Thickness Of Surface Oxide Layer Research Articles

Effects of surface oxide layer on the impact dynamic behavior of molten aluminum droplets

Oxide layer is easily formed on the surface of some metal droplets, which affects the dynamic behavior of droplet impact. In this paper, experiments were conducted for the impacting process of a molten aluminum droplet on a Teflon substrate. The thickness of surface oxide layer of aluminum droplets was controlled by varying oxygen concentrations in the gas atmosphere. The effects of oxygen concentration and Weber number on droplet spread, rebound, and splash behavior were investigated. The results show that the oxygen concentration in the environment directly affects the droplet impact behavior. The differences in the droplet retraction process at different oxygen concentrations are more significant than the spread process. Strong retraction causes droplet rebound (We = 17.11) and splash (We = 102.3) in hypoxic environments, whereas only weak retraction in air. The viscous dissipation of the droplet impact in different oxygen concentration environment is estimated by counting the droplet bounce height, and the dissipation increases with the increase in the oxygen concentration. The thickness of the oxide layer measured by scanning electron microscope became thinner as the oxygen concentration decreases and, accordingly, the aluminum droplet collisions show different dynamic behavior. The experimental results are analyzed and explained regarding the reduction in surface tension, the increase in viscous forces, and the shear-thinning properties which increase the viscous dissipation during retraction. Ryan model was used to predict the droplet maximum spreading factor ξmax with the Weber number to the power of 0.5, better than the energy conservation-based Pasandideh-Fard model.

An optical-based method to estimate the oxygen content in recycled metal powders for additive manufacturing

Powder recycling is key to enable sustainable and economically viable production of metal parts by fusion-based additive manufacturing (AM) processes. Determining the recyclability of a powder batch, however, requires continuous monitoring of the powder conditions during processing—notably the oxygen content—to avoid waste of resources while maintaining high build quality standards. In this work, we present a rapid and inexpensive method to acquire this information optically during the powder recoating step. Using a “powder bed scanner”, we capture high-resolution optical images of different powder batches and compute their relative oxygen content by assessing the colour of individual powder particles, which is a function of the surface oxide layer thickness. We compare these measurements against those obtained using conventional techniques and confirm that our method yields higher sensitivity and more consistent results. This work pinpoints a pathway to improving the recyclability of metal powders—at least of those which are heat-tintable—through continuous monitoring of their appearance during AM processes.

Bioactive Titanium Surfaces Enriched with Silver Nanoparticles Through an In Situ Reduction: Looking for a Balance Between Cytocompatibility and Antibacterial Activity

This research aims toward an antibacterial and osteoconductive Ti6Al4V surface by chemical etching–oxidation treatment and in situ reduction of silver nanoparticles. Starting from a previously developed process, already proved to enhance the osteoinductive ability of titanium, different parameters are changed to tailor the amount of silver and its distribution across the surface oxide layer thickness. The samples are characterized by scanning and transmission electron microscopy, energy‐dispersive X‐ray spectroscopy, release of silver, biofilm formation (Staphylococcus aureus), and cytocompatibility toward human osteoblasts progenitor cells. The total amount of silver in the surface oxide layer depends only on the concentration of the silver precursor. The time of the addition of the silver precursor, during the oxidation treatment, affects the oxide layer thickness, dimension, and distribution of the nanoparticles across the surface oxide: they are larger and accumulate on the outermost layer, if the addition occurs early. The maximum ion release occurs after 24 h and lasts up to 14 days; the later addition of silver precursors leads to sustaining the silver release for a longer time. The samples prepared with the higher concentration of the silver precursor are bactericide, but highly cytotoxic, whereas the other ones are bacteriostatic and moderately cytotoxic.

Analysis of surface roughness and oxidation of FeNi-based metal amorphous nanocomposite alloys

