Classical Kinetic Model Research Articles

Densification behaviors of Al2O3 ceramics during flash sintering

AbstractThe densification behaviors of MgO‐doped‐Al2O3 ceramics in the flashing stage and the steady stage were investigated using the classic kinetic model. The results show that the most densification of MgO‐doped Al2O3 was completed during the flashing stage. The densification mechanism transferred from particle rearrangement resulted from Columbic force among particles under the effect of electrical field in the flashing stage to the lattice diffusion in the steady stage. Therefore, the densification rate in the steady stage dramatically decreased. Additionally, the estimated densification activation energy in the steady stage of flash sintering is 396 kJ/mol, much lower than the activation densification of lattice diffusion measured from conventional sintering, likely due to the effect of electric field/current‐induced point defects on the diffusion.

Study of aroma generation pattern during boiling of hot pot seasoning

Hot pot is popular among consumers because it provides a rich and multi-level flavor experience during boiling. In this study, the aroma compounds of hot pot seasoning (HPS) during different boiling times were characterized by comprehensive two-dimensional gas chromatography–olfactometry–mass spectrometry. Twenty-four aroma-active compounds with high flavor dilution (FD) factors were selected by aroma extract dilution analysis. Based on the odor activity values (OAVs), 23 key aroma-active compounds were identified as characterizing the main aroma profile of HPS during boiling. Furthermore, multivariate statistical analysis was used to screen out 10 key differential aroma-active compounds, which were used to distinguish the difference in aromas for HPS during the different boiling times. Finally, kinetic fitting was used to reveal the generation regularity of these 10 compounds. The results showed significant changes in the content of acetophenone, (E)− 2-heptenal and phenylacetaldehyde, conforming to first-order kinetics during boiling. However, other compounds were not well-fitted into the classical reaction kinetics models.

Microstructural Evolution and an Improved Dynamic Recrystallization Kinetic Model of a Ni-Cr-Mo Alloy in Hot Deformation.

Microstructural evolution and dynamic recrystallization (DRX) behaviors of a Ni-Cr-Mo alloy were researched utilizing hot compressive experiments. The changed features of dislocation, subgrain and grain structure correlating to forming parameters were examined by transmission electron microscope (TEM) and electron backscatter diffraction (EBSD). Results illustrate that the consumption of dislocation and the coarsening of substructure/DRX grain are prominently enhanced with an increased forming temperature. However, the annihilation/interaction of dislocation and the expansion of subgrain/DRX grain boundary can be limited at a larger strain rate. Meanwhile, considering the discrepancy in DRX variation rates concerning the strain rate’s ranges, an improved DRX kinetic model was developed. Compared to the classical DRX kinetic model, the good consistency between the forecasted and tested results demonstrates that the established improved DRX kinetic model can precisely characterize the DRX features of the Ni-Cr-Mo alloy over a wide strain rate range. Additionally, the EBSD’s quantitative statistical results proved that the variation of DRX grain size can be supremely defined as the power formulation of the forming temperature and strain rate.

Dye adsorption properties of poly(p-phenylene terephthalamide)-embedded hollow fiber composite membranes

Hollow fiber composite (HFC) membrane with improved dye adsorption properties was prepared by the embedding of poly(p-phenylene terephthalamide) (PPTA)/polysulphone (PSF) microparticles into the polyamide (PA) composite layer of PSF hollow fiber membrane. As the polymer raw material of Aramid-1414, high modulus and hydrophilic PPTA was polycondensated in situ in PSF system and PPTA/PSF microparticles were obtained by the cloud-point precipitation method. PSF hollow fiber membrane was fabricated by the dry-jet wet-spinning technique. The variations of membrane morphology, porosity, surface charge and hydrophilicity were evaluated by the scanning electron microscope (SEM) observation, dry-wet mass difference, Zeta potential and water contact angle (WCA) measurements. The adsorption thermodynamic and kinetic processes of different kinds of dyes including anionic dye (Congo red, CR) and cationic dye (methylene blue, MB) were thoroughly investigated by three typical typical sorption isotherm models and two classical kinetic models, respectively. Compared with the PSF hollow fiber membrane and the pristine HFC membrane, the surface roughness, hydrophilicity and electronegativity had an obvious enhancement. The PPTA-embedded HFC membrane presented an increased dye adsorption capacity. The adsorption isotherms for CR and MB of the PPTA-embedded HFC membrane could fit well with the Langmuir and Sips models. The adsorption kinetics for CR and MB are in good agreement with the pseudo-first-order model and pseudo-second-order model, respectively. The prepared PPTA-embedded hollow fiber composite membranes are expected to be a promising candidate for the treatment of textile dyeing wastewater.

