This paper describes the synthesis of ZrW 2 O 8 by the use of an aqueous citrate-gel method in order to prepare a fine, pure and homogeneous oxide mixture suitable for ceramic processing. The thermal expansion coefficient thus obtained for α-ZrW 2 O 8 is −10.6 × 10 −6 °C −1 (50–125 °C) whereas for the β-ZrW 2 O 8 a value of −3.2 × 10 −6 °C −1 (200–300 °C) is obtained. The advantages of the use of a sol–gel method is expressed in the very homogeneous end-products. The paper describes crystallographic data, morphological structure and the thermal expansion properties of the ZrW 2 O 8 material. Moreover, photoluminescence and photochromic properties specific to the precursor gel are described and analyzed. These effects support our views that the precursors show homogeneity up to nanometer level.

Today, the deposition of coated conductors on a variety of substrates is often performed using a vacuum or low pressure technique. However, obtaining uninterrupted deposition at high speed, increasing flexibility in composition and attaining independence of geometric constraints of the substrates are areas in which vacuum techniques will need sustained development in order to answer industrial demands. The development of the next generation of deposition methods, based on deposition under atmospheric environment and from aqueous precursor solutions is a real challenge. This work describes the deposition of thin NdBa 2 Cu 3 O 7-y layers on SrTiO 3 single crystals based on a new sol-gel dip coating process using aqueous precursor solutions. Two inorganic aqueous sol-gel routes were investigated, a metal nitrate–citric acid based and a metal acetate–triethanol amine based solution. Using detailed thermal analysis, it is shown that adjusting the different parameters during thermal treatment can be used to control the morphology of the films. Also 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.

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.

In general, the sol-gel method is a very attractive route for ceramic synthesis because it permits direct fabrication of multi-component ceramics in different configurations without powder intermediates. This diversity, in which materials can be formed, has made the sol-gel method an important synthesis route in several domains of research. For (RE) Ba2Cu3O7-y superconducting thin film development, chemical solution deposition (CSD) techniques starting from sol-gel precursors can offer a cost-effective and more flexible large-scale alternative synthesis route in comparison to the common used vacuum techniques. This work describes the deposition of thin NdBa2Cu3O7-y layers on SrTiO3 single crystals based on a new sol-gel dip coating process using aqueous precursor solutions. Two inorganic aqueous sol-gel routes were investigated, a metal nitrate - citric acid based and a metal acetate - triethanol amine based solution.

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 T-c,T-onset of 91 K and J(c) of 0.3 MA cm(-2).

The formation of three sols by fluorine-free aqueous and non-aqueous processes were analyzed and modified to vary the chemical properties of the sols (inks) to suit a variety of deposition processes such as dip-coating and ink-jet coating/printing. Ink-jet printing requires high wetting angles; choosing the right complexing agents to modify the ink allows the formation of droplets with high wetting angles on the surface. Dip-coating and ink-jet coating require low wetting angles; additives added to the sols reduce wetting angles to 10∘ and allow complete coverage of the substrate surface. The deposition theories and requirements are briefly discussed, as are some initial tests with the printing and converting of the developed superconducting inks.

Since the 1960s, Nb-Ti, exhibiting a superconducting transition temperature Tc of 9K, and Nb3Sn, with a Tc of 18K have been the materials of choice for superconducting applications. The prospects for the future changed dramatically with the discovery of ceramic high temperature superconductors exhibiting Tc values well above the boiling temperature Of liquid nitrogen (77K). These materials are now widely considered for large power applications, electronics and magnets including a.o. power transmission cables, motors, generators, fault current limiters, transformers, NMR and MRI. The fabrication of useful conductors out of these layered cuprates encountered some problems in areas such as chemical and structural purity, stability, oxygen stoichiometry and weak links. However, a first generation of silver sheathed composites based on Bi2xPbxSr2Ca2Cu3O10 has already been commercialised. It is now a widespread view that superconducting wires with high performance under strong magnetic fields and at elevated temperatures above liquid nitrogen, will need to be realised using the (RE)Ba2Cu3Oy materials. Because of the weak link nature of these materials, a second generation of biaxially aligned coated conductors was developed As a consequence, many deposition techniques have been studied to grow thin films of the superconducting (RE)Ba2Cu3Oy and adequate buffer layers on suitably prepared textured substrates. In this paper, the critical parameters in the deposition of thin films using vacuum and non-vacuum techniques will be reviewed. Finally, this review will address the measurement of the obtained properties of these coated conductors. The most important practical characteristic of a superconductor is its critical current density. Spectroscopic methods such as I.R. play an important role in the development of adequate precursors for chemical solution deposition of thin films. Finally, microstructural analysis using XRD, SEM and TEM is important to reveal the relation of these features on the transport properties of the films.

Development of computer controlled printing techniques for CeO2, NdBa2Cu3O7-δ (NBCO) and YBa2Cu3O7-δ (YBCO) coated conductors is discussed in detail and presented. This method of continuous deposition of YBCO material allows non-vacuum formation of complex multi-layer superconducting patterns on silver substrates. Sol-ink processes were used to print single droplets of CeO2, NBCO and YBCO on polycrystalline silver substrates. The formation and the stability of the sol-ink with respect to pH and concentration has been studied and discussed herein. Printing and substrate parameters that alter solid-liquid interface properties were also investigated. In order to control the flow properties of the sol media dynamic viscosities were determined. Characterisation by X-Ray Diffraction, Differential Thermal Analysis,Thermal Gravitometry and, Scanning Electron Microscopy was used to examine the sol-ink samples, whilst AC susceptibility was used to assess the superconductivity of the printed samples.

