Oxidation Time Research Articles

High-Degree Oxidative Desulfurization of a Commercial Marine Fuel Using Deep Eutectic Solvents and Their Recycling Process

Escalating environmental concerns have dictated the need to develop innovative methods for efficiently desulfurizing marine fuels (heavy fuel oils). In this work, the oxidative desulfurization method using deep eutectic solvents (DESs) was applied to reduce the sulfur content in a commercially available heavy fuel oil (HFO) below 0.5 wt.%, as current regulations demand. Initially, the S-compounds in the fuel were oxidized using an oxidative mixture of H2O2 with carboxylic acid (either acetic or formic acid). Subsequently, the oxidized S-compounds were extracted from the fuel using a series of environmentally friendly deep eutectic solvents (DESs), the best of which was proven to be a mixture of choline chloride with ethylene glycol at a 1/2 molar ratio. The process was optimized by investigating the effect of several process parameters on the desulfurization efficiency, namely, the H2O2/S molar ratio, the H2O2/acid molar ratio, the acid type, the oxidation temperature and oxidation time, the solvent/fuel mass ratio, the extraction time, and the extraction temperature. A desulfurization efficiency of 75.7% was achieved under the optimized conditions, reducing the S content in the fuel to 0.33 wt.%. Furthermore, different methods to recycle the DESs were investigated, and consecutive desulfurization and solvent regeneration cycles were performed. The most efficient recycling method was determined to be the anti-solvent addition of excess water, which resulted in 89.5% DES purification by causing precipitation of the dissolved solids. After three cycles of desulfurization and regeneration using different recycling routes, it was found that the regeneration degree declines gradually; however, it is more than 79.3% in all cases.

Preparation and characterization of the bonding performance of a starch-based water resistance adhesive by Schiff base reaction

Starch is one of the important raw materials for the preparation of biomass adhesives for its good viscosity and low-cost properties. However, the drawbacks of poor water resistance and bonding performance seriously restrict its application in the wood industry. To resolve those problems, an environment-friendly renewable, and high water resistance starch-based adhesive (OSTH) was prepared with oxidized starch and hexanediamine by Schiff base reaction. In order to optimize the adhesive preparation process, the effect of different oxidation times and oxidant addition on the mechanical performance of plywood were investigated. In addition, the curing behavior characteristics, thermomechanical properties, and thermal stability of the OSTH adhesives were analyzed by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and thermogravimetric analysis (TG). Fourier-transform infrared (FTIR) spectrometry and Liquid Chromatography-Mass Spectrometry (LC-MS) were used to explain the reaction mechanisms involved. The results show this adhesive has an excellent bonding performance at the oxidation time of 12 h with 11 % (w/w, dry starch basis) NaIO4 as an oxidant. The dry shear strength, 24-hour cold water, and 3-hour hot water (63 °C) soaking shear strength of the plywood bonded with this resin were respectively 1.87 MPa, 0.96 MPa, and 0.91 MPa, which satisfied the standard requirement of GB/T 9846-2015 (≥0.7 MPa). Thus, this study provided a potential strategy to prepare starch-based wood adhesives with good bonding performance and water resistance.

