Publications

. The remineralisation of sinking particles by prokaryotic heterotrophic activity is important for controlling oceanic carbon sequestration. Here, we report mesopelagic particulate organic carbon (POC) remineralisation fluxes in the North Atlantic along the GEOTRACES-GA01 section (GEOVIDE cruise; May–June 2014) using the particulate biogenic barium (excess barium; Baxs) proxy. Important mesopelagic (100–1000 m) Baxs differences were observed along the transect depending on the intensity of past blooms, the phytoplankton community structure, and the physical forcing, including downwelling. The subpolar province was characterized by the highest mesopelagic Baxs content (up to 727 pmol L−1), which was attributed to an intense bloom averaging 6 mg chl a m−3 between January and June 2014 and by an intense 1500 m deep convection in the central Labrador Sea during the winter preceding the sampling. This downwelling could have promoted a deepening of the prokaryotic heterotrophic activity, increasing the Baxs content. In comparison, the temperate province, characterized by the lowest Baxs content (391 pmol L−1), was sampled during the bloom period and phytoplankton appear to be dominated by small and calcifying species, such as coccolithophorids. The Baxs content, related to oxygen consumption, was converted into a remineralisation flux using an updated relationship, proposed for the first time in the North Atlantic. The estimated fluxes were of the same order of magnitude as other fluxes obtained using independent methods (moored sediment traps, incubations) in the North Atlantic. Interestingly, in the subpolar and subtropical provinces, mesopelagic POC remineralisation fluxes (up to 13 and 4.6 mmol C m−2 d−1, respectively) were equalling and occasionally even exceeding upper-ocean POC export fluxes, deduced using the 234Th method. These results highlight the important impact of the mesopelagic remineralisation on the biological carbon pump of the studied area with a near-zero, deep (> 1000 m) carbon sequestration efficiency in spring 2014.

The isothermal curing kinetics of epoxy/nano-glassflake (NGF) was studied using isothermal differential scanning calorimetry (DSC) technique. The results of the isoconversional method show that the effect of conversion on activation energy (E a ) is negligible for both the neat resin and NGF-filled system. Model-fitting methods were used to determine the kinetic triplet, i.e., pre-exponential factor [A], activation energy [E a ], and reaction order [n], by a simultaneous treatment of all isothermal curing experimental data. The kinetic triplet showed reduction in presence of NGF. A good agreement between experimental data and nth-order model is found for all curing temperatures. Although both methods show that the E a of epoxy/NGF are lower than those of the systems without NGF, the reaction is slower in the presence of NGF. Additional investigations on the glass transition temperature and curing kinetic curves show that vitrification did not occur during the curing reaction.

No abstract is provided for this article.

The mechanisms governing coating/metal oxide delamination are not fully understood, although adhesive interactions at the interface are considered to be an important prerequisite for excellent durability. This review aims to better understand the formation and degradation of these interactions. Developments in adhesion science made it clear that physical and chemical interfacial interactions are key factors in hybrid structure durability. However, it is very challenging to get information directly from the hidden solid/solid interface. This review highlights approaches that allow the (in situ) investigation of the formation and degradation of molecular interactions at the interface under (near-)realistic conditions. Over time, hybrid interfaces tend to degrade when exposed to environmental conditions. The culprits are predominantly water, oxygen, and ion diffusion resulting in bond breakage due to changing acid–base properties or leading to the onset of corrosive de-adhesion processes. Therefore, a thorough understanding on local bond interactions is required, which will lead to a prolonged durability of hybrid systems under realistic environments.

