Direct electrodeposition of aluminium nano-rods

Electrodeposition of aluminium within an alumina nano-structured template, for use as high surface area current collectors in Li-ion microbatteries, was investigated. The aluminium electrodeposition was carried out in the ionic liquid 1-ethyl-3-methylimidazolium chloride:aluminium chloride (1:2 ratio). First the aluminium electrodeposition process was confirmed by combined cyclic voltammetry and electrochemical quartz crystal microbalance measurements. Then, aluminium was electrodeposited under pulsed-potential conditions within ordered alumina membranes. A careful removal of the alumina template unveiled free standing arrays of aluminium nano-rods. The nano-columns shape and dimensions are directly related to the template dimensions. To our knowledge, this is the first time that direct electrodeposition of aluminium nano-pillars onto an aluminium substrate is reported.     

Determination of aluminium in natural water samples

The atmospheric deposition of terrestrial dust into the ocean is an important factor in controlling Earth's climate. Aluminium can be used as a tracer for the magnitude and location of dust transported from the land to surface ocean. The element is ideal for this purpose since its primary input is via aeolian dust deposition and it has a short surface water residence time. The accurate determination of dissolved aluminium in seawater is difficult due to the complexity of the matrix and the trace (nanomolar) concentrations at which the metal exists. This paper presents a critical review of the different sampling and analytical methods for the determination of the concentration of aluminium in natural waters, with particular focus on techniques successfully applied to shipboard analysis of seawater.     

Influence of aluminium precursor on physico-chemical properties of aluminium hydroxides and oxides

The paper concerns aluminium hydroxides precipitated during hydrolysis of aluminium acetate in ammonia medium, as well as aluminium oxides obtained through their calcination at 550, 900 or 1200°C for 2 h. The following techniques were used for analysing of obtained materials: thermal analysis, IR spectroscopy, X-ray diffraction, low-temperature nitrogen adsorption, adsorption-desorption of benzene vapours and scanning electron microscopy. Freshly precipitated boehmite/pseudoboehmite had high value of S _BET, very good sorption capacity for benzene vapours, developed mesoporous structure and hydrophilic character. After prolonged refluxing at elevated temperature its crystallinity increased which was accompanied by a decrease of specific surface determined from nitrogen adsorption, decrease of sorption capacity for benzene vapours and weakening of the hydrophilic character. Calcination of all hydroxides at the temperature up to 1200°C resulted in the formation of α-Al₂O₃ via transition forms of γ-, δ-and θ-Al₂O₃. The samples of aluminium oxides obtained after calcination at 550 and 900°C were characterised with high values of specific surface area and displayed quite high heat resistance, probably due to a specific morphology of starting hydroxides. The process of ageing at elevated temperature developed thermal stability of aluminium oxides.     

Influence of aluminium precursor on physico-chemical properties of aluminium hydroxides and oxides

The process of hydrolysis of aqueous aluminium sulfate was carried on in ammonia medium at 100°C and for different time intervals (0, 20, 39 or 59 h). The products thus obtained were calcined at 550, 900 or 1200°C for 2 h with the aim to obtain aluminium oxides. The materials were studied with the following methods: thermal analysis, IR spectroscopy, X-ray diffraction, low-temperature nitrogen adsorption, adsorption–desorption of benzene vapours and scanning electron microscopy. Freshly precipitated material was an amorphous basic aluminium sulfate which after prolonged refluxing at elevated temperature in a mother liquor underwent a phase transformation into highly crystalline NH₄Al₁₃(SO₄)₂(OH)₆ containing tridecameric unit Al₁₃. It was accompanied by a decrease of specific surface area and the formation of a porous structure less accessible for benzene molecules. Regardless of the duration of the hydrolysis process, all products were characterised with poorly developed porous structure and hydrophilic character. Their calcination at the temperature up to 1200°C resulted in the formation of α-Al₂O₃ via transition forms of γ/η- and δ-Al₂O₃. The samples of aluminium oxides obtained after calcination at 550 and 900°C had higher values of specific surface area than starting materials due to processes of dehydroxylation and desulfurization. The process of calcination up to 900°C was reflected in developing of not only porous structure but also hydrophobic character of prepared materials. The S _BET values calculated for the oxide samples obtained from aged products of hydrolysis at 1200°C were lower than for the analogous sample prepared without the ageing step. It was concluded that prolonged refluxing at elevated temperature of the products of hydrolysis of aluminium sulfate decreased thermal stability of final aluminium oxides.     

