Method for producing magnesium diboride based high-temperature superconductors

FIELD: electrical engineering; production of magnesium diboride based high-temperature superconductors.

SUBSTANCE: proposed method for producing single-core and multicore superconductors for critical current density includes production of hollow metal ampoule, its filling with powder in the form of mixture of stoichiometric composition incorporating homogeneous granulated magnesium having clean passivated surface obtained by centrifugal spraying of magnesium heated to 650-850 °C from crucible revolving at speed of 1000-6000 rpm, as well as crystallization of sprayed magnesium in helium environment and amorphous boron powder, deformation of ampoule-powder element by extrusion at temperature of 450-500 °C and extrusion coefficient of 3-6, followed by drawing with deformation degree of 5-10% per pass, and heat treatment at 800-900 °C for 1-10 in vacuum or argon environment.

EFFECT: improved quality of superconductor core due to higher quality of magnesium powder and especially improved condition of magnesium powder surface.

5 cl

 

The invention relates to the technical field of superconductivity, in particular to a technology for long composite stranded wire-based superconducting compounds, designed for creating electrical products.

A method of obtaining single long-length superconductors based on magnesium diboride, which consists in filling a metal pipe (hollow metal capsules) commercial powder magnesium diboride, deformation obtained new powder element, heat treatment [1]. The disadvantage of this method is filling capsules synthesized fine powder magnesium diboride containing certain impurities in the source substances taken for the synthesis of magnesium diboride and included in the synthesis process. In addition, when filling capsules synthesized fine powder magnesium diboride created favorable conditions for its pollution in the course of the preparatory operations for filling in process of filling capsules. It is obvious that in the described method, the heat treatment is not carried out for the synthesis of the superconductor, and for the implementation of the diffusion interaction of individual particles of magnesium diboride. It should be noted that due to the structural peculiarities of magnesium diboride diffusion welding of particles is Trunina. Contaminated boundaries of the particles of magnesium diboride, which are concentrated impurities, create additional challenges for the diffusion welding by heat treatment, which may have a negative impact later on superconducting characteristics of the conductors.

Closest to the proposed technical solution is the method of obtaining a single long-length superconductors and multi-fiber cables based on them using magnesium diboride [2] is a prototype that includes filling a metal pipe (hollow metal capsules) with a mixture of powders of magnesium and boron in the desired stoichiometry, strain obtained new powder item first extrusion, then rolling, heat treatment. When carrying out the synthesis of magnesium diboride in the ampoule at the same time, there are two processes: the synthesis of magnesium diboride and diffusion processes in magnesium diboride, resulting in the issue of the purity of the boundaries of the particles of magnesium diboride is not as acute as in the method described in [1] - obviously, at the end of the synthesis of magnesium diboride in the ampoule boundary particles are more pure than when using the process of diffusion welding powder magnesium diboride. However, the foregoing is true only in the case when the powder of boron and magnesium in vials not included impurities. Therefore, when the wire is Denia synthesis of magnesium diboride vials of particular importance is the purity of the used powders of boron and especially magnesium. Magnesium is among quite active chemical elements. Due to its high chemical activity it vigorously reacts with oxygen of the air, so when receiving a mixture of powders of boron and magnesium, as well as when completing this mixture ampoules contaminate powder specific impurities. The presence in the synthesis of magnesium diboride, during heat treatment, impurities adversely affects the quality of the superconducting core. When the heat treatment, during the synthesis and behaviour of diffusion processes in magnesium diboride, on the border with the ampoule in the presence of the introduced impurities, the formation of low-melting non-superconducting phases, which significantly reduces the superconducting characteristics of the wire. The disadvantages of the prototype method are: the quality of the powder of magnesium, especially the state of the surface of particles of the magnesium, the possible presence of non-superconducting phases and impurities in the core of the wire and, consequently, low values of critical characteristics, namely, the critical current density, Jc≈5×105A/cm2at 4.2 K in a private field [2].

An object of the invention is to increase the critical current density of superconductors based on magnesium diboride by improving the quality of the powder of magnesium, especially the surface condition of the particles of magnesium and, to the to the investigation, improve the quality of the superconducting core wire.

The problem is solved in that in the method prototype, including the formation of hollow metal ampoule filling these capsules powder containing components of the superconducting compound, the deformation obtained new powder element and its heat treatment, the ampoule is filled with powder which is a mixture of stoichiometric composition consisting of a homogeneous powder granulated with purified magnesium passivated surface and powder of amorphous boron, distort new powder element by extrusion followed by drawing to receive a billet core wire, the heat treatment is carried out at a temperature of 800-900°With, for 1-10 hours in a controlled environment.

