Sestak Berggren Model Research Articles

The crystallization kinetics studies of the two crystallization stages of As37.5Se37.5Ag25 glass using the model-fitting and model-free approaches

The kinetic transformation parameters of the overlapped crystalline peaks of As37.5Se37.5Ag25 glass were examined through the model-fitting and model-free approaches. The analysis of the crystallization kinetic parameters of the studied glass utilizing the model-free approaches showed that the activation energy of crystallization is not constant but change with the conversion fraction. These results reflect the changes of the reaction mechanism and reveal that the free model is more realistic than model-fitting approach which assumes a constant mechanism. Furthermore, the present results showed that the conversion process of the first and second crystallization peak of As37.5Se37.5Ag25 glass may be described by Avrami-Erofeev model An (g(χ) = [−ln(1−χ)]1/n) with n = 2 and 3, respectively. Comparing the experimental differential scanning calorimetry data with calculated ones indicated that Sestak-Berggren (SB) model is more realistic for describing the crystallization mechanism of both crystallization peaks of the studied composition.

Thermogravimetric Characteristics and Non-isothermal Kinetics of Macro-Algae With an Emphasis on the Possible Partial Gasification at Higher Temperatures

Pyrolysis of Turbinaria ornata was realised in a thermogravimetric analyzer. The process was crudely classified into primary and secondary reaction zones. In the primary reaction zone, the thermal decompositions of the low-thermal stable components produced volatiles and biochar. The solid products obtained from the primary decomposition reactions contained inorganics with heavy metals. At mild-to-high temperatures, the catalytic effects accompanied gasification using oxygen, which was partially supplied by the oxygen carriers present in the solids and evolved gases. In order to study the pyrolytic conversion, combined and multiple reaction schemes were employed. While the model-free methods helped to provide the accurate activation energies and the initial value of the pre-exponential factor, the non-linear regression optimized the chosen model parameters. In this study, a simple order-based model was compared with the versatile Sestak-Berggren (SB) model considering combined and multiple reactions. The application of a multiple reaction scheme to the primary and secondary reaction zones concluded that a simple order-based model suffices for the kinetic analysis. The secondary decomposition was shown to start with a high activation energy, which decreased appreciably when the conversion proceeded towards completion.

Kinetic and mechanism studies of the isothermal degradation of local chitin, chitosan and its biocomposite bentonite/chitosan

In this work, the kinetic and the mechanism of isothermal degradation of local chitin (CN), chitosan (CS) and the biocomposite Bentonite/Chitosan (5%Bt/CS) were investigated by thermogravimetric analysis in air atmosphere and in the temperatures range 285–330 °C. Fourier transform-infrared, X-ray diffractogram and differential scanning calorimetry analyses were used to determine the structure of the as prepared samples. DTG curves of the samples show that CN and CS presented one peak, while those of 5%Bt/CS presented one to three peaks as the isothermal degradation increases. This difference was linked to the strong interactions between CS and Bentonite, which improve the stability of CS in the biocomposite 5%Bt/CS. The common first DTG peak appearing in each sample was treated using the Friedman method, leading to the activation energy (Ea) of Ea(CN) = 127.18 kJ/mol > Ea(CS) = 103.90 kJ/mol > Ea(5%Bt/CS) = 80.64 kJ/mol. The auto-catalytic Sestak–Berggren model was found to be qualitatively matched the isothermal degradation process of each sample. The thermodynamic parameters show the appearance of an order in the activated complex with respect to the initial state and that the isothermal degradation process is endothermic and is not spontaneous.

