XPS Surface Analysis Research Articles

Controlled synthesis of highly spherical nano-PbO2 particles and their characterization

This letter describes the chemical synthesis of highly mono-dispersed spherical nano-PbO2. In the first step, sodium borohydride in the presence of TritonX-100 was used to reduce Pb(NO3)2 to highly spherical nano-Pb, and the second NaOCl was used to oxidize nano-Pb to nano-PbO2 (both reactions were performed at room temperature). TEM, SEM, XRD, and XPS surface analyses showed that the prepared Pb and PbO2 particles were spherical, 95% were mono-dispersed and of the size of 30nm. In addition, electrochemical active surface area studies confirmed the nano-particulate nature of the prepared PbO2 particles. The developed procedure is straightforward, rapid, performed at room temperature, and scalable to the industrial level.

Mesoporous Pt-TiO2 thin films: Photocatalytic efficiency under UV and visible light

The preparation, characterization, and photoactivity of mesoporous Pt-TiO2 thin films were investigated. Titania based thin films were prepared by evaporation induced self assembly (EISA) process, Pt being introduced by a non-photochemical process via two different ways. Whatever the synthesis method and the Pt content (between 0.5% and 3%), the prepared films were thin (around 200nm) and mesoporous with an average pore size of 5nm. XPS surface analysis showed that Pt was present in different oxidation states: mainly Pt0 but also Pt2+ and Pt4+. The presence of Pt0 nanoparticles was also clearly evidenced by Transmission Electronic Microscopy. The photocatalytic efficiency of the mesoporous titania films was determined by two different tests under both UV and visible light: the reaction rates and photonic efficiencies were determined for the mineralization of stearic acid (SA) at the gas–solid interface and for the solid–liquid photobleaching of Methylene Blue (MB). In all the cases, Pt-doped titania films were less active than pure TiO2 films under UV light and slightly more active under visible light. Preliminary results on the HO production on the surface of the films were obtained from the reaction of a specific probe (terephtalic acid, TA) in basic aqueous solutions. These results were discussed relative to literature data.

Localized Photoelectrochemistry on a Tungsten Oxide–Iron Oxide Thin Film Material Library

A WO3-Fe2O3 thin film combinatorial library was fabricated using a vapor phase co-deposition method followed by a combined thermal annealing and oxidation process. The scanning electron microscopy (SEM) analysis of the library microstructure combined with X-ray diffraction (XRD) investigations suggested that α-Fe2O3 grains preferentially grow from boundaries of domains, containing finer grains of WO3 and Fe2WO6, forming filiform networks on the surface. The surface density of the hematite networks depends on the amount of Fe present in the library. Photocurrents measured at different applied biases using Photo Electrochemical Scanning Droplet Cell Microscopy (PE-SDCM) were analyzed and mapped along the entire compositional spread. A distinctive photocurrent peak was detected at 21.9 atom % Fe, and its appearance was correlated to the higher amount of hematite present in the library at this specific composition together with a specific WO3 crystallographic orientation ((222) orthorhombic or (400) monoclinic). This finding is confirmed by qualitative and quantitative XPS surface analysis at the photocurrent peak position in the material library. Thus the enhancement of the photocurrent cannot be exclusively attributed to certain surface modifications since only hematite was found on the library surface at the peak composition.

2-Mercaptobenzoxazole as a copper corrosion inhibitor in chloride solution: Electrochemistry, 3D-profilometry, and XPS surface analysis

2-Mercaptobenzoxazole (MBOH) was studied as a corrosion inhibitor for Cu in 3wt.% NaCl solution using EIS, a potentiodynamic curve, 3D-profilometry, and XPS measurements. It was shown that Cu corrosion in solution containing MBOH follows kinetic-controlled and diffusion-controlled processes and that MBOH is a mixed-type inhibitor. The diffusion coefficient of the Cu ions travelling through the solid surface layers was estimated to be on the order of 10−15–10−14cm2s−1. It was also demonstrated that the Cu(I)–MBOH complex is formed on the Cu surface and that the thickness of this surface layer is 1.4±0.4nm.

Preparation of eutectic substrate mixtures for enzymatic conversion of ATC to l-cysteine at high concentration levels

High concentration eutectic substrate solutions for the enzymatic production of L-cysteine were prepared. Eutectic melting of binary mixtures consisting of D,L-2-amino-Δ(2)-thiazoline-4-carboxylic acid (ATC) as a substrate and malonic acid occurred at 39 °C with an ATC mole fraction of 0.5. Formation of eutectic mixtures was confirmed using SEM, SEM-EDS, and XPS surface analyses. Sorbitol, MnSO4, and NaOH were used as supplements for the enzymatic reactions. Strategies for sequential addition of five compounds, including a binary ATC mixture and supplements, during preparation of eutectic substrate solutions were established. Eutectic substrate solutions were stable for 24 h. After 6 h of enzymatic reactions, a 550 mM L-cysteine yield was obtained from a 670 mM eutectic ATC solution.