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.     

Surface modification of aluminium with reactive microgels

The adsorption and organisation process of reactive microgels has been investigated on technical aluminium. The aim was to replace the present chromating procedure on reactive metals like aluminium because this process was been considered as an ecological problem. By means of a two‐step emulsion polymerization with phosphate substituted monomer we have obtained polymeric nano‐particles with phosphate groups on the surface. The core is synthesized by copolymerization from styrene (St) and butyl acrylate (BuA). The results of several analytical methods like contact angle SEM or TEM measurements showed, that these microgels were able to adsorb spontaneously onto the substrate surface and subsequently a structured molecular order was formed. The properties of the adsorbed microgel layers were confirmed by industrial linked adhesion and corrosion tests.     

The ubiquitous Beilby layer on aluminium surfaces

In 1996, it was found that the Beilby layer on rolled aluminium sheet could be imaged in the transmission electron microscope (TEM) on ultramicrotomed cross sections of the sheet surface. Following from this observation, we have examined Beilby layers on all types of aluminium surfaces that have been subject to high shear processing treatments such as rolling, grinding or machining. The layers are microcrystalline rather than amorphous, and they strongly influence properties like corrosion resistance and reflectance. Preferential precipitation in these deformed surface layers results in their electrochemical activation and it is responsible for the development of underfilm corrosion in most architectural and automotive alloys. More recently, it has been possible to directly image Beilby layers on ultramicrotomed stubs using the new generation of low kilovoltage high‐resolution scanning electron microscopes and to carry out high‐resolution TEM of sections cut from precisely located surface features. The paper presents an overview of all the recent investigations of high shear induced Beilby layers on aluminium alloys and discusses their control of surface properties. Copyright © 2010 John Wiley & Sons, Ltd.     

A field aluminium speciation method to study the aluminium hazard in water

The toxicity of aluminium is governed by its bioavailability. Therefore, the speciation of aluminium in drinking water becomes of prime importance to understand its fate and the population exposure, and to develop guidelines for the concentration levels. At Health Canada, a field speciation method has been developed to perform on-site speciation followed by measurement of Al in the laboratory. The following species are generated: 1) total recoverable; 2) total acid-leacheable; 3) total dissolved; 4) dissolved extracted; and 5) dissolved non extracted. The field extractions are performed by percolation through chelation columns, which are later processed in the laboratory. Aluminium determinations can then be performed by numerous methods, such as by Inductively Coupled Plasma Mass Spectrometry (ICPMS), Graphite Furnace Atomic Absorption Spectrometry (GFAAS) or Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). Examples of results for raw or treated/ distributed surface waters, as well as for groundwaters, are used to illustrate the validity of the method, and the importance of considering aluminium speciation in characterizing the aluminium hazard in water.     

Aspects of polyaniline electrodeposition on aluminium

Electrodeposition of polyaniline (PAni) from acid solutions on spontaneous passivating electrodes such as Al is not so obvious as on active metals (Fe and Ni). The methods that can result in deposition are: (1) surface pre-treatment with a chelating agent (alizarin) to block the hydrogen evolution reaction on aluminium and (2) a suitable monomer concentration (critical monomer concentration) to decrease the polymerisation induction time. The oxidation of aluminium to thick porous film limits the growth kinetics of PAni during deposition by cyclic voltammetry. We found that after reducing hydrogen evolution by surface chelation, for film growing in 0.5 M H₂SO₄ a concentration of 0.4 M aniline is required.     

