Variation Of Activation Energy Research Articles

Heterogeneous Kinetics of Thiourea Electro-Catalytic Oxidation Reactions on Palladium Surface in Aqueous Medium.

The electrochemical behaviors of thiourea (TU) oxidation have been studied at Palladium (Pd) electrode in the acidic medium by recording cyclic voltammograms (CVs). The influence of pH was investigated in the pH range of 1.0 to 9.0. Facilitated adsorption of TU on electrode surface results in enhanced catalytic response in acidic medium and maximum electro-catalytic response was found at pH∼3.0. Chronoamperometric (CA) experiment determined this oxidation as 1e- transfer process and the variation of TU concentration reveals a 1st order kinetics. In the CV responses, the large value of peak separation (▵Ep >380 mV) calculated by the variation of scan rate indicates that oxidation of TU is an irreversible process. With the aid of convolution potential sweep voltammetry (CPSV), the standard rate constant (k°) for the reaction was found to be 7.1×10-4 cm/s and the formal potential constant (E°' ) was evaluated to be ∼0.37 V vs Ag/AgCl (sat. KCl). The value of transfer coefficient (α) was found to vary from 0.74 to 0.40 with applied potential (E). From the potential dependent variation of transfer coefficient (α) and activation energy (▵G≠ ), it was concluded that the overall electrochemical oxidation of TU follows a stepwise mechanism at lower potential (<0.40) V and a concerted one at relatively higher potential (>0.40) V. The FTIR analysis of the product after oxidation of TU molecules confirmed the appearance of a new sharp band near 530 cm-1 due to the formation of S-S bonds suggesting formation of formamidine disulfide (FD) ions.

Thermal Oxidative Decomposition of Soybean Straw: Thermo-Kinetic Analysis via Thermogravimetric Analysis and Artificial Neural Networks

Keeping in view the energy shortage problem, the bioenergy potential of soybean straw have been evaluated by thermos-kinetic study using thermogravimetric analysis and artificial neural networks. TG-DTG curves at 10, 20, and 30°C min−1 revealed that the thermal oxidative decomposition of soybean straw could be divided into three stages and the second stage (180 to 380°C) would be the most suitable for thermal conversion of soybean straw into energy and chemicals. Kinetics analysis results showed that the activation energy values of models ranges were: KAS (87.57-819.24 KJ mol−1), and OFW (92.01-790.85 KJ mol−1), respectively. The variation of activation energy indicated the thermal decomposition process of soybean straw is complicated and may be consisting of several reactions. Furthermore, an ANN model was applied to predict the thermal decomposition of soybean straw. The good fitness between experimental and predict data (R2 = 0.999) validated the accuracy of the model in predicting the mass loss of thermal oxidative decomposition process.

Co-pyrolysis behaviors of low-rank coal and polystyrene with in-situ pyrolysis time-of-flight mass spectrometry

In-situ detection of the primary volatiles is vital for co-pyrolysis interactions of coal and waste plastics, and can reveal their interactions based on the primary volatiles distribution and kinetics. In this study, a novel in-situ pyrolysis time-of-flight mass spectrometry (Py-TOF-MS) was applied to analyze primary volatiles distribution and evolved behaviors of co-pyrolysis of a low-rank Pingshuo coal (PC) and polystyrene (PS), and disclose the interaction mechanisms of PC/PS co-pyrolysis combined with different kinetic models. TG results indicated that the blending ratio of PC to PS being 7:3 has the best interaction in improving volatiles evolved performance. According to in-situ Py-TOF-MS analysis, the addition of PS can promote early release of volatiles from the peak of 418 °C (PC) to 389 °C, and dramatically enhance H-transfer. Among them, the increase of monocyclic aromatic hydrocarbons ascribed to the Diels-Alder and dehydration reaction, while the styrene monomer obviously increases from 2.15% to 7.34% due to the co-pyrolysis enhances the cleavage of Car-Cβ bond on the PS main chain. Moreover, kinetics study identified that the variation of activation energy can provide effective supplements to the co-pyrolysis interactions.

