AU742588B2 - Cryogenic deformation of ceramic superconductors - Google Patents

Description

-1I- Regulation 3.2

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

(ORIGINAL)

:0 0 Name of Applicant: Actual Inventors: University of Wollongong S. X. Dou Q.Y. Ru Y.C. Guo H.K. Liu Address for Service: Invention Title: DAV~IES COLLISON CAVE, Pattm Attcrzy-s,.

Cryogenic deformation of ceramic superconductors Details of Associated Provisional Application No: Australian Patent Application No: 76428/96 The following statement is a full description of this invention, including the best method of performing it known to us: Q:\OPER\MLA\76428-96.3S2.- 19/12/97 The present invention relates to the method and manufacture of ceramic superconductors.

In particular, the present invention relates to the manufacture of ceramic high temperature superconductors. The process of the present invention is particularly useful in the manufacture of tapes and wires of ceramic superconductors such as sheathed high temperature superconductors and will be described hereinafter with reference to that apparatus. Moreover, it will be appreciated that the invention is not limited to that particular field of use.

Ceramic superconductors in the form of tapes or wires have been manufactured by the technique known as Powder In Tube (PIT). The PIT technique is essentially a deformation process whereby a tube, typically silver or a silver alloy, is packed with a powdered ceramic Sosuperconductor or a precursor thereof and repeatedly drawn and/or rolled whereby the ceramic powder is compacted in a sheath, and is subsequently sintered. This process may typically be used to produce a metal/superconductor composite wire or tape which consists of one or more continuous superconducting filaments embedded in a metal matrix. It is 15 desirable that the metal provides mechanical support to the ceramic superconductor material, has good thermal conductivity to provide cryostability (maintenance of an even temperature throughout the ceramic superconductor material) and may serve as an electrical conductor in the event that the ceramic superconductor material reverts to the state in which it has normal conductivity, i.e. is no longer superconducting.

In one example of the PIT technique, a multifilament tape may be manufactured by packing a precursor powder of partially reacted oxides into a sealed silver tube or billet which is then reduced to around 1mm diameter by drawing through dies. The wire may then be passed through a rolling mill to produce a tape. The drawing and rolling processes may be repeated several times, with intermediate annealing of the silver sheath and heat treatment/sintering of the ceramic, resulting in high temperature superconductor tape typically 3-4mm wide and 0.2-0.5mm thick. A multifilament tape is produced by stacking a bundle of drawn wires into another tube, drawing it down to 1-2mm diameter and rolling and heat treating as before. It is preferred to use Bismuth Strontium Calcium Copper Oxide [(Bi,Pb) 2 Sr 2 Ca 2 Cu 3 (BSCCO-2223) high temperature superconductors in which the achievement of high critical current density is typically obtained with a microstructure of well-aligned superconducting grains with clean grain boundaries and strong flux pinning.

It is well known that the heat treatment of sintering schedule both during and after tape forming is critical to achieving the required ceramic composition and properties to provide optimum tape performance. It is widespread opinion in the art that better results could be obtained if drawing and rolling could be performed at temperatures comparable with the heat-treatment temperature of the material (in the region of 800-850'C), but the practical difficulties of doing so are generally considered insurmountable.

High temperature superconductors have been the subject of considerable development, particularly in processes for their manufacture, over the last ten years. High temperature •..superconductors often require high critical current density J, in high strength magnetic fields. It has been suggested that Jc and Jc-field performance of high temperature superconductors is limited by both weak links at grain boundaries and poor flux pinning e which causes rapid flux creep in high temperature superconductors. Intensive work has been carried out to increase Jc and significant advances have been made. In the manufacture of ceramic superconducting materials, powder processing, mechanical deformation and heat •oooo treatment are important processes among many fabrication techniques. These three key processes determine the microstructure of the ceramic superconductor and hence its electromagnetic and electrostatic properties. Mechanical deformation is a critical step in the processing and plays a major role in achieving grain alignment, densification and enhancement of flux pinning. Numerous mechanical deformation processes have been developed for fabricating ceramic superconducting materials. In particular, hot deformation including hot-pressing, isostatic hot-pressing, hot forging and hot rolling have been intensively investigated in the past ten years. Hot deformation processes, typically about 800 to 850C have been understood to be superior to room temperature deformation in achieving texture and grain connectivity, which result in improvements of Jc and Jc-field performance.

