Formation Of Oxide Layer Research Articles

Alkaline-Metal Cations Affect Pt Deactivation for the Electrooxidation of Small Organic Molecules by Affecting the Formation of Inactive Pt Oxide.

The activity of Pt for the electro-oxidation of several organic molecules changes with the cation of the electrolyte. It has been proposed that the underlying reason behind that effect is the so-called noncovalent interactions between the hydrated cations and adsorbed OH (OHad). However, there is a lack of spectroscopic evidence for this phenomenon, resulting in an incomplete understanding at the microscopic level of these electrochemical processes. Herein, we explore the electro-oxidation of glycerol (EOG) on platinum (Pt) in LiOH, NaOH and KOH using in situ surface-enhanced infrared absorption spectroscopy in the attenuated total reflectance mode (ATR-SEIRAS) and in situ X-ray absorption spectroscopy (XAS). Our results show that the electrolyte cation influences the rate and potential at which adsorbed CO (COad), a catalytic poison, is formed and oxidized. We attribute this to the cation-dependent stability of oxygenated species on the metallic Pt surface and the different intensities of the electric field at the electrode/electrolyte interface. We also demonstrate that the formation of an inactive Pt oxide layer is indirectly also cation-dependent: the formation of this layer is triggered by the cation-dependent oxidative removal of reaction intermediates (for instance, CO). This phenomenon explains the well-known cation-induced differences in the voltammetric profiles, of not just glycerol, but generally of alcohols and polyols.

Corrosion of stainless steel and molybdenum used as PCC in Na//Sb-Bi liquid metal batteries under cycling conditions

Material compatibility is a major challenge in the development of liquid metal batteries. In this study, the corrosion behavior of two candidate positive current collector materials, austenitic stainless steel and molybdenum, in Na//SbBi9 liquid metal batteries is investigated. In-situ corrosion in operating cells is compared with static corrosion in SbBi9 (corresponding to the fully charged state) and Na0.30Sb0.07Bi0.63 (representing the fully discharged state) at 450 °C. Stainless steel shows a much better corrosion resistance in Na-Sb-Bi alloy (corrosion depth below 1 μm after 750 h static exposure) than in SbBi9 (7–9 μm corrosion layer) thanks to the formation of a thin oxide layer. The corrosion under cycling conditions shows similar characteristics (formation of solid Fe-Cr-Ni-Sb compounds), though accelerated, as static exposure to SbBi9. Molybdenum exhibits a very good corrosion resistance both in static and in cycling conditions, showing merely a minor dissolution into the adjacent alloy.

Insight into the formation mechanism of oxidation layer on the amorphous boron nanocluster surface

Boron (B) powder with a high-energy density can enhance the energy of propellants. It has two different forms, namely amorphous B and crystalline B, which have different behaviors during the oxidation. Especially, the oxidation layer (OL) on its surface inhibits the ignition and combustion (IC). To comprehend the formation of OL on the amorphous B nanocluster (BNC) and elucidate its oxidation mechanism, the investigation was conducted on the oxidation of amorphous BNC at various oxygen contents and temperatures (300–1900 K). An analysis of the initial oxidation products (OP), the formation process of the oxidation layer, the reaction path, and the oxidation rate were encompassed and the microscopic oxidation mechanism that cannot be observed experimentally was revealed. The morphology of B (crystalline or amorphous B) does not significantly affect the OP and the thickness of OL. The initial OP of amorphous BNC are BO2 rather than B2O3, and the ultimate OP consist of BO2, BO, and polymer BmOn (m≠1). The oxidation layer on the B surface exhibits a relatively thin thickness. The oxidation rates of two different types of B both follow a parabolic law. The atomic structure of B cluster has an important influence on the reactivity of B. The oxidation rate is influenced by both the surface structure and the oxygen content of amorphous BNC. Based on the above research, a novel oxidation mechanism of amorphous BNC was proposed.

