Kinetics Of Isothermal Decomposition Research Articles

A study on the isothermal decomposition kinetics of energetic cellulose-rich materials using a vacuum stability test

A study on the isothermal decomposition kinetics of energetic cellulose-rich materials using a vacuum stability test

Semi–interpenetrating networks based on epoxy resin and oligophosphonate: Comparative effect of three hardeners on the thermal and fire properties

Traditional materials are being constantly replaced by synthetic polymers, most of which are highly flammable. Epoxy resins are versatile and among the most important class of polymers, due to their multiple crosslinking capacity endowed by the oxirane ring, their applications ranging from adhesives to aeronautics. This study investigates the comparative effect of three hardeners (aromatic, cycloaliphatic, aliphatic) and the addition of an oligophosphonate on the thermal behavior and fire performance of bisphenol A diglycidyl ether semi–interpenetrating polymer networks. Networks with epoxy resin and 2% phosphorus loading were prepared. Evolved gases analyses, thermal and fire experiments were used to propose the action mode of the hardeners and oligophosphonate in the fire performance enhancement of the epoxy resin. Non–isothermal decomposition kinetics studies were conducted. The oligophosphonate in the epoxy resins promoted a significant reduction in the peak of heat release rate values (33 to 55%) in microscale combustion calorimeter experiments. A UL 94–V0 classification was achieved for the network with oligophosphonate and aromatic curing agent. The obtained results recommend the semi–interpenetrating network cured with aromatic hardener as a potential matrix for flame retardant composites or coatings.

Isothermal decomposition kinetics and possible decomposition process of pentaerythritol tetranitrate

ABSTRACT The isothermal decomposition kinetics of pentaerythritol tetranitrate (PETN) was studied through a self-established isothermal thermal decomposition gas metering device. The pressure versus time curves of the gas generated by PETN decomposition under different temperature conditions were divided into two parts, showing the remarkable effect of temperature and melting point on PETN decomposition. Model-fitting calculation result showed that the decomposition of PETN at 90–110°C conformed to the No. 8 model, namely, the anti-Jander equation, and a corresponding activation energy Ea of 107.1 kJ·mol−1 with ln(A/s−1) = 6.97. Within a temperature range of 112–130°C, the decomposition model of PETN conformed to the No. 28 model with reaction order n = 4. The device was simultaneously used to predict the time of PETN to reach a certain decomposition extent. Results showed that the time of PETN was extrapolated to 54.4 years when the extent of reaction reached 0.1% at ambient temperature (25°C). Furthermore, Fourier transform infrared spectroscopy and scanning electron microscopy were used to characterize PETN decomposition residues with different decomposition depths to understand the decomposition process.

Study on the isothermal decomposition kinetics and mechanism of nitrocellulose

Nitrocellulose (NC) was investigated via an improved isothermal decomposition dynamics research instrument at temperature intervals from 378.15 to 398.15 K. Arrhenius equation and model-fitting method were used to calculate the thermal decomposition kinetic parameters. Results of these approaches were consistent, with an average Ea of 144.7 kJ mol−1 and lnA of 27.39. The storage life of NC was estimated using the Berthelot equation. Results showed that the effective storage life of NC at ambient temperature (298.15 K) was extrapolated to 10.57 years with the extent of reaction reaching 0.1% and 52.91 years with the extent of reaction reaching 0.5%. The thermodecomposition gas and residues of NC were verified by GC, FT-IR, and SEM. The possible reaction mechanism of the isothermal decomposition of NC was provided.

Isothermal decomposition kinetics of nickel (II) hydroxide powder

Nickel (II) hydroxide powder was investigated by thermogravimetry for isothermal decomposition kinetics and verification of the Ni–O–H ternary phase diagram at low temperatures. The activation energy and frequency factor were measured as Ea=134kJ/mol and A=1.27×1010s−1, respectively. The validity of the first-order random nucleation model was confirmed, as opposed to diffusion and or moving-boundary models. The dependence of TGA results on specimen size was noted. The Ni–Ni(OH)2–NiO phase triangle was confirmed. Accordingly, a thermodynamic description of the system was established in the Ni-rich corner, and the isotherm at room temperature is calculated.

