Initial Stages Of Oxidation Research Articles

The high-temperature oxidation behavior of vacuum cladding CrNiFeMoCo high-entropy alloy (HEA) coatings was investigated. The HEA coating has a strong metallurgical bonding with the substrate and an FCC + σ eutectic structure. The HEA coating at 600 °C follows a single linear oxidation law, with k and n values of 4.15 × 10−5 mgn cm−2n min−1 and 1.118, while two steps make up the oxidation process at 700–800 °C: the initial stage of rapid oxidation and the steady-state stage of slow oxidation with lower k and higher n values. The oxidation product at 600 °C was Cr2O3, while oxidation products at 700–800 °C primarily consisted of Cr2O3 with a trace quantity of (Cr,Fe)2O3. The oxide layer's flat surface at 600 °C shows low-speed thickening behavior, while the oxide layer at 700–800 °C exhibits a two-stage thickening behavior: rapid thickening and densification during initial oxidation, and a low thickening rate during stable oxidation. The main oxidation mechanism is the prolonged interaction of O2 permeation, low oxide formation rate, and metal diffusion coefficient at 600 °C, while the HEA coating still exhibits excellent oxidation resistance at 700–800 °C due to the continuous generation and protection of dense oxidation products with Cr2O3 as primary oxide.

ABSTRACTSeveral newly designed Fe–Ni‐base alloys with different Fe content are prepared and the steam oxidation resistance of these alloys in high‐temperature steam at 650°C and 700°C was investigated by oxidation mass gain method, SEM observation and XRD analysis. The results show that the oxidation kinetics of 37Fe and 42Fe alloys at 650°C and 700°C both conform to the parabolic rule, the outer Ni–Fe spinel and the inner Cr2O3 are formed after oxidized for 1000 h, also accompanied by the internal oxidation of Al. The protective oxides containing external Cr2O3 and internal Al2O3 were obtained faster and more by the acceleration of Cr diffusion rate, which made the alloys have excellent steam oxidation resistance at 700°C. The 47Fe alloy loses mass after oxidation at 650°C for 60 h due to the formed iron oxides are easy to peel off at the initial oxidation stage, but follow the parabolic rule of stable oxidation at 700°C. When the Cr content in Fe–Ni–Cr alloy is lower than 18%, the corresponding Fe content should be lower than 42% to achieve the transformation of internal oxidation to external oxidation for Cr2O3 oxide. The oxidation mechanism and the influence of constituent elements were elucidated.

The early stages of oxidation and the development of transient initial oxides on 304HCu stainless steel (SS) were investigated by isothermal oxidation at 650 and 750 °C in a pure oxygen environment using thermogravimetry. At 750 °C, the formation of the continuous oxide layer occurs more rapidly, exhibiting protective parabolic kinetics, where the slow diffusion of iron through the oxide layer governs the oxidation rate. The oxide scales primarily consist of binary oxides of iron and chromium, with noticeable segregation of manganese and niobium in the early stages. Distinct morphological differences were observed in the transient initial oxide scales formed at the two temperatures, each providing additional nucleation sites for oxide formation. The GDOES depth profiles indicated the migration of Cu from the oxide/scale interface to the oxide scale. The role of the oxide composition and its morphology on the oxidation behavior of 304HCu SS are discussed in detail.

This study investigates the influence of Pt addition on the oxidation behavior of a Cr2O3‐forming superalloy. Inconel 718 (IN718) alloys with varying Pt content were prepared and subjected to isothermal oxidation tests. The results demonstrate that Pt significantly enhances the oxidation resistance of IN718, as evidenced by reduced weight gain, thinner oxide layers, and smaller oxide particles. Pt addition also increases the activation energy for both initial interface oxidation and ion diffusion during long‐term oxidation. Furthermore, Pt promotes the formation of a Cr2O3 layer while suppressing the formation of other undesirable oxides, resulting in a more cohesive and stable oxide layer. The improved oxidation resistance is attributed to two key factors: during the initial oxidation stage, Pt, as a noble element, reduces the activity of the primary oxide‐forming element Cr to oxidative environments, thereby lowering its susceptibility to initial oxidation at the metal–oxidant interface. During long‐term oxidation, Pt preferentially substitutes for Ni in major phases such as γ‐Ni(Cr,Fe) and γ′‐Ni3(Al,Ti), locally increasing the Cr composition. This promotes Cr oxidation, effectively suppressing the oxidation of Ni or Fe. These findings suggest that Pt addition is a promising approach for enhancing oxidation resistance in alloy design.

