High Surface Oxidation Research Articles

Surface Oxide Ion Conduction of a - Axis Oriented Ce0.75Sm0.25O2- δ Thin Film Prepared on (200) YSZ Substrate

Fuel cells are attracting attention as a clean energy source because their only waste product is water. Solid oxide fuel cells (SOFC), which use oxide with oxygen ion conductivity as the electrolyte, can simplify the configuration of the power generation system and facilitate management, but they require a high operating temperature of 800 ℃ or higher [1]. Yttria-stabilized zirconia, which is currently in practical use as an electrolyte, exhibits high oxygen ion conductivity at temperatures above 800 ºC. Therefore, an electrolyte that exhibits high ion conductivity at low temperatures is required.Fluorite-type CeO2-δ oxides are good solid electrolyte candidates for solid oxide fuel cells due to their high oxygen ion conductivity in high-temperature regions above 800 ℃ because they take on a mixed valence state of Ce3+ and Ce4+ in the high temperature. Furthermore, it is known that doping CeO2 with trivalent dopants increases the amount of oxygen defects and improves ionic conductivity [2-4]. While we have reported the surface ionic conduction Sm-doped CeO2 thin films, the conductivity was not sufficiently high for practical applications [5].In this study, in order to realize high surface oxide ion conductivity, we prepared a - Axis Oriented Sm-doped CeO2 (Ce0.75Sm0.25O2- δ : SDC) Thin Film without lattice distortion and investigated its surface oxide ion conduction.The SDC thin films were prepared on YSZ (200) substrates by RF magnetron sputtering using ceramic targets. The flow rate of Ar gas controlled by a mass-flow controller was kept at approximately 2.81 sccm. The pressure of Ar gas was fixed at 3.5 × 10−3 Torr during the deposition. The prepared thin films were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and A.C impedance method using a frequency response analyzer.The prepared SDC thin films showed a 200 peak and a 400 peak on the YSZ substrates, indicating no change in lattice constants with the ceramics. Figure shows an Arrhenius plot of the conductivity of the As-deposited and Wet-annealed SDC thin films. As a reference, the Arrhenius plot of the conductivity of the YSZ substrate and ceramics is shown. The conductivity of the SDC thin film is much higher than that of the YSZ substrate and ceramics because the amount of oxygen vacancies increased more than those. The conductivity does not much change by wet annealing and depends on the film thickness. The conducting carrier above 200 °C is considered to be oxide ion. In this presentation, the author will show the details of the conductivity and discuss including XPS results as well as details of the conductivity.

Biochar assisted synthesis of α-MnO2 nanowires with superior performance for non-radical activation of peroxymonosulfate

Non-radical activation of peroxymonosulfate (PMS) is a promising water treatment technology for removing refractory organics, but its mechanism is still ambiguous and the development of highly efficient catalyst is still a challenge. Herein, α-MnO2 nanowires were synthesized by a hydrothermal method with the assistance of biochar and their performance for PMS activation was studied. The characterization results show that the addition of biochar had little effect on the crystal phase and valence state of MnO2 but significantly reduced the size of nanowires. These nanowires had mesoporous structure, high surface area and oxidation ability, resulting in their superior performance for removing organic pollutants with PMS activation. The degradation of phenol by α-MnO2-PMS followed first order kinetics with an activation energy of 14.82 kJ mol−1. Electron paramagnetic resonance and radical scavenging experiments demonstrated that this activation process followed the non-radical mechanism. The quenching effect of scavengers led to the misleading role of singlet oxygen. In fact, surface activated PMS (MnO2–PMS*) rather than singlet oxygen was the reactive species. Weak acidic condition was conducive for the formation of MnO2–PMS* complexes. This catalyst exhibited good reusability and high activity for removing various organic pollutants, and the common substances in real water had little effect on its performance, suggesting its potential application in wastewater treatment.

