Surface Oxidation Research Articles

Effect of AlCrCuFeNi high entropy alloy reinforcements with and without B4C on powder characteristic, mechanical and wear properties of AA5083 metal-metal composites

This study presents a novel approach to enhancing the properties of the AA5083 alloy by incorporating a high entropy alloy (HEA), specifically AlCrCuFeNi, through mechanical alloying. The Al/HEA composites were thoroughly characterized in terms of powder morphology, microstructure, fracture and wear surface morphology, phase composition, and oxidation behavior using XRD, SEM-EDS, and TGA. The impact of HEA, both with and without B4C reinforcement, on the hardness, density, tensile strength, and wear properties of the AA5083 matrix composites was comprehensively evaluated. The findings revealed that the AA5083 alloy exhibited a baseline hardness of 74.7 HB and a tensile strength of 174.1 MPa. However, with the addition of HEA + B4C, these properties were markedly enhanced, with the hardness increasing to 150.1 HB (a 100 % increase) and tensile strength to 247.1 MPa (a 50 % increase). Furthermore, the wear resistance of the composite experienced a substantial improvement, with a nearly six-fold increase due to the HEA + B4C reinforcement.

The influence of ultrafast laser processing on morphology and optical properties of Au-GaAs composite structure

The results of direct femtosecond laser structuring of GaAs wafer coated with continuous semitransparent gold (Au) film are presented. The obtained structures demonstrate a combination of different features, namely laser-induced periodic surface structures (LIPSS) on semiconductor and metal film, nanoparticles, Au islands, and fragments of exfoliated Au film. The properties of Au-GaAs samples are studied with scanning electron microscopy (SEM), Raman scattering, and photoluminescence (PL) spectroscopy. The behaviour of phonon modes and enhancement of band-edge PL of Au-GaAs composite sample are discussed. The Raman spectra of Au-GaAs sample processed at different levels of irradiation pulse energy reveal forbidden TO and allowed LO phonon modes for selected geometry of experiment, as well as the manifestation of GaAs surface oxidation and amorphization. A 12-fold increase of PL intensity for Au-GaAs sample with LIPSS compared to initial GaAs surface is observed. The detected PL enhancement is caused by an increase of absorption in GaAs due to the light field enhancement near the Au nanoislands and a decrease of nonradiative surface recombination. The blue shift of PL band is caused by the quantum size effect in GaAs nano-sized features at laser processed surface. The combination of GaAs substrate with surface micro- and nanostructures with Au nanoparticles can be useful for photovoltaic and sensorics applications.

Anti-oxidation effect of chromium addition for TiFe hydrogen storage alloys

Anti-oxidation properties of Cr substitution were investigated by comparing TiFe and TiFe0.9Cr0.1. Kinetic measurements reveal that the degradation rate of TiFe0.9Cr0.1 is slower than that of TiFe, indicating that Cr substitution drastically enhances the anti-oxidation properties of the mother alloy TiFe. In order to understand the mechanism of this effect, X-ray photoelectron spectroscopy (XPS) was used to identify the surface chemical state of these alloys, which indicates that Cr plays quite an important role in the suppression of surface oxidation. It is clarified that the deactivation of TiFe is caused by the oxidation of Ti on the surface and, as a result, the obstruction of hydrogen penetration. On the contrary, with the substitution of Cr for Fe in TiFe0.9Cr0.1, the Ti oxidation becomes more difficult even though the Cr was totally oxidized, which makes it easier to keep the initial activated state of hydrogenation (Ti with a low oxidation state). It also further demonstrated that Cr acts as a sacrificial element, undergoing complete oxidation to protect Ti from oxidation, and assists in keeping metallic Ti0, which is crucial for maintaining the hydrogen absorption kinetics. Therefore, the Cr substitution for Fe significantly improves the anti-oxidation properties of TiFe-based alloys.

Exceptional hardness in multiprincipal element alloys via hierarchical oxygen heterogeneities

Refractory multiprincipal element alloys (RMPEAs) are potential successors to incumbent high-temperature structural alloys, although efforts to improve oxidation resistance with large additions of passivating elements have led to embrittlement. RMPEAs containing group IV and V elements have a balance of properties including moderate ductility, low density, and the necessary formability. We find that oxidation of group IV-V RMPEAs induces hierarchical heterogeneities, ranging from nanoscale interstitial complexes to tertiary phases. This microstructural hierarchy considerably enhances hardness without indentation cracking, with values ranging between 12.1 and 22.6 GPa from the oxide-adjacent metal to the surface oxides, a 3.7 to 6.8× increase over the interstitial-free alloy. Our fundamental understanding of the oxygen influence on phase formation informs future alloy design to enhance oxidation resistance and obtain exceptional hardness while preserving plasticity.

