Non-isothermal Kinetic Analysis Research Articles

Complex thermal analysis and runaway reaction of 2,2′-azobis (isobutyronitrile) using DSC, STA, VSP2, and GC/MS

A severe manufacturing accident involving 2,2′-azobis (isobutyronitrile) (AIBN) occurred in China on April 14, 2011, which created high-pressure gas release killing nine people and severely damaging equipment and buildings. Eliminating chemical catastrophes in the petrochemical industry is a global concern. A new approach, which combines non-isothermal kinetic modeling, runaway reaction, and product analysis, was employed to determine decomposition mechanisms of AIBN by separately using differential scanning calorimetry, simultaneous thermogravimetric analyzer, vent sizing package 2, and gas chromatography/mass spectrometer. The results indicated that azo compound AIBN exhibits higher level of thermal decomposition with a maximum temperature of 294 °C and maximum pressure of 367 psig in comparison to the other azos. Moreover, various critical thermokinetic parameters, such as time to maximum rate, exothermic onset temperature, adiabatic temperature rise, and pressure gradients were obtained. A combination of thermal hazards and reaction pathways was subsequently employed to investigate the thermokinetics and mechanisms of AIBN decomposition.

Thermal Stability and Non-isothermal Kinetic Analysis of Suspension Poly(vinyl chloride) Films Formulated with Phosphonium-Based Ionic Liquids

This work addresses the short-term thermal stability of suspension poly(vinyl chloride) (PVC) films formulated with phosphonium ionic liquids, PhILs (trihexyl(tetradecyl)phosphonium dicyanamide, [P...

Effect of Modified Vermiculite on the Interface of a Capric Acid-expanded Vermiculite Composite Phase Change Material with Phase Transition Kinetics

A new type of capric acid (CA)-acid expanded vermiculite (AEV) composite phase change material (PCM) with improved adsorption ability and interface adhesive strength was developed. Through the analysis of non-isothermal phase transition kinetics, modified vermiculite was observed to change and affect the phase transformation mechanism of the composite. AEV was treated with hydrochloric acid to improve the specific surface area and micro-pore structure. The surface area measured by BET increased from 81.94 m2/g for expanded vermiculite (EV) to 544.13 m2/g for AEV. CA-EV and CA-AEV composite PCMs were prepared by direct impregnation. The non-isothermal phase transition isotherms of CA-EV and CA-AEV were recorded by DSC at different heating rates (1, 5, 10, 15, and 20 ℃/min), which indicated that the phase transition rate increased with the heating rate and the phase transition process changed. Kinetics parameters were analyzed by a double extrapolation method. The activation energy (E) under the original state (Eα→0) of CA-AEV and CA-EV was 1 117 kJ/mol and 937 kJ/mol, respectively, and 1 205 kJ/mol and 1 016 kJ/mol under the thermal equilibrium state (Eβ→0). The most probabilistic mechanism function of CA-AEV satisfied G(α)=α2/3, which followed the Mample special rule, and the function of CA-EV satisfied G(α)=[(1+α)(1/3)−1]2, which followed the anti-Jander function.

Electrospinning and thermal characterization of nitrocellulose nanofibers containing a composite of diaminofurazan, aluminum nano-powder and iron oxide nanoparticles

Electrospinning was used to fabricate composite nanofibers based on nitrocellulose (NC), and some additives comprising aluminum nanoparticles, Fe2O3 nanoparticles and diaminofurazan (DAF). The appropriate mechanical properties (such as elasticity, stiffness and tensile strength) accompanied by the suitable combustion rate of these fibers make them attractive for the utilization in the propellant formulations. The results of this work show that the average diameter of electrospun composite nanofibers (NC fibers containing Al/Fe2O3/DAF) is 80 nm. Thermal behavior of the fabricated nanofibers was characterized by DSC technique. The results showed that thermal decomposition of the nanofibers happens at the temperature 190 °C. In this study, two non-isothermal kinetics analysis methods (i.e., Kissinger and Starink) were used to predict kinetic parameters of thermal decomposition, such as activation energy and frequency factor; as well as, thermodynamic parameters (ΔG#, ΔH#, and ΔS#). The results yield activation energies about 219 kJ mol−1 for thermal decomposition of the nanofibers. Moreover, it was found that the thermal stability of Al/Fe2O3/NC nanofibers in the presence of DAF improves and hence it has a positive effect on the safety of this nanocomposite.

Isokinetics.

