Model-free Isoconversional Method Research Articles

Thermal and Kinetic Behaviour ofPongamia GlabraOil Fatty Amide

N,N-bis(2-hydroxyl ethyl) Pongamia glabra oil fatty amide (HEPA) was synthesised by the aminolysis of pongamia oil. The structural elucidation of HEPA was carried out by FTIR,1H NMR and13C NMR spectroscopy. Physico-chemical studies were carried out by standard laboratory methods. Melting point of pongamia glabra oil and HEPA was measured through differential scanning calorimetry. Thermogravimetry/differential thermogravimetry analysis (TG/DTGA) was used to evaluate the thermal and kinetic behaviour of synthesised HEPA in nitrogen atmosphere under nonisothermal conditions with heating rates of 5, 10, 20, and 30 °C min−1. The TG curves of polymers at four heating rates were approximately in the same shape which indicated that mass loss is independent of heating rate. Obtained TGA data were analysed by the means of model-free isoconversional methods using Flynn–Wall–Ozawa and Kissinger–Akahira–Sunoseon applications on the whole range of temperature, and were found to be consistent. It was found that at the end of the decomposition process, the value of activation energy increases.

Synthesis, characterization, and thermal degradation kinetics of biuret–formaldehyde polymeric ligand and its polymer metal complexes

In the present study, biuret–formaldehyde (BF) polymeric ligand was prepared by condensation reaction, and its polymer metal complexes [BF-M(II)] were prepared with transition metal ions. Synthesized polymers were characterized by elemental, spectral, and thermal analyses. The geometry of central metal ions was determined using magnetic susceptibility measurement and electronic spectra, which reveals that Co(II) and Ni(II) ions have octahedral geometry, while Cu(II) and Zn(II) ions have square planer and tetrahedral geometry, respectively. Thermogravimetric (TG) analysis was used to estimate thermal and kinetic behavior of polymers at heating rates of 10, 15, and 20 °C min−1 under helium atmosphere. The TG curves of polymers at three heating rates were more or less in similar shape, which indicated that mass loss is independent of heating rate. Thermogravimetric data were analyzed by means of model-free isoconversional method of Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose on the whole range of temperature. It was found that values of apparent activation energy (E a) of [BF-M(II)] polymers are higher than BF and influenced by the metal type.

Glass transition, kinetics of crystallization and anomalous phase transformations in tellurite melts

A lead-tellurite (0.3PbO:0.7TeO2) eutectic glass was investigated through a combination of thermal, structural and vibrational spectroscopic studies to examine the kinetics of crystallization and phase transformations during the heating of the glass and the cooling of the liquid. A linear relation was found to correlate the glass transition and crystallization temperatures, from which the ideal glass transition was determined. Among the several kinetic models that were analyzed, the primary crystallization was found to agree most to the Johnson–Mehl–Avrami model, suggesting the microstructural evolution as a two-dimensional crystallization and growth. The complexity of the transformation process was evidenced from the dependence of activation energy (E) on the crystallized fraction (α) using model-free isoconversional methods. The decreasing trend of E(α) was found to be characteristic of a reversible process followed by an irreversible one. Furthermore, nucleation was found to maximize at a temperature much lower than the experimentally observed crystallization onset. The structural evolution of the devitrified phases depicted the coexistence of phases (PbTeO3 and α-TeO2) during the two-stage crystallization. Anomalous crystallization into the Pb2Te3O8 phase was observed when the devitrified melt was cooled. Such an anomaly is explained using amorphous phase separation, which is inherent to the tellurite glass system owing to the presence of unique asymmetric structural units in the corresponding melts.

The Effect of Mechanical Activation on Non-isothermal Decomposition Kinetics of Ag2O–Graphite Mixture

The effect of mechanical activation for 0, 2 and 4 h using high-energy planetary ball mill on the thermal decomposition kinetics of Ag2O–graphite powder mixture, i.e., mechanochemical decomposition, is systematically investigated by thermogravimetric analysis and a differential scanning calorimeter (DSC) in terms of a model-free advanced isoconversional method of Vyazovkin. The DSC results showed the mechanochemical decomposition shifts the reaction temperature in the range of 140–436°C (for as-received sample) to 170–335°C and 161–250°C after 2 and 4 h milling, respectively. The results show that decomposition of as-received Ag2O–graphite mixture with the average activation energy of 118.93±3.95 kJ mol−1 consists of two steps. The first step is a complex process with the participation of at least of two mechanisms, and the second step is a single-step process. The thermal decomposition of mechanically activated Ag2O for 2 h is a multi-steps process with the average activation energy of 99.38 ± 2.36 kJ mol−1. Moreover, the thermal decomposition of mechanically activated Ag2O–graphite powder for 4 h is a single-step process with the average activation energy of 93.68± 2.26 kJ mol−1.

