X-ray Photoelectron Spectroscopy Surface Analysis Research Articles

Impact of Graphene Oxide on SERS Enhancement of Arylated Gold Nanospheres: Mechanistic Insight.

The performance of gold nanospheres as substrates for surface-enhanced Raman spectroscopy (SERS) investigation has been compromised by their low adsorption efficiency, high colloidal dispersibility, and diminishing hot spots. However, gold nanosphere substrates modified using aryldiazonium gold(III) chemistry via durable gold-carbon bonds are promising for SERS enhancement due to their controlled organic layer density. In this study, arylated gold nanospheres AuNSs-COOH have shown SERS enhancement when incorporated into graphene oxide (GO) to form nanocomposites (NCs) labeled AuNSs-COOH/GO (AuNCs). Our investigation using X-ray photoelectron spectroscopy (XPS) surface analysis showed that the gold-aryl nanospheres reached their maximum SERS enhancement with an optimal coating. The evaluation included the Au 4f chemical environment and compact graphitic layers for the SERS substrate optimization. The fabricated AuNC substrates demonstrated superior efficiency and reproducibility. A broad linear range of 10-3-10-7 M 4-nitrophenol detection was obtained with exceptional repeatability, as evidenced by the relative standard deviation (RSD) of 9.32%. A detailed investigation of the energy profiles, particularly the valence band maximum (VBM) and band gap values of the substrate and analyte, depicted the electromagnetic (EM) and charge-transfer-induced enhancement and the role of GO inclusion in substrate efficiency in SERS enhancement mechanisms. The finite-difference time domain (FDTD) simulation results revealed that AuNCs incorporated with graphitic nanostructures exhibited the most substantial SERS effect through an EM field enhancement mechanism. This study demonstrated significant SERS enhancement using gold-aryl nanospheres when modified with GO, in contrast to the typical reliance on anisotropic nanostructures.

Flexible Copper Films Modification via Spontaneous Reduction of Aryldiazonium Gold Salts: Unraveling Surface Properties and Energy Profile.

In this study, we report the modification of flexible copper films via the spontaneous reduction of aryldiazonium gold salts [X-4-C6H4N≡N]AuCl4 (X═COOH, NO2). The electroless modification involves dipping of flexible copper films in the aryldiazonium gold solutions for a few seconds, under ambient conditions, followed by a washing step with deionized water to obtain a mechanically robust gold-aryl coating. The chemical composition, morphology, electronic structure, and optical properties of the gold-aryl layer and the flexibility of the modified copper films are supported by the results from X-ray photoelectron spectroscopy (XPS), electrochemistry, contact angle, scanning electron microscopy (SEM), and ultraviolet photoelectron spectroscopy (UPS). XPS surface analysis showed metallic gold in addition to C-C, C-O/C-N, and C═O functional groups from the grafted aryls. Cu 2p showed metallic copper as a major component and a small amount of Cu(II) ions. Wettability studies showed that Au-COOH@Cu increased the contact angle of the bare copper films from 68.0 ± 0.7° to 82.0° ± 0.7°, while Au-NO2@Cu increased the contact angle to 134.0° ± 0.3°. UPS energy profile analysis of [HOOC-4-C6H4N≡N]AuCl4 (valence band maximum = 1.91 eV) exhibited greater reducibility than [O2N-4-C6H4N≡N]AuCl4 (valence band maximum = 2.91 eV). The lower ionization potential of [HOOC-4-C6H4N≡N]AuCl4 (IP = 4.33 eV) enhanced the reactivity upon copper film contact, potentially inducing efficient energy level alignment, compared with [O2N-4-C6H4N≡N]AuCl4 (IP = 5.62 eV). UPS results were further supported by electrochemistry investigation which revealed that [HOOC-4-C6H4N≡N]AuCl4 is easily reducible compared with [O2N-4-C6H4N≡N]AuCl4. The findings presented here hold significant implications for developing flexible copper films and pave the way for future advancements in electronic material modification for industrial applications.

