Physica C 392–396 (2003) 677–683
www.elsevier.com/locate/physc

Thermal and mechanical properties of high Tc
bulk superconductors and their applications
K. Noto a,b,*, T. Oka b, K. Yokoyama b, K. Katagiri a, H. Fujishiro a,
H. Okada b, H. Nakazawa a, M. Muralidhar c, M. Murakami caFaculty of Engineering, Department of Welfare Engineering, Iwate University, Ueda 4-3-5, Morioka 020-8551, Japanb
Iwate Industrial Promotion Center, 3-35-2 Iioka-Shinden, Morioka 020-0852, Japanc
ISTEC-SRL, 3-35-2 Iioka-Shinden, Morioka 020-0852, Japan
Received 13 November 2002; accepted 27 January 2003

Abstract
The Iwate CREATE (Collaboration of Regional Entities for the Advancement of Technological Excellence) Project,‘‘Advanced Applications of Magnetic Field’’, started since October 1999, aims a creation of a COE and a new industrial
area in the ﬁeld of magnetic ﬁeld applications and magnetic measurements. The basic study group in this project ismaking extensive measurements on mechanical properties (strength, toughness and so on) and thermal properties(thermal conductivity, thermal diﬀusivity, Seebeck eﬀect, and so on) of melt-textured high Tc bulk superconductors inorder to build up a database and feed it back to the higher performance bulk material processing technique in the
future. This group also studies the magnetizing technique for these materials and realization of various magnetic ﬁeld
environment for the application to the magnetic separation, highly oriented polymer ﬁlm and so on.
 2003 Elsevier B.V. All rights reserved.
Keywords: Iwate project; Bulk superconductor; Mechanical properties; Thermal properties; Pulsed ﬁeld magnetization; Magnetic
separation

1. Introduction
The CREATE (Collaboration of Regional Entities for the Advancement of Technological Excellence) Project, initiated in 1997, aims a creation*

Corresponding author. Address: Faculty of Engineering,
Department of Welfare Engineering, Iwate University, Ueda 43-5, Morioka 020-8551, Japan. Tel.: +81-19-621-6357; fax: +8119-621-6357/6373.
E-mail address: noto@iwate-u.ac.jp (K. Noto).

of a COE and a new industrial area in each regions. So, the Iwate CREATE project ‘‘Advanced
Applications of Magnetic Field’’, started in October 1999, aims a creation of a COE and a new
industrial area in the ﬁeld of magnetic ﬁeld applications and magnetic measurements. There arethree major groups. (A) Applications of strong
magnetic ﬁeld, (B) magnetic measurement techniques, (C) basic study group.
The basic study group is making extensive
measurements on mechanical properties (strength,
toughness, and so on) and thermal properties

0921-4534/$ - see front matter  2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0921-4534(03)01026-8

K. Noto et al. / Physica C 392–396 (2003) 677–683(thermal conductivity, thermal diﬀusivity, Seebeck
eﬀect, and so on) of melt-textured high Tc bulk
superconductors in order to build up a database(DB) and feed back it to higher performance bulk
material processing techniques in the future. This
group also studies the magnetizing technique forthese materials and realization of various magnetic
ﬁeld environment for the application to the magnetic separation, highly oriented polymer ﬁlm
preparation, and so on.
In this paper, a part of the results of mechanicaland thermal property measurements on various
melt-textured high Tc bulk materials, studies ofmagnetizing techniques and magnetic ﬁeld generation by them, and an experiment of high gradientmagnetic separation (HGMS) by bulk superconducting magnets are reported.

2. Mechanical properties of bulk superconductors
The parameters of the mechanical properties ofthe bulk superconductors have been evaluated.
They are the hardness number and the fracture
toughness by Vickers hardness test and the elastic
parameters, the fracture strength and the fracture
toughness by tensile test and bending test. Some of
the results are to be reported in these Proceedings.
Highly c-axis oriented REBa2 Cu3 Oy (1 2 3)/10–
40 mol% RE2 BaCuO5 (2 1 1)/small amount of Pt
with or without 10 wt.% Ag single grain bulk
superconductors fabricated by top seeded melt
growth method were used (RE: Y, Sm, Gd, Sm–Gdand Nd–Eu–Gd (NEG)).
Tensile test [1–4]: For the tensile test, 3 · 3 · 4
mm3 specimens were cut out from the samples so
as to the longitudinal axis is in the direction of a, b
or c axis. A closed loop electro-hydraulic testingmachine was used. Tests have been conducted at
293 and 77 K. Strains of the specimens during thetest was measured by attaching a pair of strain
gauges.
Stress vs. strain curves varied widely, presumably, depending on the defects included in thespecimen. For Sm–Gd(1 2 3) sample, the maximum
value of YoungÕs modulus, E, was 147 GPa andthe higher the tensile strength was, the higher the E
was. Although specimens with high tensile strength