The enzymatic action of Vipoxin on insoluble long-chain phospholipid Langmuir monolayers

In recent years some toxins such as Vipoxin that is isolated from the venom of Vipera ammodytes meridionalis have provoked scientific interest due to their intriguing structure, enzymatic activities, and potential for medical applications. This paper considers the kinetics of the enzymatic action of Vipoxin on long-chain phospholipids’ monolayers of Palmitoyl-oleoyl-phosphatidyl-choline (POPC), Palmitoyl-oleoyl-phosphatidyl-glycerol (POPG), and Palmitoyl-oleoyl-phosphatidyl-ethanolamine (POPE) spread at air-water interfaces. To analyze theoretically the enzyme activity that is altered by the presence of insoluble lipolytic products we adapted the classical Michaelis-Menten kinetic model and an experimental approach that utilizes the β- cyclodextrin ( β-CD ) as a solubilizing agent. This allowed us to obtain the global kinetic constants of the enzymatic reaction catalyzed by the Vipoxin. Using AFM, we also analyzed the influence of the monolayer structure on the kinetics of the enzyme reaction by measuring the observed structures and microheterogeneities of the LB films transferred from monolayers that either contained β-CD or without β-CD . • Kinetics of the enzymatic action of Vipoxin on long-chain phospholipid monolayers is studied. • An adapted Michaelis-Menten kinetic model for fitting the data is applied. • The global kinetic constants of Vipoxin action are obtained. • The interfacial behavior of studied systems is visualized by AFM.

Optimisation of reaction parameters for a novel polymeric additives as flow improvers of crude oil using response surface methodology

In recent years, polymeric additives have received considerable attention as a wax control approach to enhance the flowability of waxy crude oil. Furthermore, the satisfactory model for predicting maximum yield in free radical polymerisation has been challenging due to the complexity and rigours of classic kinetic models. This study investigated the influence of operating parameters on a novel synthesised polymer used as a wax deposition inhibitor in a crude oil pipeline. Response surface methodology (RSM) was used to develop a polynomial regression model and investigate the effect of reaction temperature, reaction time, and initiator concentration on the polymerisation yield of behenyl acrylate-co-stearyl methacrylate-co-maleic anhydride (BA-co-SMA-co-MA) polymer by using central composite design (CCD) approach. The modelled optimisation conditions were reaction time of 8.1 h, reaction temperature of 102 °C, and initiator concentration of 1.57 wt%, with the corresponding yield of 93.75%. The regression model analysis (ANOVA) detected an R2 value of 0.9696, indicating that the model can clarify 96.96% of the variation in data variation and does not clarify only 3% of the total differences. Three experimental validation runs were carried out using the optimal conditions, and the highest average yield is 93.20%. An error of about 0.55% was observed compared with the expected value. Therefore, the proposed model is reliable and can predict yield response accurately. Furthermore, the regression model is highly significant, indicating a strong agreement between the expected and experimental values of BA-co-SMA-co-MA yield. Consequently, this study’s findings can help provide a robust model for predicting maximum polymerisation yield to reduce the cost and processing time associated with the polymerisation process.

