High-temperature Oxidation In Air Research Articles

Microstructure evolution and high temperature air oxidation behaviour of thick Cr coatings at 1200 °C

The thick Cr coated Zr-4 alloys were prepared by magnetron sputtering deposition and their microstructure evolution and high-temperature air oxidation behaviour were investigated. Oxidation tests showed that the thick Cr coatings can improve the high-temperature air oxidation resistance of Zr-4 alloy even if the α-Zr(O) layer was formed at some regions. The mechanism of high-temperature air oxidation was also discussed in detail, and these experimental results could provide data for establishing a reliable prediction model of this degradation.

Electronic Oxide-Metal Strong Interactions (EOMSI) Localized at CeOx-Ag Interface.

Electronic oxide-metal strong interactions (EOMSI) refer to the electronic oxide-metal interactions (EOMI) between oxide adlayers and underlying metal substrate that is strong enough to stabilize supported oxide adlayers in a low-oxidation state, which individually is not stable under an ambient condition, from high temperature oxidation in air to a certain extent. Herein we report the deposition and electronic structure of CeOx adlayers on capping ligand-free cubic Ag nanocrystals, i.e., CeOx/Ag inverse catalysts. The EOMI occur via the charge transfer from Ag substrate to CeOx adlayers in the CeOx/Ag inverse catalyst, and the EOMSI are observed in the CeOx/Ag inverse catalyst with the average thickness of CeOx adlayers about 0.9 nm to exclusively form Ce2O3 adlayers stable against oxidation at 400 °C. As the thickness of CeOx adlayers increases, ceria adlayers with oxygen vacancies (CeO2-x) emerge and grow in the CeOx/Ag inverse catalysts, and the Ce3+/Ce4+ ratio decreases. Catalytic performance of CeOx/Ag inverse catalysts in the CO oxidation reaction is closely linked with the thickness and electronic structure of CeOx adlayers. These results demonstrate that the EOMSI and EOMI in the oxide/metal inverse catalysts are localized at the oxide-metal interface and sensitively vary with the thickness of oxide adlayers, offering a strategy of thickness engineering to tune electronic structures of oxide adlayers in oxide/metal inverse catalysts.

High Temperature Air and Steam Oxidation and Fireside Corrosion Behavior of 304HCu Stainless Steel: Dichotomous Role of Grain Boundary Engineering

High Temperature Air and Steam Oxidation and Fireside Corrosion Behavior of 304HCu Stainless Steel: Dichotomous Role of Grain Boundary Engineering

Overpotential on Oxygen-Evolving Platinum and Ni-Fe-Cu Anode for Low-Temperature Molten Fluoride Electrolytes

To eliminate climate gas emissions from aluminum electrolysis, modifying a cryolite-based electrolyte partly replacing Na with K reduces liquidus, allowing a process temperature of 800°C. This enables the use of various metallic alloys for oxygen-evolving inert anode technology. This alternative process requires a higher energy efficiency to compensate for an increased reaction voltage, which highlights the importance of evaluating the kinetics and overpotential on oxygen-evolving anodes. This study evaluates anodic overpotentials using steady-state polarization on platinum and three Ni-Fe-Cu-based alloy compositions in a KF-NaF-AlF3-Al2O3(sat.) electrolyte at 800°C. The polarization curve on the platinum anode reveals two linear Tafel regions, while Ni-Fe-Cu anodes exhibit a single Tafel region. Notably, Ni-Fe-Cu anodes treated with high-temperature air oxidation to develop a pre-formed oxide layer exhibit better electrocatalytic activity than untreated anodes of corresponding composition. The kinetic equations, based on a theoretical model for the proposed mechanism of the oxygen evolution reaction, are derived and utilized to simulate overpotential and current, taking into account surface coverage. This model accurately predicts the two experimentally observed Tafel regions on the platinum anode, indicating a two-step charge transfer-controlled mechanism. We illustrate that multiple Tafel slopes can be attributed to the potential-dependent surface coverage of an adsorbate and can be correlated with the particular rate-determining step.