Fabrication of novel covalently-coupled graphene oxide-per-6-amino-β-cyclodextrin composite with abundant active oxygen- and nitrogen-containing sites for azo dyes removal

The presence of diverse pollutants in wastewater highlights critical opportunities and urgent needs to develop effective strategies and technologies for their removal. In the present study, a novel composite of per-6-amino-β-cyclodextrin (PACD) covalently modified graphene oxide (GO) was fabricated by a facile one-step procedure. The morphologies, composition and bonding modes of GO-PACD composite were investigated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermalgravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and specific surface analysis by the Brunauer-Emmett-Teller (BET) method. The prepared GO-PACD composite was used as an efficient adsorbent for the removal of azo dyes (alizarin yellow R) from colored wastewater. The maximum adsorption capacity of GO-PACD was 130.92 mg g−1 at 298 K. The influencing factors such as contact time, solution pH, initial dye concentration and temperature were investigated and optimized by a batch adsorption experiment. Adsorption kinetics, isotherms and thermodynamics were also investigated to reveal the possible adsorbent-adsorbate mechanisms. GO-PACD composite could be regenerated by a facile acid-soaking process. The results showed that the GO-PACD composite exhibited high stability and excellent reusability during 10 cycles of consecutive loading and regeneration. In summary, the developed GO-PACD composite is highly-efficient, regenerable, stable and facile-to-synthesize, making it be a potential candidate for azo dyes removal by adsorption.

Rational surface modification of zirconium-based metal–organic framework nanomaterials for the adsorption and recovery of coloured drugs and proteins from aqueous solutions

Coloured drugs and proteins in pharmaceutical wastewater cause environmental pollution. Metal–organic frameworks (MOFs) can be used for the adsorption and recovery of pollutants from wastewater, however selective adsorption and desorption on MOFs are challenging. Herein, UiO-66 and various polyethylene glycol (PEG)-modified MOFs (UiO-66 @mPEG-PO3 and UiO-66 @DSPE) were synthesised to selectively adsorb and separate model drugs [curcumin (CUR) and myricetin (MYR)] and proteins [Bovine serum albumin (BSA) and ovalbumin (OVA)]. Results show that UiO-66 adsorption efficiency for CUR and MYR in aqueous solution reached 93% and 98%, respectively. Additionally, CUR and MYR adsorbed on the UiO-66 surface exhibit good antioxidant activity during the recycling process. X-ray photoelectron spectroscopy and Hirshfeld surface analysis indicate that the adsorption mechanisms of both CUR and MYR by UiO-66 are belonging to the intermolecular interactions. The UiO-66 @mPEG-PO3 significantly reduces the surface area of UiO-66 (216 m2/g) but does not alter the adsorption behaviour of drugs. In the process of desorption and separation of CUR and MYR, the UiO-66 @PEG-PO3 exhibits a higher desorption rate than UiO-66. By contrast, the UiO-66 @DSPE MOFs exhibits optimal protein adsorption and selectively enhances the desorption of OVA rather than BSA in a 40% acetonitrile solution. This method can be used to capture and detect OVA proteins in cell lysates. Rational surface modification is an effective way to improve the adsorption selectivity and recovery efficiency of zirconium-based MOFs, providing an effective way to use MOFs in treating novel water pollutants.

XPS surface analysis of ceria-based materials: Experimental methods and considerations

X-ray photoelectron spectroscopy (XPS) analysis of cerium is ubiquitous amongst the catalytic and materials literature however errors in experimental procedure and data analysis are often easily proliferated. In this work we focus on the best practice for experimental construction when approaching the task of understanding chemical environments in cerium-based materials by XPS.

Non-thermal atmospheric pressure plasma treatment increases hydrophilicity and promotes cell growth on titanium alloys in vitro