Preparation of long-flame coal flotation collector from waste cooking oil

There is currently a need to develop efficient and environmentally friendly (green) collectors to improve the poor flotation performance of long-flame coal (LFC) due to its vast porosity and high oxidation degree. Herewith, this study introduces ozone (O3) and ultraviolet (UV) oxidation methods to modify waste cooking oil collector (WCOC) and analyzes their effects on the LFC flotation performance. Furthermore, the separation efficiency (SE) of WCOC, O3-WCOC, UV-WCOC and common collectors (diesel, kerosene, DEP) were compared. Fourier Transform Infrared Spectroscopy (FTIR) and Gas chromatography-mass spectrometry (GC–MS) were used to observe the effects of O3 and UV oxidation on WCOC functional groups and chemical composition. The functional groups and wettability changes of LFC treated via common collectors, including WCOC, O3-WCOC and UV-WCOC adsorption were analyzed. Results revealed that a shorter O3 oxidation time resulted in better flotation performance and higher SE compared to UV oxidation. After O3 (5 min) and UV (9 h) oxidations, CH bonds in WCOC were oxidized and the content of oxygen-containing functional groups (particularly –OH) increased to 4.25% and 4.93% from 0.79%, respectively. Compared to common collectors, O3-WCOC and UV-WCOC demonstrated better reactions with oxygen-containing functional groups (especially O = CO and CO) on the LFC surface. This phenomenon led to a substantial increase in contact angle. This novel oxidation method could potentially be applied in wastewater treatment, mineral processing, and other fields.

Dense porous carbon from chemical welding the oxidized coal liquefaction residue for enhanced volumetric performance supercapacitors

Coal liquefaction residue (CLR) has the advantage of high carbon content. Its conversion into high value-added carbon materials is of great significance for solid waste treatment. Herein, we prepare dense porous carbons (DPCs) by chemical welding and homogenous activation from the oxidized CLR (OCLR). With the extension of oxidation time for CLR, the OCLR shows a reduced particle size, an increased amount of edge sites, and an improved oxygen content. Moreover, oxidation etching removes numerous defects, leading to an enhanced conjugation degree of the OCLR. Therefore, the dense porous carbon obtained from small-sized OCLR (ca. 5 nm) exhibits abundant edge oxygen-bearing groups, good electrical conductivity, large specific surface area (1368 m2 g−1) and high compaction density (0.98 g cm−3). As supercapacitor electrode, it shows good gravimetric capacitance and enhanced volumetric capacitance of 268.5 F g−1 and 263.1 F cm−3 at 1 A g−1, respectively. The assembled symmetric supercapacitor displays an enhanced volumetric energy density of 8.26 W h L−1 at 124.9 W L−1, as well as excellent cycle stability. Our work provides a new idea for the efficient use of CLR.

Low-cost synthesis of titanium dioxide nanotubes/reduced graphene oxide heterostructure for pH sensor applications

In this work, we deposit Graphene Oxide (GO) films on Titanium Dioxide nanotubes (TiO2NTs); electrochemical characterization of this system shows that this structure has potential applications as a pH sensor. TiO2NTs were obtained by electrochemical anodization technique, the GO was fabricated by modified Hummer's method, and deposited by dip coating technique, at room temperature. The thermally treated TiO2NTs/GO structure shows a reduction of the GO deposited film. The samples were characterized by Raman spectroscopy, X-ray Photoelectron Spectroscopy, and Scanning Electron Microscopy. Depending on the GO oxidation time and thermal treatment, we observe a uniform reduced GO film on the TiO2NTs. A pH electrode characterization shows a linear response of the TiO2NTs/GO of 57 mV/pH with non-hysteresis effect.

Characterization and determination of casein glycomacropeptide in dairy products by UHPLC–MS/MS based on its characteristic peptide

The ultra-high-performance liquid chromatography tandem mass spectrometry (UHPLC-MS) method was built to quantify the casein glycomacropeptide (CGMP) in bovine dairy products accurately based on targeted proteomics. Qualitative analysis of theoretical peptides was carried out using high-resolution mass spectrometry (HRMS) and protein software. Isotope-labeled characteristic peptides were acquired via the labeled amino acid condensation method to correct the matrix effects. Peptide MAIPPK was the representative characteristic peptide for distinguishing the CGMP from κ-casein through trypsin digestion. After optimizing the pre-treatment conditions, the final 8% oxidant concentration was selected and the 10% formic acid concentration with 2.5 h oxidation time. Moreover, the results of methodological verification showed that the recovery rate was 103.7%, meanwhile the precision of inter-day and intra-day was less than 5%. In conclusion, the research demonstrated the characteristic peptide MAIPPK could quantitatively applied to detect CGMP in dairy products.

