Abstract As superconducting materials find their way into applications, there is increasing need ... more Abstract As superconducting materials find their way into applications, there is increasing need to verify their performance at operating conditions. Testing of critical current with respect to temperature and magnetic field is of particular importance. However, testing facilities covering a range of temperatures and magnetic fields can be costly, especially when considering the cooling power required in the cryogenic system in the temperature range below 65 K (inaccessible for LN2). Critical currents in excess of 500 A are common for commercial samples, making the testing of such samples difficult in setups cooled via a cryocooler, moreover it often does not represent the actual cooling conditions that the sample will experience in service. This work reports the design and operation of a low-cost critical current testing facility, capable of testing samples in a temperature range of 10–65 K, with magnetic field up to 1.6 T and measuring critical currents up to 900 A with variable cooling power.
In this paper, we present ink-jet printing as an attractive alternative to lithography and etchin... more In this paper, we present ink-jet printing as an attractive alternative to lithography and etching methods for the development of multi-filamentary YBa2Cu3O7-$\delta$ coated conductors. Our research is mainly focused on the study of the influence of rheological parameters on the printability of water-based inks in order to produce superconducting patterns on SrTiO3 and CeO2-La 2Zr2O7-Ni5at{\%}W substrates. An aqueous YBCO precursor ink with a total metal ion concentration of 1.1 mol/L with a viscosity of 6.79 mPa s and a surface tension of 67.9 mN/m is developed. Its printing behavior using several ink-jet printing devices is verified using a camera with strobed illumination to quantify droplet velocity and volume. After optimization of the deposition parameters, YBCO tracks with different dimensions could be printed on both types of substrates. Their shape and dimensions were determined using optical microscopy and non-contact profilometry, showing 100-200 nm thick and 40-200 $\mu$m wide tracks. Finally, resistivity measurements were performed on the widest tracks on SrTiO3 showing a clear drop in the resistivity starting from 88.6 K with a $\Delta$Tc of 1.4 K. {\textcopyright} 2013 Materials Research Society.
The interest of functional ceramics coatings based on low cost and flexible manufacturing has bee... more The interest of functional ceramics coatings based on low cost and flexible manufacturing has been pushed up by the effectiveness shown by the Chemical Solution Deposition (MOD-CSD) of metal-organic salts route, based habitually on the use of spin coating, deep coating or slot die techniques previous to the thermal treatment to achieve the decomposition of the starting salts. The possibility to implement effective Drop on Demand (DoD) systems in the manufacturing process allows a more efficient way to homogeneously extend the precursor solution over the substrate, being so able to control the thickness of the ceramic coating among other manufacturing advantages as control of solvent evaporation. In this work we report on our experiments concerning ink jet coating of functional complex ceramics as LSMO over single crystalline substrates by using a single nozzle piezolectric dispenser. Characterization of both the rheological properties of the developed ink, and the resulting coating by XR diffiaction, SEM, and rrmgnetic behavior are reported.
\textcopyright}2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility ... more \textcopyright}2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Guest Editors. Considerable progress has been made with the development of YBa2Cu3O7-$\delta$ and related rare-earth (REBCO) coated conductors in recent years. The introduction of BaZrO3 (BZO) nanoparticles has resulted in enhanced critical current density (Jc) for magnetic field orientations away from the intrinsic ab peak, with the absolute Jc and the degree of anisotropy depending on the geometry and orientation distribution of the nanoparticles; and REBCO coated conductors with a variety of substitutions and additions (Gd, Sm, Ba, Zr, Sn) are becoming commercially available in kilometre lengths. It is therefore increasingly important to characterise the magnetic field orientation dependence of critical current (Ic) in full-width coated conductors without destructive sample preparation, both for fundamental pinning studies and the design of large-scale applications. A two-axis goniometer has been developed, allowing the critical current to be measured as a function of both the magnitude and orientation of the applied magnetic field, Ic(B,$\theta$,$\Phi$), on full-width samples. Measurements of Ic(B,$\theta$,$\Phi$) at 77 K are reported for four REBCO tapes made by metal organic chemical vapour deposition (MOCVD) with different rare earth content and the results interpreted in relation to rare earth substitution and pinning centre populations. The implications of the field orientation dependence for low and intermediate field applications are discussed.
