Rate Constant Decreases Research Articles

A Debittered Complex of Glucose-Phenylalanine Amadori Rearrangement Products with β-Cyclodextrin: Structure, Molecular Docking and Thermal Degradation Kinetic Study.

Non-volatile flavor precursors could be used to overcome the flavor loss problems of volatile flavor enhancers during long-term storage. Glu- and Phe-derived Amadori rearrangement products (ARPs) produce pleasant aroma tones thermally but are bitter. We used β-cyclodextrin (β-CD) for debittering Glu-Phe ARPs. ITC analysis indicated that CD-ARP complexes with 1:1 stoichiometry were obtained. NMR analysis indicated that the aromatic ring of Glu-Phe ARPs was embedded in the β-CD cavity. Molecular docking simulations of the bitter taste receptor hT2R1 showed that CD-ARP complex was inactive compared to Glu-Phe ARPs. Complexation with β-CD resulted in the thermal stabilization of Glu-Phe ARPs and a decrease in the degradation rate constant. Compared to Glu-Phe ARPs, the CD-ARP complex in the thermally treated food system slowed down the formation of browning compounds but didn’t inhibit flavor compound formation. The CD-ARP complex is a promising flavor enhancer for applications in flavored and heated foods.

Kinetics of the Gas-Phase Reaction of Hydroxyl Radicals with Dimethyl Methylphosphonate (DMMP) over an Extended Temperature Range (273-837 K).

The kinetics of the reaction of hydroxyl radical (OH) with dimethyl methylphosphonate (DMMP, (CH3O)2CH3PO) (reaction 1) OH + DMMP → products (1) was studied at the bath gas (He) pressure of 1 bar over the 295–837 K temperature range. Hydroxyl radicals were produced in the fast reaction of electronically excited oxygen atoms O(1D) with H2O. The time-resolved kinetic profiles of hydroxyl radicals were recorded via UV absorption at around 308 nm using a DC discharge H2O/Ar lamp. The reaction rate constant exhibits a pronounced V-shaped temperature dependence, negative in the low temperature range, 295–530 K (the rate constant decreases with temperature), and positive in the elevated temperature range, 530–837 K (the rate constant increases with temperature), with a turning point at 530 ± 10 K. The rate constant could not be adequately fitted with a standard 3-parameter modified Arrhenius expression. The data were fitted with a 5-parameter expression as: k1 = 2.19 × 10−14(T/298)2.43exp(15.02 kJ mol−1/RT) + 1.71 × 10−10exp(−26.51 kJ mol−1/RT) cm3molecule−1s−1 (295–837 K). In addition, a theoretically predicted pressure dependence for such reactions was experimentally observed for the first time.

An electrophoretic co-deposition of metal oxides followed by in-situ copper manganese spinel synthesis on AISI-430 for application in SOFC interconnects

Electrophoretic co-deposition of copper and manganese oxides followed by in-situ reactive sintering is investigated as a method of Cu–Mn spinel coating for application in SOFC interconnects. Effect of electrophoretic deposition parameters including time, voltage, solid concentration and dispersant content on the quality and quantity of deposition are examined. A uniform layer of oxides is co-deposited at 100 V, in 10 min, with 10 g/L oxides in ethanol-acetone solution and 1:16 w/w dispersant:oxides. Based on XRD and SEM-EDS results, rate of Fe and Cr diffusion is unacceptable at above 850 °C. 3 h of sintering in air at 800 and 850 °C is best to synthesize spinel without severe Fe–Cr contamination. In a 100-h cyclic oxidation test, coatings prevent chromium poisoning and reduce the oxidation rate by a minimum of two orders of magnitude decrease in the parabolic rate constant of oxidation from 1.34 × 10−12 in uncoated to 8.50 × 10−14 g2 cm−4 s−1 and 32.3% decrease in Cr at.% in the coated samples.

