Kinetic Activation Energy Research Articles

Thermal Oxidation of Carbonaceous Nanomaterials Revisited: Evidence of Mechanism Changes

Kinetic data, for example, activation energy and reaction order, are crucial for the understanding of chemical reactions and processes. Here, we describe a novel method for obtaining kinetic data based on thermogravimetric measurements (TGA) that exploits in each measurement multiple successive isothermal steps (SIS). We applied this method to the notoriously challenging carbon combustion process for vastly different carbons for oxygen molar fractions between 1.4 % and 90 %. Our obtained apparent EA values are within the wide range of results in the literature and vary in a systematic way with the oxygen partial pressure. The improved accuracy and large amount of obtainable data allowed us to show that the majority of experimentally obtained apparent data for apparent EA are neither in a kinetic regime nor in a diffusion-controlled one but rather in a transition regime.

Characterization of raw and alkali treated new natural cellulosic fibres extracted from the aerial roots of banyan tree

The objective of this investigation is to check the suitability novel cellulosic fibre extracted from the aerial roots of Banyan tree (ARBFs) as reinforcement in fibre reinforced plastics. The Fundamental properties of ARBFs such as density, tensile strength, chemical composition, crystallinity index, crystalline size, thermal stability, maximum degradation temperature and surface roughness were studied. The chemical analysis results revealed that after the alkalization cellulose content was improved while hemi-cellulose, lignin and wax content were demised. The enhancement in the crystallinity index (76.35% from 72.47%) and crystalline size (7.74 nm from 6.28 nm) of alkali treated ARBFs were evidenced by the X-ray diffraction analysis. Thermal analysis results confirmed that maximum degradation temperature (368 °C) and kinetic activation energy (75.45 kJ/mol) of alkali treated ARBFs had increased from 358 °C and 72.65 kJ/mol respectively. The results of scanning electron microscopic and atomic force microscopic analysis exhibited that impurities and wax on the outer surface of the ARBFs were removed after the alkali treatment. All the above finding concluded that ARBFs is the appropriate material to use as a reinforcement in fibre reinforced plastics.

Comparative study on thermal behaviors between micrites and thrombolites using thermogravimetric analysis

Although micrites (abiotic limestone) and thrombolites (typical biotic limestone), according to the sedimentation and biological action, can be primarily distinguished from intuitively field observation and rock slices analysis. However, further analysis of thermal decomposition unique characteristics to distinguish them has rarely been reported. Here, the comparative studies of thermal decomposition behavior between micrites and thrombolites were carefully investigated using thermogravimetric analyzer in nitrogen atmosphere at multi-heating rates of 5, 10, 20 and 30 K min−1 from 323.15 to 1273.15 K. Moreover, the mineralogical compositions were both analyzed by powder X-ray diffraction followed by the results of calcite acting as the basic constituent for further verified. The kinetic model function and kinetic parameters were calculated by Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose and Popescu methods, respectively. The results showed that the kinetic parameter activation energy (E) of thrombolites was obviously higher than that of micrites, which suggests the former have a higher crystallinity. In addition, the results of difference significance analysis showed extremely significant differences (P < 0.01) via statistical analysis using SPSS v19.0 for the E values between micrites and thrombolites calculated by different methods. These above results further confirmed that the thermal stability and crystallinity of thrombolites were obviously higher under the inducing effects by typical microorganisms. This provided very important useful information for understanding the mechanisms of abiotic and biotic limestones formed in nature; in particular, the thermal analysis of thrombolites maybe also provides an important guiding significance for both indoor and outdoor similar studies.

