Oxide Scale Research Articles

High-temperature corrosion behavior of Cr2AlC with solid NaCl deposit in 30 vol% O2 + 70 vol% H2O environment at 1000 °C

Corrosion behavior of Cr2AlC in a high-temperature marine environment (with solid NaCl deposits in a 70 vol% H2O + 30 vol% O2) at 1000 °C was systematically investigated for the first time. This behavior was elucidated through analysis of complex corrosion products, microstructure of the oxide scale, and phase composition of the degraded region, supplemented by thermodynamic calculations. Synergistic effects of molten NaCl and water vapor, along with voids within the oxide scales and Na-induced amorphous Al2O3, promoted the loss of Al from substrate. Despite these factors, Cr2AlC was capable of spontaneously forming a protective oxide scale, which mitigates degradation. After 100 h of corrosion in a simulated marine environment at 1000 °C, Cr2AlC remained stable, exhibiting excellent corrosion resistance. Consequently, it holds significant promise for applications in high-temperature marine corrosion protection.

Oxidation kinetics and electrical properties of oxide scales formed under exposure to air and Ar–H2-H2O atmospheres on the Crofer 22 H ferritic steel for high-temperature applications such as interconnects in solid oxide cell stacks

A 100 h isothermal oxidation kinetics study for Crofer 22H was conducted in air and the Ar–H2-H2O gas mixture (p(H2)/p(H2O) = 94/6) in the range of 973–1123 K. The parabolic rate constant was independent of oxygen partial pressure in the range from 6.2 × 10−24 to 0.21 atm at 1023 and 1073 K, while at 973 and 1123 K it was higher in air than in Ar–H2-H2O. The scales consisted of Cr2O3 and manganese chromium spinel with an Mn:Cr ratio dependent on the oxidation conditions. Cross-scale resistance was evaluated with regards to the application of the steel in solid oxide fuel cells using a number of methods, including X-ray diffraction, scanning electron microscopy, confocal Raman imaging and area-specific resistance measurements.

Upcycling iron oxide scale slag into a high‐performance, sustainable ozone catalyst

Upcycling iron slag into a monolithic catalyst has led to low‐cost heterogeneous catalytic ozonation (HCO) strategies for water treatment. The primary industrial challenges are the low chemical oxygen demand (COD) reduction rate in treating authentic wastewater and difficulties sustaining close‐loop reaction cycles. In this study, we present a monolithic catalyst transformed from low‐cost iron oxide scale slag (IOSM) for highly efficient, sustainable ozone catalysis. The IOSM, constituted of 59.70% Fe2O3 and 40.30% Fe3O4, effectively decomposes ozone into superoxide radicals (·O2⁻) through a close‐loop cyclic reaction facilitated by interfacial charge transfer. This mechanism enables super‐fast degradation of 100 mg·L⁻¹ tetracycline at ozone concentrations below 1.00 mg·L⁻¹ in just four minutes, with the iron leaching merely at 59 μg·L‐1 after 10 cycles. In tests with authentic antibiotic wastewater, the IOSM‐based HCO system achieves a record‐breaking 81.70% COD reduction within two hours. This research underscores the potential of upcycling industrial waste into highly effective ozone catalysts for sustainable practices in wastewater treatment.

Upcycling Iron Oxide Scale Slag into a High-Performance, Sustainable Ozone Catalyst.

Upcycling iron slag into a monolithic catalyst has led to low-cost heterogeneous catalytic ozonation (HCO) strategies for water treatment. The primary industrial challenges are the low chemical oxygen demand (COD) reduction rate in treating authentic wastewater and difficulties sustaining close-loop reaction cycles. In this study, we present a monolithic catalyst transformed from low-cost iron oxide scale slag (IOSM) for highly efficient, sustainable ozone catalysis. The IOSM, constituted of 59.70 % Fe2O3 and 40.30 % Fe3O4, effectively decomposes ozone into superoxide radicals (⋅O2 -) through a close-loop cyclic reaction facilitated by interfacial charge transfer. This mechanism enables super-fast degradation of 100 mg L-1 tetracycline at ozone concentrations below 1.00 mg L-1 in just four minutes, with the iron leaching merely at 59 μg L-1 after 10 cycles. In tests with authentic antibiotic wastewater, the IOSM-based HCO system achieves a record-breaking 81.70 % COD reduction within two hours. This research underscores the potential of upcycling industrial waste into highly effective ozone catalysts for sustainable practices in wastewater treatment.

Synergy of Nanocrystallinity, Temperature, and "the Third Element Effect" for Uncommon Oxidation Resistance of Fe-Cr-Al Alloys.