3D printing of porous Ti6Al4V bone tissue engineering scaffold and surface anodization preparation of nanotubes to enhance its biological property

Abstract Porous structures and surface morphology of bone tissue scaffolds play an important role in improving the biocompatibility and antibacterial properties for bone repair. In this study, we investigated the effect of different anodic oxidation parameters on the nanotubes morphology in 3D printed porous titanium scaffolds. Micron-scale pores were fabricated by 3D printing first, and then the nano-scale tubes were obtained via anodizing treatments. The results demonstrated that the morphology of the nanotubes depended on the anodic oxidation time and voltage, respectively. Longer anodic oxidation led to the formation of circle-like nanotubes, and the diameter of the nanotubes increased with the voltage. The scaffolds anodized at 30 V showed the best cell proliferation potential. The presence of nanotubes on the surface of scaffold altered the adhesion of bacteria so that it improved the antibacterial properties of scaffold. The formation of nanotubes improved the drug-loading ability of the scaffold, which are used for loading of minocycline antibacterial drugs. The proposed 3D printed porous Ti6Al4V scaffold with nanotubes surface modification showed obvious antibacterial effect, which is expected to have a promising application in antibacterial bone prosthesis.

Effect of oxidation time on the structure and properties of Ti–25Nb–3Zr–2Sn–3Mo titanium alloy microarc oxide film layer

In order to improve various properties of medical titanium alloys, Ti–3Zr–2Sn–3Mo–25Nb titanium alloy specimens were subjected to microarc oxidation (BMAO) in 0.1 mol/l sodium tetraborate electrolyte to cover the substrate with a micro-nano double-graded structured coating. The effect of oxidation time on the microstructure, physical phase, hardness, corrosion resistance, and wettability of the micro-nano film layer was investigated. The results show that the microporous size of the film increases with the increase in oxidation time, and the hardness of the BMAO film increases with the increase in oxidation time; the corrosion resistance of the BMAO film is better than that of the substrate, and the self-corrosion potential is the largest at 14 min of oxidation time, reaching −0.1349 V, which is 65% higher than that of the substrate, and the self-corrosion current is the lowest, at 1.1376 × 10−9 A cm−2, which is one order of magnitude lower than that of the substrate; the micro-nano film layer exhibits superhydrophilicity, which increases and then decreases with time, and the contact angle is the smallest at 6 min of oxidation time, 4.4°, which is one order of magnitude lower than that of the substrate, 73.75°.

Study on the influence of micro-alkali texturing and micro-alkali polishing process on the passivation and contact performance of n-TOPCon solar cells

The matching between the morphology of the backside of n-TOPCon solar cells and the tunnel oxide/n + polysilicon structure is the key to achieving high efficiency. In this work, based on the requirement of edge isolation, micro-alkali polishing and micro-alkali texturing were performed on the acid-polishing back surface. Their effects on surface morphology, passivation effect, contact resistance, and photoelectric conversion efficiency were investigated. Adding a short-time micro-alkali texturing process after acid polishing can form a surface morphology with both regional polishing and local microtexture. This can improve the contact characteristics without significantly affecting the passivation characteristics, enabling solar cells to achieve higher FF (83.30%) and average efficiency (24.15%). Compared with the acid polishing sample, the efficiency of the micro-alkali texturing sample is increased by 0.12%. The deterioration of ohmic contact caused by alkali polishing has not been eliminated by optimizing the reaction process of alkali polishing. The study of different surface morphologies-modified samples under different tunnel oxide layer growth time, also reveals the difference in the influence of tunnel oxide layer characteristics on samples with different morphologies. The acid-polishing samples show more stable FF and conversion efficiency at different thermal oxidation time, and the micro-alkali texturing samples have a significant FF advantage at shorter thermal oxidation time. These studies can be applied and validated in the photovoltaic industry.