A Framework for Incorporating Transient Solute-Keratin Binding Into Dermal Absorption Models

Interpretation of experiments involving transient solute binding to isolated keratin substrates is analyzed and discussed in terms of their impact on transient permeation of topically-applied compounds through human stratum corneum. The analysis builds upon an earlier model (Nitsche and Frasch 2011 Chem Eng Sci 66:2019-41) by adding a second level of homogenization (ultrascopic-to-microscopic) prior to the microscopic-to-macroscopic conversion. Here “ultrascopic” refers to isolated keratin suspensions, “microscopic” to corneocyte interiors and “macroscopic” to tissue-averaged properties in the stratum corneum. Results are interpreted in the context of current parameterizations of the underlying ultrascopic binding parameters. The present analysis, which is limited to linear binding isotherms common in dilute solutions, reveals a maximum in the macroscopic forward binding rate constant as a function of solute lipophilicity, whereas the underlying equilibrium constant increases monotonically and the macroscopic reverse binding rate constant decreases monotonically. The size and location of the maximum depends upon the hydration state of the stratum corneum. Explicit equations expressing these findings allow both equilibrium and kinetic binding data in isolated keratins to be applied to the kinetics of transient absorption through the skin. They will enable more quantitative estimation of the long-recognized stratum corneum reservoir function.

Fabrication of ZnO thin film by dip-coating technique and study of photocatalytic activity in Rhodamine B degradation reaction

In this study, ZnO thin films were fabricated by dip-coating technique used solution synthesized by sol-gel method. The influence of film area and RhB concentration on the photocatalytic activity of ZnO films was determined. Accordingly, the survey results irradiation with a UV lamp 5W showed that both the efficiency and the rate constant increased when the film’s area used increased, but the mass of RhB decomposed in 1 hour calculated according to 1 m2 films again decreased. In the case of increased RhB concentration, the results show that the efficiency and the reaction rate constant decrease in value. Finally, an important point to mention is the film samples can be reused many times showing high potential for practical applications.

Kinetic Study of SN2 Reaction between Paranitrophenyl Benzoate and Hydrazine in the Presence of CTAB Reverse Micelles

Kinetic study of the reaction between p-Nitrophenyl benzoate (PNPB) by hydrazine (HYN) in the presence of Cetyltrimethylammonium bromide (CTAB)/Chloroform/Hexane reverse micellar medium shows that the reaction obeys first order kinetics with respect to each of the reactants. The rate of the reaction is much slower in reverse micellar medium compared to aqueous medium under identical conditions (kˈAq = 2.84×10−3 sec−1, krm =1.34×10−4 sec−1). The rate constants for the reaction in the reverse micellar medium have been determined at different values of W {W=[H2O]/[CTAB]} and at different concentrations of CTAB. It was found that the observed rate constant decreases with W. This kinetic behaviour was interpreted by using modified Berezin pseudo phase model, taking into consideration the distribution of the reactants, PNPB and hydrazine between the three pseudo phases, i.e., water pool, interface an organic phase. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

X-ray Crystal Structures of Methane Monooxygenase Hydroxylase Complexes with Variants of Its Regulatory Component: Correlations with Altered Reaction Cycle Dynamics.

Full activity of soluble methane monooxygenase (sMMO) depends upon the formation of a 1:1 complex of the regulatory protein MMOB with each alpha subunit of the (αβγ)2 hydroxylase, sMMOH. Previous studies have shown that mutations in the core region of MMOB and in the N- and C-termini cause dramatic changes in the rate constants for steps in the sMMOH reaction cycle. Here, X-ray crystal structures are reported for the sMMOH complex with two double variants within the core region of MMOB, DBL1 (N107G/S110A), and DBL2 (S109A/T111A), as well as two variants in the MMOB N-terminal region, H33A and H5A. DBL1 causes a 150-fold decrease in the formation rate constant of the reaction cycle intermediate P, whereas DBL2 accelerates the reaction of the dinuclear Fe(IV) intermediate Q with substrates larger than methane by three- to fourfold. H33A also greatly slows P formation, while H5A modestly slows both formation of Q and its reactions with substrates. Complexation with DBL1 or H33A alters the position of sMMOH residue R245, which is part of a conserved hydrogen-bonding network encompassing the active site diiron cluster where P is formed. Accordingly, electron paramagnetic resonance spectra of sMMOH:DBL1 and sMMOH:H33A complexes differ markedly from that of sMMOH:MMOB, showing an altered electronic environment. In the sMMOH:DBL2 complex, the position of M247 in sMMOH is altered such that it enlarges a molecular tunnel associated with substrate entry into the active site. The H5A variant causes only subtle structural changes despite its kinetic effects, emphasizing the precise alignment of sMMOH and MMOB required for efficient catalysis.