\textcopyright} 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility... more \textcopyright} 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Guest Editors. A complete reaction path for the pyrolysis of trifluoroacetate-derived YBa2Cu3O7-$\delta$ precursor solution is reported based on the authors' investigations of the separate trifluoroacetate salt decompositions using thermal analysis and infrared spectroscopy of evolved gases. Optimal conditions for the pyrolysis of inkjet printed films are proposed, and the influence of pyrolysis on the YBa2Cu3O7-$\delta$ crystal growth on a fully buffered Ni-5{\%}W substrate is revealed. Optimisation of the annealing step revealed a strong dependence of the superconducting properties on the heat treatment temperature and duration. The critical temperature (Tc) and critical current density (Jc) of fully chemical solution deposited coated conductor samples were examined by means of inductive and Hall probe measurements.
\textcopyright} 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility... more \textcopyright} 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Guest Editors. The ability of high temperature superconducting bulks to trap magnetic fields of several tesla allows them to generate very high levitation force. This paper reports the development of a bulk-bulk superconducting rotary bearing design which uses superconducting bulks on both the rotor and the stator. An evaluation is made of the effectiveness of pulsed fields for magnetizing bulks. Modeling of the bulks using the perfectly trapped flux model is also reported to assess the limits of the bearing design. The results demonstrate the feasibility of a (RE)BCO-MgB2 bulk bearing capable of force densities of the order of 100N/cm2. The design and construction of a unique system capable of magnetizing a 25 mm (RE)BCO bulk and measuring levitation force between this bulk and a coaxial MgB2 hollow cylinder is outlined.
The feasibility of inkjet printing of electrodes for direct carbon solid oxide fuel cells (DC-SOF... more The feasibility of inkjet printing of electrodes for direct carbon solid oxide fuel cells (DC-SOFC) was tested. A variety of materials was deposited by direct ceramic inkjet printing (DCIJP). The technology allows for easy modification of the coatings, including thickness control, porosity graduation and precise infiltration with catalytically active materials. The comparative tests showed a similar performance for screen printed and inkjet printed cells (peak power density of ca. 80 mW cm-2 at 780°C). In addition DCIJP offers minimization of the usage of expensive precursor materials. It was also found that infiltration of the anode by inkjet printing of sol inks (CuNiO3) can lead to an improvement in DC-SOFC performance. {\textcopyright} The Electrochemical Society.
\textcopyright} 2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility... more \textcopyright} 2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Guest Editors. Recent advances in the design of Cu-sheathed in situ MgB2 wires have shown promising results and made this kind of wire more competitive in terms of price to performance ratio in comparison to conductors with diffusion barriers made with metals inert to reaction with Mg. Recently reported additions of copper powder to the core of in situ Cu-sheathed MgB2 wires have shown that these additions 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. In this paper additional experimental results for toluene doping are reported and compared to wires with and without copper additions. All three wires were investigated by SEM, XRD and transport critical current measurements Jc(B) at 4.2 K. The results showed that copper additions were effective in the whole measured field region, whereas toluene doping improved performance in the high field region.
In order to investigate the high temperature exposure effect on Nb-Ti/Cu superconducting strands,... more In order to investigate the high temperature exposure effect on Nb-Ti/Cu superconducting strands, as might be encountered in joining by soldering and in cabling annealing, X-ray diffraction and resistometry measurements were performed in situ during heat treatment, and complemented by conventional metallography, mechanical tests and superconducting properties measurements. Changes of the Nb-Ti nanostructure at temperatures above 300°C are manifested in the degradation of critical current in an applied external magnetic field, although degradation at self field was insignificant up to 400°C for several minutes. Above 500°C, the formation of various Cu-Ti intermetallic compounds, due to Ti diffusion from Nb-Ti into Cu, is detected by in situ XRD albeit not resolvable by SEM-EDS. There is a ductile to brittle transition near 600°C, and liquid formation is observed below 900°C. The formation of Cu-Ti causes a delayed reduction of the residual resistivity ratio (RRR) and adversely affects the deformation behaviour of the strands. {\textcopyright} (2010) Trans Tech Publications.