Comparative curing kinetics study of high char yield formaldehyde- and terephthalaldehyde-phenolic thermosets

Phenol-Formaldehyde (PF) resoles exhibit excellent thermal properties, high temperature degradation and high char yield. The formaldehyde can be replaced by terephthalaldehyde (TPA), a non-toxic aromatic dialdehyde. The thermal performances of phenol-TPA (PTPA) resole are very interesting for further development and industrialization. The present investigation presents for the first time a thermo-kinetics study of curing of PTPA, in comparison with a commercial PF resole. Non-isothermal, at constant heating rates DSC experiments are performed on both resoles. PF shows one single exothermic peak, whereas PTPA exhibits two DSC peaks, suggesting a two-step curing mechanism which appears to be conversion-dependent. In addition, isoconversional analysis is used to elucidate the activation energies as a function of the degree of curing. Differential Friedman and integral Vyazovkin methods are considered for computations, giving equivalent results. Furthermore, the whole kinetic triplets (E, A, f) is elucidated for both resoles with Sestak-Berggren model fitting. Finally, isothermal isoconversional predictions are compared to experimental data.

Oxidation mechanism and non-isothermal kinetic studies on carbonate iron ore by thermogravimetric analysis

Due to the uncertain and heterogeneous compositions of carbonate iron ore after magnetization roasting, an oxidation pretreatment was applied to increase the uniformity of the composition of the ore. The oxidation of carbonate iron ore was characterized using a thermogravimetric method over a temperature range of 723–948 K. It is shown that the oxidation process of carbonate iron ore is complicated and consists of multiple reactions that include the decomposition and oxidation of carbonates such as FeCO3, MnCO3, MgCO3 and CaMg(CO3)2. The main product that results from oxidation is Fe2O3. Because of the low content of other carbonates (MnCO3, MgCO3 and CaMg(CO3)2) in raw carbonate iron ore and the small change in the apparent activation energies during oxidation, the oxidation of carbonate iron ore can be treated as a single-step FeCO3 oxidation reaction. Based on the Ozawa–Flynn–Wall method, which is one of the model-free methods, the apparent activation energy for the oxidation of carbonate iron ore is 284.50 kJ mol−1. The most probable reaction model for the oxidation of carbonate iron ore is the Sestak–Berggren model as determined by the theoretical and actual master plot and eigenvalues of the Malek method. The reaction orders n and m are 1.317 and 0.0295, respectively. The pre-exponential factor is 2.628 × 1017 min−1.

Thermal dehydration kinetic mechanism of Mn1.8Co0.1Mg0.1P2O7·2H2O using Málek's equations and thermodynamic functions determination

Abstract Mn1.8Co0.1Mg0.1P2O7·2H2O was synthesized via hydrothermal method and the thermal dehydration product was confirmed to be Mn1.8Co0.1Mg0.1P2O7. The thermogravimetry/differential thermogravimetry/differential thermal analysis, Fourier transform infrared, atomic absorption spectrophotometry, X-ray diffraction and scanning electron microscopy techniques were employed for sample characterization. Non-isothermal kinetics was studied under air atmosphere at four heating rates and the single thermal dehydration process was observed. Iterative Kissinger–Akahira–Sunose equation was used to calculate the apparent activation energy Eα values. Dehydration process was confirmed to be a single-step kinetic process with the unique kinetic triplets. Malek's equations were used to determine the kinetic model f(α) and pre-exponential factor A. Sestak–Berggren model was suggested to be the mechanism function for the dehydration process. The best fit led to the kinetic triplets of Eα=(79.97±6.51) kJ/mol, ln A=16.83 and f(α)=α0.520(1–α)1.255 (α is the extent of conversion). The thermodynamic functions of activation were calculated using activated complex theory together with A value.

Assessment of kinetic model for ceria oxidation for chemical-looping CO2 dissociation

