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Direct coating methods using metal particles from aqueous solutions or solvent-based inks become central in the roll-to-roll fabrication processes as these methods can lead to continuous or pre-defined conductive layers on a large variety of substrates. For good electrical conductivity, the metal particles have to be brought into contact, and traditionally, additional sintering treatments are required. Such treatments can degrade the sensitive substrates as paper or polymer films. In this study, the possibility of obtaining conductive layers at room temperature is investigated for direct coating methods with an emphasis on drop-casting and inkjet printing. Thus, it is shown that electrical conductive layers can be achieved if the metal particles can compact during the drop-substrate impact interaction. It is theoretically shown that the compaction process is directly related to the particle and ink drop size, the initial fractional particle loading of the ink, solvent viscosity, and drop velocity. The theoretical predictions on compaction are experimentally validated, and the particle compaction's influence on changes in the electrical conductivity of the resulting layers is demonstrated. [ABSTRACT FROM AUTHOR]

Measurements of transport critical current of superconducting conductors with respect to temperature and magnetic field are of particular importance for medical and energy applications. The main interest of using the superconducting materials such as MgB2, Bi-based and YBa2Cu3O7 is in the range of 4-40 K and testing facilities covering such a range of temperatures and magnetic fields can be costly, especially when considering the cooling power required in the cryogenic system and also a dramatically growing cost of liquid helium and its shortage. Transport critical currents in excess of 1000 A at temperatures above LHe are common for commercial wires, making the testing of such samples difficult in setups cooled via a cryocooler even by force gas cooling. There is also a fundamental interest in the study of superconducting conductors in magnetic fields higher than B = 20 T; such magnetic flux density can be obtained by using pulse techniques, however data interpretation can be difficult and there are some potential discrepancies. In the current paper we present how improved stepwise pulse current and signal averaging procedure combined with stepwise pulse transport current and flat-top pulse magnetic field measurements can deliver results identical to the combined DC transport current and DC magnetic field in milliseconds and also with a minimum boil-off of helium. [ABSTRACT FROM AUTHOR]

Analysis of the applicability of the low cost powder-in-tube technology of technical Nb3Sn, Bi2Sr2CaCu2O8+d and MgB2 superconducting conductors has been presented in respect of their complexity in emerging hydrogen cryomagnetic technology where temperature of the liquid hydrogen can be as low as 14.1 K, and all above conductors can be considered having a comparable Jc(B; T) characteristics. The new emerging hydrogen economy where liquid hydrogen can serve as an energy carrier and cryogenic coolant with exceptionally high latent heat value presents opportunities for the range of superconducting materials characterised by Tc applicable at hydrogen technologies. All above powder-in-tube conductors are exploring solid-liquid reactive diffusion processes originated from the complex compounds or intermetallics, defining the actual "technical price" in (€/(kA m)) of the resulting wire compound based on Jc(B; T) characteristics and materials as well as manufacturing cost and complexity. This rather complex techno-economic aspect of superconducting powder-in-tube conductors needs to be addressed and analysed to help to solve a trilemma concerning powder-in-tube conductors at low temperatures. [ABSTRACT FROM AUTHOR]

Discusses a study which examined the effect of the time dependent angular distribution of the intergrain magnetic field on the transport critical current in Ag-(Bi,Pb)[sub2]Sr[sub2]Ca[sub2]Cu[sub3]O[subx] conductor. Theoretical background; Methods used; Results.

Focuses on a study which reported the differences between the transversal and longitudinal in-plane transport critical current of Ag-(Bi,Pb)[sub2]Sr[sub2]Ca[sub2]Cu[sub3]O[subx] tape form conductor. Experimental procedures; Influence of the cold deformation procedures on the critical current distribution of the tape form conductor; Significance of superconductors to engineering applications; Results and discussion.

Stacks of superconducting tapes can be used as trapped-flux magnets and applied in a fully superconducting motor. In such application, they can be subjected to an angled magnetising field. In this work, the results of the numerical analysis of the stacks with different sizes, magnetised by angled magnetic fields, are presented. The numerical model applied bases on H-formulation. The optimum number of tapes in which the magnetisation per tape is the highest is sought. The dependence is obtained and presented for 40 mm wide tapes, similar in size to the ones applied in a future motor. It was shown that the optimal number of tapes increases with the strength of the magnetising field and decreases with its deviation from the direction normal to the stack. [ABSTRACT FROM AUTHOR]