Plasmonic drag photocurrent in graphene at extreme nonlocality

It is commonly assumed that photocurrent in two-dimensional systems with centrosymmetric lattice is generated at structural inhomogenities, such as p-n junctions. Here, we study an alternative mechanism of photocurrent generation associated with inhomogenity of the driving electromagnetic field, termed as 'plasmonic drag'. It is associated with direct momentum transfer from field to conduction electrons, and can be characterized by a non-local non-linear conductivity $\sigma^{(2)}({\bf q},\omega)$. By constructing a classical kinetic model of non-linear conductivity with full account of non-locality, we show that it is resonantly enhanced for wave phase velocity coinciding with electron Fermi velocity. The enhancement is interpreted as phase locking between electrons and the wave. We discuss a possible experiment where non-uniform field is created by a propagating graphene plasmon, and find an upper limit of the current responsivity vs plasmon velocity. This limit is set by a competition between resonantly growing $\sigma^{(2)}({\bf q},\omega)$ and diverging kinetic energy of electrons as the wave velocity approaches Fermi velocity.

(Invited) Characterization of Charge Transfer and Recombination Processes at Metal Oxide Semiconductors for Solar Water Splitting

Metal oxide (MO) semiconductors based on abundant, low-cost materials are attractive for application in photoelectrochemical water splitting systems related to their inherent stability, specifically against oxidation. In addition, these materials provide a wide-ranging versatility in terms of composition, physical and chemical properties, and configuration of multi-component architectures. The semiconducting MO must at least comply with three requirements: (i) absorb sunlight efficiently; (ii) the valence and conduction band edges must be situated at the appropriate energies; and (iii) the electrochemical reaction must have favorable kinetics compared with charge separation, transport and recombination kinetics. Many systems have been evaluated for photo-oxidation of water in the past 10 years, with some of the more popular materials being Fe2O3, WO3, BiVO4, TiO2, etc.In order to improve the efficiency of a solar water splitting system, the specific loss mechanisms need to be elucidated; based on these insights strategies may then be developed to improve performance. However, it is not straightforward to determine the precise loss mechanisms and generally non-steady state methods need to be applied in combination with steady-state techniques. Intensity-modulated photocurrent spectroscopy (IMPS) is a powerful technique to study the carrier dynamics in a photoelectrochemical cell: the photocurrent admittance corresponds to the frequency-dependent external quantum efficiency, and time constants for charge separation, charge transfer and surface recombination may be deduced. The kinetic model applicable to the specific system determines the interpretation of the results. On the other hand, theoretical modeling is a very powerful method to validate the interpretation of the results, and to complement the experimental studies in order to obtain a clear picture of the dominant processes and effects.In this presentation, the results from IMPS studies on a variety of systems will be discussed and strategies to improve performance are presented and tested, both experimentally and theoretically: (i) planar, compact WO3 / BiVO4 heterojunction systems are compared with nanorod array WO3 / BiVO4 heterojunctions, with and without a hole scavenger; (ii) CuBi2O4 with and without catalysts and an alternative electron acceptor; and (iii) specific examples of other materials to highlight the proposed interpretations. The results are compared with calculations of the IMPS response using a classic kinetic model and a continuity equation approach in order to incorporate the effects of charge transport and electric field within the electrode.The authors gratefully acknowledge funding from CONACYT, SENER, and CICY through the Renewable Energy Laboratory of South East Mexico (LENERSE; Project 254667; SP-4), and CONACYT under the Basic Sciences (CB) project A1-S-28734. We also thank the Ministerio de Ciencia e Innovación, the Agencia Estatal de Investigación (AEI), and the European Regional Development Fund of the European Union through Project PID2019-110430GB-C22. AR thanks the Spanish Ministry of Education, Culture and Sports via a PhD grant (FPU2017-03684). Finally, we would like thank Dr. Antonio Zapien and the NANOMXCN initiative to foment scientific collaboration between Mexico and China for support.

Removal of oxytetracycline by graphene oxide and Boron-doped reduced graphene oxide: A combined density function Theory, molecular dynamics simulation and experimental study

