Influence Of Surface Oxidation Research Articles

Influence of Surface Oxidation on the Wettability and Filtration Properties of Coal

Influence of Surface Oxidation on the Wettability and Filtration Properties of Coal

Ab initio-guided X-ray photoelectron spectroscopy quantification of Ti vacancies in [formula omitted] thin films

Ab initio calculations were employed to investigate the effect of oxygen concentration dependent Ti vacancies formation on the core electron binding energy shifts in cubic titanium oxynitride (Ti1−δOxN1−x). It was shown, that the presence of a Ti vacancy reduces the 1s core electron binding energy of the first N neighbors by ∼0.6 eV and that this effect is additive with respect to the number of vacancies. Hence it is predicted that the Ti vacancy concentration can be revealed from the intensity of the shifted components in the N 1s core spectra region. This notion was critically appraised by fitting the N 1s region obtained via X-ray photoelectron spectroscopy (XPS) measurements of Ti1−δOxN1−x thin films deposited by high power pulsed magnetron sputtering. A model to quantify the Ti vacancy concentration based on the intensity ratio between the N 1s signal components, corresponding to N atoms with locally different Ti vacancy concentration, was developed. Herein a random vacancy distribution was assumed and the influence of surface oxidation from atmospheric exposure after deposition was considered. The so estimated vacancy concentrations are consistent with a model calculating the vacancy concentration based on the O concentrations determined by elastic recoil detection analysis and text book oxidation states and hence electroneutrality. Thus, we have unequivocally established that the formation and population of Ti vacancies in cubic Ti1−δOxN1−x thin films can be quantified by XPS measurements from N 1s core electron binding energy shifts.

Influence of surface oxidation on the quantification of polypropylene microplastics by pyrolysis gas chromatography mass spectrometry

The influence of photo-oxidation on the quantification of isotactic polypropylene by Pyrolysis Gas Chromatography/Mass Spectrometry (Pyr-GC/MS) was assessed. Beads (oval shape, ~5 mm) and fragments (irregular shaped, 250–50 μm and 500–1000 μm) were subjected to relatively harsh simulated accelerated weathering conditions (using a filtered xenon-arc reproducing sunlight's full spectrum) for up to 37 and 80 days, respectively. Samples collected (n = 10 replicates for each treatment) at increasing number of weathering days were analysed by Fourier-transform infrared spectroscopy with Attenuated Total Reflection (FTIR-ATR), scanning electron microscopy, and differential scanning calorimetry in order to assess the extent and the rate of degradation. The rate of surface oxidation occurred faster for fragments compared to beads, probably due to their higher surface area. Quantification of the polypropylene trimer (2,4-dimethyl-1-heptene) via double shot Pyr-GC/MS, showed that the signal of the trimer relative to the mass of polypropylene was reduced through weathering with a degradation rate of 1:3 faster for fragments over beads. Signal reduction and carbonyl index were correlated to show that polypropylene with a carbonyl index of ≥13 has a significantly reduced 2,4-dimethyl-1-heptene signal when compared to virgin material. Consequently, the quantification of polypropylene subjected to weathering under harsh conditions may be underestimated by 42% (fragments, carbonyl index: 18) to 49% (beads, carbonyl index: 30) when quantified by Pyr-GC/MS and using virgin polypropylene calibration standards. Pyrolysis at a lower temperature (350 °C) identified six degradation specific markers (oxidation products) that increased in concentration with weathering. Further comparisons between virgin and weathered microplastics may need to be considered to avoid underestimation of microplastic concentrations in future studies.