Accelerated Formation of Oxide Layers on Zircaloy-4 Utilizing Air Oxidation and Comparison with Water-Corroded Oxide Layers.

For the dry storage of Canada Deuterium Uranium (CANDU) spent nuclear fuels, the integrity of Zircaloy-4 fuel cladding has to be verified. However, the formation of ~10 µm-thick oxide layers in typical CANDU reactor operating conditions takes several years, which makes sample preparation a slow process. To overcome such limitations, in this study, an accelerated formation of an oxide layer on Zircaloy-4 cladding tube was developed with a combination of high-temperature water corrosion (HT-WC) and air oxidation (AO). First, Zircaloy-4 tubes were corroded in oxygenated (2 ppm dissolved oxygen) high-temperature water (360 °C/19.5 MPa) for 500 h. Then, the tubes were air-oxidized at 500 °C for 30 h. Finally, the tubes were corroded again in HT-WC for 500 h to produce ~10 µm-thick oxide layers. The morphology and characteristics of the oxide layer in each step were analyzed using X-ray diffraction, scanning and transmission electron microscopy. The results showed that the oxide layer formed in the accelerated method was comparable to that formed in HT-WC in terms of morphology and oxide phases. Thus, the accelerated oxide formation method can be used to prepare an oxidized Zircaloy-4 cladding tube for CANDU fuel integrity analysis.

Performance Evaluation of Low-Temperature KF-NaF-AlF3 Electrolytes for Aluminum Electrolysis Using Vertical Inert Cu–Ni–Fe Alloy Anodes

In this study, the performance of low-temperature electrolytes in a 40 A laboratory oxygen-evolving aluminum electrolysis cell with vertical inert electrodes for two compositions of NaF-KF-AlF3 based electrolyte is investigated. Two compositions of Cu–Ni–Fe alloy, single-phase homogenized, 20Cu-42Ni-38Fe wt% and 5Cu-48Ni-47Fe wt%, are evaluated as anodes. Titanium diboride (TiB2) is used as a wetted cathode. The characteristics of a protective oxide layer, pre-formed on the anode through high-temperature air oxidation, are examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM). It is found that a multilayered oxide morphology, revealing Fe2O3 and NiFe2O4 as major constituents, is dense and adherent to the base alloy. The effects of electrolyte compositions, anode alloys, and electrolysis conditions on cell voltage evolution, current efficiency, contamination levels in the electrolyte and produced aluminum, and anode wear rate are systematically studied. A protective oxide layer, formed through oxidation treatment on the 20Cu-42Ni-38Fe wt% alloy, not only remains compact post-electrolysis but also performs significantly better in a K-rich electrolyte in terms of wear rate and the purity of the aluminum obtained. Influences of electrolyte composition on anode degradation behavior are discussed.

REDOX NANOSTRUCTURING OF BIPOROUS NICKEL (II) SINTERED USING A SPACE HOLDER

Permeable metallic nickel and ceramic nickel-oxide materials with nanostructured surface and multilevel hierarchical porosity were created by cyclic redox post-treatment of biporous nickel (II) consolidated in the sintering-dissolution process. Additional levels of intraparticle porosity – Kirkendall pores and shrinkage nanopores – were formed during the stages of high-temperature oxidation in air and reduction in hydrogen, respectively.

The dynamic thermophysical properties evolution and multi-scale heat transport mechanisms of 2.5D C/SiC composite under high-temperature air oxidation environment

The variations in thermophysical properties and dynamic heat transfer mechanism of 2.5D C/SiC ceramic matrix composites (2.5D C/SiC-CMC) under a high-temperature air oxidation environment are investigated by experiments and numerical simulations. A new multi-scale thermal analysis model of 2.5D C/SiC-CMC under high-temperature oxidation is proposed to predict its equivalent thermal conductivity and analysis its multi-scale heat transport mechanisms. The multi-scale thermal analysis model is developed by blending the multi-scale asymptotic thermal analysis method and oxidation kinetics theory, which includes the micro-scale model and mesoscale model. The micro-scale model simulates the oxidation process of the carbon fibers and PyC interface through oxidation kinetics, which predicts the varying equivalent thermal conductivity of yarns with oxidation. The mesoscale model is constructed based on the experimental statistics which reflect the multi-scale structure within the 2.5D C/SiC-CMC with oxidation. The mesoscale model introduces oxidation characteristics by considering dynamic variations in yarn thermal properties. The dynamic thermophysical properties of the 2.5D C/SiC-CMC with oxidation are tested in the experimental study, which verifies that the multi-scale thermal analysis model has highlighted prediction accuracy. The results show that high-temperature oxidation causes significant variations in the dynamic thermal behavior of 2.5D C/SiC-CMC which is critical for the practical thermal protection design of 2.5D C/SiC-CMC hot components in engineering applications.

