Influence of grain orientation on zinc enrichment and surface morphology of an Al?Zn alloy

Zinc is an important alloying element in the 7000 series aluminium alloys. It is also an element that may enrich near the alloy surface during treatments of aluminium alloys by processes such as electropolishing, alkaline anodic etching and alkaline etching. The enrichment may occur since the change in Gibbs free energy per equivalent for formation of ZnO is less negative than that for formation of Al₂O₃. The enriched alloying element is present in an alloy layer up to ～5 nm thick located immediately beneath the alloy/film interface. In the present study, the dependence of the enrichment of zinc on the grain orientation of the alloy is investigated for a solid solution Al‐1.1at.%Zn alloy. The enrichment of the zinc is developed by alkaline etching of the alloy. The grain orientation is determined by electron backscattering diffraction, with enrichments quantified on selected grains by Rutherford backscattering spectroscopy and medium energy ion scattering. The morphologies of the surfaces of the etched grains are characterised by scanning electron microscopy and atomic force microscopy. The findings reveal that the zinc enrichment ranges from 1.7 × 10¹⁵ atoms/cm² to 3.9 × 10¹⁵ atoms/cm², with the greatest enrichment occurring on a grain of (100) orientation, while differing surface topographical textures are developed on the various grains. Copyright © 2009 John Wiley & Sons, Ltd.     

The distribution of hydroxyl ions at the surface of anodic alumina

Barrier‐type anodic films 3–15 nm thick have been formed on electropolished 99.999% aluminium. Variable‐angle XPS has been used to identify a significant proportion of hydroxyl ions at the surface of the relatively compact alumina films. The location of an oxygen‐rich region at the outer surface of the oxide has been confirmed by medium‐energy ion scattering (MEIS). Combining the information from these two techniques leads to the conclusion that a hydroxyl‐containing surface region is responsible for this oxygen‐rich surface layer, MEIS revealing an approximately linear relationship between the total oxide thickness and the thickness of the hydroxyl‐rich surface region. From consideration of the mechanisms of amorphous alumina formation by ionic transport, with incorporation of electrolyte‐derived species into the thickening film, the generation of the hydroxyl‐rich outermost region is considered to result from the formation of gel‐like material at the film/electrolyte interface. Copyright © 2003 John Wiley & Sons, Ltd.     

AuAg bimetallic nanoparticles film fabricated based on H2O2-mediated silver reduction and its application

A method to fabricate AuAg bimetallic nanoparticles film by H₂O₂-mediated reduction of silver was reported. Gold nanoparticles (Au NPs) were first adsorbed onto the surface of a self-assembled 2-aminoethanethiol monolayer-modified gold film or 3-aminopropyltriethoxysilane (APTES) monolayer-modified quartz slide. Upon further treatment of this modified film with the solution containing silver nitrate (AgNO₃) and H₂O₂, silver was deposited on the surface of Au NPs. The size of the AuAg bimetallic particles could be readily tuned by manipulating the concentration of H₂O₂. Surface plasmon resonance (SPR) was used to investigate the process, the deposition of silver on Au NPs modified gold film resulted in an obvious decrease of depth in the SPR reflectance intensity and minimum angle curves (SPR R-θ curves), which may be utilized for the quantitative SPR detection of the analyte, H₂O₂. Combination of the biocatalytic reaction that could yield H₂O₂ by using the enzyme, glucose oxidase, with the deposition of silver may enable the design of a glucose biosensor by SPR technique. Furthermore, we evaluated the AuAg bimetallic nanoparticles film for their ability to be an effective substrate for surface-enhanced Raman scattering (SERS).     

