Homogeneous Kinetics Research Articles

Molecular Unravelling of the Structural Effect of Quinone Redox Mediators on Oxygen Reduction Reaction in Aprotic Lithium-Oxygen Batteries.

Redox mediators (RMs) provide tantalizing solutions to unlock the energy capabilities of aprotic lithium-oxygen (Li-O2) batteries by driving solution-mediated Li2O2 growth. However, the structural effect of RMs on the catalytic efficiency of the oxygen reduction reaction remains incompletely understood. Herein, we present the interplay between the structure of RMs and their discharge capabilities by a comparative study of model quinone (Q)-based RMs. Specifically, at low current densities, incorporating electron-withdrawing groups onto the Q ring can positively move the discharge potential and deliver larger discharge capacity by extending the lifespan of the LiQO2 intermediate and allowing for Li2O2 growth into deeper electrolyte regions. Conversely, at high current densities, the absence of electron-withdrawing groups facilitates homogeneous reaction kinetics from LiQ to regenerate Q (i.e., decreased lifespan of LiQO2), mitigating electrode potential polarization and preserving catalytic activity of Q for higher discharge capacity. The work establishes structure-property relationships that guide the rational design of RMs toward next-generation Li-O2 batteries.

Development and validation of a 1D gas–liquid model for dissolved Mn(II) removal by oxidation process in a square bubble column

Modeling multiphase reactors requires an in-depth multidisciplinary analysis of various phenomena including the chemical kinetics, oxygen mass transfer, as well as the simulation of flows within these contactors. In this study, a 1D model of two-phase flow for Mn(II) removal from drinking water by aeration process is developed and validated. This model is based on the Eulerian description of two-phase gas–liquid flow with the comparison between a one-medium bubble size and a two-bubble class description to represent the bubble population in the heterogeneous flow regime. All the relevant chemical species are simulated by coupling hydrodynamics, gas–liquid mass transfer, and reaction kinetic. A pseudo-first-order model accounting for homogeneous and heterogeneous kinetics is considered for Mn(II) oxidation. The performance of the developed 1D model is compared and validated with experimental data. The 1D model was able to predict quantitatively Mn oxidation as a function of pH, initial Mn(II) and initial Mn(IV) concentrations.

Mechanism of homogenization temperature and time on Fe-containing phase transition in AA8014 aluminum alloy

The presence of coarse Fe-containing phases detrimentally affects the fracture toughness of 8xxx aluminum alloys, and their complete dissolution during homogenization is unattainable. Therefore, it is essential to determine the optimal homogenization temperature and time to facilitate particle breakup during hot rolling, necessitating the development of effective homogenization processes. This study systematically examines the effect of homogenization temperature and time on the transition of Fe-containing phases in AA8014 aluminum alloy using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The transition mechanisms of Fe-containing phases during homogenization were elucidated through first-principles calculations, thermodynamics, and kinetics calculations. Under homogenization conditions of 610–650 ℃/12 h and 630 ℃/1–20 h, the Al6(Fe,Mn) phase initially transforms into the α-Al12(Fe,Mn)3Si phase with a “micropore structure” via the reaction. Subsequently, the α-Al12(Fe,Mn)3Si phase transforms into the Al3(Fe,Mn) phase. First-principles calculations confirm the sequential stability enhancement of the Al6(Fe,Mn), α-Al12(Fe,Mn)3Si+6Al, and Al3(Fe,Mn) phases. Homogenization kinetics indicate an optimal homogenization time of 11.5 h at 630 ℃, rationalizing the observed phase transitions and homogenization treatment. This study provides a foundation for the manufacture of 8xxx series aluminum alloys.

