Publications

Hydrogen chloride is found in important hydrogen gas streams of the chemical industry and needs to be removed for safety and environmental concerns. Here, a systematic study is presented on HCl removal from hydrogen gas by adsorption on zeolites, including cation free and high cation loaded materials, as well as ion-exchanged zeolites (with alkali, alkaline earth and transition metal ions). The HCl removal performance was studied by a fixed-bed breakthrough method under high gas velocities (>0.3 m/s), at high pressures (30 bar) and at room temperature, and with low HCl concentrations (<200 ppm). The zeolite screening indicated that the 13X zeolite outperforms the other tested materials. The ion-exchanged X zeolites were extensively characterized via SEM-EDX, XRD, ATR-FTIR, TGA and argon adsorption isotherms. The results revealed that the ion-exchange was successfully achieved with expected tendencies in XRD and ATR-FTIR spectra, and porosities. The breakthrough experiments demonstrated that the hydration of the zeolite prior HCl adsorption improves the hydrogen gas purification performance. The characterization after HCl adsorption supports the hypothesis that HCl is taken up by the material by forming salt molecules within the zeolite cavities by reaction with the cations and, which is, moreover, enhanced by the presence of pre-adsorbed water. The type of cation present in the zeolite framework structure notably affected the HCl removal adsorption capacity as well as uptake rate. Among the ion-exchanged zeolite samples, the Zn2+ form exhibited the highest adsorption capacity at saturation, attributed to the over-exchange of the zeolite cations. The investigation revealed important parameters such as cation radius, atomic mass and electronegativity, which played a noteworthy role in defining the HCl removal performance of ion-exchanged zeolites.

The diffusion and trapping of hydrogen in iron alloys is commonly studied using the Devanathan-Stachurski cell. In this cell, the hydrogen flux through a metal membrane is studied. At the exit side of the membrane, an oxide layer is commonly developed and stabilized as a consequence of the anodic polarization imposed. The process of hydrogen diffusion through the oxide layer and its consecutive oxidation is not fully understood yet. In this paper, we propose a modelling approach that provides additional insights in this process. In particular, we highlight the impact that the presence of the oxide layer can have on the overall hydrogen transport throughout the metal membrane. Moreover, we highlight the complexity of this mechanism and discuss the possible reactions taking place in and at this interface. As a conclusion a possible alternative process to explain the findings is proposed.

Thin-film silane coating (<1μm) has been introduced as a chromium free multi-metal surface pre-treatment for corrosion protection, adhesion promotion and surface passivation of metals such as aluminium, steel, zinc, magnesium and others. Bis-1,2-(triethoxysilyl)ethane (BTSE) has received much attention as it is, after hydrolysis, highly reactive towards (covalent) metal/film bonding and cross-link formation for the creation of barrier properties. Much of the past work on BTSE was performed on methanol-based laboratory solutions due to the low solubility of BTSE in water. For industrial applications these solutions are not considered suitable anymore because of the high process cost as well as ecological and health issues associated with methanol and the high monomer content of such solutions. For industrial practice water-based silane solutions are being considered. In the present work water-based BTSE solution is compared to a reference methanol-based solution. The silane solution is analysed using 29Si NMR spectroscopy, and the deposited silane films are morphologically characterised using infra-red spectroscopic ellipsometry and field-emission gun-scanning electron microscopy.

