Pieter Vermeir

Ink-jet printing of YBa2Cu3O7 superconducting coatings and patterns from aqueous solutions

The objective of this paper is the development of ink-jet processing as a new technique for chemical solution deposition of YBCO coatings and patterns. Our research is mainly focused on the investigation and determination of the rheological parameters towards the printability of water-based inks in order to produce continuous YBCO coatings or multi-filamentary patterns on SrTiO3 substrates. A 0.185 mol L−1YBCO ink with a viscosity of 4.77 mPa s and a surface tension of 67.9 mN m−1, resulting in a ratio Re/We1/2 of 7.37, is developed. Its printing behaviour is further verified using a camera with strobed illumination to quantify the droplet velocity and volume. After optimization of the deposition parameters, a 350 nm thick YBCO coating showing preferential c-axis orientation could be grown on SrTiO3. This layer exhibits a critical current of 0.67 MA cm−2 at 77 K in self-field. Finally, the shape and dimensions of printed YBCO tracks were determined using optical microscopy and non-contact profilometry, showing 200 nm thick and 200 μm wide tracks.

A water-based sol–gel technique for chemical solution deposition of (RE)Ba2Cu3O7−y (RE = Nd and Y) superconducting thin films

The achievement of low-cost deposition techniques for high critical current (RE)Ba2Cu3O7?y-coated conductors is one of the major objectives in achieving a widespread use of superconductivity in power applications. Chemical solution deposition techniques are appearing as a very promising methodology to achieve highly textured oxide thin films at a low cost, so an intense effort is being carried out to develop routes for all chemically coated conductor tapes. In this work recent achievements will be presented towards the goal of the development of an environmentally friendly, completely water-based sol?gel technique for the deposition of thin superconducting films on SrTiO3 single-crystal substrates using the dip coat technique. A comparison is made between aqueous sol?gel synthesis of two (RE)Ba2Cu3O7?y superconducting systems: YBa2Cu3O7?y and its homologue NdBa2Cu3O7?y. Our conclusions are that YBa2Cu3O7?y still remains the material of choice for coated conductor development using this sol?gel technique, with a Tc,onset of 91?K and Jc of 0.3?MA?cm?2.

Elucidation of the Mechanism in Fluorine-Free Prepared YBa2Cu3O7−δ Coatings

In this work, the reaction mechanism used in the preparation of fluorine-free superconducting YBa(2)Cu(3)O(7-delta) (YBCO) was investigated. To determine which precursor interactions are dominant, a comprehensive thermal analysis (thermogravimetric analysis-differential thermal analysis) study was performed. The results suggest that a three step reaction mechanism, with a predominant role for BaCO(3), is responsible for the conversion of the initial state to the superconducting phase. In the presence of CuO, the decarboxylation of BaCO(3) is kinetically favored with the formation of BaCuO(2) as a result. BaCuO(2) reacts with the remaining CuO to form a liquid which ultimately reacts with Y(2)O(3) in a last step to form YBCO. High temperature X-ray diffraction experiments confirm that these results are applicable for thin film synthesis prepared from an aqueous fluorine-free sol-gel precursor.

Comments on the wetting behavior of non-porous substrates for ceramic coated-conductor applications

This work gives an overview of the possibilities to improve the wetting behavior of precursors for coated conductors on non-porous substrates. Within this work, all coatings were performed on a metallic Ni–W/La2Zr2O7/CeO2 substrate using water-based Y, Ba, Cu containing precursors. The results described in this paper can be used for different technologies of chemical solution deposition, as there are ink jet printing, dip coating, spin coating etc. Starting from the forces involved during wetting, a separation between solid and liquid modifications was made. This study revealed that if a good cleaning procedure of the substrate, whether or not combined with a targeted modification of the precursor is applied, water-based solutions can be used without restriction towards their wetting behaviour leading to a sustainable technology within the coating industry. Within this work, special attention is given to (1) fast determination of the substrate cleaning procedure quality by the creation of wetting envelopes and (2) the use of a screening design of experiment to study the effects of intrinsic solution factors, such as precursor formulation, influencing the coating behavior. All modification discussed are expandable to all kinds of precursors and substrates.

Characterisation of the sol–gel process in the superconducting NdBa2Cu3O7−y system

The objective of this paper is to obtain a better insight into the sol–gel mechanism of water-based precursors for the development of thin NdBa2Cu3O7−y (NBCO) superconducting films. The influence of metal complexation behaviour on the formation of transparent and homogenous gels after the combination of different metal salts and ligands has been studied for several metal salts (Cu2+, Nd3+ and Ba2+). Two inorganic aqueous sol–gel precursors have been studied: a metal nitrate–citric acid-based and a metal acetate–triethanolamine-based solution. The characteristics of the precursor solution are based on the determination of the stability constants by the computer program Superquad. The prediction of the complex stability in this solution was related to the complexation of the three metal ions (Cu2+, Nd3+ and Ba2+) with a certain ligand. IR-spectroscopy was used for the determination of the gel. This resulted in a better understanding of the composition of the solution and could be used for preparation of more stable sol–gel precursors for the synthesis of homogeneous end products. These sol–gel systems were used for the deposition of highly textured superconducting thin films on SrTiO3 substrates by dip-coating. Using detailed thermal analysis, it is shown that the morphology of the films can be optimised by adjusting the parameters during thermal treatment, resulting in dense and highly textured thin films. Special attention is given to the microstructure of the thin film because of its relevance to the superconducting transport properties of the coated conductor system.