Supported nanostructured materials play a key role in the improvement of energy conversion and storage technologies, such as fuel cells, electrolyzers, batteries and supercapacitors. Nickel-based nanoparticles (NPs) are ideal for a wide range of (electro)catalytical applications, more specifically for the oxygen evolution reaction (OER), where a stable, highly active and cost effective electrocatalyst is needed to overcome the sluggish kinetics. Electrodeposition permits the growth of the NPs directly on the support of interest, enabling this way an increase in their electroactivity. However, for that purpose, the electrochemical processes occurring during nanoscale electrodeposition need to be understood. In this context, Deep Eutectic Solvents (DESs) have generated great enthusiasm as a new generation of non-aqueous electrolytes [1] for electrochemical deposition. By adding water to the DESs, the electrolyte behavior has been found to be remarkably different [2], opening an interesting line of investigation for nanoscale electrodeposition investigations. Here, we present our studies on the electrodeposition of nickel nanostructures from several choline-chloride based DESs with different hydrogen bond donors and different amounts of added water. By combining electrochemical techniques, with FE-SEM, XPS, HAADF-STEM, and EDX, the electrochemical processes occurring during nickel deposition and the effect of added water are now better understood. UV-Vis spectroscopy and Molecular Dynamics (MD) help to clarify the intriguing electrochemical behavior that can be seen for very small amounts of water in the DESs [3-4]. Our studies, show that the ability of understanding the effect (and controlling the amount) of water in DES is essential to tune the chemical and morphological nature of the electrodeposited Ni based nanostructures, thereby obtaining highly electroactive NPs [5-6]. At sufficiently negative potentials, Ni growth is halted due to water splitting and the (electro)chemical reduction of the DES components. Under certain conditions, the formation of a mixed layer of Ni/Ni(OH) 2(ads) is favored [5-6] and further 3D growth of the Ni containing nanostructures can be halted. Hence, Ni nanostructures are embedded in a 2D crystalline Ni containing network that is formed in the inter-particle region [7]. The presence of a mixed layer (Ni/NiO x (OH) 2(1-x) ) and a 2D network rich in oxide and hydroxide species is shown to enhance the electrocatalytic activity of the nickel based nanomaterials towards the OER. References: L. Smith, A.P. Abbott, K.S. Ryder. Chemical Reviews , 114 (2014) 11060–11082. Du, B. Zhao, X-B. Chen, N. Birbilis, H. Yang. Scientific Reports , 6 (2016) 29225. M.H. Mamme, SLC Moors, H Terryn, J Deconinck, J Ustarroz, F De Proft, The journal of physical chemistry letters 9 (2018), 6296-6304. M.H. Mamme, SLC Moors, H Terryn, E.A. Mernissi Cherigui, J Deconinck, J Ustarroz, F De Proft, Submitted (2019) E.A. Mernissi Cherigui, K. Sentosun, P. Bookenooge, H. Vanrompay, S. Bals, H. Terryn, J. Ustarroz. The Journal of Physical Chemistry C , 121 (2017) 9337-9347. E.A. Mernissi Cherigui, K. Sentosun, M. H. Mamme, M. Lukaczynska, H. Terryn, S. Bals, J. Ustarroz. The Journal of Physical Chemistry C , 122 (2018) 23129-23142. E.A. Mernissi Cherigui, K. Sentosun, H. Terryn, S. Bals, J. Ustarroz. Submitted (2019).

Sodium silicate solutions are widely used chemicals for a variety of applications. In particular, they are commonly used in pre‐treatments of aluminium alloys as cleaners and corrosion inhibitors. Another application is found in offset printing, where after graining and anodising, a silicate‐based post‐anodic treatment (PAT) is considered to optimise the aluminium plate characteristics. It is, however, not clear what type of interaction takes place between the oxide‐covered aluminium and the silicate solution. In this work, silicate‐based PAT is studied. Different barrier‐type and porous‐type aluminium oxides are silicate‐treated by dipping in a water‐based sodium silicate solution and the effect of time on the deposition is studied. Particular attention is given to the role of rinsing when the alumina surface is washed in water after the silicate treatment. A good understanding of the role of rinsing allows us to obtain information on the characteristics of the silicate layer which is formed after dipping. The surface modifications induced by the silicate treatment on the aluminium oxides were monitored by means of field emission scanning electron microscopy and infrared spectroscopic ellipsometry. Quantitative measurements on the amount of deposited silicate were taken by X‐ray fluorescence, and relative comparisons between different oxides are shown. Auger electron spectroscopy was used to study the in‐depth composition of the silicate deposition. Experiments show a high affinity of the silicate to the anodic oxide film. A thin nanometric chemisorbed (alumino)silicate layer is present on the surface after rinsing, while the physisorbed part of the layer is washed away. Copyright © 2009 John Wiley & Sons, Ltd.