Nanocrystalline structure, oxidation temperature, and "The Third Element Effect" are among the factors that can profoundly govern the characteristics of the oxide scales that develop on oxidation-resistant alloys, thereby, their synergistic effect can considerably influence alloys' oxidation kinetics. As a result of the synergy, certain iron-chromium-aluminium (Fe-Cr-Al) alloy showed superior oxidation resistance at 800°C than at 700°C (whereas oxidation resistance commonly decreases with the increase in temperature). The superior resistance at higher temperatures is considerably enhanced when the structure of the alloy is nanocrystalline vis-à-vis the common microcrystalline structure. Nanocrystalline alloy oxidizes at a negligible rate (c.f., its microcrystalline counterpart). The characterization of the oxide scale demonstrates that the oxidation temperature governs the formation of the protective oxide scale with/without the assistance of the "Third element Effect". The findings may potentially have considerable commercial implications.

Tribological performance of TiO2 nanoparticle-oil-water emulsion in the hot rolling process

This study aims to evaluate the lubrication performance of a nano-TiO2 oil-in-water (O/W) emulsion during the hot rolling process. A series of O/W emulsions with varying concentrations of TiO2 nanoparticles (0.05, 0.1, 0.3, and 0.5 wt.%) were synthesized. Tribological tests were conducted under a load of 70 N for 10 minutes to determine the optimal concentration based on anti-frictional properties. The O/W nano-emulsion optimized with a 0.1 wt.% concentration of TiO2 applied in the hot rolling process of IS 2062 E250 grade steel. This application resulted in a reduction of rolling force (RF) and surface roughness, suggesting its potential as an alternative lubricant. The results indicated superior antifriction performance at a TiO2 concentration of 0.1 wt.%, leading to a 15% reduction in RF. Additionally, the use of the nano-emulsion contributed to a significant reduction in oxide scale formation. Surface roughness measurements of the rolled samples revealed a 19% decrease, with a roughness value of 2.125 µm, compared to samples rolled with a nano-free O/W emulsion. These findings suggest that nano-TiO2 O/W emulsions could serve as an effective alternative to conventional O/W emulsions in future industrial metalworking applications.

An innovative strategy against oxide spallation of hot formed steels

Hot forming is a prominent technique to produce lightweight automotive steels. However, the generation of a weakly adhering oxide scale during hot forming and the subsequent post-processing of the scale pose a great threat to the shape precision of the product. Here, we propose a cost-effective solution to the spallation issue by incorporating minor silicate-molybdate additives into the rinse following pickling. The pre-deposited film serves as an effective barrier against high-temperature oxidation. Our innovative strategy enables the formation of an oxide scale that sticks to the substrate and paint layer, potentially eliminating the necessity for scale removal in industrial settings.

Element redistribution in the oxide scale during air oxidation of Kanthal AF alloy

The oxidation mechanism of Kanthal AF (FeCrAl alloy) was studied in the temperature range of 800–1200 °C through isothermal and thermo-cyclic oxidation tests. At 800 °C, tests involved 12-h cycles (up to 36 cycles), while at 1000 °C and 1200 °C, they were conducted isothermally (up to 432 h). Oxidation constants, oxide scale thickness, surface microstructure, and elemental composition were analyzed using TGA, SEM-EDXS, TEM, AES, XPS, GIXRD, and ToF-SIMS. The results show that the Al2O3 layer has a multilayer structure, defined by a naturally formed thin Cr-rich oxide layer on the alloy surface, which exhibits temperature-dependent selective permeability of metal cations, influencing the oxide scale growth. At 800 °C, inward oxide diffusion dominates due to limited cation permeability in the Cr-rich layer, while at higher temperatures, outward growth of the alumina scale is facilitated by increased permeability to metal cations. Despite the low Mg concentration in the alloy (0.01 wt%), Mg diffuses into the alumina rapidly, forming Mg-Al-Fe oxides that transform into MgAl2O4 spinel, impacting scale integrity and adhesion due to associated porosity. Consequently, Mg is considered an undesirable impurity, even at trace levels. Titanium forms separate oxides in the alumina scale, while zirconium and yttrium incorporate uniformly into the alumina scale.

