Oxidation Time Research Articles

Wet oxidative removal of low-valent sulfur by addition of H2O2 to Bayer fluid

ABSTRACT The presence of sulfur in sodium aluminate solution can disrupt the Bayer process in alumina production. H2O2 is used as an oxidant to convert low-valent sulfur (S2−) into high-valent sulfur (i.e. S2O3 2−, SO3 2−, and SO4 2−). This paper combines thermodynamic calculations and experimentation to propose the mechanism of the oxidation reaction between H2O2 and different valences of sulfur (i.e. S2O3 2−, SO3 2−, and SO4 2−) in sodium aluminate solution with the oxidation effect of S2− being the most obvious. By studying the oxidation effect of H2O2 dosage, oxidation time, and oxidation temperature on different valences of sulfur in sodium aluminate solution, it was found that the removal rate of S2− reached 91.85% with 9% H2O2 dosage, 260 °C oxidation temperature, and 60 min oxidation time. The experimental results were consistent with the thermodynamic calculations. Finally, the reaction between H2O2 and different valences of sulfur in sodium aluminate solution was described in detail, providing theoretical support for the desulfurisation of high-sulfur bauxite in the production of alumina through the Bayer process.

Raising the Oxidation Resistance of Low-Alloyed Mg-Ca Alloys Through a Preheating Treatment in an Argon Atmosphere

With the rise and development of aerospace, communications, electronics, medical, transportation and other fields, magnesium (Mg) and its alloys have attracted much attention for their high specific strength and stiffness, good electromagnetic shielding properties, excellent damping properties and other advantages. However, magnesium has a high affinity for oxygen, producing magnesium oxide (MgO), and MgO’s Pilling–Bedworth ratio (PBR) of 0.81 is not protective. The occurrence of catastrophic oxidation is unavoidable with the increase of oxidation time and temperature. A promising approach is to perform an appropriate pretreatment in conjunction with alloying to obtain a dense and compact composite protective film. In this work, the effect of a preheating treatment on the oxidation resistance (OR) of Mg-xCa (x = 1, 3 and 5 wt. %) was investigated. The preheating was carried out in an Ar atmosphere at 400 °C for 8 h. Upon it, a dense and compact MgO/CaO composite protective film was formed on the surface, which is CaO-rich especially in the vicinity to the surface. The alloys’ oxidation resistance was strongly increased due to the composite protective film formed during the preheating treatment, in particular for Mg-3Ca. Relative to the Mg-hcp phase, the OR of the Mg2Ca phase was significantly raised.

Kinetic Studies on MB Adsorption by Graphene like Material from Coconut Shell Charcoal

Coconut shell (CS) activated carbon is widely used for water purification, but its adsorption capacity is inferior compare to graphene oxide (GO). GO has oxygen functional groups so it can effectively bind pollutants like methylene blue (MB). In this study we synthesized graphene-like material from CS charcoal using the modified Hummers method by varying its oxidation times. The XRD decomposition results for H-CS3.2 show a structural composition similar to GO material. The diffraction peak at 10.7° (3.04%) falls within GO's characteristic range of 8°-11°, supported by a Raman ID/IG ratio of 0.95. In contrast, H-CS3.1 material does not exhibit GO's structural composition, with a diffraction peak at 13.9° (1.09%). An increasing of oxidation time, enhanced adsorption capacity in the equilibrium state of H-CS3.2 (22.368 mg/g) surpassing H-CS3.1 (17.079 mg/g). The heightened adsorption was linked to an increased O/C ratio or higher % of atomic oxygen (0.04 for H-CS3.1 and 0.17 for H-CS3.2). The pseudo second-order Ho (PSO) adsorption kinetic model demonstrated the adsorption mechanism, with active sites (oxygen functional groups) such as carbonyl (C = O) and epoxy (C – O) at basal plane carbon. Steric hindrance caused by hydroxyl functional groups (C – OH) led to a reduction in π-π interactions and decreased adsorption ability of the H-CS3.1 material. Desorption of H-CS3.1 material was influenced by MB detachment through interface diffusion.