Mechanism for the multi-stage precipitation of Fe-Ni based alloy

This work lays great emphasis on the distribution evolution of sigma (σ) phase in Fe-Ni based N08028 alloy during aging process, the result of which could provide new insights into phase change and precipitation mechanism. It is found that the σ phase, in any case, tends to separate out with a granular shape at grain boundaries (GBs) primarily, and with the increment of time, it is obliged to precipitate in grain interiors (GIs) with a lamellar structure. The mechanisms for the evolving volume fraction and morphology of σ phase are discussed, and a model appropriate for the multi-stage behavior transforming from intergranular to intragranular precipitation is derived, as well as revealing the thermodynamics and transformation kinetics corresponding to this process. The results reveal that the occurrence of multi-stage precipitation is correlated with the redistribution of solute atoms and with the difference in coupling effect of thermodynamic driving force and kinetic activation energy between the intergranular and intragranular precipitation.

Physico-Chemical Properties of Fiber Extracted from the Flower of Celosia Argentea Plant

ABSTRACT This study was aimed at understanding the characteristics of Celosia argentea fiber (CAF) and its physicochemical properties. The physicochemical properties of CAF were analyzed by FT-IR, XRD, TGA, SEM, and AFM analysis. Cellulose content (64.34wt.%), density (843 kg/m3) and crystallinity index (52.54%) properties were identified in the CAF while the thermal studies performed by TG and DTG technique revealed that the maximum degradation temperature is 324°C with a kinetic activation energy of 61.393 kJ/mol. From the results, it is evident that the CAF could be one of the future reinforcement materials for green composites applications.

Use of Genetic Algorithm and Particle Swarm Optimization in the Estimation of Kinetic Parameters of Green Coconut Biomass

The development of more economically and energy-efficient processes for the sustainable production of fuels and chemicals is becoming increasingly necessary. In this context, it is relevant to understand the behaviour of thermal degradation of different biomasses in oxygen free atmosphere to investigate the breakdown of polymer chains, which can be converted into new products. Good effects on the acceleration of degradation of organic molecules can be achieved with the use of catalysts in these breaking processes, thus increasing the yield of bio-oil production. In this work, fiber of crushed and sifted green coconut shell, submitted to thermogravimetry analysis (TG), was used as biomass. Some types of a catalyst were incorporated into the biomass, based on cobalt ferrite, Fe2CoO4. The design of a biomass pyrolysis reactor requires knowledge of kinetic parameters, activation energy (Ea), pre-exponential factor (k0) and order of reaction (n). In this context, the present study aimed to perform the thermogravimetric (TG) analysis in an inert atmosphere of pure nitrogen, and to determine the kinetic parameters involved in the lignin pyrolysis process, to assist in the design of biomass conversion reactors. This work presents a solution to obtain the kinetic parameters for thermogravimetric reaction of lignin breaking present in the biomass of the green coconut. Two computational methods were used: genetic algorithm and particle swarm optimization. The results obtained for activation energy, pre-exponential factor and order reaction are in the range of values found in the literature.

Nanoinstabilities of Cu2O porous nanostructured films as driven by nanocurvature effect and thermal activation effect

In this work, the instabilities at the nanoscale (i.e. nanoinstabilities) of triangular pyramids-like Cu2O porous nanostructured films (PNFs) are studied by heating treatments under different atmosphere and temperature. It is found that the nanoscale building triangular pyramids turn round preferentially at the sharp angles and/or coalesce with their contacting ones by directional diffusion and plastic flow of atoms, which are driven by the nonuniformly-distributed surface nanocurvature. As a result, the triangular pyramids become quasi-sphere shape and the PNF evolves into a big, dense particles film. It is also observed that the heating or thermal activation effect efficiently promotes the reduction or oxidation of Cu2O pyramids and the crystallization or growth of the as-achieved Cu or CuO grains. The above physical and chemical instabilities or changes at the nanoscale of Cu2O PNFs can be well accounted for by the combined mechanism of nanocurvature effect and thermal activation effect. The nanocurvature effect can lower the energy barrier for the atom diffusion or plastic flow and lower the activation energy for the chemical reactions, while the thermal activation effect can supply the required kinetic energy or activation energy and make the atomic transportations and reactions kinetically possible. The findings reveal the evolution laws of morphology, crystal structure and composition of triangular pyramids-like Cu2O PNF during heating treatments, which can further be extended to other types of Cu2O PNFs. Also, the findings have important implications for the nanoinstabilities of Cu2O PNFs-based devices, especially those working at a high temperature.