X-ray photoelectron spectroscopy surface oxidation study of remote plasma-enhanced chemical vapor deposition-grown Ge1−xSnx/Si alloys

Recent progress in the remote plasma-enhanced chemical vapor deposition of Ge1−xSnx grown directly on Si substrates has improved crystal structure quality. To understand the impact of postgrowth storage, we study oxidation states of Ge1−xSnx alloys, for x values of 7.5%, 8.8%, 12.5%, and 19.3%. A surface oxidation layer formed naturally at room temperature over five months is quantified using angle-resolved x-ray photoelectron spectroscopy. The GeSn alloys exhibit a high surface oxide concentration with a minimum of 77% in Sn 3d peak analysis. Ge is less susceptible to oxidation than Sn, with oxidation percentages ranging from 25% to 86%. The Sn dopant enhances the oxidation features associated with the Ge 3p peak, aiding surface oxidation and penetrating further into the film. It is feasible that the 4+ state Sn from the precursor readily oxidizes postgrowth resulting in an oxide-rich surface layer.

Degradation of sodium butylxanthate in flotation wastewater by natural pyrite via visible light-assisted advanced oxidation processes: A comprehensive study

The advanced oxidation process (AOPs) based on natural pyrite (NP) as a catalyst is a promising strategy for flotation wastewater purification. However, the slow Fe(III)/Fe(II) cycle limits the number of active sites during oxidant activation. Therefore, this work attempts to accelerate Fe(III)/Fe(II) reduction on NP surface by introducing visible light irradiation. By comparing the degradation performance of sodium butylxanthate (SBX) via various oxidants (peroxydisulfate, periodate, hydrogen peroxide, and sulfite) activation under visible light, periodate was selected as the most suitable oxidant for SBX removal. Although peroxydisulfate exhibits optimal SBX degradation in acidic environments, its failure in alkaline environments and poor reusability caused by high surface oxidation limit its application. The investigation of active species suggests that O2[Formula: see text] are the dominant active species in hydrogen peroxide and sulfite activation systems, while the electron transfer process is the dominant active species in peroxydisulfate and periodate activation systems. Electrochemistry elucidates the interaction of different oxidants on the NP surface. XPS analysis revealed that the photogenerated electrons induced by visible light irradiation accelerate the Fe(III)/Fe(II) cycle on NP surface, thereby improving the continuous activation of NP towards the oxidants. In addition, the ecotoxicity of wastewater treated by the periodate activation system is greatly reduced. This work provides a new idea towards flotation wastewater purification.

Comparative study on the status of microplastics in different functional areas of Tuticorin, Southeast coast of India

Microplastics (MPs) and the pollutants associated with them pose a significant risk to the aquatic ecosystems. This study analysed the spatial and seasonal differences in MPs in terms of diversity, inventory and associated heavy metals, and assessed the risk carried by MPs in different functional areas of Tuticorin, southeast coast of India. The mean MPs abundance varies from 5.67 ± 3.1 to 94.66 ± 6.5 items/L in water and 6 ± 1.73 to 147 ± 18.6 items/kg in sediment. More MPs are found in monsoon water and post-monsoon sediment. Fibre-shaped polyethylene (PE) and polypropylene (PP) MPs have a dominant presence in all seasons. They might derive from synthetic clothing, derelict fishing gear and improper dumping of plastic waste in this region. The carbonyl index (CI) of PE varies from 0.01 to 1.2 and that of PP from 0.03 to 0.98. The high surface oxidation rate (with CI ≥ 0.31) indicates the weathering level of MPs. The high microplastics diversity index (MPDII) of the Fishing Harbour points to the diverse pollution sources. The inventory of MPs is expressed in terms of their weight-based accumulation. Higher inventory of MPs is detected in the water (0.018 ton/km2) and sediment (2.03 ton/km2) of Fishing Harbour. The scanning electron microscope (SEM) images of MPs reveal various surface morphologic features like cracks, protrusion, void space, and adsorbed microorganisms. Energy dispersive X-ray spectroscopy (EDAX) shows the presence of metals (Mn, Cu, Zn, Ni, K, Ca, Cr, Mg, Ti, Cd, As, Se, Fe, Al, and Si) on the MPs surfaces. The polymer hazard index (PHI) indicates a III to IV chemical risk level. All the information obtained from the analysis presents a clear image of the nature and distribution of MPs in this region.

