DE10049663A1 - Precursor material used in the production of an oxide superconductor contains a bismuth-containing phase as the main component and copper oxide - Google Patents

Abstract

Precursor material contains a bismuth-containing 2223-phase as the main component and 0.1-20 wt.% Cu2O. An independent claim is also included for a process for the production of a precursor material comprising heat treating a starting material containing Bi, Pb, Sr, Ca and Cu in a ratio of (Bi, Pb): (Sr, Ca): Cu of 0.5-1.2: 1.0-1.8: 1 so that the precursor material obtained contains 0.1-20 wt.% Cu2O. Preferred Features: The heat treatment is carried out in air above 900[deg]C or in a reducing atmosphere.

Description

The invention relates to a precursor material for production of an oxide superconductor, the superconducting property essentially through a bismuth-containing 2223 phase be determined, as well as a method for producing a such precursor material and a method for manufacturing of a superconductor with such a precursor material.

Such superconductors belong to the so-called high-T _C superconductor materials and have cuprates based on the Wis mut material system Bi-Sr-Ca-Cu-O, whereby individual components of this material system can be at least partially replaced by others. In particular, a corresponding, partial substitution of the Bi component by Pb is possible. In a 2223 phase there are 3 copper-oxygen network levels within a crystalline unit cell. This phase is particularly stable when Bi is partially substituted by Pb. The 2223 phase has a transition temperature of approximately 110 K.

The superconductors are usually in the form of ribbons or Wires, each with one or more filaments, generated. One method considered suitable for this is the so-called "powder-in-tube technique", corresponding to the one Pre-product (a so-called precursor material) in a tube shaped carrier or in a matrix of normal conductive Ma material, in particular made of silver or a silver alloy is introduced. The precursor material can be in the form of pul ver or a pressed body, such as a sta bes, available.  

In general, the precursor material contains the Bi-2212 phase as the main component. The 2212 phase differs from the 2223 phase essentially in that instead of 3 there are only 2 copper-oxygen network levels in its crystalline unit cell. The jump temperature of the 2212 phase is about 85 Kelvin. The precursor material generally also includes alkaline earth cuprates and in small amounts alkaline earth plumbates (in particular CaPbO ₄ and the 3321 phase) and CuO. The precursor material often contains further secondary phases, including, for example, a 2201 phase and alkaline earth metal oxides.

That by filling the precursor material into the carrier or structure obtained in the matrix is then by means of Deformation steps, which may be by at least one egg NEN heat treatment step can be interrupted, compact animals and brought to a desired dimension. After that the wire or ribbon-shaped intermediate conductor thus obtained product for adjusting or optimizing the superconducting egg properties or to develop the desired 2223 phase subjected to a final annealing, which is at least partially in an oxygen-containing atmosphere, for example in air, is carried out. This annealing treatment can also be done in several Steps or at several temperatures, with further deformation treatments to form the final dimension of the superconductor interposed could be.

If one bundles several corresponding ones in a manner known per se ribbon or wire superconductors or their conductors human or intermediate products, so you can also conductors with more ren superconducting conductor cores, so-called multi-core or Receive multifilament conductor.

Part of the diffuses during the generation of the 2223 phase Copper of the precursor in the normal conductive carrier or in the matrix so that a copper deficit can arise that  electrical properties of the superconductor, e.g. B. the critique cal current density, can affect negatively.

The invention has for its object a precursor rial with which an oxide superconductor whose superconducting properties essentially through a wis mutant 2223 phase can be determined can, the improved compared to the prior art e has electrical properties. A procedure is also intended for the production of such a precursor material and a Process for producing a superconductor from a sol Chen precursor material can be specified.

The object is achieved by a precursor material with a bismuth-containing 2212 phase as the main component and with a proportion of Cu ₂ O which is between 0.1 and 20 percent by weight.

Instead of CuO, the precursor material contains Cu ₂ O or a combination of CuO and Cu ₂ O. It has been shown that such a precursor material has a significantly increased reactivity. With this precursor material, a superconductor with the 2223 phase can thus be produced much faster, so that copper or CaCu levels can be built into the 2212 phase in a very short time. As a result, the copper has less time available to diffuse into the carrier or into the matrix, so that the risk of a copper deficit is reduced. Consequently, a superconductor made with such a precursor material has improved electrical properties.

