D. Gajda - Academia.edu (original) (raw)

Papers by D. Gajda

Applied Physics Letters, 2016

Superconducting MgB2MgB_2MgB2 wires in Cu, GlidCop or Monel sheath with Nb or Fe barrier are prepared. ... more Superconducting MgB2MgB_2MgB2 wires in Cu, GlidCop or Monel sheath with Nb or Fe barrier are prepared. Wires vary by sheath material, number of superconducting cores and their chemical composition. Wires are HIP-ed (Hot Isostatic Pressing) at various temperatures ($600-800^oC$) and pressure (up to 1.4 GPa). SEM pictures of cross sections are investigated in order to investigate barrier reactivity and cracking, superconducting material density and grain sizes. Transport measurements are made in magnetic field up to 14 T leading to calculations of critical current density jcj_cjc and global pinning force FpF_pFp. Improvement of transport properties due to higher density of superconducting material is shown.

Journal of Alloys and Compounds, 2015

ABSTRACT

Materials Letters, 2015

We present a new method for detecting damage to Nb barriers in MgB 2 wires by using a four-contac... more We present a new method for detecting damage to Nb barriers in MgB 2 wires by using a four-contact probe. The transport measurements and scanning electron microscope images indicate that a newly identified jump in resistance means that there is damage to the Nb barrier. Damage detection is important for application because it allows us to avoid reactions between the filament and the sheath material, and to develop implementation methods for MgB 2 with high critical current density. Our methods for damage detection proposed in this paper are simple, fast, and easy to use.

Journal of Alloys and Compounds, 2015

We explored the incorporation of field sweep (constant current and rapidly increasing magnetic fi... more We explored the incorporation of field sweep (constant current and rapidly increasing magnetic field) into the four-probe method as a new technique to detect defects in barrier layers in superconducting MgB 2 wires. This method allows us to observe jumps in the electric field in low magnetic fields. The scanning electron microscopy results indicate that such a jump originates from cracks in Nb barriers and ex-situ MgB 2 barriers. Our research indicates that the field sweep allows us to detect damage to barriers that are made of superconducting materials. This method can be the basis for an industrial method for detecting damages in MgB 2 wires. These defects reduce the critical current of MgB 2 wire. Detection and removal of these defects will allow us to produce MgB 2 wires with ex-situ MgB 2 and Nb barriers that will have improved critical current density. Manufacturing of MgB 2 wires with new ex-situ MgB 2 barriers is a new technological concept. This type of barrier is cheaper and easier to manufacture, leading to cheaper MgB 2 wires. Moreover, we show that critical current can be measured by two methods: current sweep (constant magnetic field and quickly increasing current) and field sweep.

Superconductor Science and Technology, 2014

Unreacted MgB 2 wires were made at Hyper Tech Research, USA by a continuous tube forming and fill... more Unreacted MgB 2 wires were made at Hyper Tech Research, USA by a continuous tube forming and filling method using mixtures of Mg and B with and without SiC powder additions. All of the wires underwent hot isostatic pressure (HIP) treatment at the Institute of High Pressure. The first part of the wire was annealed at a pressure of 1 GPa, and the second part was annealed at 0.1 MPa. In this work, we show the influence of high pressure on critical current density (J c ), pinning force (F p ), critical temperature (T c ), irreversible magnetic fields (B irr ) and the F p scaling and microstructure of MgB 2 wires. The results obtained indicate that after annealing at high pressure, the MgB 2 wires show increases of J c and F p in high magnetic fields (8 T-12 T); in SiC doped MgB 2 wires, F pmax shifts to higher magnetic fields. We also compared the J c of the doped and undoped MgB 2 wires (without HIP and with HIP). The scanning electron microscope (SEM) results show that HIP increases the density of MgB 2 material and improves its uniformity.