La0.6Sr0.4Co0.2Fe0.8O3−δ/Ce0.9Gd0.1O1.9 composite cathodes were nano-engineered via“dual” inkjet printing infiltration of nitrate salt solutions in a single step procedure. After calcination in air at 700 °C the cathodes were decorated with Ce0.9Gd0.1O1.9 and CoxOy nanoparticles (∼20 nm in size). The effects of the as-created nano-decoration on the electrochemical activity and the performance stability in the intermediate temperature range (500–700 °C) were investigated. The nano-engineered microstructure was found to extend the active three-phase boundary and to promote adsorption–dissociation–surface exchange reactions. Electrochemical impedance tests conducted on symmetric cells showed a reduction in the polarisation resistance of between 1.5 and 7.0 times depending on temperature (500–700 °C). High-resolution X-ray photoelectron spectroscopy and in situ high temperature Raman spectroscopy were used to study aging and thermal cycling effects on the cathodes' surface chemistry. Aging tests of the infiltrated electrodes up to 100 hours in air revealed an enhanced stability of the decorated electrodes ascribed to the suppression of SrO surface segregation. This work demonstrated that the sequence of infiltration of both inks introduces noticeable differences in the oxygen reduction reaction. [ABSTRACT FROM AUTHOR]

The effect of inkjet printing infiltration of Gd0.1Ce0.9O2-x in NiO-Gd0.1Ce0.9O2-x anodes on the performance of symmetrical and button cells was investigated. The anodes were fabricated by inkjet printing of suspension and sol inks. Symmetrical cells were produced from composite suspension inks on Gd0.1Ce0.9O2-x electrolyte. As-prepared scaffolds were infiltrated with Gd0.1 Ce0.9O2 ink. Increasing the number of infiltration steps led to formation of ‘‘nano-decoration’’ on pre-sintered anodes. High resolution SEM analysis was employed for microstructural characterization revealing formation of fine anode sub-structure with nanoparticle size varying in the range of 50–200 nm. EIS tests were conducted on symmetrical cells in 4% hydrogen/argon gas flow. The measurements showed substantial reduction of the activation polarization as a function of the number of infiltrations. The effect was assigned to the extension of the triple phase boundary. The i–V testing of a reference (NiO-8 mol% Y2O3 stabilized ZrO2/NiO-Gd0.1Ce0.9O2-x/Gd0.1Ce0.9O2-x/Gd0.1Ce0.9O2-x-La0.6Sr0.4Co0.2Fe0.8O3-δ) cell and an identical cell with infiltrated anode revealed ~2.5 times improvement in the maximum output power at 600 °C which corresponded with the reduction of the polarization resistance of the symmetrical cells at the same temperature (2.8 times). This study demonstrated the potential of inkjet printing technology as an infiltration tool for cost effective commercial SOFC processing. [ABSTRACT FROM AUTHOR]

Electron-phonon coupling is one of the most common interaction in superconducting materials ranging from Nb3Sn, MgB2, iron-based superconductors and high temperature cuprates such as YBa2Cu3O7-δ and HgBa2Ca2Cu3O8+δ. However an importance of the electron-phonon coupling constant, λep, should not be underestimated for characterisation of the electronic properties of superconducting materials, but it is important that the enhanced flux pinning mechanism can be hold responsible for the applicability of the A15 superconducting materials in emerging hydrogen cryomagnetic technology where temperature of the liquid H2 can be as low as 14 K. [ABSTRACT FROM AUTHOR]

Electromagnetic compaction of in situ MgB2/Cu wire has been achieved using a custom-built 200 J device. The monofilament core packing density was increased by 8% and up to 31% for unreacted and reacted wires respectively. The higher density of the MgB2 core resulted in a critical current density increase of up to 75% in comparison to that for cold-drawn-only wire. Applying this treatment to a wire with Cu powder additions to the core and with an optimized heat treatment resulted in one of the highest ever reported values of Jc for MgB2/Cu wires of 6.83 × 103 A cm−2 at 4.2 K and 6 T. [ABSTRACT FROM AUTHOR]

Recent results on powder-in-tube in situ Cu-sheathed MgB2 wires have shown that copper powder additions to the core can accelerate the formation of MgB2, increasing its volume fraction and greatly decreasing the amount of Mg-Cu intermetallic phases present in the core after heat treatment. The amount of added copper and heat treatment conditions strongly affect the critical current of the wire and require optimization. To identify the optimum parameters, eight wires with starting core compositions of Mg+2B+xCu with x = 0, 0.01, 0.03, 0.05, 0.07, 0.09, 0.12 and 0.15 were prepared with two heating ramp rates and their properties were investigated by SEM, XRD and Jc and n-value measurements. The highest Jc was found to be for x = 0.09, whereas x = 0.03 resulted in the highest n-value. The results are relatively independent of the heating ramp rate used for heat treatment. [ABSTRACT FROM AUTHOR]

