Publications

Galvanic compatibility of corrosion protective coatings with AA7075 aluminum alloy

The galvanic compatibility of aerospace aluminum alloy AA7075 with cadmium (Cd), zinc (Zn), and zinc–cobalt–iron (Zn–Co–Fe, 32–37%Co and 1%Fe) alloys was investigated. A comparison of open circuit potential [OCP vs. saturated calomel electrode (SCE)] measurements in 0.6 mM NaCl showed that all coatings would act anodically to AA7075 with an exception of Zn–Co–Fe (37%Co + 1%Fe) alloy which was electropositive to AA7075. During the zero resistance ammetry (ZRA) measurement in 0.6 M NaCl electrolyte the coupled OCP and current density were measured during 7 days of immersion and both Zn and Cd acted anodic and thus sacrificial to AA7075. Galvanic coupling of AA7075 with (37%Co + 1%Fe) Zn–Co–Fe alloy resulted in the consequent dissolution of the AA7075 aluminum alloy. In contrast, Zn–Co–Fe (32%Co + 1%Fe) alloy was found to be anodic to AA7075 during the first 26 h of immersion but after dezincification and cobalt enrichment at the surface became cathodic to the AA7075 aluminum alloy. During coupling with Zn, some pitting was also observed on AA7075.

Study of the use of different charge compensation techniques during field emission – AES factor analysis of aluminium oxides

The concept of a novel approach to control MIC corrosion in civil structures

Impressed current cathodic protection (CP) based on pulse technology has been proven to be a more efficient and effective alternative of traditional CP for reinforced concrete applications. Essentially, the superiority of pulse CP is in achieving the required steel polarization with otherwise reduced side effects (e.g. influence on bond strength or cement-based bulk matrix properties are minimized); further utilization of lower anodic surface is possible with pulse CP as a result of a better “current throw” at certain frequency and duty cycle of the pulse. The technique has not been tested so far with respect to microbiologically induced corrosion (MIC) and marine applications of steel structures. This paper will present the concept of recently initiated research for MIC corrosion control through the synergetic action of pulse CP and bio-based coatings. The emphasis is on steel structures for marine applications. An essential part of the expected corrosion control is based on the action of hybrid bio-based coatings, involving competitive microorganisms. The application targets self-healing with respect to MIC and hydrogen-induced damage. Control of anaerobic MIC will be one of the main goals of this research. Extending the application to reinforced concrete and underground pipe-network is also foreseen. The fundamental mechanisms with respect to MIC corrosion will be defined in parallel to the mechanisms of cathodic polarization when MIC is involved. Clarifying the reasons for steel ennoblement in anaerobic conditions under CP will be achieved and an optimum polarization level will be derived. The first step in this research will be studying the electrochemical behavior of steel in simulated environment as within aerobic, anaerobic and mixed MIC conditions (at open circuit and under cathodic polarization) and the results coupled to steel surface analysis and bacterial viability under conventional and pulse CP.

Laser ablation- and plasma etching-based patterning of graphene on silicon-on-insulator waveguides

We present a new approach to remove monolayer graphene transferred on top of a silicon-on-insulator (SOI) photonic integrated chip. Femtosecond laser ablation is used for the first time to remove graphene from SOI waveguides, whereas oxygen plasma etching through a metal mask is employed to peel off graphene from the grating couplers attached to the waveguides. We show by means of Raman spectroscopy and atomic force microscopy that the removal of graphene is successful with minimal damage to the underlying SOI waveguides. Finally, we employ both removal techniques to measure the contribution of graphene to the loss of grating-coupled graphene-covered SOI waveguides using the cut-back method.

Aluminium Surface Science and Technology (ASST 2006)

No abstract is provided for this article.