Atomic-Scale View of Water Chemistry on Nanostructured Iron Oxide Films.

The interaction of water with solid surfaces is crucial for a wide range of disciplines, including catalysis, environmental science, corrosion, geology, and biology. In this study, we present a combined experimental and theoretical investigation that elucidates the interaction of water with a model iron oxide surface under near ambient conditions (i.e., room temperature and water vapor in the mbar range). Our findings reveal that surface hydroxylation can be controlled at the nanoscale by the local properties of the oxide film, such as local rumpling and electrostatic potential. The iron oxide surface presents alternating hydrophilic and hydrophobic domains, creating after water exposure a hexagonal pattern with a pitch of approximately 3 nm, where the highly hydroxylated regions act as nucleation centers for nanoconfined water molecule clusters.

Unravelling molecular origins of improved tribological properties of amino acid ionic liquid water-based lubricants

In the quest for sustainable lubrication, this study explores the potential of water-based lubricants (WBLs) with amino acid ionic liquid (AAIL) additives. The research combines experimental and reactive molecular dynamics (MD) simulations to assess the tribological and rheological enhancements provided by AAILs. Specifically, tetrabutylphosphonium (P4444) cations paired with Serine (Ser) and Tryptophan (Trp) anions were mixed into water to create AAIL WBLs. The introduction of AAILs significantly improved the lubricants’ rheological properties and reduced the coefficient of friction by up to 34 %. This reduction is attributed to the formation of hydration shells around the amino acid anions, which create a chemically adsorbed tribofilm on iron oxide surfaces, and P4444 cations that establish a load-bearing layer in the middle regions of the lubricant. This dual-layer structure, supported by hydration lubrication, effectively maintains lubricant fluidity while bearing substantial loads. Among the AAIL WBLs tested, those with a thicker, more stable, hydrated amino acid tribofilm demonstrated more significant friction reduction. These insights into the molecular mechanisms behind AAIL WBLs’ tribological behaviour underscore their promise as eco-friendly lubricants, contributing to advancing a circular economy in industries reliant on lubrication.

Electrical and optical properties of g-GaN/Al0.5Ga0.5N 2D/3D heterojunction under surface oxidation via first-principles

In this paper, the structural stability, charge transfer, band structure, density of states, absorption coefficient and reflectivity of g-GaN/Al0.5Ga0.5N heterojunction after surface oxidation are investigated. Our results reveal that formation energy of adsorptive oxidation process is negative and the oxidized surface can be formed spontaneously. The substitutional oxidation process is heat-absorbing and structure is unstable, which is not easy to occur. Band structure show that new energy levels are created due to charge transfer between O atom and heterojunction after surface oxidation. The electronic states of O-p orbitals hybridize with those of Ga-s, Ga-p, and Al-p orbitals, while O-s orbitals affect energy levels at low-energy end. Meanwhile, work function of heterojunction increases after oxidation, weakening electron emission properties of material surface. The results of optical properties illustrate that substitutional oxidation is detrimental to light absorption, while adsorption oxidation slightly enhances light absorption, especially when adsorption oxidation occurs in g-GaN layer, which is competitive for improvement of optical properties. This study can be useful for the removal of surface oxides from g-GaN/AlGaN heterojunction.

Determining the oxidation stability of SnSe under atmospheric exposure

AbstractUnderstanding surface stability becomes critical as 2D materials like SnSe are developed for piezoelectric and optical applications. SnSe thin films deposited by molecular beam epitaxy showed no structural changes after a two-year exposure to atmosphere, as confirmed by X-ray diffraction and Raman spectroscopy. X-ray photoelectron spectroscopy and reflectivity show a stable 3.5 nm surface oxide layer, indicating a self-arresting oxidative process. Resistivity measurements show an electrical response dominated by SnSe post-exposure. This work shows that SnSe films can be used in ambient conditions with minimal risk of long-term degradation, which is critical for the development of piezoelectric or photovoltaic devices. Graphical Abstract

Chemistry of Formate and Water Ligands on Metal Oxide Cluster Nodes of Metal-Organic Framework hcp Hf-UiO-66: Keys to Understanding Reactivity of Paired μ2-OH and Defect Sites.