Journal of Applied Physics, 2015

ABSTRACT The powder-in-tube (PIT) technique has been used to fabricate copper-sheathed magnesium ... more ABSTRACT The powder-in-tube (PIT) technique has been used to fabricate copper-sheathed magnesium diboride (MgB2) wires using an insitu reaction method. The effect of copper powder additions, magnesium–boron molar ratio and heat treatment is studied by SEM, XRD, transport critical current Ic(B) and resistivity ρ(T, B) measurements. The results show that addition of copper powder to the core of the wire accelerates the formation of MgB2 and hence increases its amount and greatly decreases the amount of Mg–Cu intermetallic phases present in the core of the wire after heat treatment. Excess magnesium proved to be effective in compensating for Mg loss due to interdiffusion with the Cu of the wire sheath and resulted in less unreacted boron in the core for wires without added Cu, but seems to oppose the accelerated formation of MgB2 in Cu added wires. The highest critical current density, 2.8 × 104 A cm−2 at 3 T and 4.2 K, was achieved for a wire with a stoichiometric Mg:B ratio and 3 at.% added copper powder heat treated at 700 °C for 5 min.

Superconductor Science and Technology, 2015

Multifilamentary MgB 2 wires were annealed under the high pressure of low-friction, solid state m... more Multifilamentary MgB 2 wires were annealed under the high pressure of low-friction, solid state media such as BN and graphite powders. The idea was to replace the hot isostatic pressing in argon medium, which is beneficial to wires transport properties but is difficult for application on an industrial scale. The experimental results show that annealing in BN or graphite under 200 MPa leads to enhancement of the critical current, similar to that observed earlier for high pressure argon annealing. An unwanted effect of the process is the flattening of the round wires, which after the treatment yields an elliptical cross section with b to a ratio of around 85 ± 5%. Comparison of critical currents and microstructure of samples synthesized with different parameters are presented.

Physics Procedia, 2012

ABSTRACT Recent advances in the design of Cu-sheathed in situ MgB2 wires have shown promising res... more ABSTRACT 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.

Acta Physica Polonica A, 2007

Superconductor Science and Technology, 2013

ABSTRACT Recent results on powder-in-tube in situ Cu-sheathed MgB2 wires have shown that copper p... more ABSTRACT 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.

Physica C: Superconductivity, 2012

ABSTRACT The powder-in-tube (PIT) technique has been used to fabricate copper-sheathed magnesium ... more ABSTRACT The powder-in-tube (PIT) technique has been used to fabricate copper-sheathed magnesium diboride (MgB2) wires using an insitu reaction method. The effect of copper powder additions, magnesium–boron molar ratio and heat treatment is studied by SEM, XRD, transport critical current Ic(B) and resistivity ρ(T, B) measurements. The results show that addition of copper powder to the core of the wire accelerates the formation of MgB2 and hence increases its amount and greatly decreases the amount of Mg–Cu intermetallic phases present in the core of the wire after heat treatment. Excess magnesium proved to be effective in compensating for Mg loss due to interdiffusion with the Cu of the wire sheath and resulted in less unreacted boron in the core for wires without added Cu, but seems to oppose the accelerated formation of MgB2 in Cu added wires. The highest critical current density, 2.8 × 104 A cm−2 at 3 T and 4.2 K, was achieved for a wire with a stoichiometric Mg:B ratio and 3 at.% added copper powder heat treated at 700 °C for 5 min.

Low Temperature Physics, 2010

The effect of equal-channel, multiple-angle pressing combined with hydroextrusion and drawing, on... more The effect of equal-channel, multiple-angle pressing combined with hydroextrusion and drawing, on the critical current density, pinning force, and superconducting transition temperature of bimetallic Nb+ 60 at.% Ti wires is examined.