Novel pyridine-derived platinum complexes

Pyridine-derived platinum(II) complexes with the general formula [PtCl2L2] (L1: 3,5-dimethylpyridine, L2: 2-amino-5-bromopyridine, L3: 4-(4-nitrobenzyl)pyridine) were synthesized. Characterization of the synthesized complexes was made via FT-IR, UV–Vis, 1H-NMR and 13C-NMR techniques. While the thermal behavior of the complexes was investigated via DTA/TG combined system, their kinetic parameters were investigated by using Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS) methods. The activation energy of the decomposition kinetics of the complexes was calculated to be 196.5–31.7 kJ mol−1 for FWO and 203.4–29.2 kJ mol−1 for KAS. The cytotoxic effect of the complexes against the colon cancer cell line (DLD-1), which is one of the most common types of cancer observed both in humans and animals, was investigated. The complexes showed high cytotoxicity on DLD-1. In particular, [PtCl2L 2 1 ] complex was found to be the most effective compounds against colon cancer cell line during the 24 h incubation period. According to these results, the pyridine-derived platinum(II) complexes would contribute to oncologic treatment as chemotherapeutic agents.

Artificial neural network model for the evaluation of chemical kinetics in thermally induced solid-state reaction

The artificial intelligence technique is utilized to improve evaluation of thermally induced solid-state reaction kinetics. A general regression neural network (GRNN) model was applied to directly determine the kinetic triplets, i.e., activation energy, pre-exponential factor, and mechanism model. The effect of number of heating rate on prediction performance of the GRNN model was assessed based on the estimation indictors. The obtained kinetic triplets based on the triple heating rates were considered to be accepted. The prediction ability of the GRNN model was very robust at more than three heating rates. The relative errors for kinetic parameters derived from five heating rates were within ± 4%, and the cognition rates for mechanism models were up to 99.6%. The developed GRNN model was successfully applied in the high-temperature synthesis of Li4Ti5O12/C composites. It is expected that the model also could be extended to estimate the kinetics of other solid-state reactions.

Chemical optimization towards superior electrocatalysis of Janus 1T-MoSX (X = O, Se, Te) for hydrogen evolution: Small composition tuning makes big difference

Transition metal dichalcogenides (TMDs) can be used as promising nonprecious catalysts for hydrogen evolution reaction (HER), but there has still been a problem of inert basal plane. Inspired by a recent progress in the experimental preparation and characterization of the sandwiched monolayer (ML) Janus MoSSe, we use first-principles methods to explore the stability and HER activity of Janus ML 1T-MoSX (X = O, Se, Te) and optimize the HER activity by tuning the content of anionic X atom. According to the calculated thermodynamic and kinetic properties, we find that both excellent stability and high catalytic performance of 1T-MoSX can be simultaneously obtained when the content of X atom on surface reaches 0.22. Among different types of X, the introduction of O can yield the most favored adsorption energy of H adatom, the lowest kinetic activation energy for the H desorption, and the largest exchange current density (i0) for the HER of 1T-MoSX. It is a remarkable and important finding that the i0 of 1T-MoSX is in the same magnitudinal order as that of the precious Pt electrode. The electronic-structure mechanism underlying the superior HER performance of 1T-MoSX is also analyzed in depth. This work indicates a promising application of the new 1T-phase TMDs in high-performance HER catalysis, and the chemical trends present here can also be readily validated by future experiments.

