Effect Of Surface Oxidation Research Articles

Effects of oxidation on the effective thermomechanical properties of porous ultra-high temperature ceramics in compression via computational micromechanics and MPM

Due to the harsh flight environment of hypersonic platforms, Ultra-High Temperature Ceramics (UHTCs) imbued with macroscale porosity have been introduced as candidates for providing thermal insulation of sensitive on-board components. This study employs an oxidized state approach for modeling the coupled effects of surface oxidation and continuum damage in the effective thermomechanical response of such materials within the framework of computational micromechanics. Using an in-house Material Point Method (MPM) computational tool, two-dimensional plane strain simulations were performed on representative hexagonal structures of TiB2 with 10%, 40% and 70% macroporosity. Oxide layers ranging from 5 to 50 μm were applied to the structures in place of a transient, diffusion-based oxidation solver. Simulations with applied compressive strains of up to 30% were then performed on hexagonal structures with and without the oxide layer present. A range of dynamic thermal gradients were also applied to investigate the damage due to thermal expansion coefficient mismatch. Finally, the oxidized state modeling approach was applied to large porous structures derived from micro computed tomography images of TiB2 foam.

Annealing dependence on magnetization dynamics and two-magnon scattering in Co40Fe40B20 thin films

Investigation of magnetization dynamics of low-damping ferromagnetic layers is of paramount interest for the realization of spin-based electronic devices. Here, we report the effect of surface oxidation on the structural properties, magnetization reversal and spin dynamics of Co40Fe40B20 (CFB) films. X-Ray diffraction results show that both as-deposited and annealed CFB layers up to 250 °C exhibit an amorphous state. Partial crystallization of CoFe is observed in CFB films above 350 °C. Magnetization reversal curves measured using longitudinal magneto-optic Kerr effect indicate a characteristic square loop along the easy axis for all samples. Ferromagnetic resonance (FMR) results show that the resonance field (Hr) shifts due to changes in the structural phase or microstructure. FMR linewidth (ΔH) is linear for both as-deposited and all annealed CFB above 10 GHz, whereas anomalous behaviour in ΔH as a function of frequency is observed below 10 GHz frequency for annealed thin films. The extracted damping parameter manifests extrinsic contributions in the annealed samples compared to the as-deposited. Angular-dependant FMR results show ΔH and Hr exhibit opposite trends in CFB film annealed at 450 °C due to the presence of inhomogeneities. It suggests the signature of two-magnon scattering in the 450 °C annealed CFB. Our systematic study helps in the understanding of the effect of annealing on the crystallinity and magnetization dynamics in CFB thin films.

Quantum state-resolved methane scattering from Ni(111) and NiO(111) by bolometer infrared laser tagging: The effect of surface oxidation.

We describe a novel ultrahigh vacuum state-to-state molecule/surface scattering apparatus with quantum state preparation of the incident molecular beam and angle-resolved quantum state detection of the scattered molecules. State-resolved detection is accomplished using a tunable mid-infrared laser source combined with a cryogenic bolometer detector and is applicable to any molecule with an infrared-active vibrational transition. Results on rotationally inelastic scattering of CH4 methane from a Ni(111) surface and NiO(111)/Ni(111) oxide film, obtained by the new apparatus, are presented. Molecules scattering from the oxidized surface, compared to those scattering from the bare nickel surface, are more highly excited rotationally and scatter into a broader distribution of angles. The internal alignment of molecular rotation is in addition found to be stronger in molecules scattering from the bare surface. Furthermore, the maxima of the state-resolved angular distributions shift toward and away from surface normal with increasing rotational quantum number J for the oxidized and bare surface, respectively. Finally, the rotational state populations produced in scattering from the oxidized surface are well-described by a Boltzmann distribution, while those produced in scattering from the bare surface exhibit large deviations from their best-fit Boltzmann distributions. These results point toward a marked enhancement in molecule-surface collisional energy exchange induced by oxidation of the nickel surface.

Exchange Bias Effect of Ni@(NiO,Ni(OH)2) Core/Shell Nanowires Synthesized by Electrochemical Deposition in Nanoporous Alumina Membranes.