The aim of this study is to process Ag-doped Nd1Ba2CU3Oy (NBCO) powders using spray drying and consequent calcinations and sintering. The influence of sintering conditions on the microstructure and superconductivity is investigated using thermal analysis (TG-DTA), X-ray diffractometry (XRD), Scanning electron microscopy (SEM), susceptibility and resistivity measurements. During sintering, a low oxygen partial pressure (1% O-2/Ar) was necessary to avoid Nd for Ba substitution. Sintering was performed at temperatures greater than or equal to990 degreesC. After annealing in pure oxygen, superconducting material exhibiting Tc = 95 K was obtained. The addition of Ag whiskers led to improved grain growth and decreased intergrain contact in the superconducting phase. Negligible structural and morphological interaction between NBCO and Ag was,observed. (C) 2003 Elsevier Ltd. All rights reserved.

The kinetics of the hydrogen–deuterium (H–D) exchange reaction of isobutane over deuterated acid FAU- and MFI-type zeolites were studied using a batch recirculation reactor. On MFI-type zeolites, a fast exchange reaction takes place in the temperature range 140–200°C, while on FAU-type zeolites, higher temperatures (200–260°C) are required. On fully deuterated zeolites, the initial product is i-C4D9H. The degree of deuteration of the methyl hydrogen atoms is equal to that of the zeolite, while the methine hydrogen atom cannot be exchanged. On MFI-type zeolites, the exchange rate increases as the aluminium content [i.e., the Al/(Si+Al) ratio] increases, while on FAU a maximum exchange rate is found for a sample with Si:Al=5.5 [Al/(Si+Al)=0.15]. A good correlation was found between the amount of non-framework aluminium and the H–D exchange rate. The reaction is thought to proceed via carbenium ions that are formed during the induction period by hydride abstraction on Lewis acid non-framework aluminium species. Hydride abstraction takes place on the methine hydrogen atom, to form stabilised t-isobutyl carbenium ions that undergo a fast H–D exchange reaction. The carbenium ions leave the surface by hydride abstraction from a new isobutane molecule, thus not allowing for deuterium exchange of the methine hydrogen atom. The apparent activation energy for the H–D exchange reaction is 23–32kJmol−1. The kinetic isotope effect is ±1.4.

The kinetics of the consecutive H–D exchange reactions between methane and deuterated acid FAU- and MFI-type zeolites was studied with on-line mass spectrometric product analysis, in the temperature range 450 to 550°C. On both zeolite types, the rate constant of H–D exchange increases with decreasing Al content. At the same Al content, the reaction rate constant of MFI is ca. three times larger than that of FAU, showing that chemical composition and structural effects are important in determining the rate of exchange. The apparent activation energy is in the range 122–150 kJ/mol, independent of the Al content and structure type. A kinetic isotope effect of approximately 1.7 was found, which is in disagreement with the earlier proposed concerted reaction mechanism (G. J. Kramer, R. A. van Santen, C. A. Emeis, and A. K. Nowak,Nature363, 529, 1993).

The mobility of Cr n+ in inorganic oxides has been investigated by combined diffuse reflectance (DR)–EPR spectroscopies as a function of the Cr oxidation state, the type of inorganic oxide (silica, alumina and mordenite) and the environmental conditions (hydrated and dehydrated state). Cr n+ ions are mobile under hydrated and dehydrated conditions and Cr n+ preferentially migrates from silica to alumina and, to a lesser extent, to mordenite, although only a small amount of migration of Cr n+ is observed from alumina to mordenite and vice versa. The observed preference sequences are discussed in relation to the properties of the inorganic oxides.

UNLABELLED:During the ejection phase of the cardiac cycle, left ventricular muscle fibres shorten while generating force. It was hypothesized that fibres are oriented in the wall such that the amount of shortening is the same for all fibres. We evaluated this hypothesis for the equatorial region of the left ventricle. In a finite element model of left ventricular wall mechanics fibre orientation was quantified by a helix angle which varied linearly from the inner to the outer wall. Fibre length was characterized by sarcomere length, set at 1.95 microns everywhere in the passive state of 0 transmural pressure. For a cavity pressure of 15 kPa, considered representative for ejection, inhomogeneity in mechanical loading was expressed by the variance of the sarcomere length. The variance was minimized by adapting the transmural course of fibre angle. First, only the slope was optimized and in a second optimization this was done for both slope and intercept. Optimal helix fibre angles were 69.6 degrees endocardially, 0 degree at the middle of the wall and -69.6 degrees epicardially for the first optimization and 78.2 degrees, 20.7 degrees and, -36.7 degrees respectively for the second. Sarcomere length changed from 1.95 to 1.975 +/- 0.012 and 1.981 +/- 0.004 microns (mean +/- SD) respectively.CONCLUSION:After optimization calculated helix fibre angles were in the physiological range. Describing the transmural course of fibre angle with slope and intercept significantly improved homogeneity in mechanical load.