It has been found that improved flux pinning in a ceramic superconductor may be obtained by subjecting the ceramic superconductor or a precursor thereof to cryogenic deformation (deformation at depressed temperatures).

According to a first aspect of the invention, there is provided a process for producing a ceramic superconductor which comprises the steps of: RA forming a ceramic superconductor material having a metal sheath; cryogenically deforming the sheath; and sintering the material.

Ceramic superconductor materials suitable for use in the process of the present invention include, but are not limited to, ceramic high temperature superconductors such as Yttrium barium copper oxide (YBa 2 Cu 3 0 7 (YBCO 123); Bismuth Strontium Calcium Copper Oxide (Bi 2 Sr 2 CaCu2Ox) (BSCCO 2212); Lead stabilised Bismuth Strontium Calcium Copper Oxide [(Bi,Pb) 2 Sr 2 Ca 2 Cu 3 Ox] (BSCCO 2223); Thallium Barium Calcium Copper Oxide (TilBa 2 Ca 2 Cu 3 Oy) (TBCCO 1223); Thallium Barium Calcium Copper Oxide S(T12Ba 2 CaiCu 2 O) (TBCCO 2212); Thallium Barium Calcium Copper Oxide 10 (Tl2Ba 2 Ca 2 Cu 3 Oy) (TBCCO 2223); Mercury Barium Calcium Copper Oxide (HgBa 2 Ca 2 Cu 3 Oy) (HBCCO 1223); and 1212 type superconductors such as [(Pb,Cd).

Sr 2 (Y,Ca) Precursor materials of the ceramic superconductor materials include oxides, carbonates, nitrates and other compounds which contain the metal elements in the desired proportions.

Where the precursor materials are a mixture of separate components, the components are Sgenerally combined in amounts which promote the formation of the ceramic superconductor material. For example, in the formation of Bismuth Strontium Calcium Copper Oxide (BSCCO 2223) the desired precursor materials are powders prepared by co-decomposition of metal nitrate solutions having the cation ratio of Bi:Pb:Sr:Ca:Cu 1.84:0.35:1.91:2.05:3.06. The powders may be calcined and may contain the 2212 as the major phase. The precalcined powders may be transformed to the 2223 phase by sintering at about 830 0

C.

The ceramic superconductor material or precursor material thereof may be formed into a structure suitable for cryogenic deformation by any convenient means, including by moulding, pressing, slip casting and extrusion.

P (PEP :ILA .IITS P'Ri) I: The ceramic superconductor material or precursor material thereof is cryogenically deformed.

By the term "cryogenically deformed" it is meant permanent deformation of the ceramic superconductor material or precursor material thereof as a result of stress applied to the material at a temperature below ambient, or room, temperature. Advantageously the cryogenic deformation is conducted at a temperature below 0°C, preferably in the range of from 0 C to 269°C. More preferably the cryogenic deformation is conducted at a temperature in the range of from -40 0 C to -269 0 C. Most preferably the cryogenic deformation is conducted at a temperature in the range of from -150 0 C to -210 0 C. Conveniently, the cryogenic deformation may be conducted at temperatures resulting from cooling under liquid nitrogen conditions.

Alternative means of cooling suitable for use in the present invention include the use of dry ice (solid carbon dioxide), liquid helium, or refrigeration with a suitable liquid such as brine, kerosene or an ozone-friendly halohydrocarbon.

The cryogenic deformation may be conducted by any convenient deformation process which may 15 be adapted for use at the depressed temperatures. Suitable deformation processes include drawing, rolling, swaging, pressing and forging. The selection of appropriate deformation o. processes will depend on the size and shape of the ceramic superconductor. Typically, the process for the manufacture of a ceramic superconductor will involve more than one deformation process. In order to obtain improved flux pinning it is necessary for at least one of the deformation processes to be a cryogenic deformation.