The study of the rates of chemical reactions and their relationship to temperature began in the 19th century with empirical measurements of the time required to reach a particular reaction end point at a constant temperature. By the mid-20th century, the theory of reaction rates had advanced and instruments had been developed in which the temperature of the sample could be increased at a constant rate. These nonisothermal methods are now widely used to determine the kinetic parameters of reactions because of their convenience. In this paper, the mathematical relationship between measurements at constant temperature (isothermal) and constant heating rate (nonisothermal) is developed and it is shown that there is a point in the temperature history of a single-step reaction at which the isothermal and nonisothermal reaction rates are equal. This equal (iso) kinetic point occurs at a temperature early in the heating history of nonisothermal analyses at which the reaction rate begins to accelerate. The isokinetic temperature is the basis for a new method of nonisothermal kinetic analysis that provides a direct measurement of the Arrhenius frequency factor A and activation energy Ea for the elementary step of a solid-state reaction without any assumptions about the relationship between these parameters (i.e., kinetic compensation) or the reaction mechanism.

RAFT mediated miniemulsion copolymerization of ethylene and BMA and their non-isothermal model-free kinetic analysis

Miniemulsion copolymerization of ethylene and butyl methacrylate (BMA) was carried out at 60 °C using 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid as the reversible addition fragmentation chain transfer (RAFT) agent, sodium dodecyl sulphate as emulsifier and potassium per sulphate as free radical initiator under extremely low ethylene feed pressure of 5–20 bar. In the absence of a co-stabilizer, very stable emulsion was obtained, wherein the RAFT agent acted both as the chain transfer agent and as the co-stabilizer. FT-IR as well as NMR analysis established the formation of poly(ethylene-co-BMA) copolymer nanoparticles. The SEM analysis was used to study the morphological behaviour of poly(ethylene-co-BMA) copolymer nanoparticles. DLS analysis confirmed that the particle diameter Zavg of copolymer nanoparticles is in the range 100–140 nm and confirmed miniemulsion polymerization. In order to establish the stability of copolymers against thermal degradation, the kinetics and mechanism of thermal degradation of copolymers were investigated by thermogravimetric analysis. Thermogravimertic analysis established that thermal decomposition of poly(ethylene-co-BMA) copolymer nanoparticles occurred in the range 250–450 °C. This range is lower than the decomposition temperature of neat polyethylene (350–580 °C). Kinetic parameters were determined according to the model-free approaches of Friedman and Flynn–Wall–Ozawa. The multivariate nonlinear regression analysis was performed to determine the kinetic model and the corresponding kinetic triplets.

Melting and Crystallization Behaviors of Poly(Lactic Acid) Modified with Graphene Acting as a Nucleating Agent

Graphene (GN)-filled polylactic acid (PLA) nanocomposites were prepared through a solution blending method with GN weight percent ranging from 0.5 to 2 wt%. Rheological, melting and crystallization behaviors of the prepared PLA/GN nanocomposites were investigated by means of dynamic rheological measurements and differential scanning calorimetry (DSC). The shear viscosities of the PLA/GN nanocomposites decreased with increasing GN content, which was remarkably different from previous reports on the modifications using traditional nanofillers (e.g., clay, carbon nanotubes, etc.). The nonisothermal melt crystallization kinetic analysis suggested that GN served as a nucleating agent and could considerably promote the PLA’s crystallization through heterogeneous nucleation. Our findings suggested that at relatively low cooling rates (ϕ ≤ 10 °C/min) even a small amount of GN promoted the nucleation and considerably increased the crystallization rate. However, the crystallinity began to decrease at higher cooling rates (e.g., ϕ ≥ 20 °C/min), especially when the GN content was high (e.g., 2 wt%), possibly owing to the GN aggregation effect considering PLA is a slowly crystallizing polymer.

TGA/MS/FT-IR study for kinetic evaluation and evolved gas analysis of a biomass/PVC co-pyrolysis process

This study aims to investigate the thermal behaviours of a specific biomass and a polymer sample through co-pyrolytic degradation. Therefore, a non-edible food processing waste (cherry seed: CS) and a typical plastic waste (polyvinyl chloride (PVC)) were selected and their interaction was studied using a combined TGA/MS/FT-IR system. By the help of TGA data, the non-isothermal kinetic analysis was performed using four different kinetic methods [Friedman, Flynn-Wall-Ozawa (FWO), Vyazovkin and distributed activation energy (DAEM)]. The kinetic results showed that the activation energy values were in agreement over the conversion degree values between 0.1 and 0.9. For determination of the synergistic or inhibitive interactions, theoretical and experimental thermogravimetry values were also compared. Moreover, in situ determination of the main pyrolytic and co-pyrolytic degradation compounds such as methyl, water, methoxy, hydrogen chloride, carbon dioxide and benzene with respect to temperature and time was studied for the first time. By this way, primary and secondary reactions related to methylation, dehydration, aromatization, fragmentation, dehydrochlorination were interpreted. Consequently, PVC was found to change pyrolytic degradation behaviour of lignocellulosic biomass by changing reactivity, activation energy and reaction mechanisms.