Tuning and controlling the magnetic properties of nanomaterials is crucial to implement new and reliable technologies based on magnetic hyperthermia, spintronics, or sensors, among others. Despite variations in the alloy composition as well as the realization of several post material fabrication treatments, magnetic heterostructures as ferromagnetic/antiferromagnetic coupled layers have been widely used to modify or generate unidirectional magnetic anisotropies. In this work, a pure electrochemical approach has been used to fabricate core (FM)/shell (AFM) Ni@(NiO,Ni(OH)2) nanowire arrays, avoiding thermal oxidation procedures incompatible with integrative semiconductor technologies. Besides the morphology and compositional characterization of these core/shell nanowires, their peculiar magnetic properties have been studied by temperature dependent (isothermal) hysteresis loops, thermomagnetic curves and FORC analysis, revealing the existence of two different effects derived from Ni nanowires' surface oxidation over the magnetic performance of the array. First of all, a magnetic hardening of the nanowires along the parallel direction of the applied magnetic field with respect their long axis (easy magnetization axis) has been found. The increase in coercivity, as an effect of surface oxidation, has been observed to be around 17% (43%) at 300 K (50 K). On the other hand, an increasing exchange bias effect on decreasing temperature has been encountered when field cooling (3T) the oxidized Ni@(NiO,Ni(OH)2) nanowires below 100 K along their parallel lengths.

Influence of Water Quality on Sulphide Ore Oxidation and Speciation of Sulphur Anions during Autogenous Milling

Earlier studies at the Kevitsa Cu-Ni concentrator plant have indicated that seasonal variations of the properties of the process water affect the oxidation of the surface of the minerals, and further, the pentlandite flotation performance. However, it is not clear whether the differences in flotation performance are solely due to changes in the mineral surface oxidation, and/or also due to surface oxidation-induced changes in the aqueous phase of the pulp. This paper investigates the effects of the mineral surface oxidation of Kevitsa Cu-Ni ore on the properties of the aqueous phase of the slurry. A systematic study was formulated to monitor the surface oxidation related changes in the mill circuit of the Kevitsa concentrator plant. The study was timed to coincide with a seasonally observed drop in the concentrator plant’s flotation performance, which happens during the summer months (June, July, and August). Both physicochemical parameters, as well as sulphur oxyanions in the plant process water, mill discharge, and hydrocyclone overflows were monitored. Also, the bubble size in selected rougher and cleaner cells was monitored. The results show that season-related changes in mineral surface oxidation cause clear differences in the aqueous phase chemistry of the mill circuit. The increased concentration of reduced sulphur species in the mill discharge is an indication of extensive oxidation of the ore during milling. Also, the bubble size of the flotation cells reacts to the observed seasonal change. The findings of the study confirm that the consequences expected, based on the theory of mineral surface oxidation, are observable downstream in the aqueous phase of the milling circuit. Based on these results, it is not yet possible to say whether the poor flotation performance is caused solely by the oxidation of the mineral surface or also by the properties of the aqueous phase of the slurry after milling. However, the results show that the plant needs both to find ways to limit oxidation rates in the summer, and to consider installing a more robust frother, capable of maintaining efficacy during the warm season. The findings of this study may help the plant to develop ways to enable a timely response to changes in the recycled process water quality, to prevent harmful impacts on pentlandite flotation. The former could be achieved by lowering the temperature of the process water and flotation air, whereas the latter could mean using a different frother.

Effect of surface oxides on tritium entrance and permeation in FeCrAl alloys for nuclear fuel cladding: a review

Abstract Iron-chromium-aluminum (FeCrAl) alloys are being considered for the cladding of uranium dioxide fuel in light water reactors (LWRs). FeCrAl alloys have good mechanical properties at temperatures of 300 °C and higher, and have superlative resistance to attack by steam at temperatures of up to 1000 °C and higher. A concern has been raised that the use of FeCrAl for cladding would result in a higher content of tritium in the reactor coolant as compared with the current system where the cladding is a zirconium based alloy. This review shows that the flux of tritium from the fuel rod cavities to the coolant across the fuel cladding wall will be greatly reduced by the presence of oxides on the surface of the cladding. The review of current literature and permeation data show that (a) protective oxides are expected to be present on both sides of the FeCrAl cladding, and (b) depending on the characteristics of these oxide layers it is reasonable to expect about two–three orders of magnitude reduction in tritium permeation, relative to the permeation response in clean, unoxidized condition for FeCrAl steels of interest, around 277 °C–377 °C temperatures.