Amphoteric surfactant of octadecyl dimethyl betaine as an efficient corrosion inhibitor for cold rolled steel in phosphoric acid solution

The inhibition effect of amphoteric surfactant of octadecyl dimethyl betaine (BS-18) on cold rolled steel (CRS) in H3PO4 solution was studied by weight loss, electrochemical technique, surface analysis and quantum chemical calculations. The results show that BS-18 acts as an efficient inhibitor on CRS in 1.0 M H3PO4 medium at 20–50 °C, and the maximum inhibition efficiency is 87.1% with 50 mg L−1 at 20 °C. Its adsorption on steel surface obeys Langmuir adsorption isotherm, which is endothermic process accompanying with the increase of entropy. Compared with uninhibited solution, apparent activation energy, pre-exponential factor, activation enthalpy and activation entropy become higher in inhibited solution, while both reaction constant and rate constant decrease after adding BS-18. Inhibition performance remains more stable from 3 to 48 h, and fluctuates slightly with the acid concentration from 0.5 to 5.0 M. BS-18 is a mixed-type inhibitor through “geometric blocking effect”. EIS is a time constant with one depressed capacitive loop in Nyquist plot and one phase angle in Bode phase plot, and the charge transfer resistance turns to become more larger in the presence of BS-18. SEM and AFM micrographs of inhibited CRS surface appear little corrosion, and its contact angle is increased. There are functional groups of C–N and C–N+ in the adsorptive film of BS-18 on CRS surface using XPS analysis. Critical micelle concentration (CMC) of BS-18 is about 20 mg L−1 from surface tension measurements. Quantum chemical calculations confirm that the active adsorption site of BS-18 is the hydrophilic group of N+ and –CH2COO−.

Effect of cyclodextrins’ cavity on the kinetics of alkaline hydrolysis of tris(1,10-Phenanthroline)Fe(II) in presence of surfactant

The kinetics of alkaline hydrolysis of tris(1,10-phenanthroline)Fe(II) has been explored spectrophotometrically in the presence of cyclodextrins (CDs), quaternary amphiphile (CTAB), and their mixed systems. All kinetics run in pseudo-first order conditions with excess concentration of alkali at 298 K (± 0.1 K). The reaction rate accelerates in the presence of CTAB. However, in the presence of CDs, the observed rate constant decreases continuously and also the catalytic properties of amphiphile diminishes, indicating the inclusion of both tris(1,10-phenanthroline)Fe(II) and surfactant into the CD cavity in the hydrolysis reaction. The cavity size of γ-CD among all of the CDs favors the incorporation of both Fe(II) complex and CTAB, which significantly reduces the micellar surface catalysis of CTAB. The decreasing sequence of the rate in CTAB-CDs mixed systems is observed as γ-CD > β-CD > α-CD. All the experimental kinetic results have been well explained based on the pseudo-phase model (PP model) of micelles and CD-inhibited model of CD systems. The calculated theoretical rate constant values are well consistent with the experimental data. In the absence and presence of CTAB, the calculated values of equilibrium binding constant between Fe(phen)3 2+ and γ-CD () are 109.17 (±1.03) and 414.74 (±3.63) (L mol−1), respectively, which support the diminishing of the catalytic properties of CTAB in the presence of γ-CD in the hydrolysis reaction. The experimental results also corroborate that fact. Finally, the effect of temperature on the reaction rate has been observed and the thermodynamic activation parameters have been evaluated. The linear plot of standard activated enthalpy with standard activated entropy reveals an iso-kinetic relationship that confirms a common mechanism for the reaction in different environments.

Insight into BDD electrochemical oxidation of florfenicol in water: Kinetics, reaction mechanism, and toxicity

Antibiotics in the environment provoke serious consequences on living beings and can be effectively remediated by prominent advanced oxidation process. In this study, electrochemical advanced oxidation treatment in a lab-scale reactor for the degradation of florfenicol (FLO) was studied with the aid of boron-doped diamond anode (BDD). The results exhibited that the FLO degradation follows pseudo-first-order kinetics. As the current intensity rose from 60 mA to 250 mA, the FLO removal efficiency increased and the corresponding reaction rate constant increased from 0.0213 to 0.0343 min−1, which was likely due to the more efficient participation of free hydroxyl radical (•OH) generated at the BDD anode. Faster degradation and higher mineralization of electrolyzed FLO solution were achieved at higher current intensity as well as in higher SO42− concentration medium, as a consequence of catalytic participation of oxidants (free •OH as well as sulfate radical (SO4•−) and persulfate (S2O82−)). The increase in FLO concentration from 30 to 50 mg L−1 resulted in a reaction rate constant decrease (from 0.0235 to 0.0178 min−1). Eight transformation by-products (m/z = 372.99, 359.8, 338.0, 324.04, 199.00, 185.02, 168.99 and 78.989) and three inorganic ions (NO3−, Cl− and F−) were analyzed by UPLC‒Q‒TOF‒MS/MS and Ion‒chromatography, respectively. The Vibrio fischeri bioluminescence inhibition revealed an increase of toxicity during the electrochemical oxidation that could be attributed mostly to the generated organic chlorinated by-products (m/z = 372.99, 359.8) and inorganic species (ClO2− and ClO3−).