Influence of aluminium precursor on physico-chemical properties of aluminium hydroxides and oxides

An attempt to obtain aluminium hydroxide that could give aluminium oxides of increased thermal stability was made. Aluminium hydroxide was precipitated during a hydrolysis of aluminium chloride in ammonia medium. The influence of preparative conditions, such as a dosing rate of aluminium precursor, pH, duration of the precipitate refluxing and temperature of calcination, on the properties of obtained hydroxides and oxides was investigated. The materials were studied with the following methods: thermal analysis, IR spectroscopy, low-temperature nitrogen adsorption and adsorption–desorption of benzene vapours. Precipitated boehmites had high values of S _BET determined from nitrogen adsorption (220–300 m²g^–1), good sorption capacity for benzene vapours, developed mesoporous structure and hydrophilic character. It has been proved that a high pH value during the precipitation of aluminium hydroxide favoured better crystallisation of boehmite structure, higher temperature of its dehydroxylation into γ-Al₂O₃, and delayed transformation of γ phase into α-Al₂O₃. Aluminium oxides derived from the hydroxides precipitated at a high pH were the most stable at high temperatures, and were characterised with the best surface properties. The online version of the original article can be found at     

Electron Rutherford back‐scattering case study: oxidation and ion implantation of aluminium foil

Electron Rutherford back scattering (ERBS) is a new spectroscopy for determining the composition of surfaces. In this work the surface sensitivity of ERBS was investigated by changing the entrance and exit angle of the electron beam while keeping the scattering angle constant. It was found that in this way the surface sensitivity of the technique can be varied considerably. We use aluminium as a test case for ERBS, as it is well studied. The technique has been used to investigate the oxide film of aluminium foil as manufactured and the native oxide (Al₂O₃) film formed on a clean aluminium surface exposed to air. We have also used ERBS to investigate the presence of Xe, implanted during the sputter cleaning process, at a variety of depths within an aluminium matrix. Copyright © 2007 John Wiley & Sons, Ltd.     

Surface modified aluminium hydroxide in flame retarded noise damping sheets

Flame retarded polyethylene compounds were prepared using a series of aluminium hydroxide of different particle size applying a milling processes and special precipitation technologies. The processability and flame retardant efficiency of the flame retarded systems were compared. The effects of various surface modifications were analysed in case of one selected type of aluminium hydroxide. A silicone terminated reactive surfactant promoted not only the processability but also the flame retardant efficiency. Noise damping sheets were prepared by simultaneous application of aluminium hydroxide and barium sulphate in an elastomer blend matrix. V0 flame retardant grade could be achieved this way accompanied with improvement in the acoustic properties and maintenance of the mechanical properties.     

Filiform corrosion of aluminium alloys after a phosphate treatment

The role on filiform corrosion (FFC), after an automotive painting process with a phosphate treatment, of the near surface deformed layer (NSDL) formed during mechanical processing on AA8006 aluminium alloys is investigated. Samples subjected to specific surface pretreatments are examined before and after different steps of the phosphating process in order to identify the characteristics of the NSDL that are responsible for the susceptibility to FFC. The thickness, the structure and the composition of this NSDL are determined by SEM, RBS, XPS and transmission electron microscopy. The presence of a 200‐nm thick NSDL which is not completely eliminated during the degreasing step of the phosphating process increases dramatically the FFC susceptibility of AA8006 aluminium alloys compared with beforehand etched samples. The influence of Pb and Mg segregation on top of the surface is found to be negligible whereas the specific microstructure of the NSDL characterised by nanograins with boundaries decorated by nano‐sized oxide intermetallic particles seems to play a major role on FFC. Copyright © 2014 John Wiley & Sons, Ltd.     

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.     

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.     