Extended dynamic vapor sorption of glutinous rice flour observed in logarithmic time scale and its modeling as a process with varying activation energy

AbstractWith the objective of characterizing water sorption kinetics of glutinous rice flour during extended water vapor exposure, water adsorption and desorption measurements were conducted at nine relative humidity (RH) levels for up to 1,500 min per step, and displayed in a logarithmic time scale. A three‐stage sorption kinetics was observed, and the final stage was characterized with a very long and slow process. The final sections of the kinetic curves were concave to log(t) axis for adsorption while linear for desorption, even after the flour was gelatinized. Increment in RH step and flour particle size, and variation in water content can only postpone starting of the linear stage. Analysis using an Elovich‐type model indicated that both adsorption and desorption can be treated as processes whose activation energy varied consistently during sorption. Reaction order difference between adsorption and desorption was the major contributor to their distinct kinetic responses in the final stages.Practical ApplicationsWater sorption kinetic measurements are necessary for exploring mass transfer mechanism, and determining parameters such as water diffusivity and interfacial mass transfer coefficient. Extended measurement duration allows one to catch the entire characteristics of a kinetic process. Distinct kinetic features between adsorption and desorption of glutinous rice flour were observed when the data were plotted against logarithm of time. The later stage was a slow process. Further analysis using an Elovich‐type model indicated that both adsorption and desorption were processes with varying activation energy. This information can be potentially helpful in optimizing both the quality of food product and the economics of many food processes involving water transfer.

Variation of activation energy determined by a modified Arrhenius approach: Roles of dynamic recrystallization on the hot deformation of Ni-based superalloy

The hot deformation behaviors of Ni18Cr9Co9Fe5Nb3Mo superalloy were explored in the formation temperature range free of γ’ phase with various strain rates applied. The hot deformation behaviors are initially modeled with Arrhenius equation which gives an average activation energy of 581.1 kJ mol−1. A modified Arrhenius approach, including the updated Zener-Hollomon parameter is proposed to consider the change of activation energy under different deformation conditions which turns out a relatively accurate computation for activation energy of hot deformation, i.e., the standard variance for modified model calculated in the covered deformation condition is just 35.4 % of that for Arrhenius equation. The modified model also proposes a map for activation energy which ranges from 571.5-589.0 kJ mol−1 for various deformation conditions. Microstructural features of the representative superalloy specimens were characterized by electron backscattered diffraction (EBSD) techniques in order to clarify the influence of activation energy on the microstructural formation. It is found that the Ni-based superalloy samples with higher activation energy are promoted by the degree of dynamic recrystallization which suggests that the rise in activation energy gives either a better recrystallization rate or finer grains.

Observation of low temperature superplasticity in an ultrafine grained AA6063 alloy

In the present work, mechanical properties and low temperature superplasticity behavior of a nano/ultrafine grained AA6063 alloy fabricated by accumulative roll bonding (ARB) was investigated. To that end, superplasticity was evaluated at various deformation temperatures and for different strain rates in an AA6063 alloy ARBed up to seven cycles. Results showed that the nano/ultrafine grained AA6063 alloy exhibited an excellent low temperature superplasticity (low peak stress of 40 MPa and maximum elongation up to 270%) at 300 °C & 350 °C and under the nominal strain rates of 5 × 10−3s−1, 5 × 10−2s−1, 5 × 10−1s−1. The best condition of superplasticity, together with a stable microstructure, was obtained at 300 °C. Results also showed that at the deformation temperature of 250 °C, and under all strain rates, the elongation does not exceed 95%, hence for the absence of proper superplasticity at this temperature. It was found that although high amount of total elongation can be obtained at 350 °C and under low strain rates of 5 × 10−2s−1, 5 × 10−3s−1, the microstructural instability of these cases made them unsuitable for industrial applications. During superplastic deformation, low angle grain boundaries (LAGBs) gradually transformed into high angle grain boundaries (HAGBs) to sustain grain boundary sliding and to accommodate dynamic recovery. Constitutive equations were built, and strain rate sensitivity, as well as apparent activation energy variation were calculated. Using Zener-Hollomon parameter, the dominant hot deformation mechanism(s) in each deformation temperature was explained in conjunction with work hardening, dynamic recovery, dynamic recrystallization (DRX) and grain boundary sliding. As well, results indicated that the grain boundary sliding was the predominant deformation mechanism at 350 °C. Finally, a truly superplastic regime was achieved at the temperature of 300 °C and for the strain rate of 5 × 10−2 s−1.