We report on a systematic investigation of newly developed (Fe 70 Ni 30 ) 80 Nb 4 B 14 Si 2 metal amorphous nanocomposites (MANCs) and the factors affecting their surface roughness, including oxide formation and phase evolution during the nanocrystallization process. Analysis of surface roughness using atomic force microscopy (AFM) revealed an average roughness of 9.33 nm after heat treatment compared with as-cast amorphous ribbons, which exhibited a roughness of 4.21 nm. A surface oxide layer thickness has been determined using X-ray photoelectron spectroscopy (XPS). For samples annealed at 400 °C for 1 h, 450 °C for 1 h, and 550 °C for 3 h in air, the average surface oxide layer thickness was determined to be 10.9, 11.7, and 54.4 nm, respectively. It was observed that oxygen is enriched at the outermost surface and decreases rapidly as the XPS sputtering depth increases. Fe-oxide appeared as a predominant metal oxide at the top surface, followed by the presence of Nb oxide. A boron content increase was observed at the interface between the top surface oxide layer and the bulk of the sample. A protective surface oxide layer on FeNi-MANCs, such as observed in this work, can provide sufficient electrical insulation to reduce interlaminate eddy current losses and lower overall losses in magnetic components. • Surface roughness and oxidation of FeNi-based metal amorphous nanocomposites. • Surface roughness in amorphous ribbon using atomic force microscopy (AFM). • Crystallization and activation energies in metal amorphous nanocomposite ribbons. • Phase fractions in metal amorphous nanocomposite ribbons. • Surface oxides partitioning in amorphous and nanocrystalline alloys.

Oxidation Response of Transpiration-Cooled on a Hypersonic Stagnation Point

This work presents the oxidation response of a transpiration-cooled hypersonic stagnation point made of porous . Low-order models are used to calculate the surface temperature and oxygen concentration for a given flight condition. An analytical material oxidation model computes the surface recession and oxide layer thickness. A 500 s steady-state trajectory at 44 km altitude and velocity is found to lead to 2.2 mm recession of the 3 mm nose radius. A constant mass injection at a blowing parameter of 0.6 reduces the recession to just 0.21 mm. The displacement of freestream oxygen by transpiration cooling has a significant effect on oxidation. Not accounting for the displacement of oxygen at the surface would increase the recession by up to 197%. The recession along the transient trajectory of an envisioned hypersonic vehicle with a 3 mm nose radius is found to exceed 0.94 mm with no mass injection. It is shown that nitrogen and helium injection at a blowing parameter of 0.6 can reduce the recession to 0.13 and 0.075 mm, respectively.

The exceptional oxidation of Ti6Al4V alloy with a pre-deposited silver layer

For the first time, we discovered the exceptional oxidation phenomenon on Ti6Al4V alloy. A thin layer of silver was pre-deposited via PVD on a Ti6Al4V alloy surface before ceramic conversion treatment (CCT) based on thermal oxidation in air at 620 °C. The pre-deposited silver particles accelerated the oxidation of the Ti6Al4V alloy by up to 50 times, and also helped to produce a thick compact surface oxide layer with a larger surface area compared to a non-silver pre-treated surface. However, silver had a less profound effect on the oxidation of other titanium alloys that didn’t contain vanadium, additionally the silver particles tended to agglomerate on their surfaces, particularly for commercially pure titanium (CPTi). Systematic work examining the impact of vanadium found that vanadium together with silver played a critical role in activating oxygen and promoting its diffusion in the oxide layer, thus dramatically accelerating the oxidation of the vanadium-containing titanium alloys with a pre-deposited Ag layer in CCT. SEM/EDX, TEM, XRD and XPS analyses on the surface phase constituents and microstructure helped to explicate the rapid oxidation mechanism of pre-deposited silver on Ti6Al4V surfaces, and thus provide a new insight into modifying the titanium alloys surface efficiently.

Composition and electronic structure of porous silicon nanoparticles after oxidation under air- or freeze-drying conditions

A controlled change in the composition and electronic structure of porous silicon nanoparticles by variation the drying conditions is proposed. Two types of nanopowders were obtained from mechanically milled porous silicon films with subsequent air- or freeze-drying processing. Obtained nanoparticles surface morphology and structure were investigated. Silicon atoms local surrounding specificity and electronic structure probing of studied powders were performed with the use of synchrotron ultrasoft X-ray absorption near edge structure spectroscopy technique. Noticeable changes in surface composition and structure are observed. The air-dried porous silicon nanoparticles were characterized by the presence of a thick surface oxide layer, while the presence of unoxidized silicon atoms at a depth of less than 3 nm was demonstrated for the lyophilized ones.

Specific Electrical Contact Resistance of Copper in Resistance Welding

The electrical contact resistance (ECR) of copper (Cu‐ETP R200, soft) contacts for resistance welding (RW) is characterized. ECR plays a major role in the RW process and provides local heat generation between the parts. A special determination method is used on different testing variants to observe the influence of contact pressure (two levels: 68, 155 MPa), contact temperature (20–550 °C), and surface parameters, like roughness or oxide layer thickness, on the specific electrical contact resistance (SECR). For each surface parameter, three different levels are investigated. The study shows decreasing SECR with higher mechanical load on the contact and a more complex behavior for increase in contact temperature. SECR shows a characteristic behavior for contact states near the temperature‐dependent tensile strength of the base material for rough and clean surfaces, where SECR approaches toward zero. The variation of oxide layer thickness and surface roughness has a strong influence on the resulting SECR and both surface parameters show a strong coupling regarding their effects.

