Oxidation Time Research Articles

Structures and contributions of active substances in the latent oxidation of coal based on the oxygen isotope tracer method

The oxygen isotope tracer method was used to determine the structures and contributions of the active substances that trigger coal spontaneous combustion (CSC). After artificially changing the oxygen isotope ratio, the coal samples were subjected to isothermal oxidation under different conditions (different temperatures, different oxidation times and different coal types) in an 18O2 atmosphere. First, the oxidation gases were obtained with cyclic oxidation experiments. The basic parameters were provided for tests of the gas isotopes. The oxidation products labeled with 18O were then analyzed with an isotope ratio mass spectrometer. The original active substances in the coal were determined. Evolution of the functional groups in the coal was determined by XPS. The transformation paths of the active substance were analyzed. The results showed that during the oxidation process, more than 70 % of the CO was generated from the original hydroxyl and aldehyde groups in the coal, and more than 99 % of the CO2 was generated from the original carboxyl groups in the coal. Inhibition of oxidative decomposition of hydroxyl, aldehyde and carboxyl groups can effectively control CSC and solve the problem of CO overflow caused by low-rank coal oxidation.

Application of electro oxidation process for treating wastewater from petrochemical with mixed metal oxide electrode

Petrochemicals require a large volume of water for their operation, which results in the production of a large volume of wastewater. Treatment of petrochemical wastewater is an important process before discharging it into the environment. This research examines the treatment of real petrochemical wastewater using the electrochemical oxidation process. Direct anodic oxidation is an effective advanced electrochemical oxidation process (AEOP), with different electrodes using a parallel plate electrochemical reactor. Four types of real wastewater were received from different petrochemical units were treated by AEOP. Real wastewater samples with chemical oxygen demand (COD) concentrations ranging from 20,450 to 52,300 mg/l. The main goal of this research is to make electrodes of Mixed Metal Oxide (MMO), which can reduce the treatment time and electricity consumption for oxidation, greater stability of the surface of the electrodes. Investigation of the rate constant kinetics shows that high COD removal efficiency can be achieved following the pseudo-second order reaction rate (R2 > 98%). When the wastewater pH is less than 5, COD removal efficiency is higher and the treatment process will be successful, which succeeded in removing 79% COD, but in alkaline wastewater, COD reduction efficiency was not satisfactory. The electricity consumption for 79% removal during 6 min was 117 kWh/m3. As a result, due to the very short time of the process (6 min), it can be used as one of the pre-treatment steps of petrochemical wastewater with acidic pH.

HfSi2-HfB2-SiC coating prepared at low temperature to protect SiC-coated C/C composites against oxidation at 1473–1973 K

To improve the oxidation resistance of carbon/carbon (C/C) composites in 1473–1973 K, a HfSi2-HfB2-SiC coating was prepared on the surface of SiC-coated C/C composites by a combined method of slurry dipping and oxidation sintering at low temperature (below 1473 K). The Hf-Si-O multiphase layer generated by the oxidation of the coating acted as oxygen barriers at 1473–1973 K in air. The in-situ formed HfSiO4 particles enhanced the thermal stability of the SiO2 glass, terminated propagation of the crack, and relieved CTE mismatch between the inner and outer coating. Besides, B2O3 filled pores in the early stage of oxidation and then SiO2 took the place of the B2O3 as a new filler with the increase time of oxidation. As a result, the coating can protect C/C composites for 516 h at 1473 K, 744 h at 1773 K, and 64 h at 1973 K with a mass gain of 0.63 wt%, 1.41 wt% and −1.91 wt%, respectively.

An analytical model to estimate the oxidation time required to reach spontaneous ignition with heat loss being considered

During air injection into an oil reservoir, an oxidation reaction generates heat to raise the reservoir temperature. When the reservoir temperature reaches an ignition temperature, spontaneous ignition occurs. There is a time delay from the injection to ignition. There are mixed results regarding the feasibility of spontaneous ignition in real-field projects and laboratory experiments. No analytical model is available in the literature to estimate the oxidation time required to reach spontaneous ignition with heat loss. This paper proposes an analytical model considering heat loss. The feasibility of spontaneous ignition from theoretical points, and experimental and field project observations are discussed. Using analytical models with and without heat loss, the factors that affect spontaneous ignition are investigated. Based on the discussions and investigations, we find that it is more difficult for spontaneous ignition to occur in laboratory experiments than in oil reservoirs; spontaneous ignition is strongly affected by the initial reservoir temperature, oil activity, and heat loss; spontaneous ignition is only possible when the initial reservoir temperature is high, the oil oxidation rate is high, and the heat loss is low.

