Effect Of Surface Oxidation Research Articles

Deep desulfurization of model fuels by metal-free activated carbons: The impact of surface oxidation and antagonistic effects by mono- and poly-aromatics

The main novel objective of this work is the evaluation of the adsorptive “deep” desulfurization efficiency under ambient conditions and studying in detail the effects arisen from the presence of competitors as in real fuels. Towards this direction, several activated carbons (commercially available and chemically modified/oxidized counterparts) were examined using a (diesel) model fuel containing initially 20 ppmwS of 4,6-dimethyldibenzothiophene (4,6-DMDBT) and 20 ppmwS of dibenzothiophene (DBT), as well as mono- and di-aromatic competitors, namely benzene and naphthalene, in hexadecane. To gain better insights regarding the adsorption sites, the involved mechanisms, and the impact/antagonistic effect arisen by the presence of the aromatics in high concentration, simpler model fuels were also utilized while emphasis was also given on exploring which physicochemical features, textural (N2 adsorption) or surface chemistry (Boehm titration and surface pH measurements), play a key role. In all cases, the oxidation treatment enhanced the adsorption capacity of the carbons, despite a decrease on the porosity, by introducing additional surface functional groups, indicating that surface chemistry plays a vital role in adsorptive desulfurization and that difference in chemical nature adsorption sites exists. The best performing oxidized carbon (SX PLUS-ox) presented a 92.1% (5.2 mgS/g capacity) removal of DBT in hexane and a 67.7% 4,6-DMDBT removal (4.0 mgS/g) in pure hexadecane. In the case of 4,6-DMDBT in hexadecane, the addition/co-presence of the aromatics in low concentration led to slightly lower desulfurization of 57.8% (3.6 mgS/g), revealing the limited antagonistic effect due to the aromatics. When DBT was also present, the 4,6-DMDBT removal was 51.2% (3.5 mgS/g) while the DBT removal 50.9 % (3.6 mgS/g), leading to a high total thiophenic adsorption capacity of 7.1 mgS/g. Even with the addition of the mono- and di-aromatics with concentrations as in real diesel fuel, the best performing carbons after oxidation demonstrated a superior desulfurization performance, since >10 ppmwS can still be removed from the model fuel. The results designate that the oxidation of porous activated carbon can be considered as an effective materials design strategy in adsorptive deep desulfurization, since different oxygen containing surface functional groups that can act as adsorption sites are created and have a crucial selectivity towards thiophenes compared to the aromatics.

Quantitative effects of surface oxidation on biochar derived from long-root Eichhornia Crassipes plants as Cd2+ adsorbent

Quantitative effects of surface oxidation on Cd2+ adsorption performance of biochar derived from long-root Eichhornia Crassipes plants were systematically investigated. It was revealed that oxidation degree was positively related with the intensity of surface functional groups and harmless for the structural stability, while biochar yield would decline sharply resulting from for over-oxidization. Correspondingly, the Cd2+ adsorption capacity exhibited an uptrend with the increasing oxidation on account of the abundant adsorption sites. Moreover, Cd2+ adsorption on the biochar with different oxidation degrees were also investigated comprehensively, indicating adsorption performances in a similar trend highly sensitive to solution pH and ionic strength. In addition, the adsorption isotherms were found to manifest the saturated adsorption capacity for Cd2+ increased from 0.333 mol/g to 0.487 mmol/g at 30 °C by strengthening oxidation. All synthesized biochar could keep consistent adsorption performance in multiple adsorption-desorption cycles.

Hydrogen Isotopes Permeation in Clean or Unoxidized FeCrAl Alloys: A Review

The US Department of Energy is working with fuel vendors to develop accident tolerant fuels (ATF) for the current fleet of light water reactors (LWRs). The ATF should be more resilient to loss of coolant accident scenarios and help extending the life of the operating LWRs. One of the proposed ATF concepts is to use iron-chromium-aluminum (FeCrAl) alloys for the cladding of the fuel. A concern in using ferritic FeCrAl is that this type of cladding may result in an increase in the concentration of tritium in the coolant. The objective of the current critical review is to collect and assess information from the literature regarding diffusion or permeation of hydrogen (H) and its isotopes deuterium (D) and Tritium (T) across industrial alloys (including FeCrAl) used or intended for the nuclear industry. Over a hundred years of data reviewed shows that the solubility of hydrogen in ferritic alloys is lower than in austenitic alloys but hydrogen permeates faster through a ferritic material than through austenitic materials. The tritium permeation rates in FeCrAl alloys are between those in austenitic stainless steels and in ferritic FeCr steels. The activation energy for hydrogen permeation is approximately 30 pct higher in the austenitic alloys compared with the ferritic (typically ∼ 50 kJ/mol in ferritic vs. ∼ 65 kJ/mol in the austenitic). None of the major elements in FeCrAl alloys react with hydrogen to form detrimental hydride phases. The effect of surface oxides on FeCrAl delaying hydrogen entrance into FeCrAl alloy is not part of this review.

