Powder In Tube Technique Research Articles

Rolling characteristics of multi-filamentary Bi-2223/AgAu tapes and roller diameter′s effect on transport properties

37-filamentary Bi-2223/ AgAu tapes were fabricated by powder in tube technique. The round wire (φ1.51 mm) were rolled to 0.30 mm tapes by 150 mm, 250 mm and 300 mm roller through flat rolling, respectively. A fundamental understanding of filaments deformation and roll diameter′s effect on critical current properties were systematically investigated. By analyzing the stress distribution on cross section during rolling, it can be understood that the deformation of the filaments at different positions during the rolling of multi-filamentary Bi-2223/AgAu tape is inhomogeneous. According to the deformation extent of filaments, the cross section of the tape can be divided into three areas, namely easy deformation zone, difficult deformation zone and free deformation zone. The average filament width in the free deformation zone is only 65.1 % of the filament width in the easy deformation zone. It can be noticed that the Jc values increase monotonously with increasing roller diameter. Due to more sufficiently deformed filament and flat interfaces, Jc reached the maximum value of 15.7 kA/cm2 on the 300 mm roller sample.

Effect of Cu Cladding on the Mechanical Properties of Iron Sheath Material in the Drawing of Superconducting MgB2 Wires

In the present study, a novel choice of sheath materials for drawing long superconducting MgB2 wire by using the powder-in-tube technique (PIT) is reported. This would eliminate the need for an intermediate strain-relieving annealing process and would reduce the time and cost of fabrication. Our strategy involved the use of a composite sheath instead of a sheath made of a single material. The relatively inert Fe constituted the inner sheath around the MgB2 powder while the Cu—which is capable of efficient heat dissipation—was used as the outer sheath. Important mechanical properties of the wire such as elastic modulus, ultimate tensile strength, yield strength, hardness, and microstructure were carefully studied at different stages of the drawing process using tensile and microhardness tests. To clearly delineate the effect of Cu cladding on the ductile behavior of the iron sheath, another MgB2 wire with only an Fe sheath was prepared; its mechanical properties were measured and compared with those of the composite Cu–Fe-sheathed MgB2 wire. After a few drawing steps, the composite Cu–Fe-sheathed wire showed a lower elastic modulus and tensile strength than those of its Fe sheath counterpart. While both types of wires showed an increase in hardness as the drawing process progressed, the composite-sheath wire consistently showed a lower hardness than that of its counterpart, implying its lower susceptibility to fracture; it can therefore be safely drawn to small diameters without the need for intermediate annealing during the wire drawing process.

An intermetallic powder-in-tube approach to increased flux-pinning in Nb3Sn by internal oxidation of Zr

We report on the development of multifilamentary Nb3Sn superconductors by a versatile powder-in-tube technique (PIT) that demonstrates a simple pathway to a strand with a higher density of flux-pinning sites that has the potential to increase critical current density beyond present levels. The approach uses internal oxidation of Zr-alloyed Nb tubes to produce Zr oxide particles within the Nb3Sn layer that act as a dispersion of artificial pinning centres (APCs). In this design, SnO2 powder is mixed with Cu5Sn4 powder within the PIT core that supplies the Sn for the A15 reaction with Nb1Zr filament tubes. Initial results show an average grain size of ∼38 nm in the A15 layer, compared to the 90–130 nm of typical APC-free high-Jc strands made by conventional PIT or Internal Sn processing. There is a shift in the peak of the pinning force curve from H/Hirr of ∼0.2 to ∼0.3 and the pinning force curves can be deconvoluted into grain boundary and point-pinning components, the point-pinning contribution dominating for the APC Nb-1wt%Zr strands.

The critical parameters in in-situ MgB2 wires and tapes with ex-situ MgB2 barrier after hot isostatic pressure, cold drawing, cold rolling and doping

