Effect of alloying addition of Pr on the dissolution rate of melt-spun Mg in 3% NaCl solution

Melt-spun Mg-1 and 15 wt % Pr binary alloys were immersed in a 3% NaCl solution saturated with Mg(OH)2 for up to 72 h. The dissolution rate was evaluated by hydrogen evolution method. Surface characterization of the pristine and corroded surfaces has been carried out using X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The surfaces of both the pristine and corroded samples were found to consist mainly of Mg(OH)2 and MgO. However, results of XRD and SEM showed that the dominant product formed on the corroded sample was Mg(OH)2. SIMS depth profiling showed that there was a depletion of Pr at the surfaces of Mg–Pr samples. © 1998 Chapman & Hall     

Development of corrosion resistant magnesium alloys Part 1 Characterisation of splat quenched Mg–10Al and Mg–16Al alloys

Abstract

The surfaces and bulk of splat quenched Mg–10Al and Mg–16Al (wt-%) alloys were investigated. The surfaces were studied using X-ray photoelectron spectroscopy (XPS) , X-ray excited Auger electron spectroscopy (X-AES), Rutherford backscattering spectrometry (RBS) , scanning electron microscopy (SEM), and electron probe microanalysis (EPMA) and the bulk using X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The solid solubility of Al in Mg was extended to at least 16 wt-%. The quantity of Al ions present on the surfaces of the alloys increased with Al content. Contrary to the suggested layered MgO/Mg–Al–oxide/alloy structure, the surfaces of the alloys consisted of an admixture of magnesium spinel (MgAl₂O₄) in periclase (MgO) and brucite (Mg(OH)₂) of non-uniform thickness varying between 10 and 50 nm, determined via RBS, X-AES, and depth profiling using XPS.

MST/1714a     

Co-precipitated RuO2-Al2O3 catalysts: bulk and surface characterization

A series of co-precipitated RuO₂-Al₂O₃ samples was characterized by means of bulk and surface techniques such as X-ray diffraction (XRD), specific surface area measurements, X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The existence of a substitutional solid solution of Al³⁺ ions in RuO₂ is suggested on the basis of XRD results. A more detailed study of such a phase was hindered by its thermal instability. XPS and AES quantitative data indicate a strong enrichment of Al on the surface. A simple model based on a reciprocal masking action of the particles of the two oxides with respect to the primary beam (X-rays or electrons) was found to fit the surface composition data well.     

Mg-based hydrogen storage materials: Surface segregation in Mg2Cu and related catalytic effects

Fresh surfaces of Mg₂Cu polycrystals cleaved in UHV have been investigated by AES, XPS and X-ray induced AES at room temperature. They show chemical decomposition of the surface leading to pronounced increase of surface Mg content. In contrast to the Mg the Cu remains essentially metallic, even on air exposed samples. It is suggested that this segregation prevents the formation of a compact oxide or hydroxide layer, thereby enabling dissociation of molecular hydrogen at the metallic Cu precipitations and/or the metallic Mg₂Cu subsurface. The results support comparable conclusions drawn earlier for LaNi₅, FeTi and Mg₂Ni.     

Effect of surface oxidation on the hydriding and dehydriding of Mg<Subscript>2</Subscript>Ni alloy produced by hydriding combustion synthesis

Hydriding combustion synthesis (HCS) has been regarded as an innovative process for the preparation of high active magnesium-based hydrogen storage alloys. For the purpose of understanding the interrelation of the unique hydrogen storage properties and the surface characteristics of the HCS product, the samples of Mg₂Ni alloy/hydride with and without exposure to air were prepared from the HCS product of Mg₂NiH₄. The hydriding and dehydriding properties were compared and the surface compositions were analyzed by means of X-ray photoelectron spectroscopy (XPS) and auger electron spectroscopy (AES). It was shown that the air exposure considerably decreases the hydriding activity of Mg₂Ni. Absorbing of 3.0 wt.% of hydrogen under the conditions of 603 K and 3.0 MPa after the air exposure takes 1500 s, which is six times longer than for the unexposed alloy. The hydrogen desorption of the hydride are also impeded by the air-exposure, which results in the increase of dehydriding temperature from 450 K to 540 K. XPS and AES analyses indicated that Mg segregates and exists in the form of hydroxide on the surface of the air-exposed sample, which is responsible for the degradation of the hydriding and dehydriding properties. It was confirmed that the fresh surfaces generated during the dehydriding process of the as-synthesized hydride product contributes to the high activity of the HCS product in the first cycle of the hydriding determination.     

