Protective Oxide Research Articles

High temperature oxidation behaviour of polycrystalline and single crystal Ta stabilized γ'-strengthened Co-Ni-Al-Ta-Cr alloys

Isothermal oxidation was carried out on the polycrystalline and single crystal γ'-strengthened Co-Ni-Al-Ta-Cr alloys at 800–1000 ℃. The oxidation kinetic of both alloys follows logarithmic, cubic and parabolic law at 800 ℃, 900 ℃ and 1000 ℃, respectively. The polycrystalline alloy exhibits superior oxidation resistance at 800–1000 ℃, which can be explained by the effects of grain boundary. Grain boundary diffusion enhances the formation of the protective spinel oxides layer at 800–900 ℃. The beneficial effect of the grain boundary on the spallation resistance of oxides results that the polycrystalline alloy maintains better oxidation properties at 1000 ℃.

Effect of WSi2 content on oxidation behavior of MoSi2-20 vol% Al2O3 composites

(Mo,W)Si2–20 vol%Al2O3 composites containing 0, 2.5, 5 and 10 mol% WSi2 were prepared by pressureless sintering at 1550 °C in H2 atmosphere, with the raw materials of ultrafine (Mo,W)Si2 and nano-sized Al2O3 powders. All of the samples underwent isothermal oxidation experiments at 1500 °C in air, and surfaces of samples were covered by an intact and dense oxide layer consisting of amorphous SiO2 and Al2O3. It was concluded that introduction of WSi2 into the MoSi2-Al2O3 composites effectively reduced oxidation losses and enhanced oxidation resistance, and meanwhile, the effect was more pronounced with the increase in addition amount. The enhanced oxidation resistance after adding WSi2 was mainly attributed to higher diffusion energy barrier of Si atoms in WSi2 than in MoSi2. Moreover, the lattice distortion initiation by the W dissolved in MoSi2 suppressed the formation of the MoO3/WO3 and promoted the generation of an intact protective oxide scale.

Study on the role of solution treatment on corrosion behavior of duplex lightweight steel in different environments

Diverse microstructure and complex application environments increases the uncertainty of the corrosion resistance of lightweight steels. The effect of solution treatment on the corrosion behavior of Fe–16Mn–10Al–1.5C–0.1Ti lightweight steel in Cl−, HSO3− and Cl−–HSO3− environments was investigated using electrochemical measurement, scanning electron microscope (SEM) and X–ray photoelectron spectroscopy (XPS). The lightweight steels are dominated by austenite and contain a small amount of ferrite. The increase in solution treatment temperature leads to more ferrite formation, but it has less effect on grain size. The decrease in austenite content results in more corrosion microcells and a porous oxide film; therefore, the corrosion resistance of the steel deteriorates with increasing temperature. In addition, in the Cl−–HSO3− environment, the synergistic effect of Cl− and HSO3− leads to the formation of a weak protective oxide film, resulting in a significant increase in corrosion rate compared to the Cl−and HSO3− environment.

Construction of C/SiC–Cu3Si–Cu interpenetrating composites for long-duration thermal protection at 2500 °C by cooperative active-passive cooling

Developing materials which can resist long-term ablation at ultra-high temperatures above 2200 °C in oxygen-containing environments is of prime importance for the thermal protection of aerospace vehicles, but remains a great challenge. C/SiC composites are attractive candidates for long-term use, but they are often severely ablated above 1650 °C due to the damage of protective oxide scale. Here, C/SiC–Cu3Si–Cu interpenetrating composites with interconnected ceramic and metal matrixes are developed by the selective ceramization of carbon-fiber reinforced carbon aerogel preforms. The heat radiation of C/SiC–Cu3Si–Cu, transpiration of Cu2O, evaporation of SiO2, as well as inhibition of oxygen diffusion in the glassy scale, jointly lead to the cooperative active-passive cooling during ablation. Resultantly, their surface temperatures are 150 °C, 450 °C and 750 °C lower than those for C/SiC (1900 °C, 2200 °C and 2500 °C) with a duration of 600 s ablation, respectively. They also exhibit remarkably low mass and linear ablation rates with respective 0.054–0.064 mg cm−2 s−1 and -0.157–0.018 μm s−1. Additionally, the composites can endure 1160 s ablation with a surface temperature of 1750 °C under the ablation condition where the surface temperature of C/SiC is 2200 °C. The developed C/SiC–Cu3Si–Cu interpenetrating composites are so far the only known light-weight (<3.0 g cm−3), non-ablation materials which can offer long-duration (≥600 s) thermal protection at 2200–2500 °C in high-enthalpy-flow and oxidizing environments.