Nanofilms Produced by Magnetron Enhanced Plasma Polymerization from Methane and Oxygen for Coating of Rigid Contact Lenses

Although soft contact lenses are more widespread, rigid contact lenses have been around for decades and their materials have been greatly improved, especially in terms of oxygen permeability. Protein adsorption and wettability are, however, complex challenges still faced by both soft and rigid contact lenses (CLs). This study aims at improving these two major attributes by means of a low‐pressure magnetron enhanced 15 kHz plasma polymerization process. The wide parameter range of the process allowed the tailoring of the surface properties and delivered stable, reproducible plasma coatings. The XPS, FT‐IR, WCA, and QCM surface analysis methods were used to study the nanofilms. A contact angle of down to 18° and a protein (lysozyme) adsorption of only 0.2 µg cm−2 were achieved. Some correlations with the more commonly used “PEO‐like” coatings helped to explain the measurement results.

Scratch Resistance of New Polystyrene Nanocomposites with Ionic Liquid-Modified Multi-walled Carbon Nanotubes

Multi-walled carbon nanotubes, both neat (MWCNT) and modified (MWCNTm) by the room-temperature ionic liquid (IL) 1-octyl-3-methylimidazolium tetrafluoroborate ([OMIM]BF4), were added in a 1 wt% to polystyrene (PS) to obtain the new nanocomposites (PS + MWCNT and PS + MWCNTm). Friction coefficients and abrasive wear from instantaneous penetration depth, residual depth and viscoelastic recovery were determined for compression-moulded materials as a function of applied normal load and of the number of successive scratches. The new nanocomposites improve the abrasion resistance of neat PS and of the analogous PS nanocomposites containing neat and IL-modified single-walled carbon nanotubes. The lowest friction coefficient and residual depth values, after 15 scratches, under the whole range of applied loads are obtained for PS + MWCNTm, with maximum reduction under the most severe conditions. The influence of sliding direction with respect to flow was studied for injection-moulded PS + MWCNTm under multiple scratching. The most severe surface damage is observed in the transverse direction to injection flow, while the lowest friction coefficient and the highest abrasion resistance and viscoelastic recovery values are obtained in the direction parallel to injection flow, due to the higher mobility of the polymer chains and the additives. Thermal analysis (DSC and TGA), Raman spectroscopy, transmission electron microscopy, X-ray diffraction and XPS surface analysis have been used as characterization techniques. XPS shows that the IL molecules are present on the nanotube surface. According to TGA, the IL content in MWCNTm can be estimated to be of a 12 wt%. Mechanisms of surface damage are discussed upon scanning electron microscopy, 3-D surface topography, surface roughness and profilometry observations.

Corrosion Behavior of High Nitrogen Nickel-Free Fe-16Cr-Mn-Mo-N Stainless Steels

The purpose of the current study is to develop austenitic nickel-free stainless steels with lower chromium content and higher manganese and nitrogen contents. In order to prevent nickel-induced skin allergy, cobalt, manganese, and nitrogen were used to substitute nickel in the designed steel. Our results demonstrated that manganese content greater than 14 wt pct results in a structure that is in full austenite phase. The manganese content appears to increase the solubility of nitrogen; however, a lower corrosion potential was found in steel with high manganese content. Molybdenum appears to be able to increase the pitting potential. The effects of Cr, Mn, Mo, and N on corrosion behavior of Fe-16Cr-2Co-Mn-Mo-N high nitrogen stainless steels were evaluated with potentiodynamic tests and XPS surface analysis. The results reveal that anodic current and pits formation of the Fe-16Cr-2Co-Mn-Mo-N high nitrogen stainless steels were smaller than those of lower manganese and nitrogen content stainless steel.

