Oxidation Time Research Articles

Valoration of the Synthetic Antioxidant Tris-(Diterbutyl-Phenol)-Phosphite (Irgafos P-168) from Industrial Wastewater and Application in Polypropylene Matrices to Minimize Its Thermal Degradation.

Industrial wastewater from petrochemical processes is an essential source of the synthetic phenolic phosphite antioxidant (Irgafos P-168), which negatively affects the environment. For the determination and analysis of Irgafos P-168, DSC, HPLC-MS, and FTIR methodologies were used. Solid phase extraction (SPE) proved to be the best technique for extracting Irgafos from wastewater. HPLC-MS and SPE determined the repeatability, reproducibility, and linearity of the method and the SPE of the standards and samples. The relative standard deviations, errors, and correlation coefficients for the repeatability and reproducibility of the calibration curves were less than 4.4% and 4.2% and greater than 0.99955, respectively. The analysis of variance (ANOVA), using the Fisher method with confidence in 95% of the data, did not reveal significant differences between the mentioned parameters. The removal of the antioxidant from the wastewater by SPE showed recovery percentages higher than 91.03%, and the chemical characterization of this antioxidant by FTIR spectroscopy, DSC, TGA, and MS showed it to be structurally the same as the Irgafos P-168 molecule. The recovered Irgafos was added to the polypropylene matrix, significantly improving its oxidation times. An OIT analysis, performed using DSC, showed that the recovered Irgafos-blended polypropylene (PP) demonstrated oxidative degradation at 8 min. With the addition of the Irgafos, the oxidation time was 13 min. This increases the polypropylene's useful life and minimizes the environmental impact of the wastewater.

Long-term oxidation behavior for Ni-5Al coating in air-H2O at 650 ℃

The oxidation behavior of the Ni-5Al coating produced by high-velocity oxygen-fuel on the Fe-Cr alloy was investigated at 650 ℃ in air containing 20% water vapor. The oxidation kinetics of the Ni-5Al coating were establish by classical oxidation theory for 8000 h. According to the oxidation kinetic data, we calculated the time of breakaway oxidation occurred and compared between experimental measurement and model calculation of internal oxidation. And then the correlation between oxidation depth and oxidation time was plotted according to the measurement and model calculation.

Low-cost surface modification of a biomedical Zr-2.5Nb alloy fabricated by electron beam melting

• Thermal oxidation is an effective way to prepare oxide layer on a Zr-2.5Nb alloy fabricated by electron beam melting (EBM). • The morphology, phase constituents, and surface color of oxide layer change in the oxidation process. • Grain refinement significantly delays the breakaway oxidation. • A dense and black oxide layer with a hardness of 902 HV is prepared on a EBM- built Zr-2.5Nb alloy by oxidation at 600°C for 3 hours. The Zr-2.5Nb alloy with a fine microstructure consisting of α laths was successfully prepared by electron beam melting (EBM). The thermal oxidation behaviors and kinetics of the as-built, and the EBM-built and hot isostatically pressed (HIPed) Zr-2.5Nb materials in a temperature range of 450–600°C were investigated and compared with those of the alloy prepared by conventional casting and forging. It was found that the oxidation kinetics of the as-built and the forged materials followed the parabolic rate law during isothermal oxidation at 550°C, but the HIPed materials exhibited a parabolic-to-linear kinetic transition, suggesting that the larger grain sizes enhanced the oxidation. The oxide layers of all materials were composed of a large fraction of monoclinic zirconia phase ( m -ZrO 2 ) and a small fraction of tetragonal zirconia phase ( t -ZrO 2 ), and transformed from t -ZrO 2 to m -ZrO 2 with increasing oxidation time. The surface hardness of the as-built, the forged and the HIPed materials increased from 215, 204, and 188 HV before oxidation to 902, 1070, and 1137 HV after oxidation, respectively. The cross-sections of the materials showed the presence of micropores and microcracks inside the oxide layers with thicknesses ranging from 4 to 8 µm. With the oxidation temperature of 600°C and oxidation time duration of 3 h, a dense black m -ZrO 2 oxide layer with smooth surface and 902 HV hardness was obtained on the EBM as-built Zr-2.5Nb materials.