MgB2 precursor wires were prepared using powder in tube technique by Institute of High Pressure PAS in Warsaw. All samples were annealed under isostatic pressure generated by liquid Argon in the range from 0.3 GPa to 1 GPa. In this paper, we show the effects of different processing routes, namely, cold drawing (CD), cold rolling (CR), hot isostatic pressure (HIP) and doping on critical current density (Jc), pinning force (Fp), irreversible magnetic-field (Birr), critical temperature (Tc), n value, and dominant pinning mechanism in MgB2/Fe wires with ex situ MgB2 barrier. The results show that medium pressures (∼0.35 GPa) lead to high Jc in low and medium magnetic fields (0 T – 9 T). On the other hand, higher pressures (∼1 GPa) lead to enhanced Jc in high magnetic fields (above 9 T). Transport measurements show that CD, CR, and HIP have small effects on Birr and Tc, but CD, CR, HIP, and doping enhance Jc and Fp in in situ MgB2 wires with ex situ MgB2 barrier. Transport measurements on in situ undoped MgB2 wire with ex situ MgB2 barrier yield a Jc of about 100 A/mm2 at 4.2 K in 6 T, at 10 K in 4 T and at 20 K in 2 T. The results also show that cold drawing causes increase of n value.

Magnetic investigation of silver sheathed Sr0.6K0.4Fe2As2 superconductor

Magnetic investigation of a silver sheathed Sr0.6K0.4Fe2As2 tape prepared by ex-situ powder-in-tube technique (PIT) is reported. A transition temperature of 34.2K was achieved. Dc magnetic measurements were performed in fields up to 14 T between 4.2 K and Tc. From hysteresis loops magnetic critical current densities Jc were determined. The tape exhibits excellent Jc performance. In low fields, the observed steep decline of Jc in increasing field is comparable to that measured in MgB2, although at a significantly lower absolute value. A kink-like crossover to a much flatter dependence at higher fields allows for a much better high field performance than that of MgB2. Such kink is also visible in the field dependence of the mean activation energies U, which were determined from magnetic relaxation measurements. The obtained U values are similar (< 40 meV at 4.2K and 1 T) to those of Bi2212 tapes, but an order of magnitude smaller in comparison with good MgB2 wires.

Process Developments And Applications Around The Powder In Tube Technique

The purpose of this presentation is to give an overview of techniques available to produce original optical fibers and application dedicated. Some alternative fabrication solutions to the well-know stack and draw technique will be developed, following by the interest to join the stack and draw technique to other ones like Repusil® Technique, Rod in Tube and finally the Powder in Tube methods, first described by the Bell Lab in the seventies and up to date since some years by several groups in the world. Realization of performing optical devices such as light sources or optical sensors can be purposed by this two last original ways.

Fabrication and transport properties of ex situ powder-in-tube (PIT) processed (Ba,K)Fe2As2 superconducting wires

Soon after the discovery of Fe based superconductors, attempts of wire fabrication started using a powder-in-tube (PIT) technique, because their high transition temperature and extremely high upper critical field bring the hope of high field applications. Although the transport critical current density, Jc, reported in the early stage was disappointingly low, it has been rapidly improved during the past one year to the orders of 104 and 105 A/cm2 by optimizing various processing parameters of the PIT technique. This paper reports one of the works which brought such rapid progress. (Ba,K)Fe2As2 superconducting wires were fabricated by an ex situ powder-in-tube (PIT) process using a melt processed precursor material. The paper also discusses the influence of Ag addition, critical current irreversibility, critical current anisotropy of the tape sample, and finally future prospect in the development of Fe based superconducting wires.

Fabrication and magnetoresistivit of ex-situ processed MgB2/Fe monofilament tapes without any intermediate annealing

We have fabricated MgB2/Fe monofilament wires and tapes by a powder-in tube (PIT) technique, using an ex-situ process without any intermediate annealing. MgB2/Fe monofilament tapes were annealed at 650–1,050°C for 60 min and 950°C for 30–240 min. We have investigated the effect of annealing temperatures and times on the formation of MgB2 phase, activation energy, temperature dependence of irreversibility field H irr(T) and upper critical field H c2(T), transition temperature (T c), lattice parameters (a and c), full width at half maximum, crystallinity, resistivity, residual resistivity ratio, active cross-sectional area fraction and critical current densities. We observed that the activation energies of the MgB2/Fe monofilament samples increased with increasing annealing temperature up to 950°C and with increasing annealing time up to 60 min while it decreased with increasing magnetic field. For the MgB2/Fe monofilament tape, the slope of the H c2–T and H irr–T curves decreased with increasing annealing temperature from 850 to 950°C as well as with increasing annealing time from 30 to 60 min. The transport and microstructure investigations show that T c, J c and microstructure properties are remarkably enhanced with increasing annealing temperature. The highest value of critical current density is obtained for the sample annealed at 950°C for 60 min. The J c and T c offset values of the sample annealed at 950°C for 60 min were found to be 260.43 A/cm2 at 20 and 38.1 K, respectively.

