The kinetic parameters, namely the triplet activation energy EA, model function f(α) or g(α) and pre-exponential factor A of the oxidation of Constantan tapes in 1atm of oxygen have been determined from both isothermal and non-isothermal thermogravimetry. For isothermal experiments, with temperatures ranging from 650°C to 900°C, the results from direct conversion of the weight increase as a function of the time and curve fitting, are compared with the isoconversion method. For the non-isothermal experiments, with heating rates from 1°C/min to 20°C/min, comparison is made between the Friedman differential method and the integral methods of Kissinger, Ozawa and Li and Tang. All methods give apparent activation energies with relative standard deviations as low as 3%. The results converge to the identification of three stages in the oxidation behaviour. A parabolic law for reaction extents α below 15% with EA=246±7kJmol−1, lnA=14.3, is followed by two linear stages with EA=244±4kJmol−1 and lnA=15.3 for 0.18<α<0.35 and EA=228±15kJmol−1, lnA≈13 for α>45%, respectively.

We report on the reaction kinetics for the Cao,80Cu01.~~ phase prepared by the sol-gel method using acrylamide for gelification. The phase was prepared 95% pure after a 2 hour treatment at 800°C. Comparative stability under vacuum and oxygen has been determined. The kinetics parameters for the decomposition have been established : the activation energy is E,= 626 kJ/mol and the pseudo reaction order n = 0.5.

In the framework of preparing metallic substrates for high temperature superconductors of the second generation, the Ce–Ni–Cu system in Ce-poor field has been studied by means of DTA/TG, X-ray diffraction, SEM with EDX attachment and optical microscope. For the solid state equilibrium, the existence of a continuous solid solution Ce(Ni1−xCux)5 has been confirmed and it was found that this solid solution extends in poor Ce compositions. No ternary phase could be evidenced in the investigated field. CeCu6 was found to dissolve up to 5at.% Ni. The cerium solubility in the (Ni,Cu) solid solution is less than 0.5at.%. At high temperatures, for the equilibrium implying a liquid phase, a ternary eutectic reaction L↔Ce(Ni,Cu)6+Ce(Ni,Cu)5+(Ni,Cu) occurs at T=871°C for Ce0.10Ni0.07Cu0.83, i.e for a Ce composition 1at.% higher than in the binary systems. Finally, the polythermal section of the system has been estimated and the isoplethic sections with the 16.7at.% Ce, 14.3at.% Ce and 9at.% Ce are proposed.

Copper rich Cu-Ni alloys have been textured with the RABiTS method in order to get non-magnetic and cost efficient substrates for coated conductor wires. The study is focused on two industrial compositions: Cu55Ni45 (Constantan) and Cu70Ni30. Studies on surface roughness have been done. The effects of annealing conditions (temperature and atmosphere) on the grain boundaries deepness were analyzed. Electrolytic polishing was also applied to improve the surface quality. RX pole figures and micro hardness measurements have been achieved on samples annealed up to 950°C. Attention has been paid to the rolling texture and to the annealing processes. The rolling texture has been found to be mainly copper-type (C, S and B contributions). Beginning of recrystallization occurred between 400°C and 600°C and stabilized between 900°C to 950°C, depending on the nickel content of the alloy. Finally both samples, rolled and annealed under the appropriate conditions, have been characterized. Pole figure measurements gave the global in plane and out of plane disorientations of our samples which are in-plane 7.4° and out-plane (RD) 4.3° for both samples. EBSD maps have shown the details of the distribution and have allowed us to quantify the ratio between cubic {100}<001> and twined {122}<21-2> orientations.

An isothermal kinetics study of the transformation of Tl-2212 into Tl-2223 has been carried out at four different temperatures. The Tl-2223 and Tl-2212 weight fraction have been deduced from Rietveld analysis of XRD patterns and the transformed fraction α has been calculated for each sample. The results indicate that the transformation is limited by diffusion and particularly by the thickening of large plates after lateral impingement.

We have studied the thermal treatments necessary to texture Cu-Ni alloys in view of applications as substrate for the YBCO coated conductors. Several alloy compositions chosen in order to avoid magnetism of the tapes have been elaborated by the rolling (RABiTS) method. Analyzes of the texture as a function of annealing temperature have been done by X-ray and neutron diffractions, pole figures by EBSD and X-rays. The results show that the annealing temperature is dependant of the alloy composition and must be determined precisely for each composition. Good biaxial textures have been obtained on these cheap alloys.