High-temperature oxidation and TGO growth behaviors of laser-modified YAG/YSZ double-ceramic-layer TBC

Yttrium—aluminum garnet/yttria-stabilized zirconia (YAG/YSZ) double-ceramic-layer thermal barrier coating (TBC) with NiCoCrAlY bond coating was deposited by atmospheric plasma spraying (APS) on Inconel 738 alloy substrate, and laser modification was carried out on the surface of YAG ceramic coating to improve the high- temperature oxidation resistance of TBC. Then, isothermal oxidation tests were designed to study the high-temperature oxidation and thermally grown oxide (TGO) growth behaviors of the as-sprayed (AS) and the laser modified (LM) YAG/YSZ TBC. Results show that TGO thickness and structure of both AS-TBC and LM-TBC exhibit the similar evolution trend, TGO thickness increases with the increasing of isothermal oxidation time, and TGO structure develops from single Al2O3 layer to the double-layer structure of upper mixed oxides and lower Al2O3. Because of the crucial inhibition effect of the laser modification on oxygen permeation, the appearance time of mixed oxides in LM-TBC is postponed, and the total TGO thickness of LM-TBC is reduced at the middle and final oxidation stages. The Al2O3 layer thickness proportion of total TGO in LM-TBC is always greater than or equal to that in AS-TBC at the same isothermal oxidation time. Compared with the AS-TBC, the parabolic oxidation rate of LM-TBC is decreased by 18.42%. Therefore, YAG/YSZ LM-TBC presents better oxidation resistance and lower TGO growth rate than AS-TBC.

Growth mechanism of 2024 aluminum alloy micro-arc oxide layer in cobalt-containing electrolyte

The coatings were prepared on the surface of 2024 aluminum alloy by micro-arc oxidation. The effect of the addition of cobalt salt on the growth mechanism of the coating was investigated. The addition of cobalt salt prolonged the spark discharge phase of microarc oxidation and achieved the co-film formation of the solution component and the substrate. XRD, SEM, EDS, and XPS were used to investigate changes in the physical composition, surface morphology, and chemical composition of coatings prepared at different times. The hardness and corrosion resistance of the coatings were investigated as oxidation time increased. The surface of the coatings can be divided into two regions: the loose “cobalt-rich zone” and the dense “aluminum-rich zone”, and with the increase of oxidation time, the surface of the coating becomes more dense and flat, and the pores are mostly closed. The time-voltage curve shows that the growth of the micro-arc oxide coating in cobalt-containing electrolyte can be divided into three stages. The coating grows rapidly in the first 15 min, and a black coating is obtained, with the color-revealing substance being CoO; the coating turns from black to blue after 15 min, as CoO transforms to blue CoAl2O4. XPS and XRD analyses showed that the addition of cobalt salt significantly promoted the formation of alumina in the coating, and the conversion of CoO to CoAl2O4 and γ-Al2O3 to α-Al2O3 occurred at the later stage of micro-arc oxidation, when the hardness of the coating would obtain a large enhancement. The corrosion resistance test results showed that the coating prepared by treatment in the cobalt-containing electrolyte for 60 min showed the best corrosion resistance with a corrosion potential 100.3 mV higher than that of the substrate and a corrosion current reduced by 4 orders of magnitude to 6.20 × 10−9 A·cm−2.

