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Thermal conductivity of DI-BSCCO tapes with stacked or sandwiched structureThis article has been downloaded from IOPscience. Please scroll down to see the full text article.
2010 J. Phys.: Conf. Ser. 234 022025(http://iopscience.iop.org/1742-6596/234/2/022025)
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9th European Conference on Applied Superconductivity (EUCAS 09)
Journal of Physics: Conference Series 234 (2010) 022025

IOP Publishingdoi:10.1088/1742-6596/234/2/022025

Thermal conductivity of DI-BSCCO tapes withstacked or sandwiched structure
Tomoyuki Naito1 , Hiroyuki Fujishiro1 , and Yuichi Yamada212

Faculty of Engineering, Iwate University, Morioka 020-8551, Japan
Sumitomo Electric Industries, Ltd., 1-1-3 Shimaya, Konohana-ku, Osaka 554-0024, Japan

E-mail: tnaito@iwate-u.ac.jp
Abstract. We have measured the temperature dependence of the thermal conductivity, κ(T ),for DI-BSCCO tapes sandwiched by various kinds of alloy tapes and for a stacked bundle inwhich six DI-BSCCO tapes were soldered. For the sandwiched samples, the shape of κ(T ) is
qualitatively the same as that for the bare DI-BSCCO tape and the absolute value of κ(T )depends on the species and the thickness of the alloy tape. κ(T ) for the stacked bundle nearlycoincides to that for the bare DI-BSCCO. The κ(T ) for the sandwiched and stacked samples
can be reproduced by the κ(T ) of each constitutional part.

1. IntroductionHigh temperature superconductive tape named DI-BSCCO is a commercial silver sheathed
Bi2223 tape which is produced by Sumitomo Electric Industries, Ltd. [1]. Recently, a higher
critical current Ic =218 A has been achieved at 77 K in self-field [2] and the DI-BSCCO tape has
a potential for various superconducting devices and large scale applications [3].
For the applications, the heat intrusion through the tape from the outside and the heatgeneration in the inside of the tape affect the operating condition of the apparatus. The thermalconductivity, κ(T ), is a basic and important parameter to estimate the heat transfer, Qt , throughthe material by the relation,Z hS T
κ(T )dT,
Qt =L Tl
where S is the cross section, L the length of the material, and T l and T h are the temperaturesat the low- and high-temperature ends of the material.
To increase the mechanical strength, the DI-BSCCO tapes are usually reinforced by various
kinds of alloy tapes such as stainless steel and brass. In this paper, we report the thermalconductivity, κ(T ), of DI-BSCCO tapes sandwiched by various kinds of alloy tapes. The κ(T )for a stacked bundle which consists of six DI-BSCCO tapes was also measured. The measured
κ(T ) was compared with the κ(T ) which was estimated using the κ(T ) values of the bare DIBSCCO tape, the reinforcing alloy tape and the solder.
2. Experimental procedure
DI-BSCCO tapes were fabricated by the powder in tube (PIT) method with the ControllingOverpressure (CT-OP) sintering technique. The details of sample preparation have beenc 2010 IOP Publishing Ltd1

9th European Conference on Applied Superconductivity (EUCAS 09)
Journal of Physics: Conference Series 234 (2010) 022025

IOP Publishingdoi:10.1088/1742-6596/234/2/022025

Table 1. Specifications of the DI-BSCCO tapes
TypeHHT-SUS20 HT-Bz50 HT-Bs50 HT-Bs100
alloy tape–SUSBronze
Brass
Brass
thickness of alloy (µm)–
205050100
cross section (mm2 )
0.94
1.35
1.59
1.58
2.03
width (mm)
4.25
4.50
4.55
4.50
4.50
thickness (mm)
0.22
0.28∗
0.35∗
0.35∗
0.47∗

H6–
–
5.88
4.42
1.33∗

∗ including the thickness of solder layers.