Effects of surface nanotexturing on the wickability of microtextured metal surfaces

Hypothesis: Achieving spontaneous, rapid, and long-distance liquid transport is crucial for many practical applications such as phase change heat transfer and reactions at solid–liquid interfaces. Surface nanotexturing has been widely reported to improve the wickability of microtextured metal surfaces. Although surface nanotextures show high capillary pressure, the high fluid flow resistance through nanotextures prevents fluid transport. The underlying mechanisms responsible for the enhanced wickability of nanotextured surfaces are still unclear.Experiments: Herein, we prepared a variety of microtextures and nanotextures on copper surfaces by femtosecond laser micromachining and chemical oxidation, respectively. The wickability of these textured surfaces was quantitively compared by measuring wicking coefficient and capillary rise speed. We designed experiments to eliminate any possible effects of surface oxidation and metal composition on wickability. A theoretical model describing the vertical and horizontal capillary flow in V-shaped microgrooves was proposed and utilized to analyze the experimental results. The effects of time-dependent wettability on wickability were also examined.Findings: Surface nanotexturing can enhance surface wettability while altering the micrometer-scale structural characteristics. The greatly enhanced wickability of nanotextured surfaces can only be observed when the surface microtextures have a very small aspect ratio. Otherwise, for metal surfaces with fine microgrooves, the latter effect is more pronounced, and thus the surface wickability may deteriorate after preparing surface nanotextures; for surfaces with wide microgrooves, both effects are minimal, and the surface wickability enhances only marginally after surface nanotexturing. Furthermore, the wickability of microtextured surfaces will decay rapidly due to the adsorption of airborne organics, whereas adding surface nanotextures can significantly inhibit this degradation. The anti-contamination capability of surface nanotextures is considered likely to be a potential mechanism responsible for the greatly enhanced wickability of nanotextured surfaces noted in some studies.

Annealing and electrochemically activated amorphous ribbons: Surface nanocrystallization and oxidation effects enhanced for oxygen evolution performance

Annealing and cyclic voltammetry (CV) are essential for the activation of amorphous alloy ribbons. Various amorphous alloy ribbons have been activated in the fields of environmental catalysts using either annealing or CV. However, the combination of the two methods for improving the oxygen evolution reaction (OER) performance has rarely been reported. This combination is expected to significantly improve the OER performance of amorphous ribbons. Here, we developed an “annealing +CV-activation” integrated strategy to treat a free-standing NiFeBSiP ribbon, which as an efficient and stable oxygen-evolving electrode. The “annealing +CV-activation” strategy induces the nanocrystallization and oxidation effects on the surface of the NiFeBSiP ribbon. The effects significantly increase the electron transfer ability, the Ni/Fe/P oxidation state and the surface area of the NiFeBSiP ribbon, which consequently leads to enhancing the OER performance. As a result, the treated ribbon exhibits a low overpotential of 269 mV at 10 mA cm−2 and a small Tafel slope of 40.5 mV dec−1, which are much better than the OER performance of the as-spun ribbon. The enhanced OER performance of the NiFeBSiP ribbon demonstrates the significant and promising effect of the “annealing +CV-activation” integrated strategy for designing high-efficiency amorphous alloy ribbons electrocatalysts.

Oxidative Dissolution of Low-Grade Ni-Cu Ore and Impact on Flotation of Pentlandite