Long-Term Oxidation of Zirconium Alloy in Simulated Nuclear Reactor Primary Coolant—Experiments and Modeling

Oxidation of Zr-1%Nb fuel cladding alloy in simulated primary coolant of a pressurized water nuclear reactor is followed by in-situ electrochemical impedance spectroscopy. In-depth composition and thickness of the oxide are estimated by ex-situ analytical techniques. A kinetic model of the oxidation process featuring interfacial reactions of metal oxidation and water reduction, as well as electron and ion transport through the oxide governed by diffusion-migration, is parameterized by quantitative comparison to impedance data. The effects of compressive stress on diffusion and ionic space charge on migration of ionic point defects are introduced to rationalize the dependence of transport parameters on thickness (or oxidation time). The influence of ex-situ and in-situ hydrogen charging on kinetic and transport parameters is also studied.

Mode mixing performance evaluation and influence of elements on the fiber system behaviour

Abstract This study has clarified various micro electro mechanical system (MEMS) processes performance evaluation based on MEMSolver simulation software. The spin time against final resist thickness for the spin coating of a thin film of photo resist and the oxidation time versus oxide thickness for silicone dioxide growth for <100> silicon in wet oxide are clarified. The diffusion profile for Boron after predeposition and drive in of dopants in silicon and the thickness of silicon dioxide mask for Boron diffusion are demonstrated. The dopant distribution resulting from ion implantation and drive in and the percentage of dose penetrating photo resist mask versus thickness of the mask are reported. The film stress versus the film thickness from wafer bow measurements, aluminum deposition rate against temperature using the electronic beam evaporator and the deposition rate of polysilicon versus silane partial pressure are reported. The etch rate of the thermal oxide against percentage concentration of KOH, the etch rate against the etchant temperature for silicon nitride in hot phosphoric acid, and the etch rate against the etchant temperature for the thermal oxide using buffered hydrofluoric acid (BOE) are outlined.

Enhanced electrocatalytic elimination of fenitrothion, trifluralin, and chlorothalonil from groundwater and industrial wastewater using modified Cu-PbO2 electrode

In this study, fenitrothion (FTH), trifluralin (TRL), and chlorothalonil (CHT) pesticides were studied as simultaneous degradation candidates for the anodic oxidation (AO) process. Characterization experiments including FE-SEM, XRD, cyclic voltammetry, electrochemical impedance spectroscopy, linear polarization, and accelerated service lifetime test (ASLT) were performed to evaluate the effect of Sn@Sb, PbO2, and PbO2/Cu electrodes. The doping of Cu into PbO2 electrode played an important role in improving the electro-catalytic activity of the electrode and can further increase the •OH generation capacity. Simultaneous removal FTH, TRL, and CHT using the AO process was optimized by response surface methodology. Analysis of variance revealed that the R2 of removal efficiency for FTH, TRL, and CHT were 0.9848, 0.9791, and 0.9770, respectively. Moreover, the adjusted R2 for degradation of FTH, TRL, and CHT were 0.9822, 0.9756, and 0.9738, and the predicted R2 were 0.9770, 0.9694, and 0.9685, respectively. The complete removal efficiency for FTH, TRL, and CHT was achieved under the optimal condition including FTH concentration 8.0 mg L−1, TRL concentration 12.0 mg L−1, CHT concentration 16.0 mg L−1, pH 6.0, current density 6.0 mA cm−2, and oxidation time of 60 min. In the optimum condition COD removal efficiency and energy consumption were 74.3% and 4.4 kWh m−3 using PbO2/Cu electrode, respectively. The kinetic of FTH, TRL, and CHT degradation on Sn@Sb, PbO2, and PbO2/Cu electrodes best fitted on a pseudo-first-order kinetic model. The oxygen evolution overpotential was 1.914, 1.983, and 2.138 V vs. SCE for Sn@Sb, PbO2, and PbO2/Cu electrodes, respectively. The ASLT of PbO2/Cu electrode is 344 h, which is 2.3 and 4.2 times longer than that of PbO2 and Sn@Sb electrodes. The degradation mechanism was evaluated using GC–MS technique and a possible degradation pathway for the anodic oxidation of FTH, TRL, and CHT was proposed based on the identified intermediates. As a result, the AO technology using PbO2/Cu electrode could be considered a nice solution to the treatment of pesticides-polluted wastewater.