Deposition of polysiloxane‐like nanofilms onto an aluminium alloy by plasma polymerized hexamethyldisiloxane: characterization by XPS and contact angle measurements

In this work, aluminium (Alclad 2024‐T3) substrates were cleaned by an r.f. (13.56 MHz) plasma, using argon (Ar), oxygen (O₂) and a mixture of O₂/Ar (50:50) gases. The effectiveness of plasma cleaning was checked in situ using X‐ray photoelectron spectroscopy (XPS) and ex situ using water contact angle measurements. XPS O/Al surface atomic ratios are in excellent agreement with those of the crystalline boehmite and the pseudoboehmite. Oxygen O 1s peak‐fitting was used to quantify the proportion of hydroxyl ions and the functional composition on the aluminium surface: the surface cleaned with O₂ plasma contains 50% of aluminium hydroxides, the ones cleaned with Ar plasma and with Ar/O₂ plasma contain, respectively, 25 and 37% hydroxyl ions. The binding energy separation between Al 2p and O 1s is characteristic of AlO(OH). Thin SiO_x films were subsequently deposited from a mixture of hexamethyldisiloxane (HMDSO) and oxygen. In the absence of oxygen, a hydrophobic (Θ≥ 100° ) film characteristic of polydimethylsiloxane (PDMS) is formed: polysiloxane‐like thinner films (SiO_x) are obtained with the introduction of oxygen. XPS and contact angle measurements confirmed both the composition and the structure of these films. More importantly, contact angle measurements using different liquids and interpreted with the van Oss‐Good‐Chaudhury theory allowed determination of the surface free energy of the deposited films: the calculated values of surface tension of the film formed from HMDSO/O₂: (50/50) are in excellent agreement with those of reference silica‐based materials such as a silicon wafer and cleaned glass. Copyright © 2007 John Wiley & Sons, Ltd.     

Preferential anodic oxidation of second‐phase constituents during anodising of AA2024‐T3 and AA7075‐T6 alloys

Model analogues of the metallurgical phases found in 2xxx and 7xxx series aluminium alloys were produced by magnetron sputtering and employed to investigate the local and general anodising behaviour of the alloys. Electrochemical tests, allied with scanning and transmission electron microscopy, enabled insight into the local anodising behaviour of the constituents and related effects on the overall porous oxide morphology. Under potentiodynamic conditions, the observed anodic current peaks of the commercial alloys were related with the anodic oxidation of specific second‐phase particles. At 0 V, magnesium‐containing particles, including S‐phase, were preferentially removed from the alloy surface; at 5–6 V_SCE, the copper‐ and/or iron‐containing particles, such as θ phase and Al₇Cu₂Fe particles were anodically oxidised. The initial voltage transient revealed for the commercial alloys during galvanostatic anodising was related to the previous findings and reproduced by the use of coupled alloy analogues. Transmission electron microscopy revealed that the voltage transient associated with oxidation of second‐phase material influence the morphology of the anodic film formed on the aluminium matrix. Copyright © 2010 John Wiley & Sons, Ltd.     

Effects of elastic scattering and analyzer‐acceptance angle on the analysis of angle‐resolved X‐ray photoelectron spectroscopy data

We have made calculations of N 1s, O 1s, Si(oxide) 2p, Hf 4f, and Si(substrate) 2p photoelectron intensities at selected emission angles for films of SiO_1.6N_0.4 and HfO_1.9N_0.1 of various thicknesses on silicon. These calculations were made with the National Institute of Standards and Technology (NIST) Database for Simulation of Electron Spectra for Surface Analysis (SESSA) to investigate effects of elastic scattering and analyzer‐acceptance angle that could be relevant in the analysis of angle‐resolved X‐ray photoelectron spectroscopy (ARXPS) experiments. The simulations were made for an XPS configuration with a fixed angle between the X‐ray source (i.e. for the sample‐tilting mode of ARXPS) and with Al and Cu Kα X‐ray sources. The no‐loss intensities changed appreciably as elastic scattering was switched ‘on’ and ‘off’, but changing the analyzer‐acceptance angle had a smaller effect. Ratios of intensities for each line from the overlayer film for the least realistic model condition (elastic scattering switched ‘off’, small analyzer‐acceptance angle) to those from the most realistic model condition (elastic scattering switched ‘on’, finite analyzer‐acceptance angle) changed relatively slowly with emission angle, but the corresponding intensity ratio for the Si(substrate) 2p line changed appreciably with emission angle. The latter changes, in particular, indicate that neglect of elastic‐scattering effects can lead to erroneous results in the analysis of measured ARXPS data. The elastic‐scattering effects were larger in HfO_1.9N_0.1 than in SiO_1.6N_0.4 (due to the larger average atomic number in the former compound) and were larger with the Al Kα X‐ray source than with the Cu Kα source because of the larger cross sections for elastic scattering at the lower photoelectron energies. Copyright © 2010 John Wiley & Sons, Ltd.     