Catalyst studies on the ring opening of tetrahydrofuran–dimethanol to 1,2,6-hexanetriol

The metal catalyzed hydrogenolysis of the biomass-derived THF–dimethanol to 1,2,6-hexanetriol using heterogeneous catalysts was investigated. Bimetallic Rh–Re catalysts (4wt% Rh and a Re/Rh (mol. ratio of 0.5) on a silica support gave the best performance and 1,2,6-hexanetriol was obtained in 84% selectivity at 31% conversion (120°C, 80bar, 4h); the selectivity reaches a maximum of 92% at 80°C. The product distribution at prolonged reaction times or higher temperatures or both shows the formation of diols and mono-alcohols, indicating that the 1,2,6-hexanetriol is prone to subsequent hydrodeoxygenation reactions. Different silica supports were investigated and optimal results were obtained with an amorphous silica featuring an intermediate surface area and an average mesopore size of about 6nm. TPR and XPS surface analysis support the presence of mixed Rh and Re particles. The redox Reδ+/ReTotal surface ratio correlates with the conversion in a volcano type dependency. Both gas phase as well as Rh200Re1OH cluster DFT calculations support an acid–metal bifunctional mechanism and explain the products distribution.

Surface interactions, corrosion processes and lubricating performance of protic and aprotic ionic liquids with OFHC copper

In order to select possible candidates for use as lubricants or as precursors of surface coatings, the corrosion and surface interactions of oxygen-free high conductivity (OFHC) copper with two new protic (PIL) and four aprotic (APIL) room-temperature ionic liquids have been studied. The PILs, with no heteroatoms in their composition, are the triprotic di[(2-hydroxyethyl)ammonium] succinate (MSu) and the diprotic di[bis-(2-hydroxyethyl)ammonium] adipate (DAd). The four APILs contain imidazolium cations with short or long alkyl chain substituents and reactive anions: 1-ethyl-3-methylimidazolium phosphonate ([EMIM]EtPO3H); 1-ethyl-3-methylimidazolium octylsulfate ([EMIM]C8H17SO4); 1-hexyl-3-methylimidazolium tetrafluoroborate ([HMIM]BF4) and 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIM]PF6). Contact angles between the ionic liquids and OFHC copper surface were measured. Mass and roughness changes of OFHC copper after 168h in contact with the ionic liquids have been determined. Copper surfaces were studied by XRD, SEM–EDX and XPS surface analysis. FTIR spectra of the liquid phases recovered after being in contact with the copper surface were compared with that of the neat ionic liquids. The lowest corrosion rate is observed for the diprotic ammonium adipate PIL (DAd), which gives low mass and surface roughness changes and forms adsorbed layers on copper, while the triprotic ammonium succinate salt (MSu) produces a severe corrosive attack by reaction with copper to form a blue crystalline solid, which has been characterized by FTIR and thermal analysis (TGA). All imidazolium APILs react with copper, with different results as a function of the anion. As expected, [EMIM]C8H17SO4 reacts with copper to form the corresponding copper sulphate salt. [EMIM]EtPO3H produces severe corrosion to form a phosphonate–copper soluble phase. [HMIM]BF4 gives rise to the highest roughness increase of the copper surface. [HMIM]PF6 shows the lowest mass and roughness changes of the four imidazolium ionic liquids due to the formation of a solid layer containing phosphorus and fluorine. The results described in the present study are in agreement with the outstanding good tribological performance of the diprotic ammonium adipate (DAd) ionic liquid for the copper–copper contact, in pin-on-disc tests, preventing wear and giving a very low friction coefficient of 0.01. Under the same conditions, [HMIM]PF6 gives a friction value of 0.03, while the reactivity of MSu towards copper produces maximum friction peaks of 0.05. In contrast with the absence of surface damage on copper, an abrasive wear mechanism is observed for MSu and [HMIM]PF6. The results confirm a better lubricating performance for a lower corrosion rate.

The passivation behaviour of copper-containing high-performance ferritic stainless steels in the cathode environment of polymer electrolyte membrane fuel cells

The passivation behaviour of copper-containing high-performance ferritic stainless steels in the cathode environment of polymer electrolyte membrane fuel cells was investigated using electrochemical tests and XPS surface analyses. The addition of copper to the alloy deteriorated the corrosion resistance at a passive region of 0.6VSCE. With an increase of the copper content, the passivity of the alloy degraded due to an increase of the formation of Cr-containing inclusions, and a decrease of the Cr oxide and hydroxide in the passive film.

Oxidative removal of tokamak codeposits using NO2 and O2

The rate of removal of deuterium from DIII-D codeposits has been directly compared for thermo-oxidations using NO 2 and O 2 . At 286 and 350 °C and pressures of 2 and 20 kPa, NO 2 is significantly more effective than O 2 in removing D from the codeposits. With both NO 2 and O 2 , only weak pressure dependence is seen for D removal. The gaseous products formed during oxidation have also been studied. Low levels of D-containing gaseous compounds have been detected in comparison to the amount of D removed as measured by post-oxidation laser thermal desorption spectroscopy . Post-oxidation XPS surface analysis showed increased boron concentration , but no increase in the nitrogen content of the codeposits.