Bonding Mechanisms in Cold Spray: Influence of Surface Oxidation During Powder Storage

Cold spray is a solid-state process in which solid particles are subjected to severe plastic deformation to form a coating. The effect of naturally occurring oxides on bonding in the cold spray was investigated in this work. Deposition characteristics of copper powder with different surface oxide thicknesses on steel substrate were examined using a local pull-off test. This enables the investigation of individual particle/substrate interfaces. X-ray photoelectron spectroscopy was used to study thoroughly the powder surface chemistry and the oxide thickness as a function of exposure time. This study revealed that the oxide film thickness grew from 6 nm for the as-received powder to 11.6 nm after 2 months of exposure to atmospheric conditions. Scanning electron microscopy and x-ray energy dispersive spectroscopy were used to characterize the particle/substrate interfacial bonding. Adhesion test results show that the bond strength is highly influenced by the surface oxide thickness. Different bonding behaviors and a drop in coating deposition efficiency were observed as the oxide thickness increased. Finite element simulations supplemented our understanding of the particle adhesion dynamics as the oxide film thickness increases. They were also used to study the surface oxide cleanup and bonding mechanism for particles with different oxide film thicknesses.

Influence of Oxygen-Containing Functional Groups on the Environmental Properties, Transformations, and Toxicity of Carbon Nanotubes.

Carbon nanotubes (CNTs) have unique physical and chemical properties that drive their use in a variety of commercial and industrial applications. CNTs are commonly oxidized prior to their use to enhance dispersion in polar solvents by deliberately grafting oxygen-containing functional groups onto CNT surfaces. In addition, CNT surface oxides can be unintentionally formed or modified after CNTs are released into the environment through exposure to reactive oxygen species and/or ultraviolet irradiation. Consequently, it is important to understand the impact of CNT surface oxidation on the environmental fate, transport, and toxicity of CNTs. In this review, we describe the specific role of oxygen-containing functional groups on the important environmental behaviors of CNTs in aqueous media (e.g., colloidal stability, adsorption, and photochemistry) as well as their biological impact. We place special emphasis on the value of systematically varying and quantifying surface oxides as a route to identifying quantitative structure-property relationships. The role of oxygen-containing functional groups in regulating the efficacy of CNT-enabled water treatment technologies and the influence of surface oxides on other carbon-based nanomaterials are also evaluated and discussed.

Martensitic transformation in free-standing Cu-Al-Ni thin films with micrometric grain size

The martensitic transformation of polycrystalline thin films based on shape memory alloys is usually affected by the average grain size and by the thickness. We have carried out a study of the temperature driven martensitic transformation in micrometric grain size Cu-Al-Ni films with 18R structure. Thin films with a thickness of 6 μm were grown by sputtering on highly oriented pyrolytic graphite HOPG (0001) substrate at 873 K. After that, the samples were peeled-off from the substrate and annealed at 1123 K for 30 min. The observed microstructure shows an average grain size of 3.7 (± 0.2) μm. The martensitic start temperature (Ms) for different films ranges from 170 K to 370 K due to small changes in the chemical concentration. The influence of surface oxides and changes in the atomic order produced by post-quench aging treatments is analyzed. The results show that while surface passivation has a weak influence, changes in the atomic order increase Ms without impacting significantly on the hysteresis. Comparison with previous results of nanometric and micrometric grain size samples reveals that the barriers for the transformation are mainly given by plastic deformation at grain boundaries.

Spectroscopic ellipsometry extraction of optical constants for materials from oxide covered samples: Application to the plutonium/oxides system

Spectroscopic ellipsometry is combined with scanning electron microscopy and multisample analysis of the measured oxide thickness difference from one sample at two different times during the oxide growth phase or from two separate samples to obtain the optical constants of the oxides. With the obtained thickness and optical constants of the oxides, the optical properties of the substrate material can be uniquely deduced. This methodology has been applied to obtain, the refractive indices and extinction coefficients of delta plutonium (δ-Pu) metal with 0.5 wt. % Ga in the wavelength region from 435 nm to 850 nm, without the influence of surface oxides. The presented methodology can also be applied to metals and semiconductors from surface oxidized samples, even when the oxides do not possess a common set of optical characteristics.