The reactive diffusion and phase formation sequences in two types of 'internal tin' superconducti... more The reactive diffusion and phase formation sequences in two types of 'internal tin' superconducting wires designed for the ITER project, which investigates the production of electricity by means of nuclear fusion, have been studied during heat treatments both in situ, using electrical resistometry [1] and ex situ, using optical and scanning electron microscopy, energy dispersive X-ray spectrometry (EDS) and X-ray Micro-Tomography (XMT). XMT reveals long pores in the longitudinal direction which may result in tin deficiency thereat and hence local off-stoichiometric Nb3Sn. Microscopy suggests there are incomplete conversion of elemental tin to copper-tin intermetallics before ramping above the tin melting temperature, non-uniform distribution of tin before formation of Nb3Sn, and filament movement and bridging, stacking cracks and unreacted niobium at the end of the heat treatment. FEGSEM shows a fine microstructure which nevertheless could still be improved.
The bronze process is a mature technology for the production of Nb 3Sn superconducting wires expl... more The bronze process is a mature technology for the production of Nb 3Sn superconducting wires exploiting reaction diffusion behaviour in the Cu-Nb-Sn system. However, the superconducting properties depend strongly on the applied heat treatment, and optimisation of the heat treatment is still largely by trial and improvement. Modelling of the reaction-diffusion behaviour would allow improved heat treatments to be designed; combination of this with a non-destructive in situ characterisation technique would also permit improved superconducting wires to be produced. A finite difference reaction diffusion model has been designed to permit rapid calculation of the bronze matrix composition and Nb3Sn layer thickness profiles across the wire cross-section as a function of time for any applied heat treatment. The model has also been designed to calculate the electrical resistivity of the wire, which has previously been demonstrated as a suitable in situ characterisation technique. This model has been applied to isothermal and more complex heat treatments and compared with experimental results. Good qualitative agreement has been found, and plans for further improvement of the model are described in detail.
Abstract As superconducting materials find their way into applications, there is increasing need ... more Abstract As superconducting materials find their way into applications, there is increasing need to verify their performance at operating conditions. Testing of critical current with respect to temperature and magnetic field is of particular importance. However, testing facilities covering a range of temperatures and magnetic fields can be costly, especially when considering the cooling power required in the cryogenic system in the temperature range below 65 K (inaccessible for LN2). Critical currents in excess of 500 A are common for commercial samples, making the testing of such samples difficult in setups cooled via a cryocooler, moreover it often does not represent the actual cooling conditions that the sample will experience in service. This work reports the design and operation of a low-cost critical current testing facility, capable of testing samples in a temperature range of 10–65 K, with magnetic field up to 1.6 T and measuring critical currents up to 900 A with variable cooling power.
In this paper, we present ink-jet printing as an attractive alternative to lithography and etchin... more In this paper, we present ink-jet printing as an attractive alternative to lithography and etching methods for the development of multi-filamentary YBa2Cu3O7-$\delta$ coated conductors. Our research is mainly focused on the study of the influence of rheological parameters on the printability of water-based inks in order to produce superconducting patterns on SrTiO3 and CeO2-La 2Zr2O7-Ni5at{\%}W substrates. An aqueous YBCO precursor ink with a total metal ion concentration of 1.1 mol/L with a viscosity of 6.79 mPa s and a surface tension of 67.9 mN/m is developed. Its printing behavior using several ink-jet printing devices is verified using a camera with strobed illumination to quantify droplet velocity and volume. After optimization of the deposition parameters, YBCO tracks with different dimensions could be printed on both types of substrates. Their shape and dimensions were determined using optical microscopy and non-contact profilometry, showing 100-200 nm thick and 40-200 $\mu$m wide tracks. Finally, resistivity measurements were performed on the widest tracks on SrTiO3 showing a clear drop in the resistivity starting from 88.6 K with a $\Delta$Tc of 1.4 K. {\textcopyright} 2013 Materials Research Society.