Controlling Reactive Battery Interfaces Using Electron-Accepting Surface Layers

Understanding the reactivity of electrolyte and solvent molecules as well as electroactive species at operating battery interfaces enables the rational design of improved battery technologies. This molecular-level understanding, however, is often challenging to obtain due to the heterogeneity of electrode surfaces and the complexity of chemical transformation occurring under applied electric fields. For example, battery electrode surfaces contain various distributions of metal-oxides, -hydroxides, -carbonates, and -halides. Subsequently, redox and electron transfer properties vary widely over these heterogeneous surfaces. In this work, we provide a comprehensive outlook and delineate the reactivity of selected polysulfide electroactive ions on well-defined reactive lithium surfaces and propose an approach to modulate the surface reactivity by using electron-accepting surface layers. We used ion soft landing to deposit mass-selected lithium polysulfide ions (LiS4 - and Li5S12 -) on oxidized and fluorinated lithium surfaces. Ion soft-landing is a versatile mass spectrometry-based deposition technique that allows ionic molecules to be selectively deposited onto electrode surfaces without counter-ions and solvent molecules. The reactivity of the deposited polysulfide ions was studied using a combination of experimental and theoretical approaches. Specifically, i n-situ X-ray photoelectron and Raman spectroscopy revealed the presence of both reduced (Li2S) and oxidized (LixSOy) polysulfide species on electron-accepting lithium oxide surfaces. Ab-initio molecular dynamics calculations corroborated the formation of species observed in the experimental study. Bader charge analysis of the systems showed multi-electron transfer reactions for sulfur atoms, starting from neutral species and reacting to oxidation states ranging from +3 to -2. Calculations also indicate that a relatively thick (> 1 nm) surface oxide layer is required to promote reactivity, and that thinner layers can inhibit reaction. Our study provides fundamental insights into the complex redox chemistry and decomposition mechanism that occurs at heterogeneous lithium electrodes and will lead to rational design of efficient and stable battery interfaces.

Deoxidation Behavior of Zr Powder Manufactured by Using Self-Propagating High-Temperature Synthesis with Mg Reducing Agent

In this study, the deoxidation behavior of Zr powder with the use of a Mg reductant is discussed. The original Zr powder was produced by the hydride-dehydride (HDH) method. The raw Zr powder has a thick surface oxide layer of 43 nm as well as high oxygen concentration in the inner part of the powder. The raw Zr powder carries out the reduction reaction with the Mg agent, which maintains self-propagating high-temperature synthesis (SHS) by releasing significant exothermic heat, thereby decreasing the oxygen content. The surface oxide layer of the deoxidized Zr powder is thinner than that of the raw Zr powder, as observed by transmission electron microscopy (TEM) and Auger electron spectroscopy (AES). Furthermore, the oxygen atoms in the inner part of the Zr powder are easily released by a bcc structure providing more active migration of interstitial atoms induced by the open structure at high temperature, and the emitted oxygen atoms readily react with the Mg agent. The lattice parameters of the deoxidized Zr powders, therefore, are decreased with the reduction of oxygen content in comparison with the raw Zr powder because of shrinkage by the decrease of the excess oxygen interstitial atoms. These results are consistent with the observation that the oxygen content in the raw and deoxidized Zr powder was reduced from 0.595 to 0.338 wt pct due to the decreased surface oxide layer and oxygen content in the inner part of the Zr powder, respectively. It is, thus, confirmed that the Mg agent is capable of playing an important role in the deoxidation behavior in Zr powder to obtain high-purity Zr powder.

Development of chemically synthesized spherical plasmonic LaB6 nanoparticles for biomedical applications

LaB6 is a unique plasmonic material, for which the localized surface plasmon resonance (LSPR) absorption band intrinsically lies in the near infrared (NIR) region. In this work, we synthesized spherical LaB6 nanoparticles with a tunable size within 50–200 nm. The optical properties of these LaB6 nanospheres were found to be sensitive to the thickness of surface oxide layer that was formed during the synthesis, purification and dispersion processes. In order to enhance the stability of LaB6 nanoparticles in aqueous environment, LaB6@SiO2 with a core-shell structure was successfully prepared. Both LaB6 and LaB6@SiO2 demonstrated low cytotoxity in biomedical tests when their concentrations were limited to 0.2 mg mL−1. The in vitro photothermal therapy experiment showed that 4T1 cancer cells were eventually apoptotic after being exposed to a 980 nm laser for 5 min at a considerably low power density of 0.82 W cm−2 and a low dose of 0.1 mg mL−1 for LaB6@SiO2. The results suggest that these LaB6 nanospheres are viable photothermal agents for biomedical applications.