Mechanisms and kinetics of the decomposition of calcium barium sulfoaluminate

To control the manufacturing process of the new clinker system of belite-calcium barium sulfoaluminate cement, the mechanisms and kinetics of the decomposition of calcium barium sulfoaluminate (2.75CaO·1.25BaO·3Al2O3·SO3, Ca2.75Ba1.25Al6$O16, C2.75B1.25A3$) were investigated by SEM–EDS (scanning electron microscope–energy dispersive spectroscope), DSC–TG (differential scanning calorimetry–thermogravimetry), and X-ray diffraction analyses. Isothermal decomposition kinetics was studied by the model fitting and differential isoconversional method. The results show that the C2.75B1.25A3$ starts to decompose at around 1,370 °C, and generates mainly BaO·Al2O3, 3CaO·Al2O3, and SO3. The model fitting result indicates that the decomposition of C2.75B1.25A3$ is controlled by the interfacial chemical reaction mechanism and that the decomposition kinetics is well characterized by the spherical model equation R3 = 1 − (1 − α)1/3 (R3 is the equation symbol, and α is the degree of decomposition) with an apparent activation energy of 518 kJ mol−1. The results of the differential isoconversional method match the results of the model fitting method.

Thermal decomposition and non-isothermal decomposition kinetics of carbamazepine

The thermal stability and kinetics of isothermal decomposition of carbamazepine were studied under isothermal conditions by thermogravimetry (TGA) and differential scanning calorimetry (DSC) at three heating rates. Particularly, transformation of crystal forms occurs at 153.75°C. The activation energy of this thermal decomposition process was calculated from the analysis of TG curves by Flynn-Wall-Ozawa, Doyle, distributed activation energy model, Satava-Sestak and Kissinger methods. There were two different stages of thermal decomposition process. For the first stage, E and logA [s−1] were determined to be 42.51 kJ mol−1 and 3.45, respectively. In the second stage, E and logA [s−1] were 47.75 kJ mol−1 and 3.80. The mechanism of thermal decomposition was Avrami-Erofeev (the reaction order, n = 1/3), with integral form G(α) = [−ln(1 − α)]1/3 (α = ∼0.1–0.8) in the first stage and Avrami-Erofeev (the reaction order, n = 1) with integral form G(α) = −ln(1 − α) (α = ∼0.9–0.99) in the second stage. Moreover, ΔH ≠, ΔS ≠, ΔG ≠ values were 37.84 kJ mol−1, −192.41 J mol−1 K−1, 146.32 kJ mol−1 and 42.68 kJ mol−1, −186.41 J mol−1 K−1, 156.26 kJ mol−1 for the first and second stage, respectively.

Thermal Stability of Ionic Liquids for Their Application as New Absorbents

The thermal stability of three ionic liquids (ILs) with the same anion and different lengths of imadazolium cations was investigated using thermogravimetric analysis to consider their usefulness for their potential application as absorbents in absorption heat pumps and refrigeration cycles. First, the influence of experimental conditions such as sample mass, heating rate, and atmosphere was analyzed for one of these ILs. Afterward, dynamic and isothermal studies were performed for the three ILs. From dynamic results, onset temperature has been often selected to define the thermal stability. Nevertheless, to obtain a more precise value, long-term isothermal studies at temperatures lower than the onset one were required, showing that the thermal stability decreases slightly as the length of the cations increases. Using the Arrhenius relationship, the kinetics of isothermal decomposition was also evaluated, and an upper limit for the “working” time of these ILs as potential absorbents was estimated.

Non-isothermal decomposition kinetics of diosgenin

The thermal stability and kinetics of isothermal decomposition of diosgenin were studied by thermogravimetry (TG) and Differential Scanning Calorimeter (DSC). The activation energy of the thermal decomposition process was determined from the analysis of TG curves by the methods of Flynn-Wall-Ozawa, Doyle, Satava-Sestak and Kissinger, respectively. The mechanism of thermal decomposition was determined to be Avrami-Erofeev equation (n = 1/3, n is the reaction order) with integral form G(α) = [−ln(1 − α)]1/3 (α = 0.10–0.80). Ea and logA [s−1] were determined to be 44.10 kJ mol−1 and 3.12, respectively. Moreover, the thermodynamics properties of ΔH≠, ΔS≠, and ΔG≠ of this reaction were 38.18 kJ mol−1, −199.76 J mol−1 K−1, and 164.36 kJ mol−1 in the stage of thermal decomposition.