The effect of surface grinding and Si addition on the corrosion of Fe-12Cr ODS steels in supercritical CO2

In this study, the effects of surface grinding and Si addition on the corrosion behaviors of Fe-12Cr oxide dispersion strengthening (ODS) steels in supercritical carbon dioxide were investigated by multiscale characterizations. The surface grinding resulted in the formation of an ultrafine grained layer, effectively promoting the formation of protective oxide scales. The addition of Si in this steel with a ground surface can further increase the oxidation and carburization resistance by forming a more stable SiO2 and Cr2O3 scale. The synergistic effects of the Si addition and surface grinding on the oxidation behaviors of the ODS steel are discussed.

Properties and microstructure of Cf/HfC‐SiC composite prepared by combined process

AbstractThe Cf/HfC‐SiC composite was produced by precursor infiltration and pyrolysis combined with gaseous silicon infiltration and an open porosity as low as 5.4% was achieved. Cf/HfC‐SiC composite has a thermal conductivity of 21.4 W·m−1·K−1, in addition, its flexural strength, elastic modulus, and fracture toughness are 328.9 ± 58.4 MPa, 48.9 ± 2.8 GPa, and 10.2 ± 1.2 MPa·m1/2, respectively. The compact matrix and the toughing mechanism by fibers account for the good mechanical properties. The Cf/HfC‐SiC composite survives the oxyacetylene torch test and the formation of a protective oxide scale by joint action of SiO2 and HfO2 contributes to good ablation performance of the composite.

Redox status of blood lymphocytes in patients with soft tissue sarcomas

Introduction. The proven significance of free radical disorders in oncopathology determines the relevance of their study in soft tissue sarcomas (STS), which are characterized by a tendency to recurrence and high mortality of patients.Aim. To study the indicators of free radical oxidation and antioxidant protection in blood lymphocytes in primary and recurrent STS, depending on the sex and age of patients.Materials and methods. In 51 patients with primary STS, T2bN0M0 (17 men and 34 women) and in 34 patients (14 men and 20 women) with relapses, the level of lipid peroxidation products – malondialdehyde and diene conjugates, activities of superoxide dismutase and glutathione peroxidase, total peroxidase activity, the level of reduced glutathione were studied by spectrophotometric methods. Patients were divided by age: ≤45 years and &gt;45 years. The comparison groups (donors) consisted of 12 men and 17 women divided into the same age subgroups.Results. In men &gt;45 years old with primary sarcomas, there was an increase in diene conjugates by 2.2 times, with relapses by 2.4 times, and in young men - only with relapses by 2.6 times. The level of malondialdehyde in men did not change with primary sarcomas, with relapses it was reduced in both age groups by 2.4–2.6 times. In women with primary STS, there was an increase in most of the studied parameters in both age groups by 1.6–1.9 times. The increase in diene conjugates level and superoxide dismutase activity was the most pronounced (&gt;3 times) in patients of the older age group. The increase in glutathione peroxidase activity in primary STS in young women was 2.3 times, and in the older age group in patients of both sexes it was 5 times. In half of the women with relapses developed no earlier than 3 years after treatment, a decrease in both lipid peroxidation products by 2.6–3.4 times was found, and in all women almost 4-fold activation of superoxide dismutase and 8-fold glutathione peroxidase with an increase in the level of reduced glutathione by 7 times took place, which was significantly higher than in men. For women of the older age group, a 3-fold increase in the ratio of superoxide dismutase/total peroxidase activity is characteristic for primary STS and almost 5-fold for recurrence.Conclusion. In primary STS, the activation of lipid peroxidation products and antioxidant enzymes in women is more pronounced than in men. Changes in most indicators are more typical for patients of older age groups, in which relapse was accompanied by a decrease in malondialdehyde in patients of both sexes and maximum activation of superoxide dismutase and glutathione peroxidase in women.