The interest of functional ceramics coatings based on low cost and flexible manufacturing has bee... more The interest of functional ceramics coatings based on low cost and flexible manufacturing has been pushed up by the effectiveness shown by the Chemical Solution Deposition (MOD-CSD) of metal-organic salts route, based habitually on the use of spin coating, deep coating or slot die techniques previous to the thermal treatment to achieve the decomposition of the starting salts. The possibility to implement effective Drop on Demand (DoD) systems in the manufacturing process allows a more efficient way to homogeneously extend the precursor solution over the substrate, being so able to control the thickness of the ceramic coating among other manufacturing advantages as control of solvent evaporation. In this work we report on our experiments concerning ink jet coating of functional complex ceramics as LSMO over single crystalline substrates by using a single nozzle piezolectric dispenser. Characterization of both the rheological properties of the developed ink, and the resulting coating by XR diffiaction, SEM, and rrmgnetic behavior are reported.
\textcopyright}2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility ... more \textcopyright}2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Guest Editors. Considerable progress has been made with the development of YBa2Cu3O7-$\delta$ and related rare-earth (REBCO) coated conductors in recent years. The introduction of BaZrO3 (BZO) nanoparticles has resulted in enhanced critical current density (Jc) for magnetic field orientations away from the intrinsic ab peak, with the absolute Jc and the degree of anisotropy depending on the geometry and orientation distribution of the nanoparticles; and REBCO coated conductors with a variety of substitutions and additions (Gd, Sm, Ba, Zr, Sn) are becoming commercially available in kilometre lengths. It is therefore increasingly important to characterise the magnetic field orientation dependence of critical current (Ic) in full-width coated conductors without destructive sample preparation, both for fundamental pinning studies and the design of large-scale applications. A two-axis goniometer has been developed, allowing the critical current to be measured as a function of both the magnitude and orientation of the applied magnetic field, Ic(B,$\theta$,$\Phi$), on full-width samples. Measurements of Ic(B,$\theta$,$\Phi$) at 77 K are reported for four REBCO tapes made by metal organic chemical vapour deposition (MOCVD) with different rare earth content and the results interpreted in relation to rare earth substitution and pinning centre populations. The implications of the field orientation dependence for low and intermediate field applications are discussed.
\textcopyright} 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility... more \textcopyright} 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Guest Editors. A complete reaction path for the pyrolysis of trifluoroacetate-derived YBa2Cu3O7-$\delta$ precursor solution is reported based on the authors' investigations of the separate trifluoroacetate salt decompositions using thermal analysis and infrared spectroscopy of evolved gases. Optimal conditions for the pyrolysis of inkjet printed films are proposed, and the influence of pyrolysis on the YBa2Cu3O7-$\delta$ crystal growth on a fully buffered Ni-5{\%}W substrate is revealed. Optimisation of the annealing step revealed a strong dependence of the superconducting properties on the heat treatment temperature and duration. The critical temperature (Tc) and critical current density (Jc) of fully chemical solution deposited coated conductor samples were examined by means of inductive and Hall probe measurements.
\textcopyright} 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility... more \textcopyright} 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Guest Editors. The ability of high temperature superconducting bulks to trap magnetic fields of several tesla allows them to generate very high levitation force. This paper reports the development of a bulk-bulk superconducting rotary bearing design which uses superconducting bulks on both the rotor and the stator. An evaluation is made of the effectiveness of pulsed fields for magnetizing bulks. Modeling of the bulks using the perfectly trapped flux model is also reported to assess the limits of the bearing design. The results demonstrate the feasibility of a (RE)BCO-MgB2 bulk bearing capable of force densities of the order of 100N/cm2. The design and construction of a unique system capable of magnetizing a 25 mm (RE)BCO bulk and measuring levitation force between this bulk and a coaxial MgB2 hollow cylinder is outlined.