High-temperature oxidation behavior of a 9Cr oxide dispersion strengthened alloy under limited oxygen condition

Hot compression bonding is a promising process to fabricate large-scale oxide dispersion strengthened alloys. Inevitable interface oxidation could affect the effectiveness of the joint. The high-temperature oxidation behavior of a 9Cr ODS alloy under limited oxygen condition was investigated. The oxidized surface consisted of inner Fe2O3 scale and outer Cr2O3 particles at 800 °C. Reoxidation at 1000 °C, Cr2O3 particles were decomposed and converted into Cr(Ti)O2. With increasing oxidation time, Fe2O3 and Cr(Ti)O2 were decomposed and Y2O3 pegs formed. Furthermore, TiO2, Y2O3 and Y-Ti-O nanoparticles formed along grain boundaries. In conclusion, the oxide evolution could be summarized as Fe2O3→Cr2O3→Cr(Ti)O2→TiO2→Y2O3→Y-Ti-O nanoparticles. The evolution from initial coarse Cr-rich and Fe-rich oxides to fine Y-Ti-O nanoparticles is expected to be critical for hot compression bonding processes.

Magnetic properties of an Fe-based amorphous soft magnetic composite prepared via in-situ steam oxidation

Reducing the core losses of motors and transformers is an important way to address the global environment and energy resource problems. Soft magnetic composites (SMCs) comprising of electrically insulated ferromagnetic powder has shown vast potential for applications at low to high applied frequencies. In this work, in-situ steam oxidation was used to coat the surface of amorphous Fe75.5Si4B6P8C6Mo0.5 powder with an insulating layer. The thickness and composition of the Fe-oxide layer were controlled by tuning the in-situ steam oxidation time, and more cracks and Fe2+ were formed on the powder surface with the extension of oxidation time. The magnetic Fe-oxide layer of amorphous powder not only plays an insulating role to reduce the Pe, but also affects the magnetic coupling of particles that leads to the change of Ph. And the amorphous SMCs with 10 h in-situ steam oxidation treatment exhibits good comprehensive soft magnetic properties, i.e., the magnetic loss (Pcv), effective permeability (μe) and DC bias are 61.44 W/kg (50 mT, 100 kHz), 30.4 (to 10 MHz) and 71.5% (100 Oe), respectively.

Fluoxetine removal by anodic oxidation using different anode materials and graphite cathode

ABSTRACT Fluoxetine (FLX) is a selective serotonin reuptake inhibitor (SSRI) medication commonly used to treat mental health disorders, but it can be harmful to the environment if not properly disposed of due to incomplete metabolism. In this study, electrochemical anodic oxidation with mixed metal oxide anodes was studied as a method to remove FLX from water and wastewater. Iridium dioxide-coated titanium (Ti/IrO2) and ruthenium dioxide-coated Ti (Ti/RuO2) electrodes were found to be more effective than platinum-coated Ti (Ti/Pt) electrodes, with removal efficiencies of 91.5% and 93.9%, respectively. Optimal conditions for FLX removal were determined to be an applied current of 150 mA, initial pH of 5, and oxidation time of 120 min. The rate of FLX degradation (kFLX) for the Ti/Pt, Ti/IrO2, and Ti/RuO2 electrodes were determined to be 0.0081 min−1 (R2:0,8161), 0.0163 min−1 (R2:0,9823), and 0.0168 (R2:0,9901) min−1 for 25 mg/L initial FLX concentration, respectively. The kFLX values varied based on the initial FLX concentration and decreased as the initial FLX concentration increased. The specific energy consumption (SEC) after 120 min of operation was 51.0 kWh/m3 for the Ti/Pt electrode, 39.6 kWh/m3 for the Ti/IrO2 electrode, and 48.6 kWh/m3 for the Ti/RuO2 electrode under optimised conditions. Overall, electrochemical anodic oxidation is an effective method for removing FLX from water and wastewater, with Ti/IrO2 and Ti/RuO2 electrodes providing superior performance compared to Ti/Pt electrodes.