Advanced corrosion resistance and mechanistic insights of electroless Ni-P-PTFE coatings on L245NS substrate in H2S-saturated environments

The extraction and transportation of oil and gas pose significant challenges due to corrosive environments, particularly hydrogen sulfide (H2S) exposure. This study investigates the use of polytetrafluoroethylene (PTFE) to enhance the corrosion resistance of nickel‑phosphorus (NiP) coatings in H2S-rich environments. Electroless deposition was employed to prepare Ni-P/PTFE coatings, which were then subjected to simulated H2S corrosion tests. Results indicate that the incorporation of PTFE led to a more uniform NiP coating with reduced porosity, significantly improving corrosion resistance. The coatings exhibited enhanced protective performance by stabilizing corrosion product layers and preventing the formation of corrosion channels. Ni-P-PTFE coatings overcame the existing research challenge of NiP coatings' corrosion in H2S environments, showing no penetration of the corrosive medium into the substrate after 720 h of immersion. The corrosion rate of the coating is only 0.0261 mm/year, only 4.27 % of the corrosion rate of the L245NS substrate in the early stage of corrosion. Moreover, after characterization by SEM, XRD and XPS, it was found that the presence of PTFE altered the corrosion mechanism, promoting the formation of stable nickel sulfide and oxide layers on the surface. This study sheds light on the mechanisms underlying PTFE-enhanced corrosion resistance in NiP coatings, offering promising implications for extending the lifespan of equipment in the oil and gas industry.

Dynamic splitting tensile mechanical behavior of magnesia-carbon refractories under impact loading

To enhance understanding of the dynamic tensile failure mechanism of MgO-C refractories, the Split Hopkinson Pressure Bar test combined with digital image correlation techniques were utilized. The dynamic failure behavior of specimens with different heat treatments and graphite content was investigated under various impact velocities. The MgO-C specimens exhibit severer damage and a more tortuous crack path with higher impact velocity. The SiC and forsterite phases generate during heat treatment are advantageous in inhibiting crack propagation, while the formation of oxide layer makes the material more susceptible to brittle fracture. Due to the presence of microcracks, high graphite samples lead to a reduction in tensile strength, but result in a wider fracture zone, which dissipates impact energy. Compared with the significant increase of strength under compressive impact loading, the critical tensile strain rate of MgO-C is easier to achieve after which the tensile strength decreases.

Enhanced resistance to electrochemical degradation and hydrogen permeation by grain boundary and strain engineering in cobalt-graphene oxide composite coatings

Cobalt (Co) and cobalt-graphene oxide (Co-GO) coatings were electrodeposited on mild steel. The Co-GO coating with an optimum volume fraction of GO (Co-GO-3) displayed significantly reduced corrosion current density (5.3 μA/cm2) compared to pristine cobalt coating (21.4 μA/cm2) in 3.5 wt% NaCl solution. Formation of a stable CoO passive oxide layer and a higher proportion of low energy grain boundaries (low-angle grain boundaries and CSL boundaries) contributed to the enhanced anti-corrosion properties. The Co-GO-3 coating also exhibited the lowest hydrogen permeation current, attributed to its higher fraction of relatively closed grain boundaries and presence of compressive strain within the coating.

Surface Degradation of Mg2X-Based Composites at Room Temperature: Assessing Grain Boundary and Bulk Diffusion Using Atomic Force Microscopy and Scanning Electron Microscopy.

Practical application of thermoelectric generators necessitates materials that combine high heat-to-electricity conversion efficiency with long-term functional stability under operation conditions. While Mg2(Si,Sn)-based materials exhibit promising thermoelectric properties and module prototypes have been demonstrated, their stability remains a challenge, demanding thorough investigation. Utilizing atomic force microscopy (AFM) and scanning electron microscopy (SEM), we investigate the surface degradation of a composite material comprising Si-rich and Sn-rich Mg2(Si,Sn) solid solutions. The investigation reveals a pronounced dependence of stability on Sn content, with the Sn-rich phase Mg2Si0.13Sn0.87 displaying the formation of a nonprotective oxide layer. Subsequent AFM measurements provide evidence of dominating grain boundary diffusion of loosely bound Mg, compared to bulk diffusion, observed within a few days, ultimately resulting in a complete surface oxidation of the Sn-rich phase within several weeks. On the other hand, Mg2Si and Si-rich Mg2Si0.80±0.05Sn0.20±0.05 remain stable against Mg diffusion to the surface even after prolonged exposure. Comparison with previous investigations confirms that the degradation rate is found to be highly dependent on the Sn content, with markedly higher rates observed for x = 0.87 compared to x = 0.70 in Mg2Si1-xSnx. These findings contribute to a better understanding of the stability challenges associated with Mg2(Si,Sn)-based materials, essential for the development of robust thermoelectric materials for practical applications.