Enhancement of NH3 and water adsorption by introducing electron-withdrawing groups with maintenance of pore structures

Activated carbons have been well-used for separation, removal, and storage for various gases. Pore width and surface functional groups are primal factors of interactions with adsorbed molecules. Surface functional groups especially influence adsorptions of acidic and basic molecules, although all molecules are considerably influenced by pore width. Controlling optimal pore width and surface functional group is however very difficult, because both factors of pore width and surface functional groups are simultaneously changed in preparation process. We here attempted to prepare oxygen-introduced activated carbon with different surface oxides into activated carbons and with the similar pore structure. NH3, CO2, acetaldehyde, isoprene, and water were used for evaluating the influence of surface oxides in carbon pores. As the surface oxides increased, NH3 adsorbed amounts were considerably increased accompanying an irreversible adsorption and a threshold pressure of water adsorption was shifted to lower relative pressure, while adsorption isotherms of the other molecules were rarely changed. A comparison of interaction between any surface oxides and adsorbed molecules indicated that NH3 and water molecules having the electron donor were strongly adsorbed on the acid surface oxides. The oxygen-introduced activated carbons without any destruction of the pore structure exhibited a considerable adsorption potential for molecules having the electron donor, and maintained an adsorption potential for molecules having the nonpolar and electron acceptor, proposing effective removal and separation with high adsorption capacity.

Influence of surface oxide on mechanical properties of laser-welded hot-press-forming steel with strength of 1.8 GPa

The hot-press-forming (HPF) steel has been proposed to overcome the insufficient formability of the GPa-grade high-strength steel. During the HPF process, a steel sheet is heated over a full austenitization (Ac3) temperature and thick oxidation scales are formed on the surface unless it is protected with an appropriate coating layer. In this study, the laser weldability of 1.8-GPa-grade HPF steel was investigated, and the effect of oxidation scales on the sheets was examined. Bead-on-plate welding and overlap welding were conducted on the 1.8-GPa HPF steel sheets with the oxidized surface layer. The oxide was diluted into the weld metal, which changed the microstructure of the weld metal and had a detrimental effect on the mechanical properties. The oxide layer on the sheet should be removed prior to welding so as to improve the weld strength.

Achieving Ultrafast and Stable Na-Ion Storage in FeSe2 Nanorods/Graphene Anodes by Controlling the Surface Oxide.

Designing transitional metal selenides (TMSes) with superior rate and cyclic performance for sodium-ion storage remains great challenges. To achieve this task, the influence of surface oxides on Na-ion storage behavior of FeSe2 is investigated by designing FeSe2 with varying oxide content. It is found that surface oxide has an inhibitory effect on the activity of FeSe2. Small-sized FeSe2 on graphene with higher surface oxide content exhibits obviously inferior performance compared to large-sized FeSe2 with lower oxide content. By controlling oxide content, the prepared FeSe2 nanorods/graphene exhibits a high capacity of 459 mAh/g at 0.1 A/g and superior rate performance. Only 10% capacity decrease occurs with the increase in current density from 0.1 to 5 A/g. Even at 25 A/g (∼50 C), it delivers a capacity of 227 mAh/g with almost no decay after 800 cycles. The influence mechanism of surface oxide is investigated. The oxide can be converted to a sodiated shell with high mechanical strength and poor conductivity, which generates phase-transition resistance to suppress the sodiation of FeSe2 core, blocks the transfer of Na-ions and electrons in subsequent sodiation processes. Understanding the effect of surface oxide on Na-ion storage will be helpful in designing TMSes and other active materials.