Chemical looping technologies are identified as to have an excellent potential for CO2 capture and fuels synthesis. Oxygen carriers are the fundamental component of a chemical looping process, and the choice of stable and efficient carriers with fast redox kinetics is the key to the successful design of the process. Hence, understanding the reaction kinetics is of paramount importance for the selection of an appropriate oxygen carrier material. This work provides a method for kinetic model selection based on a statistical approach to identify the reaction mechanism. The study experimentally investigates the oxidation kinetics of CeO2−δ by CO2 and applies a statistical method for the selection of the best-fitting kinetic model for the reaction. The kinetic study is performed in the temperature range of 700–1000 °C with a CO2 concentration between 20 and 40 vol% in the feed. The measured peak rates of CO production on ceria were influenced both by temperature and concentration of reactant. The total CO production was more influenced by the temperature than by CO2 concentration, with a maximum CO yield of 33.66 ml/g at 1000 °C and 40% CO2. The identification of the oxidation kinetic model is performed by fitting different reactions models to the measured reaction rates and statistically comparing them using the Residual sum of squares (RSS), Akaike information criterion (AICc) and the F-test for the selection of the best-fitting one. Models corresponding to the nucleation and grain growth reaction mechanism provided a good fit of the data, with the Sestak-Berggren (SB) model showing the best approximation of the measured rate of reaction with an evaluated activation energy of 79.1 ± 6.5 kJ/mol for the CO2 oxidation.

Kinetic analysis of crystallization in Li2O-Al2O3-SiO2-B2O3-BaO glass-ceramics

The crystallization mechanisms for Li2O-Al2O3-SiO2-B2O3-BaO glass-ceramics were studied by differential scanning calorimetry (DSC) under non-isothermal conduction. The activation energy and Avrami exponent of the glass-ceramics had been calculated by Kissinger method and Kissinger-Akahira-Sunose (KAS) method. Comparison of the measured DSC data with calculated curves at different heating rates using Sestak-Berggren (SB) model and Johnson-Mehl-Avrami-Kolmogorov (JMAK) model revealed the commonly used JMAK was not a suitable kinetic model for this glass-ceramic. However, the empirical SB model was found to be acceptable for analyzing the kinetics of crystallization for the studied glass composition. This model matched well with the DSC curves, with slight deviations at the tails of the peaks. Furthermore, the crystalline phases and microstructure of samples sintered at 730 °C for 2 h were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Energy dispersive spectrometer (EDS). The LiAlSi2O6 and LiAlSi3O8 constituted as the predominant phases in the studied glass-ceramic.

The thermal decomposition behavior and kinetics of epoxy resins cured with a novel phthalide-containing aromatic diamine

The thermal decomposition behaviors and kinetics of diglycidyl ether of bisphenol A (DGEBA) epoxy resin cured by a novel phthalide-containing aromatic diamine (BAPP), were studied by thermal gravimetric analysis (TGA) technique in comparison with these of epoxy systems cured by 4,4′-diaminodiphenylsulfone (DDS) and equimolar mixture of DDS/BAPP, respectively. The initial decomposition temperature (Tinitial) and integral procedure decomposition temperature (IPDT) were used to evaluate the thermal stability of cured epoxy resins. Tinitial values are reduced with increasing BAPP content, while IPDT results show the cured DGEBA/BAPP system has the highest inherent thermal stability. The microstructure morphology of charred products, derived from the thermal decomposition of the cured epoxy networks, were characterized by scanning electron microscope (SEM). The decomposition kinetics was investigated by isoconversional approach and the activation energy (Ea) calculated by Starink equation exhibits different dependence on conversion (α) for three epoxy systems. Truncated Sestak-Berggren model was used to describe the thermal decomposition mechanism, and the result shows a good agreement between the experimental data and the theoretical model.

Thermal degradation kinetic study of polystyrene/organophosphate composite

A polystyrene/bis (2, 4-dicumylphenyl) pentaerythritol diphosphate (DPP) composite (PS-DPP) with a DPP loading of 10% (w/w) was prepared by the melt-compounding method. Results indicated that DPP had a thermal destabilization effect at temperatures below 380 °C. A comparative degradation kinetic analysis was performed employing the Kissinger method and the isoconversional methods of Friedman, Starink and Advanced Isoconversional Method (AICM). Variation of activation energy with extent of conversion (α) results from all the isoconversional methods showed that activation energy did not vary significantly with α for both pure PS and PS-DPP. Activation energies obtained from the Starink method above 380 °C were very close to those obtained from AICM consistent with activation energy values not varying significantly with α. The y(α) master plots and the Friedman methods where used to identify the reaction model and calculate the frequency factor respectively. The Sestak-Berggren model was identified as the most appropriate model to describe the thermal degradation of both PS and PS-DPP. The overall results indicates that activation energies of the composite were not significantly higher than those of pure PS at low conversion (α < 0.2) where DPP had a destabilizing effect but became higher when DPP had a stabilization effect.