Investigation on the microstructure and high-temperature properties of AlN coating through oxygen addition

This study meticulously examines how oxygen incorporation alters the microstructure, mechanical, and high-temperature properties of AlN coating prepared via cathodic arc deposition. Substitution of nitrogen by oxygen in the AlN lattice leads to the formation of Al(OxN1-x)y metastable solid solutions from wurtzite Al(O)N structure to cubic AlO(N) structure, culminating in a full conversion to γ-Al2O3 with increased oxygen content. This substitutive solid solution induces solid solution strengthening and grain refinement effect, thereby escalating hardness from ∼18.5 GPa for AlN to ∼23.9 GPa for Al(O0.18N0.82)1.09. Despite an observed tendency towards enhanced thermal decomposition of oxynitride coatings upon annealing, the occurrence of α-Al2O3 oxide phase significantly preserves the mechanical integrity at elevated temperatures, outperforming pure AlN coating. Notably, the strategic alteration by minimal oxygen incorporation facilitates the formation of an Al-rich oxide layer, which exhibits superior anti-oxidative characteristics. After oxidation at 1100 °C for 10 h, the Al(O0.10N0.90)1.03 with an oxide layer of ∼1.2 μm exhibits remarkable oxidation resistance.

Assessment of the microstructure, adhesion and elevated temperature erosion resistance of plasma-sprayed NiCrAlY/cr3C2/h-bn composite coating

This study uses an air jet erosion tester to investigate the erosion behavior of NiCrAlY/Cr3C2/h-BN composite coatings that are plasma-sprayed at three different temperatures and 40 m/s on T22 boiler steel alloy. 30 and 90° are the impingement angles. To identify the erosion mechanism, SEM and X-ray diffraction techniques are used to analyze the surface morphology and phase generated on the eroded surface. Findings of erosion test indicate that the erosion resistance was notably enhanced by addition of Cr3C2 and h-BN because of its lubricating characteristics and capacity to reduce frictional forces during erosion. The combined influence of Cr3C2 and h-BN enhanced the coating hardness and erosion wear resistance, thereby improving its overall resistance to erosion. The weight loss method was employed to calculate the erosion rate, and the NiCrAlY/Cr3C2/h-BN coating showed up to 30.55% and 34.48% lower erosion rate as compared to uncoated T22 substrate at 600 °C for 30° and 90° impact angles, respectively. This characteristic is affected by the hard reinforcement Cr3C2's high-temperature stability, the h-BN's self-lubricating ability, the formation of a protective oxide layer that forms at 600 °C, and the eroded coating's ductile behavior of material removal. The study also reveals that the NiCrAlY/Cr3C2/h-BN coating system on T22 boiler steel alloy has excellent erosion resistance, making it suitable for use in high-temperature and erosive environments in boiler systems and similar industries.

Mixed phase iron oxides thin layers by atmospheric-pressure chemical vapor deposition method

This paper provides a simple method for producing a metal oxide thin layer methodology by atmospheric pressure chemical vapor deposition (APCVD) synthesis over stainless steel substrates. This methodology enables the formation of thin iron oxide layers at its performance at various temperatures of 330 °C, 430 °C, and 530 °C. The deposition arises from thermal decomposition of the iron organometallic precursor Fe3(CO)12, forming a thin layer of iron oxide is, by the ozone present in the reaction chamber promoting the deposition of the iron oxide particles over the substrate. The Raman characterization suggest that at 330 °C, a mixture of hematite and magnetite is predominant on the as deposited substrates, also hematite modes show to be more pronounced as the band at 300 cm-1 narrows. Conversely, magnetite is prominent at higher synthesis temperatures, exhibiting a more intense Eg5 mode at 680 cm-1. The particles exhibit a uniform morphology, with both metal oxide phases coexisting. The average diameter of the particles is 50 nanometers as scanning electronic microscopy shows in a transversal sample section.•The formation of particles is attributed to the combination of iron ions +2 and +3 in the deposition process and their interaction with oxygen in the given synthesis parameters at atmospheric pressure chemical vapor deposition (APCVD).