Investigations on structural and radiation shielding properties of Er3+ doped zinc bismuth borate glasses

Novel optical glasses 10ZnO-5Na2CO3-10Bi2O3-(75-x)B2O3-xEr2O3 with x = (0, 0.1, 0.3, 0.5, 0.7, 1.0) mol%, were synthesized by melt quench technique and characterized through XRD, EDAX, optical and luminescent properties, before and after irradiating them with high energy (1.3 MeV) gamma rays. Moreover, the gamma photons attenuation characterizations for the samples under study were studied. The mass attenuation coefficients for the selected glasses were affected with the addition of Er2O3. Based on the findings from the mass attenuation coefficients, ZNBBEr-5 has better photon attenuation features in comparison with the other samples. Also, arising the Er2O3 content in the glasses, led to increase the effective atomic number. The mean free path for the prepared samples were compared with some shieling glasses. Shielding performance of the present glass samples against gamma radiation reveals pair production is prominent at 1.3 MeV. UV-VIS–NIR absorption edge was red shifted after gamma irradiation indicating the formation of electron/absorption centers in the glass matrix. Thermally stimulated Luminescence (TL) spectroscopy technique showed five electron trap centers at 445K, 491K, 545K, 590K, 620K with acceptable FOM [< 5%] values. The number of overlapping peaks and their trapping parameters like kinetic order, activation energy, peak temperature, frequency factor and half life were determined using the Computerized Glow Curve Deconvolution (CGCD). Linear behaviour obtained through the dose response of the glass (5 kGy–50 kGy) proved their suitability for dosimetric application in the food irradiation zones and in red LEDs (<50 kGy).

Kinetic study on the anisotropic grain growth of elongated iron-containing mullite

Abstract Elongated iron-containing mullite exhibiting anisotropic grain growth was prepared using fused silica, α-alumina, and Fe2O3 powders as raw materials at elevated temperatures. The effects of different Fe2O3 contents on the anisotropic growth of mullite columnar crystals were investigated, and phase compositional analysis and structural characterisation were carried out by X-ray diffraction and field emission scanning electron microscopy. The kinetic index and activation energy for the anisotropic grain growth of elongated mullite crystals were calculated, and the surface energy of each crystal plane of the elongated crystal and the solid solution behavior of the iron ions in the mullite were calculated using the density functional theory (DFT) approach. It was found that the addition of Fe2O3 promotes the anisotropic grain growth of mullite, and the aspect ratio of the elongated crystals increased upon increasing the Fe2O3 content. The solid solubility upper limit of the iron-containing mullite in this system is 9 wt% of iron addition. After sintering at 1973 K, for Fe2O3 contents of 3, 6, and 9 wt%, the growth kinetics indices obtained by calculations in the longitudinal direction were 2.22, 2.50, and 3.85, while the reaction activation energies were 457.3, 442.1, and 411.9 kJ mol−1. The calculation results on the surface energy of the elongated mullite crystal showed that the smallest surface energy is on the (001) crystal plane, which is the preferred growth direction. Upon comparison of the surface energies for different Fe2O3 contents on the (001) surface, a decrease was observed upon increasing the quantity of Fe2O3, and both the growth tendency of the mullite crystals and the aspect ratio of the elongated crystals also increased. The refractoriness under load of the prepared elongated iron-containing mullite was 1664 °C, demonstrating its excellent high-temperature mechanical properties.

Effects of KNbO3 catalyst on hydrogen sorption kinetics of MgH2

The influences of Nb-containing oxides and ternary compound in hydrogen sorption performance were investigated. As faster desorption kinetic and lower activation energy were reported by addition of a ternary compound catalyst such as K2NiF6, the influence of KNbO3 on hydrogen storage properties of MgH2 has been investigated for the first time. The MgH2 - KNbO3 composite desorbed 3.9 wt% of hydrogen within 10 min, while MgH2 and MgH2-Nb₂O₅ composites desorbed 0.66 wt% and 3.2 wt% respectively under similar condition. For MgH2 with other Nb-contained catalysts such as Nb, NbO and Nb₂O3, the desorption rate was almost the same as the one registered for as-milled MgH2. The analysis of differential scanning calorimetry (DSC) showed that MgH2-KNbO3 composite started to release hydrogen at ∼335 °C which is 50 °C lower compared to as-milled MgH2 without any additives. The activation energy for the hydrogen desorption was estimated to be about 104 ± 6.8 kJ mol−1 for this material, while for the as-milled MgH2 was about 165 ± 2.0 kJ mol−1. It is believed that Nb-ternary oxide catalyst (KNbO3) showed a good catalytic effect and enhance the sorption kinetics of MgH2.