Supported nickel nanoparticles (NPs) are widely used as catalysts for fuel cells and electrosynthesis, as well as for biosensors and supercapacitors. These nanomaterials can be fabricated by multiple methods. However, electrodeposition offers several advantages since it permits the growth of the NPs directly on the support of interest and allows obtaining highly electroactive nanostructures [1]. In order to produce highly electroactive nanostructures, the electrochemical processes on the nanoscale need to be understood. In this context, Deep Eutectic Solvents (DESs) have generated great enthusiasm as a new generation of non-aqueous electrolytes. They offer plenty of advantages compared to traditional aqueous electrolytes or to highly expensive ionic liquids [2]. Moreover, by adding water to the DESs, the electrolyte behavior could be remarkably different. The ability of understanding the effect (and controlling the amount) of water in DES has been proven essential to tune the chemical nature of the electrodeposited Ni nanostructures, thereby obtaining highly electroactive NPs for a wide range of applications [3-4]. The electrodeposition of nickel nanostructures on glassy carbon was investigated in 1:2 choline chloride – urea (1:2 ChCl-U) DES containing different amounts of added water. By combining electrochemical techniques, with ex-situ FE-SEM, XPS, HAADF-STEM and EDX, the electrochemical processes occurring during nickel deposition and the effect of added water were better understood. At highly negative potentials, Ni growth is halted due to water splitting and the formation of a mixed layer of Ni/Ni(OH) 2(ads) [3]. Moreover, under certain conditions, the choline cations can also be (electro)chemically reduced at the electrode surface, blocking further 3D growth of the Ni NPs. Hence, a 2D crystalline Ni network can be formed in the inter-particle region, as depicted in the figure [5]. These novel nickel nanostructures can be of great interest for their electrocatalytic activity for different processes, such as the oxygen evolution reaction (OER). References: G-R. Li, H. Xu, X-F. Lu, J-X. Feng, Y-X. Tong, C-Y. Su. Nanoscale , 5 (2013) 4056-4069. E.L. Smith, A.P. Abbott, K.S. Ryder. Chemical Reviews , 114 (2014) 11060–11082. E.A. Mernissi Cherigui, K. Sentosun, P. Boockenooge, H. Vanrompay, S. Bals, H. Terryn, J. Ustarroz. The Journal of Physical Chemistry C , 121 (2017) 9337-9347. C. Du, B. Zhao, X-B. Chen, N. Birbilis, H. Yang. Scientific Reports , 6 (2016) 29225. E.A. Mernissi Cherigui, K. Sentosun, S. Bals, H. Terryn, J. Ustarroz. Manuscript in preparation (2017). Figure 1

Organic primer coatings loaded with environmentally harmful Cr(VI) corrosion inhibitive pigments still play an important role in corrosion protection of aluminium alloys for the aerospace industry. A potential “green” alternative coating system has recently been developed, loaded with lithium salt corrosion inhibitors. Under exposure to neutral salt spray, lithium salts leach from the organic coating into coating defects to induce the formation of a corrosion protective layer. In this work the composition and growth of this protective layer is investigated by time-of-flight secondary ion mass spectrometry (ToF-SIMS). ToF-SIMS imaging is successfully applied to monitor the lateral spread of leaching lithium salts in artificial 1-mm-wide scribes. The chemical composition of the protective layer is revealed by comparing the mass spectra of salt spray exposed scribe areas to the mass spectra of pseudoboehmite and aluminium-lithium layered double hydroxide reference samples. The insights obtained in this work have led to a thorough understanding of the formation mechanism of the protective layer and provide local chemical and structural information which can be linked to corrosion protection behavior.

No abstract is provided for this article.

No abstract is provided for this article.

Lithium leaching coatings have recently been developed as eco-friendly active corrosion protection technology for aerospace aluminium alloys (AAs) by the formation of a conversion layer at coating defects. While general conversion layer formation characteristics were studied and reported before, here we study the local layer formation process with sub-micron resolution at and around intermetallic particles (IMPs) in AA2024-T3. Top- and cross-sectional-view morphological electron micrograph observations along with open circuit potential (OCP) measurements are performed, mimicking coating defect conditions upon lithium carbonate leaching from the coating matrix. The results revealed five stages of the conversion process in which the alloy matrix and different IMPs evolve morphologically, compositionally, and electrochemically. Besides, we found a correlation between the OCP response of the AA2024-T3 system and the morphological and compositional evolutions of the alloy matrix and IMPs at different stages of exposure. Passive layer and alloy matrix dissolution leading to surface Cu-enrichment and S-phase dealloying occur at early stages of exposure. They precede the formation of a columnar layer on the alloy, followed by the establishment of a dense-like layer at the final stage. Dealloying of Al2CuMg can assist the conversion process by providing local supersaturation. Through complementary experiments in a sodium carbonate solution and besides X-ray diffraction analysis, we found out that lithium plays a critical role in stabilising the corrosion product throughout the conversion process.