Beyond Antioxidant Activity: Redox Properties of Catechins May Affect Changes in the DNA Methylation Profile-The Example of SRXN1 Gene.

The role of catechins in the epigenetic regulation of gene expression has been widely studied; however, if and how this phenomenon relates to the redox properties of these polyphenols remains unknown. Our earlier study demonstrated that exposure of the human colon adenocarcinoma HT29 cell line to these antioxidants affects the expression of redox-related genes. In particular, treatment with (-)-epigallocatechin (EGC) downregulated transcription of gene encoding sulfiredoxin-1 (SRXN1), the peroxidase involved in the protection of cells against hydrogen peroxide-induced oxidative stress. The aim of this study was to investigate whether the observed SRXN1 downregulation was accompanied by changes in the DNA methylation level of its promoter and, if so, whether it was correlated with the redox properties of catechins. The impact on DNA methylation profile in HT29 cells treated with different concentrations of five catechins, varying in chemical structures and standard reduction potentials as well as susceptibility to oxidation, was monitored by a methylation-sensitive high-resolution melting technique employing the SRXN1 promoter region as a model target. We demonstrated that catechins, indeed, are able to modulate DNA methylation of the SRXN1 gene in a redox-related manner. The nonlinear method in the statistical analysis made it possible to fish out two parameters (charge transfer in oxidation process Qox and time of electron transfer t), whose strong interactions correlated with observed modulation of DNA methylation by catechins. Based on these findings, we present a proof-of-concept that DNA methylation, which limits SRXN1 expression and thus restricts the multidirectional antioxidant action of SRXN1, may represent a mechanism protecting cells against reductive stress caused by particularly fast-reacting reductants such as EGC and (-)-epicatechin gallate (ECG) in our study.

In-situ one-step preparation of anatase/rutile TiO2(A/R) with oxygen vacancy modification derived from 2D Ti3C2 for enhanced visible-light-driven photodegradation of tetracycline

The accumulation of residual tetracycline in water environment is an environmental problem that needs to be solved urgently. As an attractive photocatalyst for antibiotic removal, TiO2 has limited photocatalytic activity due to its low solar light utilization efficiency and low quantum yield. Herein, the oxygen vacancy modified Ti3C2/TiO2(anatase/rutile) (TTO(A/R)) heterojunction photocatalyst was successfully synthesized and regulated by adjusting the hydrothermal oxidation time using Ti3C2 as the metal material and homologous titanium. The TTO(A/R)8 h heterojunction photocatalyst with optimal composition percentage of (Ti3C2) 30.93%, (A-TiO2) 54.58% and (R-TiO2) 14.49% showed the best photocatalytic degradation efficiency of TC, which was increased by 1.5 times compared with commercial P25. Further characterization results indicated that the local states formed by the introduced oxygen vacancy broadened the visible range of TTO(A/R)8 h to ∼700 nm. The separation of photogenerated electrons-holes was highly promoted by biphasic TiO2 and the interface Schottky junction between TiO2 and Ti3C2, which would provide more photogenerated electrons and holes to participate in the photocatalytic reaction. Our research provided a new idea for constructing composite photocatalyst derived from Ti3C2 to treat refractory organic pollutants.