In situ formation of micro arc oxidation ceramic coating on refractory high entropy alloy

Micro arc oxidation (MAO) coatings were in situ prefabricated on refractory high entropy alloys (RHEAs). We systematically studied the evolution of the surface and cross-sectional morphologies and composition of the MAO ceramic coatings on AlTiCrVZr substrate with oxidation time. It was found that the surface elements in AlTiCrVZr exhibit competitive oxidation behavior during the MAO process. The inner layer of the MAO ceramic coating was mainly composed of ceramic oxides of the substrate elements, and the outer layer primarily consisted of ceramic oxides formed by the solute ions. Finally, we propose a growth model of the ceramic oxide coatings based on the formation mechanism of the MAO ceramic coating and the physical and chemical properties of the ceramic oxides formed by the principal elements in the RHEAs.

High temperature oxidation behaviors of steels at initial stages in air

The initial stage oxidation behaviors of commercial low carbon steel (LCS) and advanced high strength steel (AHSS) were comparatively studied at 1150 °C in air. Two reaction fronts were in situ observed during the oxidation of LCS, which was not found for AHSS. It was confirmed that the early detachment of LCS occurred after 30-s oxidation, however, the scale of AHSS maintained adherence due to the formation of a liquid phase. Besides, the scale thickness increased parabolically with oxidation time for both LCS and AHSS, with the estimated parabolic rate constants of 4.7 × 10−6 µm2/s and 4.9 × 10−6 µm2/s, respectively.

High temperature and short-term oxidation behavior of a TiBw/TA15 network composite in an air environment at 950 °C

The oxidation behavior of materials used in aerospace is crucial for their service life, and short-term oxidation behavior is an essential means to reveal the oxidation mechanism. The high temperature and short-term oxidation behavior of the TiBw/TA15 network composite in an air environment at 950 °C for 5 min, 15 min, 30 min, and 60 min was investigated. The experimental result indicates that the composite shows a slight mass change over the whole test times. The all-oxide scale mainly contains two-layer. From the top to the bottom of the oxide scale, an Al2O3 layer and a TiO2 layer existed, which increased with the oxidation time. The oxidation mechanism of the initial oxidation behavior of the network composite has been established, which is crucial for promoting its application in high-temperature service environments.

Effects of Ni content on microstructure and performance of MAO coatings on binary Al–Ni alloys

In this study, the pure Al and binary Al–Ni alloys with Ni addition of 1, 3, 6, and 10 wt % were coated via micro arc oxidation (MAO) in a tetraborate and phosphate based electrolyte for 60 min. With increased Ni content, the color of MAO coating became darker due to increased Ni-containing compounds on the surface. The Ni played a negative effect on the coating growth, decreasing both the coating thickness and surface roughness. The coatings on the Al–Ni alloys were mainly composed of γ-Al2O3 and α-Al2O3, and the Ni facilitated the formation of α-Al2O3 in the coating. Nanoparticles of NiO were generated around the edge of discharge channels for Al–6Ni and Al–10Ni alloys after a certain oxidation time. All coatings exhibited a uniform and dense surface structure, with the outer layer being more compact than the inner layer. Many tiny pores were found in the inner layer. Despite the corrosion resistance was decreased, the anti-wear performance of MAO treated samples was improved with the increased Ni content in the matrix. While, the corrosion resistance of the coated samples decreased with the adding of Ni content in the matrix.

Exploring the oxidation behavior of undiluted and diluted iron particles for energy storage: Mössbauer spectroscopic analysis and kinetic modeling.

Iron is an abundant and non-toxic element that holds great potential as energy carrier for large-scale and long-term energy storage. While from a general viewpoint iron oxidation is well-known, the detailed kinetics of oxidation for micrometer sized particles are missing, but required to enable large-scale utilization for energy production. In this work, iron particles are subjected to temperature-programmed oxidation. By dilution with boron nitride a sintering of the particles is prevented enabling to follow single particle effects. The mass fractions of iron and its oxides are determined for different oxidation times using Mössbauer spectroscopy. On the basis of the extracted phase compositions obtained at different times and temperatures (600-700 °C), it can be concluded that also for particles the oxidation follows a parabolic rate law. The parabolic rate constants are determined in this transition region. Knowledge of the particle size distribution and its consideration in modeling the oxidation kinetics of iron powder has proven to be crucial.