The cryogenically deformed ceramic superconductor is subsequently sintered. The sintering of the cryogenically deformed ceramic superconductor may be conducted at temperatures usually employed in sintering ceramic superconductors such as those used in respect of ceramic superconductors which have been subjected to conventional deformation processes. It is desirable for the sintering process to promote the formation of a continuous structure with good grain connectivity, increase the alignment of the grains and increase the density of the ceramic superconductor. In some instances the sintering process will also serve to promote the change of microstructure and/or phase of the ceramic superconductor.

rM 1 large number of applications ceramic superconductors are manufactured in the form of composites with conducting metals. Typically, ceramic superconductors exhibit high electrical resistance at temperatures in excess of the superconducting transition temperature.

A composite of conducting metal and ceramic superconductor is often used to permit the current to flow through the conducting metal in the event of the transition of the ceramic superconductor to normal conductivity. In the production of ceramic superconducting wires, tapes and the like it is often convenient to form the ceramic superconductor as a composite due to the practical difficulties of manufacturing fine elongate ceramic articles.

It has been found that it is possible to achieve improved control over the shape and dimensions of the ceramic superconductor component of a ceramic superconductor/metal composite manufactured by a process in which the composite is subjected to deformation processes.

According to a second aspect of the invention there is provided a process for producing a ceramic superconductor/metal composite comprising the steps of.

fort-ning a metal composite with a ceramic superconductor material or precursor material thereof, see.

cryogenically deforming the composite; and sintering the cryogenically deformed composite.

It has been found that in the production of elongate ceramic superconductor/metal 0: composites such as sheathed wires or tapes, improved uniformity of cross section may be achieved in the ceramic superconductor component by the process of cryogenic deformation of an elongate metal composite with a ceramic superconductor material thereof According to a third aspect of the invention there is provided a process for producing an elongate ceramic superconductor/metal composite comprising the steps offorming an elongate metal composite with a ceramic superconductor material or precursor material thereof, cryogenically deforming the elongate composite; and I RAq sintering the cryogenically deformed elongate composite.

Oe D IVTO' 21930-O'O.DOC -7- Ceramic superconductor/metal composites of the second aspect include pellets, disks and various shaped composites for specialised applications.

Elongate ceramic superconductor/metal composites include sheathed wires, taped, coils, leads and cables made therefrom.

The metal is typically selected according to the desired properties of the composite. For example, in the production of high temperature superconducting wires or tapes it is desirable to use silver or silver alloys to sheath the high temperature superconducting material. It is also desirable that that metal sheath has a sufficiently high yield stress or flow stress to control the uniformity of cross section of the ceramic superconductor and to limit the effects of "sausaging". "Sausaging" is the variation in cross-section of the ceramic core along its length which has been postulated to result from the difference in "hardness" too: ,06 between the core and the sheath. Other metals may be used to form composites and may be 4 15 selected according to specific applications.

°0 S•The metal composite with a ceramic superconductor material or precursor material thereof of the second and third aspects of the invention may be formed by any convenient means including by the PIT technique, the doctor/blade process, the dip coating process and the 20 like. Processes such as the PIT technique result in the ceramic superconductor material or 4.o.

precursor material thereof being encased in a metal conductor. Processes such as the o4 0 doctor/blade and the dip coating process result in the ceramic superconductor material or S° precursor material thereof forming a thick film on a metal substrate. It will be understood that the process by which the composite is formed is not narrowly critical. However, it has been found that the formation of the elongate metal composite with a ceramic superconductor material or precursor material thereof by the PIT technique is particularly advantageous.

While not wishing to be bound by theory, it is believed that as a result of the cryogenic deformation cold conditions, the yield stress or flow stress of metal is increased significantly which allows for greater control of and potentially increased pressure to be applied to the ceramic superconductor during the cryogenic deformation process. In the Xformation of silver sheathed ceramic superconductors it is believed that the increased yield 21930-00.DOC stress or flow stress of the silver sheath gives rise to the enhanced effects of improvements in grain alignment, grain connectivity and smoothness of silver-oxide core interface similar to those achieved by using a more expensive silver alloy in conventional deformation processes.

