Note: Descriptions are shown in the official language in which they were submitted.
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Method for producing ceramic oxide superconductor
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The present invention relates to a method for
producing a ceramic oxide superconductor. More
partlcularly, it relates to a method for producing a
ceramic oxide superconductor by flame spraying onto a
substrate to form a composite material comprising the
substrate and said ceramic superconductor.
Recently, ceramic oxide superconductors with a high
critical temperature Tc have attracted much attention. As
such high Tc ceramic superconductors, those having a pero-
vskite type crystal structure are known and have a Tcvalue not lower than 30 K. Generally, a ceramic superconductor is produced by
molding powdery compounds, such as oxides and carbonates
of the elements that constitute the superconductor, into a
desired shape, followed by sintering.
Since molding for pressing the powder is essential in
the conventional method, the superconductor cannot in some
cases be formed into the desired shape. For example, the
powdery raw materials cannot be shaped into an elongate
Eorm or into a thin wire form. Therefore, a super-
conductive wire or a thin wire for a superconductor device
cannot be produced by the conventional method.
One object of the present invention is to provide
r~
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a method for producing a superconductor composite material
comprising a substrate and a superconductor layer formed
thereon, which composite material has an arb:itrary shape
such as a long or thin wire.
Another object of the present invention is to provide
a method for producing a superconductor on a substrate, in
which the superconductor resists peeling from the sub-
strate.
A further object of the present invention is to provide
10 a method for producing a superconductor on a substrate in
which the oxygen content in the superconductor is easily
adjusted.
According to the present invention, there is provided
a method for producing, on a substrate, a superconcluctor
hav.ing a composition o.E the formula:
Ml M2 M3 (I)
wherein Ml is at least one element selected from the
elements of the Ia, IIa and IIIa groups, M is at least
one element selected from the elements of the Ib, IIb and
IIIb groups, and M is at least one element selected
from the group consisting of oxygen, nitrogen, fluorine,
carbon and sulfur, which method compr;ses flame spraying
raw material selected from the group consisting of complex
ceramics comprising the elements M1, ~2 and M3 and a
mixture of the elements Ml, M and M or compounds
each comprising at least one of the elements M , M
and ~3, and optionally heating the composite materlal of
the superconductor and the substrate.
In the drawings:
Fig. 1 shows a method for producing a superconductor
composite material according to an embodiment of the
present invention;
Fig. 2 shows a method for producing an elongate super-
~,
~3~
conductor composite material according to an embodiment of
the present inventi.on; and
Fi.g. 3 is a cross section of a superconductor co~posite
material.
According to the method of the present invention,
complex ceramics comprising the elements M, M and
M3 or a mixture of these elements or of compounds of
these elements is flame sprayed onto a substrate. When a
substrate of a desired shape, such as a wire or a tape, is
used, or when the raw material is flame sprayed in a
desired pattern, a superconductor composite material having
the desired shape can be produced.
When the ceramic superconductor itself is used as the
complex ceramics, the resulting superconductor has
exce.l.lent superconductive properties without post-heati.ng.
In a preferred embodiment, instead oE flame sprayillg
al]. the raw material.s, the elements Ml and M2 or thei:r
compounds are flame sprayed onto the substrate and are
then heated in an atmosphere containing the element M3
or a compound comprising the element M3. In this case,
the concentration of the element M3 in the heating
atmosphere is preferably not smaller than 10 atomic %. In
a modified embodiment, the flame spraying can be carried
out in the presence of the element M3 to incorporate it
in the sprayed material, whereby the elements Ml and
M2 react more homogeneously and reliably with the element
M3 during post-heating in the atmosphere containing the
latter element.
The flame spraying can be carried out by any of the
conventional methods, such as a thermospray process in
which powdery raw materials are melted by an oxygen-
acetylene flame and are injected, or a plasma process in
which powdery raw materials are supplied to a high
temperature high pressure plasma to melt them, and the
melted materials are injected.
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The flame spraying can be carried out under elevated,
normal or reduced pressure in the presence or absence of
the element M3 in various atmospheres according to ~he
kinds and composition of the elements contained in the raw
materials and so on. Generally, when the spraying is
carried out under reduced pressure, a superconductor with
high consistency and good quality can be produced.