Detection of Cysteine Using Graphene Quantum Dots/Titanium Dioxide Nanotube-Based Biosensor

The objective of this research was to analyze the diagnostic value of a graphene quantum dots (GQDs)-titanium dioxide (TiO2) nanotube-based biosensor for L-cysteine (Cys). TiO2 nanotubes were prepared using anodic oxidation, GQDs were synthesized using thermal decomposition of citric acid, and TiO2-GQDs composite materials were fabricated using electrophoresis. A biosensor based on TiO2-GQDs was constructed, and the stability and photocatalytic efficiency of the TiO2-GQDs material were analyzed using X-ray diffraction (XRD) and a dual-beam ultraviolet-visible spectrophotometer (UVS). Cys detection was performed using the TiO2-GQDs biosensor, and the sensitivity, pH, time response, and selectivity of TiO2-GQDs towards Cys were analyzed using a fluorescence spectrophotometer (FS). The results revealed that TiO2 nanotubes with optimal diameter and length were obtained at an oxidation voltage of 80 V and oxidation time of 2 hours, with a greatly increased specific surface area (SSA) compared to those at 40 V and 50 V (P <0.05). Under constant oxidation voltage, longer oxidation time resulted in longer nanotube length. The microstructure of GQDs was clear, and the diffraction peaks and photocatalytic efficiency of GQDs in TiO2-GQDs increased with increasing GQDs content. The fluorescence quenching intensity (FQI) of TiO2-GQDs solution increased with increasing Cys concentration. After the addition of Cys, the FQI of TiO2-GQDs solution was much higher than that of 19 other amino acids (AAs) (P <0.05). However, difference in the F0−F value between Cys and interference AAs in TiO2-GQDs solution was not great (P >0.05). In conclusion, TiO2-GQDs material exhibited good stability and photocatalytic efficiency. The biosensor based on TiO2-GQDs demonstrated high sensitivity and selectivity towards high-concentration Cys solutions, showing promising applications in biomedicine.

Catalytic conversion of glycerol to formic acid under mild condition over an iron-based catalytic system

Glycerol, produced in large amounts as the main by-product of biodiesel production from biomass, has great potential to be converted into formic acid which is a potential hydrogen carrier. This research aims to evaluate the performance of an iron-based catalytic system in the oxidation process of glycerol to formic acid. The methods used include preparing an iron (II) oxalate catalyst, determining the reaction medium and reaction time for glycerol oxidation, optimizing the conditions of the glycerol oxidation process, and analysing the glycerol oxidation products. Optimization of process conditions includes the influence of temperature, substrate/catalyst molar ratio, and oxidant/substrate molar ratio. The research showed that water was a better reaction medium for glycerol oxidation, with a reaction time of 240 minutes. Oxidation of glycerol with an iron (II) oxalate catalyst can produce formic acid products with the best results obtained at pH 5, temperature 50°C, substrate/catalyst molar ratio of 100, and oxidant/substrate molar ratio of four with 83.18% converted glycerol. The yield and selectivity of formic acid were 47.77% and 57.43% respectively. These results indicate that the iron-based catalytic system has the potential to be an effective catalytic system for glycerol oxidation under mild conditions.

In situ growth of self-supported CuO nanorods from Cu-MOFs for glucose sensing and elucidation of the sensing mechanism.

Herein, we present a simple and mild method to in situ prepare CuO nanostructures for non-enzymatic glucose sensing. A Cu-metal organic framework (Cu-MOF) precursor was first directly grown on a pencil lead electrode with 3D graphene-like surfaces (EPLE) and then in situ transformed into CuO nanorods. The CuO nanorod-modified EPLE (CuO/EPLE) shows high sensitivity (1138.32 μA mM-1 cm-2), fast response time (1.5 s) and low detection limit (0.11 μM) for glucose oxidation. It has been found that NaOH promoted the generation of ˙OH groups and Cu(III) on the CuO surface, which then facilitated the electrochemical oxidation of glucose. Signals characteristic of hydroxyl and carbon-centered radical adducts were detected by EPR. Furthermore, the CuO/EPLE sensor also shows good accuracy in glucose determination in human serum samples.

Base-free aerobic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid over a Fe single-atom catalyst

A non-precious Fe single atom catalyst affords superior catalytic performance in terms of activity and stability with a FDCA yield of 99.8% and reusability of five recycle times in the catalytic oxidation of HMF to FDCA under base-free conditions.