Non-isothermal oxidation and kinetic analysis of pure magnesium powder

With high energy densities, metals appear as innovative energy carriers. In the present study, magnesium powder is considered as fuel for energy production through slow combustion. Thermogravimetric analyses (TG) were carried out to extract the kinetic parameters and determine the mechanism of the overall slow combustion reaction. TG experiments were performed under synthetic airflow and under different heating rates (from 1 to 20 °C min−1) from ambient temperature to 900 °C, with two Mg size fractions. The optimal kinetic parameters were determined solving a kinetic model and applying an optimization procedure, both using the Scilab software. The Avrami–Erofeev reaction function of second order, which is a nucleation model, gave the best results for both size fractions. The activation energies were found equal to 146.1 kJ mol−1 and 290.0 kJ mol−1 for the 20–50 µm and 50–71 µm fractions, respectively. The corresponding optimal pre-exponential factors were found equal to 1.2 × 106 s−1 and 2.0 × 1015 s−1, respectively.

Thermodynamic and kinetic study of the recovery of tungsten and cobalt from tool waste

In the present research work, the recovery of tungsten and cobalt from waste coming from tungsten carbide-cobalt (WC-Co) tools, which are widely used in the metalworking industry, was analyzed. The WC-Co waste was characterized by X-ray diffraction and scanning electron microscopy with microanalysis (SEM/EDS). The process started with the oxidation of the waste to obtain a mixture of oxides (WO3 and CoWO4). The ΔH and ΔG were calculated both for the oxidation and reduction processes. Thermodynamic and non-isothermal kinetic analyses were carried out to obtain a stability diagram where theoretical and experimental data are defined by transformation lines as a function of temperature; in addition, the apparent activation energy was determined. By a hydrogen reduction process, high-purity tungsten and cobalt in metallic form were obtained.

Effect of the Particle Size of Iron Ore on the Pyrolysis Kinetic Behaviour of Coal-Iron Ore Briquettes

High reactivity coke is beneficial for achieving low carbon emission blast furnace ironmaking. Therefore, the preparation of highly reactive ferro-coke has aroused widespread attention. However, the effects of the particle size of iron ore on the pyrolysis behaviour of a coal-iron ore briquette are still unclear. In this study, the effect of three particle sizes (0.50–1.00 mm, 0.25–0.50 mm and <0.74 mm) of iron ore on the thermal and kinetic behaviours of coal-iron ore briquettes were investigated by non-isothermal kinetic analysis. The results showed that the synergistic effect of iron ore and coal during coking mainly occurred during the later reaction stage (850–1100 °C) and smaller particle sizes of iron ore have a stronger synergistic effect. The addition of iron ore had little effect on T0 (the initial temperature) and Tp (the temperature at the maximum conversion rate) of briquette pyrolysis, however itgreatly affected the conversion rate and Tf (the final temperature) of the briquettes. T0 decreased with the decrease of iron ore particle sizes, while Tp and Tf showed opposite trends. After adding iron ore into the coal briquette, the reaction kinetics at all stages of the coal-iron ore briquettes changed. The weighted apparent activation energy of the caking coal (JM) briquette was 35.532 kJ/mol, which is lower than that of the coal-iron ore briquettes (38.703–55.627 kJ/mol). In addition, the weighted apparent activation energy gradually increased with decreasing iron ore particle sizes.

Non-isothermal oxidation kinetics of FeSiAl alloy powder for microwave absorption at high temperature

Exploring efficient microwave absorbers at high temperature is a hot topic in the practical application. Non-isothermal oxidation kinetics of FeSiAl alloy powder sized of ∼45 μm were investigated by thermogravimetry analysis (TG) and differential scanning calorimetry (DSC) under linear temperature control program (ranging from 30 to 1200 °C) at different heating rates (5, 10, 15, 20 and 25 K/min) in air. It can be found that the melt point of FeSiAl alloy powder is about 1165 °C. The oxidation of FeSiAl alloy powder can be divided into two stages including solid-oxidation stage (before melting) and liquid oxidation stage (after melting). Non-isothermal kinetic analysis of oxidation of FeSiAl alloy powder were performed by using Flynn-Wall-Ozawa (FWO) method. Besides, the surface morphology of particles present a smooth trend by scanning electron microscope. And the microwave absorption performance of FeSiAl alloy powder is confirmed to be a good potential candidate in case of high temperature with the lowest refection loss value of −25.14 dB and effective absorbing bandwidth in range of 4–18 GHz adjusting the thickness.