Evaluation of particle and bed integrity of aqueous size-exclusion columns packed with sub-2 µm particles operated at high pressure

The performance of columns packed with 1.7 µm particles for aqueous size-exclusion chromatography was assessed at high-pressure conditions and linked to particle- and column-bed integrity. Decreasing the particle size from 3.5 µm to 1.7 µm increases the resolution due to the improved mass-transfer characteristics, allowing to significantly speed-up analysis without compromising the selectivity. A sub-minute separation of intact proteins was realized on a 4.6 mm i.d × 75 mm long column packed with 1.7 µm SEC particles applying a flow rate of 1.8 mL/min, corresponding to a column pressure of 530 bar. Ultra-high pressure operation (exceeding manufacturer's recommendations) resulted in peak deformation, a shift towards earlier retention times, and an alteration in selectivity. To gain insights in the mechanisms of column deterioration, short 30 mm long columns were operated at UHPLC conditions, maximizing the pressure drop over individual particles. This resulted in the presence of fractured particles situated at the column outlet, as verified by scanning electron micrographs. Mercury-intrusion porosimetry and argon-adsorption measurements did not reveal significant differences in intraparticle volume between particle batches sampled before and after pressure stress testing. As particles at the column outlet fracture (but not collapse) at high pressure operation, a void was formed at the column inlet. The degradation of the separation performance appeared to be the result of a decrease in interparticle pore volume.

Influence of SiO2/Na2O ratio and temperature on the mechanism of interaction of soluble sodium silicates with porous anodic alumina

Porous anodized aluminum oxides were silicate-treated by dipping in a water-based sodium silicate solution. The surface modifications occurring on the oxide layer during immersion in solution are studied as a function of the SiO2/Na2O ratio and the temperature of the silicate solution. The anionic speciation in the silicate solution was studied by means of 29Si NMR. The reactions happening at the anodic alumina surface were studied by monitoring the open circuit potential as a function of time. The presence of silicate in the pores of the anodic layer is analyzed by means of GDOES and the morphological changes occurring on the oxide surface during immersion are observed by FE-SEM. The mechanism of the deposition is extended to silicate solutions with SiO2/Na2O=1.

Growth mechanism of industrial Ti/Zr no-rinse sprayed conversion coating applied on automotive aluminium coils: preferential deposition on the intermetallic phases

No abstract is provided for this article.

AES and SIMS investigation of different CuxS/CdS solar cells

No abstract is provided for this article.

Feasibility of Fourier transform laser microprobe mass spectrometry for the surface analysis of aluminium

No abstract is provided for this article.

Ageing of aluminium oxide surfaces and their subsequent reactivity towards bonding with organic functional groups

An infrared reflection absorption spectroscopy investigation was performed of the changes that occur to a freshly prepared aluminium substrate upon ageing in ambient air and upon ageing in a clean, dry environment. Moreover, the bonding capacity of the oxide surfaces was evaluated after prior ageing, by adsorbing an aliphatic carboxylic acid and determining the amount of molecules that were capable of chemisorption with the oxide surface. Ageing in the ambient resulted in the adsorption of water and organic species on the oxide surface, which could not be removed using solvents. The adsorbed water caused hydroxylation and growth of the oxide layer. Because of the adsorbed species, the oxide surface was found to loose 60% of its initial bonding capacity during the first 20h of ageing. Ageing in a clean and dry environment resulted in considerably less changes to the oxide surface. Because of this, during the first 20h of ageing, the substrate was found to loose only 35% of its initial reactivity.

Numerical characterization of an ultra-high NA coherent fiber bundle part I: modal analysis

Advances in fiber optics and CCD technology in the last decades have allowed for a large reduction in outer diameter (from centimeters to submillimeter) of endoscopes. Attempts to reduce the outer diameter even further, however, have been hindered by the trade-off, inherent to conventional endoscopes, between outer diameter, resolution and field of view. Several groups have shown the feasibility of further miniaturization towards so called micro-endoscopes, albeit at the cost of a very reduced field of view. In previous work we presented the design of an ultra-high NA (0.928) Coherent FiberBundle (CFB) that, in combination with proximal wave front shaping, could be used to circumvent this trade-off thus paving the way for even smaller endoscopes. In this paper we analyze how the modal properties of such an ultra-high NA CFB determine the required input field to achieve any desired output field. We use the periodicity of the hexagonal lattice which characterizes a CFB, to define a unit cell of which we analyze the eigen-modes. During the modal analysis, we also take into account realistic variations in lattice constant, core size and core shape due to the limitations of the fabrication technology. Realistic values for these types of fabrication-induced irregularities were obtained via SEM images of a CFB fabricated according to the aforementioned design. The presence of these irregularities results, for a desired output, in the required input to be different from the required input for a defect-free CFB. We find that of the different types of fabrication-induced irregularities present in the CFB, variations in core ellipticity have the biggest impact on the required input for a given desired output.