Graphene-based nanomaterials have demonstrated great potential in the field of environmental applications, especially on water treatment processes. Accordingly, herein, in order to be used as adsorbent in the removal of oxytetracycline (OTC), graphene oxide (GO) and boron doped reduced graphene oxide (B-rGO) was investigated. GO was obtained through the oxidation/exfoliation process using the modified Hummers’ Method and further etched by a thermal annealing approach to obtain B-rGO, utilizing boric acid as boron source for the study. FT-IR, TEM and XRD were used to characterize the morphology properties of GO and B-rGO and confirm the success of these synthesis. To evaluate the degradation potential of OTC by GO and B-rGO, pH of the sample, GO and B-rGO concentration, initial OTC concentration, reaction time and temperature has been selected as effective parameters. Based on the obtained experimental results GO and B-rGO were found to possess favorable adsorption efficiencies reaching 86% and 100% for GO and B-rGO, respectively, rapidly uptake rate with up to 85% of total removal occurring within the initial 10 min. In addition, it is noteworthy that OTC removal from solution was strongly dependent on pH but independent of temperature. The classical isotherm and kinetic adsorption models suggested that the process perfectly conformed to Freundlich and Pseudo-second-order model (R2 ≥ 0.95). Furthermore, density functional theory (DFT) simulation performed at the B3PW91 level of theory as well as a topological analysis were introduced to elucidate theoretically the interfacial interaction at the molecular-scale associated with OTC sorption on both adsorbents.

Microfluidics-based encapsulation of isoniazid in egg white/carrageenan microparticles for sustained release

The prevalence of tuberculosis continuously grows and there is an imperious need to improve the therapeutic efficacy of approved drugs for clinical use. Here we report the encapsulation of isoniazid (INH) in egg white/κ-carrageenan microparticles, which are intended for drug vehiculation through the gastrointestinal tract and controlled release in the ileum. Spherical and highly monodisperse microparticles (255 mm average diameter) were obtained by droplet-based microfluidics and subsequent microwave irradiation. The entire amount of INH added to the particles was encapsulated. Infrared spectra revealed the formation of esters, hydrogen bonding, and Maillard reaction in the biopolymer matrix. In vitro release experiments were carried out in media that systematically emulate the stomach and intestinal tract conditions: 37 °C, NaCl 0.05 mol/L, pH 1.6, for the first 2 h, and Tris–HCl 0.1 mol/L, pH 7, for the next 24 h. A small fraction of the loaded INH was released in the first medium and most of the drug was progressively delivered in the second medium. The release profiles of microparticles were analyzed by using classical kinetic models, which enabled to hypothesize the release mechanism of INH from the biopolymer matrix. This knowledge, together with the ability to control the governing parameters of microfluidic elaboration, opens further possibilities for designing optimal prototypes for sustained release.

Analysis and Modeling of Oxide Reduction Processes for Uranium Oxides

This article describes a kinetic model for the reduction process of used oxide nuclear fuel with molten LiCl at 650°C. In this process, metal oxides, primarily UO2, react to form metallic U and Li2O. As UO2 is gradually reduced, metallic U and Li2O form in molten LiCl, in and through which Li2O dissolves and diffuses. To capture the prescribed chemical and physical phenomena, two classical kinetic models are integrated sequentially to describe Li2O formation, dissolution, and diffusion behaviors. The first part of the integrated model uses a shrinking core kinetics to explain the formation, dissolution, and diffusion of Li2O while accounting for the expanding metallic uranium layer. The second part of the integrated model begins with the completion of Li2O dissolution and deals with the diffusion of excess Li2O in the metallic uranium layer. A Fick's second law without an external source describes the second part of the process behavior. The integrated model explains engineering scale kinetic measurement data from the literature with the effective Li2O diffusion coefficient range between 2 and 6 (10−5cm2/sec).

Photocatalytic activities of NiFe2O4/nitrogen-doping graphene oxide synthesized by hydrothermal method

The NiFe2O4/N-doped GO composites were successfully synthesized by the hydrothermal method from graphene oxide GO, urea, iron nitrat, and niken nitrat. GO was synthesized by a modifìied Hummers, method. The obtained composites exhibited photocatalytic activities for methylene blue degradation (MB) under visible light irradiation. MB photodegradation efficiency reaches 98% after 240 minutes of illumination. The NiFe2O4/N-doped GO (NF/GO-N) was of better photocatalytic than that of the NF and GO-N. A kinetic model was proposed by the combination of classical Langmuir-Hinshelwood kinetic model, the experimental data fit well the proposed model.