Effect of Nickel Doping on the Cure Kinetics of Epoxy/Fe3O4 Nanocomposites

This short communication aims to evaluate the cure kinetics of epoxy/NixFe3−xO4 nanocomposites. Differential scanning calorimetry (DSC) provided support for cure kinetics analysis based on the variation of activation energy (Eα) as a function of the extent of crosslinking reaction, α. The average values of Eα calculated based on Kissinger and Friedman methods were 59.22 and 57.35 kJ/mol for the neat epoxy, 43.37 and 48.74 kJ/mol for the epoxy/Fe3O4, and eventually 50.48 and 49.19 kJ/mol for the epoxy/NixFe3−xO4 nanocomposites. The partial replacement of Fe2+ ion sites in the Fe3O4 crystal lattice by the Ni2+ ions changed to some content the cure kinetic profile because of the fact that a lower level of energy was needed for curing by incorporation of NixFe3−xO4 into the epoxy matrix. The rate of reaction calculated theoretically adequately fitted with experimental profiles obtained in DSC experiments.

Research on the oxidation characteristics of zinc sulfite in the zinc oxide desulfurization process

ABSTRACT Aiming at the pollution problem of low-content SO2 in non-ferrous metal production industry, the oxidation kinetics of zinc sulfite in the zinc oxide desulfurization process was studied. The concentration change of Zn2+, variation of pH, temperature and apparent activation energy in the oxidation process of two ZnSO3 samples were investigated systematically. The results indicate that the raw material with different crystal water has little effect on the oxidation kinetic of zinc sulfite. The reaction process comprises two stages: the dissolution process and the oxidation process. The zinc ion concentration is linearly rising with the action time during the oxidation process. The pH value rises quickly in the dissolution process and goes down slowly with reaction time in the oxidation process. The process is mainly controlled by a diffusion step and less effected by the temperature. The apparent activation energy E a obtained for the two samples are 8.662 and 9.645 kJ/mol, respectively. Integrated with the kinetic model, the oxidation rate of zinc sulfite is controlled by the diffusion of HSO3 − and O2 to the gas–liquid interface.

Electronic structure benchmark calculations of CO2 fixing elementary chemical steps in RuBisCO using the projector-based embedding approach.

Ribulose 1,5-bisphosphate carboxylase-oxygenase (RuBisCO) is the main enzyme involved in atmospheric carbon dioxide (CO2 ) fixation in the biosphere. This enzyme catalyzes a set of five chemical steps that take place in the same active-site within magnesium (II) coordination sphere. Here, a set of electronic structure benchmark calculations have been carried out on a reaction path proposed by Gready et al. by means of the projector-based embedding approach. Activation and reaction energies for all main steps catalyzed by RuBisCO have been calculated at the MP2, SCS-MP2, CCSD, and CCSD(T)/aug-cc-pVDZ and cc-pVDZ levels of theory. The treatment of the magnesium cation with post-HF methods is explored to determine the nature of its involvement in the mechanism. With the high-level ab initio values as a reference, we tested the performance of a set of density functional theory (DFT) exchange-correlation (xc) functionals in reproducing the reaction energetics of RuBisCO carboxylase activity on a set of model fragments. Different DFT xc-functionals show large variation in activation and reaction energies. Activation and reaction energies computed at the B3LYP level are close to the reference SCS-MP2 results for carboxylation, hydration and protonation reactions. However, for the carbon-carbon bond dissociation reaction, B3LYP and other functionals give results that differ significantly from the ab initio reference values. The results show the applicability of the projector-based embedding approach to metalloenzymes. This technique removes the uncertainty associated with the selection of different DFT xc-functionals and so can overcome some of inherent limitations of DFT calculations, complementing, and potentially adding to modeling of enzyme reaction mechanisms with DFT methods.

