether of bisphenol-A（DGEBA） in an equivalent ratio of 2:3 to incorporate phosphorous into the main chain.The curing kinetics of the epoxy blend with synthesized aromatic amide-amines was investigated by non-isothermal DSC technique using multiple heating rate method（5,10,15 and 20 K/min.）.The activation energies were determined by fitting the experimental data into Kissinger and Ozawa kinetic models.The activation energies obtained through Ozawa method were slightly higher than those of Kissinger method but were comparable.However,both the energies were found to be dependent on the structure of amines.The thermal stability and weight loss behavior of isothermally cured thermosets were also investigated using thermogravimetric analysis（TGA） in nitrogen atmosphere.All the samples showed improved thermal stability in terms of char yield than using only amines as hardeners.