Nitrogen quantification and tracking during high temperature oxidation in air of titanium using 15N isotopic labelling

Isotopic labelling was used to track the diffusion of nitrogen during the oxidation of Titanium in air at 700 °C. Alternate exposure in 15N2–labelled air and regular air was used. The nitrogen is mainly located at the oxide/metal interface and forms essentially a nitride phase close to Ti2N. Each nitrogen isotope was quantified by Nuclear Reaction Analysis. Nitrogen quantity doubles between 5 and 20 h, which represents 16% respectively 12.5%, of the total mass gains. The nitrogen is partially renewed by both inward and outward diffusion during the oxidation. A model for nitrides migration is proposed.

On the high-temperature oxidation of ZnSb for thermoelectric applications

Thermoelectric ZnSb has a native surface oxide layer of Sb2O5 +ZnO, while HT oxidation in air resulted in selective oxidation to ZnO, with no detectable Sb by STEM-EDS. The ZnO consisted of an inner nano-granular and a more columnar outer layer. Thermogravimetry showed parabolic oxidation kinetics at 200–325 °C with an activation energy of 117 kJ/mol, comparing well with literature for oxidation of Zn. Two-stage 16O2 +18O2 oxidation followed by SIMS suggests growth by mixed Zn and O diffusion through a protective ZnO layer that still cannot prevent considerable high temperature oxidation in air, with formation of insulating electrical contacts, unless metallised.

Oxidation kinetics and microstructure evolution of air oxidation behavior of TC18 alloy

The high-temperature air oxidation behaviors at 600 °C, 700 °C and 800 °C of the TC18 alloy were systematically studied. The oxidation kinetics of TC18 alloy, the phase composition, microscopic morphology and chemical composition of the surface oxide films were analyzed to elucidate possible oxidation mechanisms. The results revealed that the oxidation behavior of TC18 alloy followed a linear-parabolic law at 600 °C and 700 °C while being governed by a simple linear law at 800 °C. The long-term oxidation for 24 h at 600 °C and 700 °C resulted in the oxide films composed of both Ti3O and TiO2, with dominant Ti3O and TiO2 respectively for the oxide films formed at 600 °C and 700 °C specifically. Especially for the oxidation at 800 °C, the oxide film was revealed to consist of three layers of the outer layer Al2O3, the secondary outer layer TiO2 and the dominant inner layer TiO2.

A comparative study on high-temperature air oxidation of Cr-coated E110 zirconium alloy deposited by magnetron sputtering and electroplating

Chromium coatings were deposited either by magnetron sputtering and electroplating on E110 zirconium alloy. The as-deposited Cr coatings showed dense microstructure, but different mechanical properties and adhesion behavior depending on the deposition technology. High-temperature oxidation was performed in air at 1100 °C for 40 min. The magnetron-deposited coatings had a stable oxidation behavior which was improved by increasing coating thickness. Surface activation of E110 alloy prior to Cr electroplating resulted in formation of the interlayer with a thickness of 7–12 μm between the coating and the alloy containing hydride and fluoride phases. It was shown that cracks and defects in this interlayer of the electroplated Cr coatings affected the coating adhesion and resulted in lower oxidation resistance compared to the magnetron-deposited coatings.