Characterization of aluminium surface treatments by means of gas adsorption measurements

Adsorption measurements were used to determine the specific surface area of a.c. electrolytically grained aluminium and the porosity distribution diagram of porous anodized aluminium. Alternating current electrolytic graining of aluminium is used to increase the specific surface area for the preparation of litho sheets or capacitor foil. The specific surface area S (calculated by the BET procedure from the nitrogen adsorption isotherm) was studied as a function of the graining frequency between 0.1 and 1000 Hz. The results were related to the graining morphology by comparing them with scanning electron microscopy micrographs. It is concluded that in contrast to the more common surface investigation techniques the method can be used to measure quantitatively the gain in surface area after such a treatment as a.c. electrolytic graining. In the second part of the paper the pore size distribution diagrams are calculated from the adsorption isotherm for porous sulphuric acid films. It is shown that the dominant pore diameter corresponds rather well to the pore diameter observed in transmission electron microscopy sectional views. This means that the adsorption method can be applied to study the porosity of the aluminum oxide films. The method was then used to study the influence of the pretreatment on the porous oxide film morphology.     

Interfacial chemistry of adhesives on hydrated aluminium and hydrated aluminium treated with an organosilane

The adsorption of a commercial adhesive and two of its major components—an amine curing agent [2,4‐toluene diisocyanate urone (TDI urone)] and an adhesive prepolymer resin [diglycidyl ether of bisphenol A (DGEBA)]—on a hydrated aluminium surface and the hydrated surface coated with γ‐glycidoxypropyltrimethoxysilane (GPS) has been investigated by x‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). The study of TDI urone adsorption indicated that adsorption was of the chemisorption type, and a specific interaction involving this molecule and the GPS immobilized on the hydrated aluminium surface was identified. From XPS and ToF‐SIMS data it was found that the types of interaction of the curing agent with the bare substrate were of the donor–acceptor type. Study of the DGEBA adsorption showed different‐shaped isotherms for the bare and the GPS‐coated substrates. It was found that the typical Langmuir isotherm type was obtained for the GPS‐coated substrate whereas no adsorption plateau was observed for the bare substrate within the concentration range studied. This resulted from a change in the conformation of the DGEBA molecule on the substrate when the concentration of DGEBA solution was increased. The bonding of DGEBA with both types of substrates was assumed to be via acid–base interactions (i.e. donor–acceptor interactions). Adsorption of the commercial adhesive on the hydrated surfaces was of BET Type IV form, rather than the simple monolayer adsorption isotherm (Langmuir type). This indicates multilayer adsorption, presumably in the pores of the hydrated substrate, as a result of a process analogous to adsorption condensation. Copyright © 2004 John Wiley & Sons, Ltd.     

A new approach to nickel electrolytic colouring of anodised aluminium

Energy dispersive X-ray spectroscopy and scanning electron microscopy were used to analyse nickel on anodic aluminium surfaces after stripping the anodic aluminium oxide. The metal was electroplated at the bottom of the pores of anodised aluminium during electrolytic colouring in solutions without (Watts) and with (citrate) complexing agents, respectively. A relation between the anodic-cathodic processes, changes of the structure and composition of the coating in dependence on the used solution were studied. A morphology study performed after stripping the anodic aluminium oxide revealed the crucial influence of the anodic process/cycle and the complexing agent on the nickel structure on the aluminium surface. Off-time of half-way rectified current influenced the nickel deposition in the pores of anodic alumina negatively.     

Aluminium nitrate as a precursor of mesoporous aluminium oxides

The thermal transformations of the products of hydrous aluminium nitrate hydrolysis in ammonia medium were studied by thermal analysis, mass spectrometry, infrared spectrophotometry, X-ray phase analysis, and sorption methods. Experiments have shown that the hydrolysis of hydrous aluminium nitrate in ammonia medium at pH=6-7 leads to the formation of boehmite. The degree of crystallinity of this product increases, if the hydrolysis is carried out for 264 h at 100°C, with respect the samples separated from the mother liquor just after completing the dosage of the reagents. It has also been found that aluminium oxide, obtained by thermal decomposition of the products of hydrolysis carried out for 264 h at an increased temperature, is characterized by a well developed specific surface, stable at high temperatures, amounting to about 100 m2 g^-1, after calcination for 2 h at 1200°C. This revised version was published online in July 2006 with corrections to the Cover Date.