The Influence of Microstructure on Oxidation Rate Of V–Cr–Ta–Zr Alloy During Its Chemical-Heat Treatment

Using the methods of scanning (electron backscatter diffraction) and transmission electron microscopy, an investigation of the influence of microstructure of a V–Cr–Ta–Zr alloy on the rate of surface oxide scale formation in the course of its chemical-heat treatment using oxidation in air is performed. It is shown that a preliminary plastic deformation, ensuring a multiple increase in the density of dislocations and misorientation boundaries, results in a 10% thicker surface oxide layer and a respective increase in the concentration of oxygen in the alloy during the final stage of its chemical-heat treatment. The role of this factor in developing the chemical-heat treatment regimes is discussed.

The beneficial effect of surface carbon coating on stress corrosion cracking of Type 304 austenitic stainless steels in high temperature water

A pronounced improvement in stress corrosion cracking initiation resistance resulting from the presence of a carbonaceous surface film was investigated for specimens strained dynamically in hydrogenated high temperature water. Microstructural characterisation of the post-test samples indicated that this improvement in SCC resistance was promoted by the formation of a more uniform and thick surface oxide layer that prevented localized oxidation.

Generation and Evolution of Surface Oxide Layer of Amorphous Boron during Thermal Oxidation: A Micro/nanofabricated Slice Measurement

AbstractThe generation and evolution of the surface oxide layer of boron were thoroughly investigated due to the key role of the oxide layer in ignition and combustion of amorphous boron (B). Samples in different oxidation degrees were obtained by heating B particles until 600, 650, and 700 °C, using a temperature programmed thermobalance. A dual beam focused ion beam micro/nanofabricator was used to etch and cut the samples into thin slices (ca. 327 nm). The slices were observed under a scanning transmission electron microscope, accompanied with energy dispersive X‐ray analysis. During the thermal oxidation process, B particles initially lost mass through dehydration. Then they began to get oxidized and gain weight markedly. The sample surface became more rough as the final temperature increased. Two different reaction modes took place in sequence during the thermal oxidation of the samples. Below 650 °C, the oxidation reaction occurred only on the surface of the particle (the surface reaction mode). However, when the samples were heated to 700 °C, the particle interior was also involved in the reaction (the global reaction mode), and a large number of pores were formed. The O content of the initial surface oxide layer was fairly high. The thickness distribution was uniform (average thickness 148.1 nm) and the two edges were both smooth. During the heating, the oxygen content of the surface oxide layer increased after an initial decrease. The average oxide layer thickness increased and the thickness distribution became irregular and unequal. The sample heated until 700 °C had an average surface oxide layer thickness of 379.3 nm, and the thickness span reached 354.3 nm. During the global reaction process (700 °C), the oxidation degree within the interior of the particle was lower than that on its surface. In the particle interior, pores near the center were smaller than those close to the edge, whereas the oxidation degree was uniformly distributed. Results in this work provide a deeper understanding of the surface oxide layer, which can potentially help improve the ignition and combustion features of B.

Copper Bronze Powder Surface Studied by XPS and HR SEM

Abstract The state of the powder surface represents one of the main interests in the whole cycle of components’ production using powder metallurgy (PM) route. Large specific surface area of the powder in combination with often alloying with oxygen sensitive elements results in oxidation of the powder surface in most of the cases. The information about surface chemistry of the powder is of vital importance for further consolidation and sintering steps. Surface sensitive analytical techniques – X-ray photoelectron spectroscopy (XPS) and high-resolution scanning electron microscopy combined with energy dispersive X-ray analysis (HR SEM+EDX) were used for surface chemical analysis of the 60Cu-40Sn bronze powder. Determination of the compositional profiles and estimation of the surface oxide layer thickness was done by altering of ion etching and XPS analysis. The results showed tin oxide enrichment and presence of copper hydroxide on the surface of the powder particles. The impurities of P, Zn and Ca were also detected on the top surface of the powder in trace amounts.

Pronounced Surface Band Bending of Thin-Film Silicon Revealed by Modeling Core Levels Probed with Hard X-rays.