Kinetics of thermolysis of lanthanum nitrate with hexamethylenetetramine: Crystal structure, TG–DSC, impact and friction sensitivity studies, Part-96

The development of high energetic materials includes process ability and the ability to attain insensitive munitions (IM). This paper investigates the preparation of lanthanum metal nitrate complex of hexamethylenetetramine in water at room temperature. This complex of molecular formulae [La (NO3)2(H2O)6] (2HMTA) (NO3−) (H2O) was characterized by X-ray crystallography. Thermal decomposition was investigated using TG, TG–DSC and ignition delay measurements. Kinetic analysis of isothermal TG data has been investigated using model fitting methods as well as model free isoconversional methods. The sensitivity measurements towards mechanical destructive stimuli such as impact and friction were carried out and the complex was found to be insensitive. In order to identify the end product of thermolysis, X-ray diffraction patterns of end product was carried out which proves the formation of La2O3.

Study of the Curing Kinetics of Epoxy Resins with Biobased Hardener and Epoxidized Soybean Oil

The goal of this research was to study the kinetics of the reaction of diglycidyl ether of bisphenol A (DGEBA)-based epoxy resin cured with sebacic acid as a biobased hardener in the presence of three different loadings of epoxidized soybean oil (ESO) (i.e., 10, 20, 30 wt %). Nonisothermal differential scanning calorimetric (DSC) and model-free isoconversional method was used to analyze the curing kinetic data and determine the activation energy of the reactions. It was found that the biobased hardener increased the enthalpy of reaction as well as the activation energy of reaction in comparison to the amine hardeners that are currently used for epoxy curing. The addition of epoxidized soybean oil increased the enthalpy of reaction, maximum exothermic temperature, and activation energy of the system. Kissinger–Akahira–Sunose (KAS) and Starink methods were used to determine the activation energy of the studied systems. It was also found that the curing reaction of epoxy with 30 wt % of ESO is diffusion cont...

Estimation of kinetic parameters for the phase change memory materials by DSC measurements

The non-isothermal method for estimating the kinetic parameters of crystallization for the phase change memory (PCM) materials was discussed. This method was applied to the perspective PCM material of Ge2Sb2Te5 with different Bi contents (0, 0.5, 1, 3 mass%) for defining the kinetic triplet. Rutherford backscattering spectroscopy and X-ray diffraction were used to carry out elemental and phase analysis of the deposited films. Differential scanning calorimetry at eight different heating rates was used to investigate kinetics of thermally induced transformations in materials. Dependences of activation energies of crystallization (Ea) on the degree of conversion were estimated by model-free Ozawa–Flynn–Wall, Kissinger–Akahira–Sunose, Tang and Starink methods. The obtained values of Ea were quite close for all of these methods. The reaction models of the phase transitions were derived with using of the model-fitting Coats–Redfern method. In order to find pre-exponential factor A at progressive conversion values, we used values of Ea already estimated by the model-free isoconversional method. It was established that the crystallization processes in thin films investigated are most likely describes by the second and third-order reactions models. Obtained kinetic triplet allowed predicting transition and storage times of the PCM cells. It was found that thin films of Ge2Sb2Te5 + 0.5 mass% Bi composition can provide the switching time of the phase change memory cell less than 1 ns. At the same time, at room temperature this material has a maximum storage time among the studied compositions.