Influence of aqueous precursor chemistry on the growth process of epitaxial SrTiO3 buffer layers

In this Article, epitaxial thin films of SrTiO3 were prepared on single crystalline (100) LaAlO3 by an aqueous chemical solution deposition method. By using different chelating agents to stabilize the metal ions in water, the impact of the precursor chemistry on the microstructural and crystalline properties of the films was studied. Thorough investigation of the precursor by means of infrared and Raman spectroscopy as well as thermogravimetric analysis revealed that stable precursors can be obtained in which strontium ions can be either free in the solution or stabilized by one of the chelating agents. This stabilization of strontium ions appeared to be essential in order to obtain single phase SrTiO3 films. Precursors in which Sr(2+) remained as free ions showed SrO microcrystal segregation. Precursors in which both metal ions were stabilized gave rise to strongly textured, dense, and terraced SrTiO3 films, allowing subsequent deposition of YBa2Cu3O7-δ with superior superconducting performances.

Effect of Ion Exchange Resin Functionality on Catalytic Activity and Leaching of Palladium Nanoparticles in Suzuki Cross-Coupling Reactions

Macroporous ion exchange resin supported palladium nanoparticle (Pd‐NP) catalysts are prepared by an intermatrix synthesis. For the first time, the effect of resin functionality (weak acid, strong acid, strong base) on the NP size, their catalytic activity, and leaching is investigated in the Suzuki cross‐coupling of iodobenzene and phenylboronic acid. Whereas the smallest NPs (1.34 nm) are found in the thiol Ambersep GT74 resin, the sulfonic acid Lewatit K2629 and quaternary amine Lewatit MP500 OH resins resulted in NPs of a similar size (2.42 and 2.59 nm, respectively). Despite their smaller size, the NPs on Ambersep GT74 exhibited the lowest conversion (21.6 %), which is attributed to a too strong coordination of the NPs by the thiol groups. The conversions obtained by using Lewatit K2629 (76.8 %) and Lewatit MP500 OH (94.2 %) were considerably higher, the excellent performance of the latter catalyst being ascribed to the promoting effect of the hydroxyl groups on the transmetallation and reductive elimination steps in Suzuki cross‐coupling. No Pd leaching was observed when using Ambersep GT74 as the support, compared with Pd leaching amounting to 1.1 % and 4.8 % when using Lewatit MP500 OH and Lewatit K2629, respectively. Such low values indicate that ion exchange resins are ideal supports to stabilize the NPs. Particularly, the combination of high conversion and limited leaching on Lewatit MP500 OH opens up new perspectives for catalyzing Suzuki cross‐coupling with a heterogeneous catalyst.

Impact of Crop Husbandry Practices and Environmental Conditions on Wheat Composition and Quality: A Review

The increasing interest in the production of bread wheat ( Triticum aestivum L.) with specific quality traits requires a shift from the current breeding goal, being yield, to improved compositional and, consequently, functional traits. Since wheat is a key food crop, this must be attained while maintaining or even further increasing yield. Furthermore, as compositional requirements for specific applications are not well-defined, both protein and gluten content as well as the enzymatic activity remain most important. Given that these traits are majorly impacted by both genotype and environment, it is very complex to predict and ultimately control them. Different strategies, such as applying optimized agronomic practices, can temper these uncontrollable determinants which are equally important to steer wheat quality. As current research on their contribution to specific traits is highly fragmented, this report provides a comprehensive review of the influence of crop husbandry and environmental conditions on wheat yield and composition.

Structural and catalytic properties of Au/MgO-type catalysts prepared in aqueous or methanol phase: application in the CO oxidation reaction

AbstractAu/MgO and Au/Mg(OH)2-type catalysts for CO oxidation reaction were prepared by using two different synthesis methods in presence of either an aqueous or methanol phase. The influence of the porous and morphological properties of the starting magnesium oxide supports was analyzed and correlated with the catalytic performances of the final gold-supported catalysts. It was found that the deposition of gold in the presence of methanol as a solvent avoids the total rehydration of the MgO support and maintains the textural and morphological properties of the starting oxides. The support synthesized by a surfactant-assisted hydrothermal route, having a combined meso-macroporous structure (i.e., MgO-P) showed a positive influence on the CO oxidation reaction as it favored the dispersion of gold and the surface-to-gas phase interaction during the catalytic process.

Functional Composition of Tree Communities Changed Topsoil Properties in an Old Experimental Tropical Plantation

Forest biogeochemistry is strongly determined by the interaction between the tree community and the topsoil. Functional strategies of tree species are coupled to specific chemical leaf traits, and thus also to litter composition, which affects mineral soil characteristics. The limited understanding on this interaction is mainly based on shorter-term common garden experiments in temperate forest, and needs to be extended to other forest types and climates if we want to understand the universality of this linkage. In particular, for highly diverse tropical forests, our understanding of this interaction remains limited. Using an old experimental plantation within the central Congo basin, we examined the relationship between leaf and litter chemical composition and topsoil properties. Canopy, litter and topsoil characteristics were measured and we determined how the community-level leaf and litter chemical composition altered the topsoil carbon, major plant nutrients and exchangeable cation concentration, acidity and pH over the last eight decades. We found that functional composition strongly affected topsoil pH. In turn, topsoil pH strongly determined the soil total carbon and available phosphorus, total nitrogen and exchangeable potassium. Our results indicate that, as observed in temperate common garden experiments, trees alter chemical topsoil properties primarily through soil acidification, differently induced by functional composition of the tree community. The strong link between this community-level composition and topsoil characteristics, on a highly representative soil type for the tropics, improves our understanding of tropical forests biogeochemistry.