Enhancing the probing depth of photoemission studies by using hard X-rays allows the investigation of buried interfaces of real-world device structures. However, it also requires the consideration of photoelectron-signal attenuation when evaluating surface effects. Here, we employ a computational model incorporating surface band bending and exponential photoelectron-signal attenuation to model depth-dependent spectral changes of Si 1s and Si 2s core level lines. The data were acquired from hydrogenated boron-doped microcrystalline thin-film silicon, which is applied in silicon-based solar cells. The core level spectra, measured by hard X-ray photoelectron spectroscopy using different excitation energies, reveal the presence of a 0.29 nm thick surface oxide layer. In the silicon film a downward surface band bending of eVbb = -0.65 eV over ∼6 nm obtained via inverse modeling explains the observed core level shifts and line broadening. Moreover, the computational model allows the extraction of the "real" Si 1s and Si 2s bulk core level binding energies as 1839.13 and 150.39 eV, and their natural Lorentzian line widths as 496 and 859 meV, respectively. These values significantly differ from those directly extracted from the measured spectra. Because band bending usually occurs at material surfaces we highly recommend the detailed consideration of signal integration over depth for quantitative statements from depth-dependent measurements.

Surface oxidation effect on the electrical behaviour of Bi2Te2Se nanoplatelets

Charge transport in topological insulators is notably influenced by moisture and air in the surrounding environment. At present, however, little is known about the detailed composition of the oxidized surface and its impact on the electrical characteristics of these materials. Here, we investigate the surface oxide formation on the topological insulator Bi2Te2Se (BTS) and how this affects its electrical behavior. While ambient exposure of BTS nanoplatelets predominantly creates surface hydroxyl groups, oxygen plasma treatment yields a compact, few-nanometer thick surface oxide layer. The plasma causes p-type doping, accompanied by a decrease of the effective platelet thickness, the interplay of which is manifested in a resistance maximum as a function of plasma treatment time. It is furthermore demonstrated that the structural integrity of the plasma-derived surface oxide is sufficient to enable its use as a gate insulator layer in combination with a top gate.

Electropolished Titanium Implants with a Mirror-Like Surface Support Osseointegration and Bone Remodelling

This work characterises the ultrastructural composition of the interfacial tissue adjacent to electropolished, commercially pure titanium implants with and without subsequent anodisation, and it investigates whether a smooth electropolished surface can support bone formation in a manner similar to surfaces with a considerably thicker surface oxide layer. Screw-shaped implants were electropolished to remove all topographical remnants of the machining process, resulting in a thin spontaneously formed surface oxide layer and a smooth surface. Half of the implants were subsequently anodically oxidised to develop a thickened surface oxide layer and increased surface roughness. Despite substantial differences in the surface physicochemical properties, the microarchitecture and the composition of the newly formed bone were similar for both implant surfaces after 12 weeks of healing in rabbit tibia. A close spatial relationship was observed between osteocyte canaliculi and both implant surfaces. On the ultrastructural level, the merely electropolished surface showed the various stages of bone formation, for example, matrix deposition and mineralisation, entrapment of osteoblasts within the mineralised matrix, and their morphological transformation into osteocytes. The results demonstrate that titanium implants with a mirror-like surface and a thin, spontaneously formed oxide layer are able to support bone formation and remodelling.

Increasing the coefficient of sliding friction of NiCr at low loads by interstitial surface hardening

Low-temperature interstitial hardening of NiCr alloys by gas-phase carburizing and nitriding increases the coefficient of sliding friction (COF) at low loads by as much as 50%. While the substantial surface hardening provided by the very high concentrations of interstitial carbon or nitrogen tends to decrease the COF, the presence of these interstitial solutes also decreases the thickness of the air-formed surface oxide layer, which tends to increase the COF. The overall result is an increase in COF.

Characterization and Corrosion Behaviour Study on Biocompatible Ti-6Al-4V Component Fabricated by Electron Beam Melting

Ti-6Al-4V biocompatible material to be used as an implant, fabricated by Electron Beam Melting, was investigated for mechanical properties viz. hardness, grain size and porosity. Phase characterization was analysed by X-ray diffraction; morphological and micro structural features were assessed by Scanning Electron Microscopy and Optical Microscope respectively. The as-produced Electron beam melted Ti-6Al-4V sample had increased surface roughness and a thick surface oxide layer. The corrosion behaviour in simulated body fluid environment was compared for wrought and Electron beam melted Ti-6Al-4V samples by performing anodic polarization measurement using sequencer computer controlled potentiostat. The Electron beam melted sample had the corrosion rate of 0.0148 mils per year and wrought sample had 0.0196 mils per year.