Characterization of Musa paradisiaca L. Cellulosic Natural Fibers from Agro-discarded Blossom Petal Waste

ABSTRACT Musa paradisiaca L. blossom petal (MPBP) fibers are extracted from banana plant agro-based domestic waste. The properties of MPBP fibers were reported for the first time in this communication. X-ray diffraction analysis showed the crystallinity index and size of 56.71% and 16.38 nm, respectively. The thermogravimetric analysis indicates that the MPBP fibers are thermally stable up to 220°C. Differential Scanning Calorimetry analysis gives two thermal degradation temperatures of 368.1 and 476.8°C with kinetic activation energy of 62.43 kJ. Tensile strength, Young’s modulus, and strain at failure were determined from the single fiber tensile test as 108 MPa, 1.05 GPa, and 11.15%, respectively.

Predicting combustion characteristics in externally heated micro-tubes

This study employs a simplified analytical model to obtain qualitative predictions of transitions between non-adiabatic combustion regimes found in non-catalytic tubular micro-flow reactors, i.e. normal stable flames, flames with repetitive extinction and ignition (FREI), and weak flames that are stabilized by wall heat transfer. Assuming large activation energy for single-step kinetics, a comparison of exact solutions for constant and variable wall temperature profiles reveals that while a non-zero wall temperature gradient introduces a temperature lag, it has no impact on the structure of the flame solution itself. This result is significant as it establishes a link to quenching characteristics within heated micro-tubes, and further facilitates a simplified micro-flow reactor analysis. Predictions for sweeps of wall temperatures are combined to S-curves, which allow for a combustion regime classification for a given combination of micro-flow reactor geometry and mixture properties. A variation of parameters such as tube diameter or mixture stoichiometry yields predictions of shifts in regime transitions, thus providing insights on interactions between heat transfer and first order effects of chemical kinetics. A comparison to experimental data illustrates that the theoretical framework, – within inherent limitations, – captures qualitatively correct trends that reflect experimental observations, thus providing valuable insights for micro-flow reactor design and operation.

Novel kinetics model for adsorption of pollutant from wastewaters onto zeolites. Kinetics of phenol adsorption on zeolite-type silicalite

The kinetics of isothermal adsorption of phenol from an aqueous solution onto the zeolite-type silicalite was investigated. Zeolite-type silicalite was synthesized and its basic physico-chemical properties were determined. Isothermal adsorption kinetics curves of phenol on zeolite-type silicalite were measured at temperature range from 283 to 313 K. By applying Friedman’s differential isoconversional method it was found that the adsorption of phenol on silicalite has one rate determining step. By using the ‘model-fitting’ method it was established that the kinetic of adsorption can be described with theoretical kinetic model of the two-dimensional phase-boundary controlled reaction (model R2). The kinetic parameters, activation energy ([Formula: see text]) and preexponetial factor ( lnA = 14.1 min−1) of phenol adsorption were calculated. The thermodynamic parameters, standard enthalpy (Δ H*), standard entropy (Δ S*) and standard free Gibbs energy of adsorption (Δ G*) were calculated and discussed. A novel model for the kinetics of pollutant adsorption from wastewaters onto zeolites based on the following: zeolite pores have cylindrical shape with average radius r0, pores in zeolite are filled simultaneously by the model ‘layer by layer’, the rate of phenol adsorption is higher than the rate of the growth of the thickness of the adsorption layer was suggested. It has been found that the adsorption kinetics can be completely described by this kinetic model.