Thermokinetics behavior of epoxy adhesive reinforced with low viscous aliphatic reactive diluent and nano-fillers

The current study reports the effect of low viscous aliphatic reactive diluent (RD), MWCNT and VGCF on the curing kinetics of amine cured epoxy adhesive system employing non-isothermal differential scanning calorimetric (DSC) technique. Non-isothermal DSC thermograms of epoxy adhesive were studied at various heating rates: 5, 10 and 15 °C/min. The decrease in the exothermic peak height with the introduction of MWCNTs and VGCFs was taken as proof of the acceleration effect of nano-fillers on the epoxy-amine curing reaction. Also, increased T onset , T P and ΔH curs values were observed for epoxy/RD adhesive system at all heating rates. The value of activation energy (E a ) was determined using Kissinger and Flynn-Wall-Ozawa methods. Experimental results showed that the addition of 10 wt% RD increased the E a from 60 to 63 kJ/mol on account of the reduced viscosity, allowing better contact of resin with the curing agent. Furthermore, MWCNTs have an accelerating effect on the cure kinetics that does not change the autocatalytic cure reaction mechanism of epoxy resin. It was also found that the addition of MWCNT and VGCF decreases the overall degree of conversion, as evident with lower ΔH cure and E a of the cured adhesive when compared with epoxy/RD system. The dependency of E a on degree of conversion ranging from α =0.1 to 0.9was also investigated. The two normalized functions y(α) and z(α) were also considered in order to study the complex curing mechanism. The kinetic parameters m, n and lnA were obtained by using two parameter autocatalytic Sestak-Berggren model. The curves revealed good agreement between experimentally determined and theoretically obtained MWCNT/VGCF reinforced epoxy adhesive systems.

Gasification Characteristics and Kinetics of Coke with Chlorine Addition

The gasification process of metallurgical coke with 0, 1.122, 3.190, and 7.132 wt pct chlorine was investigated through thermogravimetric method from ambient temperature to 1593 K (1320 °C) in purified CO2 atmosphere. The variations in the temperature parameters that T i decreases gradually with increasing chlorine, T f and T max first decrease and then increase, but both in a downward trend indicated that the coke gasification process was catalyzed by the chlorine addition. Then the kinetic model of the chlorine-containing coke gasification was obtained through the advanced determination of the average apparent activation energy, the optimal reaction model, and the pre-exponential factor. The average apparent activation energies were 182.962, 118.525, 139.632, and 111.953 kJ/mol, respectively, which were in the same decreasing trend with the temperature parameters analyzed by the thermogravimetric method. It was also demonstrated that the coke gasification process was catalyzed by chlorine. The optimal kinetic model to describe the gasification process of chlorine-containing coke was the Sestak Berggren model using Malek’s method, and the pre-exponential factors were 6.688 × 105, 2.786 × 103, 1.782 × 104, and 1.324 × 103 min−1, respectively. The predictions of chlorine-containing coke gasification from the Sestak Berggren model were well fitted with the experimental data.

Non-isothermal kinetics of epoxy resin curing reaction under compressed CO2

The non-isothermal curing kinetics of epoxy resin system consisting of diglycidyl ether of bisphenol A (DGEBA) and m-xylylenediamine (MXDA) were investigated by high-pressure differential scanning calorimetry at different heating rates of 5, 10, 15 and 20 K min−1 under compressed carbon dioxide (CO2) of 0.1–8 MPa. The activation energies were determined by isoconversional Kissinger–Akahira–Sunose method and Vyazovkin numerical method, and the average values decreased from 53.5 to 46.8 and 54.1 to 44.5 kJ mol−1, respectively, when the CO2 pressure increased from 0.1 to 8 MPa. It is indicated that the curing reaction of epoxy resin occurs more easily under higher-pressure CO2 due to the promoted molecular movement, especially in the supercritical state. The non-isothermal curing kinetics were investigated by nth-order model and two-parameter autocatalytic model (Sestak–Berggren model), and the latter one analyzed by Malek method exhibited good agreement with the experimental data except the initial and final stages of the curing reaction.