An investigation on effect of tramp elements and solidification processing on homogenization kinetics of AA 7xxx series aluminum alloys

AA 7068 Aluminum alloy is produced via conventional solidification (CS) and controlled diffusion solidification (CDS) processing and homogenized at 450 °C for 6 and 12 h. Optical microscopy (OM) and scanning electron microscopy (SEM) equipped with an energy dispersive x-ray spectroscope (EDS) were used to examine the as-cast and homogenized samples. It was found that although the CS sample is more chemically homogenized in the as-solidified state, the CDS sample exhibits a higher homogenization rate during the treatment. The calculated phase diagram (CALPHAD) methodology was employed to study the effect of silicon and iron on the solidification path and homogenization of the alloy. Silicon consumes magnesium atoms on the surface of the α-Al phase to form the Mg2Si phase. Therefore, the magnesium concentration on the α-Al phase required for the formation of the σ phase must be increased. Calculations shows that all the Mg atoms at this stage are completely supplied from the bulk of the αAl phase. It can be hypothesized that during the last stage of solidification, a solid/liquid diffusion couple can be created between the primary αAl and the remaining liquid for several minutes (4 min at a cooling rate of 0.2 oC/s). As a result of the activation of this couple, the Mg atoms diffuse from the α-Al bulk to its surface, and vacancies diffuse from the surface to the bulk, forming a line of Kirkendall voids. With CDS processing, the surface of the primary phase is less Mg-concentrated than that in the CS process and this significantly reduces the formation of the Mg2Si phase. Conversely, the vacancy and Mg concentration of the αAl phase in CDS is higher than that of CS and this lets other alloying elements other than Mg diffuse to the primary phase, decreasing the homogenization time. The presence of Si in the alloy leads to the formation of the Mg2Si phase, which significantly reduces the final Mg concentration in the α-Al phase after full homogenization. In the pure alloy, the Mg concentration is 2.42 wt%, while in the FeSi-containing alloy, it is reduced to 1.58 wt% due to solid solution and dispersion strengthening mechanisms. Through CDS processing, the negative impact of Si can be reduced by disrupting the mechanism of Mg2Si formation.

Homogeneous versus heterogeneous Mn(II) oxidation in peroxymonosulfate assisting chlorination: Synergistic role for enhanced Mn(II) oxidation in water treatment

Removal of Mn(II) is an essential step for addressing water discoloration in water treatment utilities worldwide. However, conventional chlorination suffers from poor oxidation of Mn(II) due to its low homogeneous oxidation kinetics. This study explored the oxidation capability of a new chemical dosing strategy employing peroxymonosulfate (PMS) to assist the chlorination process (PMS@Cl2) for effective Mn(II) oxidation. The study comprehensively explored both oxidation kinetics and underlying mechanisms associated with homogeneous and heterogeneous oxidation within the PMS@Cl2 system. At an [Mn(II)]0 of 1 mg/L, chlorination demonstrated inability in oxidizing Mn(II), with <10 % oxidation even at an elevated [Cl2] of 150 μM (∼10 mg/L). By contrast, PMS completely oxidized 100 % Mn(II) within a 30-minute reaction at a much lower [PMS] of 60 μM (kobs = 0.07 min−1 and t1/2 = 9 min), demonstrating its superior Mn(II) oxidation kinetics (over one order of magnitude faster than conventional chlorine). PMS@Cl2 exhibited an interesting synergistic benefit when combining a lower dose PMS with a higher routine dose Cl2 (loPMS@hiCl2), e.g. [PMS]:[Cl2] at 15:30 or 30:30 μM. Both conditions achieved 100 % Mn(II) oxidation, with even better values of kobs and t1/2 (0.16–0.17 min−1 and ∼4 min) relative to PMS alone at 60 µM. The synergic benefit of PMS@Cl2 was attributed to distinct functions played by PMS and Cl2 in both homogeneous and heterogeneous oxidation processes. Reactive species identification excluded the possible involvement of SO4•−, OH•, or chlorine radicals in the homogeneous oxidation of the PMS@Cl2 system. Instead, the dominant species was O2•− radical generated during the reaction of Mn(II) and PMS. Furthermore, the heterogeneous oxidation emphasized the important role of combining Cl2 dosing, which demonstrated an increased reactivity and electron transfer with the Mn−O−Mn complex, surpassing PMS. Overall, heterogeneous oxidation accelerated the oxidation kinetics of the PMS@Cl2 system by 1.1–2 orders of magnitude relative to the homogeneous oxidation of Cl2 alone. We here demonstrated that PMS@Cl2 could offer a more efficient mean of soluble Mn(II) mitigation, achieved with a relatively low routine dose of oxidant in a short reaction period. The outcomes of this study would address the existing limitations of traditional chlorine oxidation, minimizing the trade-offs associated with high residual chlorine levels after treatments for soluble manganese-containing water.