Analysis of Iron Oxide Reduction Kinetics in the Nanometric Scale Using Hydrogen.

Iron nanopowder could be used as a sintering aid to water-atomised steel powder to improve the sintered density of metallurgical (PM) compacts. For the sintering process to be efficient, the inevitable surface oxide on the nanopowder must be reduced at least in part to facilitate its sintering aid effect. While appreciable research has been conducted in the domain of oxide reduction of the normal ferrous powder, the same cannot be said about the nanometric counterpart. The reaction kinetics for the reduction of surface oxide of iron nanopowder in hydrogen was therefore investigated using nonisothermal thermogravimetric (TG) measurements. The activation energy values were determined from the TG data using both isoconversional Kissinger–Akahira–Sunose (KAS) method and the Kissinger approach. The values obtained were well within the range of reported data. The reaction kinetics of Fe2O3 as a reference material was also depicted and the reduction of this oxide proceeds in two sequential stages. The first stage corresponds to the reduction of Fe2O3 to Fe3O4, while the second stage corresponds to a complete reduction of oxide to metallic Fe. The activation energy variation over the reduction process was observed and a model was proposed to understand the reduction of surface iron oxide of iron nanopowder.

Silane‐functionalized Al2O3‐modified polyurethane powder coatings: Nonisothermal degradation kinetics and mechanistic insights

AbstractThis work reports on nonisothermal degradation kinetics of polyurethane (PU)‐based powder coatings containing 1, 3, and 5%wt% vinyltrimethoxysilane functionalized Al2O3 (V‐Al2O3) nanoparticles. Thermogravimetric analysis of PU/V‐Al2O3 powder coatings with different V‐Al2O3 contents has been performed at different heating rates. Variation of activation energy (Ea) of PU/V‐Al2O3 powder coatings was modeled as a function of partial mass loss by using Kissinger–Akahira–Sunose, Ozawa–Wall–Flynn and modified Coats–Redfern isoconversional approaches. The results revealed hindered decomposition process of PU/V‐Al2O3 nanocomposite powder coatings, featured by an increase in activation energy of degradation from ∼158 for blank PU to 225, 183, and 229 kJ/mol for nanocomposites filled with 1, 3, and 5 wt% of V‐Al2O3, respectively. Likewise, pre‐exponential factor values increased for samples containing V‐Al2O3 nanoparticles compared to that of blank sample. Sestak–Berggren kinetic model appropriately captured thermal degradation behavior of PU/V‐Al2O3 nanocomposites than that of nth order decomposition kinetic reaction models.

Investigation of Reaction Kinetics in Carbon Anode with Nano-Fillers through Impedance Spectroscopy