A European consortium has progressed towards elementary and assembled conductors viable for AC applications in the project ACropolis. The main goal was to achieve low AC losses and high critical current densities in tapes developed for AC coils, transformers and cables. In order to verify the performance of tapes an extensive characterization programme was carried out. The dependence of critical current and AC losses on the parameters of the tape manufacturing process were scrutinized. Furthermore, SEM-EDX and DTA/TG analyses were performed to study the material microstructure, and the diffusion coefficient of oxygen through different matrix metals was measured. The homogeneity of the tapes was verified with magnetic knife and Hall sensor experiments. Transport current measurements were performed at different mechanical stress conditions and also the distribution of critical current along long tapes was determined with a quasi-continuous four-point measurement. The results confirmed that the low AC loss conductors can be produced on an industrial scale and they are competitive in power engineering applications.

A European consortium has progressed towards AC coil, transformer and cable applications made of low AC loss Bi-2223 conductors. Internally assembled ring-bundle-barrier conductors were used in AC coils and an externally assembled conductor was realized for transformer and reactor windings. For the design and optimization of HTS AC coils, a numerical tool for the prediction of AC losses in coils and coil sets had been developed. The demonstrations with air-core coils and iron-core reactors showed that the numerical tool can already be confidently used in the design and optimization of HTS AC coils at nominal operation conditions. A series of three power cable prototypes was manufactured to estimate the influence of optimized low AC loss tapes on the total losses of a cable. In order to estimate the impact of the twist pitch on the losses we also manufactured cables with short and long twist pitches. The advantages and drawbacks of low AC loss tapes in power applications are discussed on the grounds of the test results.

Superconducting Tl-1223 and Tl-2223 films have been prepared in a two steps process : deposition of Ba:Ca:Cu = 2:2:3 precursor by spray pyrolysis and ex-situ thallination. Pure textured Tl-1223 films with good superconducting properties (T-c = 113K and J(c) = 0.7 MA/cm(2) at 77K, 0T) have been obtained. Almost pure Tl-2223 films have been obtained when precursor films have been thallinated with fluorinated sources.

TlBa/sub 2/Ca/sub 2/Cu/sub 3/O/sub 9/ superconducting films, 0.5 to 1 /spl mu/m in thickness, have been prepared in a two step process. Using a nitrate solution, a precursor layer with composition Ba/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ is first sprayed on a LaAlO/sub 3/ heated substrate and then thallinated, following a procedure established for bulk samples. The critical temperature of the films ranges from 108 to 113 K, and the critical current density of the best samples reaches 0.7 MA/cm/sup 2/. The reaction kinetics for the formation of the Tl-1223 phase between 880 /spl deg/C and 910 /spl deg/C has been studied for a better control of the grain growth and texture. The effect of fluorine addition on both the microstructure and superconducting properties have been also analyzed.

It has been shown recently that the formation of Tl2Ba2Ca2Cu3O2 is conditioned by an equilibrium plane with the Tl-rich limit of the (Ca,Tl)(1-x)CuO2 solid solution as one of the apices. The parent phase for the latter solid solution is the binary compound Ca0.80CuO1.93. We report here on the phase relations in the CaO-CuO and the CaO-CuO-TlO1.5 systems. The emphasis is also put on the thermodynamic stability and the crystallographic properties of Ca0.80CuO1.93 (space group P2/c, a = 10.9456(4) Angstrom, b = 6,3192(2) Angstrom, c = 16.8408 Angstrom and beta = 104,952(2)degrees). The kinetics for phase formation and decomposition have been studied. In particular. we show that the decomposition reaction into Ca2CuO3 and CuO which occurs at 870 degreesC in p(O-2) = 1 bar and at 720 degreesC in vacuum, is rate limited by a two-dimensional process consistent with structural considerations and has an activation energy of 656 U/mol, (C) 2002 Elsevier Science B.V. All rights reserved.

We report here on promising Tl- and (Hg,Re)-1223 films prepared using in part ultrasonic spray pyrolysis. Tl- and Hg-free precursors are first deposited by the aforementioned technique from a nitrate solution on either MgO or LaAlO3 substrates heated at 800 °C. The second step consists in a thallination or a mercuration performed in a closed system. The resulting films, 0.35–2 μm in thickness, exhibit a good c-axis orientation with Δω<1° as well as an in-plane texture. Both Tl- and (Hg,Re)-1223 films are superconducting with Tc=110 K and 134 K, respectively. Jc values deduced either from a screening method (7.5×105 Acm−2 at 77 K) or from magnetisation measurements (1.6×106 Acm−2 at 77 K) are strong indications of promising transport properties.

Three intergrowth phases between the high-Tc superconducting cuprates TlBa2Ca2Cu3Oy (Tl-1223) and Tl2Ba2Ca2Cu3Oy (Tl-2223) have been detected and identified in a non-equilibrium sample with composition Tl1.05Ba2Ca2Cu3Oy. Complete structure models including space group, cell parameters and atom coordinates are derived for quantitative analysis. X-Ray diffraction, AC susceptibility and scanning electron microscopy experiments show that these intermediate phases have a long range order. The results are discussed in the light of the formation path for Tl-1223 whose final step is the transformation from Tl-2223 to Tl-1223.