In the private version of the granulated powder of magnesium receive by centrifugal atomization of molten magnesium heated to a temperature of 650-850°from the crucible of speed 1000-6000 mm. rpm and rapid crystallization of the powdered magnesium in the atmosphere of helium.

In another private embodiment, the deformation of new powder item, including and filled with powder, produced by centrifugal atomization of molten magnesium, carried out by extrusion at a temperature of 450-500°and the magnitude of the coefficient extraction with subsequent 3-6 is presented with a degree of deformation per pass 5-10%.

In another private embodiment, the heat treatment is carried out in vacuum or in argon at a temperature of 800-900°C for 1-10 hours.

In the above operations receive solid superconductors and multicore superconductors (when using complex workpieces) based on magnesium diboride with an increased critical current density by improving the quality of the superconducting core wire by improving the quality of the powder of magnesium in the first place - the surface condition of the particles of magnesium.

As noted above, upon completion of the synthesis of magnesium diboride in the ampoule boundary particles are more pure than when using the process of diffusion welding powder magnesium diboride in the case of filling ampoules previously synthesized material. To obtain clean borders requires the use of powders of boron and magnesium with the lowest possible content of impurities, it is also necessary to ensure a minimum flow of impurities in the filling powders in vials. Because magnesium is among the more active chemical elements in comparison with boron, the greatest difficulties of ensuring the purity of the mixture of these two components occur with magnesium powder. Due to their high chemical activity of fine powder of magnesium interacts with oxygen. Obviously, that is when receiving a mixture of powders of boron and magnesium, and for completing this mixture of capsules, powder magnesium were not included impurities, it is necessary to use powder granulated with purified magnesium passivated surface and homogeneous throughout the volume of the powder. The passivated surface of a powder of magnesium prevents contamination and homogeneous powder facilitates the rapid formation of stoichiometric magnesium diboride. Powder granulated with purified magnesium passivated surface and homogeneous throughout the volume of get by centrifugal atomization of molten magnesium heated to a temperature of 650-850°Since, from the crucible rotating with speed of 1000-6000 mm. revolutions per minute, and rapid crystallization raspisannogo magnesium in the atmosphere of helium. Superconducting magnesium diboride formed in the reaction vapors of magnesium with boron powder.

Thus, when filling the capsules with the mixture of powders stoichiometric composition at the expense of purified passivated surface is homogeneous throughout the volume of the powder of granulated magnesium ampoule is filled with a material with the lowest possible content of impurities.

Centrifugal atomization of molten magnesium at a temperature of 650-850°and the rotation speed of the crucible 1000-6000 mm. rpm and rapid crystallization in the helium atmosphere allow to obtain a powder of granulated magnesium cleaned up the th passivated surface and homogeneous throughout the volume.

The deformation of the new powder element by extrusion at a temperature of 450-500°and the magnitude of the coefficient extraction 3-6 with the subsequent drawing of the obtained preform core wire with a degree of deformation per pass 5-10% provides reception billet single core wire with powder core of the desired shape and size, in addition, in the process called deformations gradual compaction of the powder core, which increases the rate of synthesis of magnesium diboride.

Carrying out heat treatment at a temperature of 800-900°C for 1-10 hours in vacuum or in argon provides for the formation of the core wire of the superconducting phase of the desired composition and structure, which allows to obtain single-core superconducting wire with the required current-carrying characteristics.

When the centrifugal atomization of molten magnesium with temperatures below 650°and the rotation speed of the crucible is less than 1000 rpm is unable to conduct the process of atomization and rapid solidification of the droplets of molten magnesium due to the possible formation ISM funnel for rotating the crucible, which is formed due to low temperature of the molten magnesium. In addition, the low viscosity of the molten magnesium at a temperature below 650°does not allow to obtain a powder with the desired characteristics (on the Orme, the particle size of the powder, the surface condition of the particles). When the centrifugal atomization of molten magnesium with temperatures above 850°and the rotation speed of the crucible over 6000 rpm increases the partial pressure of magnesium vapor, which, on the one hand, leads to uncontrolled losses of magnesium, on the other hand, complicates the processes of atomization and rapid solidification of the particles of magnesium required shape and size.

The deformation of the new powder element by extrusion at a temperature below 450°leads to cracking of the billet solid wire up to the integrity of the veins due to the reduction of the ductility of the shell with decreasing temperature extrusion below 450°C.