Improved thermal shock and oxidation resistance of β-SiAlON incorporated with h-BN

β-SiAlON ceramics incorporated with h-BN were prepared by gel casting combined with reaction bonding procedure. With the h-BN addition varying from 0 to 20 wt%, the bending strength was degraded from 102.5 MPa to 60.0 MPa. Compared to monolithic β-SiAlON, β-SiAlON/h-BNs have significantly better thermal shock resistance. At high temperature in air atmosphere, mass gain curves of both β-SiAlON and β-SiAlON/h-BN exhibited platform stage after certain oxidation time. Higher temperature benefits formation of protective layer which inhibited oxygen diffusion, then the oxidation of the samples was stagnated. Addition of h-BN make it easier to form the protective layer. Furthermore, B2O3 from oxidation of h-BN could inhibit the crystalizing of the glassy phase, hence, more stable protective layer could form stagnating oxidation process. Addition of h-BN in β-SiAlON exhibited excellent enhancement on thermal shock resistance and oxidation resistance, which is of vital importance for application in high temperature environments. An empirical biexponential model was suggested for describing the oxidation behavior of the ceramic material containing open pores prepared in this work.

Influence of atmospheres on the friction and wear of cast iron against chromium plated steel at high temperatures

The aim of this study is to investigate the atmospheric effect on the wear of cast iron against chromium plated steel at temperatures up to 800 °C. Reciprocating wear tests of a cylinder-on-plate configuration were performed in air and a low-oxygen CO2-N2-O2 atmosphere and analyzed.At low temperatures an adhesive wear regime with material transfer from the cast iron cylinder onto the chromium plating was observed up to 400 °C. Higher temperatures lead to a tribologically generated oxide layer at the interface, a so-called “glaze layer”, resulting in a strong wear decrease. The micro structural analysis reveals a layered structure of differently strong compacted wear particles consisting mainly of iron oxide Fe2O3.A modification of the surrounding atmosphere to an oxygen amount of 5 vol% showed little impact on this tribological behavior above the threshold temperature of 400 °C. Sufficient oxidation times of the generated wear particles were assumed, which is a necessary step of the layer formation. Based on this finding, a temperature related sintering or phase transition process is postulated to explain the glaze layer formation independently of the surrounding, oxygen containing atmosphere.Nevertheless, for the adhesion dominated regime at temperatures below 400 °C, a positive influence on the wear behavior in the CO2-N2-O2 atmosphere was observed. This change in the tribological behavior is attributed to a carbon enriched layer of 400 nm thickness, which is formed by comparatively less oxidized spheroidal graphite of the cast iron.

Optimization of shadow evaporation and oxidation for reproducible quantum Josephson junction circuits

The most commonly used physical realization of superconducting qubits for quantum circuits is a transmon. There are a number of superconducting quantum circuits applications, where Josephson junction critical current reproducibility over a chip is crucial. Here, we report on a robust chip scale Al/AlOx/Al junctions fabrication method due to comprehensive study of shadow evaporation and oxidation steps. We experimentally demonstrate the evidence of optimal Josephson junction electrodes thickness, deposition rate and deposition angle, which ensure minimal electrode surface and line edge roughness. The influence of oxidation method, pressure and time on critical current reproducibility is determined. With the proposed method we demonstrate Al/AlOx/Al junction fabrication with the critical current variation (sigma /langle {I_{c} } rangle ) less than 3.9% (from 150 × 200 to 150 × 600 nm2 area) and 7.7% (for 100 × 100 nm2 area) over 20 × 20 mm2 chip. Finally, we fabricate separately three 5 × 10 mm2 chips with 18 transmon qubits (near 4.3 GHz frequency) showing less than 1.9% frequency variation between qubits on different chips. The proposed approach and optimization criteria can be utilized for a robust wafer-scale superconducting qubit circuits fabrication.