Deuterium thermal desorption and re-emission from RAFM steels

In the present work, deuterium (D) retention and release during and after ion irradiation of reduced-activation ferritic-marthensitic steels (Eurofer) in comparison with the D retention in pure iron (Fe) was studied. The irradiation was done with 5 keV ions at room temperature at the fluence varied in the range of 1 × 1020–1 × 1022 D m−2. Thermal desorption spectroscopy (TDS) was also performed in situ in 45 min after irradiation. The D release from both materials between the end of irradiation and the start of TDS was very intensive and the integral amount of D measured during outgassing exceeded the D retention measured by TDS. An influence of surface oxidation on the D release due to contact with an environmental air was also demonstrated by comparison of in situ and ex situ TDS. The integral D retention in Eurofer was 1–2 orders of magnitude higher than in pure iron (Fe) due to the initially high concentration of defects in Eurofer. However, pre-annealing of Eurofer at 800 K reduced the defect concentration in Eurofer and, therefore, reduced the difference in the D retention in Fe and Eurofer.

Ion Dynamics and Electrosorption in Carbon Electrodes with Bimodal Porosities and Heterogeneous Interfaces

Electrochemical capacitors offer high reliabilities and power densities and demonstrate exceptional promise in a broad range of energy storage and management applications. However, research efforts have not, to date, properly explored the influence of electrode interfaces’ heterogeneity and disorder on charge storage and dynamics of electrosorbed ions. Surface functional groups and structural carbon defects contribute quantum capacitance.[1] Specific surface functional groups, which must appropriately match the chemistries of electrosorbed ions, develop favorable interfaces that reduce impedance and improve cyclabilities.[2] Finally, ionophilic surfaces draw ions away from pore surfaces and improve electrosorption during charge and discharge processes.[3] However, these effects strongly depend on electrode pore dimensions and behaviors of ions in confinement. Furthermore, standard materials characterization and electrochemical testing techniques cannot properly assess interactions at electrode/electrolyte interfaces. Subsequently, in-depth studies must rely on combinations of well-tailored experimental model systems, in-depth X-ray and neutron scattering techniques, and computational modeling to assess the influences of disordered interfaces on capacitance. Our research investigated the effect of electrode surface heterogeneity and disorder in complex pore architectures and electrolytes with large, non-idealized electrolytes. The approach used carbide-derived carbons (CDCs) synthesized from a Mo2C precursor at 800 °C. This electrode material offered bimodal pore size distributions (0.8 nm and 2.6 nm diameter pores, shown in Figure 1a), and 1300 °C vacuum annealing or 400 °C air oxidation yielded, respectively, defunctionalized or oxidized pore surfaces. We filled these pores with 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([OMIm+][TFSI-]) room-temperature ionic liquid (RTIL). QENS measurements on these systems determined that the ions were significantly more mobile in oxidized pores than in defunctionalized pores (Figure 1b). A Cole-Cole model derived mobility information, and the RTIL diffusion coefficient in oxidized pores (2.71*10-10 m2 s-1) was more than twice as large as the one for the same RTIL in defunctionalized pores (1.05*10-10 m2 s-1) due to lower ion densities in oxidized pores. Electrochemical impedance analysis showed that electrochemically driven ionic mobility was higher in oxidized pores. On the other hand, defunctionalized pores demonstrated contained higher ion densities, and, subsequently, featured higher charge storage densities (Figure 3f). However, cyclic voltammograms suggested charge saturation and pore de-filling behaviors at low potentials; surface chemistry influenced the magnitude of this effect. Molecular dynamic (MD) simulations showed similar strong affinities of oxidized surfaces for RTIL ions, which lowered their charge storage densities in 2.6 nm diameter pores. X-ray Pair Distribution Function (PDF) analysis showed differences in ion-ion correlations between bulk and confined states and further underscored the influence of pore and ion diameter on electrode/electrolyte interactions at heterogeneous interfaces. [1] Dyatkin, B. & Gogotsi, Y. Effects of Structural Disorder and Surface Chemistry on Electric Conductivity and Capacitance of Porous Carbon Electrodes. Faraday Discussions172, 139-162, (2014). [2] Dyatkin, B., et al. Capacitance, Charge Dynamics, and Electrolyte-Surface Interactions in Functionalized Carbide-Derived Carbon Electrodes. Progress in Natural Science - Materials International25, 631–641, (2015). [3] Dyatkin, B., et al. Influence of Surface Oxidation on Ion Dynamics and Capacitance in Porous and Non-Porous Carbon Electrodes. The Journal of Physical Chemistry C, (2016). Figure 1