This paper investigated the effect of mineral surface oxidation on the floatability of Kevitsa low-grade Ni-Cu ore. Physicochemical measurements, ethylene diamine tetra acetic acid (EDTA) extraction, and oxygen uptake experiments were carried out with slurry and recycled process water samples obtained from the Kevitsa Cu-Ni sequential concentrator plant. The pH of recycled process water, copper flotation feed, and nickel flotation feed dropped by 0.7, 0.4, and 0.7 points, respectively, from May to July. The oxygen demand increased from recycled process water to the copper flotation feed, then dropped for the nickel flotation feed. The nickel flotation feed Redox potential (ORP) was lowest for July, while EDTA extractable metals increased from May to July. There was a 20% drop in nickel recoveries from May to July. Based on ORP measurements of the nickel flotation feed, good nickel flotation takes place in a moderately oxidizing (75–170 mV) and alkaline (9.2–9.7 pH) environment. Therefore, the ORP/pH of the nickel flotation feed is important to the nickel flotation. The results showed that at the Kevitsa plant, the grinding process is an electrochemically active environment, which, together with the incoming recycled process water quality, defines the degree of mineral surface oxidation for flotation. The increasing corrosiveness of the recycled process water increased mineral surface oxidation and depressed pentlandite flotation. Laboratory flotation experiments confirmed the observed poor plant flotation response when the corrosiveness of recycled process water increased. Total dissolved solids (TDS) was proven to be a reliable online parameter for the corrosiveness of the recycled process water and was inversely proportional to the pentlandite recovery. The findings of this study may help the plant develop ways to enable a timely response to changes in recycled process water quality to prevent harmful impacts on pentlandite flotation.

Effect of surface oxidization on quartz slime coating in the sulfidization-amine flotation of smithsonite

In the sulfidization-amine flotation of zinc oxide, the inevitable presence of slime deteriorates the efficiency of zinc recovery, especially in the cleaner flotation stage. However, the relevant deteriorating mechanism has yet to be clearly explained. Results of micro-flotation indicated that the surface oxidization of smithsonite samples could aggravate the adverse effects of quartz slime coating. Moreover, quartz slimes could easily cover the surface of oxidized smithsonite samples from the slime coating results. Zeta potential measurements and DLVO theory calculations confirmed the stronger interaction between quartz slime and the surface of the smithsonite samples with high oxidization. In addition, XPS analysis further illustrated that the oxidation of sulfide products to sulfate species was an important reason for the deterioration of the slime coating.

Surface modification of MWCNT to improve the mechanical and thermal properties of natural rubber nanocomposites

AbstractIn this study, we focused on the synergistic effect between carbon black (CB) and multiwall carbon nanotube (MWCNT) hybrid fillers. In particular, the surface modification of pristine MWCNT (P‐MWCNT) via an acid (oxidation) treatment was used to improve their dispersion, as well as the mechanical and thermal properties of their corresponding natural rubber (NR)‐based nanocomposites. Fourier‐transform infrared spectroscopy (FTIR), X‐ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were carried out to determine the presence of functional groups on the oxidized MWCNT (O‐MWCNT). After vulcanization, dynamic mechanical analysis (DMA), tensile properties, hardness, thermal conductivity, swelling behaviour in toluene and SEM characterizations were performed on both NR/CB/P‐MWCNT‐ and NR/CB/O‐MWCNT‐based nanocomposites. The results showed the positive effect of MWCNT surface oxidation on the fillers' dispersion and nanocomposites' properties.

Oxide overlayer formation on sputtered ScAlN film exposed to air

There has been much interest in developing scandium doped aluminum nitride (ScAlN) thin films for use in electronic devices, due to their excellent piezoMEMS response, large spontaneous polarization, and the capability for CMOS-compatible integration. As with the undoped AlN film, the formation of an oxide overlayer on the air-exposed ScAlN film can modulate its surface structure and the electrical properties. In this study, we investigate the effects of surface oxidation on a ScAlN film by characterizing the film microstructure and the elemental chemical states. We found that amorphous phase and small crystallites co-exist in the oxide overlayer, which is remarkably different from the columnar (0002) crystalline texture in the bulk ScAlN film. X-ray photoelectron spectroscopy core-level analyses confirm the formation of Al–O and Sc–O bonds. Moreover, the valence band maximum of the oxide overlayer shifts toward a higher binding energy, indicating a high energy barrier at the ScAlN/metal interface. Our results suggest that ScAlN surface oxidation is a chemical reaction-driven and self-limited process.

Comparison of the Characteristics of Recycled Carbon Fibers/Polymer Composites by Different Recycling Techniques.

In this study, three recycling methods, namely, mechanical grinding, steam pyrolysis, and the supercritical solvent process, which are used to acquire recycled carbon fibers (RCFs), were compared for their application in synthesizing polymer-matrix composites. RCF-reinforced polyethylene (PE) composites were prepared to compare the mechanical properties of the composites generated using the three recycling methods. The PE/RCF composites exhibited 1.5 times higher mechanical strength than the RCF-reinforced PE composites, probably because of the surface oxidation effects during the recycling processes that consequently enhanced interfacial forces between the RCF and the matrix. Further, the steam pyrolysis process showed the highest energy efficiency and can thus be applied on a large production scale in domestic recycled CF markets.