The complex ternary system Ba-Cu- O has been re-visited in 0.1 MPa oxygen pressure. It is established that for such pressure, the BaO2=BaO+12O2 reaction has an important role for reaching the equilibrium state. The pathway for the phase formation is then described in ternary sections BaO2-BaO-CuO. We have specified the temperatures and the forming reactions of the 3 compounds in the system: Ba2CuO3.04 decomposes by peritectic-like reaction at 1033°C and shows a structural transition from orthorhombic to tetragonal for at 825°C, BaCuO2 is a congruent melting compound at 1035°C and Ba2Cu3O5.5 undergoes a peritectoïdic decomposition into BaCuO2 and CuO at 893°C.

TlBa2Ca2Cu3O9 (Tl-1223) superconducting thick films with Jc as high as 0.8 MA/cm2 have been recently prepared in a two step process which involves (i) the deposition of the “Ba2Ca2Cu3O7” precursor on heated LaAlO3 substrates by spray pyrolysis and (ii) an ex-situ thallination treatment, following a procedure already applied for bulk samples. The kinetics for the formation of the superconducting phase has been studied to determine the optimum processing temperature and time for better control of the grain growth and the superconducting properties. The data analysis, based on a diffusion model, leads to an estimated value for the activation energy Ea of 161 kJ/mol. The effect of fluorine addition on the film morphology and microstructure is also studied. It is found that both c-axis orientation (Δω = 0.34°) and in-plane texture (Δϕ =0.43°) are significantly improved with respect to F-free films.

The reaction pathway for the formation of Tl2Ba2Ca2Cu3Oz (Tl-2223), a promising compound for applications in passive microwave devices, has been investigated by in situ neutron powder diffraction. The experiments were carried out in an initially evacuated closed system on two samples with compositions Tl1.7Ba2Ca2Cu3Oz and Tl2.3Ba2Ca2Cu3Oz. We find that, under the conditions specified above, the formation path implies Tl2BaO4, Tl6Ba4O13 and Tl-2212 according to the sequence: precursors/oxides → Tl2BaO4→ Tl6Ba4O13 → Tl-2212 → Tl-2223. The difference with respect to the sequence observed when the experiments are carried out in an open atmosphere (precursors/oxides → Tl-2201→ Tl-2212 → Tl-2223) is explained by the low temperature reaction between the TlOx vapour which becomes appreciable at 700 K in closed system and the free BaO resulting from the decomposition of BaCuO2. The conversion from Tl-2212 to Tl-2223 occurs at 800 °C and does not involve the formation of a liquid phase but the solid state diffusion of the Ca and Cu species and the restructuring of the Tl-2212 lattice. This conversion however does not occur when the Tl content is equal to 2.3 in agreement with previous reports on phase equilibria.

The Tl–Ba–Ca–Cu–O system has been investigated. We report on the superconducting properties and the pathway for the formation of the Tl-1223 phase and on equilibrium phase relations. The formation of Tl-1223 implies the double TlO layer phases and occurs at high temperature (890–910°C) by a progressive de-intercalation of TlO layers from Tl-2223. As a consequence of this non-equilibrium process, transient intergrowth phases may be formed and have been unambiguously identified. This path of formation results in a platelet-like morphology for Tl-1223 grains which, in the view of the fabrication of tapes, is much more interesting than the globular shape observed for (Tl,Pb)(Sr,Ba)2Ca2Cu3Oz. Moreover, the superconducting properties (Tc and irreversibility line) of the unsubstituted Tl-1223 phase compare well with those of (Tl,Pb)(Sr,Ba)2Ca2Cu3Oz. With regard to phase equilibria, we show the existence of a three phase field Tl2Ca3O6–(Tl-2212)–(Ca,Tl)1−xCuOy which prevents the formation of Tl-2223 for Tl contents higher than two.

Thick films of the high temperature TlBa2Ca2Cu3Oz superconductor have been prepared from a precursor Ba2Ca2Cu3Oz obtained by spray pyrolysis. In this paper, we report on the parameters which mainly control the formation of the superconducting phase: the composition of the nitrates solution, the substrate temperature and the subsequent ex-situ thallination annealing. The sample were analyzed by X-ray diffraction and by secondary electron microscopy. Epitaxial film (1 to 2 mum thick) with a critical temperature T-c=107 K and a critical density of current J(c)(77 K, 0T)=2.10(3) A/cm(2) have been obtained.