No abstract is provided for this article.

A deformed near-surface region, also referred as ‘surface layer’, is always present on rolled aluminium alloy sheets. This paper studies in detail the evolution of the surface layer along the production line on a ‘recycled’ commercial alloy (AA5050). A microscopic investigation of a step-by-step formation of the surface layer has been carried out in the roll-bite. The effect of thermo-mechanical processing on the microscopic and optical characteristics of the surface layer has been studied. The distribution of the alloying elements within the surface layer has been investigated along the production line. The importance of the Total Reflectance (TR) method has been demonstrated for accurate estimation of the average thickness of the surface layer. Based on these results, a correlation has been drawn between the microscopic characteristics of the surface layer and the TR profile which in turn shows that the TR can be used in lieu of TEM for estimation of the surface layer thickness at different production stages.

Many Quaternary silicic volcanoes in the Main Ethiopian Rift pose a potential risk due to the poorly known eruptive histories of the volcanoes in combination with a high population density. In this study we provide new constraints on the Late Pleistocene-Holocene eruptive history of the Bora-Baricha-Tullu Moye (BBTM) volcanic complex located in the central portion of the Main Ethiopian Rift (MER). BBTM constitutes three main silicic edifices (i.e. Bora, Baricha and Tullu Moye) and numerous smaller vents (including Oda and Werdi). Tephra deposits from these vents are several centimetres to meters in thickness in currently densely populated regions and where geothermal development is taking place. We present new field observations in addition to physical, petrographic, geochemical and geochronological data. BBTM experienced at least 27 explosive eruptions, of varying magnitude, in the last ca. 100 ky. The two oldest tephra deposits in our compiled stratigraphy are associated with large-magnitude, and possibly caldera-forming eruptions. The youngest of these (Meki) occurred at 107.7 ± 8.8 (2σ) ka, which makes it the youngest caldera-forming eruption identified in the Central MER so far. During the post-caldera stage, BBTM underwent at least 25 eruptions sourced from the Baricha (9 eruptions), Bora (3), Oda (8), Werdi (3) and Tullu Moye (2) edifices. The return period of explosive activity in BBTM is thus at least one moderate-to-large explosive eruption every 4000 yr. Well-exposed units have estimated eruption magnitudes (M) that are 4 to 5, while smaller-scale eruptions reach up to 2.5 and are exclusively preserved near the Tullu Moye vent. The tephra was dispersed up to 20 km from the volcanic complex suggesting that more than one hundred thousand people could be exposed to tephra fall and pyroclastic density current hazards from future of similar-magnitude eruptions in this area.

Organofunctional silanes are applied as coupling agents between organic coatings and low carbon steel substrates to promote adhesion. Although the metal oxide-silane interface plays an important role in the performance of the entire overlying coating system, it remains challenging to obtain a clear understanding of the interfacial molecular bonding mechanism and its influence on adhesion. In this work, time-of-flight secondary ion mass spectrometry is used to study interfacial interactions between aminopropyl triethoxysilane (APS) and low carbon steel. APS is shown to bond to the steel substrate through silanol steel and amine-steel interactions, and coatings are cured at varying temperatures to evaluate the influence of curing on these different types of bonding interactions. Unambiguous evidence for hydrogen bond interactions between APS silanol groups and steel surface hydroxyl groups is provided for the first time in this work through deuteration of the steel substrate and allows to tackle long-lasting doubts about the most wide-spread bonding theory that has been postulated for silane adsorption on metals.

No abstract is provided for this article.