Surface-enhanced Raman scattering characteristics of 4-nitrobenzenethiol adsorbed on palladium and silver thin films

Palladium is an important catalytic metal, and it is desirable to develop a surface-enhanced Raman scattering (SERS) technique to investigate the reagent and product species adsorbed on its surface. Unfortunately, Pt-group metals, e.g., Pt and Pd, have been commonly considered as non- or weak-SERS-active substrates. In this work, Ag and Pd thin films were deposited very efficiently and evenly onto the surface of glass substrates by using only corresponding metal nitrate salts (AgNO₃ and Pd(NO₃)₂) with butylamine in ethanolic solutions. In this process, pure ethanol was used for Ag deposition, while an ethanol–water (8:2) mixture was used for Pd deposition. The as-prepared Ag and Pd films exhibited SERS activity over a large area. The surface-induced photoconversion capabilities of these Ag and Pd films were then tested on 4-nitrobenzenethiol by means of SERS. It was found that at least under visible laser irradiation, the surface-catalyzed photoreaction occurs more readily on a Ag film than on a Pd film for the conversion of 4-nitrobenzenethiol to 4-aminobenzenethiol, even though Pd is known to be an important transition metal with high catalytic activity.     

Preparation of Macroporous Aluminium Oxide using Template of Poly(methacrylic acid‐co‐glycidylmethacrylate) Crosslinked with Methylenebisacrylamide

Poly(methacrylic acid‐co‐glycidylmethacrylate), poly(MA‐co‐GMA) samples were prepared by exposure to γ–irradiation, at fixed concentration of methylenebisacrylamide MBA, 0.5% wt/wt as crosslinker while the MA/GMA ratio was varied. FTIR spectra showed bands refer to MA, as well as GMA, indicating the involvement of both in the copolymerization. Al(NO₃)₃.9H₂O as a precursor for the preparation of aluminium oxide was templated as a guest into the crosslinked gels by soaking the gels in a methanol solution. The perturbation of the bands at 3439, 2926, 1635, 1476, 1394, and 1166 cm^?1 after the templation of the guest, provides evidence for the loading of the guest species into the gel. The swelling behavior of the prepared samples found to be dependent on the composition of the gel and the pH. The templation of the aluminium nitrate into the gel was further proved by thermal gravimetric analysis (TGA). Scanning electron microscopy (SEM) was used for investigating the produced oxide particles, which revealed macropores with maximum diameter at MA/GMA, 40∶60 wt/wt (H3) and complete disappearance at 80 wt% of methacrylic acid (H5). X‐ray diffraction (XRD) showed an amorphous structure of the aluminium oxide. Increasing the hydrophilicity of the template leads to an increase in the Lewis acidic sites on the surface of the produced aluminium oxide up to 60 wt% of methacrylic acid (H4) while a further increase was met by a redecrease in the surface acidity (H5).     

Anodic film formation on binary Al?Mg and Al?Ti alloys in nitric acid

Nitric acid is commonly used for surface treatments of aluminium alloys. It is used to clean the surfaces after alkaline etching; it has application in chemical polishing and is also used for electrograining. The majority of these treatments undergo the application of anodic polarisation that results in formation of anodic oxide film. However, little is known about the behaviour of aluminium containing magnesium or titanium in solid solution under such conditions. To reveal the effects of magnesium and titanium alloying additions on anodic film formation in nitric acid, Al‐1800 ppm Mg and Al‐800 ppm Ti alloys were investigated. It was found that porous alumina film developed on the surfaces with reduced efficiency of 40%, due to the reactive nature of nitric acid to alumina. The presence of magnesium and titanium in aluminium had little influence on the efficiency of film growth, as confirmed by the relatively similar thicknesses of oxide formed on binary alloys and aluminium. However, incorporation of magnesium ions into the alumina film led to development of a high‐population density of localised voids near the alloy/film interface. An increased titanium content was found in the film regions close to the alloy/film interface, indicating its oxidation. Copyright © 2009 John Wiley & Sons, Ltd.     