Evaluation of the depth resolutions of Auger electron spectroscopic, X-ray photoelectron spectroscopic and time-of-flight secondary-ion mass spectrometric sputter depth profiling techniques

Concentration-depth profiles of sputter-deposited Si/Al multilayered specimens were determined by model fitting to measured data obtained by depth profiling, using Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary-ion mass spectrometry (TOF-SIMS). The model used for calculation of the concentration-depth profile accounts for the broadening (“smearing”) upon experimental depth profiling owing to the effects of atomic mixing, preferential sputtering, surface roughness and information depth of either the Auger electrons (for AES depth profiling) or the photoelectrons (for XPS depth profiling) or the secondary ions (for SIMS depth profiling). The depth resolution for each technique was derived directly from the values determined for the fitting parameters in the model.     

Effect of reduced graphene oxide (rGO) on structural,optical, and dielectric properties of Mg(OH)2/rGO nanocomposites

In this paper, we report the synthesis of Mg(OH)₂ NPs and Mg(OH)₂–rGO nanocomposites (NCs) by microwave assisted co-precipitation method. The crystal phase, structural morphology and functional groups of the as-synthesized samples were analyzed by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR). Raman spectroscopy was used to study the defects in the samples. Raman spectroscopy and the SEM results validate the growth of Mg(OH)₂ NPs on the rGO nanosheets. The chemical composition of the prepared samples was analyzed by EDAX. Optical properties of the as-synthesized samples were studied by UV–visible spectroscopy and the energy band gap was calculated by Tauc relation which shows a decrease in band gap with an increase in the amount of Graphene Oxide (GO) in the NCs. The dielectric properties were studied as a function of frequency over a range of 50 Hz to 5 MHz at room temperature. The value of dielectric constant decreases with an increase in frequency, this could be due to the existence of a polarization process at the border of the rGO sheets and Mg(OH)₂ NPs. The value of dielectric loss shows a decreasing trend with an increase in frequency whereas the larger value of AC conductivity in Mg(OH)₂–rGO NCs as compared to Mg(OH)₂ NPs approves the restoration of sp² network in the graphene sheets.     

Mechanistic aspects of formation of MgO nanoparticles under microwave irradiation and its catalytic application

This work reports a preparation of Mg(OH)₂ and MgO nanoparticles (NPs) using magnesium acetate in benzylamine and mechanistic study of its formation. The benzylamine acts as a solvent, base, promoter and capping agent in this reaction. The structure and morphology of particles were analyzed by X-ray diffraction pattern (XRD), transmission electron microscopy (TEM), high resolution TEM (HRTEM), selected area energy dispersion (SAED), energy-dispersive X-ray spectroscopy (EDAX), thermogravimetric analysis (TGA), FT-IR, CO₂–temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller (BET) surface area analysis techniques. The application of as prepared MgO NPs was used in catalysis as a catalyst for the formylation of amines with recyclability studies of nanocatalyst.     

Study on activities of vanadium (IV/V) doped TiO2(R) nanorods induced by UV and visible light

Vanadium (IV/V) doped rutile TiO₂ naonorods had been successfully synthesized through a single step hydrothermal method. The photocatalyst was characterized by transmission electron microscopy (TEM), selected area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), UV–vis diffusive reflectance spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS). The results showed that the doping of V ions had significant influence on the band gap energy and the surface state of TiO₂. The photo-activities of the new catalysts were investigated under ultraviolet (UV) and visible light. The UV-photocatalytic activity of the as-prepared catalysts was hardly influenced by doping V ions; while under visible light, the samples with 1 wt% and 0.1 wt% V exhibited enhanced activity to the oxidation of methylene blue (MB) and the reduction of Cr (VI), respectively.     

SIMS,EDX, EELS,AES, XPS study of interphases in nicalon fibre-LAS glass matrix composites

Auger electron (AES), electron energy loss (EELS) and X-ray photoelectron spectroscopy (XPS) were used to identify the reaction products at the fibre-matrix interface in SiC nicalon fibre-LAS (Li₂O, Al₂O₃, SiO₂) or LAS + Nb₂O₅ glass matrix composites. Chemical bonding of the different elements was investigated by AES using sputter-depth profiling on fibres extracted from two matrices by etching in hydrofluoric acid. The chemistry of the silicium was studied by EELS in nicalon-LAS + Nb₂O₅ composite cross-sections. XPS was performed on fibres extracted from the nicalon-LAS + Nb₂O₅ composite to confirm EELS and AES results. These investigations show that in both composites the reaction scale at the fibre-matrix interface consists of a carbon layer next to the matrix and of a silicate phase rich in oxygen which contains carbon, probably in the form of a silicon oxycarbide, and which is located between the carbon layer and the fibre core.     