In an example of the third aspect of the present invention a powder of ceramic superconductor material or precursor material thereto may be packed into a silver tube. The silver tube is sealed and subsequently drawn to form a wire. The drawn wire may be subjected to further drawing or rolling to obtain the desired cross-section of the ceramic superconductor and the composite. In accordance with the invention at leats one of these drawing and/or rolling operations is a cryogenic deformation process whereby the composite is preferably drawn or rolled at a temperature resulting from application of liquid nitrogen to the composite and/or the rolling or drawing equipment.

*0•0 15 Preferred embodiments of the present invention may be used in the formation of 0@ o" •multifilamentary tapes and the like. In the formation of multifilamentary tapes sheathed ceramic superconducting wires may be packed into an outer sheath. The sheathed bundle of ceramic superconducting wires may then be subjected to cryogenic deformation and a multifilamentary tape produced and sintered.

r: *see.

•It has been found that it is necessary that at least one of the drawing or rolling steps be •conducted under cryogenic conditions. For economic reasons it may be desirable that the amount of cryogenic deformation is limited. However, it is preferable that each deformation step in the production of wires and tapes occurs under cryogenic conditions.

While not wishing to be bound by theory, it is believed that conducting the cryogenic deformation in the initial drawing and/or rolling steps the yield stress or flow stress of the metal is increased and the effects of sausaging are reduced. Also in order to reduce "sausaging" when the round wire is rolled to form a flat tape it is believed to be desirable that at least the first rolling process is a cryogenic rolling. It also appears that cryogenic deformation in the final deformation stages provides an increase in the density of defects such as dislocations and as a result enhanced flux pinning is obtained.

21930-00.DOC -9- It has been found that in the manufacture of elongate high temperature superconductor/metal composites the cryogenic deformation process improves the grain connectivity, grain alignment, metal/cor interface and consequently critical current density.

It has been found that ceramic superconductors produced according to this process exhibit enhanced flux pinning. While not wishing to be bound by theory it is believed that the enhanced flux pinning effect is attributable to the high density of defects such as dislocations introduced by the process of the present invention.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the Sexclusion of any other integer or group of integers.

o 15 The present invention is further described by reference to the following non-limiting S: examples.

Example 1 Cryogenic pressing of Ag-clad Bi2223 multi filamentary tape Ag-clad Bi-2223 multi filament wire was prepared by the powder-in-tube technique, drawn and rolled to 0.31 mm thick tape at room temperatures. Tapes were made from this wire.

The resultant tapes were sintered at 840 0 C for 50 hours. After the first sintering the tapes were processed by two different procedures.

Schedule I: the tapes were processed normally by pressing at room temperature at the different pressures listed in Table 1 and sintered at 840 0 C for 30 hours and 825°C for hours.

Schedule II (the cryogenic deformation process): the tapes were pressed in liquid nitrogen, about -196°C, at various forces listed in Table 1 and sintered with the same procedure as schedule I. The results of these two processing schedules are given in Table 1.

21930-00.DOC 9a The transport critical current density for short tapes was determined from the current/voltage curve using a 1pV/cm criterion. The measurements of the ac susceptibility, magnetisation and magnetic relaxation were performed on the Ag/Bi-2223 tapes using a Physical Property o* oo *o o 21930-00.DOC P OPEK M1LA NMM S IR(1 I: 1v Measurement System (PPMS). For the comparison of different samples, the ac amplitude and frequency are maintained at constant values of 50e and 117Hz respectively. Microstructural and compositional characterisations were performed with a JEOL JXA-840 Scanning Electron Microscope (SEM) equipped with Link Systems AN 10000 energy dispersive spectrometers.

The results of Table 1 show that after first sintering the critical current, J, for all tapes is nearly the same. For the same reduction in thickness, to 0.275mm, the J. for both cryogenically pressed tape and normal pressed tape is about the same. It has been found that at high pressure, the cryogenically pressed tape has a J 20% higher than that of the tape pressed under normal processing conditions.