The influence of surface oxides on the mechanical response of oxidized grain boundaries

The mechanical response of oxidized grain boundaries in a nickel alloy used for nuclear applications has been investigated by performing microcantilever bend tests. It was found that whilst failure can proceed along the oxide-metal interface not all oxidized grain boundaries exhibit intergranular failure. The presence of an external surface oxide has been identified as playing a crucial role in influencing the mechanical response. By removing the surface oxide, using a focused ion beam, tests were performed on the same grain boundaries with and without a surface oxide layer, and showed that surface oxides can suppress or delay fracture. Taking into account the effect of the surface oxide on microcantilever tests, it was possible to present the most accurate parameterization of the local stress at failure of oxidized grain boundaries to date and to predict the experimentally observed behavior via realistic cohesive damage finite element simulations, which further underline the experimental observations.

Influence of surface oxidation on the radiative properties of ZrB2-SiC composites

The spectral emissivities of ZrB2-20 vol.% SiC composites with various surface components of ZrB2/SiC (ZS1), silica-rich glass (ZS2) and porous zirconia (ZS3) were measured using infrared spectrometer in the wavelength range from 2.5 to 25.0μm. The relationship between surface oxidation (associated with surface component, thickness of oxide scale, testing temperature as well as roughness) and the radiative properties of ZrB2-SiC composites were investigated systematically. Surface component affected the radiative properties of composites significantly. The total emissivity of ZS1 varied from 0.22 to 0.81 accompanied with surface oxidation in the temperature range 300–900°C. The emissivity of ZS2 was about 1.5 times as that of ZS3 under the same testing conditions. The oxide scale on specimen surface enhanced the radiative properties especially in terms of short-wave range, and the emissivity in the long-wave range gradually increased with the thickness of oxide scale within a certain range. The influence of testing temperature and surface roughness was also investigated. The testing temperature had a little effect on radiative properties, whereas effect of surface roughness could be negligible.

Microstructure and Magnetic Properties of Bulk FeCo Alloys Fabricated from Mechanically Alloying and Chemically Synthesized Powders

Three different methods of fabrication of FeCo soft magnetic material using ferromagnetic powders are compared: (i) simple sintering of elemental powders of Fe and Co, (ii) sintering of mechanically alloying FeCo powder, and (iii) sintering of chemically synthesized FeCo powder. The microstructure of ferromagnetic powders and bulk sintered alloys is characterized using scanning electron microscopy and energy-dispersive X-ray spectroscopy analysis. The best magnetic properties with high saturation magnetization, Ms = 211.3 emu/g, are obtained for bulk FeCo alloy sintered from chemically synthesized powder. It consists of nearly spherical FeCo particles with diameters from 5 to 15 μ m. The mean particle size of chemically synthesized FeCo powder can be controlled by changing the melt composition, temperature, and process duration. The relatively large size of FeCo particles reduces the influence of surface oxidation on the particle magnetic properties. The low-cost chemical technology developed is promising for a large-scale production of small FeCo magnetic components of arbitrary shapes with high-dimensional precision.