50

40Stress, MPa

678

Young's modulus, GPa
147
140

30

111
20

10

0
0.00

0.02

0.04

0.06

0.08

Strain, %Fig. 1. Stress–strain curves of Sm–Gd(1 2 3) samples. Specimens with high tensile strength hold the linear relationship,
YoungÕs modulus of each sample is given in the ﬁgure, up to
fracture. The stress tend to saturate after linear relationship in
the initial stage in other specimens with relatively low strength.

hold the linear relationship up to fracture, thestress tend to saturate after linear relationship in
the initial stage in some specimens with relatively
low strength (Fig. 1). This indicates that the slow
crack extension could occur from relatively large
defects involved in the samples. The E in all thebulks increased with decrease in the temperatureand decreased with increase in the distance fromthe center of the bulk sample. Anisotropy of E as
well as PoissonÕs ratio associated with crack
opening was observed. These elastic constants arenecessary for the numerical stress analysis of thebulk materials with complex conﬁguration.
The value of tensile strength, UTS, scatteredsigniﬁcantly. Excepting the region very close to theseed crystal, the UTS increased with decreasing
distance from the seed at the center of the bulk
both in the radial and depth directions (Fig. 2).
Although the UTS in NEG(1 2 3) sample increased
with decreasing temperature, those in all otherbulks decreased with the temperature. The temperature dependence of the UTS is controlled by
not only that of the theoretical strength without
defects but also the localized stress at the involved

K. Noto et al. / Physica C 392–396 (2003) 677–683
50
CentralMiddleRemoteStress, MPa

40
30

Maximum value
Y-Ba-Cu-O

20
Maximum value
Sm-Ba-Cu-O

10
0
0.0

0.1

0.2

0.3

0.4

Stroke, mm

Fig. 2. Tensile strength of Sm–Gd(1 2 3) samples.

defects. The strength distribution of the specimens
combined with defect distribution analysis appears
to enable the estimation of overall strength of thebulk materials.

3. Thermal properties of bulk superconductors
On designing and manufacturing of cryogenic
apparatus using the melt-processed REBaCuO

TF4~300K
BF0~10Tesla
Superconducting
Magnet679

bulk superconductors, it is important to have theknowledge of the thermal and thermo-mechanicalproperties. These bulks usually consist of the
REBa2 Cu3 O7 (RE123) superconducting phase,
RE2 BaCuO5 (RE211) impurity phase and silver(Ag) and platinum (Pt) metals, which can be regarded as a composite superconducting material.
It has been found that the contents and the sizes of
the RE211 phase and Ag particles strongly inﬂuence the critical current density Jc and the magnetic ﬂux trapping ability. The thermal transport
properties (thermal conductivity j, thermal contraction DL=L, thermal diﬀusivity a, thermoelectric
power S, etc.) and their anisotropies are also crucially inﬂuenced by these quantities. For the application to power current leads of these bulks, thelow j and a values are desirable, but for the application to stronger bulk magnets, the higher heat
conduction may be necessary to prevent the temperature rise and the exudation of the trapped ﬂux.
The abundant and methodical DB of the thermal
properties, however, has not been completed forthese bulk superconductors. We constructed theliquid He free measuring station of the thermal properties at the temperature range of 6–300
K and under the magnetic ﬁeld of 0–10 T using
a GM refrigerator and a cryocooler-cooled

Thermal Conductivity
Thermal Diffusivity
Thermal Expansion
Thermoelectric PowerSpecific HeatSound Velocity

GM Refrigirator
for Sample Cooling
Sample Setting
RegionVacuum chamber

Fig. 3. A view of the liquid He free measuring station for thermal properties.