Many metal-organic frameworks (MOFs) incorporate nodes that are metal oxide clusters, and ligands that have been observed on these nodes include formates, acetates, water, hydroxyl groups, and others, all of which are potentially important in affecting reactivities for applications in separations, catalysis, and sensing. Formate is a common node ligand, arising from formic acid used as a modulator and from N,N-dimethylformamide used as a solvent in MOF syntheses. Yet only little work has been reported characterizing the reactivities of node formate ligands. Infrared spectra reported here show that formate bonds to two types of sites on the paired Hf6O8 nodes of hcp UiO-66, namely, defect and μ2-OH sites. Quantifying the number of formate ligands by 1H NMR spectroscopy of digested samples showed an almost equal number of formate ligands on the two sites, indicating the likelihood that they neighbor each other. These formate ligands interact with water molecules, reversibly switching their bonding from bidentate to monodentate. The formates on μ2-OH sites of hcp Hf-UiO-66 interact much more strongly with water than those on defect sites of the same node, and both interact more strongly than isolated defect sites of Hf-UiO-66. Correspondingly, the catalytic activities of hcp UiO-66 determined as turnover frequencies on each site are approximately twofold higher than those on UiO-66, bolstering the inference that methanol dehydration is catalyzed by a node defect site and a neighboring node μ2-OH site. The results show how MOFs, with their well-defined node structures, provide unprecedented opportunities to understand details of reactivities and catalysis on metal oxide clusters, in contrast to bulk metal oxide surfaces.

Dynamic assessment of titanium surface oxides following mechanical damage reveals only partial passivation under inflammatory conditions

Motivated by clinical problems of titanium implant degradation, we developed a workflow that enabled assessment of surface oxide dynamics as a function of clinical interventions and inflammation conditions. We found that mechanical damage led to decrease of stoichiometric TiO2 ratio in the passivation oxide film and further resulted in accelerated degradation under inflammatory anaerobic conditions. This method can be employed for the assessment of surface oxides to monitor implant safety.

Carbon nanotubes perpendicularly grown on graphene oxide nanosheets derived from metal-organic frameworks: Synergistic reinforcement of poly(l-lactic acid) scaffold

The construction of the nanohybrid composed of two carbonaceous nanomaterials is a promising strategy to inhibit their aggregation, and effectively exert the advantages of their excellent mechanical properties as reinforcement for polymers. Here, carbon nanotubes (CNTs) were in situ perpendicularly growing on the surface of graphene oxide (GO) through metal-organic frameworks (MOF)-derived strategy by chemical vapor deposition (CVD), aiming to facilitate their dispersion on poly(l-lactic acid) (PLLA) bone scaffold fabricated by selective laser sintering (SLS). Specifically, GO provided nucleation sites for the growth of MOF, and worked as the templates when CNTs grew, in which MOF provided catalysts and carbon sources simultaneously. The precursor was heated to 550 °C and kept for 2 h, then heated to 900 °C and kept for 2 h before cooling. The obtained nanohybrid (GO@CNT) exhibited a superior dispersion state than the pure GO in the scaffold at the same loading, especially when the loading was 0.75 wt%. Adding 0.75 wt% GO@CNT endowed the scaffold with a remarkable increment in tensile strength and compressive strength of 13.36 MPa and 24.72 MPa with enhancement of 55.35% and 18.85%, respectively, compared to the scaffold containing 0.75 wt% GO. A crack extension model combined with experiment results was proposed to better understand reinforcement mechanisms. Additionally, the scaffold containing GO@CNT exhibited benign cytocompatibility with a cell-spreading area of 86.31% and cell density of 564 cells/mm2 after culturing for 5 d according to the results of cell adhesion and immunofluorescence tests, making it a promising candidate for bone defect repair.

Friction Coefficient Evolution of Si3N4 Binary Coating with a Stoichiometric Ratio of 57/43

Friction coefficient depends on various factors or surface characteristics during tribological testing, and this friction coefficient can be modified by altering the properties of one of the two contacting surfaces. It is crucial to monitor the friction coefficient continuously, not only at the conclusion of the test. This research examined the evolution of friction coefficient of silicon nitride (Si3N4) coating and H13 steel over different sliding distances (250, 500, 750, 1000 m). The study assessed surface wear and oxidation through three-dimensional profilometry and SEM/EDX. The findings indicated a reduction in friction coefficient by 22%, a decrease in wear rate by 88%, and a reduction in wear volume by 87% when comparing the silicon nitride coated steel to the uncoated steel. Furthermore, the changes in friction coefficient provided insights into the timing of the complete fracture of the hard coating.Graphical abstract