The ability of superconductors to sustain persistent currents has been well exploited with (RE)BCO superconducting bulks, which can be magnetized to form a compact source of high magnetic field. However, thin films can also sustain persistent currents, which can be utilized by stacking them in layers to create a type of composite bulk. Such a stack is capable of trapping higher fields than a bulk, as reported in this paper. 12 mm wide, 55 µm thick commercial (RE)BCO tape from Superpower Inc was cut into 12 mm by 12 mm squares, stacked together and magnetized at temperatures between 10 and 77.4 K using a sequence of pulsed magnetic fields. The results are compared to a commercial 14 mm diameter YBCO bulk, showing that the stack of tapes outperformed the bulk at temperatures below approximately 60 K. Particularly high trapped fields were achieved below 50 K, with a maximum of 2.0 T at 10 K measured 0.8 mm from the stack surface. The maximum trapped field possible for a stack of tapes increases significantly with decreasing temperature down to 10 K, rather than saturating at a higher temperature as in the case of a bulk, due to superior thermal stability. The Jc, thermal and mechanical properties of commercial (RE)BCO tapes give them great potential for use as trapped field magnets activated by pulsed magnetic fields. [ABSTRACT FROM AUTHOR]

Rapid heat generation is one of the biggest problems faced in carrying out pulsed field magnetization of (RE)BCO superconducting bulks compared to other methods of magnetization. The effects of various thermal conductivities in the ab-plane (kab) and along the c-axis (kc) of a bulk on its trapped field performance following pulsed field magnetization were modelled. The E-J power law was used, coupled with the heat generation, to simulate the effect of anisotropic thermal conductivity combinations on the peak trapped field and total trapped flux. A thermally isolated bulk is not affected so strongly by thermal conductivity, but on cooling the bulk conductively from its base using a cold head, increasing kc significantly enhances both the trapped field and the flux. Embedding highly thermally conducting copper structures in the bulk material was investigated as a practical way to locally increase kab and kc. The structures investigated increased the trapped field and flux by a maximum of around 30% without increasing the size of the bulk. Different structures can be used depending on whether an application requires the highest trapped field or highest total flux. [ABSTRACT FROM AUTHOR]

In this study, an FEM code based on a critical state model is used to further understand the electromagnetic behaviour of Yb211-doped Sm123 bulk superconductor by calculating the current and magnetic field distributions in doped samples both in uniform and non-uniform external field conditions. The results of magnetization loops from the numerical modelling have been compared with experimental results and they show a good match. In the numerical calculation result, the highest trapped field value, B z, is 0.49 T for x = 0.25. In addition, the value of B z trapped field in a non-uniform applied field is calculated as 18% larger than in uniform applied field and the current density of samples as a function of radius increase particularly at the sample edge with a non-uniform applied field for the x = 0.25 sample. It can be said that this numerical method will be a useful candidate to get an easy solution to many electromagnetic problems of doped-superconductor with complex geometries and in different field conditions as the performed numerical study is successful in clarifying magnetization, trapped field and pinning properties of Yb211-doped Sm123 superconductor. [ABSTRACT FROM AUTHOR]

This paper reports the successful application of ink-jet printing to the deposition of both continuous coatings and multi-filamentary structures of YBCO. Stable inks have been prepared using both the established TFA-MOD route and novel fluorine-free precursors with appropriate rheological properties for ink-jet printing. Continuous and well textured coatings with lengths exceeding 100 m and a thickness of 0.5 ͛m have been deposited by electromagnetic ink-jet printing from TFA precursors on LZO-buffered Ni-W substrates and samples have achieved a Jc around 1.5 MA cm-2 (self-field, 77 K). On single crystal substrates, continuous coatings and multi-filamentary structures have been deposited using piezoelectric ink-jet printing both from TFA- and water-based precursors, achieving Jc values up to 3 MA cm-2. [ABSTRACT FROM AUTHOR]

