Herman Weyten

Preparation and characterization of high-Tc superconducting YBa2 Cu3 O7−x filaments

High-Tc superconducting filaments of the Y-Ba-Cu-O system were prepared using a low-cost suspension spinning method, where the solvent was removed by a phase inversion technique. The Y-Ba-Cu oxide precursor, containing polysulphone (PSF), was spun as a filament into a precipitating medium, removing the solvent by phase inversion and using water as a non-solvent. The “green product” filament was washed, dried and subjected to a heat treatment to remove the binding material and generate the oxide in, the appropriate superconducting phase. Stoichiometry, porosity and grain size were investigated by scanning electron microscopy, energy-dispersive X-ray analysis and electron probe micro analysis, while crystal structure was checked by X-ray diffraction analysis. Resistivity measurements as a function of temperature were performed by the four-point method and typicalTc values of 88 K were observed, whileJc in the range of 125 A cm−2 at 77 K and zero field.

Particle Formation Using Supercritical Carbon Dioxide

Many of the products that are sold by the process industry — as bulk products, intermediates, fine chemicals, biochemicals, and food additives — as well as by the pharmaceutical industry are solids. The particle size and size distribution of these solids is frequently not desired for subsequent chemical reaction or use of these materials [1]. The particle size of these solids, therefore, has to be reduced. Conventional techniques for particle size redistribution are either mechanical (crushing, grinding and milling) or equilibrium controlled (crystallisation from solution) [1,2].

Synthesis of YBa2Cu3O7−x superconducting thin films on LaAlO3 by means of PAMOCVD

Abstract High- T c superconducting thin films have been deposited in situ by means of a plasma assisted metal-organic chemical vapour deposition (PAMOCVD) process on LaAlO 3 . An EMCORE high-speed rotating disc reactor was used to deposit the films at a substrate temperature of 600°C to 800°C. The system is equipped with a (remote) 120 W microwave plasma generator. The oxidising plasma gas is N 2 O and/or O 2 while Ar was used as the inert carrier gas for the different metal-organics. The influence of different process parameters (such as the temperatures of the metal-organics, substrate temperature, and plasma gas composition) on the superconductive properties and on the morphology of the films was investigated. Surface morphology and composition were studied by SEM/EDX or EPMA, and AC susceptibility measurements were used to investigate the superconductive properties ( T c and J c ). X-ray diffraction measurements indicated that single-phase YBa 2 Cu 3 O 7− x films were epitaxially grown with the 〈00 l 〉 orientation perpendicular to the substrate surface. The critical temperature ( T c ) of the films is about 90 K and the critical current density ( J c ) is higher than 10 6 A/cm 2 at 77 K and zero field.

YBa2Cu3O7−x superconductive tapes and wires: a peritectic sintering procedure to improve the quality

YBa2Cu3O7−x tapes were made by a powder-in-binder technique, using polysulphone (PSF) as the organic polymer andN-methyl-2-pyrrolidone (NMP) as the solvent. The suspension is cast onto a glass substrate plate to form the tape (Doctor Blade method) and is consequently immersed into a non-solvent to remove the solvent by phase inversion. In this paper we describe the different steps in an improved “peritectic” thermal treatment that are necessary to make the green product into a superconductive tape. Three steps are important in this heat treatment. First the polysulphone binder has to be removed as much as possible without reacting with the YBa2Cu3O7−x material. Next the sample has to be sintered into a dense ceramic material. In order to improve the intergranular connections, the sample is partially melted at relative low temperature in vacuum. The sample is subsequently heated up in oxygen to the normal sinter temperature. At this high temperature the YBa2Cu3O7−x phase will be restored by a peritectic reaction of the Y2BaCuO5 with a liquid phase. The final step is a two step anneal to ensure the full oxidation of the superconductor.

Supercritical Fluid Chromathography (SFC)

Chromatography is a separation technique whereby the components of a sample are resolved from each other by allowing them to be distributed between a moving fluid phase (called mobile phase) and a non-moving surface (called stationary phase) in varying proportions. Some of the components have a great affinity for the stationary phase and, hence, migrate slowly with the mobile phase; other components, on the other hand, interact weakly with the stationary surface and, hence, migrate more rapidly with the mobile phase. This difference in migration rate between the different components of the sample produces their separation at the end of the stationary phase, the degree of separation depending on the difference in the rates of migration. After separation, the components can be identified qualitatively, determined quantitatively, and collected separately. Besides the chemical nature of the stationary phase, the solvent power of the mobile phase determines the distribution behaviour of the components. [1,2]