Study on corrosion behavior Ⅱ of hot-dipped Zn-6Al-3Mg alloy coating: Surface oxide layer and ternary eutectic corrosion

The oxide layer and ternary eutectic of Zn–6Al–3Mg alloy coating have an important effect on its corrosion behavior and corrosion resistance, but the influence of oxide layer on the corrosion behavior of the coating and the internal corrosion mechanism of ternary eutectic structure are still unclear. In this study, the oxide layer and ternary eutectic of the coating were characterized in detail, and the corrosion behavior of the oxide layer and ternary eutectic in the environment containing Cl were studied based on first principles of density functional theory. The results show that the surface oxide layer can initially prevent the erosion of Cl-, MgZn2 in ternary eutectic preferentially corrodes after the oxide layer dissolves, corrosion products are formed.

Design of air-stabilized Mg-Sc alloy with enhanced hydrogen storage properties via in-situ formation of Sc-hydride in Sc dissolved phase

Severe surface oxidation and slow kinetic rates are the main obstacles which limit the industrial application of Mg-based hydrogen storage alloys. In this work, an attempt is carried out to design and develop the highly active and air-stabilized Mg-Scx (x = 1, 2 and 3 at.%) alloys via an inexpensive and efficient method. The Sc atoms are completely dissolved in the Mg matrix to form single-phase solid solution alloy. At 325 °C and 2.0 MPa hydrogen pressure, Mg-Sc2 alloy exhibits the rapidest absorption rate with the hydrogen capacity of 6.25 wt%. The synergism of lattice distortion induced by Sc-doping and the in-situ formed ScH2 nanoparticles enhance the de/hydrogenation kinetics. After exposed to air for 800 h, almost no MgO can be detected and the hydrogen storage capacity is only reduced by 0.11 wt%, maintaining the initial total capacity more than 98 %. Sc can protect Mg-based alloys from O2 and H2O pollution, which is ascribed to the formation of an oxygen atoms exclusion zone around the solute atoms caused by valence electrons transfer.

Enhancing flotation efficiency: Optimizing galena and chalcopyrite separation through high-temperature pre-oxidation with recycled sulfuric acid

Galena and chalcopyrite pose challenges in their separation owing to their similar surface chemistry. The flotation separation of galena and chalcopyrite significantly depends on the use of depressants. However, conventional depressants are often associated with several drawbacks, such as toxicity and inefficiency. Hence, exploring efficient and environmentally friendly techniques to separate galena and chalcopyrite is vital. This study investigated the use of sulfuric acid as a surface oxidant for the pre-oxidation treatment of galena and chalcopyrite at high temperatures. This approach facilitated acid recycling and eliminated the need for multiple flotation chemicals. The floatability of galena and chalcopyrite was investigated through micro-flotation. The results revealed that at a pre-oxidation temperature of 100℃, galena exhibited a recovery rate of only 9.98 %, while chalcopyrite maintained a recovery rate of 96 % across the temperature range. The selective depressant mechanism of sulfuric acid in the flotation separation of galena and chalcopyrite was investigated through scanning electron microscopy, zeta potential measurements, X-ray photoelectron spectroscopy, thermodynamic calculations, and electrochemical analyses. The results indicated that the high temperature facilitated the dissolution of the sulfide layer on the galena surface. Consequently, S2− ions underwent oxidization into SO42− to form a stable oxide film on the galena surface through interaction with Pb2+. Conversely, the high-temperature pre-oxidation had a minimal effect on the surface of chalcopyrite, indicating selective oxidation benefits. Findings from the pre-oxidation floatation separation test of galena–chalcopyrite mixtures revealed the efficient and thorough separation of the two minerals under high-temperature pre-oxidation conditions. The lead concentrate obtained from the floatation process exhibited a Pb grade of 79.38 % and a recovery rate of 97.17 %, while the Cu concentrate featured a Cu grade of 32.14 % and a recovery rate of 97.06 %. Additionally, the sulfuric acid solution was recycled. Overall, this study provides a sustainable and cost-effective approach for the green separation of copper–lead sulfide ores.