A direct particle tracking model for predicting homogeneous precipitation kinetics in Al-Sc alloys

The Kampmann-Wagner numerical (KWN) model, although been widely used in modeling the precipitation kinetics in solid solution alloys, has its own deficiency which is mainly reflected in two aspects: inability to track the growth history of individual particles and difficulty in describing the precipitation kinetics of non-spherical particles. In this work a direct particle tracking (DPT) model, which can well handle such issues, has been proposed and implemented. The main aim of this work is to check the validity and accuracy of the DPT model. To this end, the DPT model and two KWN models with different levels of accuracy have been applied to simulate the precipitation kinetics in two Al-Sc alloys. By comparing the numerical results with literature experimental data, it is found that the DPT model can well describe the microstructure evolutions during ageing of the Al-Sc alloys, and it has nearly the same accuracy as the KWN model with the governing equation solved by the high-resolution scheme (HR-KWN model). To reduce the amplitude of the oscillations formed in the particle size distribution (PSD) curves predicted by the DPT model, we need to set a small enough value for the time intervals divided in the nucleation stage.

Review of chemical models and applications in Geant4-DNA: Report from the ESA BioRad III Project.

A chemistry module has been implemented in Geant4-DNA since Geant4 version 10.1 to simulate the radiolysis of water after irradiation. It has been used in a number of applications, including the calculation of G-values and early DNA damage, allowing the comparison with experimental data. Since the first version, numerous modifications have been made to the module to improve the computational efficiency and extend the simulation to homogeneous kinetics in bulk solution. With these new developments, new applications have been proposed and released as Geant4 examples, showing how to use chemical processes and models. This work reviews the models implemented and application developments for modeling water radiolysis in Geant4-DNA as reported in the ESA BioRad III Project.

Investigating Homogenization Kinetics in IN718 Alloy: A Comprehensive Strategy Involving Si-Enriched Scrap Utilization and Optimization of Two-Stage Heat Treatment

Investigating Homogenization Kinetics in IN718 Alloy: A Comprehensive Strategy Involving Si-Enriched Scrap Utilization and Optimization of Two-Stage Heat Treatment

Microstructure Evolution and Homogenization Kinetics of 15Cr–30Ni–Fe Heat‐Resistant Alloy

The as‐cast microstructure, microsegregation of alloying elements, and microstructure evolution during homogenization of the newly designed 15Cr–30Ni–Fe heat‐resistant alloy are studied. Ti, Nb, Si, and Mo segregate at the interdendritic region. The brittle eutectic Laves phase contains Fe, Ti, Ni, Nb, Si, and Mo, which is identified as the Fe2Ti Laves phase. The activation energy for the Fe2Ti Laves phase dissolution is close to the activation energy for Ti diffusion in the γ matrix based on the Johnson–Mehl–Avrami–Kolmogorov analysis. The back‐diffusion of Ti to the γ matrix is the limiting step for the dissolution of Fe2Ti Laves phase. The kinetic equation of homogenization considering lattice parameters and pre‐exponential factor correction is established. After the double‐stage homogenization at 980 °C/10 h + 1140 °C/4 h, the volume fraction of the Laves phase decreases from 5.11% to 0.26%, and the large eutectic Laves phase is completely dissolved. The reduction in the standard deviation of microhardness at different soaking times effectively reflects the gradual decrease in the degree of microsegregation of alloying elements. The average grain size of the alloy after homogenization is 410 ± 63.1 μm, which is beneficial to control the further refinement of grain during the subsequent hot working.