Valorization of lignin to obtain platform chemicals via bio‐electrochemical systems: batch and fed‐batch mode analysis

AbstractBACKGROUNDThere is tremendous potential for reusing lignin, which is generally discarded as waste. This research analyses the batch and fed‐batch mode of the microbial peroxide‐producing cell (MPPC), a type of bio‐electrochemical cell that produces H2O2, a potent green oxidant utilized in the oxidation of Kraft lignin to produce platform chemicals with simultaneous wastewater treatment.RESULTSThe batch mode MPPC had a total shelf life of 10 days, with a peak phase of 5 days and maximum H2O2 of 9.7 ± 0.06 mmol L−1, and voltage of 164 ± 0.021 mV. The intermittent nutrition feeding strategy of fed‐batch MPPCs aided microbe metabolic reactions, extending the system's lifespan to 21 days with a maximum voltage of 294 ± 0.01 to 525 ± 0.008 mV and H2O2 of 14.14 ± 0.12 to 32.96 ± 1.35 mmol L−1, respectively. This offered more exposure time for lignin hydroxyl radical oxidation by H2O2, with enhanced depolymerization of 37–80% of high lignin concentration in repeated cycles compared to batch mode, which accomplished only 53.46%. Fourier transform infrared spectroscopy confirmed the structural changes in lignin of all systems, displaying loss and disorientation of major functional groups with greater intensity in fed batch‐operated MPPCs. Platform chemicals with high commercial value, including guaiacol, ferulic acid, vanillin, and others, were identified using liquid chromatography–mass spectrometry. In terms of wastewater treatment, biochemical oxygen demand and chemical oxygen demand removal efficiency ranged from 59% to 83%, with fed‐batch being the most efficient.CONCLUSIONThis research suggests that fed‐batch mode MPPC is significantly more productive than batch mode MPPC for lignin valorization to produce platform chemicals, making it more sustainable, economical, and environmentally friendly. © 2023 Society of Chemical Industry (SCI).

Impact of Fulvic Acid and Acidithiobacillus ferrooxidan Inoculum Amount on the Formation of Secondary Iron Minerals.

The catalytic oxidation of Fe2+ by Acidithiobacillus ferrooxidan (A. ferrooxidans) and the synthesis of iron sulfate-based secondary minerals is considered to be of great significance to the treatment of acid mine drainage (AMD). Along these lines, in this work, the shaker experiment was carried out to study the underlying mechanism of the inoculation amount of fulvic acid (FA) and A. ferrooxidans on the synthesis process of secondary minerals. From the acquired results, it was demonstrated that the oxidation rate of Fe2+ increased with the increase in the concentration of fulvic acid in the range of 0.1-0.2 g/L. On top of that, the concentration of fulvic acid in the range of 0.3-0.5 g/L inhibited the activity of A. ferrooxidans. However, A. ferrooxidans retained its activity, and the complete oxidation time of Fe2+ was delayed. When the concentration of fulvic acid was 0.3 g/L, the TFe (total iron) precipitation efficiency was 30.2%. Interestingly, when 0.2 g/L fulvic acid was added to different inoculum systems, the incorporation of a higher inoculum amount of A. ferrooxidans led to an increased oxidation rate. On the contrary, the lower inoculum amount yielded a more obvious effect of the fulvic acid. From the mineralogical characteristics, it was also revealed that a fulvic acid concentration of 0.2 g/L and different inoculation amounts of A. ferrooxidans did not change the mineral facies, whereas pure schwertmannite was obtained.

Unveiling different oxide scales in a compositionally complex polycrystalline CoNi-base superalloy

The formation of multiple types of oxide scales on the specimen surface as well as along the grain boundaries was investigated in detail in a compositionally complex polycrystalline CoNi-base superalloy after oxidation at 900 ℃. The complex multilayered oxide scale forms under steady-state condition (oxidation time till 24 h). After the breakdown of the steady-state oxide scale (oxidation for 48 h), different types of oxide scales occur. Additionally, it is found that oxidation can gradually extend into the specimen interior along the grain boundaries. The oxide scale formed along the grain boundaries evolves when the boundaries extend from specimen surface into interior, which is caused by the selective oxidation of elements by the differences in equilibrium oxygen partial pressures. It is proposed that factors, i.e., local microstructure and oxygen concentration, greatly influence the formation and configuration of the oxide scales of the investigated alloy.