Development of hybrid first principles – Artificial intelligence models for transient modeling of power plant superheaters under load-following operation

This paper develops different approaches for synergistic integration of physics-based models with data-driven models for modeling of high temperature power plant superheaters. Two types of data-driven models are developed, namely all-nonlinear static-dynamic neural network models as well as models obtained using a Bayesian machine learning approach. Series, integrated, and parallel coupling of first-principles models and data-driven models are proposed. Algorithms for solving the training problems for the data-driven models and for simulation of the hybrid models are developed. The developed approach is applied to high temperature power plant superheaters that face considerable modeling and measurement challenges. Measurement challenges arise due to harsh operating conditions that not only make placement of sensors difficult, but life of the placed sensors very limited. Modeling challenges arise due to complex inhomogeneous spatial distribution of flue gas and steam flowrates, especially under load-following operation and uncertainties in heat transfer characteristics because of multiple factors such as stochastic spatio-temporal variation of ash deposits on the superheater tubes in coal-fired power plants, internal oxide scale formation in the tubes, etc. First-principles two-dimensional differential–algebraic equation models of two industrial superheaters, one from a natural gas combined cycle plant and another from a coal-fired power plant, are developed. The results from the models are compared against industrial operational data. For all cases studied in this work, it is observed that both for steady-state and dynamic data, the hybrid models have much higher accuracy than when only the respective first-principles models are used. For example, during prediction of the average outside tube wall temperature of superheater tubes at the combined cycle power plant, the root mean squared error observed for the standalone first-principles model improved from 12.3 °C to 0.5 °C post hybridization with data-driven models. Similarly, while predicting the main steam outlet temperature in the coal-fired plant, the hybrid models resulted in reduction of the root mean squared error value from 19.5 °C to around 2 °C. In addition, the hybrid models yield highly resolved spatio-temporal temperature profiles that can be helpful for developing monitoring approaches of these critical components under load-following operation.

Investigation on oxidation behavior and mechanical properties of FeCoNiNbAlCrTa high entropy alloy at 900 °C

In recent years, eutectic high entropy alloys have been found to have excellent mechanical properties and corrosion resistance; however, the simultaneous achievement of these mechanical properties and high-temperature oxidation resistance still constitutes a tough challenge. In this study, Ta and Cr elements are added to (FeCoNiNb)98Al2 high-entropy alloy to improve oxidation resistance, and the changes in microstructure and mechanical properties of (FeCoNiNb)98-2x(TaCr)xAl2 as well as the oxidation behaviors at 900 °C are systematically investigated. The results show that the addition of Ta and Cr elements promotes the increase and growth of the laves phase in the alloy, which improves the oxidation resistance of the alloy and maintains the excellent mechanical properties of (FeCoNiNb)98Al2. The formation of CrTaO4, CrNbO4, and Cr2O3 composite oxide scales can not only prevent the diffusion of O into the alloy, but also inhibit the external diffusion of matrix elements. This result provide experimental data and theoretical support for the optimal design of the high-entropy alloy compositions to improve their antioxidant properties while maintaining excellent mechanical properties.

Utilization of hydrogen fuel in reheating furnace and its effect on oxide scale formation of low-carbon steels

The transition from fossil-based fuel to hydrogen combustion in steel reheating furnaces is a possible way to decrease the process-originated CO2 emissions significantly. This potential change alters the furnace gas atmosphere’s composition, impacting the oxide scale formation of the slab surface. Dynamic heating tests are performed for three low-carbon steels using different simulated combustion atmospheres, including natural gas, coke oven gas, and hydrogen combustion in air, and hydrogen combustion in oxygen. Significant differences are found in the oxidation behavior of steel grades in the simulated hydrogen reheating scenario. A steel grade with low Mn content only has an 18% increase in oxidation between methane-air to hydrogen-oxygen methods, while it is 41% for a high Mn and Si steel grade and 65% for a high-Mn steel grade. Thus, in terms of material loss increase by oxidation, the transition of the heating method causes the least problems for the low-Mn steel grade.

High‐Temperature Oxidation Response of 444 Ferritic Stainless Steel in a Synthetic Automotive Exhaust Gas

The high‐temperature oxidation behavior of 444 ferritic stainless steel has been studied in cyclic oxidation experiments using synthetic automotive exhaust gas atmospheres at 950 and 1050 °C. The weight gain per unit area of the 444 ferritic stainless steel following oxidation at 950 °C for 100 h iss 85.7% lower than recorded at 1050 °C. The oxide scale at both temperatures consisted of Fe–Cr and Mn–Cr spinels in the outer layer and Cr2O3 in the inner layer. Nodule formation and spallation of the oxide scale are identified as the main causes of breakaway oxidation. The depth of the internal oxides gradually increases with the oxidation time. The nucleation and growth of internal SiO2 result in the formation of metal protrusions, which are eventually consumed in the formation of a SiO2 layer. The SiO2 layer is formed at the interface between the oxide scale and the substrate at 1050 °C. The nucleation and growth of internal SiO2, in combination with lateral growth of SiO2 at the Cr2O3 layer/substrate interface contributed to the formation of the SiO2 layer.