Non-Isothermal Crystallization Kinetics of Mg&lt;sub&gt;61&lt;/sub&gt;Zn&lt;sub&gt;35&lt;/sub&gt;Ca&lt;sub&gt;4&lt;/sub&gt; Glassy Alloy

The non-isothermal crystallization kinetics of Mg61Zn35Ca4 glassy alloy prepared via melt-spinning were studied by using isoconversion method. The crystalline characterization of Mg61Zn35Ca4 was examined by X-ray diffraction. Different scanning calorimeter was used to investigate the non-isothermal crystallization kinetics at different heating rates (3-60 K/min). The calculated value of Avrami exponent obtained by Matusita method indicated that the crystalline transformation for Mg61Zn35Ca4 is a complex process of nucleation and growth. The Kissinger-Akahira-Sunose method was used to investigate the activation energy. The activation energy of crystallization varies with the extent of crystallization and hence with temperature. The Sestak-Berggren model was used to describe the non-isothermal crystallization kinetics.

Preparation and characterization of microcapsulated red phosphorus and kinetic analysis of its thermal oxidation

Microcapsulated red phosphorus (MRP) with aluminum hydroxide/phenolic resin coating layer was prepared by a two-step coating process. The results of Fourier-transform infrared spectroscopy and scanning electron microscopy show that red phosphorus (RP) is coated by aluminum hydroxide and phenolic resin. MRP absorbs less water and is more thermally stable than RP. The thermal oxidation kinetics of MRP was investigated by TG/DTG/DTA under air atmosphere using non-isothermal experiments with the heating rates ranging from 10 to 25°C/min. The values of the apparent activation energy E a were 168 ± 9 kJ/mol as determined by the isoconversional Ozawa–Flynn–Wall method and 164 ± 12 kJ/mol according to the Kissinger−Akahira−Sunose method. Based on Malek’s procedure the kinetic reaction follows the Sestak–Berggren model with f(α) = α0.34(1 − α)0.94 (α is RP conversion) and pre-exponential factor A = 3.11 × 1012 s–1. The simulated curves were fitted with experimental curves constructed by plotting dα/dt vs temperature at different heating rates.

Synthesis and thermal analysis of poly(methyl methacrylate) oligomer functionalized polyethylene block copolymer

Living oligomers of methyl methacrylate (MMA) were synthesized photochemically with iron(III) tris(oxalato) ferrate(III) tetrahydrate (Fe[Fe(C2O4)3]·4H2O) as photoinitiator under UV irradiation of 254 nm at 40 °C in dimethyl sulfoxide in the presence of triethylamine as coinitiator. The synthesized oligomers were incorporated in the ethylene chain by reverse atom transfer radical polymerization in N,N′-dimethylformamide using 2,2′-azobisisobutyronitrile as initiator with FeCl3/2,2′-bipyridine (bpy) catalyst system. FT-IR and 1H NMR analysis confirms the incorporation of pre-synthesized poly(MMA) in the ethylene chain. Thermogravimetric analysis of the copolymer shows a three step decomposition process with the major decomposition at approximately 380 °C. Apparent activation energy (E a) of each step was calculated using non-isothermal methods of Kissinger, Friedeman, Flynn–Wall–Ozawa (FWO) and modified Coats-Redfern (MCR). The E a value obtained from FWO and MCR methods shows good agreement and the value for the final step of decomposition was calculated to be 235 kJ mol−1. The conversion dependency of decompositions on the process rate can be best explained by Sestak-Berggren model which can be established as $$\begin{aligned} f(\alpha ) = 3.67 \times 10^{2} \exp \left( {\frac{-199.28}{RT}} \right)(1 - \alpha )^{2.03} \alpha^{3.03} \hfill \\ \hfill \\ \end{aligned}$$ with pre-exponential factor (A) = 3.67 × 102 min−1.

