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Hiroaki Kumakura
National Institute for Materials Science(NIMS)
INTERNATIONAL WORKSHOP ON Construction of Low-Carbon Society Using
Superconducting and Cryogenics Technology, Mar. 7-9, Osaka
Outline
1. MgB2 wires(ALCA project)
2. BSCCO(Bi-2223 and Bi-2212) tapes
and wires
3. Summary
Bi-based high-Tc oxide and MgB2 tapes and wires
promising for CO2 emissions reduction
0
5
10
15
0 5 10 15 20 25 30 35 40
上部
臨界
磁界
, H
c2(T
)
温度, T(K)
Nb-Ti
Nb3Sn
無添加
10%SiC添加
H//c軸(薄膜)
H//ab面(薄膜)
Hc2 (
T)
10%-SiC-doped
MgB2 wire
H//c-axis
(MgB2 thin film)
MgB2 wire
w/o SiC doping
T (K)
(MgB2 thin film) H//a-b plane
Nb-Ti wire(4.2K operation)
MgB2 wire
(20K operation with
LH2 or cryocooler)
Bc2 of PIT processed MgB2 wire
High quality MgB2 single crystal
Zehetmayer M et al,
Phys. Rev. B 66(2002) 0525051-4
X. Zeng, et al., Nature Mater. 1(2002)35.
Examples of MgB2
wires and tapes
Mg+B+(SiC) powder
Metal tube
Heat treatment
Multi-filament
wire
Multi-filament
tape
Fabrication of MgB2 wire and tape
Powder-In-Tube(PIT) method
drawing
No grain orientation is required!
104
105
106
0 2 4 6 8 10 12
Jc (
A/c
m2)
Magnetic Field B(Tesla)
tape(PIT)
MgB2/-Al
2O
3 thin film
(PLD method) 4.2K
tape(PIT)20K
Nb3Sn
The density of MgB2: ~50%
Microstructure of PIT MgB2 wire
Shrinkage of volume
during heat treatment Mg+B MgB2
B: 2.34g/cm3
Mg: 1.7
MgB2: 2.6
Typical Jc-B curves of PIT processed MgB2 tape
One big problem of PIT is the low packing
density (large porosity) of MgB2 core.
Comparison of IMD and PIT
Metal Tube
B Powder Mg rod
Internal Mg diffusion(IMD) process
Mg+B Powder
PIT process PIT method
Packing density: ~50%
IMD method
Packing density: ~80%
Metal Tube
B+Mg(+SiC) powder
PIT method
B(+SiC) powder
Mg
diffusion
Mg diffusion method
Mono core wire
Cu-Ni Ta
200mm 200mm
200mm 200mm
Mg
B+SiC
7-filament wire
19-filament wire
Internal Mg Diffusion (IMD) Process
1.2 mm
Longitudinal cross sections of IMD processed MgB2 wires
(uniformity in longitudinal direction)
1000
104
105
7 8 9 10 11 12 13
En
gin
ee
rin
g J
c(J
e)
A/c
m2
Magnetic field H(T)
4.2K
PIT wire
IMD wire
104
105
0 2 4 6 8 10 12
Cri
tica
l cu
rren
t d
ensity J
c(A
/cm
2)
Magnetic field H(T)
IMD wire
PIT wire
IMD wire
PIT wire
4.2K
20K
Jc and Je comparisons of IMD and PIT
processed wires
Filament structure of IMD multi-filamentary wires
200μm
7-filaments
Ta
200μm
19-filaments
50μm
Ta Reacted Layer
The diffusion distance by
Mg liquid infiltration is
limited to <50μm !
The reduction of filament size is essential to complete the
reaction with short heat treatment time !
Single-filaments
-30 130
Measured magnetic field Bz (mT)
Lift-off: 200 mm
Jc_SiC (A/cm2)
0.0
5.0 x 105
1.0 x 106
1.5 x 106
2.0 x 106
1 2 3 4 5 6 7 8 9
Jc (A/cm2)
@10 K,0 T
x (mm)
-300 0 300
Measured magnetic field Bz (mT)
Bz |dBz0/dx,dy| superpose SEM
Locally low property Localized Mg2Si
J = 1 MA/cm2 per Bpeak = 80 mT
0.2 mm
1 mm
Local Ic distribution of SiC added IMD wire
(Analysis by scanning hole probe microscope)
LT-SHPM, Kiss Lab. Kyushu Univ.
(K. Togano et al.,
Supercond. Sci. Technol. 22 (2009) 015003)
About 3 times higher Jc is expected by the improvement of the homogeneity.
△: locally maximum Ic
estimated by the SHPM
Comparison of Jc values obtained by the resistive
method and SHPM
LT-SHPM, Kiss Lab. Kyushu Univ.