Numerical Simulations of Decomposition of Hydrate Particles in Flowing Water Considering the Coupling of Intrinsic Kinetics with Mass and Heat Transfer Rates.

During the hydrate exploitation in a shallow marine layer by the mechanical crushing, the hydrate particle decomposition in a wellbore is one of the most concerning problems. In this research, a hydrate dynamic decomposition model coupling intrinsic kinetics with mass and heat transfer rates was established. The model can simulate the hydrate particle decomposition process in flowing water. By comparison, the model calculated results are in good agreement with the measured values. The numerical simulation results show that hydrate decomposition is a non-isothermal process. In the early stage, the hydrate decomposition rate mainly depends on the heat transfer rate. However, it is mainly affected by the hydrate intrinsic kinetics in the late stage. In contrast, the mass transfer rate has little effect on it during the whole decomposition process. By analyzing the influence of sensitivity parameters, it can be found that the activation energy has an important impact on the hydrate decomposition rate, and the hydrate decomposition rate constant decreases significantly at E/R > 9000 K. Increasing the water flowing rate is beneficial to the dissolution of hydrates. System temperature and pressure are two significant factors that directly affect the hydrate decomposition rate, and increasing the temperature or reducing the pressure can effectively increase the hydrate decomposition rate.

Growth Kinetic Study of Tannic Acid Mediated Monodispersed Silver Nanoparticles Synthesized by Chemical Reduction Method and Its Characterization.

The complex process of nanoparticle formation in an aqueous solution is governed by kinetics and thermodynamic factors. This paper describes a room-temperature growth kinetic study and evaluation of thermodynamic activation parameters of monodispersed silver nanoparticles (AgNPs) synthesized in alkaline medium by chemical reduction method using AgNO3 as a source of Ag+ ions and tannic acid (TA) as a reductant (reducing agent) as well as a capping or stabilizing agent in the absence of any other external stabilizer. A simple and conveniently handled reaction process was monitored spectrophotometrically to study the growth kinetics in an aqueous solution as a function of the concentration of silver ion, hydroxide ion, and TA, respectively. The neutral nucleophilic group donates the electron density via a lone pair of electrons to Ag+ ions for the reduction process, i.e., for the nucleation of AgNPs colloid. Also, a few silver ions form a silver oxide, which also facilitates the nucleation center to enhance the growth of AgNPs colloid. The decrease and increase in rate constant on varying the TA concentration showed its adsorption onto the surface of metallic AgNPs and stabilized by polygalloyl units of TA and were the main elements to control the growth kinetics. Consequently, stabilized TA-mediated AgNPs are formed using the electron donated by quinone form of TA followed by a pseudo-first-order reaction. Apart from this, nanoparticles formed were characterized using UV–visible spectrophotometry, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and powder X-ray diffraction techniques to confirm its formation during the present kinetic study.

Effects of the Surface Charge Density of Clay Minerals on Surface-Fixation Induced Emission of Acridinium Derivatives.

Surface-fixation induced emission is a fluorescence enhancement phenomenon, which is expressed when dye molecules satisfy a specific adsorption condition on the anionic clay surface. The photophysical behaviors of two types of cationic acridinium derivatives [10-methylacridinium perchlorate (Acr+) and 10-methyl-9-phenylacridinium perchlorate (PhAcr+)] on the synthetic saponites with different anionic charge densities were investigated. Under the suitable conditions, the fluorescence quantum yield (Φf) of PhAcr+ was enhanced 22.3 times by the complex formation with saponite compared to that in water without saponite. As the inter-negative charge distance of saponite increased from 1.04 to 1.54 nm, the Φf of PhAcr+ increased 1.25 times. In addition, the increase in the negative charge distance caused the increase in the integral value of the extinction coefficient and the radiative deactivation rate constant (kf) and the decrease in the nonradiative deactivation rate constant. It should be noted that the 2.3 times increase in kf is the highest among the reported values for the effect of clay. From these results, it was concluded that the photophysical properties of dyes can be modulated by changing the charge density of clay minerals.