An evaluation of the thermal degradation kinetics of novel melt processed PET–hemp fiber composites

This work reports the thermal degradation kinetics of five formulations of polyethylene terephthalate (PET) reinforced with 1, 5, 10, 15, and 20 % hemp fibers based on thermogravimetric investigations. Two consecutive degradation steps were observed between 573 and 773 K. Moreover, their kinetic triplets were determined by nonlinear curve fitting methods, with the Sestak–Berggren and the truncated Sestak–Berggren models, respectively. The resulting kinetic parameters varied with the fiber’s concentration in the following ranges: 1.8 ≤ A ≤ 5, 2.25 ≤ n ≤ 3.17, 7.05 ≤ m ≤ 12.74, and −2.21 ≤ p ≤ −1 for the first step; and 1.76 ≤ A ≤ 10, 1.37 ≤ n ≤ 2.49, and 0.77 ≤ m ≤ 2.35 for the second. This work further confirms the thermal stability of PET–hemp fiber composites and provides key information for the reaction mechanism, a crucial developmental step for bio-composite materials with high-melting thermoplastic matrices.

Reaction pathway and kinetics of CdO nanoparticles prepared from CdCO3 precursor using thermal decomposition method

The non-isothermal kinetics of CdO nanoparticles prepared from CdCO3 precursor using thermal decomposition method was investigated. A model-fitting Malek approach and a model-free advanced isoconversional method of Vyazovkin were applied to the analysis of the DSC and TGA data. The results showed that CdO nanoparticles prepared from CdCO3 followed an autocatalytic reaction. Sestak–Berggren model could favorably describe the studied reaction process. Moreover, the apparent activation energy of CdCO3 decomposition was calculated to be (119.19±9.97) kJ/mol and the explicit rate equation form of CdCO3 decomposition was established.

Thermal stability and degradation of binuclear hexaaqua-bis(ethylenediamine)-(μ 2-pyromellitato)dinickel(II) tetrahydrate

Thermal degradation of ternary transition metal complex containing tetraanion of pyromellitic acid, pyr, and ethylenediamine, en, [Ni2(en)2(H2O)6(pyr)]·4H2O, 1, was investigated under non-isothermal conditions. The mechanism of thermal degradation, which occurs in three steps, was clarified by TG/DSC measurements in conjunction with FT-IR spectroscopy and XRPD analysis. The complexity of all degradation steps has been revealed using isoconversional methods. Dehydration comprises the loss of ten water molecules in a relatively narrow temperature interval, resulting in a very complicated reaction mechanism. In addition, density functional theory calculations have been applied for better understanding of dehydration. The second degradation step, related to loss of en, was separated into two single-step processes with Fraser–Suzuki function. The obtained individual steps were described by Johnson–Mehl–Avrami A2 model and Sestak–Berggren model, respectively. Validation of the proposed kinetic triplets for individual steps was performed using master plot and Perez-Maqueda criteria. The third degradation step is related to the fragmentation of pyr ion most likely followed with the release of a number of gaseous products.

Study of crystallization kinetics of Se77.5Te15Sb7.5 glass using isoconversional models

The crystallization process of Se77.5Te15Sb7.5 glass is studied by differential scanning calorimetry (DSC) technique under non-isothermal conditions at various heating rates. The crystallization parameters are deduced using different models. The validity of the Johnson–Mehl–Avrami (JMA) model to describe the crystallization process for the studied composition is investigated. Comparing experimental and calculated DSC curves indicate that the crystallization process of Se77.5Te15Sb7.5 glass cannot satisfactorily be described by the JMA model. In general, simulation results indicate that the Sestak–Berggren model is more suitable to describe the crystallization kinetics. The crystalline phases are identified using the X-ray diffraction technique and scanning electron microscopy.