Влияние поверхностных оксидов на механизм сцепления покрытия при плазменном напылении

Влияние поверхностных оксидов на механизм сцепления покрытия при плазменном напылении

Influence of O2 exposure on the interaction between CH4 and amorphous AlYB14

The influence of surface oxidation on the interaction between CH4 and amorphous AlYB14 (a-AlYB14) has been studied theoretically by using density functional theory and experimentally by ultra-high vacuum atomic force microscopy (UHV-AFM). CH4 mimics the –CH3 termination and aliphatic subunits of a polymer chain. Low-energy ion scattering measurements of magnetron sputtered thin films suggest that the bonding at the surfaces of pristine a-AlYB14 and O2 exposed a-AlYB14 (O2//a-AlYB14) is metal-boron and metal-oxygen dominated, respectively. Based on the ab initio calculations the adsorption energies of CH4 on a-AlYB14 and O2//a-AlYB14 decreases from −0.07 to −0.30eV, respectively. This trend is consistent with experimental data obtained by colloidal probe UHV-AFM studies with a polyethylene sphere, where larger adhesion forces for the O2 exposed surface as compared to the pristine a-AlYB14 surface were measured. No charge transfer takes place between CH4 and the pristine as well as the O2 exposed a-AlYB14. Oxygen chemisorption induces changes in surface bonding. States at the Fermi level are depleted upon oxidation, hence the surface bonding becomes more semiconducting causing a charge redistribution within the adsorbed CH4 molecule. Hence, these data serve as proof of concept for exploring the effect of O2 exposure on the interaction between aliphatic polymers and a-AlYB14 using a correlative experimental and theoretical research approach.

Possible influence of surface oxides on the optical response of high-purity niobium material used in the fabrication of superconducting radio frequency cavity

We have investigated the possible influence of surface oxides on the optical properties of a high-purity niobium (Nb) material for fabrication of superconducting radio frequency (SCRF) cavities. Various peaks in the infrared region were identified using Fourier transform infrared and Raman spectroscopy. Optical response functions such as complex refractive index, dielectric and conductivity of niobium were compared with the existing results on oxides free Nb and Cu. It was observed that the presence of a mixture of niobium-oxides, and probably near other surface impurities, appreciably influence the conducting properties of the material causing deviation from the typical metallic characteristics. In this way, the key result of this work is the observation, identification of vibrational modes of some of surface complexes and study of its influences on the optical responses of materials. This method of spectroscopic investigation will help in understanding the origin of degradation of performance of SCRF cavities.

Influence of Surface Oxidation on Ion Dynamics and Capacitance in Porous and Nonporous Carbon Electrodes

We investigate the influence of surface chemistry and ion confinement on capacitance and electrosorption dynamics of room-temperature ionic liquids (RTILs) in supercapacitors. Using air oxidation and vacuum annealing, we produced defunctionalized and oxygen-rich surfaces of carbide-derived carbons (CDCs) and graphene nanoplatelets (GNPs). While oxidized surfaces of porous CDCs improve capacitance and rate handling abilities of ions, defunctionalized nonporous GNPs improve charge storage densities on planar electrodes. Quasi-elastic neutron scattering (QENS) and inelastic neutron scattering (INS) probed the structure, dynamics, and orientation of RTIL ions confined in divergently functionalized pores. Oxidized, ionophilic surfaces draw ions closer to pore surfaces and enhance potential-driven ion transport during electrosorption. Molecular dynamics (MD) simulations corroborated experimental data and demonstrated the significance of surface functional groups on ion orientations, accumulation densities, and ...

Optical Properties and Instrumental Performance of thin Noble Metal (Cu, Au, Ag) Films Near the Surface Plasmon Resonance

Surface plasmon resonance sensors are routinely employed optical instruments for biochemical research and suited for medical diagnostics. Optical properties and associated instrumental performance of nanometer thin sputter deposited Au, Ag and Cu films at the metal-water interface are reported and compared with theoretical predictions. Prominent optical SP-excitations persist in very thin metal films on BK7 glass substrates and metal film thickness of approximately 40-50nm. Thin Au films are long-term chemically stable in neutral aqueous buffer solution. Cu and Ag films tend to deteriorate and oxidize over longer time period, especially when exposed to solutions with pH>7. Achievable sensor detectivities in the wavelength and angular interrogation modes are compared. The influence of surface oxidation on the irreversible adsorption of a common protein is also reported.