Effect of a PFAS solution on short-term behaviour of a LLDPE and an HPDE geomembrane

Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals formed by carbon chains where fluorine atoms replace one or more hydrogen atoms. These bonds are extremely stable and PFAS components are known to be persistent environmental contaminants. The impact of these contaminants on two geomembranes is studied. Specifically, the short-term behaviour of a linear-low density LLDPE and a high-density HDPE polyethylene geomembrane immersed in a PFAS solution at an evaluated temperature is examined after 6.5 months of ageing. Results are presented for a PFAS solution with each priority component at 20 ppm or 1 ppm, a control solution (deionized water with CaCO3 28 ppm), and an MSW leachate solution at two representative temperatures of landfills (65°C and 85°C). Results show significant depletion of oxidative induction time (OIT) due to the consumption of antioxidants present in these materials. The values obtained suggest the need to consider the potential impacts of PFAS on the performance of geomembranes used in barrier systems.

The impact of sodium periodate oxidation and alginate coating on the capillarity of jute fabric

This study explores the impact of sodium periodate oxidation time (30 min, 60 min, or 120 min) and alginate coating on the capillarity of jute fabrics. Raw jute fabric exhibits a rapid increase in capillary rise height ( h) over time, reaching 72 mm at 1200 s. Fabrics oxidized for 30, 60, and 120 min show significantly lower h values of 19, 18, and 28 mm at 1200 s, respectively, which can be ascribed to the oxidation process itself. Precisely, oxidation-induced conversion of hydroxyl groups of cellulose (the main constituent of jute fiber) to aldehyde groups contributed to the fabric reduced affinity for water, hence negatively affecting its capillarity. Approximately 47% and 55% lower h values of fabrics oxidized for 30 and 60 min compared to that oxidized for 120 min can be explained by their lower weight loss after oxidation as well as less pronounced liberation of elementary fibers. Oxidized fabrics characterized by low capillarity can be used for the manufacturing of packaging materials, outdoor gear, and protective covers for crops. To expand jute fabric applications in biocarpet engineering, that is, to obtain polysaccharide-based supports, raw and oxidized jute fabrics were treated with a 1% sodium alginate solution. At 1200 s, oxidized fabrics coated with alginate exhibited 4.3–5.8 times higher h values compared to solely oxidized counterparts. The diffusion coefficients of oxidized fabrics coated with alginate increase up to 35% with prolonged oxidation, emphasizing the oxidation impact on alginate binding.

Numbering up and sizing up gliding arc reactors to enhance the plasma-based synthesis of NO x.

Non-thermal plasma-based NO x synthesis from ambient air is receiving an increasing amount of interest for its potential in small-scale, sustainable fertilizer production. Nevertheless, most reported research focuses on lab-scale systems and a single reactor with limited production. In this work, two gliding arc reactors (GARs) with 2 mm discharge gaps were connected in series or in parallel to explore strategies for scaling up the productivity. A single GAR with an enlarged discharge gap of 4 mm was also investigated for comparison. Operation parameters such as flow rate, discharge power & mode, and effective residence time were tested. The NO x concentration increased for all configurations with an increase in specific energy input (SEI), and effective residence time. The case of reactors connected in series outperformed all other configurations. The energy consumptions and NO x productions achieved were 2.29-2.42 MJ molN -1 and 124.6-158.3 mmolN h-1, respectively. The NO2 selectivity could be enhanced by prolonging the post-plasma oxidation time while consuming the excess O2 in the feed and utilizing the low temperatures at the reactor(s) outlet. By using this connection strategy, NO x production can be doubled with a 20.9% improvement in energy consumption compared to a single reactor.

Substrate suppression of oxidation process in pnictogen monolayers.

2D materials present an interesting platform for device designs. However, oxidation can drastically change the system's properties, which need to be accounted for. Through ab initio calculations, we investigated freestanding and SiC-supported As, Sb, and Bi mono-elemental layers. The oxidation process occurs through an O2 spin-state transition, accounted for within the Landau-Zener transition. Additionally, we have investigated the oxidation barriers and the role of spin-orbit coupling. Our calculations pointed out that the presence of SiC substrate reduces the oxidation time scale compared to a freestanding monolayer. We have extracted the energy barrier transition, compatible with our spin-transition analysis. Besides, spin-orbit coupling is relevant to the oxidation mechanisms and alters time scales. The energy barriers decrease as the pnictogen changes from As to Sb to Bi for the freestanding systems, while for SiC-supported, they increase across the pnictogen family. Our computed energy barriers confirm the enhanced robustness against oxidation for the SiC-supported systems.