Thermal transformations of the products of partial hydrolysis of hydrous aluminium nitrate

Thermal analysis, mass spectrometry, infrared spectrophotometry, X-ray phase analysis, scanning electron microscopy, and sorption methods were used in the study of thermal transformations of the products of partial hydrolysis of hydrous aluminium nitrate in ammonia medium. It has been found that the process of aluminium nitrate hydrolysis under the conditions applied and in the presence of ammonia gives boehmite as the main product, with some admixture of a basic salt.Aluminium oxide obtained from the products of partial hydrolysis of hydrous aluminium nitrate in ammonia medium at 550°C has a crystalline -Al₂O₃ structure. Its specific surface, as determined by low-temperature adsorption of nitrogen, exceeds 200 m²g^–1. Features of the products are well developed mesopore structure and considerable ability of benzene adsorption. Calcination of the obtained aluminium oxide for 2 h at 900°C reduces its specific surface to about 110 m² g^–1.This revised version was published online in November 2005 with corrections to the Cover Date.     

Nanoconfined heliconical structure of twist-bend nematic liquid crystal phase

We produced controlled heliconical structures of a twist-bend nematic (N_TB) liquid-crystal (LC) phase in nanoconfinement in a porous anodic aluminium oxide (AAO) film. The structural parameters of the N_TB phase such as conical angle and helical pitch can be modulated by varying the surface energy of the inner surface of the porous AAO film, done by using different self-assembled monolayers (SAMs). The LC molecules tend to be more freely packed, thus forming a larger conical angle, when placed on the tri-deca-fluoro-1,1,2,2-tetrahydrooctyl-trichlorosilane (FOTS)-treated substrate, which has a relatively low surface energy. In contrast, the molecules form a more tightly packed structure, and thus a smaller conical angle, when placed on the 2-(methoxy(polyethyleneoxy)-propyl)trimethoxysilane (PEG 6/9)-treated substrate, which has higher surface energy. This work improves our collective understanding of self-assembled heliconical structures in the N_TB phase.     

Self‐assembly of stearic acid on aluminium: the importance of oxide surface chemistry

The influence of ambient atmospheric exposure on the chemistry of the magnetron‐sputtered aluminium surface has been characterized as hydroxyl incorporation to the oxide surface and concurrent adsorption of airborne carbonaceous contamination. Here, the consequence of these changes in oxide surface chemistry upon the adsorption of stearic acid from solution is investigated. Water contact angle and polarization modulation infrared refection–absorption spectroscopy (PM‐IRRAS) reveal a strong dependence of stearic acid monolayer order upon ambient exposure time prior to assembly. It is proposed that hydroxyl formation in the ambient atmosphere increases the stearic acid adsorption density and thus the self‐assembled monolayer (SAM) order, whereas airborne carbonaceous material blocks these adsorption sites and introduces disorder in the monolayers through a decrease in adsorption density. Monolayer adsorption has been correlated with the aluminium oxide surface chemistry. It is proposed that this phenomenon represents an explanation for the irreproducible results often reported for assembly on metal oxide substrates. Furthermore, it indicates that in this broad class of material surfaces assembly can be used as a means of estimating the reactivity of surfaces with respect to organic overlayers such as paints and adhesives. Removal of adsorbed carbonaceous material from the aluminium surface using an oxygen plasma resulted in a significantly increased order of the stearic acid monolayer, as assessed by water contact angle. This observation is rationalized as the removal of carbonaceous material blocking surface adsorption sites by the plasma, but retention of the underlying hydroxyl functionality. This is predicted to have important implications in the preparation of aluminium for painting and adhesive bonding. Copyright © 2004 John Wiley & Sons, Ltd.     