Lithium-ion batteries have been very successful in consumer electronics as viable and efficient power sources for many small and portable devices such as mobiles, laptop, watches, camcorders, PDAs, cameras and other communication devices [1-2]. However, poor electronic conduction in electrodes due to an unstable and fragile conducting network of traditional conducting additives is still the limitation for large scale commercialization of this energy storage technology in automotives (such as EVs, HEVs, PHEVs, etc.) where high power density is desired frequently [2, 3]. In addition, poor contact due to large size of active material and sluggish kinetics makes it difficult to achieve their full theoretical capacities at a practical level [4]. The conducting network in an electrode influences the performance of charge transfer kinetics at the electrode-electrolyte interface and ion migration through the solid electrolyte interface (SEI) layer as suggested by an earlier study [5]. In graphitic anode, when an ion of lithium is inserted into the material, the crystal structure of the active material changes with the state of charge (SOC), and the resulting changes affect the intercalation/deintercalation reactions [6].In this work, we investigate the kinetics of lithium-ion transfer for mesocarbon mocrobeads (MCMB) as active material with nano-conducting fillers, namely carbon black (CB) and multiwalled carbon nanotubes (MWCNT), by carrying out electrochemical impedance spectroscopy (EIS) measurements at different states-of-charge (SOC) and temperatures for CR2016 coin half-cells. The working electrodes were fabricated with 88% MCMB, 4% conducting additives and 8% PVDF coated on copper foil. It has recently been demonstrated that a synergistic improvement in electrical and electrochemical performance occurs with partial substitution of CB by CNT [7]. By recording impedance spectra at different temperatures and SOCs for electrodes having different conducting additives (CB, CNT or CB+CNT), we analyze the impact of conducting nano-fillers upon the kinetics of the anode reactions and the dependency of these on the SOC. The impedance spectra were measured at the set SOC with an AC perturbation of amplitude 5mV in the range 30mHz to 200kHz. The conductivity of interfacial charge transfer (1/Rct) obeys the Arrhenius equation, 1/Rct=A0exp(Ect/RT). The symbols A0, Ect, R and T stand for frequency factor, activation energy, gas constant and absolute temperature. A typical EIS spectrum of MCMB electrode in a lithium-ion half-cell and the respective resistances deconvoluted using an equivalent circuit is demonstrated in Fig. 1(a). Impedance spectra plotted at different temperatures for MCMB electrode having 4% CNT as conducting additives at OCV of 0.17V vs. Li/Li+ are illustrated in Fig. 1(b) and the corresponding Arrhenius plot of interfacial conductivity (1/Rct) obtained from impedance plot is shown in Fig. 1(c). The activation energy of charge transfer as a function of SOC and open-circuit potential is illustrated in Fig. 1(d). The lithium-ion staging process in MCMB electrode is highlighted by vertical lines as shown in Fig. 1(d). From Fig. 1(d), the variation in activation energy can be attributed to the insertion/deinsertion of lithium ions into carbon and the chemical nature of the solid-electrolyte interphase (SEI) layer deposited on the surface of the active material. The activation energy associated with Rct tends to decrease with the potential and vary with different conducting nano-fillers. This indicates that the staging phenomenon and SEI composition affect the charge transfer process. It is observed that the activation energy in stage-I is relatively high than the other stages which is attributed to the large structural change associated with lithium-ion insertion/deinsertion in this stage. For comparative analysis, the activation energy for the interfacial Li-ion transfer in electrodes having conducting additives CB, and CB+CNT will be evaluate. Moreover, Arrhenius plot for the Li-ion transport conductivity through the SEI layer and the corresponding activation energy at different SOC will also be discuss in order to better understand the reaction kinetics in MCMB carbon electrode with different conducting nano-fillers.

Analysis of ignition delay by taking Di-tertiary-butyl peroxide as an additive in a dual fuel diesel engine using hydrogen as a secondary fuel

Ignition delay (ID) is one of the important parameters that make influenced on the combustion process inside the cylinder. This ignition delay affects not only the performances but also the noise and emissions of the engine. In this regards the experiments were conducted on single cylinder 4–stroke compression ignition research diesel engine, power 3.50 kW at constant speed 1500 rpm Kirloskar model TV1 with base fuel as diesel and hydrogen as secondary fuel with and without Di-tertiary-butyl-peroxide (DTBP). Experiments were conducted to measure the ignition delay of the dual fuel diesel (DFD) engine at different load conditions and substitution of diesel by hydrogen with or without DTBP and then it was compared with predicted ID given by Hardenberg-Hase equation and modified Hardenberg-Hase equation.The experimental values of ignition delay were compared with theoretical ignition delay which was predicted on the basis of Hardenberg-Hase equation by considering mean cylinder temperature, pressure, activation energy and cetane number and variations are found in between 6.60% and 21.22%. While, the Hardenberg-Hase equation was modified (by considering variation in activation energy) for DFD engine working on diesel as primary fuel and hydrogen as secondary fuel shows variations 1.20%–11.96%. Furthermore, with DTBP it gives variation up to 18.01%. It was found that ID decreases with increase in percentage of DTBP and hydrogen in air-fuel mixture. This might be due to the cetane improver nature of DTBP, pre-ignition reaction rate and energy release rate of hydrogen fuel. The polytropic index get increased by addition of (Di-tert butyl peroxide) DTBP. Similarly, 5% Di tertiary butyl peroxide reduces Ignition delay.

