Development of high power magnetron sputtering targets prepared by flame spraying

To achieve a cost effective process for the deposition of YBCO thin films using magnetron sputtering, it is imperative to reach the highest deposition rate possible. This study describes the development of high power YBCO targets by flame spraying. The YBCO was doped with Ag to increase the electrical and thermal conductivity. The spray drying technique was used for the preparation of dedicated powder material, containing the appropriate amounts of Y, Ba, Cu and Ag. Thermal analysis, SEM and XRD were used to analyse phase composition and thermal and electrical characteristics were compared for different amounts of Ag added. The optimal particle size and distribution for flame spraying were obtained using spray drying by adjusting the spray parameters, the concentration and composition of the sprayed solutions and slurries and the spraying parameters. Test samples were made by flame spraying spray dried CuO and YBCO powder with a particle size of 40-60 micron onto a stainless steel substrate

Kinetics of consecutive reactions in the solid state : thermal decomposition of oxalates

The thermal and kinetic aspects of solid state decomposition reactions can be complex and posses a large number of parameters to investigate. The determination of the activation energies for the several intermediates in the thermal decomposition is particularly sensitive to the overlap in thermal decomposition traces. To overcome this problem we have undertaken the detailed kinetic analysis of the well-known thermal decomposition of calcium and strontium oxalates and mixtures of both. Indeed, their small difference in decomposition temperatures, from oxalate to carbonate, allowed us to simulate overlapping TGA signals and to use these data to test the validity of the experimental conditions and mathematical methods used to derive calculated kinetic values. Key-words: thermal analysis, kinetics, solid state reactions, mathematical processing of data. 1

Thermal behaviour of arsenic oxides (As2O5 and As2O3) and the influence of reducing agents (glucose and activated carbon)

In this paper the thermal behaviour of pure arsenic oxides (As2O5.aq and As2O3) and the influence of the presence of reducing agents (glucose or activated carbon) on the thermal behaviour of the arsenic oxides are studied through thermogravimetric (TG) analysis. The TG experiments with pure As2O5.aq reveal that the reduction reaction As2O5 --> AS(2)O(3) + O-2 does not take place at temperatures lower than 500degreesC. At higher temperatures decomposition is observed. Pure As2O3, however, is already released at temperatures as low as 200degreesC. This release is driven by temperature dependent vapour pressures. Comparing these results with earlier observations concerning the thermal behaviour of chromated copper arsenate (CCA) treated wood, suggests that wood, char and pyrolysis vapours form a reducing environment that influences the thermal behaviour of arsenic oxides. Therefore, the influence of the presence of reducing agents on the thermal behaviour of As2O5.aq is studied. First, TG experiments are carried out with mixtures of As2O5 and glucose. The TG and DTG curves of the Mixture are not a simple superposition of the curves of the two pure constituents. The interaction between As2O5.aq and glucose results in a faster decomposition of arsenic pentoxide. This effect is more pronounced if the purge gas nitrogen is mixed with oxygen. Second, TG experiments are performed with mixtures of As2O5 and activated carbon. The presence of activated carbon also promotes the volatilisation of arsenic for temperatures higher than 300 degreesC, probably through its reducing action. Extrapolation of the thermal behaviour of these model compounds to the real situation of pyrolysis of CCA treated wood confirms the statement that the reduction of pentavalent arsenic to trivalent arsenic is favoured by the reducing environment, created by the presence of wood, char and pyrolysis vapours.status: publishe

Anisotropic behaviour in the magnetic field dependence of the low temperature electrical resistance of calcium-doped lanthanum manganate thin films grown by RF magnetron sputtering

We report about the magnetoresistive properties of calcium-doped lanthanum manganate thin films grown by RF magnetron sputtering on single crystalline LaAiO(3) and MgO substrates. Two orientations of the magnetic field with respect to the electrical current have been studied: (i) magnetic field in the plane of the film and parallel to the electrical current, and (ii) magnetic field perpendicular to the plane of the film. The film grown on LaAlO3 is characterised by an unusual magneto resistive behaviour when the magnetic field is applied perpendicular to the film plane: the appearance of two bumps in the field dependence of the resistance is shown to be related to the occurrence of anisotropic magneto resistive effects in manganate films. (C) 2004 Elsevier B.V. All rights reserved