Low Temperature Physics, 2008

The influence of combined deformation, including equal-channel multiangle pressing (ECMAP), and h... more The influence of combined deformation, including equal-channel multiangle pressing (ECMAP), and heat treatment on the critical current density of a superconducting wire made from the alloy Nb+60 at. % Ti is investigated. It is found that the combined deformation, including ECMAP, can increase the critical current density by up to two times. The relationship between the character of the structural

Journal of Superconductivity and Novel Magnetism, 2012

ABSTRACT Superconducting tapes from MgB2 and powders of magnetic Ni, Co, and non-magnetic Ti were... more ABSTRACT Superconducting tapes from MgB2 and powders of magnetic Ni, Co, and non-magnetic Ti were fabricated by cold-processed powder-in-tube (PIT) method. The cupronickel was used as sheath material and no heat treatment was applied. The increasing of critical current was observed in the samples with additions of nickel and titanium. The microstructure and phase analysis of tape core was performed by X-ray diffraction spectroscopy. A direct correlation between type and amount of additives, and the critical current of the tapes has been observed.

Journal of Superconductivity and Novel Magnetism, 2009

An improvement of NbTi alloy functional properties by equal-channel multi-angle pressing (ECMAP) ... more An improvement of NbTi alloy functional properties by equal-channel multi-angle pressing (ECMAP) combined with hydrostatic extrusion, drawing and thermal treatment is revealed. The ECMAP method allows to increase the billet accumulated deformation with preserving its initial dimensions. The formed highly dispersed and homogeneous nanocrystalline structure with a more uniform distribution of alpha-phase precipitations as a result of ECMAP treatment improves

IEEE Transactions on Applied Superconductivity, 2000

Wires with 6 filaments of rmMgB2{\rm MgB}_{2}rmMgB2 cores surrounded by a Nb barrier, and Cu, Monel and Gli... more Wires with 6 filaments of rmMgB2{\rm MgB}_{2}rmMgB2 cores surrounded by a Nb barrier, and Cu, Monel and Glidcop sheath, drawn by Hyper Tech Inc. to diameters of 0.83 mm, have been treated in a Hot Isostatic Pressure process under high Ar pressures. The pressure of the HIP varied in different processes in order to find the optimal sintering conditions to

Applied Physics Letters, 2016

Superconducting MgB2MgB_2MgB2 wires in Cu, GlidCop or Monel sheath with Nb or Fe barrier are prepared. ... more Superconducting MgB2MgB_2MgB2 wires in Cu, GlidCop or Monel sheath with Nb or Fe barrier are prepared. Wires vary by sheath material, number of superconducting cores and their chemical composition. Wires are HIP-ed (Hot Isostatic Pressing) at various temperatures ($600-800^oC$) and pressure (up to 1.4 GPa). SEM pictures of cross sections are investigated in order to investigate barrier reactivity and cracking, superconducting material density and grain sizes. Transport measurements are made in magnetic field up to 14 T leading to calculations of critical current density jcj_cjc and global pinning force FpF_pFp. Improvement of transport properties due to higher density of superconducting material is shown.

Journal of Alloys and Compounds, 2015

ABSTRACT

Materials Letters, 2015

We present a new method for detecting damage to Nb barriers in MgB 2 wires by using a four-contac... more We present a new method for detecting damage to Nb barriers in MgB 2 wires by using a four-contact probe. The transport measurements and scanning electron microscope images indicate that a newly identified jump in resistance means that there is damage to the Nb barrier. Damage detection is important for application because it allows us to avoid reactions between the filament and the sheath material, and to develop implementation methods for MgB 2 with high critical current density. Our methods for damage detection proposed in this paper are simple, fast, and easy to use.