Most medical implants are made of titanium. When titanium is exposed to air for a long time, hydrocarbons are deposited and the surface becomes hydrophobic. Cell attachment is important for bone ingrowth to occur on the implant surface, and hydrophilicity can enhance this. We examined whether non-thermal atmospheric pressure plasma treatment could increase the hydrophilicity of the titanium surface. Samples coated with four widely used coating types [grit blasting, micro arc oxidation (MAO), titanium plasma spray (TPS), and direct metal fabrication (DMF)] were treated with plasma. Each of the four surface-treated samples was divided into groups with and without plasma treatment. We analysed wettability by surface analysis and evaluation of contact angles, cell proliferation, and adhesion using scanning electron microscopy (SEM), confocal laser scanning microscopy, absorbance tests, and alkaline phosphatase (ALP) activity assay; four different Ti6Al4V surface types were compared. After plasma treatment, the contact angle was reduced on all surfaces, and the carbon content was reduced on all surfaces based on X-ray photoelectron spectroscopy (XPS) surface analysis. Under confocal laser scanning, the cell layer was thicker on the plasma-treated samples, especially in groups TPS and DMF. Cell proliferation was 41.8%, 17.7%, 54.9%, and 83.8% greater for the plasma- than non-plasma-treated grit blasting, MAO, TPS, and DMF samples, respectively. Hydrophilicity increased significantly under plasma treatment, and biological responsivity was also improved.

Compositional changes by SIMS and XPS analyses on fresh and aged Roman-like glass

This study reports important analytical evidence of an unusual non-uniform element distribution in the superficial layers of glass matrices (from few nm up to 1 µm). The unforeseen observation was made on silica-soda-lime glass mock-ups before and after their artificial ageing, using secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS) surface analysis techniques. The analyses showed a marked non-homogeneous element distribution at the glass surface. The results indicated a very low concentration of Na at the surface up to a depth of around 500 nm below the surface, where its concentration increases reaching a plateau. In addition, the profile distribution of H in the first 200 nm of the pristine glass surface indicated a diffusion of hydrogen from the surrounding environment to the glass network. Additional modifications during the glass ageing process related to external factors (such as temperature and humidity) were also identified in relation to sodium atoms, with atoms on the glass surface showing a different chemical state from those in the bulk. This study confirms that glass composition as well as glass alteration are non-homogeneous locally supporting the importance of studying glass surface as region of interaction with surrounding environment.

The effect of the saliva formulation on brass corrosion

AbstractThe composition of natural saliva is strongly variable and unstable outside the oral cavity, therefore corrosion tests are usually performed in artificial saliva solutions. In this study the effect of the composition of various saliva solutions on the corrosion behavior of a CuZn37 alloy, exposed for 1, 3, and 16 h to the solutions, is investigated by using electrochemical measurements, optical microscopy, and X‐ray photoelectron spectroscopy (XPS). The solutions investigated in this study are: Darvell, Carter‐Brugirard, and SALMO, selected for their composition that mainly differs in the organic compounds' content. Electrochemical measurements show that the open circuit potential and the polarization resistance increase with exposure time in the solutions, indicating a decrease in the corrosion rate. The corrosion rate (µm/year) in the Darvell solution is found to be two times higher than the other artificial saliva formulations and varies in the order: Darvell > Carter‐Brugirard > SALMO. These data suggest that the presence of different organic compounds might limit the formation of a stable protective surface film as confirmed by XPS surface analyses.

XPS investigation of 5N purity Al thin foils for MEMS devices

Thin Al foils are promising materials for applications in devices of microelectromechanical systems (MEMS). In this work, three foils of high purity (5N) Al with different thickness (10, 50, and 125 μm) were analyzed by means of X‐ray photoelectron spectroscopy (XPS), before and after annealing (720 K for 30 min). XPS surface analysis and depth profiling of chemical composition were performed to investigate the distribution of Al oxide. Electron energy loss spectroscopy (EELS) measurements were also carried out in order to identify the plasmon losses and chemical state of Al. The loss peaks in the 5N‐Al thin foils were compared with those of an Al foil of commercial purity (99.95 wt%). The thickness of the oxide layer on the sample surface of all the samples is not constant and oxide is thicker in the samples of high purity than in those of commercial quality. Moreover, the thinnest foils of 5N‐Al (10 μm) exhibit the thinnest oxide layer. These findings have been discussed by considering the size effect, that is, mechanical properties of thin foils are improving as the thickness decreases. The complex morphology of the metal‐oxide interface may contribute to enhance the mechanical performances of Al foils with a thickness below ~50 μm, because the free dislocations pile up against the interface which represents an obstacle for their motion hindering plastic deformation. Obtained results suggest that Al foils to be used in MEMS devices should be of high purity and annealed to get a surface completely covered by the oxide layer.