Surface modification of carbon fibres with ammonium cerium nitrate for interfacial shear strength enhancement

An ongoing research focus in the carbon fibre (CF) field has been to identify a practical and more effective surface modification method for improving CF's interfacial adhesion and bonding capacity, which is vital for achieving high performance CF composites. In this research, carbon fibres were modified by using a new and facile treatment process in an aqueous solution of ammonium cerium nitrate (ACN) at a low temperature (20 °C–50 °C). The surface analysis results revealed that the ACN treatment imparted a combined effect of CF surface oxidation and cerium (IV)/(III) immobilisation on the oxidised CF surface through coordination bonds, leading to a significantly increased specific surface area, surface energy and surface reactivity. These new surface characteristics directly contributed to an improved CF interfacial adhesion and load transfer between the modified CFs and an epoxy matrix. The study demonstrated that under specified conditions, the new treatment method resulted in 304% increase in interfacial shear strength (IFSS) and 130% increase in interlaminar shear strength (ILSS) without any significant reduction in CF's mechanical properties. In comparison, the ACN modification yielded CFs with a much higher ILSS than the current industrial processes using electrochemical oxidation and sizing.

Effect of surface oxidation on wear and tribocorrosion behavior of forged and selective laser melting-based TC4 alloys

Traditional forging and emerging additive manufacturing techniques have been widely used to prepare Ti-6Al-4V (TC4). However, their wear and tribocorrosion properties have not been compared systematically. We simulated the body fluid environment for laboratory comparative analysis. The results revealed that forged TC4 samples exhibited better corrosion resistance than SLM-TC4, and SLM-TC4 exhibited better wear resistance than TC4. Tribocorrosion resistance was significantly affected under conditions of corrosion. The extent of damage realized for the samples was less at a high applied potential (1V) than the extent of damage realized at a low applied potential (0V) under conditions of low-frequency friction (0.083 Hz). It is believed that the oxide formed on the surface plays a protective and lubricative role.

Effect of storage time on the surface status and resistance spot weldability of TiZr pretreated 5182 aluminum alloy

TiZr pretreatment is generally applied for surface protection of aluminum alloys, especially in the automotive industry, to prevent the adverse effect of surface oxidation on the resistance spot welding (RSW) process. However, the TiZr passivation layer may deteriorate in long-term storage and affects the resistance spot weldability. This paper studies the surface status variation of TiZr pretreated AA5182-O during 18-month storage and the corresponding weld performance. It is found that the TiZr passivation layer maintains its integrity and provides effective protection to extend the acceptable storage life. During the initial three months, both nugget size and mechanical performance of the welds show a mild decrease because of the limited surface oxidation. Meanwhile, the surface resistance rises accordingly to the oxide film thickening and exhibits a high correlation with the weld quality indexes, making it a good representative indicator to assess the weldability deterioration. The early 3-month storage is essential to control the oxide growth and maintain the weldability, and it is recommended to add some additional surface protection measures during this period.

A high-temperature adhesive for stainless steel 304: Effect of Cr growth at the interface of alkali silicate adhesive

With the recent advancements in the aerospace industry, the demand for adhesive materials with resistance to high temperatures has increased. Although the existing organic adhesive materials have a high adhesion strength, their heat resistance and pyrolysis temperature are low, thus limiting their application under high-temperature conditions. Therefore, we attempted to bond stainless steel 304 using an alkali silicate, an inorganic material-based adhesive with high heat resistance but low adhesive strength and analyzed the effects of surface oxidation of stainless steel 304 on its adhesion strength. The surface treatment of SUS304 was performed using mechanical polishing (MP) and electropolishing (EP). A Cr 2 O 3 dominant layer (CODL) and a Fe 2 O 3 dominant layer (FODL) were formed by heat treatment. The adhesion failed in MP, EP, and CODL specimens, when bonding was performed using mixed silicate (MS) because of the differences in thermal expansion coefficients between the metal and glass. FODL and CODL + FODL specimens displayed MS and adhesion strengths of 8.45 MPa and 11.36 MPa, respectively. Each surface and adhesion interface was analyzed through X-ray diffraction (XRD), cross-section scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS), before and after adhesion. When CODL and FODL specimens were placed on both sides to bond with the MS, a needle-like Cr structure appeared on the MS layer from the Cr 2 O 3 layer that enhanced the mechanical adhesion with the MS and the overall adhesive strength. Based on these findings, we conclude that the adhesion strength can be improved by combining a CODL specimen and a FODL specimen and bonding with glass.