Facile synthesis of novel acidic modified magnetic graphene oxide and its application in the green synthesis of pyrimido[4,5-b]quinolines

This study aimed to create an innovative acidic nano catalyst capable of producing pyrimido[4,5-b]quinolines under environmentally friendly conditions. To achieve this objective, 1,3-benzenedisulfonyl amide (BDSA) was immobilized onto the surface of magnetic graphene oxide (GO/Fe3O4@PTRMS@BDSA@SO3H), and its surface was acidified using chlorosulfonic acid. The synthesized catalyst's structure was thoroughly examined and verified through various analyses, including FTIR, EDX, elemental mapping, FESEM, XRD, TGA, and DSC. This novel nano catalyst exhibited exceptional activity and selectivity in synthesizing pyrimido[4,5-b]quinoline derivatives under solvent-free conditions, at low temperatures, and with high efficiency. Its catalytic effectiveness stemmed from features such as easy and eco-friendly synthesis methods, abundant accessible catalytic sites, a high surface area, remarkable selectivity, and facile separation from the reaction medium. Additionally, the catalyst proved to be cost-effective, safe, scalable, and reusable for up to four times.

A durable superhydrophobic surface with bud-particle structure prepared by one-step spray method

Superhydrophobic surfaces play an essential role in numerous applications such as anti-fouling, waterproofing, and drag reduction due to their water-repellent. However, for most fabrication methods, there are high requirements for the preparation process and conditions. Meanwhile, the superhydrophobic surfaces generally have the problem of insufficient durability. In this study, a one-step method to fabricate a stable superhydrophobic surface by spraying is proposed. A new bud-particle structure is obtained by modifying micron and nano Aluminium hydroxide(Al(OH)3) particles, which helps the coated surface to demonstrate excellent superhydrophobicity with the water contact angle ∼157.0° and rolling angle ∼2.0°, and it shows great repellency to water droplet impact. Due to the compatibility of Al(OH)3with the pretreatment substrate and the reinforcing effect of nanoparticles, the coating maintained the superhydrophobicity well in the sandpaper wear and the ultrasonic damage test, which reflects the outstanding robustness of the coating.Moreover,benefiting from the control of the wetting state by micronand nanoparticles doping,the coating showed an excellent underwater drag reduction effect in the rheometer experiment, with a drag reduction rate of ∼67.7 %. The one-step spraying method proposed is a simple and convenient way to create the surface with excellent superhydrophobicity and durability, which has great potential applications in improving metal surface oxidation resistance and underwater reducing drag.

Hydrogen permeation in iron-chromium-aluminum (FeCrAl) alloys and the effects of microstructure and surface oxide

Iron–chromium–aluminum (FeCrAl) class alloys are candidates for use as cladding for accident-tolerant fuels and moderators. In this context, hydrogen isotope permeation in FeCrAl alloys is an important material property. In the present work, the apparent permeability, effective diffusivity, and apparent solubility of hydrogen in the FeCrAl alloys C26M and Kanthal D (KD) were measured with gas-driven hydrogen permeation. Permeation measurements were conducted at temperatures of 400 to 700 °C and at gas-driven pressures from 1 to 100 kPa. In particular, the effect of grain size on hydrogen transport was studied with KD samples with three different microstructures: nanocrystalline (NC), ultra-fine grained (UFG), and coarse-grained (CG). The UFG and NC specimens had higher apparent activation energies (73.4 kJ mol-1 and 65.2 kJ mol-l, respectively) for hydrogen permeability than the CG sample (46.9 kJ mol-1). An aluminum oxide layer formed on the primary- and secondary-side surfaces of all samples subjected to permeation experiments which demonstrated the propensity of FeCrAl alloys to form these innate oxide permeation barriers.

Decoding the surface of a complex oxide.

Atomic force microscopy reveals the elusive structure of the aluminum oxide surface.

The shear bond strength of orthodontic brackets after surface conditioning of Zirconia, Ceramic and E. max models

The current study aims to evaluate the shear bond strength (SBS) of metal orthodontic brackets after surface conditioning by hydrofluoric acid (HF) and aluminum oxide air abrasion (Al2O3) and using two prime types and to determines the adhesive remnant index (ARI). We compared the bond strength of different types of models (full glazed zirconia, ceramic faced zirconia and E. max faced zirconia) with different surface conditioning methods for attaching metal orthodontic brackets. The study used 60 models for each material, divided into subgroups based on the type of prime material and surface preparation method. The bond strength was measured using a universal testing machine and the results were analyzed using statistical software. Shear bond strength of the Aluminum oxide was statistically (p<0.05) higher than the hydrofluoric acid and control groups in all groups (full glazed zirconia, ceramic faced zirconia and E. max faced zirconia). The Assure® Plus primer with Aluminum oxide surface treatment give rise to the highest shear bond strength than 3M™ Transbond™ XT, while there was no significant difference between Assure® Plus and 3M™ Transbond™ XT primer for both control and hydrofluoric acid groups. The highest shear bond strength was obtained with Aluminum oxide conditioning method for all types of ceramic materials used in this study.