Improving the flotation separation of chalcopyrite from galena through high-temperature air oxidation pretreatment

A method of air oxidation pretreatment at 170 °C was developed for the selective separation of chalcopyrite and galena. Single mineral and artificially mixed mineral flotation experiments indicated that the hydrophobicity of chalcopyrite was greatly reduced, and galena maintained outstanding floatability after pretreatment by high-temperature air oxidation. Hence, the efficient flotation separation of chalcopyrite and galena was achieved. Zeta potential and FTIR analysis illustrated that the chemisorption strength of collector sodium butyl xanthate (SBX) on the surface of galena was higher than that on chalcopyrite based on the oxidation pretreatment method. XPS analysis proved that oxidation could occur on the surfaces of chalcopyrite and galena with pretreatment by high-temperature air oxidation, but the oxidation extent of chalcopyrite was greater than that of galena. Moreover, the FeOOH and CuO hydrophilic species formed on the chalcopyrite surface greatly increased the hydrophilicity of chalcopyrite and impeded the adsorption of SBX on the chalcopyrite surface. By contrast, the galena surface was extremely difficult to oxidize to PbO during air oxidation at 170 °C due to the high stability, and the chemical reaction of SBX on the galena surface was still violent. Therefore, the flotation separation of chalcopyrite and galena can be efficiently realized using high-temperature air oxidation method to treat minerals.

A Comparative Study on High-Temperature Air and Steam Oxidation of Cr-Coated Zr-4 Alloy Prepared by Multi-Arc Ion Plating

A Comparative Study on High-Temperature Air and Steam Oxidation of Cr-Coated Zr-4 Alloy Prepared by Multi-Arc Ion Plating

Improved oxidation stability of carbon-coated Ni nanoparticles synthesized by one-step electrical wire explosion

This study demonstrates a rapid one-step route to prepare high-purity carbon-coated Ni (Ni@C) nanoparticles via electrical wire explosion in methane gas used as a carbon source, and also investigates an oxidation stability of Ni@C nanoparticles. The Ni@C nanoparticles have smaller average particle size and narrower particle size distribution than the passivated Ni (Ni@P) nanoparticles and show positive dependence of carbon layer thickness on core Ni particle size. The thermal oxidation of Ni@C nanoparticles is closely related to the burn-off of protective carbon shells. From a thermogravimetry analysis to investigate the oxidation kinetics of Ni nanoparticles, the activation energy Ea for oxidation of Ni@C nanoparticles is determined to be 161.31–170.34 kJ mol−1, which is much higher than the Ea value (81.22 kJ mol−1) of Ni@P nanoparticles. This confirms that the carbon shell effectively prevents the active core Ni nanoparticles from high temperature oxidation in air.

Analysis of plasma gun sprayed coatings on SS-304 steel to evaluate cyclic oxidation and hot corrosion

Power plants, gas power turbines and chemical based plants face a very big issue of accelerated type of corrosion i.e hot corrosion, because of which the lifespan of metal decreased to large extent. In the present investigation, S-304 steel was taken which is commonly used in thermal power plants for inspection of accelerated corrosion i.e hot corrosion and high temp. oxidation behaviour. Alumina plus 13% titanium(Al2O3 + 13%TiO2), Alumina plus 3% titanium (Al2O3 + 3%TiO2) , Alumina(Al2O3)powder was applied on the boiler steel samples by using plasma spraying process. The uncoated and coated samples were exposed for 50 cycles to cyclic high temperature oxidation in air at 900 °C and hot corrosion in molten salt conditions of sodium sulphate and vanadium oxide (Na2SO4 – 60% V2O5) at 900 °C. In Oxidation study, with weight gain of 1.86% the upmost resistance against oxidation was exhibited by Alumina plus 13% titanium coated(Al2O3 + 13%TiO2) followed by Alumina plus 3% titanium coated (Al2O3 + 3%TiO2) with weight gain of 2.36% and by 2.92% by Alumina coated(Al2O3). The least resistance was shown by bare S-304 with weight gain of 3.91%.In investigation of hot corrosion, the weight gain percentages of Alumina plus 13% titanium coated(Al2O3 + 13%TiO2) is 2.46%, Alumina plus 3% titanium coated (Al2O3 + 3%TiO2) coated is 2.92%, Alumina coated(Al2O3) is 3.77% and for uncoated its 4.67%. The outcomes obtained for protection against oxidation and hot corrosion is: plus 13% titanium (Al2O3 + 13%TiO2) > Alumina plus 3% titanium (Al2O3 + 3%TiO2) coated > Alumina(Al2O3) > uncoated S-304 boiler steel.