Post-synthetic incorporation of nickel into CPO-27(Mg) to give materials with enhanced permanent porosity

Nickel cations have been introduced into framework sites of the magnesium dioxiterephthalate MOF, CPO-27(Mg), via a procedure involving post-synthetic treatment with an aqueous solution of Ni2+ cations and a weak acid. The final solids have Ni concentrations up to 70 mol% of the total cation content. Selected area EDX analysis, synchrotron X-ray powder diffraction and XPS surface analysis indicate that Ni2+ is distributed throughout the crystals with highest concentration at the external surface. A mechanism involving both crystallisation and predominant isomorphous cation replacement is proposed. The modified solids have much enhanced adsorption capacities following simple thermal evacuation under vacuum than unmodified CPO-27(Mg), particularly for N2 at 77 K, for which uptakes of 17 mmol g−1 are achieved. This is attributed to surface modification that makes the surface more stable to heating under evacuation.

A Study of the Effect of Djurliete, Bornite and Chalcopyrite during the Dissolution of Gold with a Solution of Ammonia-Cyanide

The high solubility of copper sulphide minerals is an issue in the cyanidation of gold ores. The objective of this study was to quantify the effect of individual copper sulphide minerals on the Hunt process, which showed advantages over cyanidation. High purity djurleite, bornite and chalcopyrite, with a P70 of 70–74 microns, were mixed with fine quartz and gold powder (3–8 micron) to obtain a copper concentration of 0.3%. The ammonia-cyanide leaching of slurry with djurleite proved to be more effective than cyanidation; producing comparable extraction of gold (99%), while reducing the cyanide consumption from 5.8 to 1.2 kg/t NaCN. Lead nitrate improved the Hunt leaching. The lower cyanide consumption is associated to a significant reduction of copper dissolved. XPS surface analysis of djurleite showed that lead nitrate favored the formation of Cu(OH)2 species. Lead was also detected on the surface (oxide or hydroxide). Sulphide and copper compounds (cyanide and sulphide) were reaction products responsible for inhibiting the dissolution of gold. Lead nitrate added in the Hunt leaching of bornite produced 99% gold extraction. Surface reaction products were similar to djurleite. The cyanide consumption (~4.4 kg/t NaCN) was not reduced by the addition of ammonia. Cyanidation of chalcopyrite showed a lower consumption of cyanide 0.33 kg/t NaCN compared to 0.21 kg/t NaCN for Hunt. No significant interferences were observed in gold leaching with a slurry containing chalcopyrite.

The effect of a DLC coating adhesion layer on the corrosion behavior of titanium and the Ti6Al4V alloy for dental implants

The properties of DLC layers provide for their broad use in medical applications. Their tribological properties are frequently utilized in big joint implants, and their barrier effect offers another benefit. The present work studied corrosion behavior of DLC coatings formed on titanium and Ti6Al4V alloy with a titanium or chromium inter-layer, in environments to which dental implants may be exposed. Electrochemical impedance spectroscopy, XPS surface analysis, ICP/MS chemical analysis method and a set of standard biological tests were employed in the study.The behavior of both coated systems, regardless of the basic material, was comparable in an environment that did not contain fluoride ions. An addition of fluorides revealed the occurrence of pores as deep as the DLC layer even in specimens with a surface polished prior to coating. Porosity of layers was clearly evident on jet-blasted specimens. The best corrosion behavior was recorded in specimens with a chromium inter-layer on both types of the basic material. With the titanium inter-layer applied, coatings on TiAlV exhibited higher corrosion resistance than those on commercial-pure titanium. The conducted biological tests indicated applicability of a chromium inter-layer on DLC coated implants.

Early stages of oxide growth in H-terminated silicon nanowires: determination of kinetic behavior and activation energy

Silicon nanowires (Si NWs) terminated with hydrogen atoms exhibit higher activation energy under ambient conditions than equivalent planar Si(100). The kinetics of sub-oxide formation in hydrogen-terminated Si NWs derived from the complementary XPS surface analysis attribute this difference to the Si-Si backbond and Si-H bond propagation which controls the process at lower temperatures (T < 200 °C). At high temperatures (T≥ 200 °C), the activation energy was similar due to self-retarded oxidation. This finding offers the understanding of early-stage oxide growth that affects the conductance of the near-gap channels leading towards more efficient Si NW electronic devices.

