german serrano - Academia.edu (original) (raw)

Papers by german serrano

We propose a visible light safety goggle based on various superposed polymer-dispersed liquid cry... more We propose a visible light safety goggle based on various superposed polymer-dispersed liquid crystals (PDLC). The goggles are for use in hostile environments that are too bright which can cause partial blindness or blindness, and for patients with pupillary response diseases

A complete gas chromatographic (μGC) microanalytical system for near-real-time determinations of ... more A complete gas chromatographic (μGC) microanalytical system for near-real-time determinations of marker compounds of explosives at low concentrations is demonstrated. This μGC, dubbed INTREPID, uses an adsorbent-packed micromachined DRIE-Si/glass microfocuser, a wall-coated 1 × 1 cm DRIE-Si/glass microcolumn (1-m channel length), and an integrated array of 4 chemiresistors coated with functionalized thiolate-monolayer-protected gold nanoparticle (MPN) interface layers. A high-volume sampler of conventional design is interfaced to the font-end of the microsystem to reduce limits of detection (LOD) and the analytical duty cycle. Instrument control and data acquisition are executed automatically via Labview code run from a laptop computer. The marker compounds consisted of the TNT byproducts, 2,4- and 2,6-dinitrotoluene, and the taggant, 2,3-dimethyl- 2,3-dinitrobutane. n-Tridecane was used as a representative interference. The combination of retention time and response pattern facilitated the identification of each marker. A full analysis was achieved in <; 3.5 min with LODs in the low- or sub- parts-per-billion range for a preconcentrated air-sample volume of 1 L.

... ET Zellers,1,2,3 G. Serrano,1,2 H. Chang,1,2 and LK Amos1,3 1Center for Wireless Integrated M... more ... ET Zellers,1,2,3 G. Serrano,1,2 H. Chang,1,2 and LK Amos1,3 1Center for Wireless Integrated MicroSystems (WIMS ... A double-header diaphragm pump (D737B, Parker, Cleveland, OH) is used for sample collection (pump 1). Scrubbed ambient is used as the carrier gas and is ...

The aim of the ObNet model is to provide a framework for the design, development, maintenance and... more The aim of the ObNet model is to provide a framework for the design, development, maintenance and run-time support of large, long-lived, highly configurable systems for which the integration of different programming paradigms and environments plays a major role. The model defines some basic mechanisms which can be used in developing specialized software engineering environments for specific application domains. A

The aim of the ObNet model is to provide a framework for the design, development, maintenance and... more The aim of the ObNet model is to provide a framework for the design, development, maintenance and run-time support of large, long-lived, highly configurable systems for which the integration of different programming paradigms and environments plays a major role. The model defines some basic mechanisms which can be used in developing specialized software engineering environments for specific application domains. A

Journal of Applied Physics, 2008

This work describes in detail the simultaneous enhancement of the upper critical field (Hc2) and ... more This work describes in detail the simultaneous enhancement of the upper critical field (Hc2) and the critical current density (Jc) of MgB2 bulk samples doped with nano-SiC particles, as well as single-walled and double-walled (dw) carbon nanotubes (CNTs). The magnetization properties were examined in a superconducting quantum interference device magnetometer, and four-probe transport measurements were performed using a 50T pulsed magnet to determine Hc2(T ). We found that the Jc enhancement is similar in all doped samples at 5K but nano-SiC addition is more effective to improve the flux pinning in the high temperature range (T⩾20K); this improvement cannot solely be attributed to the C incorporation to the lattice but also to the presence of other types of defects (i.e., several kinds of nanoinclusions). CNTs produce a better C incorporation that is more effective to enhance Hc2 [i.e., dwCNT-doped samples reached a record Hc2(0)˜44T value for bulk MgB2]. All the Hc2(T ) curves obtained for different types of doping can be successfully described using a model for a two-gap superconductor in the dirty limit.