Al 2 O 3 on metallic aluminium is a widely used material of high technological importance. For the local chemical characterisation of these substrates, field‐emission Auger electron spectroscopy (FE‐AES) bears potential thanks to its high lateral resolution. In this study, the O KLL and Al KLL Auger electron spectral lines are recorded with high energy resolution from pure aluminium, thin Al 2 O 3 and thick Al 2 O 3 layers on metallic aluminium. The behaviour of these aluminium oxide layers under electron beam irradiation is investigated. It is demonstrated that, thanks to the high energy resolution used, it is possible to discriminate between the metallic and oxidised aluminium on the basis of the Al 0 KL 2, 3 L 2, 3 and Al 3+ KL 2, 3 L 2, 3 Auger electron peaks recorded within one and the same spectrum. Oxygen electron‐stimulated desorption is observed for both aluminium oxides. The estimation of the effective cross‐section for the oxygen desorption shows that the thin oxide layer is less stable against this phenomenon than the thick oxide layer. It is shown that when an Al 2 O 3 layer is irradiated with an electron beam, surface charging occurs. These phenomena remain limited thanks to the presence of the underlying metallic aluminium substrate. Finally, it is shown that non‐homogeneities at the surface of the analysed oxides result in significant chemical shifts of the O KLL and Al KLL Auger electron transitions. Copyright © 2010 John Wiley & Sons, Ltd.

No abstract is provided for this article.

A metal has a typical grey "metallic" look. Different colours can appear when the metallic surface is covered with a thin transparent layer. This is of course the result of interference, and consequently the colour depends on the optical thickness of the layer. Experimental observations can be completely predicted by theoretical modelling. Using the Fresnel equations the colour can be calculated within excellent agreement of the experimental observations. Fresnel, of course, assumes perfectly flat surfaces. Roughness complicates matters: the optical path within the coating no longer depends on the local thickness of the coating only, but also on the angle of scattering at the underlying metal, both varying from point to point. In this presentation we describe how the roughness can be taken into account in predicting the colour. The scattered light was calculated using the "Modeled Integrated Scattering Tool", a computer program developed at the "National Institute of Standards and Technology" (USA). The non-uniformity of the coatings was taken into account by considering different coatings thicknesses. The resulting colour is calculated by taking the average of the obtained reflections. Finally the colours were measured with a spectrophotometer. It turned out that the modelled and the measured colours agree very well, confirming the validity of the used model.

A common approach to investigate chemical interactions at the polymer/metal oxide interface is by monitoring ultrathin polymer films onto a metal oxide substrate by a variety of surface analysis techniques. The deposition of this nanometer-thin overlayer is frequently carried out by reactive adsorption from dilute polymer solutions. However, the influence of the solvent on the metal oxide chemistry is seldom taken into account in interface studies. The overall amount of available adsorption sites on the metal oxide surface might decrease due to competing adsorption of the solvent and the polymer adsorbate. Therefore, in this work, the adsorption of a common organic solvent (methanol) onto a physical vapor-deposited aluminum oxide surface is monitored in situ by an integrated attenuated total reflectance Fourier transform infrared spectroscopy in the Kretschmann geometry and odd random phase multisine electrochemical impedance spectroscopy system. It is shown that methanol immediately physisorbs onto the aluminum oxide surface and replaces the initial adventitious carbon layer. This process is followed by methanol chemisorbing onto the oxide surface to form methoxide species at the liquid/solid interface. Additionally, chemisorption is validated ex situ by X-ray photoelectron spectroscopy.