Effect of hot coil immersion cooling process on microstructure and properties of strip steel and oxide scales

ABSTRACT Coils obtained at the end of hot rolling of four different low carbon steels (DX54D, HX180YD, DX51D and HCT590X) were subjected to immersion in water for cooling (IC) as against the normal natural cooling (NC). IC produces significant improvements in the microstructure, scale formation, distribution of mechanical properties and surface quality. A model developed to simulate thermal history in the hot coil being cooled indicates that the 0.1°C/min core cooling rate in NC increased by over 7 times in IC, thereby decreasing the temper softening effects. Results of the tests performed exhibit a greater uniformity in the longitudinal properties and a 30–50% reduction in the band spread. The volume fraction of carbide on the DX54D steel is reduced by 20–30%, and the yield platform length is increased from 2.6 to 3.4%. The IC process was observed to significantly inhibit the formation of the banded structure in the HCT590X steel and the average yield strength of the coil increased by ∼30 MPa. The thickness of the oxide scale in all the steels decreased by 30–40% and the FeO content in the scale increased by 10–20%.

New insight on the formation of uneven oxide scales on AFA steel in supercritical CO2: Roles of recrystallization degree on the high temperature corrosion resistance

Uneven oxide scale is a common phenomenon in high-temperature corrosion, but the formation mechanism has not been fully uncovered. A new alumina-forming austenitic (AFA) stainless steel with superior corrosion resistance in 650°C/15 MPa SC-CO2, has been systematically investigated. It is demonstrated that the uneven oxide was formed by the significant impact of the recrystallization behavior of AFA steel on its microstructural evolution and subsequent corrosion behavior. Compared with the thin oxide scale, the thick oxide scale was caused by the relatively higher density of dislocations and grain boundaries of matrix resulting from delayed recrystallization, which facilitated the rapid outward diffusion of ions.

Water vapor oxidation of SiC layer of tristructural isotropic particles

AbstractTristructural isotropic (TRISO) fuel particles, developed for use in high‐temperature gas‐cooled nuclear reactors, can be subjected to oxidizing environments in off‐normal accident scenarios. In this study, surrogate TRISO fuel particles were oxidized at 1000–1350°C for 4 h in 20 kPa water vapor atmosphere balanced with ultrahigh‐purity helium gas. The oxide scale morphology and thickness were studied via scanning electron microscopy, focused ion beam, and transmission electron microscopy. The oxide thickness increased as the oxidation temperature was increased. Although the oxide scale at 1000°C was completely amorphous, pockets of crystalline oxide were observed on particles oxidized at 1200 and 1300°C. Kinetic analysis was performed to deduce the oxidation mechanism by determining the apparent activation energy using linear regression analysis. The oxidation mechanism was consistent for temperatures from 1000 to 1200°C with an activation energy of 412.4 ± 8.8 kJ/mol. The activation energy then dropped to approximately 201 ± 7.1 kJ/mol for temperatures 1200–1350°C. Therefore, there is a change in oxidation mechanism at ∼1200°C. This change is attributed to the existence of a network of significant bubbles in the oxide layer at higher temperatures, which serve as rapid diffusion pathways for the transport of oxidants from the surface to the SiC/SiO2 interface, instead of relying on the bulk diffusion through the SiO2 layer at lower temperatures where only small bubbles are present along the SiC/SiO2 interface.

In-situ study on the differential evolution of He bubbles in the multilayer oxide of Fe9Cr1.5W0.4Si F/M steel corroded in lead-bismuth eutectic

The combined effects of corrosion and irradiation on nuclear components have been an important but not yet fully revealed topic. Here, the irradiation behavior of the oxide scale formed on F/M steel after lead-bismuth corrosion was in-situ investigated during He+ irradiation. The results showed that the oxide scale included a Fe3O4 outer oxide layer, a nanograin Fe(FexCr2-x)O4 spinel inner oxide layer, and an internal oxide layer. He bubbles formed in Fe3O4, Fe-Cr spinel and F/M steel were polygon, irregular elongated pores and small spheres, respectively. These differences were attributed to variations in defect generation, migration, and corrosion-induced crystal defects in different oxides. Numerous corrosion-induced nanograin boundaries and vacancies in Fe-Cr spinel exhibited more effective absorption of irradiation-induced defects. Moreover, rhombic perfect dislocation loops were detected in Fe3O4 at the late stage of irradiation, their relative positional relationship with He bubbles indicated a potential interaction between bubbles and loops.