Asymmetric coordinative modulation boosting the activity and thermal stability of Pt1/CeO2 for CO oxidation under harsh condition

Supported metal catalysts play a central role in chemical industry, but it remains a formidable challenge to realize high activity while maintaining atomically dispersed status to maximize atom efficiency under harsh conditions. Herein, a novel strategy of constructing asymmetric coordination Pt active sites via coating N-doped carbon onto ceria supported Pt single atoms (Pt1/CeO2@CN) is proposed, through which superior low-temperature CO oxidation activity and satisfactory thermal stability are achieved simultaneously. Experimental and density functional theory results confirm that the unique asymmetric N2-Pt1-O2 coordinative configuration on Pt1/CeO2@CN tailors the electronic properties of Pt 5d states, increasing the turnover frequency by 15 times for CO oxidation at 120 °C compared with that on Pt1/CeO2 and sustaining the atomically dispersed status of Pt at as high as 400 °C under H2-containing atmosphere. This strategy suggests a promising avenue to fabricating highly active and stable supported metal catalysts for practical applications under harsh conditions.

Early Stages of High‐Temperature Oxidation Behavior and Its Phase Evolution of 9% Ni Steel

Herein, the effects of oxygen partial pressure (5–20%) and oxidation time (0.5–6 h) on the growth behavior and phase structure of 9% Ni steel oxide layer are studied by means of high‐temperature oxidation experiment, scanning electron microscopy, and X‐ray diffraction. The results show that the inner and outer oxide layers of 9% Ni steel grow opposite to each other along the initial surface direction of the vertical matrix during the high‐temperature oxidation process. From the perspective of the phase, the phase transition of Fe2O3→Fe3O4→FeO mainly undergoes from the outside and the inside, the results of thermodynamic calculations show that <<<0, and the main factor affecting the phase transition is the diffusion concentration of free O and Fe atoms. During the high‐temperature oxidation process of 9% Ni steel, the diffusion of O and Fe atoms along grain boundaries promotes preferential oxidation at these boundaries. The columnar structure formed in the outer oxide layer of 9% Ni steel may be related to the uneven diffusion rate of Fe atoms at different positions at the interface between the inner and outer oxide layers.

Analysis of Oxide Layer Formation During Oxidation of AISI 4140 Steel at 1000 °C over Exposure Time

The high-temperature shaping of steels is accompanied by the formation of surface scales composed of oxide layers. However, the oxidation kinetics and morphology of these scales remain poorly understood. This study analyses the formation of oxide layers on AISI 4140 steel at varying oxidation times (20, 40 and 60 min) at 1000 °C. The analysis revealed the presence of hematite, magnetite, and transformed wustite in the oxide layers, along with clusters of alloying element oxides, predominantly chromium and iron oxide (FeCr2O4). There was a direct correlation between the duration of the oxidation process and the thickness of the scale and the number of defects observed in the material. The coating layer of alloying element oxides demonstrated insufficient adhesion to the steel substrate. Similarly, the oxides of alloying elements within this layer exhibited low cohesion among themselves. The alloying elements are present in all oxide layers, but in greater quantity in the layer in contact with the steel substrate, where a reduction in their concentrations was observed over time. This indicates that the alloying elements tend to disperse as the thickness of the alloying element oxide layer increases over time.

Impact of deacidification processes on the quality and oxidative stability of walnut oil

In order to select an appropriate deacidification process and improve the quality of walnut oil, low-temperature cold-pressed crude walnut oil was used as raw material. Deacidified walnut oil was prepared using three deacidification processes: chemical deacidification (CD), adsorption deacidification (AD), and molecular distillation deacidification (MDD). The physicochemical properties, nutritional components, and in vitro antioxidant activities of the resulting deacidified walnut oils were comparatively analyzed. The results indicate that the fatty acid content in walnut oil exhibits fluctuating changes during the three different deacidification processes. The MDD shows a higher deacidification rate, reaching 94.06%, which is superior to the other two methods. Additionally, the AD retains more total phenols and tocopherols, with retention rates of 95.79% and 74.62%, respectively; whereas MDD is more effective at retaining phytosterols, achieving a retention rate of 98.09%. All these methods displayed positive impacts on the in vitro antioxidant capacity and oil stability of walnut oil, with ferric-reducing antioxidant power (FRAP) content and oxidative stability time were significantly reduced.whencompared to the untreated crude oil Among them, AD had the greatest impact on oxidative stability index (OSI) , with its decreasing from 2.06 h to 0.82 h. Overall, compared to CD or MDD, the AD has best application prospects in preserving nutritional components.