Fabrication of Ti doped MgB 2/Cu superconducting wires by SHS method in an unsealed furnace

Mg 0.9Ti 0.1B 2/Cu wires have been successfully synthesized by the powder-in-tube (PIT) technique combined with the self-propagating high-temperature synthesis (SHS) method in an unsealed furnace. The analysis includes the studies of the sample microstructure, phase composition, critical transition temperature T c and critical current density J c . The experiments show that the PIT technique combined with the SHS method is effective in reducing the Mg volatilization and oxidation. There is little reaction between Mg and Cu in the SHS process, but with the MgCu 2 and CuO phases, the reaction does occur in the inner sheath wall of the copper tube. The findings also indicate that there is little MgO in the sample. The sample has a very strong flux pinning ability at the low magnetic fields since the TiB 2 phase may prevent the growth of MgB 2 grains and lead to a favorable effect on grain refinement. The wires exhibit a high critical current density, e.g. 2.7 × 10 5 A/cm 2 in the 1.0 T field at 4.2 K and 1.3 × 10 5 A/cm 2 in the 2.0 T field at 4.2 K.

ナノ複合化技術を活用したMg合金切削屑のリサイクル

Optimization of the recycling process of Mg alloy scrap chips to obtain superconducting MgB2 via a nano-mixing technology was carried out. In the present process, the an attrition type mechanical milling process without a milling media was used to mix and grind AZ31 scrap chips with commercial B powder. Fine AZ31/B powder mixture can be fabricated via the mechanical milling process in vacuum. The milling process can also reduce the volume of the mixture up to a half of the mixture by the blending in a plastic bottle. An AZ31/boron mixture via the mechanical milling was successfully reacted completely to MgB2 by heating at 700℃ for 3 h in reduced-pressure Ar gas, 50% shorter in reaction time than the mixture by blending in a PE bottle. The powder-in-tube (PIT) technique for producing an MgB2 coil can be conducted by using pulsed electric current sintering (PECS) with the recycled MgB2 powder encapsulated in a stainless steel tube. Dense MgB2 with less MgB4 phase can be obtained by the PIT technique with PECS. The PIT process is also useful to suppress the evaporation of Mg from MgB2 powder during sintering. Any significant reaction between stainless steel and MgB2 was not observed.

MgB2 multifilamentary tapes: microstructure, chemical composition and superconductingproperties

Multifilamentary Ni-sheathed Cu-stabilizedMgB2 tapes with a criticalcurrent density of 2.0 × 105 A cm−2 (at 20 K and 1 T) were prepared by a powder in tube technique, using pre-reactedMgB2 powders. The microstructure and chemical composition of the superconducting core and theMgB2–Ni interface were studied using SEM, EPMA and TEM. A quick, reliable andstandard-less method of B quantification using SEM-EDX is established for the analysis ofMgB2 wires and tapes. Carbon-contamination-free sample preparation was crucial for the analysisof boron.The typical size of MgB2 colonies, i.e. the arrangement of several well connected grains, in theMgB2 filaments wasbetween 1 and 6 µm. The colonies are structurally well connected to each other, althoughsub-micrometre-sized voids are present. The B to Mg mole fraction ratio in theMgB2 colonies was found to be close to two and the O mole fraction is less than 1 at.%. The typical size of theMgB2 grains in thecolonies is about 0.5–1 µm; however, numerous grains of size 30–200 nm are also present.MgO precipitates of the size of 15–70 nm were found in theMgB2 grains. Long straight dislocations with a density of1 × 1010 cm−2 are observed. Non-superconducting layers which appear as oxidelayers in SEM and TEM samples were found on the surface of theMgB2 colonies and yield poor connectivity between the colonies. It is expectedthat these layers yield a significant reduction of the critical current densityJc.A 10 µm wide intermetallic reaction layer of B, Mg and Ni is formed at theMgB2–Ni interface. Reductionof the MgB2 grain size bymilling of starting MgB2 powder and elimination of non-superconducting layers aroundMgB2 colonies could further enhance the critical current density because of improved pinning andconnectivity between colonies.