Analysis of nonisothermal crystallization kinetics of graphene oxide - reinforced polyamide 6 nanocomposites

The main objective of this work was to evaluate and characterize graphene oxide-reinforced polyamide 6 nanocomposites and to study the effects of the amount of reinforcement and the cooling rates on nonisothermal crystallization kinetics. A sequence of two processing methods was used to prepare the nanocomposites: first a masterbatch was produced by solution mixing and then diluted in the polyamide 6 (PA6) matrix via melt blending in a twin-screw extruder. Finally, the nanocomposites were submitted to differential scanning calorimetry analyses at different cooling rates in order to evaluate the effect of graphene oxide in the kinetics of crystallization of PA6 for further applications. According to previous theories used to describe the best mechanism of polymer crystallization, it was observed that Mo's theory fitted quite well within the experimental results. Secondary crystallization was strongly favoured in the nanocomposites due to the presence of graphene oxide; however, this nanomaterial decreased the degree of crystallinity of the polymer matrix.

(Fe0.9Ni0.1)77Mo5P9C7.5B1.5 bulk metallic glass matrix composite produced by partial crystallization: The non-isothermal kinetic analysis

In this study, the non-isothermal kinetic analysis of partial crystallization process in (Fe0.9Ni0.1)77Mo5P9C7.5B1.5 BMG was investigated. The XRD and FE-SEM results revealed that five nano-crystalline phases including (Fe,Ni)3P, Ni3Fe, Fe3C, α-Fe, and γ-Fe were formed during crystallization process. Also, the DTA curves showed that crystallization process in this BMG occurred at various stages. The kinetic parameters for various stages of crystallization process were determined by isoconversional Starink and Friedman (FR) methods in combination with the invariant kinetic parameters (IKP) and the g(α) master plot methods. According to isoconversional and fitting methods, it was observed that crystallization process in this BMG was controlled by activation energies equal to 170–280 kJ/mol and Avrami–Erofeev and power law models.

Synthesis, Thermal Kinetic Analysis and DFT Calculations of Pyrazine and Pyridine Complexes of Copper(II) Thiocyanate

Two NNN type ligands namely bis-2,6-(pyrazol-1-yl) pyridyne (pp) and bis-2,6-(3,5-dimethyl-pyrazol-1-yl) pyridyne (dmpp) were prepared by the use of 2,6-dichloropyridine, pyrazol and 3,5-dimethylpyrazol. Using these ligands with SCN co-ligand two mononuclear Cu(II) complexes were synthesized and characterized. The complexes were investigated by thermogravimetry (TG) and differential thermal analysis (DTA) and subjected to isothermal and nonisothermal kinetic analyses. TG and DTA results indicated that the complexes showed two distinctive degradation steps and the NNN type ligand was removed from the structure at temperatures above 300 °C. The activation energies of these complexes and same thermodynamic parameters of these thermal reactions have been calculated. The situation of d orbitals of Cu(II) ion, the electron densities of donor atoms of the ligands, natural bond orbital (NBO) analysis, the theoretical IR spectra and HOMO-LUMO energy levels computed by the use of DFT/B3LYP methods with 6-311G (d) basis set in Gaussian 09 software. These data were employed to enlighten the thermal degradation of the complexes prepared.

Non-isothermal kinetic analysis of the thermal decomposition of spruce wood in air atmosphere

Thermal decomposition of spruce wood (Picea abies) was studied using the thermogravimetric (TG) analysis in air atmosphere from 30°C to 600°C with the heating rates of 5, 10, 15, 20, 25 and 30°C.min<sup>–1</sup>. The TG results show that the main decomposition region is in the temperature range of 250–360°C, where a total disintegration of hemicellulose and cellulose with partial lignin decomposition can be observed. The values of apparent activation energy for this process are between 168.6–196.5 kJ·mol<sup>–1</sup>, 179.8–188.1 kJ·mol<sup>–1</sup> and 170.1–178.7 kJ·mol<sup>–1</sup> determined by the Friedman, Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose methods, respectively.

A theoretical method for obtaining Padé type approximation to temperature integrals via the Stieltjes integral

The normal and generalized temperature integrals originate from the use of the Arrhenius and Harcourt–Esson equations in non-isothermal chemical kinetics analysis of solid materials, where approximate expressions to them are to be required. The aim of the present theoretical exploration is to provide both useful formulas and new insights to this problem; to the end, we address this with an extended view and new method. First, we derive an analytical connection between the two temperature integrals in terms of the Stieltjes integral. Secondly, based on this finding, a unified approach to obtaining approximate expressions of them is developed, which makes use of mathematical relationships between the Stieltjes integral, Stieltjes series and Pade approximant and leads to new Pade type approximations to the two integrals. Lastly, an error analysis and comparison of the proposed approximations along with published ones is performed, showing that they are accurate enough and applicable in thermal analysis.