Nitinol Release of Nickel under Physiological Conditions: Effects of Surface Oxide, pH, Hydrogen Peroxide, and Sodium Hypochlorite.

Nitinol is a nickel-titanium alloy widely used in medical devices for its unique pseudoelastic and shape-memory properties. However, nitinol can release potentially hazardous amounts of nickel, depending on surface manufacturing yielding different oxide thicknesses and compositions. Furthermore, nitinol medical devices can be implanted throughout the body and exposed to extremes in pH and reactive oxygen species (ROS), but few tools exist for evaluating nickel release under such physiological conditions. Even in cardiovascular applications, where nitinol medical devices are relatively common and the blood environment is well understood, there is a lack of information on how local inflammatory conditions after implantation might affect nickel ion release. For this study, nickel release from nitinol wires of different finishes was measured in pH conditions and at ROS concentrations selected to encompass and exceed literature reports of extracellular pH and ROS. Results showed increased nickel release at levels of pH and ROS reported to be physiological, with decreasing pH and increasing concentrations of hydrogen peroxide and NaOCl/HOCl having the greatest effects. The results support the importance of considering the implantation site when designing studies to predict nickel release from nitinol and underscore the value of understanding the chemical milieu at the device-tissue interface.

Hidden surface channel in two-dimensional multilayers

Numerous carrier scatterers, such as atomic defects, fixed oxide charges, impurities, chemical residues, and undesired surface adsorbates, including oxygen and water molecules, strongly degrade the carrier mobility of atomically thin two-dimensional (2D) materials. However, the effect of surface adsorbates and surface oxidation on the carrier density profile along the thickness of 2D multilayers is not well known, particularly for a substantial interruption in the formation of the top-surface channel. Here, we uncover a hidden surface channel in p-type black phosphorus and n-type rhenium disulfide multilayers originating from undesired ambient adsorbates and surface oxides that not only populate hole density (or reduce electron density) but also suppress carrier mobility. The absence of a second peak in the transconductance curve under ambient conditions indicates the disappearance of the top-surface channel inside the 2D multilayers, which is a possible indicator for the cleanliness of the top surface and can be used in gas sensor applications. Moreover, the negligible variation in the drain bias polarity-dependent turn-on voltage for the bottom channel under ambient conditions validates the exclusive contribution of surface adsorbates to the formation of the top channel in 2D multilayers. Our results provide a novel insight into the distinct carrier transport in 2D optoelectronic devices and diverse sensors.

Effects of structure relaxation and surface oxidation on nanoscopic wear behaviors of metallic glass

Both structure relaxation and oxidation of surface layer induced by thermal treatment or friction heat play significant roles in reducing wear of metallic glasses (MGs). To distinguish the effects of structure relaxation and surface oxidation, we prepared Zr-based MGs at different states, i.e., as-cast MG; the annealed MGs under argon atmosphere (referred to as structure-relaxed MG) and oxygen atmosphere (referred to as oxidized MG). Nano-wear tests were carried out by atomic force microscope (AFM) to quantitatively clarify these two effects on the wear performance. Compared with the as-cast MG, the structure-relaxed MG shows an increased adhesive but slightly decreased ploughing friction. While, the oxidized MG shows the best anti-wear performance with dramatic reductions in both adhesive and ploughing friction. Classic molecular dynamics (MD) and ab initio MD simulations revealed that the introduction of O hinders the MG atoms from forming interfacial bonds with diamond, and reduces significantly the adhesion between the diamond tip and passivated MG. In addition, the synergistic effect of high hardness and elastic recovery associated with oxidization reduces ploughing friction and enhances wear resistance. This finding clarifies the importance of surface chemistry over structure modification during wear, and offers a generic pathway for tailoring ultra-wear resistant MGs.