Physical-chemical characterization of biomass samples for application iin pyrolysis process

The use of lignocellulosic biomass as an energy source has considerably increased. Due to the diverse natures of biomass materials, their properties widely range and exhibit different behaviors in thermal processes. The most important properties that provide information about a fuel are heating values, ash composition, proximate (determination of moisture, ash, volatile and fixed carbon content), and ultimate analysis (C, H, N, S and O composition). Moreover, the kinetic study of the thermal behavior of a fuel can be useful for the understanding of the complex decomposition process of each material. This study focuses on the physical-chemical characterization of six lignocellulosic biomasses, namely coffee husk, tucuma seed, sugar cane bagasse, peanut shell, rice husk and pine sawdust, widely available in Brazil. A thermogravimetric analyzer was used to study their decomposition behavior in a pyrolytic environment. Non-isothermal thermogravimetric data were used and the application of a model-free isoconversional method enabled the evaluation of the activation energy (Ea) of the biofuels. The curves also show that the behavior during thermal decomposition varies from one biomass to another and these differences imply the importance of a comprehensive characterization study of fuels for the development and optimization of reactors. The knowledge on biomass properties enables the prediction of environmental impacts and technical aspects related to thermal processes. Therefore, thermal decomposition behavior is a consequence of the feedstock physical-chemical characteristic, which also provides valuable information regarding features of the complex reactions that occur throughout the pyrolysis of the biomass.

Distinct splitting of polymeric cellulosic signals in cashew shell: a TG-diagnosis

Distinct splitting of the cellulosic polymer signal was seen in thermogravimetric analysis of cashew shell (CS). The splitting was more pronounced in CS as compared to cashew shell cake. The splitting of cellulosic polymer peaks was ascribed to cellulosic depolymerization occurring in two phases during thermal degradation of CS. Three protective tissue configurations of CS was considered responsible for this phenomenon. Kinetics were compared by using two model free isoconversional methods, namely the Friedman and Ozawa-Flynn-Wall.

Synthesis, characterization and thermolysis of lanthanide metal nitrate complexes with 1, 10-phenanthroline, Part-95

The nitrate complexes of cerium, praseodymium and neodymium with 1,10-phenanthroline (phen) of general formula [Ln(phen)2(NO3)2(H2O)2]·NO3 (where, Ln=Ce, Pr and Nd) were prepared and characterized by X-ray crystallography. Thermolysis of these complexes was investigated by simultaneous thermogravimetry (TG) and differential thermal analysis (DTA). Isothermal TG was taken to evaluate the kinetic parameters using model fitting as well as model free isoconversional methods. The thermolytic pathways were also suggested, which involves decomposition followed by ignition. All the three complexes had coordination number ten and showed multistep decompositions. In order to evaluate the response of rapid heating, ignition delay (Di) measurements were undertaken. The activation energies for ignition were found to decrease in the order: Nd>Pr>Ce.

Model free isoconversional procedure for evaluating the effective activation energy values of thermally stimulated processes in dinitroimidazoles.

The decomposition kinetics of 1,4-dinitroimidazole, 2,4-dinitroimidazole, and N-methyl-2,4-dinitroimidazole have been investigated using thermogravimetry-differential thermal analysis technique under N2 atmosphere at the flow rate 100 cm(3)/min. The Flynn-Wall-Ozawa method and the Friedman method were used for the estimation of the effective activation energy values. These model free isoconversional kinetic methods showed variation in the calculated values due to the approximation of temperature integral used in the derivations of the kinetic equations. The model compounds were decomposed by multi-step kinetics evident from the nonlinear relationship of the effective activation energy values with the conversion rate. Three different reaction pathways namely NO2 elimination, NO elimination, and HONO elimination are expected to play crucial role in the decomposition of nitroimidazoles. The model dinitroimidazoles represent different decomposition kinetics, and the reaction pathways the NO2 elimination, and NO elimination compete with each other for the decomposition mechanism. The present study is certainly helpful in understanding the decomposition kinetics, and dynamics of substituted nitroimidazoles to be used for fuel, and explosive applications.

Thermal and kinetic analyses of 2,5-bis(2-hydroxyphenyl)thiazolo[5,4-d]thiazole

Thermal behavior and UV–Vis absorption properties of 2,5-bis(2-hydroxyphenyl)thiazolo[5,4-d]thiazole were investigated in the present study. It was found that decomposition occurs in two stages which correspond to removal of both phenolic rings and degradation of remaining core structure, respectively. After the characterization of decomposition stages, apparent activation energy values of each stage were calculated using model-free isoconversional methods (FWO and KAS). Apparent activation energies of decomposition stages are determined by both methods. Their averages are calculated as 98.232 and 123.253 kJ mol−1 in consecutive order. UV–Vis absorption properties of this compound have been determined with using different solvents.

Kinetic analysis of the thermal processing of silica and organosilica.