Solid State Communications, 2010

In this work the Ti 2InN phase is investigated by X-ray diffraction, magnetic and resistivity mea... more In this work the Ti 2InN phase is investigated by X-ray diffraction, magnetic and resistivity measurements. X-ray powder patterns suggest that all peaks can be indexed with the hexagonal phase of Cr 2AlC prototype. Electrical resistance as a function of temperature reveals superconductivity below 7.3 K. M(H) hysteresis loops show typical type-II superconductivity. Using R(H) versus T measurements we estimated μoH(0)˜10.8 T and ξ(0)˜55.2 Å. The results show unambiguously that Ti 2InN is the first nitride superconductor belonging to the M n+1 AX n family.

The glassy dynamics is a consequence of the elastic properties of the vortex matter, and in princ... more The glassy dynamics is a consequence of the elastic properties of the vortex matter, and in principle may occur in any superconductor. However, whereas a large amount of experimental evidence confirms glassiness in high Tc superconductors (HTS), the applicability of the whole framework developed to describe vortex matter in HTS to other superconducting materials is unclear. In this framework, the particular creep behavior of MgB2, larger than creep of conventional superconductor materials but much lower than HTS one, had precluded a complete understanding of the vortex regimes in this material. In this work we present an experimental study of relaxation processes of pure MgB2 bulk samples measured by DC magnetization technique. We propose a novel self-consistent scaling method to analyze the data and extract the activation energies. The observed experimental behavior can be described in a glassy picture, with a unique critical exponent &mu~1, characteristic of collective creep in the intermediate vortex bundle regime.

Journal of Physics: Conference Series, 2009

Magnetization measurements in the mixed state of thick strips of carbon nanotube doped MgB2 in cr... more Magnetization measurements in the mixed state of thick strips of carbon nanotube doped MgB2 in crossed fields configurations are reported, together with numerical simulations performed with a geometry equivalent to the sample shape. The samples were subjected to magnetic field components along mutually perpendicular directions, an oscillatory field in one direction and a remanent magnetization in the perpendicular direction. The

Superconductor Science & Technology, 2009

We report on measurements and numerical simulations of the behavior of MgB 2 superconductors when... more We report on measurements and numerical simulations of the behavior of MgB 2 superconductors when magnetic field components are applied along mutually perpendicular directions. By closely matching the geometry in simulations and measurements, full quantitative agreement is found. The critical state theory and a single phenomenological law, i.e. the field dependence of the critical current density J c (B), are sufficient for a full quantitative description of the measurements. These were performed in thick strips of carbon nanotube doped MgB 2 samples. Magnetization was measured in two orthogonal directions using a SQUID magnetometer. Magnetic relaxation effects induced by the application of an oscillatory perpendicular field were observed and simulated numerically. The measurements confirm the numerical predictions, that two relaxation regimes appear, depending on the amplitude of the applied magnetic field. The overall agreement constitutes a convincing validation of the critical state model and the numerical procedures used.

Journal of Physics: Conference Series, 2009

In this work we study the microstructural and superconducting properties of doped and undoped bul... more In this work we study the microstructural and superconducting properties of doped and undoped bulk MgB2 samples prepared by solid-state reaction, with 0 and 2.5 %at. nominal TiO2 nanotubes contents, annealed at different temperatures in the 750-900°C range. We discuss the Tc, Jc and Hc2 performance and their correlation with the different synthesis parameters.

IEEE Transactions on Applied Superconductivity, 2005

We present an analysis of the effect of SiC doping and heat treatments, including hot isostatic p... more We present an analysis of the effect of SiC doping and heat treatments, including hot isostatic pressing (HIPing), on the microstructure, magnetization and transport properties of MgB2 wires and coils prepared by the powder in tube (PIT) method. The HIPed wires have higher critical current densities (Jc) than the annealed wires, especially at high temperatures and magnetic fields, and higher irreversibility field. The improvements are due to the reduction of porosity and to a high density of structural defects, which are the likely source of vortex pinning. We demonstrate that the high-quality properties mentioned above can be retained in longer wires. At 25 K our champion 6-layer coil, made with 25 meters of wire, was able to generate a field of 1 T at self-field. We were able to achieve even higher Jc's in another coil by combining the addition of SiC and HIPing. We also observed a larger upper critical field due to the SiC doping, which drives the sample to the dirty limit.