Wettability of liquid metals on PEDOT:PSS for soft electronics

Due to the high conductivity and flexibility of liquid metal, soft electronics are believed to be an ideal material for wearable electronics. However, high surface tension and surface oxides make it extremely challenging to load liquid metals onto flexible hydrophilic substrates. In this study, the excellent wettability of liquid metals on poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) was systematically examined. This property was attributed to the synergistic effect of chemical and physical adhesion of liquid metals on PEDOT:PSS. By loading PEDOT:PSS onto a hydrophilic substrate, liquid metals were selectively adhered to the PEDOT:PSS region. As a result, a simple and high efficient PEDOT:PSS-assisted method for preparing liquid–metal soft electronics was developed. More intriguingly, highly conductive PEDOT:PSS after doping treatment still maintained outstanding wettability to liquid metals, favoring the realization of non-corrosive electrical connections between liquid metals and low cost electrode material (Cu). This PEDOT:PSS-assisted strategy can be used to fabricate various liquid metal-based electronics including soft circuits, paper electronics (1D), flexible sensors (2D), and conductive foams (3D), offering huge potential for flexible electronics and wearable sensors.

UV Sterilization Effects and Osteoblast Proliferation on Amorphous Carbon Films Classified Based on Optical Constants.

Optical classification methods that distinguish amorphous carbon films into six types based on refractive index and extinction coefficient have garnered increasing attention. In this study, five types of amorphous carbon films were prepared on Si substrates using different plasma processes, including physical and chemical vapor deposition. The refractive index and extinction coefficient of the amorphous carbon films were measured using spectroscopic ellipsometry, and the samples were classified into five amorphous carbon types—amorphous, hydrogenated amorphous, tetrahedral amorphous, polymer-like, and graphite-like carbon—based on optical constants. Each amorphous carbon type was irradiated with 253.7 nm UV treatment; the structure and surface properties of each were investigated before and after UV treatment. No significant changes were observed in film structure nor surface oxidation after UV sterilization progressed at approximately the same level for all amorphous carbon types. Osteoblast proliferation associated with amorphous carbon types was evaluated in vitro. Graphite-like carbon, which has relatively high surface oxidation levels, was associated with higher osteoblast proliferation levels than the other carbon types. Our findings inform the selection of suitable amorphous carbon types based on optical constants for use in specific medical devices related to osteoblasts, such as artificial joints and dental implants.

Geochemical elements in suspended particulate matter of Ensenada de La Paz Lagoon, Baja California Peninsula, Mexico: Sources, distribution, mass balance and ecotoxicological risks

The present study aimed to evaluate multi-element concentrations (Al, As, Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Pb, Sr) in suspended particulate material (SPM) collected from Ensenada de La Paz (ELP) lagoon, Baja California Sur, Mexico in two different periods (September and May) to comprehend their origin, geochemical behavior, mass transfer and associated ecotoxicological risks. The 24 hr variation coefficient of volumetric SPM levels were found to be 51.7% in September and 40.5% in May, signifying the effects of oceanic waters. The calculated enrichment factor (EF) values for all the studied elements were of higher magnitude because of the high surface area and oxide nature of SPM, and in this study, Mo had the highest EF of 46.77 probably due to its origin from continental weathering. From the ecotoxicological perspective, the integrated toxic risk index revealed low toxic risk to the benthic community. However, the mean-ERM-Quotient calculated using the particulate concentrations of As, Cd, Cr, Cu, Ni, Pb indicated 9% probability of toxicity to biota. The comprehensive geochemical and ecotoxicological assessment of particulate metal concentrations in the ELP lagoon signify low to moderate contamination.

Ultralow-temperature superplasticity of high strength Fe–10Mn-3.5Si steel

Superplastic steels with high elongations above 300% are expected to be used for manufacturing complex-shaped mechanical parts without joining. However, their practical application is difficult due to high energy consumption and surface oxidation caused by a high deformation temperature (≥873 K). Here, we propose a new high strength Fe–10Mn-3.5Si steel, which is superplastically deformed at 763 K. This steel exhibits different microstructural and deformation features from previous superplastic steels, such as single phase before deformation, coarse elongated grains, low strain rate sensitivity, and strong texture. The superplasticity of the steel results from both dislocation creep and grain boundary sliding due to dynamic reverse transformation. Because the steel has a low material cost and is produced by conventional rolling, it is suitable for practical application.

