Note: Descriptions are shown in the official language in which they were submitted.
x~
HOE 90/H 004
The present invention relates to a ~ethod for joining
parts of ceramic high-temperature superconductor material
of the composition Bi(z+ab~(Sr(lc~Cac)(3~Pk~Cu(2+d~C~/ where a
is 0 to 0.3, b is 0 to 0.5, c is 0.1 to 0.9, d i~ 0 to 2
and x has a value depending on the state of oxidation of
the metals present.
German Patent Application P 3,830,092.3, which is not a
prior publication, has disclosed a process for preparing
a high-temperature supexconductor of the compo~ition
Bi2(Sr,Ca)3Cu20~ with x values fxom 8 to 10. In this case,
stoichiometric mixtures of the oxides or carbonates of
bismuthl strontium, calcium and copper are heated to
temperatures fxom 870 to 1100C to form a homogeneous
melt. The homogeneolls melt is cast in molds and
solidifies therein. The castings taken from the molds are
heat-treated fox 6 to 30 hours at 780 to 850C and then
treated for at least 6 hours at 600 to 830C in an oxygen
atmosphere. In this way, platelets of an edge length ox
diameter of up to several cm and rods of up to 50 cm
length and 10 mm diameter can be produced, each of which
consist of a pure phase of the compound.
A di~advantage here is that the ceramic high~-temperature
superconductor described above is so brittle that it
cannot be rolled up for transport in the form of long
current conductors onto a drum of large diame~er (for
~xample 2 m) without breaking or suffering crack~ r
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particularly if the high-temperature superconduc~or i8 to
be used for heavy current transmission.
Geramic high-temperature superconductors in powder form
have also already been filled into silver tubes and the
tubes have been elongated by swaging and deep-drawing
until "wires" of the desired diameter were obtained, the
high-temperatuxe superconductor powder present in the
interior of the silver tubes being sinterable by heat
treatment to give a coherent core. In this case, th~
oxygen required for forming the superconductor diffuses
through the wall of the silver tubes.
The said "powder in tube" conductors withstand a certain
degree of bending, so that in principle they can be used
as current transmission conductors. A disadvantag
thereof is, however, that they can be bent without
destruction only at a small diameter~ and cannot be
interconnected into complicated systems.
It is therefore the object of the present invention to
indicate a method fo~ joining parts of ceramic high-
temperature superconductor material to give complicated
and e~tended structures, in which the junctions are also
superconducting. This i5 achieved according tv the
invention by heating the end faces of the parts located
at a g~p spacing apart from one another by means of a
fuel gas/oxygen -flame to temperatures fxom 750 to 875C
and simultaneously heating a rod of the same material
above the spacing gap until the melt thereof drips off
~ 3 ~
into ~he gap between the end ~aces of the two parts,
completely filling the gap, and then heat-trea~ing ak
lea~t the ~oint region between the two parts for 7 to 100
hours at temperatures between 780 and 850C.
If desired, the process according to the invention can
also be further developed by
a~ heat-treating at temperatures from 815 to ~30C,
b) the heat treatment time depending on the thickness
of the ~unction, a thicker ~unction requiring a
longer heat treatment time and vice versa,
c) the end faces of the parts to be joined being in a
: mutually parallei arrangement,
d) the end faces of the parts to be joined being in a
wedge shaped mutual arrangement, and
e) the ceramic high-temperature conductor material
parts to be join~d being each sheathed by a silver
tube.
The co~pounds used according to the invention, for
example Bi2(Sr,Ca)3Cu20~ (with x of about 8.~) melt incon-
gruently, i~e. they do nat have a melting point, but amelting intervalO Moreover, th~ surface ~ension of this
melt to~ards the solid phase in air is so high ~hat the
melt does not Lmmediately run off from the solid phase.
The~e two properties are good prerequisites for a
behavior which is similar to the joining of metals by
autogenouæ welding.
~he melting of the compound Bi2~Sr,Ca)3Cu2O~ (with x of
about 8.2~ takes placel for example, above 875C with
loss of oxygen, the melting temperature dropping to abou~
780C at x of about 7.5. The solid present after the
solidification of this melt is no longer superconducting,
but it can be converted again into the superconducting
state by heat treatment at about ~00C in a.ir.
In the method according to the invention, care must be
taken to ensure that the end faces of the parts to be
joined together are ~o hot that they can bond to the ~elt
dripping off from the heated rod.
In the method according to the invention, a thin ~unction
is heat-treated for 8 to 15 hours, whereas a thicker
junction is heat-treated for up to 100 hours.
The heat treatment of the junction between the p~rts can
be effected by subjecting the complete newly created
shaped part to the heat treatment in an oven. However,
_he h~at treatment can also be carried out locally by
arranging an electric miniature oven with precise
temperature measurement and control around the junction,
or by local high-~requency induction heating or by direct
he~ting using electrodes arranged transversely to the
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junction, or by laser pulses.