Insights on the Roles of Nitrogen Configuration in Enhancing the Performance of Electrocatalytic Methanol Oxidation over Pt Nanoparticles.

Stabilization of the Pt in N-doped carbon materials is an effective method to improve the performance of electrocatalytic methanol oxidation reaction (MOR). Nevertheless, the roles of different N configurations (pyridinic N, pyrrolic N, and graphitic N) toward the electrochemical performance of Pt-based catalysts remain unclear. Herein, Density Functional Theory calculations are adopted to elucidate the synergistic promotion of MOR by different N-configurations with Pt nanoparticles (NPs). Guided by the theoretical study, a series of MOR electrocatalysts with different ratios of pyridinic N and pyrrolic N (denoted as Pt/N-CNT-X (500, 600, 700, 800, and 900)) are designed and synthesized. Surprisingly, the electrocatalytic activity of Pt/N-CNT-600 with a suitable ratio of pyrrolic-N and pyridinic-N for MOR reaches 2394.7mAmg-1 Pt and 5515.8mAmg-1 Pt in acidic and alkaline media, respectively, which are superior to the Pt/CNTs, commercial Pt/C, and the ever-reported Pt-based electrocatalysts. The strong metal-support interaction induced by the N-doping is the crucial reason for the superior electrocatalytic performance. More importantly, the ability of pyrrolic-N and pyridinic-N in promoting the adsorption and oxidation of CH3 OH and the oxidation of CO* is substantiated for the first time in methanol oxidation. This work provides new insights on the design of efficient electrocatalysts for MOR.

Multi-stage oxidation of iron particles in a flame-generated hot laminar flow

The paper presents multi-parameter high-speed optical diagnostics of single iron particle oxidation in a hot laminar flow consisting of O2, H2O, CO2, and N2. Prior to luminous combustion, micron-sized particles are visualized using diffuse-backlight-illumination with high temporal and spatial resolutions, enabling in situ particle sizing. The incandescent burning particles are then monitored by direct high-speed imaging. This approach allows for a successful determination of the multiple oxidation stages of individual iron particles, including the solid phase, melting, and liquid phase. Two characteristic timescales are quantified as a function of the resolved particle diameter at various O2 volume fractions, namely the solid-phase oxidation time (SOT, defined as the time between the onset of rapid particle heating and melting) and the liquid-phase combustion time (LCT, defined as the duration between melting initiation and peak luminosity). SOT shows a linear dependence on the inverse O2 mass fractions at relatively high O2 levels but it tends to plateau when the O2 content is below 20vol.%. LCT is inversely proportional to the O2 mass fraction, suggesting that liquid-phase oxidation of iron particles is limited by external oxygen diffusion. The experimental LCT quantitatively agrees with a theoretical mode developed for nonvolatile particle combustion in the diffusion-limited regime, considering O2 as the only oxidant. This also implies that at the presence of O2, the oxidizing effect of H2O and CO2 on diffusion-limited iron particle combustion is negligible.

Low temperature synthesis of VO2 and hysteresis free VOx thin films with high temperature coefficient of resistance for bolometer applications

Vanadium dioxide (VO2) is an insulator to metal phase transition material, which finds many electronic and optical applications due to its reversible switching while VOx-based bolometers are widely used in commercial uncooled infrared detectors due to their high-temperature coefficient of resistance and low resistivity. Atmospheric pressure thermal oxidation (APTO) of Vanadium (V) is a simple process used to synthesize VO2 films without the need for precise control of oxygen partial pressure unlike other synthesis methods. In this work, we report the effect of reducing the V oxidation temperature to 250–450 °C during APTO and synthesize films with different oxidation durations. For an optimized oxidation duration at each oxidation temperature, VO2 films are obtained with more than two orders of resistance switching. This optimum oxidation duration is found to decrease exponentially with increase in oxidation temperature with an activation energy of 1.05 eV. The phase transition temperature of these VO2 films is found to decrease monotonically with decrease in oxidation temperature. We also observe that partially oxidized (oxidation time less than optimized oxidation duration to form VO2) VOx films show broad resistance switching from room temperature up to 70 °C instead of steep switching at the phase transition temperature. The partially oxidized film shows a temperature coefficient of resistance (TCR) as high as ∼10%/K, which is 3–4 times greater than TCR of commercial VOx thin films used in bolometers while showing similar resistivity. The resistivity of these films also exhibits almost zero hysteresis with temperature, an important requirement for bolometer applications. This study will widen the usefulness of the APTO process for fabricating VO2-based devices and high TCR VOx films for bolometer applications. The demonstrated low temperature process will especially be suitable to integrate VO2/VOx on substrates which can sustain only low temperatures such as some of the flexible substrates.