Another advantage of the precursor material is that due to its low total oxygen content, there is significantly less bubble formation in the superconductor. It has also been shown that when superconducting the strips is produced by flat rolling processes, an improved texture of the 2212 phase and the 2223 phase compared to the prior art can be achieved if the precursor material according to the invention is used. The grain structure, texture and density of the superconductor are improved and lead to a high, critical current density, which is preferably more than 30 kA / cm ² .

The proportion of the 2212 phase in the precursor material is before preferably more than 50% by weight.

The object is further achieved by a method for manufacturing provision of a precursor material in which an output pro essentially produces the elements Bi, Pb, Sr, Ca and Cu bein holds, the ratio (Bi, Pb): (Sr, Ca): Cu 0.5 - 1.2: 1.0 - 1.8: 1. The starting material can be made from Verbin such as oxides and nitrates, which have the above elements.

The process is carried out so that the Precursorma material contains between 0.1 and 20 wt .-% Cu ₂ O. This can be done by controlling the calcining conditions.

For example, Cu ₂ O can be generated from CuO. When heated in air, CuO decomposes to Cu ₂ O and oxygen at approx. 1026 ° C. With a reduced oxygen partial pressure, the temperature at which Cu ₂ O is formed is correspondingly lower. In egg ner heat treatment of the starting product to produce the precursor material, the temperatures and the composition of the atmosphere to which the starting product is exposed during the heat treatment can be coordinated with one another in such a way that Cu ₂ O is formed. When choosing the calcining conditions it must be taken into account that Cu ₂ O can not only be formed from CuO but also from other compounds.

If the precursor material is generated by a heat treatment of the starting material in air, the temperatures are preferably above 900 ° C. The temperatures are preferably between 900 ° C and 1300 ° C. The heat treatment is preferably ended by cooling as quickly as possible in order to avoid decomposition of Cu ₂ O.

The phase diagram shown in the figure can serve as a guideline for which oxygen partial pressure at which temperatures can be used, so that the precursor material has Cu ₂ O. For example, the heat treatment is carried out at an oxygen partial pressure of less than 1% and at temperatures above 450 ° C., preferably above 650 ° C.

Alternatively, the heat treatment can take place in a reducing atmosphere, whereby Cu ₂ O is also produced at comparatively low temperatures.

For example, the heat treatment takes place in a nitrogen atmosphere or inert gas atmosphere, which has between 0.01 and 5% hydrogen, and at temperatures between 100 and 700 ° C. Other reducing atmospheres contain, for example, CO or NH ₃ .

To further increase the proportion of Cu ₂ O in the precursor material, a further heat treatment can be carried out after the heat treatment. The further heat treatment is carried out, for example, in a nitrogen atmosphere which has between 0.01 and 10% carbon monoxide and at temperatures between 200 and 800 ° C.

The object is further achieved by a method for the manufacture of an oxide superconductor, the superconducting properties of which are essentially determined by a bismuth-containing 2223 phase, in which a precursor material with a bismuth-containing 2212 phase as the main component and with a portion of the starting material Cu ₂ O, which is between 0.1 and 20 percent by weight, is used.

Since the precursor material has a low oxygen content due to the proportion of Cu ₂ O, all of the oxygen released by the precursor material can be incorporated into the 2223 phase, so that no bubbles are formed due to excess oxygen when the 2223 phase is formed. It may even be necessary to provide additional oxygen from the atmosphere in which the process is carried out to form the 2223 phase.

When performing the process in an oxygen-containing care must be taken to ensure that the resulting 2223 phase not decomposed. The decomposition temperature is from Oxygen partial pressure dependent. Suitable temperature and Pressure ranges are, for example, in DE 198 27 928, DE 198 15 140 and in the older, German registration with the registration file characters 198 60 074.7.

The oxygen partial pressure can change during the ver changing oxygen content of the precursor material be fitted to avoid blistering.

Preferably the heat treatment starts with a low one Oxygen partial pressure. The percentage of oxygen in the atmosphere is between 0.1 and 8 percent, for example. During the The partial pressure can be increased by heat treatment. In the The oxygen partial pressure is preferably cooled again decreased. A reduction in the partial pressure when cooling after the last annealing you can do without.