Fig. 1 shows the dependence of normal Jc on magnetic field for Ag-clad multi filamentary tapes processed by the two schedules. A cryogenically pressed tape (960707-17#) with 14.5% reduction holds 26% of zero field at 77K in 1T, with the field applied parallel to the tape 15 surface.

€*o It has also been observed that for the same applied pressures, the normal pressed tapes have a much larger thickness reduction than that of the cryogenically pressed tapes. For example, at a force of 7.5 tonne the reduction for normal pressed tape is 26%, while it is only 13% for the 20 cryogenically pressed tape.

Fig. 2 and Fig.3 show the SEM images for normal pressed tape and cryogenically pressed tape respectively, both having similar thickness reduction. It is evident that filaments of the cryogenically pressed tape have higher density, better alignment, less impurities and smoother interface than those of normal pressed tapes. For normal pressed tape, a large force tonne) results in the formation of undulating filaments and "sausaging effect" as shown in Fig.

4, while for the same applied pressure on cryogenically pressed tapes there is little evidence of sausaging as shown in Fig. 4.

Table 1. Multi filamentary Tapes Made from 4) 10 x 9 4 10 x 8mm Silver Tubes P:\OPER\MLA\MMHTS2.PRO- 18/12/97 11 *Original Thickness: 0.31mm Sample No. 1st Sinter Press method Press force Thickness 2nd sinter J, at T

J,

960707-19# 8.00A Normal press 4.50 t 0.275 mm 31.1A 23% 960707-15# 8.25A Normal press 7.50 t 0.23 mm 34.5A 18% 960707-16# 8.80A Cryogenic 4.50 t 0.295 mm 25.5A 960707-20# 7.00A Cryogenic 6.00 t 0.275 mm 30.8A 23% 960707-18# 8.80A Cryogenic 7.50 t 0.270 mm 34.5A 960707-17# 8.65A Cryogenic 9.50 t 0.265 mm 37.5A 26% 9 9**9 9 9 99* a *9 Example 2 Cryogenic pressing of Ag-clad Bi-2223 monofilamentary tape 15 The tapes were prepared by the same procedure as described in Example 1. The results are given in Table 2 for both normal pressed tapes and cryogenically pressed tapes. We observed that for the same thickness reduction (0.26)/(0.305) the cryogenically pressed tapes show a increase in Jc. It is also noted that to reach the same thickness, the pressure for cryogenically pressed tape is nearly double that for normal pressed tape.

P:\OPER\MLA\MMHTS2.PRO 18/12/97 -12- Table 2. Monofilamentary Tapes Made from 4 10 x 9mm 10 x 8mm Silver Tubes Original Thickness: 0.305mm Sample No 1st Sinter Press Method Press Force Thickness 2nd Sinter 960707-6# 8.70A Normal press 4.50 t 0.26 mm 41.2A 960707-4# 8.20A Normal press 7.50 t 0.21 mm 31.8A 960707-1# 8.70A Cryogenic 4.50 t 0.28 mm 34.1A 960707-3# 9.00A Cryogenic 7.50 t 0.265 mm 40.8A 960707-2# 8.90A Cryogenic 9.50 t 0.260 mm 45.5A a

S.

S..

*4

S

S.

Example 3 Cryogenic pressing of Multi filamentary Ag/Bi-2223 Tapes 15 A powder-in-tube method was used to prepare 27 filament, multifilamentary Bi-based Agsheathed Bi-2223 tapes. The procedure of Example 1 was used. Powders were prepared by co-decomposition of metal nitrate solutions having the cation ratio of Bi:Pb:Sr:Ca:Cu 1.84:0.35:1.91:2.05:3.06. The powders were calcined and contained 2212 as the major phase before loading to a silver tube. A silver tube of 10mm outer and 8mm inner diameters was filled with the pre-calcined powders and the composites were then drawn to a final diameter of 1.2 1.6mm and restacked into a silver tube of 10mm outer and 8mm inner diameters, then the multi filament composites were drawn to a final diameter of 2mm. The wires were then rolled into tapes of overall thickness of 0.2mm. The long 27-filament tape was sintered at 832 0 C for 60H, 80H, and 80h, with intermediate room temperature rolling.