High‐Temperature Oxidation Response of 444 Ferritic Stainless Steel in a Synthetic Automotive Exhaust Gas

The high‐temperature oxidation behavior of 444 ferritic stainless steel has been studied in cyclic oxidation experiments using synthetic automotive exhaust gas atmospheres at 950 and 1050 °C. The weight gain per unit area of the 444 ferritic stainless steel following oxidation at 950 °C for 100 h iss 85.7% lower than recorded at 1050 °C. The oxide scale at both temperatures consisted of Fe–Cr and Mn–Cr spinels in the outer layer and Cr2O3 in the inner layer. Nodule formation and spallation of the oxide scale are identified as the main causes of breakaway oxidation. The depth of the internal oxides gradually increases with the oxidation time. The nucleation and growth of internal SiO2 result in the formation of metal protrusions, which are eventually consumed in the formation of a SiO2 layer. The SiO2 layer is formed at the interface between the oxide scale and the substrate at 1050 °C. The nucleation and growth of internal SiO2, in combination with lateral growth of SiO2 at the Cr2O3 layer/substrate interface contributed to the formation of the SiO2 layer.

Application of Fenton's Reaction for Removal of Organic Matter from Groundwater.

In this study, the effectiveness of the Fenton process in removing natural organic matter (NOM) from groundwater was investigated. The subject of this study is groundwater characterised by increased content of NOM and iron (II) compounds. In laboratory-scale studies, the influence of the ratio of concentrations of Fe(II) ions, which are naturally occurring in groundwater, to hydrogen peroxide (H2O2) as well as oxidation time and pH on the removal efficiency of organic matter was determined. Indicators such as total organic carbon (TOC), dissolved organic carbon (DOC), UV absorbance at 254 nm (UV254), UV absorbance at 272 nm (UV272), and specific UV absorbance (SUVA254) were used to quantitatively and qualitatively assess the organic substances present in the raw water and after oxidation with Fenton's reagent. Analysis of the results obtained showed that the highest removal efficiency of organic substances in the deep oxidation process using the Fenton reaction was obtained for a concentration ratio of Fe(II) to H2O2 = 1:5. Acidification of the water samples to a pH of about 4 and extending the oxidation time to 30 min significantly increased the removal efficiency of organic substances including mainly dissolved organic substances containing aromatic rings. The organic substances containing aromatic rings, determined at a wavelength of 254 nm, were degraded to other organic intermediates.

Selective Oxidation of p-Cymene over Mesoporous LaCoO3 by Introducing Oxygen Vacancies.

The liquid-phase catalytic oxidation of p-cymene to 4-methylacetophenone is an industrially significant reaction. However, the targeted oxidation of a specific C-H bond of p-cymene is extremely difficult due to there being many branched chains in p-cymene. In here, we designed a simple method to synthesize mesoporous LaCoO3 catalysts with rich oxygen vacancy (Oov) sites. The as-prepared mesoporous LaCoO3 after 550 °C calcination (mLaCoO3) exhibits remarkable catalytic activity for solvent-free oxidation of the p-cymene reaction, with a selectivity of over 80.1% selectivity for 4-methylacetophenone and a conversion of 50.2% for p-cymene (120 °C, 3 MPa). Besides, recycling studies have demonstrated that the mLaCoO3 catalysts can be reused ten times in the aerobic oxidation of the p-cymene reaction without significant catalytic activity reduce. The experimental and characterization results indicated that the mesoporous structure of the catalyst is conducive to the generation of surface Oov, which can properly facilitate ion spread during the catalytic process and afford enough O2 for intermediate species, thus is beneficial for the generation of 4-methylacetophenone. This work demonstrates that the selectivity oxide p-cymene with an O2 employing mLaCoO3 catalyst is highly promising for chemical industrial applications.