알킬 아크릴레이트와 관능성 단량체계 다중 Core-Shell 복합입자의 제조

Core 입자로 methyl methacrylate (MMA), ethyl methacrylate (EMA)를 사용하고 shell 입자로 MMA, EMA, 2-hydroxyl ethyl methacrylate (2-HEMA), glycidyl methacrylate (GMA) 및 methacrylic acid (MAA)를 각각 사용하여 개시제 ammonium persulfate (APS), 유화제로 sodium dodecyl benzene sulfonate (SDBS)의 농도(0.01~0.03 wt%), 단량체의 종류와 조성을 변화시켜 수용성 유화중합으로 다중 core-shell복합입자를 제조하여 전환율, 입자경 및 입도분포, 평균분자량, 분자구조, 유리전이온도, 플라즈마 처리후의 접촉각, 등온열분해속도 및 인장강도를 각각 측정하여 다음과 같은 결론을 얻었다. SDBS 농도 0.02 wt%에서 MMA core-(EMA/GMA) shell 복합입자의 전환율이 98.5%로 우수하였고, 입자직경은 SDBS 농도 0.03 wt%에서 EMA core-(MMA/GMA) shell의 복합입자가 <TEX>$0.48{\mu}m$</TEX>로 높게 나왔다. 유리전이온도 측정으로부터 공중합체는 1~2개의 전이곡선 그리고 다중 core-shell 복합입자는 3개의 전이곡선을 얻었다. 전체적으로 접착박리강도의 크기는 shell 단량체가 MMA core인 경우 EMA/MAA > EMA/2-HEMA > EMA/GMA의 순으로 되었다. Multi core-shell composite particles were prepared by the water-born emulsion polymerization of various core monomers such as methyl methacrylate (MMA), ethyl methacrylate (EMA) and shell monomers such as MMA, EMA, 2-hydroxyl ethyl methacrylate (2-HEMA), glycidyl methacrylate (GMA) and methacrylic acid (MAA) in the presence of different concentrations of sodium dodecyl benzene sulfonate (SDBS). The following conclusions are drawn from the conversion, particle size and distribution, average molecular weight, molecular structure, glass transition temperature with DSC, contact angle after plasma treatment, tensile strength and isothermal decomposition kinetics. In the case of the concentration of 0.02 wt% SDBS, the conversion of MMA core-(EMA/GMA) shell composite particles was excellent as 98.5%. In the case of the concentration of 0.03 wt% SDBS, the particle size of EMA core-(MMA/GMA) shell composite particles was high as <TEX>$0.48{\mu}m$</TEX>. We confirmed that 3 points of glass transition temperatures appear for multi core-shell composite particles compared to 1~2 points of glass transition temperatures appear for general copolymer particles. Overall, the adhesion strength of shell composite particles was in the order of EMA/MAA > EMA/2-HEMA > EMA/GMA.

Preparation, characterization, and kinetics of thermolysis of nickel and copper nitrate complexes with 2,2′-bipyridine ligand

Nickel and copper nitrate complexes with 2,2′-bipyridine (bipy) as a N donor and nitrate and water as oxygen donor ligands of the general formula [M(NO3)(C10H8N2)(H2O)3](NO3), where M=Ni and Cu, have been obtained from the corresponding metal nitrate salts. These complexes were characterized by X-ray crystallography, FT-IR, and CHN analysis. Both the complexes have been found to be six coordinated. Their thermal decomposition behaviour was investigated by TG, DTA, and ignition delay measurements. TG–DTA examinations of these complexes revealed multistep thermal decomposition. The corresponding metal oxide residues obtained after thermolysis were identified from their X-ray diffraction patterns (XRD). Kinetics of isothermal decomposition of the complexes was established from both the model-fitting as well as isoconversional methods.