Journal of Alloys and Compounds, 2015

We explored the incorporation of field sweep (constant current and rapidly increasing magnetic fi... more We explored the incorporation of field sweep (constant current and rapidly increasing magnetic field) into the four-probe method as a new technique to detect defects in barrier layers in superconducting MgB 2 wires. This method allows us to observe jumps in the electric field in low magnetic fields. The scanning electron microscopy results indicate that such a jump originates from cracks in Nb barriers and ex-situ MgB 2 barriers. Our research indicates that the field sweep allows us to detect damage to barriers that are made of superconducting materials. This method can be the basis for an industrial method for detecting damages in MgB 2 wires. These defects reduce the critical current of MgB 2 wire. Detection and removal of these defects will allow us to produce MgB 2 wires with ex-situ MgB 2 and Nb barriers that will have improved critical current density. Manufacturing of MgB 2 wires with new ex-situ MgB 2 barriers is a new technological concept. This type of barrier is cheaper and easier to manufacture, leading to cheaper MgB 2 wires. Moreover, we show that critical current can be measured by two methods: current sweep (constant magnetic field and quickly increasing current) and field sweep.

Superconductor Science and Technology, 2014

Unreacted MgB 2 wires were made at Hyper Tech Research, USA by a continuous tube forming and fill... more Unreacted MgB 2 wires were made at Hyper Tech Research, USA by a continuous tube forming and filling method using mixtures of Mg and B with and without SiC powder additions. All of the wires underwent hot isostatic pressure (HIP) treatment at the Institute of High Pressure. The first part of the wire was annealed at a pressure of 1 GPa, and the second part was annealed at 0.1 MPa. In this work, we show the influence of high pressure on critical current density (J c ), pinning force (F p ), critical temperature (T c ), irreversible magnetic fields (B irr ) and the F p scaling and microstructure of MgB 2 wires. The results obtained indicate that after annealing at high pressure, the MgB 2 wires show increases of J c and F p in high magnetic fields (8 T-12 T); in SiC doped MgB 2 wires, F pmax shifts to higher magnetic fields. We also compared the J c of the doped and undoped MgB 2 wires (without HIP and with HIP). The scanning electron microscope (SEM) results show that HIP increases the density of MgB 2 material and improves its uniformity.

Journal of Applied Physics, 2015

ABSTRACT The powder-in-tube (PIT) technique has been used to fabricate copper-sheathed magnesium ... more ABSTRACT The powder-in-tube (PIT) technique has been used to fabricate copper-sheathed magnesium diboride (MgB2) wires using an insitu reaction method. The effect of copper powder additions, magnesium–boron molar ratio and heat treatment is studied by SEM, XRD, transport critical current Ic(B) and resistivity ρ(T, B) measurements. The results show that addition of copper powder to the core of the wire accelerates the formation of MgB2 and hence increases its amount and greatly decreases the amount of Mg–Cu intermetallic phases present in the core of the wire after heat treatment. Excess magnesium proved to be effective in compensating for Mg loss due to interdiffusion with the Cu of the wire sheath and resulted in less unreacted boron in the core for wires without added Cu, but seems to oppose the accelerated formation of MgB2 in Cu added wires. The highest critical current density, 2.8 × 104 A cm−2 at 3 T and 4.2 K, was achieved for a wire with a stoichiometric Mg:B ratio and 3 at.% added copper powder heat treated at 700 °C for 5 min.

Superconductor Science and Technology, 2015

Multifilamentary MgB 2 wires were annealed under the high pressure of low-friction, solid state m... more Multifilamentary MgB 2 wires were annealed under the high pressure of low-friction, solid state media such as BN and graphite powders. The idea was to replace the hot isostatic pressing in argon medium, which is beneficial to wires transport properties but is difficult for application on an industrial scale. The experimental results show that annealing in BN or graphite under 200 MPa leads to enhancement of the critical current, similar to that observed earlier for high pressure argon annealing. An unwanted effect of the process is the flattening of the round wires, which after the treatment yields an elliptical cross section with b to a ratio of around 85 ± 5%. Comparison of critical currents and microstructure of samples synthesized with different parameters are presented.

Physics Procedia, 2012

ABSTRACT Recent advances in the design of Cu-sheathed in situ MgB2 wires have shown promising res... more ABSTRACT 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.