Preparation and superconducting properties of Ag/Hg-1223 PIT wires

Silver wires of the superconducting phase (Hg 0.8Re 0.2)Ba 2Ca 2Cu 3O 8+ δ (Hg,Re-1223), were prepared by the powder in tube technique followed by a post annealing treatment in a sealed quartz tube. The sintering reaction was carried out inside the quartz tube using a superconducting ceramic pellet and a drop of Hg(l) as external mercury sources. We have studied the amalgamation process in order to avoid the decomposition of the Hg,Re-1223 due to the imminent amalgamation between the silver and the Hg from the superconducting phase. Different annealing treatments of the wires were studied in order to increase the superconducting properties. We have found that using additional liquid Hg as an external source the amalgamation process can be controlled. The critical current density ( J c) values obtained were similar to the bulk specimens.

Thermal and phase characterization of Bi-2223 superconductors

Advances in processing and fabrication of high critical current density ( J c) long length conductors, silver sheathed superconducting magnets and coils from silver sheathed Bi-2223 tapes, pancake coil magnets from 1 to 10 m length and mono-multifilament Bi-2223/2212 high critical temperature superconductors by powder in tube technique continue to bring these materials closer to commercial applications. In our laboratory Bi-2223 conductors doped with Sm, Nb, Ag and Gd were prepared by the heat treatment of rapidly quenched glass precursors. Activation energies and frequency factors, employing different models were evaluated. It was observed that both peritectic transition and reaction rates were dependent on ambient atmosphere. The resistivity measurements revealed that the critical temperature decreases with increasing Gd, Sm, Nb, and Ag concentration. The critical current density J c measured at 77 K from I–V data shows an increase with silver addition. The critical current densities of silver sheathed tapes using the powder in tube were found to be in the range 7×10 8 A/m 2. X-ray diffraction results showed that the volume fraction of the high- T c (2223) phase decreases and that of low- T c (2212) phase increases with increase of these rare-earth ion contents. These results are explained on the basis of possible variation of hole concentration with trivalent rare-earth ion substitution and also by considering the magnetic nature of the substituted ion in the composition.

Effect of γ-irradiation on silver-sheathed Bi/sub 1.6/Pb/sub 0.4/Ba/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10/ tapes

Specimens with nominal composition Bi/sub 1.6/Pb/sub 0.4/Ba/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10/ were prepared using the powder-in tube technique. The effect of /spl gamma/-irradiation at room temperature on the superconducting properties have been investigated using x-ray diffraction, resistivity measurements and I-V characteristics. The intensities of the main diffraction peaks decrease by about 25%, however, the peak positions do not change with /spl gamma/-irradiation up to a dose of 400 MR. The normal state resistance R(T) increases gradually up to a dose of 100 MR, whereas at higher doses, the effect of irradiation becomes rather negligible. The transition temperature T/sub c/ decrease slightly and the transition temperature width /spl Delta/T broadens at doses below 100 MR with almost no change at higher doses up to 400 MR. At relatively low magnetic fields and low /spl gamma/ doses, the critical current densities J/sub c/(B) increase with /spl gamma/-irradiation, while the effect of /spl gamma/-irradiation at relatively high magnetic fields is hardly observable. These results are discussed and explained in terms of the effect of /spl gamma/-rays on the weak links grain boundaries and Josephson junctions between the grains.

Transport behavior and critical current densities in MgB2 wires

We report on the transport and magnetization properties of MgB2 wires fabricated by a powder-in-tube (PIT) technique. Temperature and magnetic-field-dependent resistivity displays a high conductivity and upper critical field Hc2 generally observed in dense samples. The electronic mass anisotropy γ≈1.3±0.15 predicts some texturing in the wire. Our data on transition temperature TC, Hc2, and both magnetic and transport critical current density Jc indicate that MgB2 can be manufactured in a wire form using a PIT technique and required engineering Jc can be achieved on further optimization.