Synthesis and Characterization of TiO2 Nanotubes for High-Performance Gas Sensor Applications

In this study, we investigated the fabrication, properties, and sensing applications of TiO2 nanotubes. A pure titanium metal sheet was used to demonstrate how titanium dioxide nanotubes can be used for gas-sensing applications through the electrochemical anodization method. Subsequently, X-ray diffraction indicated the crystallization of the titanium dioxide layer. Scanning electron microscopy and transmission electron microscopy then revealed the average diameter of the TiO2 nanotubes to be approximately 100 nm, with tube lengths ranging between 3 and 9 µm and the thickness of the nanotube walls being about 25 nm. This type of TiO2 nanotube was found to be suitable for NO2 gas sensor applications. With an oxidation time of 15 min, its detection of NO2 gas showed a good result at 250 °C, especially when exposed to a NO2 gas flow of 100 ppm, where a maximum NO2 gas response of 96% was obtained. The NO2 sensors based on the TiO2 nanotube arrays all exhibited a high level of stability, good reproducibility, and high sensitivity.

Mechanical and high-temperature steam oxidation properties of Cr coatings deposited via high-power impulse magnetron sputtering

Applying protective coatings to Zr alloy cladding surfaces is one of the better methods to design fuel tolerant materials. In this study, the surface of a Zr-4 alloy was coated with Cr using high-power impulse magnetron sputtering. Furthermore, the mechanisms by which bias voltages affect the mechanical characteristics, resistance to high-temperature steam oxidation, and coating structure were elucidated. The coating exhibits a strong (200) weave structure with coarse grains at a bias voltage of -100 V. With increasing bias, the energy of deposited particles increases, grains continue to grow, (200) preferential growth orientation disappears, and the coating exhibits a (110) crystal orientation. The growth structure of the coating first shows a tendency to be dense and then loose. For the Cr coating with a (200) crystal orientation, a dense oxide layer is preferentially formed after oxidation, which can effectively block the internal diffusion of O. With increasing oxidation time, coarse Cr grains can effectively block the external diffusion of Zr. Furthermore, the Cr coating exhibiting a (110) crystal orientation was severely oxidized after oxidation, resulting in the formation of cracks at the film base; this accelerated the outward diffusion of Zr.

Accelerated oxygenation for the production of fortified (mystelle-type) sweet wines: effects on the chemical and flavor profile.

Fortified wine is an important category in the wine world with very famous wines such as Porto or Jerez-wine type. The quality of fortified wines increased significantly with barrel aging not only because of a long oxidation process, but also because, in Porto wines such as Ruby or Vintage styles, the long period in bottle permits their fining. Reducing the time of oxidation can favor the development of this technique even for less known sweet wines, making them good quality and less expensive. In the present study, we have used Gamay red variety subjected to postharvest controlled dehydration at 20-22 °C and 70-75% relative humidity with an airflow of 1 m s-1. Then the grapes were pressed, and alcohol was added to the must up to an alcohol content of 15.85% (mystelle-type wine). The mass was split into six glass jars, three were oxygenated (OX) and three not (Control), and the oxygenation lasted 62 days. Wine that was oxygenated had a slightly higher volatile acidity, lower alcohol content (13.00%), and lower anthocyanins and polyphenols content. In term of volatile organic compounds (VOCs), the Control wine had a higher content of alcohols, whereas the OX sample had a higher content of lactones, furans and esters. Sensory evaluation confirmed the VOCs analysis; the two wines had a statistically different profile depending on the oxidation treatment. In general, OX wine was more appreciated in terms of visual attractiveness, taste and olfactory pleasantness. In conclusion, the technique described in the present study could be a valid alternative to traditional aging of fortified sweet wines, reducing time and costs. © 2024 Society of Chemical Industry.