Experimental study on enhanced heat transfer during rapid cooling of modified and oxidized rods

This research investigates the effects of surface modification and surface oxidation on pool boiling heat transfer performance. An experimental facility was designed and built to perform vertical quenching testings at atmospheric pressure and close to the saturation water pool. Three surface structures (smooth, threaded, and knurled) were fabricated to study the effect of surface area variation and surface oxidation on minimum film boiling temperature (Tmin). A visualization study was performed using a high-speed camera to capture the thermohydraulic behavior of the generated vapor around the heated sample. The results showed that surface features have a significant impact on the enhancement in heat transfer as the knurled surface exhibited a strong impact on increasing Tmin, quenching time, and heat transfer coefficient (HTC). The visualization study displayed different behaviors of the vapor layer breakage where the smooth and the threaded samples experienced larger bubbles and smoother movement of the quench front. Whereas smaller and intense bubbles were generated around the knurled sample at Tmin point. The successive experiments resulted in oxidation layers on the test samples, which proved that the oxidation mechanism depends on the surface finish that caused the surface to experience different heat fluxes. The comparison between the experimental results and available correlations in literature showed the importance of incorporating the surface characteristics effect in Tmin correlations due to its significant impact on pool boiling heat transfer performance.

Effect of surface oxidation on soft x-ray optical properties of ion beam sputter deposited amorphous AlN thin film

In the present study, structural and compositional analyses of reactive ion beam sputter deposited aluminum nitride (AlN) thin film of thickness 100 Å are carried out using x-ray reflectivity and x-ray photoelectron spectroscopy techniques. Soft x-ray optical response of the film is derived from energy dependent soft x-ray reflectivity measurements performed in photon energy region of 380–1700 eV. Optical constants (δ and β) obtained from the reflectivity spectra show features corresponding to absorption edges of the constituent elements. Observed fine features in the β profile are further confirmed from x-ray absorption (XAS) measurements carried out in the total electron yield mode. The measured XAS spectra are correlated with electronic and compositional properties of the AlN film. The effects of surface oxidation on soft x-ray optical properties of the AlN thin film are discussed.

Impact of Surface Hydrophilicity on Structure and Transport at the Catalyst-Ionomer Interface: Insights from Molecular Dynamics

Understanding local reaction conditions at the catalyst/support-ionomer interface in the cathode catalyst layer of polymer electrolyte fuel cells is vital for improving cell performance and stability.1 The structure of the ionomer layer and the state of the catalyst support surface at the interface affects key properties of the system, such as water film structure and the distribution of protons and oxygen molecules at the catalyst-ionomer interface.2 The effect of catalyst surface facet and oxidation on the proton density accumulation at the interface was previously studied using molecular dynamics simulations.3 In this work, the interfacial region between catalyst and support surface and ionomer skin is further studied by expanding the classical molecular dynamics model. This water-filled nanopore model is constructed to study the impact of local charge density distribution, density of sidechains at the ionomer layer, and water layer thickness on equilibrium water structure, electrostatic conditions, and transport properties of water, hydronium, and molecular oxygen at the interface (Figure 1). Structural properties of the catalyst and support surfaces are obtained from explicit quantum mechanical Density Functional Theory simulations, and the effect of the electrode potential is simulated via surface charge density by varying the oxide coverage of both C and Pt. The analysis of simulations in a flooded pore indicates that surface hydrophilicity, which is represented by water adsorption and the formation of ice-like water clusters at the surface, is a major deterministic factor that affects interfacial proton density, ionomer sidechain mobility, and interfacial oxygen lateral movement. The results obtained in this work can guide the design of new catalyst materials, where the hydrophilicity of the surface can be tailored to minimize local proton transport resistance and improve electrode performance.Figure 1. Snapshot of the model system with the graphite slab partially covered by epoxide with a C/O ration of 4:1 as the support surface, and a Nafion skin layer of 1124 EW as the ionomer. Li, H.; Tang, Y.; Wang, Z.; Shi, Z.; Wu, S.; Song, D.; Zhang, J.; Fatih, K.; Zhang, J.; Wang, H.; Liu, Z.; Abouatallah, R.; Mazza, A., A review of water flooding issues in the proton exchange membrane fuel cell. Journal of Power Sources 2008, 178 (1), 103-117. Jahnke, T.; Futter, G.; Latz, A.; Malkow, T.; Papakonstantinou, G.; Tsotridis, G.; Schott, P.; Gérard, M.; Quinaud, M.; Quiroga, M.; Franco, A. A.; Malek, K.; Calle-Vallejo, F.; Ferreira de Morais, R.; Kerber, T.; Sautet, P.; Loffreda, D.; Strahl, S.; Serra, M.; Polverino, P.; Pianese, C.; Mayur, M.; Bessler, W. G.; Kompis, C., Performance and degradation of Proton Exchange Membrane Fuel Cells: State of the art in modeling from atomistic to system scale. Journal of Power Sources 2016, 304, 207-233. Spooner, J. A.; Eslamibidigoli, M. J.; Malek, K.; Eikerling, M., Molecular Dynamics Study of the Nanoscale Proton Density Distribution at the Ionomer-Catalyst Interface. Pacific RIM Meeting on Electrochemical and Solid State Science 2020, (I01A-2101). Figure 1