The incorporation of an organic group into sol-gel-derived silica causes significant changes in the structure and properties of these materials. Therefore, the thermal treatment of organosilica materials may require a different approach. In the present paper, kinetic parameters (activation energy, pre-exponential constant, and reaction models) have been determined from mass loss data for the dehydration, dehydroxylation, and decomposition reactions that take place upon heating silica and organosilica. Parameters were obtained by employing model-free isoconversional methods to data obtained under multiple heating rates as well as by multivariate analysis of the kinetics using a multistep reaction model with distributed activation energy. For silica, it can be concluded that the reaction atmosphere (i.e., inert or thermo-oxidative) has no influence on the reaction rate of the dehydration and dehydroxylation reactions that are responsible for the densification of the material. Under inert atmosphere, full dehydration can be reached without affecting the organic moiety. Achieving complete dehydroxylation of the organosilica is practically impossible as decomposition does manifest itself under commonly employed calcination temperatures. This indicates that prudence is required in designing a heat treatment program for these hybrid materials. To aid in optimizing the thermal treatment, a predictive model was developed, which can be used to forecast the extent of dehydration, dehydroxylation, and decomposition reactions under a multitude of temperature programs.

Crystallization kinetics of Ti20Zr20Cu60 metallic glass by isoconversional methods using modulated differential scanning calorimetry

The study of crystallization kinetics of amorphous alloys has been a matter of great interest for material researchers for past few decades, since it provides information about the kinetic parameters i.e., activation energy of crystallization and the frequency factor. These kinetic parameters can be calculated by model-free isoconversional methods. Isoconversional methods allow calculating the activation energy as a function of degree of conversion, α. Hence, these methods provide accurate results for multistep processes like crystallization. Model-free methods are categorized as linear and non-linear isoconversional methods. Linear methods are further classified as linear differential and linear integral isoconversional methods. In present work, we have used these isoconversional methods to study the effect of non-linear heating rate, employed by modulated differential scanning calorimetry (MDSC), on the non-isothermal crystallization kinetics of Ti20Zr20Cu60 metallic glass. For Ti20Zr20Cu60, MDSC curves clearly indicate a two-step crystallization process. Both crystallization peaks were studied based on the modified expressions for isoconversional methods by non-linear heating rate. The term corresponding to non-linearity comes out to be (A T ω/2β)2. The effect of non-linear heating rate on measurement of kinetic parameters by isoconversional methods is studied. The activation energy of crystallization is calculated for Ti20Zr20Cu60 metallic glass for various degrees of conversion by linear integral isoconversional methods i.e., Ozawa–Flynn–Wall, Kissinger–Akahira–Sunose, and also with Friedman method which is a linear differential isoconversional method.

Kinetics of Thermolysis of Nickel(II) Perchlorate Complex with n-Propylamine

Complex of nickel perchlorate with n-propylamine has been synthesised with molecular formula [Ni(n-pa)3(ClO4)(H2O)]ClO4. It has been characterised by elemental analysis, thermogravimetry, UV-VIS, and IR spectroscopic data. Thermal properties have been investigated by thermogravimetry (TG) in static air and by simultaneous thermogravimetry-derivative thermogravimetry-differential thermal analysis (TG-DTG-DTA) in flowing nitrogen atmosphere. Kinetics of thermolysis has been analysed applying model-fitting and model-free isoconversional method on isothermal TG data recorded at five different temperatures. To observe the response of complex towards fast heating, explosion delay time has been recorded at various temperatures and kinetics of explosion has been studied using these data.

Kinetic analysis for non-isothermal decomposition of un-irradiated and gamma-irradiated anhydrous cadmium nitrate

Abstract The thermal decomposition of untreated and γ-irradiated samples of anhydrous cadmium nitrate was performed under non-isothermal conditions at different heating rates (5, 10, 15 and 20 ℃ min –1). The results showed that the decomposition proceeds in one major step with the formation of cadmium oxide as solid residue. The data were analysed by using both isoconversional and non-isoconversional methods. The activation energy was calculated by various model-free isoconversional methods: Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS) and Friedman (FR) methods. Irradiation enhances the decomposition and the effect increases with the irradiation dose. The activation energy decreases on irradiation. The appropriate conversion model for the thermal decomposition process selected by means of the master-plot method agrees with phase boundary reaction with spherical symmetry (R3 mechanism) for both untreated and irradiated salts at all heating rates.