The fault current limiting feature of the SC transformer with the HTS 2G windings provide protection and significantly reduce wear and tear for circuit breakers and other substation power equipment. A comparison of the short circuit currents of the 64 MVA transformer wound with copper and YBCO 2G HTS tapes is made in this paper. The results of the analysis show that the YBCO 2G tapes enable to built the superconducting transformer with the ability to limit the short-circuit currents. The superconducting windings require special considerations for the induced electromagnetic forces in order to limit them below the allowable tensile stresses. Strongly anisotropic Y-123 tape used in the winding of the transformer will be exposed to different orientations and amplitudes of the local magnetic field. If the transformer is going to act also as a fault current limiter, the uniformity of the transition of the transformer winding is crucial to avoid sectional responses of the transformer. Therefore it is essential to conduct systematic current-magnetic field measurements to define ‘constant current domain’ for the conductor at a given operating temperature. [ABSTRACT FROM AUTHOR]

The successful inkjet printing of a cerium gadolinium oxide (Ce0.8Gd0.2O2) precursor solution on highly textured Ni-5%W is reported. A stable ink was synthesised from metal acetates and propionic acid with rheological properties suitable for inkjet printing and also the development of solid–liquid interface comparable with thin film formation by dip coating. Two different drop-on-demand print heads were used for deposition: a 16-nozzle piezoelectric cartridge and a single electromagnetic nozzle. Two different rastering patterns with different droplet sizes and spacing were compared. Thermogravimetry and X-ray diffractometry were used to study the thermal decomposition of the metal oxide precursors and to determine the shortest possible heat treatment of the deposited layers, potentially suitable for continuous large scale production. The results from X-ray diffraction show that the single phase Ce0.8Gd0.2O2 was obtained in all cases, but only piezoelectric inkjet printing with optimised drop overlapping produces a highly textured buffer layer. Optical micrographs and atomic force microscopy also indicate the good quality of deposited films after heat treatment. [ABSTRACT FROM AUTHOR]

The authors have studied the phase formation sequences in a Nb3Sn ‘internal tin’ process superconductor. Heat treatments were performed to convert the starting materials of tin, Ti–Sn, copper and niobium, to bronze and Nb3Sn. Specimens were quenched at different points of the heat treatment, followed by metallography to identify the phases present and X-ray microtomography (XMT) to investigate the void volume and distribution. An unexpected observation of the microstructure development was the uphill diffusion of tin during the Cu–Sn reactive diffusion. Some defects likely to affect the superconducting performance of the wires were observed. Microscopy revealed the presence of a Ti–Sn intermetallic compound displacing the niobium filaments, and XMT revealed the formation of long pores in the longitudinal direction. Two types of pore formation mechanism, in addition to Kirkendall pores, are proposed. The phase and microstructure development suggests that low-temperature heat treatment (below 415 °C) will have significant influence on optimising the final superconducting properties. [ABSTRACT FROM AUTHOR]

The objective of this paper is to prove the possibility to produce single side buffered substrates for coated conductors. We report for the first time the production of highly textured NiW/La2Zr2O7/CeO2 system by all-chemical solution deposition means using an in-house built drop-on-demand ink-jet printer. Lanthanum zirconate precursor ink was produced using lanthanum acetate and zirconium n-propoxide modified with propionic and acetic acid, respectively, and diluted with methanol. Cerium oxide precursor ink was prepared using cerium acetylacetonate dissolved in acetylacetone and diluted in methanol. Optimized ink jet control parameters (inter-droplet distance, nozzle opening time and pressure in the chamber) allowed the deposition of homogeneous highly textured films with a thickness of approximately 150–200 nm at speeds as high as 27 cm/min. La2Zr2O7 film showed in plane and out of plane misalignment of 6.6° and 7.4°, respectively, whereas values obtained for CeO2 were 7.8° and 8.1°, respectively. This study represents a step forward in the production of reel-to-reel coated conductors in an efficient and economic way. [ABSTRACT FROM AUTHOR]

The basis for the development of computer controlled printing techniques for YBa2Cu3O7- δ (YBCO) coated conductors is discussed in detail. This method of continuous deposition of YBCO material potentially enables non-vacuum formation of complex multi-layer superconducting patterns on silver substrates. Sol–ink processes were used to print single droplets of YBCO on polycrystalline silver substrates under varying printing conditions. Droplet sizes were controlled from a range of 300 μm–1200 μm. The formation and the stability of the sol–ink with respect to pH and concentration has been studied and discussed herein. For optimum results, the pH of the ink had to regulated to 6.5. Printing and substrate parameters that alter solid–liquid interface properties were also investigated such as ink concentration and surface roughness, the best results produced were with an ink concentration of 0.025 M on a polished silver surface. 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 where they were discovered to have a characteristic T c of ∼83 K. [ABSTRACT FROM AUTHOR]