Characterization of coatings

The variety of physical and chemical properties of coatings is determined by their thickness, structure and chemical composition. A fundamental understanding of coating properties, as well as of their reproducibility, therefore requires a good knowledge of these parameters.During the last few years great progress has been made in the field of chemical analysis (including depth distribution) of thin films and coatings. This progress is mainly the result of the combination of recently developed surface analytical techniques such as Auger electron spectroscopy (AES), photoelectron spectroscopy (UPS, XPS), ion scattering spectroscopy (ISS) and secondary ion mass spectroscopy (SIMS), on one hand, and controlled simultaneous surface etching by sputtering on the other.With these surface analytical techniques the chemical composition of the uppermost monolayers is detected by energy or mass analysis of ion- (ISS, SIMS), electron- (AES) or photon- (UPS, XPS) induced emission of ions (ISS, SIMS) or electron (AES, UPS, XPS), respectively. By combining these techniques with sputtering, the depth distribution of elements and compounds can also be determined with a lateral resolution of some microns.In order to recognize the capabilities and limitations of these techniques for coating analysis, the fundamental emission processes as they appear in the various analytical techniques, as well as the details of the sputtering process, have to be taken into account. The main features such as detection limits, isotope sensitivity, detection of compounds etc. of these techniques will be compared for some typical examples.Other methods, such as high energy ion backscattering and the detection of sputtered particles in the gas phase, will also be considered.     

Effect of applied potential on the microstructure,composition and corrosion resistance evolution of fluoride conversion film on AZ31 magnesium alloy

AZ31 magnesium (Mg) alloy was potentiostatic polarized in 0.1?M deaerated KF solution with pH 7.5 from ?0.4?V to ?1.4?V with an interval of ?0.2?V. The polarization process was described by the potentiostatic current decay. The resultant film was analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The results demonstrated that the deposited film included a Mg(OH)₂/MgF₂ containing inner layer and a Mg(OH)₂/MgF₂/KMgF₃ comprising outer layer. The high polarized potential produced high content of MgF₂ but low content of KMgF₃ and thin film. Conversely, the low polarized potential produced small content of MgF₂ but high content of KMgF₃ and thick film. The optimal corrosion resistance of the deposited film was obtained at ?1.4?V, which was closely related with the content of MgF₂ and KMgF₃ and the film thickness.     

Controlled growth of superhydrophobic films without any low-surface-energy modification by chemical displacement on zinc substrates

Superhydrophobic surface was prepared via immersing the clean perpendicular zinc substrate into aqueous copper (II) chloride (CuCl₂) solution and followed by anneal under the humid condition. The prepared samples were characterized by powder X-ray diffraction analysis, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy (XPS), and scanning electron microscopy (SEM), and energy-dispersive X-ray spectrometry analysis (EDX). SEM images of the films showed that the resulted surfaces exhibit micro–nano binary structures. The resulting surfaces had a high water contact angle (CA) of larger than 150° as well as a small sliding angle (SA) of less than 6°. Cu–Zn alloy formed by chemical displacement. Crystal CuZn₅ formed via crystal transition via anneal treatment. Crystal ZnO formed in air or under the humid condition. The CuZn₅–ZnO micro–nano binary structures leads to the surface superhydrophobicity.     

Carbon and sulphur on Pd(111) and Pt(111): Experimental problems during cleaning of the substrates and impact of sulphur on the redox properties of CeOx in the CeOx/Pd(111) system

The X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and CO titration has been used to detect common impurities like carbon and sulphur on Pd(111) and Pt(111) surfaces. Different experimental problems are discussed and practical tips for the cleaning of Pd(111) and Pt(111) are given. A mechanism for the carbon oxidation on closed packed platinum group metals like Pt(111) and Pd(111) is presented. The bulk carbon concentration of Pd(111) was estimated based on the Langmuir-McLean theorem. Additionally it was shown that the titration with CO and subsequent XPS measurement is a powerful yet convenient method for quantitative detection of impurities and ceria coverage determination. A CeO_x/Pd(111) inverse model system was prepared by evaporation of cerium in an oxygen atmosphere. The comparative study has shown that sulphur contamination changes the redox properties of the CeO_x in the CeO_x/Pd(111) system.     

Synthesis and photoluminescent properties of α-NaYF4:Nd/α-NaYF4 core/shell nanostructure with enhanced near infrared (NIR) emission

A simple and efficient method has been established for the synthesis of α-NaYF₄:Nd/α-NaYF₄ core/shell nanoparticles under hydrothermal conditions. The as-prepared products were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectra and lifetimes. TEM images show that the as-prepared samples have sphere-like shape. The lifetime values of the ⁴F_3/2 energy level of the α-NaYF₄:Nd/α-NaYF₄ core/shell nanoparticles increase significantly in comparison with those of α-NaYF₄:Nd core nanoparticles, with a quantum efficiency of as high as 52%.     