Insights into the Effect of Precursors on the FeP-Catalyzed Hydrogen Evolution Reaction.

Iron phosphide nanoparticles (NPs) are promising noble metal-free electrocatalysts for the hydrogen evolution reaction (HER), but they usually show inferior activity due to the limited surface area and oxidative passivation. We reported a facile synthetic method to prepare FeP hollow NPs (HNPs) with various precursors. It was proven that the structural parameters (i.e., size, phosphating temperature, phase, and surfactant) of oxide precursors were correlated to the electrochemically active surface area (ECSA), phase purity, surface oxidation, and hollow morphology of FeP HER catalysts, thus affecting the HER activity. Among the three FeP HNPs, the 9 nm FeP HNPs prepared using the Fe3O4 precursor exhibited the highest overall activity with the lowest overpotential of 76 mV to drive a cathodic current density of 10 mA·cm-2 due to the highest ECSA, while 25 nm FeP prepared using the Fe2O3 precursor showed the highest turnover frequency because of the high phase purity and low surface oxidation degree.

Effect of metal mesh addition on polymer surface etching by an atmospheric pressure plasma jet

Atmospheric pressure plasma jet has shown great potential for polymer film treatment, but the etching process of polymer surface by the plasma jet is still not developed. In this paper, the effect of a grounded metal mesh addition on the etching process of polymer surface through the plasma jet was investigated. Comparative study of polymer film treated by the plasma jet with and without a grounded stainless steel mesh (SSM) is systematically investigated by the analysis of etching rate, surface morphologies and chemical compositions. Compared with the plasma etching process with SSM, the etching results without the addition of SSM have much higher etching rate, rougher etched surface, and higher surface oxidation. Finally, the etching process occurring at the plasma/polymer interface was also discussed. Since the addition of SSM could filter out the charged particles in plasma jet, the role of charged particles in the etching process was discussed and the synergetic etching process was proposed based on the structural dependence and chemical analysis of the observed results.

In Situ Formed “Sn1–XInX@In1–YSnYOZ” Core@Shell Nanoparticles as Electrocatalysts for CO2 Reduction to Formate

AbstractElectrochemical reduction of CO2 (CO2RR) driven by renewable energy has gained increasing attention for sustainable production of chemicals and fuels. Catalyst design to overcome large overpotentials and poor product selectivity remains however challenging. Sn/SnOx and In/InOx composites have been reported active for CO2RR with high selectivity toward formate formation. In this work, the CO2RR activity and selectivity of metal/metal oxide composite nanoparticles formed by in situ reduction of bimetallic amorphous SnInOx thin films are investigated. It is shown that during CO2RR the amorphous SnInOx pre‐catalyst thin films are reduced in situ into Sn1–XInX@In1–YSnYOz core@shell nanoparticles composed of Sn‐rich SnIn alloy nanocores (with x < 0.2) surrounded by InOx‐rich bimetallic InSnOx shells (with 0.3 < y < 0.4 and z ≈ 1). The in situ formed particles catalyze the CO2RR to formate with high faradaic efficiency (80%) and outstanding formate mass activity (437 A gIn+Sn−1 @ −1.0 V vs RHE in 0.1 m KHCO3). While extensive structural investigation during CO2RR reveals pronounced dynamics in terms of particle size, the core@shell structure is observed for the different electrolysis conditions essayed, with high surface oxide contents favoring formate over hydrogen selectivity.

Effect of Water Adsorption on the Frictional Properties of Hydrogenated Amorphous Carbon Films in Various Relative Humidities.