The heating rate is preferably high in order to prevent undesirable, premature decomposition of the Cu ₂ O. For example, the heating rate is more than 20 K / h.

The superconductor can be created by using the precursor rial in a conventional manner in a carrier or in a mat rix is filled in and then through heat treatments, Extrusion, drawing, hammering, bundling of filaments  and / or flat rolls processed with a progressive sequence becomes.

The precursor material can be filled into the carrier or are present in the matrix as powder or as pressed rods.

The following is a method for producing precursor Material described according to the state of the art:

A mixed oxide powder is produced by co-precipitation with subsequent spray drying and decomposition. This mixed oxide powder is subsequently annealed in a horizontal tube furnace at 780 ° C under a nitrogen atmosphere with 1000 ppm oxygen for 10 h. An X-ray fluorescence analysis shows that the precursor material thus obtained has the following composition:

Bi: 34.7% by weight,
Pb: 6.4% by weight,
Sr: 7.1% by weight,
Ca: 15.9% by weight,
Cu: 18.4% by weight.

The phase content of the precursor material (with SdT) according to Rieveld analysis of X-ray powder data is shown in the table.

Exemplary embodiments of the invention are described in more detail below explained.

In a first embodiment, a first and a second precursor material produced.

The starting material is a physical mixture of single oxide powders with the following weights:

792.9 g Bi ₂ O ₃ ,
135.3 g PbO,
417.4 g SrO,
224.5 g CaO,
477.2 g CuO.

The starting material is internal at temperatures around 1050 ° C melted in air for half an hour in platinum crucibles and finally cast in cold copper molds. The freezer This takes place within 3 seconds. The cooled Melt ingots are crushed and in an air jet mill ground up. Part of the powder thus obtained is in a isostatic press (dry bag process) to bars with one Diameter of 12 mm and a length of 100 mm pressed.  

100 g powder and 3 sticks are in egg at 30 ° C for 30 hours ner nitrogen atmosphere with 300 ppm oxygen in one Tube furnace annealed. This results in a first precursor material consisting of 100 g powder and a second precursor material consisting of 3 rods. The phase content of the according to the precursor materials (labeled P1 and P2) Rieveld analysis of X-ray powder data is shown in the table posed.

In a second embodiment, a third pre cursor material and a fourth precursor material generated.

About a co-precipitation with subsequent spray drying and decomposition, as described, for example, in US Pat. No. 5,238,914, produces a mixed oxide powder as the starting material. The mixed oxide powder thus obtained has the following composition:

Bi: 34.8 percent by weight,
Pb: 6.4 percent by weight,
Sr: 7.2 percent by weight,
Ca: 16.0 percent by weight,
Cu: 18.1 percent by weight.

Part of the powder thus obtained is in an isostati press to bars with a diameter of 12 mm and pressed to a length of 100 mm. 100 g and 3 sticks are included 800 ° C for 30 hours in an argon atmosphere at 50 ppm Oxygen annealed in a tube furnace. This will make it third precursor material in the form of powder and the fourth Precursor material generated in the form of rods. The phase ge stop of the third precursor material and that of the fourth pre cursormaterials (labeled P3 and P4) are in the table le shown.

In a third embodiment are used as the starting material rialien the third precursor material and the fourth Precur Sormaterial as in the second embodiment. Then the third precursor material (50 g powder) and the fourth precursor material (2 rods) at 150 ° C 10 hours in a nitrogen atmosphere with 1 percent hydrogen,  post-annealed in a tube furnace. Doing a five precursor material in the form of powder and a sixth Precursor material generated in the form of rods. The phase ge stop these precursor materials (labeled P5 and P6) are also shown in the table.

In a fourth embodiment, two output measures shown materials, the fifth precursor material and the sixth precursor material from the third embodiment example. The 50 g powder and the 2 sticks who in a further heat treatment at 350 ° C for 10 hours in a nitrogen atmosphere with 5 percent carbon monoxide in post-annealed. This will make a seventh pre cursor material in the form of powder and an eighth precursorma produced in the form of rods. The phase content of this two precursor materials (labeled P7 and P8) is in shown in the table.