The thickness of the superconductor formed on the
substrate is not critical in the present invention and
depends on the desired superconductive properties, the
properties of the substrate, the kinds and composition oE
the elements constituting the superconductor an~ so on.
Preferably, the thickness is from 10 ~m to 3 mm.
As the raw material for the flame spraying, an~ of the
complex ceramics comprising the e].ements Ml, M2 and
M3 and the elements Ml, ~2 and M3 themselves or
their compounds can be used. Examples of the compounds of
the elements include oxides r carbonates and fluorides.
The complex ceramics as the raw material can be prepared
by presintering the compounds comprising the elements
Ml, M2 and/or M3.
As the atmosphere containing the element M3, oxygen
gas, nitrogen gas, fluorine gas, carbon dioxide gas,
sulfrous acid gas and mixtures thereof are exemplified.
Examples of the Ia group elements are Li, Na, K, Rb,
Cs and Fr, and examples of the Ib group elements are Cu,
Ag and Au.
Examples of the IIa group elements are Be, Mg, Ca, Sr,
Ba and Ra, and examples of the IIb group elements are Zn,
Cd and the like.
Examples of the IIIa group elements are Sc, ~,
lanthanides (e.g. La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, ~y,
Ho, Er, Tm, Yb and Lu) and actinides ~e.g. Ac, Th, Pa and
Cf), and examples of the IIIb group elements are ~ a,
In and Tl.
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-- 5
Among the superconductors, those comprising at least
one element selected from the Ib group elements, at least
one element selected ~rom the IIa and IIIa group elements
and lanthanides, and at least one e]ement selected from
5 the group consisting of oxygen, carbon and sulfur are
preferred, since a superconductor comprising those elements
has a higher Tc. Among the Ib group elements, Cu and ~g
are more preferred.
Particularly, a superconduc~or having much improved
superconductive properties can be produced, when the super-
conductor contains, as the Ml elements, at least two
elements elected from the elements of the Ia, IIa and IIIa
groups, for example, a combination of Y and Ba or La and
Sr, are used, or when the ceramic superconductor as such
is flame sprayed.
The substrate is selected from a wide variety of
materials. Examples of the substrate are inorganic
materials (e.g. glass, metals, ceramics, quartz, etc.) and
organic materials (e.g. organic polymers, etc.).
The substrate may be of any shape. Not only a plate
but also a wire, a tape, a sheet or a block can be used,
according to the end use of the superconductor composite
material.
When the substrate is an elongate substrate, such as a
25 wire or a tape, it is unwound from a supply reel and then
the raw material is continuously flame sprayed around the
substrate or onto a desired surface of the substrate. The
resulting elongate superconductor composite material is
wound onto a take-up reel. In this way, an elongate super-
30 conductor composite ~aterial can be continuously produced.
The substrate can be preheated to a temperature notlower than 500Q C . By preheating the substrate, a super
conductor having better superconductive properties can be
produced.
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6 -
If desired, the resulting superconductor composite
material can be heated at a high temperature, Eor example,
not lower than 500C, preferably not lower than 800C, and
more preferably not lower than 940C to improve its super-
conductive properties.
During such post-heating of the superconductor
composite material, the ceramic superconductor can be
peeled from the substrate due to the difference of co-
efficients of linear expansion between the superconductor
and the substrate. Therefore, the substrate preferably
has a coefficient of linear expansion not larger than
--6 / o
Examples of materials having such coefficient of
linear expansion are aluminum oxide (A12O3), iron-42%
nickel alloy, silicon nitride (Si3N4), beryllium oxide
t~eO), iron, platlnum, tun9sten and the like.
IE the post-heated superconductor composite material
is rapidly cooled, peeling of the superconductor from the
substrate is enhanced by the internal stress caused by
shrinkage. Therefore, the post-heated superconductor is
preferably cooled gradually. The cooling rate depends on
various factors, such as the kind of substrate and the
composition of the superconductor. The cooling rate is
usually from 100 to 300C per hour. To prevent a change
of superconductor composition, the post-heated super-
conductor composite material is preferably cooled in an
atmosphere containing the element M3.