Effect of Surface Oxides on the Melting and Solidification of 316L Stainless Steel Powder for Additive Manufacturing

Surface oxidation of metallic powders may significantly affect their melting and solidification behavior and limit their service life in the additive manufacturing (AM) process. In the present work, three levels of surface oxide concentration were prepared on AM-grade 316L stainless steel powders, and their melting and solidification behavior was systematically studied through in-situ observation, advanced characterization, phase-field modeling, and theoretical analysis. Si, Mn, and Cr participated in the oxidation reaction in powder with low and medium oxygen contents, whereas Fe was involved in the oxidation reaction for the powder samples with high oxygen content. A higher full melting temperature is observed to lead to an integrated melt pool in the melting of the highly oxidized powder, which is due to the reduced permeability produced by the oxide cage effect. For the droplet samples prepared from high oxygen powders, the inclusion with increased volume fraction and coarsened size is attributed to the agglomeration of inclusion particles with the residual oxide in the melt. In the high oxygen powder fusion scenario, an undesired coarse columnar grain structure with a high aspect ratio is formed in the current nonequilibrium solidification process, and a consistent microstructure is predicted using solidification conditions with a high cooling rate and high thermal gradient similar to the conventional AM process. In contrast, fine equiaxed grains in the experiment and slim columnar grains with a small aspect ratio in the phase-field simulation are obtained for the low oxygen powder condition. This study illustrates the effect of powder oxide from a processing aspect and provides insight into the importance of improving the service life of powder feedstock by effectively reducing the surface oxidation process on the powder surface.

Role of oxides in the electrochemical dissolution of Pd and its alloys

The dissolution of Pd, Pd–Pb and Pd–Cu electrodeposits proceeds predominantly from the surface free from chemisorbed oxygen. The strongest inhibiting effect of surface oxides is revealed in the dissolution of the mixed deposits.

Effects of surface oxidation on the pH-dependent surface charge of oxidized aluminum gallium nitride

Hypothesis: The properties of the oxidized surface for common materials, such as silicon and titanium, are known to be markedly different from the reduced surface. We hypothesize that surface-oxidized aluminum gallium nitride ((oxidized-AlGaN)/GaN) surface charge behavior is different to unoxidized AlGaN (with ultrathin native oxide only), which can be validated via surfactant adsorption. Understanding these differences will explain why (oxidized-AlGaN)/GaN-based sensors are better performing than AlGaN ones, which has been previously demonstrated but not understood.Experiments: The surface of an AlGaN/GaN structure was oxidized with hot piranha solution and oxygen plasma. AFM force measurements and imaging were performed to probe the charge properties of the surface in aqueous solutions of varying pH containing only an acid or base, or with an added ionic surfactant: cationic cetyltrimethylammonium bromide (CTAB) or anionic sodium dodecylsulfate (SDS).Findings: The (oxidized-AlGaN)/GaN surface is positively charged at pH 4 and pH 5.5, although pH 5.5 should be close to the isoelectric point of the surface. The surface is negatively charged at pH 10 and pH 12, and sufficiently charged to attract cooperative adsorption of CTAB aggregates at pH 12. At pH 2, the evidence is inconclusive, but the surface is most likely positively charged. Compared to unoxidized AlGaN, the (oxidized-AlGaN)/GaN surface shows a wider range of surface charge magnitude over pH values between 2 and 12. This suggests that the (oxidized-AlGaN)/GaN surface has a higher surface hydroxyl group density than unoxidized AlGaN, which explains the higher sensitivity for pH sensors based on (oxidized-AlGaN)/GaN structures.