Effect of graphene content on the tribological and corrosion behavior of high-speed-laser-clad high-entropy-alloy composite coatings

To repair oil drill pipe joints that have failed owing to dry wear and tribocorrosion, graphene-reinforced CoCrFeMo0.5NiTi0.5 high-entropy alloy composite coatings (HEACCs) were developed through high-speed laser cladding. The HEACC containing 1.5 wt% graphene exhibited dry wear and tribocorrosion rates that were 59.18 % and 32.20 % of those observed in the high-entropy alloy coating, respectively. The HEACC exhibited a corrosion current density of 2.475 × 10−7 A/cm2. The HEACC containing 1.5 wt% graphene underwent progressive damage during dry wear owing to the combined effects of abrasive wear, which created furrows; adhesive wear, which led to flaking; and oxidative wear, which formed oxide layers. During tribocorrosion, chloride ions exacerbated surface damage caused by hard abrasives and asperities, intensifying corrosive–abrasive wear interactions.

The oxidation resistance of Ni nanoparticle incorporated SiOC coating for TiAl alloy

In this work, SiOC coatings incorporated with Ni nanoparticles were fabricated on γ-TiAl alloy by dip-coating. The microstructure and high temperature oxidation behavior of the SiOC-Ni coatings with different Ni contents were investigated. Results showed that the incorporation of Ni nanoparticles improved the oxidation resistance of the SiOC coating at 850 ℃. During thermal exposure to air, the incorporated Ni particles would react with both oxygen and the SiOC coating, forming NiO and Ni2Si, respectively, therefore changing the structure of the SiOC coating. The generation of NiO and Ni2Si is beneficial in reducing the oxygen partial pressure at the coating/substrate interface, thereby facilitating the formation of a protective aluminum oxide layer.

Microstructure and corrosion properties of Al1-xWxN coatings for potential use in gas turbine blades

Herein, a numerical approach of Al1-xWxN thin film coatings on Inconel 738LC superalloys for thermal barrier applications has been studied and the experimental analysis includes deposition of Al1-xWxN films on Si (100), glass and transparent quartz substrates at 40 % N2 flow rate using a dual target DC reactive magnetron sputtering technique to investigate the morphology, microstructure, chemical bonding and corrosion behaviour. AFM analysis revealed the rms roughness, Sq and average roughness, Sa increased with the increasing W content from 22 to 70 at.%. It was found that Al1-xWxN films tend to form tiny valleys on the film surface because the values of surface skewness, Ssk lie below zero. The TEM image showed a branched snowflake structure for the specimen of Al0.58W0.42N films with discrete spots in the SAED pattern, confirming the microcrystalline nature. The blue-shifting of Ecorr towards positive potential confirmed the lower corrosion resistance of WN films than those of AlN. XRD spectra of Al0.58W0.42N films showed an amorphous nature devoid of peaks, which is also confirmed by the SAED pattern. The quasi-passive oxide layer formation was spontaneous for WN films compared to the AlN films. The bending vibrations of AlN and WN showed the coordination environment of the metal centre in the Al1-xWxN films. The computational results indicated that the thermal barrier properties of Al1-xWxN films decreased with the increasing W content, i.e., AIN > Al0.58 W0.42N > WN.

Oxidation of Sintered Refractory Alloy (Ni3Al)

Ni3Al is a superalloy which is of particular interest at high temperatures due to its high resistance to oxidation with the formation of a protective oxide layer that performs better than NiO and Cr2O3. Among the factors likely to affect the reaction mechanism and modification of the oxidation kinetics, the surface state appears to be a very important parameter. In the case of sintered materials, the surface condition will be linked to the porosity of the material and therefore to densification. This work essentially has two parts. The first consists of developing Ni3Al sinters intended for oxidation, studying the densification mechanisms and bringing together the results obtained by dilatometry at variable temperature and by differential thermal analysis which made it possible to demonstrate sintering in a reactive liquid phase extremely fast SHS type, with instantaneous formation of the Ni3Al phase. The second part is devoted to the isothermal oxidation between 1100 and 1350°C of cubic-shaped sinters (4mm edge) under a flow of oxygen for 24 hours. The shape of the parabolic curves is correlated with morphological and microstructural observations to deduce the diffusional kinetic regime which controls the speed of the reaction. On the other hand, these observations highlighted a very strong adhesion due to the indentations of the Al2O3 oxide in the metal at the oxide/metal interface. Various techniques (Density – XRD – SEM and Microanalysis) to characterize the sinters and the oxidation products complete our study.