Reduction Kinetics of Fine Hematite Ore Particles in Suspension

Suspension reduction kinetics of hematite ore particles at 1710 K to 1785 K was described by the Johnson-Mehl-Avrami-Kolmogorov model with Avrami exponent of 1.405. The apparent activation energy is 105.5 kJ mol−1 with the rate determining step of nucleation and growth. The reduction degree of the hematite at the endpoint is a linear function of temperature and the logarithmic oxygen potential of the reacting gas. A peak function of reaction rate constant with particle size has been verified in this work, and the maximum value of the reaction rate is located at around 85 µm particle size. The influence of heat transfer on the reaction process has been evaluated. The results suggest that the heating-up process for large particles, 244 µm particles, for instance, cannot be ignored. It can retard the reaction rate compared to small particles. Normally, the reaction rate constant decreases linearly with the increase of ln[p(O2)] of the reacting gas mixture. However, 95 vol pct CO2 in the reacting gas can accelerate the reaction rate of thermal decomposition of hematite due to the emissivity of CO2 gas. It results in a higher reaction rate of 110 µm particles in 95 vol pct CO2-containing gas than that in other less CO2-containing gases.

An experimental and statistical modeling study of the reactivity of Co+(CH3Br)n (n = 0,1) with methyl bromide

The temperature- and pressure-dependent kinetics of Co+(CH3Br)n (n = 0,1) + CH3Br are measured from 300 to 600 K and from 0.2 to 0.5 Torr. Results are interpreted using density functional calculations and modeled with statistical theory. In the n = 0 case, the associative product Co+(CH3Br) dominates with a rate constant between 5 and 30% of the collisional value, while a minor channel yields CoBr+ + CH3 with a rate constant increasing with temperature. 0K bond dissociation energies (BDE) are determined for Co+-Br (2.8 ± 0.1 eV) and Co+-CH3Br (2.4 ± 0.25 eV). Ligation of Co+ (i.e. n = 1) significantly increases the bimolecular reaction rate constant. CoBr+(CH3Br) + CH3 is formed and the reaction has a positive temperature dependence. Interestingly, this rate constant decreases with increasing pressure due to competition of the association channel. Ligation increases the (CH3Br)Co+-Br BDE (3.0 ± 0.1 eV) relative to Co+-Br, but decreases the (CH3Br)Co+-CH3Br BDE (1.95 ± 0.25) relative to Co+-CH3Br. Both bimolecular reactions proceed by a metal-insertion mechanism with a significantly submerged transition state that does not affect the kinetics. Instead, the endothermicity of the reaction is rate-limiting. Discussion about how energy, impact parameter, and angular momentum affect specific rate constants for dissociation to reactants, reaction to products, and association are presented.

Masa simpan tempe dalam pengemas edible film tapioka termodifikasi [Shelf life of tempe wrapped by modified-tapioca edible film

Edible film made up of modified tapioca was used to wrap tempeh and its shelf life estimation was determined. The edible films must be capable of evenly aerating and maintaining moisture without causing condensation in order mycelium to be able to grow and produce high-quality tempeh. The experiment was carried out in completely randomized design with two main factors of storage temperature and time. An accelerated shelf life test at 17oC, 27oC, and 37oC with an Arrhenius model was used to calculate the shelf life, and water content was used as quality parameter indicator. The result showed that modified-tapioca based edible film made from fermentation of tapioca by Saccharomyces cerevisiae was characterized as having elongation of 11.40 %, tensile strength of 408.37 MPa, thickness of 0.88 mm and WVTR of 12.60 g/m2/h. Rate constant of water content decrease in edible film wrapped tempeh based on Arrhenius model was 0.3832 % day-1 and Ea was 10.296 kkal/gmol, while that of in PP-plastic wrapped tempeh was 0.3831% day-1 and Ea was 9.998 kkal/gmol. The shelf life of edible film wrapped tempeh was 9.39 days at 27oC, 5.18 days at 27oC, and 2.96 days at 37oC, while shelf life of PP-plastic wrapped tempeh was 8.64 days at 17oC, 4.85 days at 27 oC, and 2.82 days at 37oC. Therefore, it can be concluded that modified tapioca based edible film increased the shelf life of tempeh.