Time-Dependent Power-Law Growth of Oxide with Anomalous Diffusion in the Thermal Oxidation of 4H-SiC\((11\bar{2}0)\) and 4H-SiC\((000\bar{1})\)

A model for the oxide growth in the thermal oxidation of SiC with a non-polar surface orientation is proposed. It is based on the reaction–diffusion equations (RDEs), in which the diffusion of both SiO and O2 molecules is considered. By taking the 4H-SiC\((11\bar{2}0)\) a-face as an example, the RDEs are integrated numerically at the oxidation temperature of T = 1150 °C and the partial pressure of oxygen molecules in the ambient environment of Pox = 0.25, 0.5, 1, 2, and 4 (atm). By analyzing the simulation results on the evolution of the oxide thickness xo, it is found that xo obtained by the simulations and those of the experiments reported in the literature collapse onto a single curve when they are plotted against the rescaled time t′ = (ωp/ω1)t, where t denotes the oxidation time and ωp is defined as ωp = Θs(Pox)νinc. Here, Θs(Pox) and νinc denote the steady-state density of the oxygen molecules chemisorbed on the oxide surface and the prefactor for the incorporation rate of the oxygen molecules from the oxide surface into the oxide layer, respectively; ω1 is a constant, which is given by \(\omega_{1} = \omega_{p}|_{P_{\text{ox}} = 1(\text{atm})}\). The curve yielded by the collapse is found to follow the time-dependent power law (TDPL) as xo(t) ∝ (t/τ)ν(t), where the exponent ν(t) is given by \(\nu (t) = 0.565 + 0.2/(1 + \sqrt{2t/\tau } )\) with τ [= 1 (h)] a constant. This property is found to be valid also for the oxidation of a polar surface, 4H-SiC\((000\bar{1})\), by comparing the results of the calculations according to xo(t) ∝ (t/τ)ν(t) with the experiments reported in the literature. Therefore, the oxide growth in these systems follows the TDPL with the anomalous diffusion of νD = 0.565, which is larger than the normal diffusion of νD = 0.5 observed in the thermal oxidation of Si. In addition, the transition between the etching mode at low Pox and the oxidation mode at high Pox on the 4H-SiC\((11\bar{2}0)\) a-face is found to occur at \(P_{\text{c}} \simeq 0.73\) (atm) at T = 1150 °C.

Microstructural evolution of Ag-0.20wt-%Mg-0.19wt-%Ni alloy in under-oxidized condition

The under-oxidized condition (insufficient internal oxidation) for Ag-0.20Mg-0.19Ni (in wt-%) alloy was conducted at 650°C for 2 h, and the microstructural evolution in the alloy was investigated. The average grain size of the oxidized region and the unoxidized region are 3.82 µm and 3.86 m, respectively. The results suggest that the oxides enriched at grain boundaries do not hinder grain growth in the under-oxidized condition. The hardness of the oxidized region increases significantly, while the hardness of the unoxidized region decreases due to recrystallization. Both the number and the distribution area of MgO precipitates at the grain boundaries are increased with the internal oxidation time. Additionally, small MgO precipitates merge to form larger oxide particles with the internal oxidation time.