Mechanism of methyl elaidate on the thermal oxidation behavior

The effects of cis–trans isomerization on the oxidation products of oleic acid (composites and structure characterization) were investigated. The reduction of thermal oxidation reaction of methyl elaidate (ME) was 6.72 % lower than that of methyl oleate (MO), and the oxidation products (core aldehydes) first increased and then decreased with the prolongation of thermal oxidation time. ME exhibited better oxidation stability than MO in free radicals, hydroperoxides, double bonds, aldehydes, and glycerides. The oxidation products were mainly 11-oxo-9-undecenoate (initial stage) and methyl 9-oxononanoate (later stage), following the free radical chain reaction mechanism. The H8 in double bond was more easily dehydrogenated in the chain initiation stage than H11, followed by the formation of core aldehyde through three intermediates and two transition states each pathway. ME required a higher energy barrier (1.3–13.6 kJ/mol) than MO reaction, making it more difficult for ME to undergo thermal oxidation reaction. The transition state 4 and 5 were rate determining steps of chain initiation reaction and proliferation reaction, respectively. This study was of great significance to further control the formation of these trans fats and their oxidation products.

Properties of micro-arc oxidation coating of selective laser melting AlSi10Mg alloy

In this paper, micro-arc oxidation (MAO) coating is prepared on SLM AlSi10Mg alloy to improve its corrosion performance. The microstructure, composition, and electrochemical properties of the substrate and the coating at different oxidation times are analyzed. The results show that the MAO coating is mainly composed of Al, γ-Al2O3, α-Al2O3, and amorphous phases. At an oxidation time of 10 min, the coating achieves its maximum density. Additionally, the corrosion current density of the coating decreases by 5 orders of magnitude, the resistance value increases by 3 orders of magnitude, and the corrosion resistance is the best. Furthermore, the coating on the XY-plane exhibits better corrosion resistance compared to the coating on the XZ-plane.

Microencapsulation of a Flaxseed and Avocado Oil Blend: Influence of Octenyl Succinic Anhydride (OSA)-Modified Starch and Rice and Pea Proteins on Powder Characterization and Oxidative Stability

This work investigated the influence of the OSA-modified starch, pea protein, and rice protein combination in the microencapsulation process of a blend of avocado and flaxseed oil (25–75%, w/w) by freeze-drying, focusing on emulsions and powders characteristics and oxidative stability. Four different ratios between the mixture of vegetable proteins (1:1) and the OSA-modified starch were analyzed, using a fixed ratio between the oils blend and the combined encapsulant agents of 1:3. Based on the creaming index, the separation of hydrophilic and hydrophobic phases was not observed. The results demonstrated a tendency to increase the droplet mean diameter with increased protein content (4.71–19.36 μm). An increase in the encapsulation efficiency was verified with the increase in the OSA-modified starch content (51.33–60.32%). Powders presented low moisture content and hygroscopicity, and an oxidative induction time value varying from 0.86 to 1.18 h. The increase in the vegetable protein content increased the powders’ oxidative stability, which could be associated with the antioxidant capacity of rice and pea proteins.

Valence-engineered catalysis-selectivity regulation of molybdenum oxide nanozyme for acute kidney injury therapy and post-cure assessment.

The optimization of the enzyme-like catalytic selectivity of nanozymes for specific reactive oxygen species (ROS)-related applications is significant, and meanwhile the real-time monitoring of ROS is really crucial for tracking the therapeutic process. Herein, we present a mild oxidation valence-engineering strategy to modulate the valence states of Mo in Pluronic F127-coated MoO3-x nanozymes (denoted as MF-x, x: oxidation time) in a controlled manner aiming to improve their specificity of H2O2-associated catalytic reactions for specific therapy and monitoring of ROS-related diseases. Experimentally, MF-0 (Mo average valence 4.64) and MF-10 (Mo average valence 5.68) exhibit exclusively optimal catalase (CAT)- or peroxidase (POD)-like activity, respectively. Density functional theory (DFT) calculations verify the most favorable reaction path for both MF-0- and MF-10-catalyzed reaction processes based on free energy diagram and electronic structure analysis, disclosing the mechanism of the H2O2 activation pathway on the Mo-based nanozymes. Furthermore, MF-0 poses a strong potential in acute kidney injury (AKI) treatment, achieving excellent therapeutic outcomes in vitro and in vivo. Notably, the ROS-responsive photoacoustic imaging (PAI) signal of MF-0 during treatment guarantees real-time monitoring of the therapeutic effect and post-cure assessment in vivo, providing a highly desirable non-invasive diagnostic approach for ROS-related diseases.