Effect of electrode wire surface integrity and surface oxides on the stability of gas metal arc welding

ABSTRACT ER70S-6 gas metal arc welding (GMAW) wire electrodes are widely used in various market segments. Stability of GMAW process is vital for obtaining desired welding performance. The random variations in voltage transients can represent welding consumable quality. In the present study, wire electrodes from three sources were analysed in standard synergic and pulse synergic GMAW using digital storage oscilloscope (DSO) and high-speed camera setup. The recorded voltage data were analysed using time domain and probability density distribution (PDD) analysis. High speed camera images were used to understand abnormal voltage variations observed in voltage oscillograms and PDD patterns. Results confirmed the presence of signatures of wire quality in the variations of analysed voltage transients along with high speed camera images. Microscopic examination confirmed damaged wire surface and presence of remnant oxide layer post manufacturing on the wire surface/sub surface as the main reasons for poor product performance and arc instability. The method adopted in this work can help end users in selecting appropriate welding wire to enhance productivity and can also help wire manufacturers to improve their product quality.

Importance of the catalytic effect of the substrate in the functionality of lubricant additives: the case of molybdenum dithiocarbamates

Molybdenum dithiocarbamates (MoDTCs) are lubricant additives very efficient in reducing the friction of steel, and they are used in a number of industrial applications. The functionality of these additives is ruled by the chemical interactions occurring at the buried sliding interface, which are of key importance for the improvement of the lubrication performance. Yet, these tribochemical processes are very difficult to monitor in real time. Ab initio molecular dynamics simulations are the ideal tool to shed light on such a complicated reactivity. In this work, we perform ab initio simulations, both in static and tribological conditions, to understand the effect of surface oxidation on the tribochemical reactivity of MoDTC, and we find that when the surfaces are covered by oxygen, the first dissociative steps of the additives are significantly hindered. Our preliminary tribological tests on oxidized steel discs support these results. Bare metallic surfaces are necessary for a stable adsorption of the additives, their quick decomposition, and the formation of a durable MoS2 tribolayer. This work demonstrates the importance of the catalytic role of the substrate and confirms the full capability of the computational protocol in the pursuit of materials and compounds more efficient in reducing friction.

Anomalous pressure-dependence in surface-modified silicon-derived nanoparticles

Surfaces can significantly alter the optical properties of nanomaterials, but they are difficult to control and their roles are hard to understand in highly reactive materials such as silicon nanomaterials. In this work, we investigate the role of the surface in controlling the optical transitions in highly luminescent silicon-derived nanoparticles. By combining high-pressure and low-temperature experiments, we experimentally correlate the anomalously intense and narrow transitions in the UV range with the surface oxides, while the visible transition and the photoluminescence (PL) are verified to originate from the Si-ligand charge transfer band. We find that the high-pressure absorption and PL depends on the rigidity of the surface ligand. This indicates that the surface plays a dominant role on the optical properties of these silicon-derived nanoparticles, and is different than other semiconductor nanomaterials, in which pressure-dependent optical transitions depend on lattice strain or phase transformations. This work presents a comprehensive understanding of the optical transitions and the effect of surface ligands and surface oxidation in these highly luminescent Si-derived nanoparticles. The new insight into the oxidation-activated and ligand-mediated transitions, and the pressure-dependent PL may help with engineering the band structure of other highly-reactive optical nanomaterials.

Effects of surface oxides and nanostructures on the spontaneous wettability transition of laser-textured copper surfaces

The spontaneous wettability transition of metal and metal oxide surfaces caused by the adsorption of airborne volatile organic compounds (VOCs) has been frequently reported. In this study, we examine the effects of surface oxides and nanostructures on the wettability transition as well as the stability of the acquired hydrophobicity under boiling conditions. The results demonstrate that the presence of a thin oxide layer enhances the surface hydrophilicity and slightly delays the spontaneous wettability transition. Short-term exposure of the prepared samples to atmospheric air does not affect the boiling performance, but long-term exposure results in a dramatic decrease of the critical heat flux (CHF). The adsorped organics can be partly removed under continuous boiling, resulting in the partly recovery of the CHF after the first boiling test as well as the partly recovery of the surface hydrophilicity after the entire boiling tests. The presence of abundant surface oxide nanoparticles can markedly enhance the stability of the original hydrophilicity, which may result from the huge specific surface area of the nanostructured surfaces. Our results help a better understanding of the spontaneous wettability transition phenomenon, benefiting the manufacturing of high-performance heat transfer devices.