Texture weakening in pure magnesium during grain growth

ABSTRACTThe microstructure and texture evolution during annealing of rolled pure Mg, at temperatures ranging from 150 to 400°C, was characterised in the present study. A grain growth exponent of n = 13 was observed and the activation energy for grain growth kinetics was found to be 95.6 kJ mol−1. Further, broadening of the normalised grain size distributions, indicating abnormal grain growth, was also observed at all temperatures of annealing. The sample had a dominant basal texture before annealing. However, after annealing up to a temperature of 300°C, the alleviation of basal texture was observed in the samples. On further annealing at a temperature of 400°C, a strong basal texture was developed in the samples. The mobility of high angle grain boundaries, which is proportional to correlated misorientation distribution, was observed to be responsible for texture strengthening of the material. The grain boundary mobility changes during grain growth led to the growth of either small or large grains. It was further observed that the growth of small grains caused the formation of basal fibre and large grains led to the weakening of basal texture.

Specific kinetic triplet estimation of Tahe heavy oil oxidation reaction based on non-isothermal kinetic results

Although the oxidation mechanisms and kinetics characteristics of heavy oils have been involved in enormous studies, little attention is paid to the specific kinetics triplet and activation energy distribution in detailed temperature ranges. In this study, the non-isothermal oxidation kinetics characteristics of the Tahe heavy oil, including kinetics triplet, activation energy distribution (E-α curve) and thermodynamic parameters under specific temperature subzones, were investigated by thermo-analysis techniques and Popescu method. And it indicated that six sequential temperature subzones were identified with different mechanism function, G(α), and rate constant, k(T). Besides, it can be seen from the E-α curve that the first obvious increasing peak was attributed to the negative temperature gradient region (NTGR) and the second mild peak corresponded to the initiation stage of the combustion process, between which positive temperature coefficient and negative temperature coefficient zones were located at the valley. Additionally the calculated thermodynamic parameters (△S*, △H*, △G*) indicated that the non-isothermal oxidation process for Tahe heavy oil is the non-spontaneous reaction and needs heat to occur under atmospheric pressure.

Kinetics of the pyrolysis process of phthalonitrile resin

Accurately modeling the kinetics of the pyrolysis reaction of phthalonitrile resin was helpful to investigate the pyrolysis mechanisms. To study the pyrolysis kinetics, phthalonitrile resin was measured by thermogravimetric analysis (TGA) at different heating rates in flowing nitrogen. The results indicated that there were two consecutive and overlapping stages in the pyrolysis process. The overlapped peaks were separated by multi-peak fitting method. Two models, namely, Kissinger, Kissinger-Akahira-Sunose (KAS), were employed to calculate activation energy at various stages of pyrolysis process. Kinetic models were determined using the differential method and Coats-Redfern method. Based on the attained kinetic models and activation energy values, the pre-exponential factor values were determined by KAS method. According to the calculated apparent activation energies, the most probable kinetic mechanism functions and pre-exponential factors, the simulated data agreed well with the experimental data.

A comparative thermal decomposition kinetics on 1,2-bis(imino-4'-antipyrinyl)ethane and 4-N-(4'-antipyrylmethylidene)aminoantipyrine Cu(II) complexes with varying counter anions

A comparative thermal decomposition kinetic studies of Cu(II) complexes of 1,2-bis (imino-4-antipyrinyl) ethane(GA) and4-N-(4'-antipyrylmethylidene) aminoantipyrine (AA) with a variety of counter anions viz. ClO4-, NO3-, Cl- and Br- has been evaluated by TG analysis. The kinetic parameters activation energy (E), pre-exponential factor (A) and entropy of activation (∆S) were calculated by using Coats–Redfern equation. This study shows that the thermal decomposition kinetics has been controlled by the ligand field as well as the counter anions.