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K. Noto et al. / Physica C 392–396 (2003) 677–683

superconducting magnet as shown in Fig. 3 [5,6].
We have measured the thermal properties (j, a,estimated speciﬁc heat Cð¼ j=aÞ, DL=L, S andthermal contact resistance Rc [7]) for the various
types of REBaCuO bulk superconductors (RE ¼
Y, Sm, Gd, (Nd, Eu, Gd), etc.) and compared withthe superconducting properties [6,8–12].
Fig. 4 shows examples of thermal conductivity
for the Ag-doped Sm-based crystals [6]. In Fig.
4(a), the ab-plane thermal conductivity jab drastically decreased with increasing the content of
Sm211 phase X . It has been found that the Ba–Sm
substitution occurs and that the low-Tc (or nonsuperconducting) phase is produced in this system.
The substitution eﬀect reduces the crystal quality

Thermal Conductivity κ ab (mW/cmK)

Sm

1+2X

Ba

2+X

Cu

3+X

O

7+5X

(Ag=10wt.%)

4. A superconducting bulk magnet system

200

(a)

X=0.1
X=0.2
X=0.3
X=0.4

150

100

50

ab-plane (0T)
0

0

100

200

300

Thermal Conductivity κ ab (mW/cmK)

Temperature (K)
200

(b)

Q//ab, B⊥abab-plane

Q

150

B
100

0T
5T
10T

50

X=0.1(Ag=10wt.%)
FC
0
0

50

of the Sm123 superconducting phase and, resultantly, deteriorates the absolute value of jab andthe jab enhancement below Tc , which is in contrast
to the Y -based system. In this way, the j measurement is a valuable tool to investigate thecrystal quality and the distribution of the secondary phase in the composite materials. Fig. 4(b)shows the jab ðT Þ for the X ¼ 0:1 specimen underthe magnetic ﬁeld which was applied perpendicular
to the ab-plane. The jab enhancement below Tc isdrastically suppressed with increasing appliedﬁeld, especially for lower ﬁeld than 5 T. This reduction can be understood as caused by the enhanced phonon scattering by the quasi-particles inthe vortex cores. We expect that these data arevaluable also for the applications.

100

150

200

Temperature (K)Fig. 4. (a) The temperature dependence of the ab-plane thermal
conductivity jab of Ag-doped Sm-based crystals for various
Sm211 contents (zero ﬁeld). (b) jab ðT Þ for the X ¼ 0:1 specimen
under the magnetic ﬁeld (B ? ab-plane).

The trapped ﬁeld of melt-textured bulk superconductors has been substantially improved bychoosing Sm in place of Y . As was reported by
Ikuta et al. [13], the maximum trapped ﬁeld attained in the Sm–Ba–Cu–O system has reached 9.0
T at 25 K. They pointed out that it is quite eﬀective
to use the excellent ﬁeld trapping property in thetemperature range lower than 77 K. So, Sm–Ba–
Cu–O bulk samples manufactured by Dowa
Mining Co. were adopted to the newly developed
superconducting bulk magnet system, as shown in
Fig. 5. A pair of bulk samples reinforced by impregnating epoxy resin with glass ﬁbers was
mounted on the respective cold stages of the GM
refrigerators in each vacuum vessel, and was cooled
down to 38 K in a few hours [14].
The bulk samples were magnetized by applying
pulsed ﬁeld by using a magnetizing coil (pulsed
ﬁeld magnetization method, PFM). A magnetizing
coil, on the right hand side of magnetic poles
shown in Fig. 5, is removed after completing the
PFM. Though the ﬂux penetration into the superconductors causes local heating in the sample
and subsequently degrades the trapped ﬁeld, anovel magnetization technique ‘‘IMRA method’’(iteratively magnetizing pulsed-ﬁeld operation with
reducing amplitudes) eﬀectively enhances the trap-

K. Noto et al. / Physica C 392–396 (2003) 677–683

681

Fig. 5. A photograph of the superconducting permanent magnet system with a magnetizing coil set around the right hand sidemagnetic pole.

trapped ﬁeld ﬁrst increases with increasing appliedﬁelds (see I in Fig. 6), then tends to saturate above
5 T (see II). When the pulses with reducing theamplitudes are applied, the trapped ﬁeld gradually
increases and exceeds 3 T (see III).