With increasing temperature extrusion new powder item above 500°violation occurs geometry of the veins due to the reduction of the strength characteristics of the material shell: is thinning ceramic lived in some places along the length of the veins and thickening ceramic lived in other places along the length of the core. In addition, with increasing extrusion temperature conditions above 500°is heating the blank to a temperature close to the melting point of magnesium, the magnesium begins to melt and collect in drops formed drops of liquid magnesium flow down to the lower end of the workpiece, which leads to narushenia.lechenie in the core. In addition, when the extrusion material, partially in liquid form, in places where fluid rupture of membranes.

Conducting extrusion new powder element when the value of drawing ratio less than 3 is impractical because of the increased cycles of extrusion and, therefore, increase the total time warp new powder element to the desired size. Conducting extrusion new powder element when the magnitude of the coefficient drawing more than 6 leads to disruption of the geometry of the veins associated with the difference in the mechanical properties of the extrudable material, which has a significant influence on the deformation of materials with increasing degrees of deformation.

Subsequent drawing blanks single core wire with a degree of deformation per pass to less than 5% is a violation of the geometric dimensions of the wire, you receive the wave-like along the length of the wire, and with a deformation degree of deformation per pass more than 10% rupture of membranes from small cracks to its complete destruction, which leads to rupture of the wire.

Carrying out heat treatment at a temperature below 800°and above 900°With in a period of time less than 1 hour and more than 10 hours can not form the core of the superconducting phase of the desired composition and structure. Since superconducting who nd magnesium diboride formed in the reaction vapors of magnesium with boron powder, at temperatures below 800°With the partial vapour pressure of magnesium is not enough for the formation of magnesium diboride in the whole volume of the core, and at temperatures above 900°With it overheating of the molten magnesium, intensive formation of magnesium vapor and, consequently, the formation of local areas gives conductance-measuring magnesium diboride.

The conduct of these operations in the described sequence and in accordance with the proposed ranges of their regimes have led to a new technical result is to increase the critical current density of superconductors based on magnesium diboride by improving the quality of the powder of magnesium, especially the surface condition of the particles of magnesium and, consequently, improve the quality of the superconducting core wire.

The example implementation. Powders are granulated with purified magnesium passivated surface and homogeneous throughout the volume received by centrifugal atomization of molten magnesium at temperatures of 650°and 850°and when the rotation speed of the crucible 1000 and 6000 rpm. Magnesium in the form of compact pieces were placed in a water-cooled copper crucible, was heated to a temperature of 650°With (and 850° (C) in the electron beam furnace in a helium atmosphere and sprayed when the rotation speed of the crucible 1000 and 6000 rpm, which was achieved by using a low-inertia the disorder for rotation of the crucible, while magnesium after rapid solidification with the formation of granules of powder collected in the chamber. Rapid crystallization of magnesium was due to the cooling rate. Granules of magnesium powder were homogeneous and had a passivated surface due to the used modes. Then the obtained powders were mixed in accordance with the stoichiometry with a commercial powder of amorphous boron to form a homogeneous mixture and the mixture was filled pipe from technically pure iron (about 99.85 wt.% Fe) with a length of 100 mm, an outer diameter of 37 mm, wall thickness 2.5 mm Received new powder elements after sealing deformed first extrusion at temperatures of 450°500°and the values of the coefficient of the hood 3 and 6 to a diameter of 5 mm After the extrusion of all the materials obtained were subjected to drawing with the degree of deformation per pass 7% up to a diameter of 1 mm and were heat treated in vacuum at a temperature of 800°900°C for 5 hours.

Determining the value of the critical current single core wires were held a standard four-pin method at a temperature of 4.2 K in their own field. The critical current was determined from current-voltage characteristics at the level of the voltage E=1 Áv/see the critical current Density was calculated as the ratio of the magnitude of the critical current to the area poperechnov the cross section of the superconducting core. All wires obtained the critical current density was not less than 5.5·105A/cm2that characterizes the advantage of the proposed method.