Recent Advances and Prospects in β-type Titanium Alloys for Dental Implants Applications.

Titanium and its alloys, especially Ti-6Al-4V, are widely studied in implantology for their favorable characteristics. However, challenges remain, such as the high modulus of elasticity and concerns about cytotoxicity. To resolve these issues, research focuses on β-type titanium alloys that incorporate elements such as Mo, Nb, Sn, and Ta to improve corrosion resistance and obtain a lower modulus of elasticity compatible with bone. This review comprehensively examines current β titanium alloys, evaluating their mechanical properties, in particular the modulus of elasticity, and corrosion resistance. To this end, a systematic literature search was carried out, where 81 articles were found to evaluate these outcomes. In addition, this review also covers the formation of the alloy, processing methods such as arc melting, and its physical, mechanical, electrochemical, tribological, and biological characteristics. Because β-Ti alloys have a modulus of elasticity closer to that of human bone compared to other metal alloys, they help reduce stress shielding. This is important because the alloy allows for a more even distribution of forces by having a modulus of elasticity more similar to that of bone. In addition, these alloys show good corrosion resistance due to the formation of a noble titanium oxide layer, facilitated by the incorporation of β stabilizers. These alloys also show significant improvements in mechanical strength and hardness. Finally, they also have lower cytotoxicity and bacterial adhesion, depending on the β stabilizer used. However, there are persistent challenges that require detailed research in critical areas, such as optimizing the composition of the alloy to achieve optimal properties in different clinical applications. In addition, it is crucial to study the long-term effects of implants on the human body and to advance the development of cutting-edge manufacturing techniques to guarantee the quality and biocompatibility of implants.

Corrosion behavior and mechanism of Inconel 625 coatings in high-temperature acidic environments for waste incineration applications

This study explores the high-temperature corrosion behavior and mechanisms of laser-clad Inconel 625 coatings applied in waste incineration environments. Inconel 625 coatings were deposited on a substrate using laser cladding technology, and corrosion tests were performed in various high-temperature acidic environments. The coatings were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and laser confocal microscopy to investigate their microstructure, composition, and corrosion products. The findings indicate that corrosion weight gain was most pronounced in HCl environments at 800 °C and HBr environments at 600 °C, underscoring the critical influence of temperature and acidity on reaction kinetics. Moreover, the corrosion morphology was closely tied to the environment, with distinct patterns observed: pitting in HCl, nodular growth in H2SO4, and cracking and spalling in HF and HBr environments. High temperatures promoted oxidation reactions, resulting in the formation of a dense oxide layer predominantly composed of Cr2O3 and NiCr2O4, which offered some degree of protection. However, pitting and cracking in acidic environments suggested that the protective oxide layer's effectiveness was compromised under extreme conditions. This study provides a comprehensive understanding of the corrosion behavior and mechanisms of Inconel 625 coatings in various acidic environments and high temperatures within waste incineration applications. It offers valuable insights into the impact of temperature and different acidic media on corrosion rates and morphologies, laying the groundwork for predicting the service life and developing protective strategies for these materials in industrial settings.

Synthesis of Samarium Nitride Thin Films on Magnesium Oxide (001) Substrates Using Molecular Beam Epitaxy

Rare-earth nitrides are an exciting family of materials with a wide variety of properties desirable for new physics and applications in spintronics and superconducting devices. Among them, samarium nitride is an interesting compound reported to have ferromagnetic behavior coupled with the potential existence of p-wave superconductivity. Synthesis of high-quality thin films is essential in order to manifest these behaviors and understand the impact that vacancies, structural distortions, and doping can have on these properties. In this study, we report the synthesis of samarium nitride monocrystalline thin films on magnesium oxide (001) substrates with a chromium nitride capping layer using molecular beam epitaxy (MBE). We observed a high-quality monocrystalline SmN film with matching orientation to the substrate, then optimized the growth temperature. Despite the initial 2 nm of growth showing formation of a potential samarium oxide layer, the subsequent layers showed high-quality SmN, with semiconducting behavior revealed by an increase in resistivity with decreasing temperature. These promising results highlight the importance of studying diverse heteroepitaxial schemes and open the door for integration of rare-earth nitrides and transition metal nitrides for future spintronic devices.