The tribological properties of hydrogenated amorphous carbon (a-C:H) films in ambient air were investigated from the microstructural point of view. a-C:H films with various microstructures (polymer-like, diamond-like, and graphite-like structures) were prepared, and the thickness of water adsorption layers on the films was measured. The adsorption behavior of water molecules on a-C:H films could be expressed with the Brunauer-Emmett-Teller (BET) isotherm, while the thicknesses of icelike and liquidlike water layers adsorbed on the films could be determined using the BET parameters C and nma. The polymer-like films exhibited the thickest icelike and liquidlike water adsorption layers, which decreased as the film structure changed to a diamond-like or a graphite-like structure. A strong relationship was observed between the thickness of water adsorption layers and the surface oxidation of the a-C:H films. The friction coefficient of the films in ambient air can be well explained by the surface oxidation and the thickness of water adsorption layers. Polymer-like films showed high friction coefficients due to the formation of a thick water layer on the films originated from the high surface oxidation of the film surface, whereas the graphite-like film exhibited a low friction coefficient due to low oxidation and a thin water adsorption layer. Furthermore, friction tests between the a-C:H films with different microstructures under ambient air were performed to determine the lowest friction pair in various relative humidities (RHs).

Study on Heat Transfer Performance and Anti-Fouling Mechanism of Ternary Ni-W-P Coating

Since the formation of fouling reduces heat transfer efficiency and causes energy loss, anti-fouling is desirable and may be achieved by coating. In this work, a nickel-tungsten-phosphorus (Ni-W-P) coating was prepared on the mild steel (1015) substrate using electroless plating by varying sodium tungstate concentration to improve its anti-fouling property. Surface morphology, microstructure, fouling behavior, and heat transfer performance of coatings were further reported. Also, the reaction path, transition state, and energy gradient change of calcite, aragonite, and vaterite were also calculated. During the deposition process, as the W and P elements were solids dissolved in the Ni crystal cell, the content of Ni element was obviously higher than that of the other two elements. Globular morphology was evenly covered on the surface. Consequently, the thermal conductivity of ternary Ni-W-P coating decreases from 8.48 W/m·K to 8.19 W/m·K with the increase of W content. Additionally, it goes up to 8.93 W/m·K with the increase of heat source temperature 343 K. Oxidation products are always accompanied by deposits of calcite-phase CaCO3 fouling. Due to the low surface energy of Ni-W-P coating, Ca2+ and [CO3]2− are prone to cross the transition state with a low energy barrier of 0.10 eV, resulting in the more formation of aragonite-phase CaCO3 fouling on ternary Ni-W-P coating. Nevertheless, because of the interaction of high surface energy and oxidation products on the bare matrix or Ni-W-P coating with superior W content, free Ca2+ and [CO3]2− can be easy to nucleate into calcite. As time goes on, the heat transfer efficiency of material with Ni-W-P coating is superior to the bare surface.

Energy Coupling of Laser Radiation on AISI 304 Stainless Steel: Effect of High Temperatures and Surface Oxidation.

The industrial application of laser materials processing methods is still far ahead of research into the physical phenomena occurring during these processes. In particular, the effect of high temperatures on the energy coupling of laser irradiation of metals is poorly understood. However, most processes in laser materials treatment involve temperatures above the melting point or even cause evaporation. This study therefore evaluates the effect of high temperatures on the energy coupling efficiency of stainless steel experimentally for three typical laser wavelengths (515 nm, 1.07 µm, 10.6 µm). As a result, it is shown that the effect of temperature on the energy coupling efficiency depends on the wavelength. In this context the relevance of the X-point phenomenon known from the emissivity theory could be demonstrated for laser material processing. Further, the effect of a process-induced surface oxidation is analyzed. At temperatures above 650 °C the energy coupling efficiency dramatically increases to around 65% at melting point and stays at this high level even in the liquid phase.

Thermal Fatigue Failure of Low-Pressure Turbine Blade in a Low-Bypass Turbofan Engine

Failure of low-pressure (LP) turbine rotor blade in a low-bypass turbofan engine is analyzed to determine its root cause. Forensic and metallurgical investigations are carried out on the affected blades. High surface oxidation on damaged blade is found to be the reason for crack initiation in blades. Thermal fatigue is the probable cause of failure in the blades due to prolong operation at maximum condition and malfunction of engine control system.