Influence of electrode geometry on zinc corrosion under thin electrolytes

No abstract is provided for this article.

Composition and thickness of non-functional organosilane films coated on aluminium studied by means of infra-red spectroscopic ellipsometry

Surface treatments of metals, leading to the deposition of thin films, are generally performed in order to create or change certain surface properties such as corrosion resistance or adhesion. For the past few years, the use of organosilanes for aluminium surface treatments are more and more considered as they provide both corrosion protection and adhesion properties. It has been previously shown that the silane bath concentration strongly influences the thickness of the silane films deposited on aluminium substrates. A linear increase of the layer thickness with the silane bath concentration has been underlined. In this paper, the chemistry of the deposited silane films has been studied as a function of the silane bath concentration. For this, Infra red spectroscopic ellipsometry (IRSE) has been used. It is a method similar to reflection absorption infra red spectroscopy (RAIRS), which is a non-destructive infra red reflection technique, allowing chemical characterisation of thin films on metals. It will be shown that differences in the positions and strength of absorption bands are visible when the silane concentration of the solution is varied. Such changes can result in a difference in the film chemistry or in the film thickness. Since IRSE offers chemical information along with the thickness information, modifications occurring in an IRSE spectrum can be understood more easily. It will be demonstrated that the use of an optical model, describing the absorption bands and thickness of the films, permits the determination of the chemistry and the thickness of the silane films.

Multinuclear 1D- and 2D-NMR study of the hydrolysis and condensation of bis-1,2-(triethoxysilyl)ethane

This paper focuses on the study of the effect of aging on the composition of the solutions used for deposition of silane films onto metals. Such films are used for corrosion protection and adhesion applications. The silane films interact with metallic surfaces by reactions between the OH groups of both materials with elimination of water. Therefore, prior to the immersion of the metal into the silane solution, the silane has to be hydrolysed in order to generate a maximum of silanol (SiOH) groups, while minimizing condensation leading to siloxane (SiOSi) groups. One of the main factors influencing the amounts of silanol and siloxane groups produced is the solution aging. This paper demonstrates by NMR spectroscopy that in the case of a bridged silane, namely bis-1,2-(triethoxysilyl)ethane, a stable plateau offering a good compromise between hydrolysis and condensation in the solution is obtained between 24 h and a few days of aging.

Copper effect on pitting and intergranular corrosion of model AlMgSi(Cu) alloys

No abstract is provided for this article.

The FIB/TEM method for the Characterisation of rolled Al Surfaces

For the characterisation of Al surfaces after thermo mechanical processing of rolled strips TEM is imperative. Especially cross-sectional TEM specimens highlight the multi-layered structures of the surface area. The specimen preparation of cross-sections is a critical step in TEM analysis. A common technique is ultramicrotomy, where a diamond knife is used to cut electron transparent slices. The major disadvantage of the method - especially in the case of aluminium - is the strong mechanical deformation resulting from cutting. Another technique is the conventional ion beam milling. In order to provide views of subsurface regions, the sample surfaces are initially glued together, then cut perpendicular to the sheet surface, mechanically thinned, cut to form disks, dimpled, and ion beam thinned. Here, a new method for preparing cross-sectional TEM specimens of aluminium surfaces is introduced: Focused Ion Beam thinning (FIB), which became a standard method for preparation in the semiconductor industry. This technique has the potential of introducing nearly no chemical and structural modifications in the specimen. TEM lamellae of equal thickness can be produced in less than two hours and the success rate is nearly 100%. As an example for this new preparation method the paper reports about a (S)TEM investigation of a FIB prepared specimen of the surface of an AlMg0.5 hot rolled strip.

Patina formation and degradation during the atmospheric corrosion of zinc

No abstract is provided for this article.