Study on the thermal decomposition of aluminium chloride hexahydrate

ABSTRACTThis paper presents a preliminary study on the thermal decomposition process of aluminium chloride hexahydrate (AlCl3·6H2O) crystal with non-isothermal thermal kinetic analysis and static calcination experiments. The ‘kinetic triplets’ including activation energy, pre-exponential factor and mechanism function for the decomposition reaction were determined through thermal analysis from Differential Scanning Calorimetry–Thermos Gravimetric Analysis results. It is found that the average activation energy and pre-exponential factor were 59.668 kJ mol−1 and 6.67 × 105 min−1, respectively, and the most suitable conversion function was . The emission rates of the gaseous products, water (H2O) and hydrogen chloride (HCl), were calculated from the chlorine content evolution obtained from the static calcination tests, respectively. The phase transformation and the change of particle morphology during the decomposition process were also investigated through X-ray diffraction and scanning electron microscope technologies.

Non-isothermal kinetic analysis of reversible ageing in asphalt cements

The AASHTO M320 specification for thermal cracking – meant to limit damaging temperatures to only a 1 in 50 risk in any given winter – stipulates that asphalt cement chemically (irreversibly) aged in the rolling thin film oven and pressure ageing vessel be tested after minimal cold conditioning. Creep stiffness and creep rate (m-value) are determined with specimens rapidly cooled to 10°C above the pavement design temperature and then conditioned for only an hour prior to testing. As a result, materials are often tested in a non-equilibrium state and pavements end up under-designed for thermal cracking; adjacent sections can show from best-case to worst-case performance. Several Ontario user agencies have recently implemented a specification to effectively limit cracking due to reversible ageing: “determination of performance grade of physically aged asphalt binder using the extended bending beam rheometer (EBBR) method” (Ministry of Transportation of Ontario designation LS-308 and recently adopted by AASHTO under designation TP 122-16). This empirical protocol tests beams after 72 h of cold conditioning to determine a low-temperature grade as well as a grade loss from the 1 h results specified in AASHTO M320. Grade losses are sensitive to the presence of deleterious additives (waxes, air blown residues, recycled engine oil bottoms). Furthermore, by testing recovered material from paving mixtures, the protocol also provides a secure way to account for the presence of reclaimed asphalt pavement, and to monitor for overheating during production. The extended BBR method has several limitations: (1) it requires a relatively large quantity of 150 g of aged material; (2) it takes a relatively long 72 h to complete and (3) it quenches the binder from room temperature to two cold temperatures, namely 10°C and 20°C above the pavement design limit (Td+10 and Td+20), and therefore, because of its empirical nature, it is unclear if the results obtained are relevant for other thermal histories. Since these drawbacks have slowed implementation, current research is focused on the following improvements: (1) modelling the ageing/hardening processes within the Ozawa theoretical framework; (2) reducing sample requirement to less than 12 g; (3) shortening testing time to less than 24 h; (4) conditioning at more temperatures between ambient and the pavement design limit and (5) automating the procedure. Modelling efforts are based on an analysis of non-isothermal phase transformation kinetics. This paper presents results obtained from differential scanning calorimetry and dynamic mechanical analysis three-point bending tests on a number of Ontario asphalt cements under varying cooling rates. The application of the Ozawa theory provides an improved understanding of how thermal history and variable ageing tendencies can explain vast performance differences between pavement sections of identical AASHTO M320 grades. It is suggested that by adding an upper limit on the Ozawa exponent to the low-temperature asphalt cement specification, in order to reduce the rate of reversible ageing, user agencies will be able to better control this type of cracking.

Catalytic Combustion of Heavy Oil in the Presence of Manganese-Based Submicroparticles in a Quartz Porous Medium

We synthesized manganese oxide(II) submicroparticles stabilized with oleic acid and used them as oil-dispersible catalyst precursor promoting a heavy oil oxidation process. Size, morphological properties, as well as composition of the catalyst were studied in depth by X-ray phase diffraction analysis, thermogravimetric–mass spectrometry analysis, scanning electron microscopy, energy dispersive X-ray analysis, and nitrogen adsorption measurements. We applied nonisothermal kinetic analysis coupled with an isoconversional approach to study the influence of catalyst on the combustion process and showed that Mn-based submicroparticles accelerate predominantly the high-temperature oxidation process.