Acta Physica Polonica A, 2007

Superconductor Science and Technology, 2013

ABSTRACT Recent results on powder-in-tube in situ Cu-sheathed MgB2 wires have shown that copper p... more ABSTRACT 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.

Physica C: Superconductivity, 2012

ABSTRACT The powder-in-tube (PIT) technique has been used to fabricate copper-sheathed magnesium ... more ABSTRACT The powder-in-tube (PIT) technique has been used to fabricate copper-sheathed magnesium diboride (MgB2) wires using an insitu reaction method. The effect of copper powder additions, magnesium–boron molar ratio and heat treatment is studied by SEM, XRD, transport critical current Ic(B) and resistivity ρ(T, B) measurements. The results show that addition of copper powder to the core of the wire accelerates the formation of MgB2 and hence increases its amount and greatly decreases the amount of Mg–Cu intermetallic phases present in the core of the wire after heat treatment. Excess magnesium proved to be effective in compensating for Mg loss due to interdiffusion with the Cu of the wire sheath and resulted in less unreacted boron in the core for wires without added Cu, but seems to oppose the accelerated formation of MgB2 in Cu added wires. The highest critical current density, 2.8 × 104 A cm−2 at 3 T and 4.2 K, was achieved for a wire with a stoichiometric Mg:B ratio and 3 at.% added copper powder heat treated at 700 °C for 5 min.

Low Temperature Physics, 2010

The effect of equal-channel, multiple-angle pressing combined with hydroextrusion and drawing, on... more The effect of equal-channel, multiple-angle pressing combined with hydroextrusion and drawing, on the critical current density, pinning force, and superconducting transition temperature of bimetallic Nb+ 60 at.% Ti wires is examined.

Low Temperature Physics, 2008

The influence of combined deformation, including equal-channel multiangle pressing (ECMAP), and h... more The influence of combined deformation, including equal-channel multiangle pressing (ECMAP), and heat treatment on the critical current density of a superconducting wire made from the alloy Nb+60 at. % Ti is investigated. It is found that the combined deformation, including ECMAP, can increase the critical current density by up to two times. The relationship between the character of the structural

Journal of Superconductivity and Novel Magnetism, 2012

ABSTRACT Superconducting tapes from MgB2 and powders of magnetic Ni, Co, and non-magnetic Ti were... more ABSTRACT Superconducting tapes from MgB2 and powders of magnetic Ni, Co, and non-magnetic Ti were fabricated by cold-processed powder-in-tube (PIT) method. The cupronickel was used as sheath material and no heat treatment was applied. The increasing of critical current was observed in the samples with additions of nickel and titanium. The microstructure and phase analysis of tape core was performed by X-ray diffraction spectroscopy. A direct correlation between type and amount of additives, and the critical current of the tapes has been observed.

Journal of Superconductivity and Novel Magnetism, 2009

An improvement of NbTi alloy functional properties by equal-channel multi-angle pressing (ECMAP) ... more An improvement of NbTi alloy functional properties by equal-channel multi-angle pressing (ECMAP) combined with hydrostatic extrusion, drawing and thermal treatment is revealed. The ECMAP method allows to increase the billet accumulated deformation with preserving its initial dimensions. The formed highly dispersed and homogeneous nanocrystalline structure with a more uniform distribution of alpha-phase precipitations as a result of ECMAP treatment improves

IEEE Transactions on Applied Superconductivity, 2000

Wires with 6 filaments of rmMgB2{\rm MgB}_{2}rmMgB2 cores surrounded by a Nb barrier, and Cu, Monel and Gli... more Wires with 6 filaments of rmMgB2{\rm MgB}_{2}rmMgB2 cores surrounded by a Nb barrier, and Cu, Monel and Glidcop sheath, drawn by Hyper Tech Inc. to diameters of 0.83 mm, have been treated in a Hot Isostatic Pressure process under high Ar pressures. The pressure of the HIP varied in different processes in order to find the optimal sintering conditions to