Four sets of tape segments were cut from the sintered tape. A first set of tape segments were used as reference without further treatment. This first set was designated as the Rolled Sample. A second set of tape segments were pressed at room temperature which is designated as the Pressed Sample. A third set of tape segments were sandwiched between stainless steel plates and pressed under at 15MPa for 15 min at 800°C under Argon, which were designated as the Hot-Pressed Sample. A fourth set of tape segments were pressed in liquid nitrogen P:\OPER\MLA\MMHTS2.PRO- 18/12/97 13 which were designated as the Cryogenically Pressed Sample. The Pressed, Cryogenic- Pressed and Hot-Pressed Samples were then further sintered at 832 0 C for 80h in air.

Figure 5 shows the dependence of J, on magnetic fields at 77K with field applied perpendicular to the tape surface. At low magnetic field, a rapid drop in J, may be attributed to the Josephson weak links in the grain boundaries. It is noticed that J, shows a large drop in low magnetic field for Rolled Sample. The Jc for Cryogenic Pressed tapes was also lower than that for the Hot-Pressed Sample in low fields up to 100 Oe. In high fields, however, the J, of the Cryogenic Pressed Sample crosses over that of the Hot Pressed Sample and drops io.

10 more slowly with increasing field above 150 mT than'the Hot-Pressed Sample or the Rolled Sample. These results indicate that the hot-pressing improves the grain connectivity and hence the weak link behaviour in low fields whereas the cryogenic pressing induces more defects, resulting in improvement in flux pinning.

o 15 Figure 6 shows the normalised pinning force density for the Rolled, Cryogenically Pressed and Hot Pressed Samples in magnetic fields. The peak field for the Cryogenically Pressed Sample is higher than for the Rolled Sample. The peak of the Rolled Sample is in turn higher than that for the Hot Pressed tape and is consistent with the J H measurement results.

Figure 7 shows the irreversibility lines (IL) of Rolled, Pressed and Hot-Pressed and Cryogenically Pressed Samples which were all taken from an original 27-filamentary tape, all having the same mass and dimensions. The IL were determined from the position of the peaks in the imaginary part of the ac susceptibility as described previously. The 27filamentary tape had already been subjected to three rolling-sintering cycles prior to the additional pressing and sintering. It is seen that the IL for the Pressed Sample is positioned at higher temperatures than the Rolled Sample while the position of the IL for the Hot-Pressed Sample is lower than the that of the Rolled Sample.

P:\OPER\MLA\MMHTS2.PRO- 18/12/97 14- The most significant shift in the IL position from the Hot-Pressed Sample to the Pressed Sample occurs in the temperature region of 40K-70K with a shift of about 10K. It has been established that the IL is a measure of the coupling strength between the superconducting CuO 2 planes. For the same compound, the IL is dependent of flux pinning strength. The sample size and geometry will also influence the position of the IL. Since all the three samples are the same high temperature superconductor compound, the distance between CuO 2 planes is the same. Also all three samples have similar dimensions and the shift in the IL position believed to be solely attributable to the difference in pinning strength.

10 Figure 8 shows the hysteresis loops for the Rolled, Pressed and Hot-Pressed 27 Multi filamentary tapes at 77K. It is seen that the Hi, follows the same sequence as those determined by ac susceptibility measurements in figure 7, confirming that cryogenic deformation improves the pinning compared with the Hot Pressed Sample.

C.CC

It is believed that cryogenic deformation produces more defects than normal or hot deformation. Although it is difficult to calculate precisely the density of dislocations, high density of dislocations are commonly observed in cold pressed tapes. It is believed that the high density of dislocations in the cryogenically pressed tapes is responsible for the improvement in irreversibility behaviour.