The feasibility of inkjet printing of electrodes for direct carbon solid oxide fuel cells (DC-SOF... more The feasibility of inkjet printing of electrodes for direct carbon solid oxide fuel cells (DC-SOFC) was tested. A variety of materials was deposited by direct ceramic inkjet printing (DCIJP). The technology allows for easy modification of the coatings, including thickness control, porosity graduation and precise infiltration with catalytically active materials. The comparative tests showed a similar performance for screen printed and inkjet printed cells (peak power density of ca. 80 mW cm-2 at 780°C). In addition DCIJP offers minimization of the usage of expensive precursor materials. It was also found that infiltration of the anode by inkjet printing of sol inks (CuNiO3) can lead to an improvement in DC-SOFC performance. {\textcopyright} The Electrochemical Society.
\textcopyright} 2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility... more \textcopyright} 2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Guest Editors. Recent advances in the design of Cu-sheathed in situ MgB2 wires have shown promising results and made this kind of wire more competitive in terms of price to performance ratio in comparison to conductors with diffusion barriers made with metals inert to reaction with Mg. Recently reported additions of copper powder to the core of in situ Cu-sheathed MgB2 wires have shown that these additions 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. In this paper additional experimental results for toluene doping are reported and compared to wires with and without copper additions. All three wires were investigated by SEM, XRD and transport critical current measurements Jc(B) at 4.2 K. The results showed that copper additions were effective in the whole measured field region, whereas toluene doping improved performance in the high field region.
In order to investigate the high temperature exposure effect on Nb-Ti/Cu superconducting strands,... more In order to investigate the high temperature exposure effect on Nb-Ti/Cu superconducting strands, as might be encountered in joining by soldering and in cabling annealing, X-ray diffraction and resistometry measurements were performed in situ during heat treatment, and complemented by conventional metallography, mechanical tests and superconducting properties measurements. Changes of the Nb-Ti nanostructure at temperatures above 300°C are manifested in the degradation of critical current in an applied external magnetic field, although degradation at self field was insignificant up to 400°C for several minutes. Above 500°C, the formation of various Cu-Ti intermetallic compounds, due to Ti diffusion from Nb-Ti into Cu, is detected by in situ XRD albeit not resolvable by SEM-EDS. There is a ductile to brittle transition near 600°C, and liquid formation is observed below 900°C. The formation of Cu-Ti causes a delayed reduction of the residual resistivity ratio (RRR) and adversely affects the deformation behaviour of the strands. {\textcopyright} (2010) Trans Tech Publications.
The reactive diffusion and phase formation sequences in two types of 'internal tin' superconducti... more The reactive diffusion and phase formation sequences in two types of 'internal tin' superconducting wires designed for the ITER project, which investigates the production of electricity by means of nuclear fusion, have been studied during heat treatments both in situ, using electrical resistometry [1] and ex situ, using optical and scanning electron microscopy, energy dispersive X-ray spectrometry (EDS) and X-ray Micro-Tomography (XMT). XMT reveals long pores in the longitudinal direction which may result in tin deficiency thereat and hence local off-stoichiometric Nb3Sn. Microscopy suggests there are incomplete conversion of elemental tin to copper-tin intermetallics before ramping above the tin melting temperature, non-uniform distribution of tin before formation of Nb3Sn, and filament movement and bridging, stacking cracks and unreacted niobium at the end of the heat treatment. FEGSEM shows a fine microstructure which nevertheless could still be improved.
The bronze process is a mature technology for the production of Nb 3Sn superconducting wires expl... more The bronze process is a mature technology for the production of Nb 3Sn superconducting wires exploiting reaction diffusion behaviour in the Cu-Nb-Sn system. However, the superconducting properties depend strongly on the applied heat treatment, and optimisation of the heat treatment is still largely by trial and improvement. Modelling of the reaction-diffusion behaviour would allow improved heat treatments to be designed; combination of this with a non-destructive in situ characterisation technique would also permit improved superconducting wires to be produced. A finite difference reaction diffusion model has been designed to permit rapid calculation of the bronze matrix composition and Nb3Sn layer thickness profiles across the wire cross-section as a function of time for any applied heat treatment. The model has also been designed to calculate the electrical resistivity of the wire, which has previously been demonstrated as a suitable in situ characterisation technique. This model has been applied to isothermal and more complex heat treatments and compared with experimental results. Good qualitative agreement has been found, and plans for further improvement of the model are described in detail.
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