Generally, the flame spraying is carried out in the
presence of oxygen, especially in air. The content of
oxygen in the flame spraying atmosphere is usually from
10 to 100% by volume, preferably from 16 to 60~ by volume.
If the flame spraying is carried out in the presence
of oxygen, the superconductor absorbs or reacts with the
oxygen and therefore an excess amount of oxygen is
contained in the Eormed superconductor, which results ln a
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deviation of the composition of the superconductor from
the intended composition and a decrease of the super-
conductive properties such as the critical temperature and
the critical current densi~y.
In such a case, the superconductor composite material
is post-heated in an oxygen-free atmosphere to eliminate
excess oxygen from the superconductor and thus adjust the
composition. The post-heating in the absence of oxygen
can be carried out at substantially the same temperature
as the above described post-heating. The "oxygen-free
atmosphere" herein referred to means an a~mosphere
containing substantially no oxygen and includes a reducing
atmosphere, such as a hydrogen atmosphere or a carbon
monoxide atmosphere, an inert gas atmosphere, such as
nitrogen, helium or argon, and an atmosphere having reducqd
pressure of, for example, not higher than lO Torr.
In another measure for preventing excess oxygen in the
formed superconductor, the content ~z'~ of the element M3
in the raw material is made smaller than the content (z) of
the element M3 in the formed superconductor. Thereby,
it is made possible to control the supply amount of oxygen
during flame spraying, and, in turn, the content (z) of the
element M in the formed superconductor. More
particularly, when the relationship between the contant z'
of the element M3 in the raw material, the oxygen content
in the flame spraying atmosphere and the supply amount of
oxygen, and the content z of the element ~3 in the
produced superconductor is established, the content z can
be precisely controlled. The content z' of the element
M3 in the raw material can be suitably adjusted according
to the oxygen content in the flame spraying atmosphere and
other spraying conditions. Preferably, the contents z'
and z satisfy the following equation:
O.l<z' /z<.l .0
especially
0.2<z'/z<0.5.
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A method for producing a superconduc-tor on a substrate
is il`Lustrated in the accompanying drawings.
Fig. 1 schematically shows a method for flame spraying
the raw material onto a substrate 1 to form a super-
5 conductor layer 3 thereon.
The raw materials, such as the complex ceramics, the
elements or the compounds, are sprayed from a spray nozzle
2 onto a suitable surface area of the substrate. Thereby,
the superconductor ]ayer 3 is formed to produce a super-
10 conductor composite material 4.
Fig. 2 shows a method for forming a superconductorlayer on an elongate substrate such as a wire or tape. An
elongate substrate 11 is unwound from a supply reel 13.
Then, the raw materials are flame sprayed around or onto a
15 surface of the elongate substrate 11 ;Erom a noz~le 12 to
form a superconductor layer. The superconductor composlte
material 15 comprising the substrate 11 and the
superconductor layer is wound onto a take-up reel 14. If
desired, the wound composite material can be subjected to
20 post-treatment, such as post-heating.
The present invention will be further explained by the
following Examples.
~ x_mpl__l
On a copper tape as a substrate, a ceramic super-
25 conductive material having a composition ofLal 6SrO 4CuO4 is flame sprayed to continuously
form a ceramic superconductor film having substantially
the same composition and a thickness of 0.5 mm on one
surface of the substrate.
The ceramic superconductor composite material is
heated in the air at l,OOOQC for 3 hours and thereby the
superconductive properties are further stabili~ed.
The ceramic superconductor composite material has a
critical temperature of 20 K and no defect such as
35 cracking
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Exampl__2
On a copper tape as a substra-te, a film of a material
having a composition of Lal 6Sr0 4Cu and a thickness
of 0.5 mm is con~inuously formed. Then, it is heated in
the oxygen atmosphere at 950C for 6 hours to form a
ceramic superconductor film having a composition of
Lal 6Sro.4CU4
The ceramic superconductor composite material has a
critical temperature of 20 K and no defect such as
crackin~.