4

Trapped Field BT(T)

III
II

3
I
2

4.1. Magnetic ﬁeld distribution
1
Sm123
38K
0
0

2

4

6

8

Applied Field Bex (T)Fig. 6. History of the trapped ﬂux density magnetized by
IMRA method at 38 K.

ped ﬁeld [15]. Fig. 6 shows the history of trapped
ﬁeld by the IMRA method operated at 38 K. The

The trapped ﬂux distributions measured by aHall sensor (F.W. Bell BHA921) along the poleaxis as a function of various gap distances areshown in Fig. 7. The maximum trapped ﬁeld between the magnetic poles has reached 3.15 T. This
performance exceeds the maximum value of largescale electromagnets and is by far stronger thanthat of conventional permanent magnets such as
Nd–Fe–B. The magnetic ﬁeld in the gaps decreases
with increasing gap distance, showing 1.8 T at thecenter in the case of 20 mm gap distance. The

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K. Noto et al. / Physica C 392–396 (2003) 677–683
Sample surface(Right pole)

Magnetic Field Bz(T)4Chamber surface(Right pole)

3Open gap
2

2mm
10mm

1

20mm
30mm

0
—30 —20 —10

010Position (mm)

20

30

40mm
50mm

Fig. 7. Magnetic ﬁeld distribution along the axis of magnetic
poles as a function of the gap distances.

following magnetic separation experiment is operated in this open space.

Fig. 8. Magnetic separation system using a face-to-face typesuperconducting bulk magnets. A separation pipe with magnetic ﬁlters is placed between magnetic poles. The magnetic ﬂux
direction is from left to right hand side and the slurry ﬂows
from under to upper side. The original slurry has muddy color
but the separated water becomes transparent.

5. HGMS using superconducting bulk magnets
We aim to apply superconducting bulk magnets
to a magnetic separation that is to remove dirt orto capture useful materials from slurry by acting
the magnetic force to the separating particles.
Fig. 8 shows the photograph of a magnetic
separation system using the face-to-face type superconducting bulk magnet system. A separation
pipe with magnetic ﬁlters is placed between magnetic poles of 20 mm gap. The magnetic ﬂux direction is from left to right hand side and the slurry
ﬂows from under to upper side. Using the 500 ppm
of a-hematite (Fe2 O3 , averaged diameter: 1 lm)
mixed slurry, hematite particles are separated at a
ﬂow rate of 0.1–3.0 l/min and a separation percentage is investigated.
Fig. 9 shows the puriﬁed samples. No. 1 isoriginal slurry. Nos. 2–6 are the puriﬁed sample at
a ﬂow rate of 0.1, 0.5, 1.0, 2.0 and 3.0 l/min, respectively. Up to the ﬂow rate of 1.0 l/min, mosthematite particles are captured and samples istransparent. For higher ﬂow rate than 1.0 l/min,on the other hand, the particles are leaked fromthe separation ﬁlter because it is saturated, andsamples become muddy.

Fig. 9. Comparison of puriﬁed samples. No. 1: original slurry.
Nos. 2–6: the ﬂow rate is 0.1, 0.5, 1.0, 2.0 and 3.0 l/min,
respectively.

Fig. 10 illustrates the relationship between theseparation percentage and the ﬂow rate. Up to 0.5
l/min, over 99% of hematite particles is separated.
The separation percentage at 1.0, 2.0 and 3.0 l/min
is 94.6%, 93.2% and 71.4%, respectively.

K. Noto et al. / Physica C 392–396 (2003) 677–683

683

Acknowledgements
The authors would like to thank under graduate
student Miss Y. Fujiwara for many assistances inthe experiments of bulk superconductor magnetization and HGMS. This manuscript was preparedby Mrs. S. Sakai.

Separation percentage (%)

100

80

60

References

40

20

0

0

1

2

3

Flow rate (I/min)Fig. 10. The relationship between the separation percentage
and a ﬂow rate.

6. Summary(1) In the Iwate CREATE project ‘‘Advanced Applications of Magnetic Field’’, the basic study
group is making an extensive study on mechanical and thermal properties of high Tc bulk
materials in order to build up a DB and feed it
back to higher performance bulk material processing techniques in the future.
(2) The basic study group also studies magnetizing
techniques and realization of various magnetic
environments for the application to the magnetic separation, highly oriented polymer ﬁlm
preparation, metallic structure control of hightemperature spring materials, and so on. Maximum 3 T magnetic ﬁeld was achieved up tonow.
(3) As a ﬁrst application we made a HGMS experiment, in which weak paramagnetic hematite
particles were removed from water.

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