described elsewhere [1]. The DI-BSCCO tape sheathed with silver (“type H”) is a standard
tape. The Ag/Bi2223 ratio, which is defined by the ratio of the volume fraction between theBi2223 core and the Ag sheath, was about 1.8. The type HT tape was prepared to achieve a highyield stress, in which the type H tape was sandwiched from both surfaces by the thin alloy tapeswith various thicknesses using the commercial solder (LFM-48). A stainless steel (SUS), bronze(Bz) or brass (Bs) were used as the reinforcing material. The type HT tape with SUS tapes 20µm in thickness was named HT-SUS20. Other HT samples were named by this rule as shown in
Table 1, in which the specifications of the DI-BSCCO tapes studied here were summarised. A
stacked bundle was also prepared, consisting of six type H tapes that were joined by the solder.
Hereafter, we refer to this sample as type H6.
The thermal conductivity along the tape surface, i.e.,cHeateralong the ab plane of the Bi2223 filament, was measuredb(a)by a steady-state heat-flow method [4]. The experimental
setup for the κ(T ) measurement is illustrated in Fig. 1.
a(b)
QT.C.
One end of the tape was soldered to the sample stage,
and a small metal chip resistor (1 kΩ) was adhered to thetape∆T (L)
other end of the tape as a heater using GE7031 varnish. κis estimated by the relation, κ = (Q/∆T )·(L/S), where Q
is the applied heat flow, ∆T the temperature difference,
L the distance between the thermocouples, and S thesample stage
cross section of sample. ∆T was measured using two
chromel-constantan thermocouples (76 µm in diameter)that were adhered to the sample with GE7031 varnish. QFigure 1. The schematic experiwas generated by flowing current to the chip resistor andmental setup for the κ(T ) measurewas automatically controlled to maintain ∆T of 0.5–0.8 K.
ment, where the coordinate axes
To eliminate the radiation loss, κ was measured below 200
represent the crystallographic axes
K. The temperature of the sample stage was controlledof Bi2223 filaments.
using a Gifford-McMahon cycle helium refrigerator.
3. Results and Discussion
Figure 2(a) shows the temperature dependence of the thermal conductivity κ(T ) for the type
H, four sandwiched type HT and type H6 tapes. On the cooling run, κ(T ) of the type H tapedecreases moderately from 200 K down to 100 K and subsequently increases below 100 K. It
begins to increase rapidly below 60 K, and takes a maximum of about 800 W m−1 K−1 around
15 K. The shape of κ(T ) for all the type HT tapes is qualitatively similar to those for the type
H and the type H6. However, the absolute value of the thermal conductivity, κabs (T ), depends
on the species and thickness of the alloy tape, because κabs (T ) of alloy strongly depends on thespecies of element and the composition. Figure 2(b) shows the measured κ(T ) for the SUS tape
20 µm in thickness and the solder (LFM-48). The reported data for bronze (Cu:Sn=9:1) [5] and2

9th European Conference on Applied Superconductivity (EUCAS 09)
Journal of Physics: Conference Series 234 (2010) 022025

100011-)
Km500W(κ103H
HT-SUS20 3HT-Bz50
HT-Bs50 )K
HT-Bs100 002H6(2102/κκ1-101-0100200T(K))
Km10W(κType H [mes]Solder (LFM-48)
Bronze (ref.[5])Brass (ref.[6])1SUS20 [mes]100DI-BSCCO00IOP Publishingdoi:10.1088/1742-6596/234/2/022025(a)10010 010200T(K)(b)-1101T(K)102Figure 2. (a) The temperature dependence of the thermal conductivity, κ(T ), for the type H,
four kinds of type HT and the type H6 tapes. The inset shows the κ(T )/κ(200 K) for the samesamples. (b) The measured κ(T ) for the type H tape, the SUS tape 20 µm in thickness and thesolder (LFM-48), the reported κ(T ) for bronze (Cu:Sn=9:1) [5] and the recommended κ(T ) forbrass (Cu:Zn=7:3) [6].

the recommended data for brass (Cu:Zn=7:3) [6] are also shown. κ(T ) for the solder increases
very gradually with decreasing temperature from 200 K down to around 40 K. It begins toincrease rapidly below 40 K with decreasing temperature. κ(T ) for other alloys (SUS, bronze,brass) decreases monotonically with decreasing temperature. The κabs (T ) for the SUS tape isabout one to three orders of magnitude smaller than that for the type H tape. For bronze andbrass, κabs (T ) is somewhat smaller than that for the type H tape above 30 K and is one to twoorders of magnitude smaller below 30 K. The inset of Fig. 2(a) shows the κ(T ) normalized by theκ value at 200 K, κ(T )/κ(200 K). The κ(T )/κ(200 K) curves for the types H, HT-SUS20, HTBs50 and H6 tapes almost coincide with each other, which means that the contribution of thealloy tape to the heat transport can be neglected and the applied heat almost flows through thesilver sheath in the type H tape. On the other hand, the κ(T )/κ(200 K) for the types HT-Bz50
and HT-Bs100 tapes deviates from that for the type H tape, indicating that the contribution ofthe alloy tapes cannot be ignored to the heat transport.
We try to estimate the κ(T ) for both HT-Bz50 and HT-Bs100 tapes using κ(T ) for eachelemental material. The schematic image of the heat flow through a composite sample which
consists of n kinds of materials is illustrated in the inset of Fig. 3(a). Assuming that the applied
heat flows in parallel, the total heat through the composite sample, Qtot , is given by
Qtot =nX

Qi ,i=1

where, Qi is the heat flow through the i-th part. Since the ∆T and L are the same for all theparts, the total thermal conductivity, κtot , can be estimated byκtot =

Ã nX!