Quantitative chemical composition of thin films with infrared spectroscopic ellipsometry: application to hydrated oxide films on aluminium

A method to quantify the composition of thin films using infrared spectroscopic ellipsometry (IRSE), supplemented by visible spectroscopic ellipsometry (VISSE), is proposed. Because ellipsometry measures the thickness and optical constants of a surface layer simultaneously, the absorption coefficient of the film as a function of wavelength can be obtained. Using values of the absorption coefficients for the pure components of the film, the percentages (mol.% or wt.%) of each component in the film can be calculated. The method is demonstrated in a study of the hydration of oxide films on electropolished aluminium and the anodically formed barrier oxide film. The IRSE technique shows that hydration of the films by immersion in boiling water results in the conversion of aluminium oxide to pseudoboehmite. Copyright © 2003 John Wiley & Sons, Ltd.     

Influence of albumin adsorption on physico-chemical properties of alumina surfaces

The effect of albumin adsorption on neutral active aluminium oxide was investigated in the presence of polar and non-polar liquids. The adsorbed values were highest near the isoelectric point of albumin and varied in the range 5–10 and 3–11 mg g^–1 with phosphate buffer and potassium chloride respectively after 2 and 24 h. In the case of aluminium oxide the effect of albumin adsorption on total heterogeneity of adsorbents is not explicit. On the one hand, the modified samples showed decreasing surface area with increase of surface coverage with albumin. On the other hand, modifications under the same conditions but without albumin caused similar changes. These effects suggest the strong influence of medium pH on surface properties (due to surface polarization) and competitive co-adsorption of ions on the process. The volumetric fractal dimensions of the studied materials change in the range 2.25–2.32 for pure aluminium oxide and BSA modified from the phosphate solution. E _d,max values (desorption energy in the maximum of distribution function) diminish (in the range 40–45 kJ mol^–1) compared with pure aluminium oxide (E _d,max=52 kJ mol^–1) for water thermodesorption at modified surfaces to the increase of a number of active centers of hydrophobic character, and weakening of the adsorbent–adsorbate increases.     

The influence of Mn2+ and Ni2+ ions on the surface properties of the aluminium oxide samples using Q-TG and Q-DTG data

The paper presents the complex studies of adsorption and porosity of pure and modified–aluminium oxides samples. The presence of Mn²⁺ and Ni²⁺ modifiers on the aluminium oxide surface causes increase in water adsorption capacity and its decrease in the case of benzene and n-octane. This is due to decrease of specific surface area, volume and radius of pores as a result of surface impregnation and microcrystals formation during modification with manganese and nickel chlorides. Microcrystals formation on the surface and porosity decrease where confirmed by the AFM and SEM studies. From the Q-TG and Q-DTG data, the energies of liquid desorption from the surface of the samples and the functions of desorption, energy distribution were calculated. High degree of nonlinearity of the run of the functions resulting from great heterogeneity of the studied surface was found. Adsorption of cations creates more homogeneous surface of aluminium oxide, and it is responsible for the change in adsorbate molecule interaction energy and changes mechanism of adsorption and desorption as well as thickness and structure of the adsorbed film. From the experimental data some parameters characterizing adsorption properties and porosity of the studied samples were determined using the measuring methods (thermal analysis, sorptomate, porosimetry, AFM).     

Electropolishing of aluminium: processing and assessment of visual appearance

The process of electropolishing aluminium and its influence on the visual appearance are studied. Angle‐resolved scattering (ARS) and total integrated scattering (TIS) are used to investigate the influence of electropolishing on surface roughness. The ARS apparatus is built similar to the ASTM E430‐97A standard. This standard test method is used for measurement of distinctness of image and haze by goniophotometry. These visual appearance parameters, together with TIS, reflect the changes in surface roughness. Total reflectance is correlated to the composition of the aluminium as well as the composition and thickness of the layer formed on the aluminium. Copyright © 2003 John Wiley & Sons, Ltd.     