Curing Kinetics and Mechanical Properties of endo-Dicyclopentadiene Synthesized Using Different Grubbs’ Catalysts

Isothermal curing of endo-dicyclopentadiene (endo-DCPD) using the first and second generation Grubbs’ catalysts as the polymerization initiators was studied by means of differential scanning calorimetry (DSC) according to model-free isoconversional and model-fitting approaches. It revealed that the two Grubbs’ catalysts exhibited apparent differences in ring-opening metathesis polymerization (ROMP) of endo-DCPD. The second generation catalyst was more efficient in catalytic activity for overall ROMP of endo-DCPD than the first generation catalyst, as evident from the reaction rate and fractional conversion (α). The model-free isoconversional method showed similar dependence of the activation energy (Eα) on α for the two catalyst systems; however, the second generation catalyst system involved a higher Eα, up to α ≈ 0.8, above which the Eα value suddenly drops with increase of conversion. The model-fitting method of the ROMP was satisfactorily described by the decelerating reaction and the autocatalytic reaction mechanisms for the first and the second generation catalyst systems, respectively. The effect of diffusion-control was incorporated into the model-fitting method to describe the ROMP reaction throughout the entire conversion. For fully cured samples (poly-DCPD), the first generation catalyst system has higher cross-linking density and lower tensile toughness relative to the second generation. Dynamic mechanical behaviors were also different for poly-DCPD formed using the two catalysts.

Kinetics of thermal degradation of wood biomass

AbstractPyrolysis kinetics of a hardwood representative, beech (Fagus sylvatica), was investigated by two different kinetic approaches: model-free isoconversional method and model-fitting method. The model-free isoconversional method was used for the determination of apparent kinetic parameters, i.e. the activation energy and pre-exponential factor. The model fitting method was used for the optimization of kinetic parameters of the reaction pathways of three selected reaction mechanisms: one-step, two-step, and three-step one. In both approaches, thermo-gravimetric data were used at five heating rates: 2°C min−1, 5°C min−1, 10°C min−1, 15°C min−1 and 20°C min−1. As the most suitable mechanism, the three-step mechanism containing the intermediate degradation step was chosen. This selection was supported by experimental results from the 13C NMR analysis of solid residues prepared at the key temperatures within the range of 230–500°C. The progress of mass fraction values of each component in this mechanism was simulated. Conclusions from the simulation were confronted with experimental results from the 13C NMR.

PREPARATION, CHARACTERIZATION, AND THERMAL BEHAVIOR OF COBALT(II) AND ZINC(II) PERCHLORATE COMPLEXES WITH N-PROPYLAMINE

Two complexes of cobalt and zinc have been prepared with the molecular formula [Co(n − pa)3(ClO4)(H2O)]ClO4 and [Zn(n − pa)3(ClO4)(H2O)]ClO4, where n − pa = n-propylamine. These complexes have been characterized by elemental analysis, thermogravimetry (TG), ultraviolet/visible, and infrared spectroscopic data. The thermal properties have been investigated using TG in static air and by simultaneous TG/derivative TG/differential thermal analysis inflowing nitrogen atmosphere. The kinetics of thermolysis has been analyzed by applying model-fitting and model-free isoconversional methods using isothermal TG data recorded at five different temperatures. To observe the response of these complexes to fast heating, the explosion delay time has been recorded at various temperatures and their kinetics has been studied using these data.

Novel silicon-modified phenolic novolac resins: Non-isothermal curing kinetics, and mechanical and thermal properties of their biofiber-reinforced composites

A silicone-contained biphenol type monomer, 4,4′-(1,3-dipropyl-tetramethyldisiloxane)bis-2-methoxyphenol(SIE), was used to modify phenolic novolac resin by being copolymerized with phenol and formaldehyde to yield SIE-modified phenolic resins (SPNs). The curing behavior of SPNs with hexamethyleneteramine (HMTA) was analyzed by DSC tests, and the non-isothermal curing kinetics were analyzed using the model-fitting and model-free isoconversional methods. Then, SPN/HMTA was used as the resin matrix, while surface-treated chopped sisal fiber was used as the reinforced filler to produce the silicon modified phenolic molding composites (SIEC). The finished composites expressed improved mechanical and thermal resistance properties compared with unmodified composites.