Fabrication of Graphene-Based TiO2@CeO2 and CeO2@TiO2 Core-Shell Heterostructures for Enhanced Photocatalytic Activity and Cytotoxicity.

Development of light-harvesting properties and inhibition of photogenerated charge carrier recombination are of paramount significance in the photocatalytic process. In the present work, we described the synthesis of core–shell heterostructures, which are composed of titanium oxide (TiO2) and cerium oxide (CeO2) deposited on a reduced graphene oxide (rGO) surface as a conductive substrate. Following the synthesis of ternary rGO-CeO2@TiO2 and rGO-TiO2@CeO2 nanostructures, their photocatalytic activity was investigated toward the degradation of rhodamine B dye as an organic pollutant under UV light irradiation. The obtained structures were characterized with high-resolution transmission electron microscopy, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, Brunauer–Emmett–Teller, X-ray photoelectron spectroscopy surface analysis, and UV–Vis spectroscopy. Various parameters including pH, catalyst dosage, temperature, and contact time were studied for photocatalysis optimization. Heterostructures showed considerable advantages because of their high surface area and superior photocatalytic performance. In contrast, rGO-CeO2@TiO2 showed the highest photocatalytic activity, which is attributed to the more effective electron–hole separation and quick suppression of charge recombination at core–shell phases. A biological assay of the prepared heterostructure was performed to determine the cytotoxicity against breast cancer cells (MCF-7) and demonstrated a very low survival rate at 7.65% of cells at the 17.5 mg mL–1 concentration of applied photocatalyst.

Impedimetric Detection of Albumin-Bound Fatty Acids Using Graphene Oxide Electrode

The fatty acid/albumin (FA/Alb) molar ratio is ≤1 in healthy subjects; this ratio can reach 3–4 in patients with acute myocardial ischemia. We describe the spontaneous desorption–adsorption kinetics of FAs from albumin to a graphene electrode at neutral pH. Albumin-depleted human serum was prepared via ultrafiltration and then mixed with defatted human albumin and sodium oleate at different FA/Alb molar ratios, at a final albumin concentration of 0.6 mM. A commercially available screen-printed graphene oxide (GO)-modified carbon electrode was used for the electrochemical experiments. Frequency-ranged Faradaic electrochemical impedance spectroscopy (EIS) and a single-frequency non-Faradaic impedance measure (chronoimpedance) were used to derive the desorption–adsorption kinetics. The surface of the GO electrode was finally evaluated with the aid of X-ray photoelectron spectroscopy (XPS). With the chronoimpedance experiment, the measured impedance increased accordingly to the FA/Alb ratios. The frequency-ranged EIS showed good linearity between the impedance and the FA/Alb ratio, with a limit of quantification value of 1.06. XPS surface analysis revealed that the FA was adsorbed onto the electrode, with the amount of the adsorbed FA proportional to the FA/Alb ratio. The electrochemical method applied on this peculiar desorption–adsorption kinetics of FAs has the ability to differentiate serum having excess FAs.

Solution-Processed Multistacked Tin-Doped Indium Oxide Nanoparticle Conductors for Cost-Effective Thin Film Heaters

Tin-doped indium oxide (ITO) nanoparticle (NP) films were fabricated as a cost-effective and highly transparent electrode for high-performance thin film heaters (TFHs), using a solution coating process on glass substrate. The electrical and optical properties of the ITO NP films depended on the number of spin coatings and post-annealing with various conditions (temperature, time, and ambient gas). The optimized three layer ITO NP films annealed at 600 °C under ambient N2 showed a low sheet resistance of 14 Ω/sq and a high optical transmittance of 88% in the visible wavelength region of (400–800) nm. Cross-sectional TEM images showed the ITO nanoparticles to be evenly dispersed in the thin film with good crystallinity and well-defined elliptical shape in the range of 10 to 25 nm. X-ray diffraction analysis confirmed that heat treatment increased the size of the ITO NPs. The KPFM result exhibited that as the heat treatment duration increased, the surface roughness of the ITO NP films reduced. X-ray photoelectron spectroscopy surface analysis showed a relatively higher area ratio of oxygen vacancies and a more stable Sn state in the chemical states of the O 1s and Sn 3d5/2 spectra than those of typical ITO films deposited by a magnetron sputtering after heat treatment. Due to the thermal stability and uniformity of the ITO NP film, ITO NP-based TFHs showed a stable time–temperature profile and uniform IR imagery. Therefore, solution-processed ITO NPs films can be applied to a promising low-cost transparent electrode in the next-generation smart window for buildings and automobiles.