IEEE Transactions on Applied Superconductivity, 2009

Starting from commercial MgB2 325 mesh powder, we further reduced the agglomerates by attrition m... more Starting from commercial MgB2 325 mesh powder, we further reduced the agglomerates by attrition milling in nitrogen atmosphere to minimize oxidation. The milling time was varied between 10 and 40 hours, using two different types of milling media: yttria stabilized zirconia and CW balls. We studied the influence of milling time and milling media on the broadening of x-ray diffraction peaks and the superconducting properties of the powders. A highly energetic milling markedly decreased the crystallite size but damaged the superconducting properties. We observed a decrease of the Tc, consistent with the observed crystallinity loss. We prepared tapes with the 40-hours-milled powders and analyzed the resulting microstructures when using a soft (silver) and a hard (stainless steel) metal sheath, heat treated for 1 hour at 615degC in argon. This temperature was chosen after observing the existing reactions between magnesium diboride and silver by DTA analysis of the powders, so as to minimize the reaction at the superconductor-silver interface. We characterized the superconducting properties by determining the magnetic Jc in a SQUID. We performed 4-point bending micro-tests on the tapes to evaluate their mechanical strength.

IEEE Transactions on Applied Superconductivity, 2011

Starting from commercial MgB 2 powder of 325 mesh, we further reduced the agglomerates by attriti... more Starting from commercial MgB 2 powder of 325 mesh, we further reduced the agglomerates by attrition milling in nitrogen atmosphere to minimize oxidation. Using different milling media (tungsten carbide, yttria stabilized zirconium oxide and stainless steel balls), we obtained different milling energies and, consequently, powders with different strain states. Crystallite size and micro-strain within the grains were estimated by x-ray diffraction. We investigated the changes in the superconducting properties with the use of different milling media by measuring the magnetic moment as a function of temperature in a SQUID magnetometer, after zero field cooling. Single-filament stainless steel-sheathed wires and tapes were prepared with the obtained powders. The flexural properties of the tapes were determined by 4-point bending micro-tests. The use of a precursor powder with a higher strain resulted in more flexible wires and tapes, with lower flexural strength. Three different regions were determined for the maximum normal stress-strain curves. Some in-situ monel-sheathed hollow wires and ex-situ titanium-sheathed tapes and monel-sheathed 7-filament tapes were measured for comparative purposes. We discuss the correlation between sheath yielding and superconducting core cracking with the possible critical current degradation due to mechanical failure of the wires and tapes.

Solid State Communications, 2010

In this work the Ti 2 InN phase is investigated by X-ray diffraction, magnetic and resistivity me... more In this work the Ti 2 InN phase is investigated by X-ray diffraction, magnetic and resistivity measurements. X-ray powder patterns suggest that all peaks can be indexed with the hexagonal phase of Cr 2 AlC prototype. Electrical resistance as a function of temperature reveals superconductivity below 7.3 K. M(H) hysteresis loops show typical type-II superconductivity. Using R(H) versus T measurements we estimated µ o H c2 (0) ∼ 10.8 T and ξ (0) ∼ 55.2 Å. The results show unambiguously that Ti 2 InN is the first nitride superconductor belonging to the M n+1 AX n family.

IEEE Transactions on Applied Superconductivity, 2009

Abstract—Starting from commercial MgB2 325 mesh powder, we further reduced the agglomerates by at... more Abstract—Starting from commercial MgB2 325 mesh powder, we further reduced the agglomerates by attrition milling in ni-trogen atmosphere to minimize oxidation. The milling time was varied between 10 and 40 hours, using two different types of milling media: yttria stabilized ...