Effect of particle size on magnesite flotation based on kinetic studies and machine learning simulation

This research focused on the effect of particle size and flotation time on magnesite flotation, and the flotation performance of various size fractions were predicted by a machine learning (ML) method. Four kinetic models were used to fit the recovery of MgO and SiO2 in various size fractions of magnesite flotation. The results demonstrated that the flotation of magnesite exhibits good agreement with the classical first-order kinetic model. Besides, the effect of various particle sizes on MgO recovery and selectivity index was predicted by ML method. It was shown that the proposed ML model could accurately reproduce the effects of particle size and flotation time on magnesite flotation performance. Furthermore, the developed model revealed that the optimal mean size range for magnesite flotation is 30 to 48 μm. Therefore, this paper is of great significance to the application of ML methods in the prediction of various magnesite size flotation performance.

Mathematical Model of Low-Concentration Disperse Suspension Fractionation in a Plane Vertical Hydroclassifier

A continuum mathematical model of low-concentration suspension transfer without mixing in a plane vertical gravitational classifier under conditions of phase flux balance is suggested. The flow of a carrier medium is assumed to be laminar, and no limitations on the particle sedimentation rate are imposed. Analytical relationships to calculate the local counting functions of the particle size distribution density have been derived. A computational experiment has confirmed the fractionation of a monodisperse suspension and the presence of fine particles in the “heavy” fractions of polydisperse suspensions. The latter fact is explained by a low velocity of the disperse medium at the “wetted” surfaces of the hydroclassifier. The results are in agreement with available experimental data and data calculated in terms of classical kinetic models.

Scaling law of Brownian rotation in dense hard-rod suspensions.

Self-diffusion in dense rod suspensions are subject to strong geometric constraints because of steric interactions. This topological effect is essentially anisotropic when rods are nematically aligned with their neighbors, raising considerable challenges in understanding and analyzing their impacts on the bulk physical properties. Via a classical Doi-Onsager kinetic model with the Maier-Saupe potential, we characterize the long-time rotational Brownian diffusivity for dense suspensions of hard rods of finite aspect ratios, based on quadratic orientation autocorrelation functions. Furthermore, we show that the computed nonmonotonic scalings of the diffusivity as a function of volume fraction can be accurately predicted by an alternative tube model in the nematic phase.

Modeling and Estimation of Nuclear Reactor Performance Using Fractional Neutron Point Kinetics with Temperature Effect and Xenon Poisoning

This paper discusses modeling of the performance of a VVER-type nuclear power plant using the Fractional Neutron Point Kinetics (FNPK) model. The modeling intent is to achieve a nonlinear system of fractional-order differential equations that are solved using SIMULINK by developing a scheme with the FOMCON Toolbox in the Matlab® environment. The model is shown to be identifiable, and the goodness of fit between the measurements and the model’s output is improved as a result of employing the optimized fractional differential equation. Benchmarking the results of the FNPK model against those from the optimized Classical Neutron Point Kinetics model shows that the FNPK model is superior.

The potential of acoustic sound to improve flotation kinetics

Improving the kinetics of flotation with a given feed often involves adding more reagents or changing the reagent scheme. However, this approach could greatly increase operational cost and cause downstream problems. The present work demonstrates a novel approach to improving the flotation kinetics by applying acoustic sound on flotation. Quartz particles were used as model particles and the flotation tests were carried out in batch mode. The experimental variables were focused on sound frequency (250–500 Hz) and amplitude (90–125 dB). The flotation recovery-versus-time data were fitted to the classical first-order kinetic model and two other kinetics models considering the distribution of rate constants. It was found that use of acoustic sound at 350 Hz and above 110 dB and at 400 Hz and 125 dB could increase the apparent flotation rate constant, suggesting that acoustic sound when applied at proper conditions can improve the flotation kinetics.