Influence of Cr Content on the High-Temperature Oxidation Behavior and Mechanism of Low-Alloy Steels.

The high-temperature oxidation behavior of low-carbon steel (AISI 1015, AISI 8617, AISI 4115) was investigated over the temperature range from 600 to 1000 °C in humid air containing 25% water vapor. Mass gain of oxidation measurement was performed to study the oxidation kinetics. The microstructure, thickness, and composition of the oxide scale formed were investigated via optical microscope (OM), scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS), X-ray diffraction (XRD), and electron probe microanalyzer (EPMA). The oxidation process was performed from 2 to 100 min. As the oxidation time increased, the trend of mass gain per unit area switched from a linear to a parabolic law, regardless of the steel grade used. As the chromium content increased, the duration of time during which the oxidation rate followed a linear relationship decreased. In the low-alloy steel with higher chromium content, the thickness of the mixed oxide layer containing Cr increased and the oxidation rate decreased at all oxidation temperatures.

Impact of thermal oxidation parameters on micro-hardness and hot corrosion of Ti-6Al-3Mo-2Nb-2Sn-2Zr-1.5Cr alloy

Protective oxide layers on Ti-6Al-3Mo-2Nb-2Sn-2Zr-1.5Cr (TC21) alloy with equiaxed microstructure considerably influence micro-hardness and hot corrosion resistance. The present work’s thermal oxidation of TC21 alloy was performed at 600, 700, and 800 °C for 5, 20, and 50 h durations. Hot corrosion methods in NaCl and NaCl + Na2SO4 salt media were applied to raw (unoxidized) and oxidized samples at 600 and 800 °C for 50 h. Hot corrosion was conducted at 600 °C for 5 cycles with 10-h steps. The best oxide layer thickness was observed at 800 °C, which increased with increased oxidation time and temperature. The surface hardness of the oxide layer at 800 °C was 900 ± 60 HV0.05 owing to the formation of TiO2 and Al2O3 phases. Raw material hardness was 342 ± 20 HV0.05, increasing threefold due to thermal oxidation. In the case of NaCl, weight loss dominated all samples except at 800 °C for 5 h. In the case of NaCl + Na2SO4, weight gain occurred at 600 and 800 °C for 5 h. Weight loss occurred for the raw samples and those processed at 800 °C for 20 and 50 h, where the oxide layer flaked off. Surface hardness increased upon hot corrosion testing because of the formation of brittle phases, such as TiO2 and Na4Ti5O12. Samples that oxidized at 800 °C for 5 h had the highest hardness and corrosion resistance.

Integration of a novel Chemical Looping Combustion reactor into a thermochemical energy storage system

This study analyses the performance of a back-up power process that uses a novel chemical looping packed bed air reactor to oxidize a batch of reduced solids while heating high pressure flowing air. In this arrangement, the solids are slowly oxidized by a diffusionally-controlled flow of oxygen perpendicular to the main air flow, thus imposing very long oxidation times for all reacting particles. A decay in the thermal power output of the reactor can be expected with time due to the increasing resistance to O2 diffusion towards the unreacted oxygen carrier particles as the reaction progresses. In this work, integration of the dynamic system formed by the reactor and the power plant used to produce power from the exploitation of the variable thermal output of the reactor is investigated. Different case studies are assessed for decarbonization of energy production and storage of renewable energy. The reactor is rated at a maximum 50 MWth power output in all cases, employing iron- or nickel-based particles as oxygen carrier. A simplified model for mass and heat transfer in the proximity of the wall orifices allows the definition of operating windows and reactor dimensions. In the chosen case examples, each single reactor operates in discharge mode for around 4–5 h (depending on plant configuration) as a back-up power generator, heating up a compressed air stream up to ∼ 1000 °C and achieving an energy density between 816 and 2214 kWhth/m3. Gas turbines in recuperative, steam injected and combined cycle power plant architectures integrated in the novel chemical looping combustion (CLC) reactor are investigated. Cycle efficiencies up to 49% are calculated for systems that make use of a single reactor configuration and exploit the residual heat for power production through a organic Rankine cycle (ORC) bottomed system. A more flexible multi-reactor configuration is also investigated to address the unavoidable decay in power output during discharge and provide power output controllability. The levelized cost of electricity (LCOE) is estimated be comparable to system elements from the literature when H2 is used as reducing gas. The use of biogas to reduce the solids during the energy charge stage is found to be particularly advantageous, leading to LCOE values between ∼ 120 and 175 €/MWh for the reference reactor system using iron-based solids. This also allows achieving negative CO2 emissions if the captured CO2 generated during the reduction stage is stored.