A two-dimensional diffusion-kinetic model is proposed to research the effect of oxygen diffusion along grain boundaries on the oxidation dynamics of the intermetallic alloy Ti3Al. The contribution of grain boundaries is evaluated by comparing the dynamics of processes in a structure with clearly defined grains and boundaries and in a material with effective properties, where the diffusion coefficient was calculated depending on the fraction of the boundary phase. Oxygen diffusion occurs in a mixed kinetic mode typical of additively fabricated nanoscale structures. The structure with an explicit consideration of grains and boundaries in the model has its symmetry. Rectangular grains are located relative to each other similar to "brickwork" so that they form triple junctions. The material with effective properties is a continuous rectangular region, in which the fraction of the boundary phase is taken into account through the diffusion coefficient. A constant oxygen source is specified on the surface. The problem is solved numerically in dimensionless variables. An implicit difference scheme of splitting by coordinates is used to solve the diffusion equation. To solve the kinetic equations, a method similar to the explicit Euler method is used with the organization of the iterative process. The results are compared for the isothermal mode and for the conditions of linear heating with subsequent cooling. The study is carried out for the initial stage of oxidation of the nanosized intermetallic alloy Ti3Al. The contribution of grain boundaries to the oxidation dynamics is estimated in the range of the fraction of the boundary phase from 0.1 to 0.5, which changes due to the variation of the grain sizes relative to the boundary width. The results obtained are in a qualitative agreement with the literature data.

Atomistic insight into the interfacial reaction and evolution between FeCr alloys and supercritical CO2 with impurities

Transforming oxidation: The impact of martensitic transition on Zr-O-N coating

Effect of Co distribution on the oxidation behavior of aluminide coatings in Mo-rich Ni-based single-crystal superalloy

Sanicro-25 is a high-temperature material used as the structural material for steam superheaters and reheaters in advanced ultra-supercritical power plants. The air oxidation behavior of Sanicro-25 with various surface roughnesses is being assessed at 650 °C for about 1000 h. Different surface-roughened samples were studied, namely polishing the sample up to diamond finish, grinding up to (80-grit finish and 600-grit finish) and grit blasted. The diamond finish sample showed more weight gain than others, and higher weight gain was observed in the initial oxidation stage. Attributed to different surface preparations leads to defects at different levels, which further alters the diffusion of various elements. The diamond finish sample showed the presence of Cr-rich oxides, and other samples showed the presence of Fe-rich oxides. Smooth surfaces promoted the formation of thick protective oxide scales.

Oxidation behavior of Fe-Ni Invar alloy under high pressure: A ReaxFF molecular dynamics study

The effect of crown ethers and polyglycols on the liquid-phase oxidation of cyclohexane and alkylaromatic hydrocarbons (toluene and p-xylene) with molecular oxygen catalyzed by transition metal salts has been investigated. It has been determined that crown ethers increase the reaction rate at both low and high conversion levels of cyclohexane and alkylaromatic hydrocarbons. The additives under study primarily affect the selectivity of the oxidation products. Crown ether and polyglycol additives to cobalt naphthenate increase the cyclohexanone to cyclohexanol molar ratio in cyclohexane oxidation. The crown ether additives to cobalt acetate increase the selectivity for alcohol in the initial stage of toluene and p-xylene oxidation. At higher alkylarene conversion, the additives enhance the selectivity for carboxylic acids. We assume that crown ethers and polyglycols form complexes with transition metal ions, changing the redox potential of the ions. This change in redox potential affects both the reaction rate and the selectivity of the oxidation products. The study concludes that crown ether and polyglycol additives influence the stages of the catalytic liquid-phase oxidation of hydrocarbons.

Combined dual-exposure test and DFT investigations into effects of interstitial hydrogen on oxide film of Alloy 600 in high temperature water

The stagnant water above the coal seam flows into the goaf, causing the goaf coal to be soaked by water for a long time. Compared with dry raw coal, water-soaked coal has a stronger tendency for spontaneous combustion, which poses a serious threat to mining operators. To unravel the impact of water immersion on coal's self-heating properties, an investigation was conducted employing techniques such as simultaneous thermogravimetric analysis/differential scanning calorimetry (TG/DSC), scanning electron microscopy (SEM), low-temperature nitrogen adsorption based on the BET theory, and Fourier transform infrared spectroscopy (FTIR). The variations in the characteristic temperature, microphysical structure, and active functional groups of bituminous coal with water immersion degrees of 10, 30, 50, and 100% were studied, and the experimental results showed that (1) during the initial stage of coal self-ignition oxidation, moisture can cause a delay in the characteristic temperature points of bituminous coal. When the degree of water saturation in bituminous coal reaches 100%, both the critical temperature (T 1) and the cracking temperature (T 2) peak at 48.14 and 205.06 °C, respectively. However, after the water evaporation phase is complete, water soaking promotes the spontaneous combustion of bituminous coal. (2) The number of pores and fractures in bituminous coal is positively correlated with the amount of water soaked, with the average pore diameter increasing from 10.124 nm in raw coal to 15.547 nm in the A4 coal sample. Moreover, when the degree of water immersion reaches 100%, the proportion of mesopores and macropores increases to 38.89 and 19.95%, respectively. (3) Compared to untreated coal, the number of functional groups in water-soaked coal samples increases. With the increase in water immersion, the hydroxyl (-OH) content of raw coal and four kinds of bituminous coal with different degrees of immersion was 40.8, 41.3, 42, 43.9, and 42.9%, respectively, showing a trend of increasing first and then decreasing. When the degree of water immersion of bituminous coal is 50%, the natural tendency is the strongest. These findings contribute to elucidating the underlying mechanism of water immersion's impact on coal self-ignition, thereby holding significant implications for enhancing fire safety measures in mine working areas.