Surface chemistry of oxidised pyrite during grinding: ToF-SIMS and XPS surface analysis

In the processing of minerals, the ore is ground to small particles to liberate the valuable minerals which are then separated from the ore waste material by froth flotation. The conditions of the grinding process have an impact on the surface chemistry of the minerals which is critical for the subsequent flotation process. This study aims to investigate the effect of different grinding conditions on the evolution of the surface chemistry of pyrite during the grinding process. The hydrophobicity of the ground pyrite is determined using Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and the surface chemistry speciation is characterized by X-ray Photoelectron Spectroscopy (XPS). The results show that when grinding with forged steel media, the new surfaces produced on pyrite particles during grinding are oxidised or react rapidly in the mill, resulting in low surface hydrophobicity. In contrast, when grinding with high chrome steel media under nitrogen gas atmosphere, the reaction rate of fresh surfaces can be markedly reduced, hence, increasing the natural hydrophobicity of pyrite. This paper provides a comprehensive understanding of how surface chemistry of pre-oxidised pyrite changes during grinding. This knowledge is critical for devising control strategies to optimise grinding and flotation operations in mineral processing plants.

Development of a combined XRF/XPS surface-analysis system for the surface-layer quantification of 28Si spheres

<p class="Abstract">To achieve a new kilogram definition using the X-ray crystal density method, the Center for Measurement Standards, Industrial Technology Research Institute in Taiwan has established the combined XRF (X-ray fluorescence)/XPS (X-ray photoelectron spectroscopy) surface analysis system for the quantitative surface-layer analysis of Si spheres. The surface layer of a Si sphere is composed primarily of an oxide layer, carbonaceous contamination and physisorbed/chemisorbed water. This newly combined instrument has been implemented to measure the XRF for the direct determination of the mass deposition of oxygen (ng/cm<sup>2</sup>) with a calibrated silicon drift detector and the XPS for the ratio between the elements (O, Si, C) and composition identification. These two complementary methods of X-ray metrology allow an accurate determination of the surface-layer mass of the Si sphere. In this paper, the construction of a combined XRF/XPS surface-analysis system is reported, including the surface characterisation method, the assembly of parts of the load-lock chamber and ultra-high-vacuum analysis chamber, the vacuum-system design, hardware integration and the intended research on surface-layer measurement. It is anticipated that the measured surface-layer mass will be combined with the core mass of the Si sphere.</p>

Corrosion Behavior of a Nickel-Free High-Nitrogen Stainless Steel with Hydrogen Charging

Hydrogen permeation usually facilitates the corrosion of stainless steel remarkably. Herein, the corrosion behavior of a nickel-free high-nitrogen stainless steel (HNSS) containing 0.96 wt.% nitrogen with hydrogen charging is investigated by means of electrochemical measurements and x-ray photoelectron spectroscopy surface analysis. The results show that hydrogen charging not only increased the passive current density but also increased the pitting potential of HNSS. The increase in passive current density was attributed to the increased carrier density, depleted Cr content, and decreased O2−/OH− ratio in the passive film, while the increase in the pitting potential resulted from the enrichment of N element in the passive film and the replacement of Ni with Mn in HNSS.

Effect of Thermo-Mechanical Processing on the Corrosion Behavior of Fe−30Mn−5Al−0.5C TWIP Steel

Electrochemical corrosion of thermo-mechanically processed (TMP) and recrystallized Fe−30Mn−5Al−0.5C twinning-induced plasticity (TWIP) steels containing 30 wt.% Mn was studied in a 1.0 wt.% NaCl electrolyte solution. The alkaline nature of the corrosion products containing manganese oxide (MnO) increases the dissolution kinetics of the TWIP steel in acid media, obtaining Mn2+ cations in solution, and producing the hydrogen evolution reaction (HER). X-ray photoelectron spectroscopy (XPS) surface analysis revealed an increased Al2O3 content of 91% in the passive layer of the recrystallized TWIP steel specimen, while in contrast only a 43% Al2O3 was found on the TMP specimen. Additionally, the chemical composition of the surface oxide layer as well as the TWIP alloy microstructure was analyzed by optical microscopy (OM) and scanning electron microscopy (SEM). The results indicate an enhanced corrosion attack for the TMP high-Mn TWIP steel.