In addition, from the blank of single core wire with a diameter of 4 mm, obtained after drawing but before heat treatment (at a temperature of 800-900° (C)the manufacturing of the stranded wire. This billet core wire cut-to-length part, and formed a complex workpiece by placing the 19 named dimensional parts in the shell complex workpieces. As the membranes of complex workpieces used pipes made of high-purity copper with a length of 100 mm and a diameter of 25 mm with a wall thickness of 2.5 mm After sealing was performed complex extrusion billet at a temperature of 530°S, the magnitude of the coefficient hood 7 with subsequent drawing to a diameter of 1 mm with a degree of deformation per pass 12%. Heat treatment of the obtained materials was performed in vacuum at a temperature of 850°C for 5 hours. Then measurements of the critical current on the samples obtained stranded wire.

Along with this, a stranded wire made of solid wires with a diameter of 4 mm, obtained after heat treatment (at a temperature of 800-900°). Single core wire with a diameter of 4 mm cut-to-length part, and formed a complex workpiece by placing the 19 named the dimensional parts in the shell complex workpieces. As the membranes of complex workpieces used pipes made of high-purity copper length 100 mm, diameter 25 mm, wall thickness 2.5 mm After sealing was performed complex extrusion billet at a temperature of 530°S, the magnitude of the coefficient hood 7 with subsequent drawing to a diameter of 1 mm with a degree of deformation per pass 12%. Heat treatment of the obtained materials was performed in vacuum at a temperature of 830°C for 3 hours. Then measurements of the critical current on the samples obtained stranded wire.

Thus, to obtain the stranded wire used billet core wire obtained after deformation new powder element by extrusion with subsequent drawing (but prior to the heat treatment at a temperature of 800-900°). This blank is cut-to-length part, formed a complex workpiece by placing in a metal shell complex workpieces called dimensional parts.

In addition, for the manufacture of stranded wire used already received solid wire, i.e. the last heat treatment at a temperature of 800-900°C for 1-10 hours in a controlled environment after deformation new powder element by extrusion followed by drawing. This solid wire cut-to-length part, and formed a complex workpiece by the size of the assumptions are encased in metal complex workpieces called dimensional parts.

In both cases, the formation of complex workpieces by placing in a metal shell or dimensional pieces solid wire or measuring parts of the core wires of a complex workpiece deformed by extrusion followed by drawing to the final size and thermoablative. In the first case, the heat treatment is conducted at a temperature of 800-900°C for 1-10 hours, and in the second case - when 780-880°C for 1-5 hours. All it provides high-quality stranded wire with the required amount of leads. It was found that the complex deformation of the workpiece by extrusion at a temperature of 500-550°and the magnitude of the coefficient extraction 5-9 with the subsequent drawing to the degree of deformation per pass 7-15% provides getting stranded long wire to the desired shape and size.

In addition, carrying out heat treatment of complex workpieces formed from cut-to-length part single core wire, at a temperature of 800-900°C for 1-10 hours in vacuum or in argon, and conducting heat treatment of complex workpieces formed from cut-to-length part of the core wire at a temperature 780-880°C for 1-5 hours in a vacuum or in argon, ensure the formation of a stranded core wire of the superconducting phase t is bamogo composition and structure, that allows to obtain a superconducting wire with the required current-carrying characteristics.

While carrying out the extrusion at a temperature below 500°leads to cracking complex workpiece until the integrity lived due to the reduction of the ductility of the shell with decreasing temperature extrusion below 500°C.

With increasing temperature extrusion of complex procurement above 550°violation occurs geometry lived due to the reduction of the strength characteristics of the material shell: is thinning ceramic lived in some places along the length of the veins and thickening ceramic lived in other places along the length of the core. In addition, with increasing extrusion temperature conditions above 550°is heating the blank to a temperature close to the melting point of magnesium, the magnesium begins to melt and collect in drops formed drops of liquid magnesium flow down to the lower end of a complex workpiece, which leads to the violation of stoichiometry in a stranded core. In addition, when the extrusion material, partially in liquid form, in places where fluid rupture of membranes as a complex procurement and membranes of the core wire and the workpiece single core wire.

Carrying out the extrusion of complex workpiece when the value of drawing ratio less than 5 is telecourse by increasing the cycles of extrusion and, therefore, increasing the total time of the deformation complex of the workpiece to the desired size. Carrying out the extrusion of complex workpiece when the magnitude of the coefficient drawing more than 9 leads to the violation of the geometry of the veins associated with the difference in the mechanical properties of the extrudable material, which has a significant influence on the deformation of materials with increasing degrees of deformation.

When receiving the workpiece stranded wire after the extrusion of the drawing with the degree of deformation per pass less than 7% is a violation of the geometric dimensions of the wire, you receive the wave-like along the length of the wire, and with a deformation degree of deformation per pass more than 15% rupture of membranes from small cracks to their complete destruction, which leads to rupture of the wire.