Hyperbranched RCA-mediated construction of a dendritic DNA nanostructure for ratiometric fluorescence biosensing

As a robust isothermal strand amplification technique, rolling circle amplification (RCA) is popularly adopted for constructing various homogeneous fluorescence biosensing strategies. However, the limited functional unit decoration on linear RCA products and the slow homogeneous reaction kinetics usually restrict their performance. Herein, by designing a target biorecognition-triggered hyperbranched RCA reaction to construct an Mg2+-dependent DNAzyme (MNAzyme)-decorated dendritic DNA nanostructure, a novel ratiometric fluorescence biosensing method was proposed. The catalyzed cleavage of MNAzymes toward a short stand labeled with the FAM fluorophore and its quencher realized a “signal-on” fluorescence output. Meanwhile, a “signal-off” fluorescence output of 2-aminopurine (2-AP) labeled at a DNA hairpin was realized through the DNA hybridization with the nanostructure. Besides efficient acceleration of homogeneous reaction kinetics, these fluorescence responses were dramatically amplified by the high decoration of MNAzymes on the dendritic nanostructure and its strong signal suppression toward 2-AP. Together with the exonuclease III-amplified target biorecognition reaction, a very low detection limit of 0.53 fg mL–1 and a six-order magnitude linear range were endowed for kanamycin antibiotic assay. This excellent analytical performance and its high selectivity, and good operability determine promising prospect of the method for practical applications.

New model for predicting homogenization kinetics of typical wrought superalloy

A new homogenization kinetics prediction model for wrought superalloys based on the concept of diffusion distance was proposed. The micro-segregation and homogenization kinetics of Ni-based wrought superalloy, GH4141, were systematically studied by using the quantitative electron prob X-ray micro-analyzer (EPMA) analyses. There is a discrepancy between the predicted homogenization kinetics by the residual segregation index model and the experimental measurement. Both the experiments and theoretical analyses reveal that the homogenization kinetics can be reasonably predicted by the diffusion distance model under 1D-diffusion condition, with considering the diffusion-direction factor that is usually ignored. The new model provides a new option for predicting the homogenization kinetics with only necessarily knowing the original dendrite arm spacing and diffusion coefficient.

Investigation of Laves Phase Dissolution and Homogenization Kinetics in IN718 with 0.4 Wt.% Si Through a Combination of Characterization and Calculations

Investigation of Laves Phase Dissolution and Homogenization Kinetics in IN718 with 0.4 Wt.% Si Through a Combination of Characterization and Calculations

Kinetics of Homogeneous Reaction of Potassium Methoxide Based on K2CO3 Catalyst in Transesterification of RBDPO to Biodiesel

Biodiesel production is generally catalyzed by potassium methylate or sodium methylate catalysts based on KOH and NaOH and these catalysts are still imported. The search for a cheap and effective catalyst continues to be carried out by researchers. One of the catalyst support materials currently in use involves impregnating K2CO3 with various substances, resulting in a heterogeneous catalyst. In this study, it was tried to use K2CO3 dissolved in methanol to produce a homogeneous potassium methylate catalyst. Potassium methylate-based homogeneous catalyst K2CO3-methanol is proven to have a very high function in the transesterification reaction of Refined Bleached Deodorized Palm Oil (RBDPO) into biodiesel, this is evidenced by the use of a catalyst percentage of 2% w and 30% w methanol to the weight of RBDPO resulting in an acid content in biodiesel of only 0.12% and a total glycerol of 0.124% in reaction time 3 hours, with the purity of the methyl ester in biodiesel reaching 98.80%. Meanwhile, for the calculation of homogeneous reaction kinetics, a reaction rate equation is produced where the order of the RBDPO transesterification reaction is order 2 (two) and the reaction rate constant is 0.0044.

Maximizing hydrogen-rich syngas production from rubber wood biomass in an updraft fluidized bed gasifier: An advanced 3D simulation study

BackgroundThis research focuses on biomass gasification as a solution to the global energy crisis. The study aims to optimize the production of syngas by simulating an updraft fluidized bed gasifier using rubber wood as fuel. The goal is to maximize CO and H2 at the gasifier outlet by investigating different vertical positions and angles of the biomass feed inlet. MethodsThe research utilizes 3D simulation and Computational Fluid Dynamics (CFD) through the implementation of the ANSYS Fluent® software package. Realistic assumptions and the K-epsilon turbulence model simplify the analysis. The model assumes a steady state, adiabatic conditions, homogeneous gas phase kinetics, and ideal fluid behavior. Significant findingsThe optimal biomass feed inlet position is 200 mm, yielding higher CO, while a position of 250 mm produces more H2. A 45° feed inlet angle slightly improves syngas quantities but increases CO2. Using a gasifying agent with higher CO2 enhances combustion, while limited O2 facilitates gasification. Increasing oxygen content from 20 % to 50 % raises H2O content. More steam in the inlet boosts H2 production, but excessive H2O reduces steam quality, making expensive steam less effective than air. These findings offer valuable insights for optimizing fluidized bed biomass gasification systems.