Journal of Physics: Conference Series, 2008

We present a study on the angular dependence of the critical current density (Jc) of SiC-doped Mg... more We present a study on the angular dependence of the critical current density (Jc) of SiC-doped MgB2 tapes fabricated by powder-in tube (PIT) with stainless steel (SS) as sheath material. The microstructure and texturing of the tapes are analysed to understand the effects of the rolling degree on the superconducting properties. The microstructure is studied by x-ray diffraction and scanning

IEEE Transactions on Applied Superconductivity, 2009

Abstract—Starting from commercial MgB2 325 mesh powder, we further reduced the agglomerates by at... more Abstract—Starting from commercial MgB2 325 mesh powder, we further reduced the agglomerates by attrition milling in ni-trogen atmosphere to minimize oxidation. The milling time was varied between 10 and 40 hours, using two different types of milling media: yttria stabilized ...

Journal of Physics: Conference Series, 2008

In this work a combination of stainless steel, copper, titanium and silver are used as sheath mat... more In this work a combination of stainless steel, copper, titanium and silver are used as sheath materials to fabricate SiC doped MgB2 wires and tapes by the powder-in-tube (PIT) method. The samples are cold deformed to the final dimension with several intermediate and final heat treatments between 200°C and 900°C. The microstructure and phase composition of the tapes are followed during the deformation and heat treatment processes by Scanning Electron Microscopy (SEM) and X-Ray Diffractometry (XRD). Critical current densities (Jc) were determined by magnetization. The correlation between the superconducting properties and the microstructural characteristics is discussed.

Superconductor Science & Technology, 2007

The use of MgB2 in superconducting applications still awaits for the development of a MgB2-based ... more The use of MgB2 in superconducting applications still awaits for the development of a MgB2-based material where both current-carrying performance and critical magnetic field are optimized simultaneously. We achieved this by doping MgB2 with double-wall carbon nanotubes (DWCNT) as a source of carbon in polycrystalline samples. The optimum nominal DWCNT content for increasing the critical current density, Jc is in the range 2.5-10%at depending on field and temperature. Record values of the upper critical field, Hc2(4K) = 41.9 T (with extrapolated Hc2(0) ~ 44.4 T) are reached in a bulk sample with 10%at DWCNT content. The measured Hc2 vs T in all samples are successfully described using a theoretical model for a two-gap superconductor in the dirty limit first proposed by Gurevich et al.

We propose a visible light safety goggle based on various superposed polymer-dispersed liquid cry... more We propose a visible light safety goggle based on various superposed polymer-dispersed liquid crystals (PDLC). The goggles are for use in hostile environments that are too bright which can cause partial blindness or blindness, and for patients with pupillary response diseases

A complete gas chromatographic (μGC) microanalytical system for near-real-time determinations of ... more A complete gas chromatographic (μGC) microanalytical system for near-real-time determinations of marker compounds of explosives at low concentrations is demonstrated. This μGC, dubbed INTREPID, uses an adsorbent-packed micromachined DRIE-Si/glass microfocuser, a wall-coated 1 × 1 cm DRIE-Si/glass microcolumn (1-m channel length), and an integrated array of 4 chemiresistors coated with functionalized thiolate-monolayer-protected gold nanoparticle (MPN) interface layers. A high-volume sampler of conventional design is interfaced to the font-end of the microsystem to reduce limits of detection (LOD) and the analytical duty cycle. Instrument control and data acquisition are executed automatically via Labview code run from a laptop computer. The marker compounds consisted of the TNT byproducts, 2,4- and 2,6-dinitrotoluene, and the taggant, 2,3-dimethyl- 2,3-dinitrobutane. n-Tridecane was used as a representative interference. The combination of retention time and response pattern facilitated the identification of each marker. A full analysis was achieved in <; 3.5 min with LODs in the low- or sub- parts-per-billion range for a preconcentrated air-sample volume of 1 L.

... ET Zellers,1,2,3 G. Serrano,1,2 H. Chang,1,2 and LK Amos1,3 1Center for Wireless Integrated M... more ... ET Zellers,1,2,3 G. Serrano,1,2 H. Chang,1,2 and LK Amos1,3 1Center for Wireless Integrated MicroSystems (WIMS ... A double-header diaphragm pump (D737B, Parker, Cleveland, OH) is used for sample collection (pump 1). Scrubbed ambient is used as the carrier gas and is ...