Nanoparticles Application in Promoting the Growth of a More Protective Oxide Scale at High Temperatures

Nanoparticles Application in Promoting the Growth of a More Protective Oxide Scale at High Temperatures

Extending the Passive Region of CrFeNi‐Based High Entropy Alloys

AbstractThis study provides principles for designing new corrosion resistant high entropy alloys. The theoretical framework is a percolation model developed by Newman and Sieradzki that predicts the ability of an alloy to passivate, i.e., to form a protective surface oxide, based on its composition. Here, their model is applied to more complex materials than previously, namely amorphous CrFeNiTa and CrFeNiW alloys. Furthermore, the model describes a more complex passivation process: reforming the oxide layer above the transpassive potential of Cr. The model is used to predict the lowest concentration of Ta or W required to extend the passive region, yielding 11–14 at% Ta and 14–17 at% W. For CrFeNiTa, experiments reveal a threshold value of 13–15 at% Ta, which agrees with the prediction. For CrFeNiW, the experimentally determined threshold value is 37–45 at% W, far above the predicted value. Further investigations explore why the percolation model fails to describe the CrFeNiW system; key factors are the higher nobility and the pH sensitivity of W. These results demonstrate some limitations of the percolation model and offer complementary passivation criteria, while providing a design route for combining the properties of the 3d transition metal and refractory metal groups.

Microstructural evolution and corrosion behavior of Al-20Mg2Si composites with trace La addition

Trace La element was introduced in Al-20Mg2Si composites to regulate the microstructure and corrosion performance. The modification mechanism of trace La and the corrosion behavior of the newly developed composites were systematically investigated by thermal analysis, microstructural observations and electrochemical tests. Our study reveals that the addition of only 0.10% La can refine the size of the primary Mg2Si phase from 77.6 to 26.7 µm, modify its morphology from a coarse dendrite to a fine truncated octahedron and reduce the corrosion current density from 5.96 μA cm−2 to 3.03 μA cm−2. Trace La refines the primary Mg2Si phase size by forming a tiny LaAlSi phase which can provide effective heterogeneous nuclei for the primary Mg2Si phase during solidification. Excess La atoms can selectively adsorb on the {100} facets of the primary Mg2Si phase and suppress the preferential growth of the Mg2Si phase, eventually resulting in the morphological transition of the primary Mg2Si phase from dendrite to truncated octahedron shape. The enhanced corrosion resistance of the La micro-alloyed Al-20Mg2Si composites can be attributed to the formation of stronger protective surface oxide films and finer primary Mg2Si phase. The protective oxide films can effectively hinder the penetration of the corrosive medium and the finer primary Mg2Si phase can weaken the localized corrosion tendency of the Al-Mg2Si composites.

Effect of synergistic variation in Ti and Zr elements on the microstructure and properties of laser cladding AlCoCrFeNi high-entropy alloy coatings

AlCoCrFeNiTi1-xZrx (x = 0, 0.25, 0.5, 0.75, and 1.0) high-entropy alloy coatings were prepared on the surface of 45# steel by laser cladding, and the results showed that the coatings gradually changed from a double body-centered cubic (BCC) + metal carbide (MC) phase to a BCC + face-centered cubic (FCC) + MC phase with the increase in x. The grain morphology transitioned from equiaxed crystals to dendrites and was gradually refined. The solid solution strengthening, fine grain strengthening, and diffusion strengthening made the coatings' microhardness increase substantially to approximately 2.6 to 3.2 times of that of 45# steel. The wear resistance of the coatings was approximately 5.9 to 16.0 times that of the 45# steel, with the highest microhardness and the greatest wear resistance when x = 0.5. The wear mechanism of coatings was mainly abrasive wear and oxidation wear. The corrosion resistance of the coatings was better than that of 45# steel, but the corrosion resistance of the coatings gradually decreased with the increase in x. The increase in grain boundary density makes the galvanic corrosion intensify, and the corrosion resistance of the coating when x = 0, which was approximately 4.2 to 74.0 times that of other coatings. Grain refinement allows for more rapid formation of protective oxide layers with the increase in x, in this study, the resistance of the coating to high-temperature oxidation (800 °C) increased and then decreased with the increase in x, and the coating showed the greatest high-temperature oxidation resistance (800 °C) when x = 0.75, which was 1.4 to 3.5 times that of other coatings. However, the generation of microcracks reduced the high-temperature oxidation resistance of the coating when x = 1.0.