Straightforward determination of homogeneous kinetics using Fourier transform alternating current voltammetry (FTACV)

This work describes a novel method by which the homogeneous kinetics for an ErevCirrev system can be deduced using only the forward scan of second harmonic FTACV. We show that ratio of the heights of the two lobes of the 2nd harmonic voltammograms readily provides this information by fitting data to a working curve modelled by the simple equation ilobe,right/ilobe,left=1/(1+kτs), where τs is the characteristic voltammetric timescale. The validity of the relationship was tested by comparison with both simulated and experimental data. This novel approach offers the advantage of quick and easy determination of kf, while increasing accuracy by omitting the ambiguity in determining a baseline and minimising the effects of electrode passivation. We also show that these changes can be explained by considering the change in surface concentration of the [Ox] and [Red] species over the course of a scan, which are more profoundly expressed in the FTACV response compared with CV.

The C2H4O isomers in the oxidation of ethylene

A combined rotational spectroscopy, thermochemistry, and kinetic modeling study explores the mechanism of acetaldehyde (ethanal), vinyl alcohol (ethenol), and ethylene oxide (oxirane) formation in the oxidation of ethylene (ethene). Multiplexed quantitative detection of oxidation intermediates and products exiting a SiO2/SiC microreactor at 1700 K is demonstrated with the BrightSpec W-band chirped-pulse Fourier transform millimeter-wave spectrometer. The broadband rotational spectrum contains transitions of formaldehyde (CH2O), methoxy (CH3O), methanol (CH3OH), ketene (CH2CO), acetaldehyde (CH3CHO), syn-vinyl alcohol (syn-CH2CHOH), anti-vinyl alcohol (anti-CH2CHOH), oxirane (c-CH2OCH2), propyne (CH3CCH), and syn-propanal (syn-CH3CH2CHO). We focus on the three C2H4O species and deduce their concentration ratio [CH3CHO]:[CH2CHOH]:[c-CH2OCH2] = 1:0.7(2):0.06(2) by comparing the observed line intensities to those simulated with the PGOPHER software. Detailed thermochemistry of the C2H4O isomers and conformers is provided by Active Thermochemical Tables. The observed excess concentrations of vinyl alcohol and oxirane relative to the more stable acetaldehyde compared to the equilibrium ratio at 1700 K (1:0.087:0.000024), point to direct chemical pathways to these higher energy isomers. The mechanism for the formation of the three C2H4O isomers is analyzed using a 0-D homogenous reactor kinetics simulation for ethylene oxidation. The ratios of the C2H4O isomers concentrations predicted by the kinetic model are compared to the experimental values.

Kinetics of high pressure homogenization assisted protein extraction from Chlorella pyrenoidosa

Protein extraction kinetics from microalga Chlorella pyrenoidosa by applying High Pressure Homogenization pretreatment was studied. Untreated and treated (400–800 bar, 1 and 4 passes) aqueous microalgal suspensions were incubated at 20–40 °C for up to 24 h. A four-pass treatment at 800 bar caused maximization of carbohydrate (103 mg carbohydrates/g dry biomass immediately after treatment) and protein recovery (382.0 mg proteins/g dry biomass after extraction at 40 °C for 24 h). Protein characteristic extraction time was significantly dependent on pretreatment conditions and extraction temperature (5.16 h for untreated sample at 20 °C vs. 1.34 h for 800 bar/4 passes treated biomass at 40 °C). A combination of a two-hour ethanolic extraction at 60 °C prior to a six-hour aqueous extraction from biomass treated at 800 bar/4 passes maximized chlorophyll separation (16.3 mg chlorophylls/g dry biomass) and led to aqueous extracts of high protein content (764.7 mg proteins/g dry extract).