Corrosion mechanism of pure aluminium in aqueous alkaline solution

The corrosion of pure aluminium in alkaline solution has been explored using an open circuit potential transient, potentiodynamic polarization experiment and a.c. impedance spectroscopy. The steady-state value of the open circuit potential (E _ocp ^ss ) of pure aluminium in alkaline solution was observed to decrease with increasing rotation rate of the specimen, which is ascribed to the enhanced anodic reaction. The extent of anodic polarization for the aluminium dissolution reaction on pure aluminium at E _ocp ^ss was found to be greater than that of cathodic polarization for the water reduction reaction. This indicates that the rate of corrosion of pure aluminium is mainly determined by the anodic reaction in alkaline solution. Based upon the experimental results, a corrosion mechanism for pure aluminium has been proposed in the presence of the native surface oxide film in alkaline solution, involving consecutive oxide film formation and dissolution, and simultaneous water reduction.     

Light scattering of polyaniline films responding to electrochemical switching

When a laser with 543, 668 or 790±50 nm was used to irradiate the reduced polyaniline film on an indium tin oxide electrode in hydrochloric acid, the light was scattered in all directions. The intensity of the scattered light decreased with increase in the detection angle up to the right angle. When the electrode potential was scanned between the insulating and the conducting domain, the intensity varied sigmoidally with hysteresis. The intensity increased with a decrease in the absorbance. The scattering of the light can be ascribed to multiple reflection, luminescence, or Rayleigh scattering. The spectra of the scattered light was identical with that of the incident light, suggesting the absence of luminescence. The intensity increased with an increase in thickness of the film, indicating a negligible contribution of multiple reflection. Since the volume of the oxidized film is larger than that of the reduced one, the film synthesized in the oxidized state is deformed by the electrode reduction. Then, the film density becomes locally inhomogeneous and this may give rise to the Rayleigh scattering. The potential-variation of the light scattering occurred at a more negative potential than that of the absorbance at 310 nm and of the current did.     

In Situ High‐Energy Synchrotron Radiation Study of Boehmite Formation,Growth, and Phase Transformation to Alumina in Sub‐ and Supercritical Water

Boehmite (AlOOH) nanoparticles have been synthesized in subcritical (300 bar, 350 °C) and supercritical (300 bar, 400 °C) water. The formation and growth of AlOOH nanoparticles were studied in situ by small‐ and wide‐angle X‐ray scattering (SAXS and WAXS) using 80 keV synchrotron radiation. The SAXS/WAXS data were measured simultaneously with a time resolution greater than 10 s and revealed the initial nucleation of amorphous particles takes place within 10 s with subsequent crystallization after 30 s. No diffraction signals were observed from Al(OH)₃ within the time resolution of the experiment, which shows that the dehydration step of the reaction is fast and the hydrolysis step rate‐determining. The sizes of the crystalline particles were determined as a function of time. The overall size evolution patterns are similar in sub‐ and supercritical water, but the growth is faster and the final particle size larger under supercritical conditions. After approximately 5 min, the rate of particle growth decreases in both sub‐ and supercritical water. Heating of the boehmite nanoparticle suspension allowed an in situ X‐ray investigation of the phase transformation of boehmite to aluminium oxide. Under the wet conditions used in this work, the transition starts at 530 °C and gives a two‐phase product of hydrated and non‐hydrated aluminium oxide.     

Enhancing the Performance of Dye‐Sensitized Solar Cells with a Gold‐Nanoflowers Box

To improve the electron collection, electron lifetime, and light‐harvesting efficiency of dye‐sensitized solar cells simultaneously, Au nanoflowers were prepared and used to cover the entire TiO₂ film. Deposition of Au nanoflowers around the TiO₂ film formed a light‐scattering “box” that covered the entire TiO₂ film. Compared with a light‐scattering layer that only covers the top surface of TiO₂, the Au‐nanoflowers box exhibited better light‐harvesting efficiency due to omnidirectional light scattering, faster electron transport (attributed to the formation of electron channels between the metallic Au nanoflowers and the electron‐collection electrode), and slower charge recombination. As a consequence, the short‐circuit photocurrent and open‐circuit photovoltage were both enhanced significantly, which improved the power conversion efficiency from 8.12 to 10.91 % (34 %) when an Au‐nanoflowers box was wrapped around the photoanode.