Effect of oxidized pyrite activating persulfate on the degradation of aniline aerofloat: Mechanism and degradation pathway

Aniline aerofloat (dianilinodithiophosphoric acid, DDA) is a common flotation collector for sulfide minerals, but it is also toxic and difficult to be degraded. In this study, oxidized pyrite was used to degrade DDA through activating persulfate (PS). It was found that oxidized pyrite was far more effective than fresh pyrite at removing DDA from a PS system over a wide pH range. The effect of the pyrite oxidation time, initial pH, PS concentration, pyrite dosage and pyrite particle size on DDA degradation in the pyrite-PS system were studied and optimal conditions determined. Through analysis of the total Fe ions concentration, radical species identification and XPS analysis of the change of surface species Fe and S, the DDA degradation mechanism in the oxidized pyrite-PS system was determined. The degradation products were measured by gas chromatography-mass spectrometry (GC–MS) and a potential DDA degradation pathway was hypothesized. The results in this study suggest a template for the utilization of oxidized pyrite in gangue minerals to remove DDA from the wastewater in mineral processing plants.

High temperature oxidation behavior of porous MoAlB ceramic from 800 °C to 1100 °C in air

MoAlB possesses the characteristics of both metals and ceramic materials, which has attracted extensive attention due to its excellent high-temperature oxidation resistance. For this reason, porous MoAlB is considered applicable to the practice of filtration under harsh environment. In this study, the high-temperature oxidation behavior of porous MoAlB ceramics is systematically studied at the temperatures ranging from 800 to 1100 °C. According to the results, the porous MoAlB exhibits good oxidation resistance at a maximum temperature of 1000 °C. The oxidation kinetics of porous MoAlB can be divided into three stages, and the estimated activation energies of the three stages are 253.83 kJ·mol−1, 367.48 kJ·mol−1 and 317.84 kJ·mol−1, respectively. In the stable stage at 1000 °C, the quadratic mass gain per unit area shows linearity over time, and the oxidation rate of porous MoAlB reaches 37.31 mg2·cm−4·h−1. As revealed by the analysis of the composition and microstructure of oxide layers, the main components of the oxide layer include MoO3, MoO2, Al2O3, B2O3. With the extension of oxidation time, the content of Al2O3 in the oxide films increases. The average pore size, permeability and open pore porosity of porous MoAlB show a trend of first decreasing and then tending to be stable. In addition, a discussion is conducted on the high-temperature oxidation mechanism of porous MoAlB.

Tensile crack inhibition of a PtReAl coated Ni3Al-based single crystal superalloy after long-term oxidation

Tensile behavior of Pt-aluminide (PtAl) coating with and without a middle NiRe layer on a Ni3Al-based single crystal superalloy after different oxidation times were investigated at room temperature (RT) and 1100 °C. The results revealed that the existence of the NiRe layer not only improved the oxidation resistance of the coating, but also performed a significant inhibition of crack propagation, contributing to a superior ductility of the oxidized Re modified PtAl (PtReAl) coated specimen. The tensile and cracking behaviors of the coated specimens at RT and 1100 °C were discussed in detail.