High-temperature air-oxidation of NiCoCrAlx medium-entropy alloys

The oxidation behaviour of four NiCoCrAlx medium-entropy alloys (x = 0, 0.1, 0.3, or 0.5 mol.) was investigated in dry air at 600–900 °C. The oxidation kinetics of all the alloys followed the parabolic rate law at T> 700 °C, and the oxidation rates increased with an increase in temperature and a decrease in Al content. Discontinuous oxide granules were formed on all the alloys at 600 °C, while complex scales were detected, strongly depending on the Al content and temperature. Internal attack of AlN precipitates was also observed for Al-containing alloys at T> 700 °C.

Protection of Zr Alloy under High-Temperature Air Oxidation: A Multilayer Coating Approach

Metallic Cr and multilayer CrN/Cr coatings with a thickness of 2.5 µm were deposited onto E110 alloy by magnetron sputtering. Oxidation tests in air were performed at 1100 °C for 10–40 min. The gravimetric measurements showed better protective properties of multilayer CrN/Cr coatings in comparison with metallic Cr coating. Multilayer coating prevented fast Cr–Zr inter-diffusion by the formation of a ZrN layer beneath the coating. The appearance of ZrN is caused by interaction with nitrogen formed from the decomposition of CrN to Cr2N phases. Optical microscopy revealed a residual Cr layer for the multilayer CrN (0.25 µm)/Cr (0.25 µm) coating for all the oxidation periods. Additional in situ X-ray diffraction (XRD) studies of coated alloy during linear heating up to 1400 °C showed that the formation of the Cr2Zr phase in the case of multilayer coatings occurred at a higher (~150 °C) temperature compared to metallic Cr. Multilayer coatings can decrease the nitrogen effect for Zr alloy oxidation. Uniform and thinner oxide layers of Zr alloy were observed when the multilayer coatings were applied. The highest oxidation resistance belonged to the CrN/Cr coating with a multilayer step of 0.25 µm.

High-Temperature Air and Steam Oxidation and Oxide Layer Characteristics of Alloy 617

Nickel-based superalloys are the candidate materials for many high-temperature applications, especially in advanced ultra-supercritical coal-fired power plants and in the next-generation nuclear power plants. This paper reports the results of a comprehensive study on chemical composition, structure and kinetics of oxide film formation of a nickel-based superalloy, alloy 617, in ambient air and steam at 750 °C for a duration of 500 h. The morphology and nature of oxide scales have been characterized by scanning electron microscope with energy-dispersive x-ray attachment, grazing incidence x-ray diffraction technique and glow discharge optical emission spectrometry (GDOES). The mass gain of alloy 617 in steam was higher than that in air, and followed a parabolic rate law for both atmospheres. The depth profiles of the oxide films obtained by GDOES showed the presence of an outer chromium oxide scale with mixed oxides of nickel and aluminum at the interface. The oxidation kinetics of alloy 617 and the nature of oxide scales formed during the steam and air oxidation are discussed.

Electronic Oxide-Metal Strong Interaction (EOMSI).

Strong metal-support interaction of supported metal catalysts is an important concept to describe the effect of metal-support interactions on the structures and catalytic performances of supported metal particles. By using an example of CeOx adlayers supported on Ag nanocrystals, herein a concept of electronic oxide-metal strong interaction (EOMSI) is put forward; this interaction significantly affects the electronic structures of oxide adlayers through metal-to-oxide charge transfer. The EOMSI can stabilize oxide adlayers in a low oxidation state under ambient conditions, which individually are not stable; moreover, the oxide adlayers experiencing the EOMSI are resistant to high-temperature oxidation in air to a certain extent. Such an EOMSI concept helps to generalize the strong influence of oxide-metal interactions on the structures and catalytic performance of oxide/metal inverse catalysts, which have been attracting increasing attention.