Thermal-oxidation coupled analysis method for unidirectional fiber-reinforced C/SiC composites in air oxidizing environments below 1000 °C

The thermal analysis method for unidirectional fiber-reinforced C/SiC composites (C/SiC-UFRC) in air oxidizing environment below 1000 °C is developed, including a mathematical theoretical model and a finite element model. The mathematical model (MM) is established by combining the thermal resistance network method and the oxidation kinetics theory. The influence of oxidation characteristics on C/SiC-UFRC axial thermal conductivity is firstly introduced into MM, which provides a reference for the theoretical calculation method of C/SiC-UFRC axial thermal conductivity under oxidation conditions. The finite element model (FEM) is constructed on the representative volume element (RVE) of C/SiC-UFRC and the numerical heat transfer method. The FEM numerically simulated the microstructure in the oxidation process and firstly be applied to study the effects of oxidation on the micro temperature field and heat transfer of C/SiC-UFRC. Through the mutual confirmation of MM and FEM, the prediction of thermal conductivity of CMC in air oxidation environment is verified. The effects of oxidation time, oxidation temperature and random distribution of initial cracks are investigated to reveal their influences on the heat transfer behavior of C/SiC-UFRC.

Electrospun graphene oxide–polyvinylidene fluoride composite film preparation and application for air filtration

In this work, polyvinylidene fluoride (PVDF) and graphene oxide (GO) composite membranes were fabricated using electrospinning technology for particulate matter (PM) filtration. The preparation conditions like GO oxidation time, electrospinning solution composition, and GO content in the composite film, and the basic properties and filtration performance of PVDF–GO films were systematically analyzed. It was found that GO with lamellar structure was of great benefit to endow the membrane with excellent mechanical properties and particle capture capacity. The as-prepared PVDF–GO membranes with GO addition of 0.6 wt.% exhibited the highest tensile strength and PM filtration efficiency. This work demonstrated that blending GO in PVDF is a feasible modification to fabricate an effective PM filtration membrane.

Evaluation of Short-Term Oxidation Mechanism of Laser Cladded Ni–Cr–C Coating on Titanium Aluminide Substrate

In the present investigation, a NiCr–Cr3C2 powder mixture was deposited on titanium aluminide substrate by laser cladding. The kinetics and mechanism of oxidation of the substrate and coating were studied at 800–1100 °C using XRD, SEM, ToF–SIMS and XPS characterization techniques. The results demonstrated that the Ni–Cr–C coating had improved oxidation resistance, as compared to the substrate. The oxidized surface of the coating was covered with Cr2O3 and NiCr2O4 phases at the early stages of the oxidation. The formation of NiCr2O4 could be attributed to the reaction of NiO (an oxidation product of the NiCr phase) and Cr2O3 (an oxidation product of the chromium carbide phase) during oxidation. Increasing the oxidation time at 900 °C led to the partial formation of CrO3 as a result of the oxidation of Cr2O3. It was also found that the parabolic rate constant ratio of $$\left( {K_{{\text{p}}}^{{{\text{substrate}}}} /K_{{\text{p}}}^{{{\text{coating}}}} } \right)$$ increased with the temperature, which showed, comparatively, the better oxidation resistance of the coating at higher temperatures.

Cobalt Electrodeposition in Nanoporous Anodic Aluminium Oxide Films with Different Oxidation Time

The anodic aluminum oxide films with different oxidation times were investigated using electrochemical techniques including electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and open-circuit potential versus time. The stable open-circuit potential versus time indicates that the longer anodization time provides a larger block for cobalt electrodeposition. The EIS monitoring revealed the capacitance characteristics of the barrier layer. When the oxidation time is 4 h, the thickness and porosity of AAO film are 1517 nm and 16.4 % corespondingly, and the radius of the capacitive reactance arc is the smallest. The reduction peak current of CV is attributed to the change in diffusion coefficient of cobalt when oxidation time changes.