Insights into service-derived Zr-Ta-O film: Morphology evolution, temperature resistance, and atomic bonding

Entropy-stabilized ceramics for ultra-high temperature oxidation protection are springing up, accompanied by complex morphology characteristics and elusive protective mechanisms. Herein, how the Ta/Zr molar ratio change affected the morphology evolution, temperature resistance, and atomic bonding of Zr-Ta-O film was revealed, which was expected to deepen the understanding on A-B-O protective film (A = Hf, Zr; B = Ta, Nb). The Zr-Ta-O film was constructed on the thermally sprayed ZrC-TaC coating utilizing oxyacetylene ablation. Morphological characteristics of the Zr-Ta-O film were found highly related to Ta/Zr molar ratios. The long-term temperature endurance limit of the service-derived Zr-Ta-O film was considered below 2000 ℃, affected by the consumption of micro-scale Ta-rich regions under high-temperature gas scouring (∼2800 ℃, 5–8 m/s). The phenomena were well explained by the binding energy difference (Ta-doped t-ZrO2 and Zr-doped α-Ta2O5) and fluctuation law of Zr-O bond length with Ta/Zr molar ratio increasing (from local instability to whole instability).

Breakdown of Protective Cr-Rich Oxide Scale Formed on Heat-Resistant Steels for Superheater Tubes in a Waste Power Generation Boiler

Breakdown of Protective Cr-Rich Oxide Scale Formed on Heat-Resistant Steels for Superheater Tubes in a Waste Power Generation Boiler

Hot salt corrosion behavior of Ti–6Al–4V alloy treated with different surface deformation strengthening processes

In this study, the effects of shot peening (SP) and ultrasonic surface rolling process (USRP) on the high-temperature oxidation and hot salt corrosion (HSC) behavior of the Ti–6Al–4V alloy were systematically investigated. The results showed that the high-temperature oxidation resistance of this titanium alloy can be significantly improved by the above two treatments. However, the hot salt corrosion resistance of Ti–6Al–4V alloy cannot be improved by SP due to surface roughness increasement, the surface defects and the complete relaxation of compressive residual stress (CRS) at high temperature. On the contrary, the hot salt corrosion resistance of USRP treated specimen was remarkably improved because USRP treatment significantly reduced the surface roughness and introduced deep CRS field with good thermal stability. In addition, the refined surface microstructure promoted the formation of a protective oxide film, which was also beneficial for inhibiting hot salt corrosion.

Metal Oxide Protection Layers for Enhanced Stability and Activity of WO3 Photoanodes in Alkaline Media

Metal Oxide Protection Layers for Enhanced Stability and Activity of WO₃ Photoanodes in Alkaline Media

Effect of Mo on the high-temperature oxidation behavior of Cr-Ni-Mo hot-work die steels

To investigate the effect of molybdenum (Mo) on the high-temperature oxidation behavior of low-carbon hot-work die steels in a Cr-Ni-Mo system, five 3Cr3MoxNiW steels were prepared. The addition of Mo resulted in a decrease in the grain size of the 3Cr3MoxNiW steel, as well as an improvement in its oxidation resistance. The addition of Mo to 3Cr3MoxNiW steel reduces the inward diffusion of oxygen and the outward diffusion of iron, which accelerates the formation of chromium oxide. The oxide of Mo can then also participate in the process of protective oxide film formation, thus improving its oxidation resistance.

Improved tribological and electrochemical behavior of concentrated chromite coatings developed by HVOF and plasma spray techniques

Mineral coatings have the ability to tackle the most common degradation processes (wear and corrosion) in industries at amazing ‘quality to cost’ ratio, as compared to synthetic ceramics. In the current study, concentrated natural chromite with 55 wt.% Chromium oxide (Cr2O3) is deposited on steel substrate through High Velocity Oxygen Fuel (HVOF) and Atmospheric plasma spray (APS) techniques. Effect of deposition processes and Cr2O3 enrichment on microstructure, hardness, tribological and electrochemical behavior of coatings is studied. Tribological tests were performed using pin-on-disc setup, coatings deposited with APS have shown excellent wear resistance behavior as compared to HVOF coating. Owing to the brittle nature of chromite coatings, they were worn by abrasive wear irrespective of the deposition process. Electrochemical behavior of coatings is evaluated by potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution. APS and HVOF coatings have exhibited very high protective efficiency of 93 and 88% respectively, against steel substrate. Equivalent electrical circuit (EEC) based on EIS results has also been conceptualized and verified with ZSimpWin analysis software. Established EEC has illustrated capacitive behavior due to the protective oxide nature of coatings. Despite having relatively higher porosities in APS coatings, they display an excellent potential for wear and corrosion resistant applications. Results revealed that hardness, compactness, tribological and corrosion performance of chromite coatings have been substantially improved due to higher Cr2O3 content.