Influence of Braking Conditions on Tribological Performance of Copper-Based Powder Metallurgical Braking Material

High-speed transportation tools demand durable and effective friction materials for practical applications. In this work, we developed a copper-based powder metallurgical friction material via spark plasma sintering, and studied its tribological performances subjected to different braking conditions. Using inertial braking test bench and temperature measuring instrument, average friction coefficient, instantaneous friction coefficient and temperature near friction surface of the material in braking process were tested at two initial speeds (28, 69 m/s) and three contact pressures (0.4, 0.6 and 0.8 MPa). The wear rate of materials was calculated accordingly. Results show that under the same exerted pressure, the average friction coefficient and wear rate at the high speed are smaller than those at the low speed. At the high test speed, the high friction temperature leads to an obvious decrease in instantaneous friction coefficient when the braking process reaches a certain stage. Based on the friction surface morphology analysis, the adhesive wear on the surface has been reduced because of the formation of oxide films at the high speed and surface oxidation wear gradually increases as the pressure increases.

Polymer etching by atmospheric‐pressure plasma jet and surface micro‐discharge sources: Activation energy analysis and etching directionality

Treatments of polymer films using either a MHz atmospheric pressure plasma jet (APPJ) or an atmospheric pressure surface micro‐discharge (SMD) plasma are investigated. While the typical approach to determine relevant reactive species is to correlate surface effects with gas phase species measurement, this does not capture potential synergistic or other complex effects that may be occurring. Activation energy and directionality of the etching process can characterize what is occurring at the surface for these processes in more detail. The APPJ source shows an apparent activation energy of ∼0.18 eV at 8 mm distance and up to ∼0.34 eV at 16 mm distance for a temperature range of 20–80 °C tested with thin polymer films. The APPJ source shows directional etching at 8 mm distance with less anisotropy the more distance is increased. The SMD source has an apparent activation energy of ∼0.8–0.9 eV at a distance of 3 mm. The SMD also only shows isotropic etching behavior. However the SMD surface chemistry changes significantly to less oxidation with increased temperature while the APPJ source induced modifications remain very similar with temperature change. The lower apparent activation energy of the APPJ‐induced etching reactions as compared with low pressure work (0.5 eV) and observation of line‐of‐sight contribution to etching suggests the involvement of a directional species at closer distances facilitating the etching which falls off with increasing distance. The high activation energy of the SMD suggests that species with less capability for etching is responsible compared to the APPJ and low pressure plasma. The high surface oxidation from low temperature SMD treatments shows that the surface is being oxidized but not sufficiently to reach the desorption step of the etching process.

Solvothermal tuning of photoluminescent graphene quantum dots: from preparation to photoluminescence mechanism

Solvothermal synthesis was employed to tune the surface states of graphene quantum dots (GQDs). Two series of GQDs with the particle sizes from 2.6 to 4.5 nm were prepared as follows: (I) GQDs with the same size but different oxygen degrees; (II) GQDs with different core sizes but the similar surface chemistry. Both the large sizes and the high surface oxidation degrees led to the redshift photoluminescence (PL) of GQDs. Electrochemiluminescence (ECL) spectra from two series of GQDs were all in accordance with their PL spectra, respectively, which provided good evidence for the conjugated structures in GQDs responsible for PL.

Micropatterning of Liquid Metal by Dewetting

Although gallium-based liquid metals are attracting growing interest thanks to its potential applications in deformable, flexible electronic devices, challenges in fabrication associated with the high surface tension and oxide skin remain to be overcome. We report a novel fabrication technique for liquid metal circuits using dewetting. An excessively thin liquid film spontaneously shrinks on a substrate to reduce surface free energy. In the case of a thin liquid metal film on a substrate with microgrooves, the oxide on the microgroove wall and the additional viscous resistance delay the shrinkage in the grooves, which separates the liquid volume inside the microgrooves from the external volume. Utilizing this mechanism, we successfully produced 20- $\mu \text{m}$ -thick conductive lines of eutectic gallium indium (EGaIn) on polydimethylsiloxane. This fabrication technique is simple, fast, and cost-effective and requires no top covering layer. The resultant metal lines show potentially applicable electrical resistance to flexible and stretchable electronic devices. [2017-0082]