(Corrosion Division Morris Cohen Graduate Student Award Address) A Systematic Study of Critical Parameters Affecting the Galvanic Corrosion between Al Alloy and Stainless Steel in Atmospheric Condition

Connections between dissimilar materials are frequently encountered in complex structures involved in the aerospace industry. In a typical aircraft structure, one of the most common couples encountered is that of an aluminum-alloy-based airframe component and noble fasteners such as stainless steel. When this type of galvanic couple is exposed to a atmospheric marine environment, it can develop cracks that pose increased risk and require costly maintenance and repair. In this work, a complementary modeling and experimental approach is applied to systematically investigate the effect of electrolyte layer thickness, solution chemistry and materials surface properties on the electrochemical and corrosion distributions in the galvanic coupling between AA7050 and SS316L, and capture the underlying mechanism of the dependence of corrosion distributions on each external variable.To validate the robustness of our modeling approach, a Laplace-Equation based modeling coupled using mathematically-fitted electrochemical kinetics from experiment as boundary conditions was applied to simulate galvanic corrosion between Zn plate and SS 316 rods under thin layer electrolyte conditions. The modeling results were compared with experimental results from a four-day modified B117 test. It shows that: electrolyte layer thickness (WL)=3,500~4, 000 \U0001d707m would be the appropriate WL range formed on the sample surface during modified B117 salt fog testing; the robustness of Laplace-Equation based modeling is highly dependent on the boundary conditions, experimentally-determined electrochemical kinetics as boundary conditions can truly reflect the electrochemical response of anode/cathode to the surrounding solution environment, which in turn yields the simulated results mostly close to experimental measurement.In the study of the effect of electrolyte layer thickness, the total cathode current capacity of a surface on the electrolyte film thickness and cathode size in a galvanic couple to support the corrosion of AA7050 was accessed. The total cathode current capacity was studied over the range of WL thickness from full immersion conditions (where the total cathode current scales directly with cathode size) to the thin film regime in which the WL is the diffusion boundary layer thickness. In order to fully assess the transition from thin film to thick film condition, an understanding of the natural convection layer thickness is required. For the conditions studied here, the natural convection boundary layer was found to be close to 800 um. The WL thickness, cathode length and electrochemical kinetics interact to create four regimes of total cathode current as a function of WL thickness.In the study of the solution chemistry, the effect of Al3+ on the electrochemical and galvanic corrosion distributions between SS316L and AA7050was emphasized as it represents the major dissolved metal species from AA7050. It is found that Al3+ accelerates the hydrogen evolution reaction (HER) kinetics due to enhanced proton diffusivity, with the effect being observed not only on Al alloys, but also on Pt and stainless steel. The cation study for the galvanic couple indicates that Al3+ is also galvanic corrosion accelerator.The effect of oxide film properties on the cathodic kinetics of stainless steel were investigated because cathodic kinetics can significantly affect the degree of galvanic corrosion based on mixed potential theory. The study focused on the oxygen reduction reaction (ORR) and was studied by electrochemical (potentiodynamic polarization, cyclic voltammetry, potentiostatic test, and electrochemical impedance) techniques and x-ray photoelectron spectroscopy surface analysis. This study shows that the kinetics of ORR on stainless steels is determined by a combined effect of oxide film composition, film thickness, and resistivity.This work has improved the fundamental understanding of the effect of several pertinent variables on the galvanic-coupling induced localized corrosion of Al alloy, provided an approachable modeling means to predict corrosion distribution at given conditions in a timely fashion as well as develop corresponding corrosion mitigation strategies, and complemented continuum/meso-scale atmospheric corrosion modeling studies in this field. Acknowledgements The financial support from the Office of Naval Research (ONR) via Grants No. N00014-14-1-0012 and No. N00014-17-1-2033, the Sea-Based Aviation Program, and William Nickerson, Program Manager is gratefully acknowledged. The assistance of my advisor, Prof. R. G. Kelly is gratefully acknowledged. Helpful technical discussions with Profs. S. J. McDonnell, J. R. Scully, and J. T. Burns (University of Virginia), Dr. Jayendran Srinivasan (the Ohio State University), Dr. Piyush Khullar (Medtronic), Dr. Veronica Rafla (SpaceX) and Mr. Victor Yang (University of Virginia) are also acknowledged.