Kinetics of isothermal decomposition of unirradiated and γ-irradiated zirconium acetylacetonate

In this study, isothermal decomposition of unirradiated and γ-irradiated zirconium acetylacetonate Zr(acac)4 using 103 kGy absorbed γ-ray dose was carried out in static air. The isothermal operating temperatures were selected to be 150, 170, 190 and 210°C. The kinetics of the decomposition were followed using both model-fitting and model-free approaches. The results of the model-fitting approach with regard to the investigated data showed that the decomposition behaviour was best described by a first-order (F1) reaction model. The analysis of the data using the model-free approach signified the dependency of activation energy E a on the extent of conversion (α). Pre-γ-irradiation of zirconium acetylacetonate Zr(acac)4 with 103 kGy absorbed γ-ray dose had no significant effect on the thermal decomposition behaviour of Zr(acac)4. The thermodynamic and kinetic parameters of the decomposition process were calculated and evaluated.

Effect of precompression on isothermal decomposition kinetics of pure and doped potassium bromate

Pure and doped samples of potassium bromate (KBrO3) were subjected to precompression and their thermal decomposition kinetics was studied by thermogravimetry at 668 K. The samples decomposed in two stages governed by the same rate law (contracting square equation), but with different rate constants, k1 (for a α ≤ 0.45) and k2 (for α ≥ 0.45), as in the case of uncompressed samples. The rate constants k1 and k2 decreased dramatically on precompression, the decrease being higher for doped samples. Cation dopants (Ba2+, Al3+) caused more desensitization effect than the anion dopants (\( {\text{SO}}_{4}{}^{ 2- } \), PO43−) of the same magnitude of charge and concentration. The results favor ionic diffusion mechanism proposed earlier on the basis of doping studies.

Thermal stability and moisture uptake of 1-alkyl-3-methylimidazolium bromide

The thermal stability of the ionic liquids (ILs) 1-n-butyl-3-methylimidazolium bromide, (BMIM)Br, and 1-n-octyl-3-methylimidazolium bromide, (OMIM)Br, was evaluated through thermogravimetry (TG). Long-term isothermal TG studies revealed that both of these ILs exhibit appreciable decomposition even at temperatures significantly lower than the onset decomposition tempera- ture, previously determined from fast scan TG experi- ments. The long-term TG studies of both the ILs showed linear mass loss as a function of time at each temperature of 10 C interval in the range 533-573 K over a period of 10 h. The kinetics of isothermal decomposition of ILs was analyzed using pseudo-zero-order rate expression. The activation energies for the isothermal decomposition of (BMIM)Br and (OMIM)Br under nitrogen atmosphere are 219.86 and 212.50 kJ mol -1 , respectively. The moisture absorption kinetics of these ILs at 25 C and 30% relative humidity (RH) and at 85 C and 85% RH were also stud- ied. Water uptake of ILs exposed at 25 C/30%RH follows a simple saturation behavior in agreement with Weibull model while that at 85 C/85%RH fortuitously fit into the Henderson-Pabis model.

Effect of pre-treatments on isothermal decomposition kinetics of potassium metaperiodate

The effect of pre-compression, pre-heating and particle size on the thermal decomposition kinetics of potassium metaperiodate (KIO 4) to potassium iodate (KIO 3) has been investigated by thermogravimetric analysis under isothermal conditions. Although the effect of pre-compression was negligible up to an applied pressure of 5 × 10 3 kg cm −2, the rate increased drastically on a further increase in pressure. Results of pre-heating indicate that gross imperfections are not as easily annealed as point defects. Studies on the effect of particle size emphasize the need for fixing the particle size to enable a meaningful interpretation of the effects of pre-treatment on solid-state reactions. The rate law (Prout–Tompkins model) as well as the mechanism (electron-transfer) for the decomposition of KIO 4 remained unaffected by these pre-treatments. The α– t data of uncompressed and compressed samples of pure KIO 4 were also subjected to isoconversional studies for the determination of activation energy values.