As-cast microstructure and homogenization kinetics of a typical hard-to-deform Ni-base superalloy

In this paper, the as-cast microstructure, microsegregation, and the kinetics of (γ+γ′) eutectic phase and Laves phase dissolution in GH4151 alloy were studied by the optical microscope (OM), scanning electron microscope (SEM), electron probe microanalysis (EPMA), differential scanning calorimetry (DSC), and high-temperature water quenching text. The results show that W and Al elements are segregated into the dendrites arm, while Mo, Nb, and Ti are segregated into the interdendritic region. The initial melting point temperature of the MB2 phase was near 1100 °C, the redissolution temperature range of γ′ phase is 1130–1160 °C, the obvious dissolution temperature of Laves phase was above 1145 °C and the γ + γ′ eutectic phase was redissolved obviously above 1165 °C. Based on the JMAK analysis, the activation energies of dissolution of Laves phase (266.3 kJ/mol) and γ+γ′ phase (279.5 kJ/mol) are close to the activation energy for the diffusion of Mo in Ni (288.15 kJ/mol) and Ti in Ni (288.15 kJ/mol), respectively. The back-diffusion of Mo and Ti into austenite is controlling the micro-mechanism for the dissolution of Laves phase and (γ+γ′) eutectic phase, respectively.

CPFD simulation of a pilot-scale CFB riser for sugar cracking to glycolaldehyde and other oxygenates: Coupling hydrodynamics and reaction kinetics

Cracking of sugars to glycolaldehyde and other value-added oxygenates has shown potential in lab-scale fluidized beds with high yield and selectivity towards glycolaldehyde. In this work, a homogeneous gas-phase kinetics model for sugar cracking available in literature is adopted and implemented into the Computational Particle Fluid Dynamics (CPFD) framework in order to simulate sugar cracking in a pilot-scale circulating fluidized bed riser operated at conditions relevant for continuous production of glycolaldehyde in the industry. An Eulerian-Lagrangian approach is applied to model the three-phase flow where liquid feed droplets are injected into the hot gas–solid fluidized bed. A modified gas-to-liquid ratio dependent Rosin-Rammler droplet size distribution is proposed to accurately represent the gas–liquid jet in the simulation. Simulated temperature and pressure distributions are in good agreement with measured ones. Prediction of the yield of glycolaldehyde at 60.9 wt%-C and other oxygenates using the the CPFD model corresponds closely to the results obtained from the same kinetic model implemented in an isothermal plug flow reactor model. This suggests that the CFB riser behaves essentially like a plug flow reactor, as hydrodynamic and thermal deviations from plug flow conditions do not have a considerable effect on the predicted yields. Comparing the model predictions to the measured yield of glycolaldehyde, a 50% overprediction is observed, suggesting that the hydrodynamic and cracking kinetics submodels need to be more closely coupled to more accurately predict the product yields, by means of e.g. heterogeneous cracking reactions.

Microstructure and Intermetallic Phase Evolution during the Homogenization of an Al–Zn–Mg–Cu–Zr–Nd Aluminum Alloy

The intermetallic phase evolution during the homogenization of an Al–Zn–Mg–Cu–Zr alloy with Nd addition is investigated. Large amounts of the eutectic interdendritic acicular‐state η (MgZn2) phase, primary phase T (AlZnMgCu), Al8Cu4Nd, and Al7Cu2Fe exist at the grain boundaries of the as‐cast Al–Zn–Mg–Cu–Zr–Nd alloy. The homogenized intermetallic phase evolves as follows: the η phase dissolves into the α (Al) matrix, most of the T phase is dissolved in 16 h, and the remaining part of the T phase is transformed into the S phase (Al2CuMg) after 24 h. The stable Al8Cu4Nd phase in the alloy captures Cu atoms and inhibits the further generation of the S phase during homogenization. The addition of Nd decreases the fraction of the S phase, and only Al7Cu2Fe, Al8Cu4Nd, and Al2CuMg remain after homogenization for 24 h. Homogenization kinetics analysis suggests that the Al–Zn–Mg–Cu–Zr–Nd alloy is suitably homogenized at 470 °C 24 h−1.