Example 4 Cryogenic rolling of Ag-clad Bi-2223 Tapes The Ag/Bi-2223 wires were prepared by PIT method as described in Example 3. The resultant wires were rolled through liquid nitrogen. For comparison, the same batch wires were also rolled at room temperature. Both tapes were rolled down to thickness of 0.15mm with reduction rate of 20%. The tapes were then cut into 30mm long pieces and sintered at 852°C for 35h. The tapes were then pressed at 2MPa and followed by sintering at 842°C for and 825 0 C for P:\OPER\MLA\MMHTS2.PRO- 18/12/97 Table 3 summarises the results of 13 tapes processed by these two processes. The average Ic for cryogenically rolled tapes is 15% to 20% higher than those rolled at room temperature.

Average J, for the cryogenic pressed tapes is 21,600 A/cm 2 at 77K zero field compared with 16,000 A/cm 2 for tapes pressed at room temperature.

Fig. 9 and 10 show SEM images for room temperature rolled tape and cryogenically rolled tape, respectively. It is evident that the cryogenically rolled tape has higher density and better texture than that of room temperature rolled tape.

4 10 Table 3 Critical Current of the Samples at 77K Sample No After 1st Sinter After 2nd Sinter Rolling type 1 1.42 7.29 RTR 2 2.40 10.0 CR 3 1.05 5.15 RTR 4 2.17 8.00 CR 1.40 6.27 RTR 6 1.56 6.78 CR 7 1.40 6.71 RTR 8 1.84 8.60 CR 9 1.27 6.34 RTR 1.45 7.24 CR 11 1.14 6.9 RTR 40 0 RTR Room Temperature Rolled CR Cryogenically Rolled P:\OPER\MLA\MMHTS.PRO- 18/12m 16- Example Effect of Reduction Rates on Critical Current Densities in Cryogenic- and Normal Deformation Processes Multi filamentary tapes, processed using the same procedure as in example 1, were pressed at varying pressures in liquid nitrogen and room temperature condition respectively. Fig. 11 shows the thickness reduction versus deformation pressures. It is seen that the thickness reduction for normal pressed tapes is twice that of the cryogenically pressed tapes. Figs 12 and 13 show the Jc versus deformation pressure and thickness reduction. It is clear that for room temperature pressed tapes at higher pressures the Jc declines with increasing pressures, S. 1 l0 while J. increases for cryogenically pressed tapes. At the same thickness reduction, the J, for cryogenically pressed tapes is consistently more than 10% higher than that of room temperature pressed tapes.

Fig. 14 shows Transmission Electron Microscope (TEM) images of both cryogenically S* 15 pressed tape and room temperature pressed tape. It is believed that the density of dislocations for the cryogenically pressed tape is 5 10 times larger than that of room temperature pressed ,tape. It is believed that the high density of dislocations is responsible for the improvement of flux pinning.

20 Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications which fall within its spirit and scope. The invention also includes all of the steps, features, compositions and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of any two or more of said steps or features.

Claims (10)

1. A process for producing a ceramic superconductor which comprises the steps of: forming a ceramic superconductor material having a metal sheath; cryogenically deforming the sheath; and sintering the material.

2. A process according to claim 1 wherein said ceramic superconductor material is formed by one of the following: moulding; pressing; slip casting; and extrusion.

3. A process for producing a ceramic superconductor/metal composite which process comprises the steps of: 10 forming a metal composite with a ceramic superconductor material or precursor material thereof; cryogenically deforming the composite; and sintering the cryogenically deformed composite.

4. A process according to claim 3 wherein said metal composite with a ceramic superconductor material or precursor thereof includes pellets, disks and various shaped composites. a A process for producing an elongate ceramic superconductor/metal composite which process comprises the steps of: forming an elongate metal composite with a ceramic superconductor material or precursor material thereof; cryogenically deforming the elongate composite; and sintering the cryogenically deformed elongate composite. P:\OPER\MLA\MMHTS2.PR 18/12/97