The aim of the ObNet model is to provide a framework for the design, development, maintenance and... more The aim of the ObNet model is to provide a framework for the design, development, maintenance and run-time support of large, long-lived, highly configurable systems for which the integration of different programming paradigms and environments plays a major role. The model defines some basic mechanisms which can be used in developing specialized software engineering environments for specific application domains. A

The aim of the ObNet model is to provide a framework for the design, development, maintenance and... more The aim of the ObNet model is to provide a framework for the design, development, maintenance and run-time support of large, long-lived, highly configurable systems for which the integration of different programming paradigms and environments plays a major role. The model defines some basic mechanisms which can be used in developing specialized software engineering environments for specific application domains. A

Journal of Applied Physics, 2008

This work describes in detail the simultaneous enhancement of the upper critical field (Hc2) and ... more This work describes in detail the simultaneous enhancement of the upper critical field (Hc2) and the critical current density (Jc) of MgB2 bulk samples doped with nano-SiC particles, as well as single-walled and double-walled (dw) carbon nanotubes (CNTs). The magnetization properties were examined in a superconducting quantum interference device magnetometer, and four-probe transport measurements were performed using a 50T pulsed magnet to determine Hc2(T ). We found that the Jc enhancement is similar in all doped samples at 5K but nano-SiC addition is more effective to improve the flux pinning in the high temperature range (T⩾20K); this improvement cannot solely be attributed to the C incorporation to the lattice but also to the presence of other types of defects (i.e., several kinds of nanoinclusions). CNTs produce a better C incorporation that is more effective to enhance Hc2 [i.e., dwCNT-doped samples reached a record Hc2(0)˜44T value for bulk MgB2]. All the Hc2(T ) curves obtained for different types of doping can be successfully described using a model for a two-gap superconductor in the dirty limit.

Solid State Communications, 2010

In this work the Ti 2InN phase is investigated by X-ray diffraction, magnetic and resistivity mea... more In this work the Ti 2InN phase is investigated by X-ray diffraction, magnetic and resistivity measurements. X-ray powder patterns suggest that all peaks can be indexed with the hexagonal phase of Cr 2AlC prototype. Electrical resistance as a function of temperature reveals superconductivity below 7.3 K. M(H) hysteresis loops show typical type-II superconductivity. Using R(H) versus T measurements we estimated μoH(0)˜10.8 T and ξ(0)˜55.2 Å. The results show unambiguously that Ti 2InN is the first nitride superconductor belonging to the M n+1 AX n family.

The glassy dynamics is a consequence of the elastic properties of the vortex matter, and in princ... more The glassy dynamics is a consequence of the elastic properties of the vortex matter, and in principle may occur in any superconductor. However, whereas a large amount of experimental evidence confirms glassiness in high Tc superconductors (HTS), the applicability of the whole framework developed to describe vortex matter in HTS to other superconducting materials is unclear. In this framework, the particular creep behavior of MgB2, larger than creep of conventional superconductor materials but much lower than HTS one, had precluded a complete understanding of the vortex regimes in this material. In this work we present an experimental study of relaxation processes of pure MgB2 bulk samples measured by DC magnetization technique. We propose a novel self-consistent scaling method to analyze the data and extract the activation energies. The observed experimental behavior can be described in a glassy picture, with a unique critical exponent &mu~1, characteristic of collective creep in the intermediate vortex bundle regime.

Journal of Physics: Conference Series, 2009

Magnetization measurements in the mixed state of thick strips of carbon nanotube doped MgB2 in cr... more Magnetization measurements in the mixed state of thick strips of carbon nanotube doped MgB2 in crossed fields configurations are reported, together with numerical simulations performed with a geometry equivalent to the sample shape. The samples were subjected to magnetic field components along mutually perpendicular directions, an oscillatory field in one direction and a remanent magnetization in the perpendicular direction. The