In the welding according to the invention of shaped parts
of high-temperature superconducting ceramic material,
sheathed with a silver tube, par~icular care must bP
taken to ensure that the fuel gas/oxygen flame does not
come into contact with the silver sheath and melts the
latter, since ~he melting points of silver and of the
high-temperature superconducting compound are not far
apart. The silver-free joint region between the two parts
joinad according to the invention can be, if desired,
sheathed with silver afterwards.
Applications of the method according to the invention are
illustrated diagrammaticall~ and in cross-section in the
attachad drawing, in which:
Figure 1 shows the joining of two round rods with end
faces arranged mutually parallel,
Figure 2 shows the joining of two thic]cer round rods
with the end faces in a ~edge~haped mutual
arrangement,
Figure 3 shows the joining of a thickex round rod and a
thinner round rod, with the end faces in a
mutually parallel arrangement,
Figure 4 shows the joining of a thin disk to a round rod
..... .. .... .. .. . . . . . . . . . . . . . .
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with the end faces in a mu~ually parallel
arrangement,
Figure 5 shows a device for the local heat trea~ment of
joints of round rods, and
~igure 6 shows temperature/resistance diagr~ms.
In Figure 1, the hatching A represen~s the solidified,
non-superconducting melt, and the hatching B represents
the superconducting compound after further heat
treatment.
Illustration a shows the joint of the round rods
Lmmediately after solidification of the melt which has
dripped into the gap, while illustration b shows the
junction after heat treatment for 24 hours at 815C.
In Figure 3, there are cavity regions in the longitudinal
axis of ~he thicker and the thinner round rod.
In Figure 5, there is a ceramic heat carrier 1, which
contains resistance-heating coils 2, is fi.xed via tube
pas~ages 4 in holders 3. 5 represents the joint se~ of
two round rods of ceramic high-tQmperature superconduc~or
~0 material. A thermocouple 6 is located closa to the ~oint
seam 5.
In Figure 6, three measurements on the parts joinsd
according to the invention by the procedure o~ E~ample 1
. . .. . . .. . .. ..
are represented; in detail, curves 1 and 2 show the
measuxements on each of the joined parts and curve 3
shows the measurement in the joint region of the two
parts beyond the weld.
Example l
Two round rods of 5 mm diameter and 150 mm length,
prepared by the process according to German Patent
Application P 3,830l092.3, were pushed to~ether on a
cer~mic substrate, leaving a gap, until their end faces
were mutually parallel. The Pnd faces were heated to
bright-red heat by means of a natural gas/oxygen flame.
SLmultaneously, a round rod o~ the same material above
the gap was heated to such a degree that melt dripped off
into the gap. The gap was uniformly ~illed with melt by
slowly rotating the two round rods '(cf. Figure l,
illustration a). After heat treatment of the joined round
rods for 12 hours at 815C in an oven, the ~oint zone
between the two ro~nd rods wa~ superconductiny (cf.
Figure 1, illu~tration b).
The transition temperature of the joint zone of the two
round rods was 85.5 ~; to the right and lef~ thereof,
~ransi~ion ~emperatures of 86.0 and 85.5 ~ respectively
w~re measured (cf. Figure 6).
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Example 2
Two round rods of 12 mm diameter and 300 mm length,
prepared by the process according to German Patent
Application P 3,830,092.3, were placed with their end
5 faces in a wedge-shap~d mutual arrangement. By means of
a propane gas/oxygen flame, the open wedge was heated and
incipiently melted from the ba~e, before melt from a
dripping round rod of the same material dripp~d from
above into the wedge and filled it completely (cf. Figure
2). The joined round rods were then heat-treated in an
oven for 24 hours at 800C.
In order to check whether the joint zone between the two
round rods was now superconducting, -the specific
resistance of the joined round rods was measured.
At 293 ~ before heat treatment: 1 n~x cm
At 293 ~ after heat treatment . 0.001 ~ x cm
At 77 R after heat treatment : 0 n x cm
Example 3
Example 2 was repeated with the modi~ication that a round
rod of 5 mm diameter and 120 mm length and a round rod of
16 m~ diameter and 40 mm length were clamped into a
holding device in such a way that their axes were
centered and theix end faces were arranged mutually
parallel (cf. Figure 33.
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The measurement of the specific re~istance of tha joined
round rods gave:
At 293 g kefore hea~ treatments 2~8 n x cm
At ~93 K after heat treatment : 0.0015 n x cm
At 77 R af~er heat ~reatmen~ : 0 n x cm
E~amplQ 4
Example 2 was repeatPd with the modification that a round
rod of 5 mm diameter and 80 mm length was joined perpen-
dicularly to a circular plate (20 mm di~meter, 5 mm
thicknes~) (cf. Figure 4). In this case, care was taken
to ensure that the heating of the thin disk was less
intensive than that of the round rod.
E~ample 5
Example 2 was repeated with the modifications that round
rods of 8 mm diameter were joined to one another and the
heat treatment was carried out by local heat trea~ment of
the joint zone. For this purpose, an electric miniatuxe
oven was used which wa~ placed around the round rod in
the region of the ~aint zone and provided with a heat
in~ulation of alumina wool. A laterally introduced
thermocouple was used for temperature control tcf. Figure
5).
. . .. . . ..