(κi × Si ) /Stot ,i=1

3

9th European Conference on Applied Superconductivity (EUCAS 09)
Journal of Physics: Conference Series 234 (2010) 022025

800

HT-Bz50(mes)HT-Bz50(cal)H(mes)
LFM-48(mes)Bronze(Ref.[5])600Q Q ...Qn
1

HT-Bs100(mes)HT-Bs100(cal)H(mes)
LFM-48(mes)Brass(Ref.[6])

2600

T.C.
1 2 ... n-1∆ T (L )1-sample stageκ-1)
Km400
W(800tot)
Km400
W(κ-1QIOP Publishingdoi:10.1088/1742-6596/234/2/022025

200200(a)(b)

000100

T(K)

200

0100

T(K)

200

800

H6(mes)H6(cal)H(mes)
LFM-48(mes)600-1

Figure 3. The measured and calculated
κ(T ) for the types (a) HT-Bz50, (b) HTBs100 and (c) H6 tapes for each element. The
inset of (a) demonstrates that a schematic
image of the heat flow through the composite
sample consisting of n kinds of materials.

κ1-)
Km400
W(200(c)
00100

T(K)

200

where, κi is the thermal conductivity and Si is the cross section for i-th part. Figures 3(a) and3(b) show the calculated κ(T ) for the types HT-Bz50 and HT-Bs100 tapes, respectively, using
this relation. The calculated κ(T ), which is depicted as the broken line, nearly corresponds tothe measured one for both tapes. We note that the disagreement between the measured andcalculated κ(T ) is found for the type HT-Bz50 tape above 40 K, which indicates the possibility
that the amount of Cu in bronze for reported κ(T ) is somewhat smaller than that in the brasstape of the type HT-Bz50 tape. The similar estimation was performed for the type H6 tape inFig. 3(c). The measured κ(T ) was well reproduced by the calculated one. These results indicatethat the κ(T ) for the composite sample can be estimated from κ(T ) for each part using theequivalent circuit for the heat flow with the simple sum rule.

49th European Conference on Applied Superconductivity (EUCAS 09)
Journal of Physics: Conference Series 234 (2010) 022025

IOP Publishingdoi:10.1088/1742-6596/234/2/022025

4. Summary
We have measured the temperature dependence of the thermal conductivity, κ(T ), for various
DI-BSCCO samples with sandwiched and stacked structure. The κ(T ) for a sandwiched sample,
which consists of the silver-sheathed DI-BSCCO (type H), the reinforcing alloy tapes and thesolder parts, is similar to κ(T ) for the type H tape. The absolute value of κ(T ) for the sandwichedsample depends on the species and the thickness of the alloy tape. When the contribution of thealloy tape to the heat transport is negligible small, the absolute value of κ(T ) for the sandwichedsample depends on the volume fraction of the type H tape in the whole sample. The κ(T ) fora stacked bundle consisting of six type H tapes almost coincides to that for the type H tape.
The measured κ(T ) for the sandwiched and stacked samples is well reproduced by the estimatedκ(T ) which was calculated using measured κ(T ) for each part. This procedure can be applicableto estimate the thermal conductivity for the composite cryogenic device such as a coil which
consists of the superconducting tape, insulator and so on.
References[1] Kobayashi S, Yamazaki K, Kato T, Ohkura K, Ueno E, Fujino K, Fujikami J, Ayai N, Kikuchi M, Hayashi
K, Sato K and Hata R 2005 Physica C 426-431 1132
[2] Yamade S, Ayai N, Fujikami J, Kobayashi S, Ueno E, Yamazaki K, Kikuchi M, Kato T, Hayashi K, Sato K,Kitaguchi H and Shimoyama J 2007 Physica C 463-465 821[3] Masuda T, Yumura H and Watanabe M 2008 Physica C 468 2014[4] Ikebe M, Fujishiro H, Naito T, Noto K 1994 J. Phys. Soc. Jpn. 63 3107
[5] Touloukian Y S, Powell R W, Ho C Y, Klemens P G 1970 Thermophysical Properties of Matter (IFI/Plenum,New York-Washington) 1 588[6] Ho C Y, Ackerman M W, Wu K Y, Oh S G, Havill T N 1978 J. Phys. Chem. Ref. Data 7 1091

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