Comparison of C24H12 and SiC addition
(IMD processed MgB2 wires)
7 8 9 10 11 1210
3
104
105
IMD wires, = 0.6 mmJc (
A/c
m2)
B (T)
undoped
SiC-added
C24-added
Jc = 1.02 x 10
5 A/cm
2 4.2 KJc = 1.1x105A/cm2
7 8 9 10 11 1210
2
103
104
Je = 1.13 x 10
4 A/cm
2
IMD wires, = 0.6 mm
B (T)
Je (
A/c
m2)
undoped
SiC-added
C24-added
4.2 KJe = 1.3x104A/cm2
Coronene(C24H12)
Decomposition temperature:
~600oC
TEM image
104
105
106
0 2 4 6 8 10 12
Critica
l cu
rre
nt
de
nsity, J
c(A
/cm
2)
Magnetic field, H(T)
4.2K
20K
PIT wire
IMD wire
PLD thin filmNb
3SnNb-Ti
PIT wire
IMD wire
PLD thin film
Present status of MgB2 wires
eirr d(Ic/Ic0)/de
IMD 0.67% 0.143
PIT 0.54% 0.213
IMD-MgB2 wire shows larger
eirr and smaller strain
sensitivity
0.67%
0.54%
slope=0.21
slope=0.14
a
a’
b
b’
c
c’
d
d’
e
e’ a
a’
b
b’
c
c’
Stress effect of PIT and IMD mono-filamentary MgB2
wires(at 10 T, 4.2 K)
Voids at the center of IMD wires
seem to have no negative effect
on strain sensitivity of Jc.
Superconducting joint of IMD processed MgB2 wire
Fe sheath
C24H12 added MgB2 wire Mg
core
B layer
Pressing
(one end)
Metal tube
Pressing
Heat treatment
(under the same
condition as the
wire)
Fe or SS tube
Examples of joints
1
10
100
0 2 4 6 8 10 12Magnetic field B(T)
Critica
l curr
en
t I c
(A)
Fe tube
Wire
S.S. tube
4.2K
Ic-B curves of superconducting joints(IMD MgB2 wire)
Crystal structure of Bi-based oxide superconductors
Bi2Sr2CaCu2O8+d
(Bi-2212) Bi2Sr2Ca2Cu3O10+d
(Bi-2223)
Bi-2212 (n = 1) Bi-2223 (n = 2)
N.S.C
S.C.
N.S.C.
S.C.
N.S.C.
Tc ~ 90K
Tc~110K
Bi
Cu
Sr
Ca
O
a-axis
b
c
Bi-based oxide wire and tape fabrication by a powder-in-tube(PIT) method
Powder Bi2O3, SrCO3, CaCO3, CuO
Metal tube(Ag)
Heat treatment
Multi-filamentary wire
(Bi-2223)
Multi-filamentary tape
drawing
Grain orientation of Bi-oxide is essential
to obtain large current transfer.
結晶粒の配向化が必須
Microstructure of Bi-2212 tape
Slow cooling from melting state
Conventional Sintering
C-axis grain orientation is obtained by the
Slow cooling from partially melting state.
Heat treatment schedule of Bi-2212 tape
• Various wire configurations to fit different application requirements- cable (0.8-
1.0 mm) and insert coil (1.0-1.5 mm)
0.8 mm 0.8 mm 1.2 mm 1.5 mm 1.0 mm
Wire configuration (filament number in
sub x number of sub bundle)
Fill factor (%) Optimized wire
diameter (mm)
19 x 36 24.0 0.8
37 x 18 24.8 0.8
55x18 24.9 1
85 x 18 25.2 1.2
121 x 18 25.4 1.5
Bi-2212 wire configurations for different operating current
demands
Examples of Bi-2212 wires
100
200
300
400
500
600
700
800
4 6 8 10 12 14 16
JE (
A/m
m2)
Magnetic Field (T)
As-drawn wire, closed ends
CIP at 100 ksi, closed ends
CIPed wire + OP HT, closed ends
1.2 mm 85 x18
1m barrel sample
Over Pressure Heat Treatment (10 bar HT by ASC/FSU)
1 bar HT, As-drawn
1 bar HT, CIP
Core densification by over pressure HT
10 bar HT
• Highly reproducible Bi-2212 wires with good Je performance
• Maximum length of Bi-2212 wire: ~1000m
4.2K
Fabrication of Bi-2223 tapes by Powder-In-Tube(PIT) method
Powder
Metal tube(Ag)
Heat treatment
Multi-filamentary wire
(Bi-2223)
Multi-filamentary tape
drawing
Formation of Bi-2223 phase Bi-2212+Ca2PbO4+Ca2CuO3+? Bi-2223
Cross section of typical Bi-2223 tape
C-axis grain oriented microstructure of
Bi-based superconducting tapes
Bi-2212 tape
Grain orientation by the slow
solidification from melting state.
Bi-2223 tape:
Grain orientation is obtained by the
combination of cold rolling and
heat treatment. (Y. Yamada, et al.)
km-class Bi2223/Ag tape
Je~20,000A/cm2
(77K, self-field)
(4.2mmwx0.22mmt)
Cross section of typical Bi-2223 tape
(4.2mmwx0.22mmt)
Recent progress of Bi-2223/Ag tape conductors