Profilometry‐Based Indentation Plastometry at High Temperature

This is a first report on profilometry‐based indentation plastometry (PIP) at high temperature (HT), covering both thermal characterization and issues for obtaining stress–strain curves. The heating system has a relatively low thermal inertia, reaching 800 °C within about 10 min, while both indentation (≈20 s) and cooling (≈20 min) are also quick. This capability is useful in terms of limiting exposure of the sample to prolonged periods at HT, and hence avoiding the formation of thick oxide layers (which can affect indent profiles and hence inferred stress–strain curves). There is good general consistency between stress–strain curves obtained via HT‐PIP and those from tensile testing. However, the possibility of creep (time‐dependent deformation) affecting the outcomes (of both types of test), particularly at higher temperatures, should be borne in mind. Creep has a characteristic effect on tensile curves, which can often be confirmed and investigated by changing the imposed strain rate. It can also be revealed by carrying out the HT‐PIP testing with different penetration velocities or by monitoring the shape of the load–displacement plot.

Mechanism of alteration in passivity of additively manufactured Ni-Fe-Cr Alloy 718 caused by minor carbon variation

Unlike conventional alloys, where carbon content typically promotes carbide compound formation and reduces localized corrosion resistance, the impact of carbon in additively manufactured materials remains largely unexplored due to rapid cooling rates inhibiting carbide formation. This study addresses the novel question of whether reducing carbon content benefits corrosion performance and its underlying mechanisms in Ni-Fe-Cr-based alloy 718. Employing high-resolution techniques and microcapillary electrochemical methods, it was revealed that higher carbon content increases dislocation density at cell boundaries. This increased dislocation density facilitates the enhanced ejection of nickel and iron from the protective chromium oxide layer on the surface, leading to the formation of a defective outer Ni-Fe oxide layer. This compromised layer subsequently diminishes the alloy's corrosion resistance, particularly under tensile stress conditions.

High-temperature corrosion mechanisms of a Ni-based alloy in simulated multi-source organic waste co-incineration environments

Due to the new trend of co-incinerating municipal solid waste (MSW) with sewage sludge, medical waste, or industrial organic waste to attain a “waste-free” status, mixing of multi-source organic wastes (MSOW) increases the complexity of solid waste, which fluctuates the composition of corrosive species in the boiler. The fluctuation of corrosive species alters the alkali metals/S/Cl ratios and increases the uncertainties of high-temperature corrosion of boiler key components. The corrosion behaviors and mechanisms in varying compositions of corrosive species are complex and remain elusive. To investigate the corrosion characteristics during the co-incineration of MSOW, this study examined the corrosion mechanisms of a nickel-based Ni59.08Cr24.31Al10.74W5.3B0.57 alloy in simulated co-incineration environments of MSOW. The environment contained either HCl, NaCl, or SO2 in wet oxygen at 600 °C. For each case experiment, the maximum possible value of each corrosive species expected in the actual incinerator and/or its absence was considered. HCl of either 0 or 1500 ppm, SO2 of 0 or 300 ppm, and NaCl of 0 or 50 mg/cm2 were systematically used in each experiment. The influence of each corrosive condition on the corrosion of the alloy was evaluated by mass gain measurements, and the corrosion mechanisms were elucidated through SEM, EDS mapping, XRD, XPS analyses, and thermodynamic equilibrium calculations. The results revealed that NaCl salt and HCl gas in wet oxygen have complementary effects, which accelerated the corrosion of alloy, reaching ∼ 65.6 mg/cm2 over one week. HCl enhanced the corrosion by affecting the chemical reactions that regenerated NaCl, which participated in prolonged corrosion processes. SO2 reduced the mass gain of the alloy to 38.4 mg/cm2. SO2 participated in the sulfation of NaCl, forming a mixed layer of Na2SO4 and (Al/Cr)2O3, reducing the mass gain by 1.71 times. In the environment without NaCl, SO2 helped in the formation of a protective oxide layer, which prevented HCl from reaching the alloy, reducing the corrosion impact by 23.5 times.