Example 3
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On a copper tape as a substrate, powder of La, Sr and
Cu is Elame sprayed in an oxygen atmosphere to continuously
form a ceramic superconductor Eilm 3 having a composition
of Lal 6Sr0 4CuO~ on one surface of the substrate 1
as shown in Fi~. 3.
On the superconductor Eilm 3, copper 5 is flame sprayed
to produce a ceramic superconductor composite material in
which the superconductor film is sandwiched between the
copper layers. The three layered ceramic superconductor
composite material is heated in an oxygen atmosphere at
950C for 6 hours, and thereby the superconductive
properties are further stabilized.
The ceramic superconductor composite material has no
defect such as cracking.
Example 4
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On a copper tape as a substrate, powder of Y2O3,
BaCO3 and CuO is plasma sprayed to continuously form a
ceramic superconductor film 3 having a composition of
Y0 3BaCu0 7zl and a thickness of 0.3 mm on one
surface o~ the substrate.
On the superconductor film 3, copper 5 is flame
sprayed to a thickness of 0.1 mm to produce a ceramic
superconductor composite material in which the super-
conduc~or ~ilm is sandwiched between the copper layers~
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-- 10 --
The three layered ceramic superconductor composite materialis heated in an oxygen atmosphere at 800C. Thereby~ a
superconductor having a composition of Y0 ~BaCU0 7z2
and ;mproved properties is obtained.
The ceramic superconductor composite material has a
critical temperature of 50 K and no defect such as
cracking.
Example_5
A mixture of Y2O3 (1,129 9), BaCO3 ~5,300 9) and
10 CuO (3,600 9~ is heated at 900C for 12 hours and then
ground.
The ground mixture is plasma sprayed onto a surface of
a substrate made of aluminum oxide to form a ceramic super-
conductor fllm having a thickness oE :L00 ~m on the
15 substrate.
The resulting ceramic superconductor composite material
is heated in air at 940C for 6 hours and thereafter cooled
at a cooling rate of 60C/hr to form a superconductor film
having a composition of YlBa2Cu3O7.
The ceramic superconductor composite material has a
critical temperature of 87 K and no defect such as
cracking or peeling.
Comparative Example
__________________
The powdery raw materials prepared in the same manner
25 as in Example 5 are plasma sprayed onto a subs~rate made
of aluminum oxide to ~orm a ceramic superconductor film
having a thickness of 100 ~m on the substrate.
The resulting ceramic superconductor composite material
is heated in air at 400C for 15 hours and thereafter
30 cooled at the same cooling rate as in Example 5 to form a
superconductor film having a composition of
YlBa 2Cu307 .
The ceramic superconductor composite material has a
critical temperature lower than that of Example 5.
Example 6
_________
A mixture of Y2O3 (1,129 g), BaCO3 (5,300 9) and
~;
.
13~15 Eii4
CuO (3,600 g) is heated at 900C for 12 hours and then
ground.
The ground mixture is plasma sprayed onto a surface of
a substrate made of aluminum oxide to form a ceramic super-
5 conductor film having a thickness of 100 ~m on thesubstrate.
The resulting ceramic superconductor composite
material is heated at 940C under a reduced pressure of 1
Torr. for 6 hours and thereafter cooled at a cooling rate
10 of 60C/hr to form a superconductor film having a
composition of Y1Ba2Cu3O7.
The ceramic superconductor composite material has a
critical temperature of 83 K and stable superconductive
properties and no defect such as cracking or peeling.
Example 7
_ . _ _ _ ___ _
~ mixture oE Y2O3 (1,129 g), BaCO3 (5,263 g) and
CuO (3,579 g) is heated at 900C Eor 12 hours in a
hydrogen atmosphere (reducing atmosphere) and then
ground. The composition of the ground raw materials is
20 YlBa2.6cu4.so2
The ground mixture is plasma sprayed onto a surface of
a substrate made of aluminum oxide in air to form a ceramic
superconductor film having a composition of
YlBa2Cu3O6 and a thickness of 100 ~m on the
25 substrate.
The resulting ceramic superconductor composite material
is heated in air at 940C for 6 hours and thereafter
cooled to form a superconductor film having a composition
of YlBa2Cu3O7 and a critical temperature of 85 K
30 and stable superconductive properties.
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