内部酸化Ａｇ‐（ＭｇＮｉ）ＯｘシースＢｉ系超伝導テープ線材の臨界電流密度におよぼす応力・ひずみと磁界の影響

High strength Ag based alloy tubes with homogeneously dispersed very fine (Mg0.8Ni0.2at%)oxides and (Mg0.5Ni0.2at%)oxides were prepared by internal oxidation. Using the tubes we fabricated high strength Bi-2223 and Bi-2212 multifilamentary tapes with 7 filaments by the powder in tube technique, which have three different arrangements of sheath material such as inner/outer sheaths of Ag alloy/Ag alloy, Ag/Ag alloy and Ag/Ag. For the tapes we examined the microstructures and the critical current IC, especially IC under tensile stress and strain in a self magnetic field at 77K and also usual critical current density JC vs. magnetic field curves at 4.2K. The IC under tensile stress and strain are improved for the high strength sheath tapes, especially those tapes with Ag/Ag alloy arrangement. The JC strongly depends on the inner sheath material, showing high JC for the Ag/Ag and Ag/Ag alloy arrangements. For the tapes with Ag alloy/Ag alloy arrangement some swellings appear in each filament on fabrication and heat-treatment process. Around the swellings observed are some voids and highly mis-aligned grains. This induces the decrease in JC on the connectivity of superconducting grains and also JC under the stress and strain.

Texture development of HTS powder-in-tube conductors

An overview of the fabrication and electromagnetic properties of high-temperature conductors processed by the powder-in-tube (PIT) technique with reference to texture development and critical anisotropy data is presented. Special emphasis is given to the optimization of the physicochemical and electromagnetic parameters of the multifilamentary and single-filament conductors with superconducting cores of Bi-2223, Tl-1223 and Y-123 superconducting phases. The influence of the multifilamentary and single-filament structures on texture development is discussed. Also, the importance of the local disturbances of the grain alignment and microdefects for the current distribution across and in the plane of the whole conductor is analysed. A comparative study of the critical current anisotropy with field direction in low magnetic fields of Tl-1223 and Bi-2223 conductors manufactured by the PIT technique is presented. For Tl-1223 PIT conductors the anisotropy coefficient shows a very pronounced minimum, followed by a monotonic reduction of anisotropy with the increase of the magnetic field. This is explained in terms of poor grain alignment with weak intergranular superconducting coupling which cause 3D current percolation and also by the demagnetizing effect of the grains and the ceramic core in the PIT Tl-1223 tapes.

Origin of J/sub c/ lateral spatial distribution in Ag-sheathed Bi-2212 HTSC tapes

Critical current density (J/sub c/) spatial distribution in the superconducting core of the Ag-sheathed Bi-2212 tapes prepared by powder in tube technique has been measured by means of tape cutting along the rolling direction to a few narrow strips and separate J/sub c/ measurements each of them. The J/sub c/ value on the edges of tapes has been found to be higher by a factor of about 3 in comparison with the central area. Unexpectedly, the measured oxide core density is shown to be in contrary the lowest in the edge regions. The thin interface layer (about 10 /spl mu/m thick) with no secondary phase has been observed by SEM on the whole circumference of Ag-sheath/core boundary. This interface layer is assumed to be responsible for the dominant contribution to the supercurrent-carrying ability of a tape. However, in fact the J/sub c/-values on the very edge of the core still are twice as high as J/sub c/ in the central region (3.6/spl times/10/sup 4/ against 1.8/spl times/10/sup 4/ A/cm/sup 2/). Thus, an optimal structure formation can be promoted by the core edge geometry.

Fabrication of Ag sheathed Bi2223 tape with supercold rolling process

A novel mechanical deformation process has been developed to fabricate high quality HTS tapes. In this process, the rolling step in the powder in tube technique is replaced by a supercold rolling conducted in liquid nitrogen. The critical current density of the Ag sheathed Bi2223 tapes is significantly enhanced by the supercold rolling. The microstructure observations of the tapes demonstrate that the supercold rolled tape has higher mass density and better grain alignment than the room temperature rolled tape, which are responsible for the high critical current density.

Preparation and characterization of silver sheathed BSCCO-2223 tapes

Critical current densities of 17000 A/cm/sup 2/ were achieved in short samples of Bi-2223/Ag tapes prepared by a conventional powder in tube technique. The preparation was varied to get an optimum grain size and texture of the microstructure. Microstructural examinations and inductive measurements of the transition temperature have been performed. The critical current and current-voltage characteristics have been studied in applied magnetic field up to 8 T and at temperatures between 4.2 K and 77 K. At temperatures close to 77 K and in fields up to 1 T the critical current density is strongly field dependent and obeys a potential law. At lower temperatures a quite different behavior is observed. In addition a small pancake-coil has been built by the wind & react method and tested at 77 K. >