Aluminium hydroxide growth on aluminium surfaces exposed to an air/1% NO2 mixture

Aluminium samples were exposed to a mixture of 1% NO₂ in air at 100%, 52% and <5% relative humidity. Auger electron spectroscopy depth profiling showed that for the 100% and 52% r.h. environments, the thickness of the surface oxide/hydroxide layer increased linearly with exposure time. X-ray photoelectron spectroscopy was used to study the surface composition as a function of exposure time. The XPS data clearly showed that a transformation from AlOOH to Al(OH)₃ was occurring with time for high humidity exposures. Thick hydroxide layers which formed after prolonged exposure, were also analysed with scanning electron microscopy, thermogravimetric analysis, and X-ray diffraction.[/p]     

Gold catalysts for the abatement of environmentally harmful materials: Modeling the structure dependency

FeO_x, TiO₂ and CeO_x layers were deposited by pulsed laser deposition (PLD) technique onto Au films or Au nanoparticles supported on SiO₂/Si(100). The samples were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), secondary ion mass spectrometry (SIMS) and their reactivity was studied in catalytic CO oxidation. Comparison was made with reference samples of FeO_x/SiO₂/Si(100), TiO₂/SiO₂/Si(100), CeO_x/SiO₂/Si(100) and Au/SiO₂/Si(100) layers. The catalytic activity of the metal-oxide/Au/SiO₂/Si(100) samples must be attributed to active sites located on the metal-oxides overlayer modified by gold underneath, since no Au was exposed to the surface according to the XPS and SIMS. We found a promoting effect of gold on the catalytic activity of the FeO_x overlayer and an inhibiting effect of gold on the TiO₂ and CeO_x overlayers. These findings are discussed in terms of electronic interactions at the Au/metal oxide interface.     

Synthesis and characterization of anatase TiO2 nanotubes and their use in dye-sensitized solar cells

Anatase TiO₂ nanotubes (NTs) with the diameter of about 12 nm and the length of several hundreds nanometers were synthesized by hydrothermal method. The samples were characterized by X-ray diffraction (XRD), transmitting electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Brunauer–Emmet–Teller (BET) measurements. The NTs are used to make composites photoanode with pristine TiO₂ nanoparticles in dye-sensitized solar cells (DSSCs). It was found that the NT/nanoparticle ratio had a pronounced impact on the performance of solar cells. The electrode composite has better photoelectric properties than the full nanoparticle and NTs solar cells. The optimum content NTs, was found to be 5%, at which content the incident photon to current efficiency was about 63.1%, an 13.8% increment compared to that using full P25 under the same condition.     

Synthesis and characterization of copper ions surface-doped titanium dioxide nanotubes

Copper ions surface-doped titanium dioxide nanotubes were prepared via an assembly process based on the reactions between Cu(NH₂CH₂CH₂NH₂)₂(OH)₂ and hydroxide radicals on the surface of TiO₂ nanotubes, followed by the heat treatment in air at 723 K. The as-prepared samples were characterized with infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, and fluorescence spectroscopy (FL). The photocatalytic activity of the copper ions surface-doped titanium dioxide nanotubes was investigated by photodegradation of Rhodamine B. The results showed that copper ions were successfully introduced onto the surface of TiO₂ nanotubes. And two kinds of copper species of Cu(I) and Cu(II) were found on TiO₂ surface. Copper ions act as electron trappers facilitating the separation of electrons and holes on the surface of TiO₂ nanotubes, which allows more efficiency for the photodegradation of Rhodamine B.     

Surface modification of magnesium alloy AZ31 by hydrofluoric acid treatment and its effect on the corrosion behaviour

In the present study, the effect of hydrofluoric acid (HF) treatment on the surface composition and corrosion behaviour of the magnesium alloy AZ 31 was investigated. The HF treatment of the samples was performed with various concentrations and at different treatment times. The samples surfaces were analysed by Fourier transform infrared spectroscopy, optical emission spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. The results showed the formation of hydroxides, oxides and compounds of the general formula Mg(OH)_xF_2 − x on the samples surfaces, as well as variations on impurities concentrations. The process led to distinct surfaces, each having its specific corrosion resistance, which was evaluated by electrochemical impedance spectroscopy and potentio-dynamic polarization. The most improved corrosion protection was achieved using the concentrations of 14 and 20 mol L^− 1 and 24 h of treatment time, resulting in corrosion rates 20 times lower than those of untreated samples. These two solutions also resulted in an improved corrosion protection for further polymeric coatings, showing that this treatment is an excellent pre-treatment for corrosion protective layers on magnesium alloys.