18- 6. A process according to claim 5 wherein said elongate metal composite with a ceramic superconductor material or precursor thereof includes sheathed wires, tapes, coils, leads and cables made therefrom. 7. A process according to either claim 5 or claim 6 wherein the elongate metal composite with a ceramic material or precursor material thereof is a metal tube filled with the superconductor material or a precursor material thereof and wherein the filled tube is drawn and/or rolled repeatedly to reduce its cross section. 8. A process according to any one of claims 1 to 7 wherein said ceramic superconductor material is selected from the group consisting of Yttrium Barium Copper Oxide (Y 1 Ba 2 Cu 3 0 7 (YBCO 123); Bismuth Strontium Calcium Copper Oxide (Bi 2 Sr 2 Ca 1 Cu20x) (BSCCO 2212); Lead stabilised Bismuth Strontium Calcium Copper 15 Oxide[(Bi,Pb) 2 SrCa 2 Cu3Ox] (BSCCO 2223); Thallium Barium Calcium Copper Oxide (Ti 1 Ba 2 Ca 2 Cu30) (TBCCO 1223); Thallium Barium Calcium Copper Oxide(T 2 Ba 2 CaCu 2 0) (TBCCO 2212); Thallium Barium Calcium Copper Oxide (Tl 2 Ba 2 Ca 2 Cu 3 Oy) (TBCCO 2223); Mercury Barium Calcium Copper Oxide (HgBa 2 Ca 2 Cu30y) (HBCCO 1223) and 1212 type superconductors such as [(Pb,Cd). Sr 2 (Y,Ca) Cu 2 07]. 9. A process according to any one of claims 1 to 7 wherein the precursor material of the ceramic superconductor material is selected from the group consisting of oxides, carbonates, nitrates and other compounds which contain the metal elements in the desired proportions. A process according to claim 9 wherein said precursor material is a mixture of powders prepared by co-decomposition of metal nitrate solutions having the cation ratio of Bi:Pb:Sr:Ca:Cu 1.84:0.35:1.91:2.05:3.06 to form Bismuth Strontium Calcium Copper Oxide (BSCCO 2223) P:\OPERMLA\MMHTS2.PRO 18/12/97 -19- 11. A process according to any one of claims 1 to 10 wherein the cryogenic deformation is conducted at a temperature below 0°C. 12. A process according to any one of claims 1 to 11 wherein the cryogenic deformation is conducted at a temperature in the range of from 0OC to -269 0 C. 13. A process according to any one of claims 1 to 12 wherein the cryogenic deformation is conducted at a temperature in the range of from -40 0 C to -269 0 C. 14. A process according to any one of claims 1 to 13 wherein the cryogenic deformation is conducted at a temperature in the range of from -150 0 C to -210 0 C. A process according to any one of claims 1 to 10 wherein the cryogenic deformation Sis conducted at a temperature resulting from cooling with dry ice(solid carbon dioxide) 15 liquid nitrogen, liquid helium, or refrigeration with a suitable liquid such as brine, kerosene or an ozone-friendly halohydrocarbon. 16. A process according to claim 15 wherein the cryogenic deformation is conducted at Stemperatures resulting from cooling under liquid nitrogen conditions. 17. A process according to any one of claims 1 to 16 wherein the cryogenic deformation is conducted by at least one process selected from the group consisting of drawing, rolling, swaging, pressing and forging. 18. A process according to any one of claims 3 to 17 wherein said metal is selected from the group consisting of silver and silver alloys.

19. A process according to any one of claims 1 to 18 wherein said process is used for the production of multifilamentary tape. A ceramic superconductor produced by the process of any one of claims 1 to 19.

21. A ceramic superconductor produced in accordance with any one of claims 1 or 2 or claims 8 to claim

22. A ceramic superconductor/metal composite produced in accordance with any one of claims 3 or 4, and claims 9 to

23. An elongate ceramic superconductor/metal composite produced in accordance with any of claims 5 to

24. A process for producing a ceramic superconductor which process comprises the steps oof: forming a PIT composite metal sheathed ceramic conductor material; cryogenically deforming the composite; and i sintering the composite. A process according to claim 1 wherein steps to are performed sequentially. A process according to claim 1 or claim 25 wherein the ceramic superconductor material is of the PIT type. DATED this 7" Day of November 2001 UNIVERSITY OF WOLLONGONG Attorney: JOHN B. REDFERN Fellow Institute of Patent Attorneys of Australia of BALDWIN SHELSTON WATERS