Atomic-Scale Dynamics of the Initial Stages of Cu and Cu Alloy Oxidation

Complex multi-element alloys are gaining prominence for structural applications, supplementing steels, and superalloys. Understanding the impact of each element on alloy surfaces due to oxidation is vital in maintaining material integrity. This study investigates oxidation mechanisms in these alloys using a model five-element equiatomic CoCrFeNiMn alloy, in a controlled oxygen environment. The oxidation-induced surface changes correlate with each element’s interactive tendencies with the environment, guided by thermodynamics. Initial oxidation stages follow atomic size and redox potential, with the latter becoming dominant over time, causing composition inversion. The study employs in-situ atom probe tomography, transmission electron microscopy, and X-ray absorption near-edge structure techniques to elucidate the oxidation process and surface oxide structure evolution. Our findings deconvolute the mechanism for compositional and structural changes in the oxide film and will pave the way for a predictive design of complex alloys with improved resistance to oxidation under extreme conditions.

Initial stage oxidation corrosion of commercial ferritic stainless steels with different Cr contents at 650 °C for solid oxide fuel cells

Diffusion of alloying elements during high temperature oxidation in a low-cost third generation Ni-based single crystal superalloy

Oxidation kinetics of typical high FeO ferrous spinels

Non-enzymatic oxidation is a primary factor affecting wine quality during bottling or aging. Although red and white wines exhibit distinct responses to oxidation over time, the fundamental mechanisms driving this transformation remain remarkably uniform. Non-enzymatic oxidation of wine commences with the intricate interplay between polyphenols and oxygen, orchestrating a delicate redox dance with iron and copper. Notably, copper emerges as an accelerant in this process. To safeguard wine integrity, sulfur dioxide (SO2) is routinely introduced to counteract the pernicious effects of oxidation by neutralizing hydrogen peroxide and quinone. In this comprehensive review, the initial stages of non-enzymatic wine oxidation are examined. The pivotal roles played by polyphenols, oxygen, iron, copper, and SO2 in this complex oxidative process are systematically explored. Additionally, the effect of quinone formation on wine characteristics and the intricate dynamics governing oxygen availability are elucidated. The potential synergistic or additive effects of iron and copper are probed, and the precise balance between SO2 and oxygen is scrutinized. This review summarizes the mechanisms involved in the initial stages of non-enzymatic oxidation of wine and anticipates the potential for further research.

We prepared 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized samples from never-dried Japanese cedar (JC) holocellulose, JC-callus, and bacterial cellulose (BC). The original never-dried samples and their TEMPO-oxidized products were characterized by neutral sugar composition analysis. TEMPO-oxidized cellulose nanofibrils (TEMPO-CNFs) were prepared from the TEMPO-oxidized samples by ultrasonication in water. The carboxy groups in TEMPO-CNFs were position-selectively esterified with 9-anthryl diazomethane (ADAM) to prepare TEMPO-CNF-COOCH2-C14H9 samples, which had UV absorption peak at 365 nm. The mass-average degree of polymerization (DPw) values of 1% lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) solutions of the original samples were determined by size-exclusion chromatography in combination with multi-angle laser-light scattering, ultraviolet absorption, and refractive index detection (SEC/MALLS/UV/RI), and were 5490, 2660, and 2380 for the JC holocellulose, JC-callus, and BC samples, respectively. The TEMPO-CNF-COOCH2-C14H9 sample solutions in 1% LiCl/DMAc were analyzed by SEC/MALLS/UV/RI to obtain SEC elution patterns. The patterns corresponded to the molar mass and carboxy group distributions of the samples, which were detected by RI and UV absorption of anthryl groups, respectively. The carboxy groups existed in the entire molar mass distribution regions of all the TEMPO-CNF samples, although their lower molar mass regions contained higher carboxy group densities. The obtained results indicate that random depolymerization occurred on the cellulose microfibril surfaces at the initial stage of TEMPO-catalyzed oxidation and/or ultrasonication in water. This depolymerization mechanism can explain all the obtained SEC-elution patterns of the TEMPO-CNFs, without considering the presence of periodically disordered regions in the cellulose microfibrils of the never-dried cellulose samples.Graphical abstract