Spontaneous Enhancement of Power Conversion Efficiency in SnO2-Based Dye-Sensitized Solar Cells

Power conversion efficiency (PCE) of SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -based dye-sensitized solar cells (DSSCs) is reported to increase slowly over a period of days after their fabrication. Thus far, underlying processes involved in this slowly increasing phenomenon of PCE are not understood. In this article, we investigate the spontaneous enhancement of PCE in SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -based DSSCs and the underlying mechanism by using the X-ray diffraction, the X-ray photoelectron spectra (XPS), electrochemical impedance spectrum, and first-principles calculations. The Sn 3d and O 1s binding energy are observed to shift toward low binding energy over time by the XPS measurements, and the ratio of O/Sn on the surface of SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> increases from 1.9 to 2.1 implying the adsorption of oxygen atom on the surface of SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . Our first-principles calculation results confirm that a shift-up in the conduction band minimum of SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> owing to its adsorption of oxygen atom. We, therefore, attribute the slowly increasing phenomenon of PCE to oxygen adsorption effect on the surface of SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . This article gives a comprehensive understanding of the surface oxidation effect on the PCE enhancement in DSSCs and provides an effective way to fabricate DSSCs based on oxide semiconductors with good performance and long-time stability.

Effects of Copper Surface Oxidation and Reduction on Shear-Bond Strength Using Functional Monomers

This study was conducted to clarify the influence of the copper surface oxidation and reduction on the shear-bond strength with functional monomers. Unheated copper specimens (UH; n = 88) were wet-ground. Three-quarters of the UH were then heated (HT). Two-thirds of the HT was then immersed in a hydrochloric acid solution (AC). Half of the AC was then reheated (RH). Each group was further divided into two groups (n = 11), which were primed by either 6-methacryloyloxyhexyl 2-thiouracil-5-carboxylate (MTU-6) or 10-methacryloyloxydecyl dihydrogen phosphate (MDP). The shear-bond strength tests were used for bonding with an acrylic resin. The surface roughness values and chemical states of the four groups were analyzed using a confocal scanning laser microscope and X-ray photoelectron spectroscopy (XPS). The shear-bond strengths of HT and RH were the lowest in the MTU-6-primed groups. The result of AC was significantly lower than others in the MDP-primed groups. The XPS results showed that the surfaces of UH and AC consisted of Cu2O and Cu. The surface changed to CuO upon heating. The presence or absence of copper-oxide films showed the opposite trends in the effectiveness of MTU-6 and MDP to improve bond strength. The results could elucidate the effects of functional monomers on copper-oxide films.

Ultrasonics induced variations in molecular structure and tensile properties of silk fibers in a chemical free environment

AbstractUltrasonics can be used as an alternative energy supply for a green silk wet processing and for enhancement of some chemical/physical properties of bio‐polymers. In this work, ultrasonically treated silk fabric were compared with that of untreated and were investigated for the changes in fiber conformation structure and subsequent tensile property. Experiments were conducted under different time duration in a chemical free environment. Fiber surface energy distribution and transformation of silk secondary structure were analyzed using X‐ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), and Fourier transform infrared spectrum (FITR). Results showed that subject to treatment time, a surface oxidation effect and a light transformation of random coil to β‐sheet can be induced from ultrasonic irradiation. Tensile testing showed that under certain treatment time, ultrasonics can lead to silk fibers with a slightly increased strength and reduced extensibility, as a result of the transition of fiber secondary structure.

Influence of atmospheric surface oxidation on the formation of H2O2 and ∙OH at pyrite-water interface: Mechanism and kinetic model