Fixed-bed column adsorption performance for ammonia removal using adsorbent from zeolite

A study on the performance of fixed-bed column adsorption using natural zeolite Sarulla for ammonia removal has been carried out. The effect of important parameters namely bed height on the breakthrough curve and adsorption performance has been investigated in laboratory scale experiments. The study results show that the adsorption efficiency increases with increasing bed height. These results reveal that the throughput volume of aqueous solution increases with increasing bed height, due to the availability of more adsorption sites and a longer time to reach saturation. Adsorption kinetics were analyzed using the Thomas and Yoon and Nelson kinetics models. The kinetics data can be described well using these two models. The maximum adsorption capacity (qo) was determined using the Thomas kinetics model, the ammonia value was 279.3589 mg / g. However, the study results show that the value of qo decreases with increasing ammonia bed height. For Yoon and Nelson’s models, the rate constant decreases with increasing bed height. The length of time required for 50% of the breakthrough increases with increasing bed height. The kinetics data can be correlated well using both models.

Simultaneous Removal of Al, Cu and Zn Ions from Aqueous Solutions Using Ion and Precipitate Flotation Methods

This paper presents the results of investigations concerning the simultaneous removal of Al(III), Cu(II), and Zn(II) from dilute aqueous solutions using ion and precipitate flotation methods. The effects of initial solution pH, surface active substance concentration, and the gas velocity on the flotations’ efficiency and course are studied. Experimental results are discussed in terms of physicochemical aspects related to aqueous solutions of metal salts. The results indicate that satisfying simultaneous flotations of aluminum, copper and zinc species are observed if the pH value ranges between 7.0 and 9.0. It was found that an increase in collector concentration results in a decrease in the flotation rate constants. An increase in the gas velocity results in an increase in the ion and precipitate flotation rates.

A Model for the Deposition of Scale Crystals on the Surface of Clay Particles

Deposition and aggregation of scale on microbial surface leads to poor stabilization of the treatment of oilfield high-scale oily wastewater. To study the deposition characteristics of scale on the surface of microbial particles, we perform the deposition and aggregation of calcium sulfate on the surface of clay particles as simulators of microbes and establish the deposition-aggregation process model. According to the theory of crystal growth, the diffuse electric double layer theory for clay, and the charged colloid theory, the scale deposition model can be divided into induction period, formative period of scale crystal nucleation, and crystal growth period. When calcium sulfate crystals deposit and aggregate on the surface of clay particles, the zeta potential and the average particle size on the surface of the clay particles increase continuously over time and tend to increase and decrease in cycles. The scale crystals are wrapped divergently around the surface of the clay particles in a needle-like form, such that the clay suspension is in a state of high aggregation. Logarithmic value of the conductivity in the formation of scale crystal has a good linear relationship with time, which conforms to the first-order rate equation. Conductivity curves can better reflect the deposition course of scale crystal on the surface of clay particles, which is divided into the induction period (6 min), transition period (1.5 min), formative period of scale crystal nucleation (10.75 min), rapid growth period of scale crystal (8.5 min), slow growth period of scale crystal (14.75 min), and stationary phase (4.75 min), and with the formation of the scale crystal, the deposition rate constant decreases gradually from 0.00945 min−1 to 0.0001 min−1. The results uncovered that Deposition and aggregation rules of scale on the surface of clay particles and the basis for further studying on microbial surface.

Effect of Co on the microstructure and oxidation behavior of CoxCrCuFeMnNi high entropy alloy powders

The microstructure, phase, alloying behavior, and oxidation behavior of the CoxCrCuFeMnNi (x = 0, 0.5, 1.0, 1.5, 2.0, named as Co0, Co0.5, Co1.0, Co1.5, and Co0.5, respectively) high entropy alloy powders (HEAPs) prepared by mechanical alloying were studied. The results indicated that the HEAPs began to be alloyed after ball milling for 5 h, and the particle size is about 40∼60 μm. After 50 h of milling, the Co0 and Co0.5 HEAPs are composed of metastable FCC and minor BCC solid solution phases, while the other HEAPs consist of single metastable FCC solid solution phase. After vacuum annealing or atmospheric oxidation at 700 °C, the metastable FCC and BCC phases decompose into FCC1 and FCC2 and ρ phases, respectively. The oxidation mass gain of CoxCrCuFeMnNi HEAPs shows a parabolic upward trend. With the increase of Co content, the oxidation rate constant decreases, indicating that the oxidation resistance of the HEAPs decreases with the increase of Co content.