Thermogravimetric analyses (TGA) of three oil palm biomass pyrolysis: Kinetics and reaction mechanisms

Oil palm biomass generated from the plantation site (i.e., oil palm trunk (OPT) and oil palm frond (OPF)) are an attractive source for pyrolysis given their abundant availability. Despite this potential, there is no comprehensive study on the pyrolysis of OPT and OPF. In this work, the pyrolysis of OPT, OPF, and PKS are compared and analysed by thermogravimetric analysis (TGA). The kinetics and reaction mechanisms of these biomass during pyrolysis were determined using Kissinger-Akahira-Sunose (KAS) model-free method and Šesták-Berggren function. Pyrolysis of the three oil palm biomass is complex and exhibits different thermal behaviours and strong overlapping reaction between the pseudo-components, which can be attributed to their different constituents. The apparent activation energy of OPT, OPF, and PKS are 17.83-116.58, -45.36-225.60, and 56.50-90.42 kJ mol-1. The variation in the apparent activation energy indicates that pyrolysis of the three oil palm biomass involves multiple reaction mechanisms. Thermal decomposition of the pseudo-hemicellulose and pseudo-cellulose in the three oil palm biomass are co-controlled by two reaction mechanisms, i.e., phase boundary reaction and nucleation, with phase boundary reaction as the dominant mechanism.

PHYSICAL PROPERTIES OF SUBLIMATED TERNARY COMPOUND CdZnS THIN FILMS

Mechanically mixed Cadmium Sulphide (CdS) powder with Zinc (Zn) (99.9% purity) was used as a source material to sublimate a ternary compound of Cadmium Zinc Sulphide (CdZnS) by using Closed Space Sublimation (CSS) under high vacuum. Annealing was carried out under optimized temperature and time for better diffusion of Zn into CdS. Xray diffraction (XRD) studies revealed that (002) was preferred orientation with hexagonal phase after annealing. Crystallite size of prepared films increased from 17 to 89 nm after annealing at higher temperatures. The surface morphology of the films was changed and the average composition of elements was confirmed by energy dispersive X-rays (EDX). The optical band gap energy increased from 2.42 eV and 2.45 eV after annealing. Electrically, the variation in mobility and increase in carrier concentration was due to the decrease of the grain boundary region. There was also variation in activation energy which confirmed the improvement in structure.

PHYSICAL PROPERTIES OF SUBLIMATED TERNARY COMPOUND CdZnS THIN FILMS

Mechanically mixed Cadmium Sulphide (CdS) powder with Zinc (Zn) (99.9% purity) was used as a source material to sublimate a ternary compound of Cadmium Zinc Sulphide (CdZnS) by using Closed Space Sublimation (CSS) under high vacuum. Annealing was carried out under optimized temperature and time for better diffusion of Zn into CdS. Xray diffraction (XRD) studies revealed that (002) was preferred orientation with hexagonal phase after annealing. Crystallite size of prepared films increased from 17 to 89 nm after annealing at higher temperatures. The surface morphology of the films was changed and the average composition of elements was confirmed by energy dispersive X-rays (EDX). The optical band gap energy increased from 2.42 eV and 2.45 eV after annealing. Electrically, the variation in mobility and increase in carrier concentration was due to the decrease of the grain boundary region. There was also variation in activation energy which confirmed the improvement in structure.