Comparative study on the corrosion behavior of Ti–Nb and TMA alloys for dental application in various artificial solutions

The corrosion behavior of Ti–Nb dental alloy in artificial saliva with and without the addition of lactic acid and sodium fluoride was investigated by electrochemical techniques, with the commercial Titanium–molybdenum alloy (TMA) as a comparison. The chemical composition, microstructure and constitutional phase were characterized via energy dispersive spectrometry, optical microscope and X-ray diffraction, meanwhile the open circuit potential, electrochemical impedance spectroscopy and potentiodynamic polarization measurements were carried out to study the corrosion resistance of experimental alloys, with the corroded surface being further characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. It was found that the corrosion behavior of Ti–Nb alloy was similar to those TMA alloy samples in both artificial and acidified saliva solutions, whereas statistical analysis of the electrochemical impedance spectroscopy and polarization parameters showed Ti–Nb alloy exhibited better corrosion resistance in fluoridated saliva and fluoridated acidified saliva. SEM observation indicated that TMA alloy corroded heavily than Ti–Nb alloy in fluoride containing saliva. XPS surface analysis suggested that Nb2O5 played an important role in anti-corrosion from the attack of fluoride ion. Based on the above finding, Ti–Nb alloy is believed to be suitable for the usage in certain fluoride treated dental works with excellent corrosion resistance in fluoride-containing oral media.

Sputtering of lunar regolith simulant by protons and singly and multicharged Ar ions at solar wind energies

We report preliminary results on sputtering of a lunar regolith simulant at room temperature by singly and multiply charged solar wind ions using quadrupole and time-of-flight (TOF) mass spectrometry approaches. Sputtering of the lunar regolith by solar-wind heavy ions may be an important particle source that contributes to the composition of the lunar exosphere, and is a possible mechanism for lunar surface ageing and compositional modification. The measurements were performed in order to assess the relative sputtering efficiency of protons, which are the dominant constituent of the solar wind, and less abundant heavier multicharged solar wind constituents, which have higher physical sputtering yields than same-velocity protons, and whose sputtering yields may be further enhanced due to potential sputtering. Two different target preparation approaches using JSC-1A AGGL lunar regolith simulant are described and compared using SEM and XPS surface analysis.

New Silica Supported HClO&lt;sub&gt;4&lt;/sub&gt; as Efficient Catalysts for Estolide Synthesis from Oleic Acid

The syntheses of estolides via condensation reaction of oleic acid were investigated using heterogenous catalysts. In this study HClO4 is supported onto suitable support to make it environmentally friendly. A series of solid acid catalyst containing 5-45 % of perchloric acid supported onto silica was synthesized and characterized using XRD, BET surface area measurement, TEM and XPS surface analysis. Silica modified with perchloric acid was found to be efficient and environmentally benign solid acid catalyst for estolide synthesis. The reaction was performed at 70 oC for 10 hours to give oleic-oleic monoestolide acid (m/z 563.51 as M-H)-. Based on the experimental findings above, optimum catalytic performance was with 15 % HClO4 loading onto SiO2 to give 98.98 % conversion of the oleic acid with 63.98 % oleic-oleic monoestolide acid selectivity.

Stainless steel reinforcing bars – reason for their high pitting corrosion resistance

AbstractIn harsh chloride bearing environments stainless steel reinforcing bars offer excellent corrosion resistance and very long service life for concrete structures, but the high costs limit a more widespread use. Manganese bearing nickel‐free stainless steels could be a cost‐effective alternative. Whereas the corrosion behavior of stainless steels in alkaline solutions, mortar and concrete is quite well established, only little information on the reasons for the high pitting resistance are available. This work reports the results of pitting potential measurements in solutions simulating alkaline and carbonated concrete on black steel, stainless steel DIN 1.4301, duplex steel DIN 1.4462, and nickel‐free stainless steel DIN 1.4456. Duplex and nickel‐free stainless steels are fully resistant even in 4 M NaCl solutions with pH 13 or higher, the lower grade DIN 1.4301 shows a wide scatter between fully resistant and pitting potentials as low as +0.2 V SCE. In carbonated solutions with pH 9 the nickel‐free DIN 1.4456 shows pitting corrosion at chloride concentrations ≥3 M. This ranking of the pitting resistance can be rationalized based on XPS surface analysis results: both the increase of the Cr(III)oxy‐hydroxide and Mo(VI) contents in the passive film and a marked nickel enrichment beneath the film improve the pitting resistance. The duplex DIN 1.4462 shows the highest pitting resistance, which can be attributed to the very high Cr(III)oxy‐hydroxide, to a medium Mo(VI) content in the film and to a nickel enrichment beneath the film. Upon time, the protective properties of the surface film improve. This beneficial effect of ageing (transformation of the passive film to a less Fe2+ containing, more hydrated film) will lead to higher pitting potentials. It can be concluded that short‐term solution experiments give conservative results in terms of resistance to chloride‐induced corrosion in reinforced concrete structures.