Selective and multicycle removal of Cr(VI) by graphene oxide–EDTA composite: Insight into the removal mechanism and ionic interference in binary and ternary associations

Graphene-based composite has demonstrated great potential in environmental remediation and wastewater treatment. Herein, graphene oxide was modified with ethylenediaminetetraacetic acid aimed to augment heterogeneous functional groups on the composite i.e., [email protected] for aqueous Cr(VI) adsorption. The characterization materials revealed that EDTA linked with GO through an amide bond, and N, O, and C are present in [email protected] in 3.25, 19.98, and 76.77%, respectively, and the specific surface area of 100.93 m2/g. Tts maximum adsorption capacity of [email protected] towards C(VI) was 36.59 mg/g, at pH 1.8. The classical isotherm and kinetic models were best correlated with the Freundlich isotherm and pseudo-second-order kinetics, respectively. The electrostatic interaction was the predominant force involved Cr(VI) adsorption onto [email protected], followed by the reduction into Cr(VI) and its complexation. The adsorption of Cr(VI) in binary and ternary association with Pb2＋, Cd2＋, and Cl−, seemed unaffected. However, the presence of S2− has a profound effect on Cr(VI) adsorption. More interestingly, the presence of Cl− with S2− in the ternary association (Cr(VI) + Cl− + S2−) suppresses the antagonistic behavior of S2− up to a certain extent that leads to enhance Cr(VI) removal. Overall, the thermodynamics and reusability study advocate the potential of [email protected] for multiple cycle Cr(VI) removal — pave the way for its application in wastewater treatment.

Analysis of Solidarity Effect for Entropy, Pareto, and Gini Indices on Two-Class Society Using Kinetic Wealth Exchange Model.

It is well known that two different underlying dynamics lead to different patterns of income/wealth distribution such as the Boltzmann–Gibbs form for the lower end and the Pareto-like power-law form for the higher-end. The Boltzmann–Gibbs distribution is naturally derived from maximizing the entropy of random interactions among agents, whereas the Pareto distribution requires a rational approach of economics dependent on the wealth level. More interestingly, the Pareto regime is very dynamic, whereas the Boltzmann–Gibbs regime is stable over time. Also, there are some cases in which the distributions of income/wealth are bimodal or polymodal. In order to incorporate the dynamic aspects of the Pareto regime and the polymodal forms of income/wealth distribution into one stochastic model, we present a modified agent-based model based on classical kinetic wealth exchange models. First, we adopt a simple two-class society consisting of the rich and the poor where the agents in the same class engage in random exchanges while the agents in the different classes perform a wealth-dependent winner-takes-all trading. This modification leads the system to an extreme polarized society with preserving the Pareto exponent. Second, we incorporate a solidarity formation among agents belonging to the lower class in our model, in order to confront a super-rich agent. This modification leads the system to a drastic bimodal distribution of wealth with a varying Pareto exponent over varying the solidarity parameter, that is, the Pareto-regime becomes narrower and the Pareto exponent gets larger as the solidarity parameter increases. We argue that the solidarity formation is the key ingredient in the varying Pareto exponent and the polymodal distribution. Lastly, we take two approaches to evaluate the level of inequality of wealth such as Gini coefficients and the entropy measure. According to the numerical results, the increasing solidarity parameter leads to a decreasing Gini coefficient not linearly but nonlinearly, whereas the entropy measure is robust over varying solidarity parameters, implying that there is a trade-off between the intermediate party and the high end.

Fractal-Like Kinetics of Adsorption Applied to the Solid/Solution Interface.

In this paper, the fractal-like multiexponential (f-mexp) equation was modified by introducing the fractional fractal exponent to each stage of the adsorption process. The new equation was used for the analysis of kinetic adsorption of copper onto treated attapulgite. The modeling results show that the modified f-mexp equation fits properly the kinetic data in comparison with the classical and fractal-like kinetic models tested. The effect of varying the initial concentration of the adsorbate on the kinetic parameters was analyzed. Artificial neural networks were applied for the prediction of adsorption efficiency. Outcomes indicate that the multilayer perceptron neural network can predict the removal of copper from aqueous solutions more accurately under different experimental conditions than the single-layer feedforward neural network. Single-site and multisite occupancy adsorption models were used for the analysis of experimental adsorption equilibrium data of copper onto treated attapulgite. The modeling results show that there is no multisite occupancy effect and that the equilibrium data fit well the Langmuir–Freundlich isotherm.