The influence of CeO2 on the oxidation resistance of TaC/Ni composites

The in-situ TaC/Ni composites with different CeO2 content (0 wt%, 1 wt%, 2 wt%) were prepared by reactive sintering method, and their oxidation behavior in air at 1073 K was analyzed by static cyclic oxidation method to investigate the influence mechanism of CeO2 on the oxidation resistance of composites. The results show that the CeO2 particles are distributed around the TaC particles in the Ni matrix, and the oxidation behavior of composites with different CeO2 content conforms to the linear kinetic law. The oxide film is mainly composed of NiTa2O6 and a small amount of NiO. The generation reactions of Ta2O5 and NiTa2O6 induce a high expansion and compressive stress in oxide scale, leading to the formation of nonprotective oxide film with pores and cracks on the surface. As the addition of CeO2 increases from 0 wt% to 2 wt%, the thickness of oxide scale on composites obviously reduces from 505 μm to 122 μm, and the Ni and Ta oxides content decreases, leading to the reduction of pores and cracks in oxide scale. The Ce ion generated from the dissolution of CeO2 particles mainly distributes in the Ta oxides during the oxidation process, which hinders the outward diffusion of Ni and Ta ions, resulted in the improved oxidation resistance of TaC/Ni composites.

Rapid α-Al2O3 Growth on an Iron Aluminide Coating at 600 °C in the Presence of O2, H2O, and KCl.

In this work, a slurry iron aluminide-coated ferritic steel SVM12 was subjected to a laboratory experiment mimicking superheater corrosion in a biomass-fired power boiler. The samples were exposed under model Cl-rich biomass conditions, in a KCl + O2 + H2O environment at 600 °C for 168, 2000, and 8000 h. The morphology of corrosion and the composition of the oxide scale and the coating were investigated by a combination of advanced analytical techniques such as FESEM/EDS, SEM/EBSD, and XRD. Even after short-term exposure, the coating developed a very fast-growing and up to 50 μm thick α-Al2O3 scale in contrast to the spontaneous formation of a protective, thin, dense, slow-growing, and very adhesive α-Al2O3 layer usually formed on metallic materials after high-temperature oxidation. In view of the literature on the formation of oxide scales on alloys and coatings, the formation of an α-Al2O3 scale at this relatively low temperature is very surprising in itself. The thick alumina scale was not protective as its formation resulted in fast degradation of the coating and rapid Fe2Al5 → FeAl phase transformation, which in turn generated porosity inside the coating. In all cases, the resulting thick Al2O3 scale was porous and consisted of both equiaxed α-Al2O3 grains and randomly oriented aggregated alumina whiskers. Potassium is concentrated in the outer part of the Al2O3 scale, while chlorine is concentrated close to the scale/aluminide interface. The unexpected formation of rapidly growing α-Al2O3 at relatively low temperature is attributed to the hydrolysis of aluminum chloride generated in the corrosion process.

A study on the machinability of DMLS In718 alloy using an electro-spark machining process

ABSTRACT The direct metal laser sintering process is used to develop the nickel base superalloy DMLS In718 for the experimentation. The DMLS In718 alloy is evaluated to ensure the metallurgical qualities and mechanical properties. Microstructure of the DMLS In718 alloy is anisotropic in nature and the hatch bands are clear to infer. The hardness of the DMLS In718 is 275 Hv which equivalent to the commercially available inconel718 material. the mechanical strength and density of the DMLS In718 alloy is justifiable to the commercial material. The machining studies are performed with electro spark erosion process to report on surface quality, kerf taper and material removal rate. the minimum pulse on time has produced a fine surface quality compared to the maximum process condition. The surface topography in terms of oxide scale and recast layers are identified during to inefficient process conditions. This paper was an opportunity to deliberate the machining quality of the wire electro spark process.

Creep-to-rupture of T91 steel in static liquid lead-bismuth eutectic: Effects of cyclic temperature and oxygen environment

The creep-to-rupture behavior of T91 steel in static liquid lead–bismuth eutectic (LBE) is investigated, focusing on the impacts of cyclic temperature and oxygen condition. The results indicate that thermal cycling, oxygen deficiency, and high applied stress levels significantly accelerate creep deformation and reduce the creep-to-rupture lifetime of T91 steel in LBE. Surface oxide scales on T91 steel and their self-healing mechanisms play a crucial role in enhancing the creep resistance by isolating the LBE contact and delaying crack initiation and propagation. However, the integrity of this oxide scale is compromised under cyclic thermal conditions and low oxygen levels, leading to premature failure. Microstructural examinations reveal the evolution of oxide scale damage and self-healing mechanisms. The findings suggest that oxide scale failure mechanisms should be considered when designing the long-term operational performance of advanced LBE-based reactors.