In a fifth exemplary embodiment, a precursor material is provided as the starting material, which has about 1.5 percent by weight Cu ₂ O and more than 70 percent by weight 2212 phase. The precursor material is available as a rod with a diameter of approx. 12 mm. The rod is filled into a silver tube with an outside diameter of approx. 16 mm. After evacuation, the filled silver tube is cold-formed by hammering and drawing to produce single filaments with a diameter of approx. 1.3 mm. Then 55 such individual filaments are bundled in a silver alloy tube made of AgMg. The filled silver alloy tube is flat-rolled after evacuation and forming into a wire with a diameter of approx. 1.4 mm to the strip conductor.

After the rolling, a first reaction annealing of the strip conductor is carried out at 825 ° C. for 10 hours in an atmosphere consisting of 8 percent O ₂ . To produce a texture, rolling is carried out with a thickness reduction of approximately 10 percent. The strip conductor is then annealed again at approx. 825 ° C for 15 hours in an atmosphere consisting of 8 percent O ₂ and rolled again with a thickness reduction of approx. 10 percent to improve the texture. Finally, another annealing takes place in a multi-stage process between 830 and 790 ° C for 105 hours in an atmosphere consisting of 8 percent oxygen. The current density over the entire strip conductor is more than 6 kA / cm ² .

In a sixth exemplary embodiment, like in the fifth exemplary embodiment, a ribbon-shaped superconductor, the superconducting properties of which is essentially determined by a bismuth-containing 2223 phase, is produced. Up to and including the second texture rolling, the process steps correspond to the process steps of the fifth exemplary embodiment. In contrast to the fifth embodiment, however, the strip conductor is only annealed for 75 hours in the final annealing. The current densities of this strip conductor are also over 6 kA / cm ² .

In a seventh exemplary embodiment, a superconducting band conductor is produced similarly to the sixth exemplary embodiment. However, when heating up in the first reaction annealing and during the final annealing, the oxygen partial pressure is increased from initially 0.1 to 8 percent with increasing temperature. In the cooling phase of the two reaction anneals and the final annealing, the oxygen partial pressure is reduced from 8 percent with decreasing temperature to 1 percent. The oxygen partial pressure is adapted to the respective temperature in such a way that decomposition of the 2223 phase is avoided. The resulting Bandlei ter also has current densities of over 6 kA / cm ² .

table

Claims (10)

1. Precursor material for the production of an oxide super conductor, the superconducting properties of which are essentially determined by a bismuth-containing 2223 phase, with a bismuth-containing 2212 phase as the main component, characterized in that the precursor material contains between 0.1 and 20% by weight of Cu ₂ O contains. 2. A method for producing a precursor material according to claim 1, wherein one essentially contains the elements Bi, Pb, Sr, Ca and Cu, the ratio (Bi, Pb): (Sr, Ca): Cu 0.5-1 , 2: 1.0 - 1.8: 1, characterized in that the process is carried out in such a way that the produced precursor material contains between 0.1 and 20% by weight of Cu ₂ O. 3. The method according to claim 2, in which at least one heat treatment is carried out, the temperatures and the composition of the atmosphere, to which the starting product is set during the heat treatment, are matched to one another such that Cu ₂ O is formed. 4. The method according to claim 3, where the heat treatment in air at temperatures above 900 ° C takes place. 5. The method according to claim 3, in which the heat treatment with an oxygen partial pressure of less than 1% and at temperatures above 450 ° C. 6. The method according to claim 3, where the heat treatment in a reducing atmosphere sphere is done.   7. The method according to claim 6, where the heat treatment in a nitrogen atmosphere, which has between 0.01% and 5% hydrogen, and at Tem temperatures between 100 ° C and 700 ° C. 8. The method according to any one of claims 3 to 7, where after the heat treatment another heat treatment in a nitrogen atmosphere between 0.01% and Has 10% carbon monoxide, and at temperatures between 200 ° C. and 800 ° C is carried out. 9. A process for producing an oxide superconductor, the superconducting properties of which are essentially determined by a bismuth-containing 2223 phase, in which a precursor material with a bismuth-containing 2212 phase as the main component and with a proportion of Cu ₂ O between 0, 1 and 20 wt .-% be used. 10. The method according to claim 9,
in which at least one heat treatment is carried out,
where the oxygen partial pressure is between 0 and 20% with each heat treatment,
in which the heat treatment is interrupted by at least one mechanical deformation step in which the starting material is rolled.