Temperature Sensitivity in Individual Components of Ecosystem Respiration Increases along the Vertical Gradient of Leaf–Stem–Soil in Three Subtropical Forests

Temperature sensitivity (Q10) of ecosystem respiration (ER) is a crucial parameter for predicting the fate of CO2 in terrestrial e cosystems under global warming. Most studies focus their attention in the variation of Q10 in one or two components of ER, but not in the integration or comparison among Q10 in major components of ER. Vertical and seasonal variations in individual components, including leaf respiration, stem respiration and soil respiration, of ER were observed synchronously along the gradient of leaf–stem–soil over a 2 year period in three forest stands dominated by masson pine, loblolly pine and oak, respectively, in a subtropical forest ecosystem of central China. We found that Q10 in individual components of ER increased along the vertical gradient of leaf–stem–soil. The vertical pattern of Q10 in individual components of ER was ascribed to variations of diurnal temperature range (DTR) and activation energy (ΔHa). These results suggest that a vertical pattern of Q10 in individual components of ER along the gradient of leaf–stem–soil should be taken into consideration in process-based models that simulate respiratory carbon flux in terrestrial ecosystems.

Thermal Degradation Behavior of a New Family of Organometallic Dendrimer

Organometallic dendrimers are one of the most attractive macromolecules owing to their unique properties that derived from the combination of the metallic moieties and the remarkable architecture of the dendrimers. A new family of organoiron dendrimers has been synthesized using divergent methodology. To gain insight into the stability of these dendrimers, we investigated their thermal property using nonisothermal thermogravimetry analysis (TGA), which reveal the kinetic triplets, the pre-exponential factor, the effective activation energy and the reaction model involved in their thermal degradation. The results were obtained at heating rates of 10, 15 and 20 °C min−1. Four nonisothermal methods, the Friedman, the Ozawa and Flynn and Wall, the Kissinger–Akahira–Sunose and the Minimizing were used to investigate the variation of the effective activation energy with the extent of crystallization and, hence, with temperature. In addition, the activation energy was calculated from isothermal data. The degradation mechanism follows the Avrami–Erofeev mechanism for solid-state reaction models.

Thermal kinetics and reactive mechanism of cellulose nitrate decomposition by traditional multi kinetics and modeling calculation under isothermal and non-isothermal conditions

Cellulose nitrate, also known as nitrocellulose (NC), is a highly flammable energetic cellulose derivatives formed by exposing cellulose to nitric acid, whose producing procedure has been greatly employed in daily life and military area. In this study, to explore its pyrolysis and combustion kinetics, NC samples were subjected to isothermal and non-isothermal DSC experiments. The isothermal experiments were carried at 150, 155, 160, and 165 °C, while the non-isothermal experiments were taken at 2, 4, 8, and 10 °C min−1 for heating rates. By model fitting methods, several classical reaction models with high fitting degree were obtained. The model corresponding to isothermal conditions was f(α) = 4(1 − α)[−ln(1 − α)]3/4, while for non-isothermal conditions the model was identified as f(α) = (1 − α)3. The variation of activation energy with conversion was calculated by model free methods including FR, KAS, FWO, and advanced Vyazovkin methods. Finally, based on the results of kinetic analysis, the adjustment function was introduced and the accurate reaction mechanism functions of NC were identified for isothermal and non-isothermal conditions, respectively. This study has a high guiding significance for the thermal decomposition and combustion kinetics of NC under isothermal and non-isothermal heating conditions.

Coupling of two types of polar regions in Na0.5Bi0.5TiO3: An impedance spectroscopic study

Polycrystalline Na0.5Bi0.5TiO3 (NBT) system has been synthesized by solid-state reaction method. The dielectric and microstructural conduction mechanism has been investigated with the help of impedance spectroscopic technique. From microstructural conduction mechanism results, it is perceived that, two short range and two long range conduction/relaxation processes are evolved in different temperature and frequency zones. The dynamics of four relaxation/conduction processes are analyzed by considering the variation of activation energy (Ea) of each relaxation/conduction process in different temperature zone and represented by a model. In this model, coupling of two polar regions in different temperature and frequency zones has been systematically discussed.