Thermal decomposition of potassium metaperiodate doped with trivalent ions

The kinetics of isothermal decomposition of potassium metaperiodate (KIO 4), doped with phosphate and aluminium has been studied by thermogravimetry (TG). We introduced a custom-made thermobalance that is able to record weight decrease with time under pure isothermal conditions. The decomposition proceeds mainly through two stages: an acceleratory stages up to α = 0.50 and the decay stage beyond. The decomposition data for aluminium and phosphate doped KIO 4 were found to be best described by the Prout–Tompkins equation. Separate kinetic analyses of the α– t data corresponding to the acceleratory region and decay region showed that the acceleratory stage gave the best fit with Prout–Tompkins equation itself whereas the decay stage fitted better to the contracting area equation. The rate of decomposition of phosphate doped KIO 4 increases approximately linearly with an increase in the dopant concentration. In the case of aluminium doped KIO 4, the rate passes through a maximum with increase in the dopant concentration. The α– t data of pure and doped KIO 4 were also subjected to isoconversional studies for the determination of activation energy values. Doping did not change the activation energy of the reaction. The results favour an electron-transfer mechanism for the isothermal decomposition of KIO 4, agreeing well with our earlier observations.

γ-Irradiation effects on the kinetics and mechanism of the thermal decomposition of silver acetate

The kinetics of the thermal decomposition of un-irradiated (pristine) and pre-γ-irradiated anhydrous silver acetate was studied in the temperature range (298–773 K) and in air using isothermal and dynamic thermogravimetric techniques. The data were analyzed using various solid-state reaction models. An integral method using the Coats–Redfern equation was applied in dynamic data analysis. The results showed that the kinetics of isothermal decomposition for the acceleratory stage was governed by a diffusion-controlled process while in non-isothermal (dynamic) decomposition the kinetics were controlled by a nucleation process. The activation energies of the main decomposition process for un-irradiated and pre-γ-irradiated samples were calculated and the results of the isothermal and dynamic integral methods were compared and discussed. The changes in texture and crystal structure of the investigated silver acetate by γ-irradiation were studied using electron microscopy and X-ray diffraction techniques.

Effects of Carbon-Supported Nickel Catalysts on MgH2 Decomposition

This paper analyzes the improvement of MgH2 decomposition by the addition of nickel-based catalysts, mostly carbon-supported nickel catalysts. Our study shows that some experimental parameters such as the catalyst content, its composition, the method of preparation, and milling time strongly affect its activity toward MgH2 decomposition. We observe that carbon-supported nickel catalysts have superior performance than those just containing carbon and nickel physically mixed and, especially, than those containing only nickel. This emphasizes the role played by carbon and by the nickel−carbon interaction on the activity of such MgH2-based materials. A decrease, followed by differential scanning calorimetry (DSC), in the decomposition temperature of MgH2 of 150 °C can be achieved with some selected supported catalysts. Suitable selection of the catalyst preparation conditions leads to materials for which decomposition of 6.6 wt % hydrogen occurs in just 9 min at 300 °C, in comparison to 240 min required for undoped MgH2, and is stable after five cycles. Comparison between catalysts supported on different carbon materials having similar compositions but different nickel particle size shows no relevant differences in their isothermal decomposition kinetics.

Thermal stabilities of di-alkylimidazolium chloride ionic liquids

Thermal stability of 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) and 1-hexyl-3-methylimidazolium chloride ([HMIM]Cl) ionic liquids was investigated using thermogravimetric analysis (TGA). The long-term isothermal TGA studies have revealed that both the ionic liquids exhibit appreciable decomposition at temperatures significantly lower than indicated by the peak or onset decomposition temperature ( T onset ) determined from fast scan TGA experiments. The long-term thermogravimetric studies of both the ionic liquids showed linear weight loss as a function of time at each temperature of 10 °C interval in the range 150–170 °C over a period of 15 hours. However, the linear weight loss regime decreased with increasing temperature for the range 180–200 °C. The kinetics of isothermal decomposition of ionic liquids was analyzed using pseudo-zero-order rate expression. Arrhenius activation energy for the decomposition of di-alkylimidazolium chloride ionic liquids in the range 150–200 °C was determined.

Kinetic parameters of decomposition of some selenites

Abstract Studying the kinetics of isothermal decomposition of thirteen selenites at isothermal heating, the values of activation energy E of the process, pre-exponential factor A in Arrhenius equation and changes of entropy for the formation of the activated complex of the reagent were calculated. Direct dependence between the thermal stability of the selenites and their cation radii on their 'hardness' or 'softness' was found. The dependence was interpreted in the terms of the generalized perturbation theory of chemical reactivity. Kinetic compensation effect was observed only for the selenites, which thermally decompose by the same mechanism.