Effect of adding Sr(OH)2 on the formation process of 2024 aluminum alloy micro-arc oxidation coatings

Micro-arc oxidation coatings with oxidation times of 15 S, 30 S, 60 S, 120 S, 240 S and 1800 S were prepared on 2024 aluminum alloy using silicate-phosphate electrolytes containing 0 g/L and 0.5 g/L Sr(OH)2, respectively. The effects of adding Sr(OH)2 on the oxidation voltage, surface morphology and phase composition of the 2024 aluminum alloy MAO coatings formation process were investigated using SEM, XRD and XPS. The results show that adding Sr(OH)2 increases and then decreases the oxidation voltage compared with that of the unadded Sr(OH)2, which has little effect on the morphology of the oxide coatings, the Sr2+ and PO43- in the solution are jointly involved in the formation of the MAO coatings. The main phase composition of the coating is γ-Al2O3, and the Sr element is uniformly distributed as SrCO3 in the coating.

Effect of oxidation times on Gas sensitivity and characterization for (In2O3) thin films produced by thermal evaporated

Abstract thin films were prepared by the thermal evaporated method of Indium metal on a glass substrate, then conventional oxides in the presence of O2 at 400° C. The indium thin films have a thickness of 400nm and different oxidation times (60, 90, and 120) min. The findings from X-ray diffraction (XRD) pertain to the polycrystalline phase. The films (In2O3) had a polycrystalline cubic structure The films have prominent peaks that match (112), (222), and (004) planes at 21.448°, 30.515, 35.38 in the order mentioned. Change with increasing oxidation time each of The amounts The text refers to the number of crystallites, the dimensions of the crystallites, the density of dislocations inside the crystallites, and the level of microstrain present in the crystallites. The UV-vis spectra were used to investigate the optical characteristics such as(The transmittance and absorbance spectra, the absorption coefficient (α) and from there, the energy gap was computed. with different times are 3.1,3.3 and 3.05 eV, respectively. The film’s gas sensing performance approaches CO2 Gas measurements were made at many oxidation times. The performance of the gas detecting system was found to have significantly improved.

Study on the relationship between high temperature oxidation and temperature rise rate of engine oil

Purpose The purpose of this paper is to study the relationship between high temperature oxidation and temperature rise rate of engine oil attempted to explore a new indicator to evaluate oil degradation. Design/methodology/approach Accelerated oxidation test combined with molecular simulation and road test is carried out in this paper. The temperature rise characteristics of mineral oil and synthetic oil under different oxidation temperatures (140°C, 155°C and 170°C) and time (50 h, 100 h, 150 h and 200 h) were determined by accelerated oxidation. The mechanism of temperature change characteristics of used oils was analyzed with molecular simulation. Two experimental vehicles carried six road tests with synthetic and mineral oil. Findings The results of this study show that the temperature rise rate of oxidized mineral and synthetic oil is higher than the new oil. The temperature rise rate is proportional to the oxidation time and oxidation temperature. The synthetic engine oil temperature rise rate is lower than that of the mineral engine oil. The same result was obtained in road tests. Molecular simulation verifies that small molecules were generated after oil oxidation which results in intermolecular friction and increased heat generation. Originality/value This paper indicates that temperature rise rate has potential to be taken as an indicator to evaluate oil oxidation which provides a new way for engine oil analysis. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-05-2024-0177/