Superconductor Science & Technology, 2009

We report on measurements and numerical simulations of the behavior of MgB 2 superconductors when... more We report on measurements and numerical simulations of the behavior of MgB 2 superconductors when magnetic field components are applied along mutually perpendicular directions. By closely matching the geometry in simulations and measurements, full quantitative agreement is found. The critical state theory and a single phenomenological law, i.e. the field dependence of the critical current density J c (B), are sufficient for a full quantitative description of the measurements. These were performed in thick strips of carbon nanotube doped MgB 2 samples. Magnetization was measured in two orthogonal directions using a SQUID magnetometer. Magnetic relaxation effects induced by the application of an oscillatory perpendicular field were observed and simulated numerically. The measurements confirm the numerical predictions, that two relaxation regimes appear, depending on the amplitude of the applied magnetic field. The overall agreement constitutes a convincing validation of the critical state model and the numerical procedures used.

Journal of Physics: Conference Series, 2009

In this work we study the microstructural and superconducting properties of doped and undoped bul... more In this work we study the microstructural and superconducting properties of doped and undoped bulk MgB2 samples prepared by solid-state reaction, with 0 and 2.5 %at. nominal TiO2 nanotubes contents, annealed at different temperatures in the 750-900°C range. We discuss the Tc, Jc and Hc2 performance and their correlation with the different synthesis parameters.

IEEE Transactions on Applied Superconductivity, 2005

We present an analysis of the effect of SiC doping and heat treatments, including hot isostatic p... more We present an analysis of the effect of SiC doping and heat treatments, including hot isostatic pressing (HIPing), on the microstructure, magnetization and transport properties of MgB2 wires and coils prepared by the powder in tube (PIT) method. The HIPed wires have higher critical current densities (Jc) than the annealed wires, especially at high temperatures and magnetic fields, and higher irreversibility field. The improvements are due to the reduction of porosity and to a high density of structural defects, which are the likely source of vortex pinning. We demonstrate that the high-quality properties mentioned above can be retained in longer wires. At 25 K our champion 6-layer coil, made with 25 meters of wire, was able to generate a field of 1 T at self-field. We were able to achieve even higher Jc's in another coil by combining the addition of SiC and HIPing. We also observed a larger upper critical field due to the SiC doping, which drives the sample to the dirty limit.

IEEE Transactions on Applied Superconductivity, 2009

Starting from commercial MgB2 325 mesh powder, we further reduced the agglomerates by attrition m... more Starting from commercial MgB2 325 mesh powder, we further reduced the agglomerates by attrition milling in nitrogen atmosphere to minimize oxidation. The milling time was varied between 10 and 40 hours, using two different types of milling media: yttria stabilized zirconia and CW balls. We studied the influence of milling time and milling media on the broadening of x-ray diffraction peaks and the superconducting properties of the powders. A highly energetic milling markedly decreased the crystallite size but damaged the superconducting properties. We observed a decrease of the Tc, consistent with the observed crystallinity loss. We prepared tapes with the 40-hours-milled powders and analyzed the resulting microstructures when using a soft (silver) and a hard (stainless steel) metal sheath, heat treated for 1 hour at 615degC in argon. This temperature was chosen after observing the existing reactions between magnesium diboride and silver by DTA analysis of the powders, so as to minimize the reaction at the superconductor-silver interface. We characterized the superconducting properties by determining the magnetic Jc in a SQUID. We performed 4-point bending micro-tests on the tapes to evaluate their mechanical strength.

IEEE Transactions on Applied Superconductivity, 2011

Starting from commercial MgB 2 powder of 325 mesh, we further reduced the agglomerates by attriti... more Starting from commercial MgB 2 powder of 325 mesh, we further reduced the agglomerates by attrition milling in nitrogen atmosphere to minimize oxidation. Using different milling media (tungsten carbide, yttria stabilized zirconium oxide and stainless steel balls), we obtained different milling energies and, consequently, powders with different strain states. Crystallite size and micro-strain within the grains were estimated by x-ray diffraction. We investigated the changes in the superconducting properties with the use of different milling media by measuring the magnetic moment as a function of temperature in a SQUID magnetometer, after zero field cooling. Single-filament stainless steel-sheathed wires and tapes were prepared with the obtained powders. The flexural properties of the tapes were determined by 4-point bending micro-tests. The use of a precursor powder with a higher strain resulted in more flexible wires and tapes, with lower flexural strength. Three different regions were determined for the maximum normal stress-strain curves. Some in-situ monel-sheathed hollow wires and ex-situ titanium-sheathed tapes and monel-sheathed 7-filament tapes were measured for comparative purposes. We discuss the correlation between sheath yielding and superconducting core cracking with the possible critical current degradation due to mechanical failure of the wires and tapes.