Role of Coke in the Passive Properties of Vitallium 2000 CoCrMo Casting Alloy in Simulated Oral Environment

The passive behaviors of Vitallium 2000 CoCrMo casting alloy in artificial saliva (AS) and Coke were studied by potentiodynamic polarization, electrochemical impedance spectroscopy, cyclic voltammetry, Mott–Schottky combined with scanning electron microscopy, Auger electron spectroscopy, and x-ray photoelectron spectroscopy surface analysis. The results show that with the increasing content of Coke, the self-corrosion current density of alloy increased sharply, the passive film corrosion resistance showed the best in AS and worst in Coke, and the Rp in Coke is reduced to half of that in AS. The thickness of passive films in AS, AS + Coke, and Coke is about 4.5, 3, and 2.5 nm, respectively. Passive films all exhibit n-type semiconductors; with more defects, the carrier density in Coke is 2.3 times more than that in AS. The Coke inhibits the oxidation of Co, Cr, and Mo, and the Co/Cr rate and Cr6+ concentration within the passive film increase. Coke weakens the formation process of protected oxides, thus reducing the stability of alloy’s passive film.

The interaction between grinding media and collector in pyrite flotation at neutral and slightly acidic pH

Gold often coexists with pyrite as micron and submicron-inclusions and pyrite is therefore floated to maximize gold recovery in gold processing plants. In practice, different types of grinding media and a great range of pH and collector concentrations are used for pyrite flotation without scientific guidance. In this study, the effect of three different types of grinding media including forged steel, 15% chromium steel and 30% chromium steel on pyrite flotation at a range of collector (potassium amyl xanthate) concentration was investigated at pH 5.0 and 7.0, and the underpinning mechanism was determined through pulp chemistry measurement, X-Ray Photoelectron Spectroscopy (XPS) surface analysis and electrochemical measurement. It was found that grinding media had a different effect on pyrite flotation at pH 5.0 and 7.0. At pH 5.0, both iron contamination originating from grinding media and xanthate oxidation played an important role in pyrite flotation. While iron contamination on the pyrite surface depressed pyrite flotation, it might be reduced by xanthate oxidation. This explains higher pyrite flotation after grinding with chromium steel than forged steel and at a higher collector concentration. At pH 7.0, pyrite flotation was mainly controlled by xanthate concentration. At a low xanthate concentration, pyrite oxidation was the predominant anodic reaction and pyrite flotation was poor due to the inability to form dixanthogen. At a high xanthate concentration, the formation of dixanthogen became predominant, which facilitated pyrite flotation.

Evaluation of the chemical and optical perturbations induced by Ar plasma on InP surface

Interfaces are of primary importance in heterostructures. The authors propose here an innovative methodologic development to access the chemical information in depth and, especially, at buried interfaces. This specific approach is based on the combination of glow discharge optical emission spectroscopy (GD-OES) plasma profiling, enabling one to quickly and precisely reach buried interfaces, with x-ray photoelectron spectroscopy surface analyses, bringing an accurate determination of the composition and the chemical environments. The representativeness of the crater chemistry is, therefore, a critical issue. On the InP substrate, the fine examination inside the GD-OES crater reveals surface modifications, chemical, morphological, and optical, and, as a consequence, the need to regenerate the initial chemical information. The authors present here a study dedicated to the evaluation of those modifications thanks to a multitechnique approach, with an important contribution of spectroscopic ellipsometry measurements. A crater regeneration strategy, by means of a nanochemical etching, is proposed and also assessed by the same analytical pathway, proving the recovery of the initial InP properties.