Melatonin delivered in solid lipid nanoparticles ameliorated its neuroprotective effects in cerebral ischemia

The current study explores the potential of melatonin (MLT)-loaded solid lipid nanoparticles (MLT-SLNs) for better neuroprotective effects in ischemic stroke. MLT-SLNs were prepared using lipid matrix of palmityl alcohol with a mixture of surfactants (Tween 40, Span 40, Myrj 52) for stabilizing the lipid matrix. MLT-SLNs were tested for physical and chemical properties, thermal and polymorphic changes, in vitro drug release and in vivo neuroprotective studies in rats using permanent middle cerebral artery occlusion (p-MCAO) model. The optimized MLT-SLNs showed particle size of ∼159 nm, zeta potential of −29.6 mV and high entrapment efficiency ∼92%. Thermal and polymorphic studies showed conversion of crystalline MLT to amorphous form after its entrapment in lipid matrix. MLT-SLNs displayed a sustained release pattern compared to MLT dispersion. MLT-SLNs significantly enhanced the neuroprotective profile of MLT ascertained by reduced brain infarction, recovered behavioral responses, low expression of inflammatory markers and improved oxidation protection in rats. MLT-SLNs also showed reduced hepatotoxicity compared to p-MCAO. From these outcomes, it is evidenced that MLT-SLNs have improved neuroprotection as compared to MLT dispersion and thereby present a promising approach to deliver MLT to the brain for better therapeutic outcomes in ischemic stroke.

Niobium Silicide Diffusion Coatings: The Impact of Cu and of Ti on the Microstructure and High-Temperature Behavior

Abstract Silicide diffusion coatings on niobium offer attractive properties for applications at temperatures above 1,000°C because of the ability to form a protective oxide, silicon dioxide. The combination of a double layer of silicides, NbSi2 and Nb5Si3, provides a gradient of properties to the coating, mitigating the formation and propagation of cracks that otherwise allow oxygen to interact with the substrate. However, a temperature above 1,200°C is required to process double-layer silicide coatings, increasing the challenge of controlling the process and incrementing the cost of the process. The need to enhance silicide coatings without compromising their competitiveness motivates the study of the individual effects of copper and of titanium. This study processed silicide coatings by double pack cementation adding copper or titanium, respectively, to the pack mixture. Three pack mixture compositions were used: with 15 % wt. silicon, with 15 % wt. silicon + 7 % wt. copper, and 15 % wt. silicon + 7 % wt. titanium. Processing was carried out at 1,000°C for 6 hours. The coatings processed with silicon resulted on a single NbSi2 layer, but the pack mixture containing silicon and copper led to thick double-layer coatings of NbSi2 and a continuous layer of Nb5Si3, in spite of the low processing temperature. In contrast, the pack mixture containing silicon and titanium led to thinner coatings composed of a layer of NbSi2 and the discontinuous presence of Nb5Si3. Results suggest that copper and titanium impact the gaseous diffusion during processing and also the vacancy concentration in the ordered structure of NbSi2. Exposure to temperature reveals a change on the oxidation mechanisms after processing with titanium and a more significant mass gain of coatings processed with copper.

Microstructure and Early-Stage Oxidation Behavior of Co-Cr-Cu-Fe-Mn-Ni High-Entropy Alloys

The microstructure and early-stage oxidation behavior of the equiatomic CoCrCuFeMnNi high-entropy alloy (HEA) and its six sub-alloys, obtained by omitting one element each, were investigated. Alloys were prepared using induction levitation melting, cold rolled, and oxidized for 1 h at 800°C in air. The Ni-free and Co-free HEAs showed an inhomogeneous microstructure associated with liquid phase separation. The other alloys were either single-phase (Cu-free HEA) or contained two face-centered cubic phases, one Cu-rich and one Cu-poor. The Cu and Mn-containing two-phase alloys showed preferential oxidation of the Cu/Mn-rich phase, leading to Mn-rich oxides that are prone to spallation. The Mn-free alloy exhibited a thicker oxide (~ 5 µm) on the Cu-rich phase, whereas the Cu-poor phase was covered by a thin base oxide (< 1 µm). The single-phase Cu-free (‘Cantor’) alloy formed an approximately 1-µm-thick oxide of the crystal structure types of Mn3O4, Mn2O3, MnCr2O4, and Cr2O3. For prospective high-temperature applications, reducing the Cu and Mn content and thus avoiding formation of a second Cu-rich phase is a promising route to facilitate formation of a protective oxide.