Solid State Communications, 2010

In this work the Ti 2 InN phase is investigated by X-ray diffraction, magnetic and resistivity me... more In this work the Ti 2 InN phase is investigated by X-ray diffraction, magnetic and resistivity measurements. X-ray powder patterns suggest that all peaks can be indexed with the hexagonal phase of Cr 2 AlC prototype. Electrical resistance as a function of temperature reveals superconductivity below 7.3 K. M(H) hysteresis loops show typical type-II superconductivity. Using R(H) versus T measurements we estimated µ o H c2 (0) ∼ 10.8 T and ξ (0) ∼ 55.2 Å. The results show unambiguously that Ti 2 InN is the first nitride superconductor belonging to the M n+1 AX n family.

IEEE Transactions on Applied Superconductivity, 2009

Abstract—Starting from commercial MgB2 325 mesh powder, we further reduced the agglomerates by at... more Abstract—Starting from commercial MgB2 325 mesh powder, we further reduced the agglomerates by attrition milling in ni-trogen atmosphere to minimize oxidation. The milling time was varied between 10 and 40 hours, using two different types of milling media: yttria stabilized ...

Journal of Physics: Conference Series, 2008

We present a study on the angular dependence of the critical current density (Jc) of SiC-doped Mg... more We present a study on the angular dependence of the critical current density (Jc) of SiC-doped MgB2 tapes fabricated by powder-in tube (PIT) with stainless steel (SS) as sheath material. The microstructure and texturing of the tapes are analysed to understand the effects of the rolling degree on the superconducting properties. The microstructure is studied by x-ray diffraction and scanning

IEEE Transactions on Applied Superconductivity, 2009

Abstract—Starting from commercial MgB2 325 mesh powder, we further reduced the agglomerates by at... more Abstract—Starting from commercial MgB2 325 mesh powder, we further reduced the agglomerates by attrition milling in ni-trogen atmosphere to minimize oxidation. The milling time was varied between 10 and 40 hours, using two different types of milling media: yttria stabilized ...

Journal of Physics: Conference Series, 2008

In this work a combination of stainless steel, copper, titanium and silver are used as sheath mat... more In this work a combination of stainless steel, copper, titanium and silver are used as sheath materials to fabricate SiC doped MgB2 wires and tapes by the powder-in-tube (PIT) method. The samples are cold deformed to the final dimension with several intermediate and final heat treatments between 200°C and 900°C. The microstructure and phase composition of the tapes are followed during the deformation and heat treatment processes by Scanning Electron Microscopy (SEM) and X-Ray Diffractometry (XRD). Critical current densities (Jc) were determined by magnetization. The correlation between the superconducting properties and the microstructural characteristics is discussed.

Superconductor Science & Technology, 2007

The use of MgB2 in superconducting applications still awaits for the development of a MgB2-based ... more The use of MgB2 in superconducting applications still awaits for the development of a MgB2-based material where both current-carrying performance and critical magnetic field are optimized simultaneously. We achieved this by doping MgB2 with double-wall carbon nanotubes (DWCNT) as a source of carbon in polycrystalline samples. The optimum nominal DWCNT content for increasing the critical current density, Jc is in the range 2.5-10%at depending on field and temperature. Record values of the upper critical field, Hc2(4K) = 41.9 T (with extrapolated Hc2(0) ~ 44.4 T) are reached in a bulk sample with 10%at DWCNT content. The measured Hc2 vs T in all samples are successfully described using a theoretical model for a two-gap superconductor in the dirty limit first proposed by Gurevich et al.