Numerous studies have reported that the atmospheric surface oxidation of pyrite profoundly affects its surface characterization and species. However, controversy remains regarding the influence of atmospheric surface oxidation on the reaction activity of pyrite. Kinetic experiments, the Monte Carlo (MC) simulation, and a kinetic model were used to comprehensively investigate the effect of atmospheric surface oxidation on the production of hydroxyl radicals (·OH) and hydrogen peroxide (H2O2) by pyrite and its reaction activity. The production of ·OH and H2O2 by dissolved Fe(II) (Fe(II)aq) in the suspensions of surface-oxidized pyrite (SOP) was impeded. The primary reason is that Fe (hydr)oxide on the SOP surface can decompose H2O2 to H2O, and the production of ·OH via the Fenton reaction was inhibited subsequently. However, the production of ·OH and H2O2 by Fe(II) sites on the SOP surface (Fe(II)pyrite) was promoted because Fe(III) sites in Fe (hydr)oxide (Fe(III)oxide) enhanced the electron transfer from Fe(II)pyrite to O2. The proportion of Fe(III) sites determined the degree of influence on the production of ·OH and H2O2 by Fe(II)aq and Fe(II)pyrite. The Sb(III) oxidation reaction also indicated that atmospheric surface oxidation altered the oxidation activity of pyrite. In conclusion, atmospheric surface oxidation has a significant effect on the environmental behavior of pyrite and the fate of redox-active substances.

Effect of surface oxidation on photoluminescence of silicon vacancy color centers in the nanocrystalline diamond films

The effect of three different surface oxidation approaches (air annealing, acid oxidation and oxygen plasma) on microstructural evolution and silicon vacancy (SiV) photoluminescence (PL) in the nanocrystalline diamond (NCD) films is investigated. All oxidation methods lead to the bonding of oxygen functional groups at diamond surface. The SiV centers exhibit the PL enhancement of about 105-fold in the air-annealed sample, compared with the as-deposited films. Nevertheless, the PL enhancement is about 7-fold and 2-fold in the acid- and plasma- treated samples, respectively. Combination of Raman spectra, HRTEM imaging with cross-sectional oxygen mapping confirms that such different PL behavior originates from the formed different thick oxidation layers. The air oxidation results in a thicker oxidation layer with improved crystallinity than the other two methods. In addition, when the air-annealed films are re-terminated with hydrogen, the SiV PL emission tends to drop remarkably under the same crystallinity. It indicates that hydrogen termination leads to the PL quenching of SiV centers. Therefore, our work reveals that the direct bonding of oxygen to sp3 carbon or the improvement of diamond crystalline quality plays an effective role in the PL enhancement of SiV centers during the oxidation of hydrogen-terminated NCD particles or films.

A comparative study on liquid metal embrittlement susceptibility of three FeCrAl ferritic alloys in contact with liquid lead-bismuth eutectic at 350°C

Liquid metal embrittlement (LME) susceptibility of three FeCrAl alloys (i.e., Fe10Cr4Al, Fe15Cr4Al and Fe10Cr6Al, wt%) was tested in oxygen-saturated and -depleted liquid lead-bismuth eutectic (LBE) at 350 °C using slow strain rate tensile tests. The results show that all three alloys are very susceptible to LME, manifested by a severe reduction in total elongation to failure and prevailing cleavage on fracture surfaces. LME is delayed in oxygen-saturated LBE, due to a dewetting effect of surface oxides. In three alloys, Fe10Cr6Al is most susceptible to LME, especially in presence of oxygen-depleted LBE.

Computational investigation of the plasmonic properties of TiN, ZrN, and HfN nanoparticles: the role of particle size, medium, and surface oxidation

Group 4 transition metal nitride (TMN) nanoparticles (NPs) display strong plasmonic responses in the visible and near-infrared regimes, exhibit high melting points and significant chemical stability, and thus are potential earth-abundant alternatives to Au and Ag based plasmonic applications. However, a detailed understanding of the relationship between TMN NP physical properties and plasmonic response is required to maximize their utility. In this study, the localized surface plasmon resonance (LSPR) frequency, bandwidth, and extinction of titanium nitride (TiN), zirconium nitride (ZrN), and hafnium nitride (HfN) NPs were examined as a function of the particle size, surface oxidation, and refractive index of the surrounding medium using finite element method (FEM). A linear redshift in the LSPR frequency and a linear increase in the associated full width at half maximum (FWHM) was observed with increasing the particle size, oxidation layer thickness, and medium refractive index. We show that the effect of surface oxidation on plasmonic properties of TMN NPs is strongly size-dependent with a significant LSPR redshift, intensity reduction, and broadening in small NPs compared with larger NPs. Furthermore, the performance and efficiency of HfN, ZrN, and TiN, as well as Au NPs for narrowband (photothermal therapy, PTT) and broadband (solar energy conversion) applications, was investigated in detail. The results indicate that narrowband and broadband photothermal performance of NPs strongly depend on the particle size, surface properties, and in case of narrowband absorption, excitation wavelength.