Carrying out heat treatment of complex workpieces formed from cut-to-length part of the core wire at a temperature below 780°and above 880°With in a period of time less than 1 hour and more than 5 hours is not possible to form a multi-core superconducting phase of the desired composition and structure. That is, the diffusion processes in magnesium diboride go in such a manner that there is no diffusion welding of individual particles of magnesium diboride, and overgrowth of micro-cracks in the core wire formed inthe Assembly of the complex procurement and subsequent deformation.

Carrying out heat treatment of complex workpieces formed from cut-to-length part of the billet core wire at a temperature below 800°and above 900°With in a period of time less than 1 hour and more than 10 hours is not possible to form a multi-core superconducting phase of the desired composition and structure. Since superconducting magnesium diboride formed in the reaction vapors of magnesium with boron powder at a temperature below 800°With the partial vapour pressure of magnesium is not enough for the formation of magnesium diboride in the entire volume of stranded core, and at temperatures above 900°With it overheating of the molten magnesium, intensive formation of magnesium vapor and, consequently, the formation of local areas gives conductance-measuring magnesium diboride.

Determining the value of the critical current stranded wires were held a standard four-pin method at a temperature of 4.2 K in their own field. The critical current was determined from voltampere characteristics on the voltage level E=1 Áv/see the critical current Density was calculated as the ratio of the magnitude of the critical current to the cross-sectional area of the superconducting core. All wires obtained the critical current density was not less than 6.0·105A/cm2that characterizes the advantage of pre the proposed method.

Sources used

1. R.Nast, S.I.Schlachter, S.Zimmer, H.Reiner, W.Goldacker. Mechanically reinforced MgB2wires and tapes with high transport currents, Physica C. 372-376 (2002), 1241-1244.

2. B.A.Glowacki, M.Majors. MgB2conductors for dc and ac application, Physica C. 372-376 (2002), 1235-1240.

1. The method of obtaining high temperature superconductors based on magnesium diboride, including the formation of hollow metal ampoule filling capsules with powder containing components of the superconducting compound, the deformation obtained new powder element and its heat treatment, characterized in that the powder is a mixture of stoichiometric composition consisting of a homogeneous powder granulated with purified magnesium passivated surface and powder of amorphous boron, deformation of new powder element is carried out by extrusion followed by drawing, heat treatment is carried out at a temperature of 800-900°With, for 1-10 hours in a controlled environment.

2. The method according to claim 1, characterized in that the powder of granulated magnesium receive by centrifugal atomization of molten magnesium heated to a temperature of 650-850°Since, from the crucible, rotating with a speed of about 1000-6000 mm../min, and crystallization of powdered magnesium in the atmosphere of helium.

3. The method according to claim 1, characterized in that the extrusion is carried out at a temperature of 450-500°and the magnitude of the coefficient extraction 3-6 with the placenta is brilliant drawing with the degree of deformation per pass 5-10%.

4. The method according to claim 2, characterized in that the extrusion is carried out at a temperature of 450-500°and the magnitude of the coefficient extraction with subsequent 3-6 drawing with the degree of deformation per pass 5-10%.

5. The method according to claim 1 or 2, or 3, or 4, characterized in that the heat treatment is carried out in a vacuum.

6. The method according to claim 1 or 2, or 3, or 4, characterized in that the heat treatment is carried out in argon.



 

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2 cl, 3 dwg

FIELD: electrical engineering; devices designed for operation at liquid helium temperature.

SUBSTANCE: proposed method for manufacturing composite wire includes production of primary composite billet incorporating external sheath and axial cylindrical block, sealing of primary composite billet, reduction, and extrusion, followed by deformation to obtain rod of desired shape and size, its cutting into measured lengths, formation of secondary composite billet by assembling rod in external sheath, sealing of secondary composite billet, reduction, and extrusion, followed by deformation to final size of wire; composite billet reduction involves its pre-extrusion press-fitting in container; total cross-sectional area of composite billet components is 95-99% of that of inner space of container sleeve and inlet part of composite billet external sheath is made in the form of transition zone having cylindrical part whose outer diameter is smaller than that of container sleeve and conical part, volume of voids within composite billet amounting to 1-17% of that of external sheath inner space.

EFFECT: provision for pre-extrusion hot compression of composite billet without additional time requirement.

6 cl, 2 dwg

FIELD: electrical engineering; production of magnesium diboride based high-temperature superconductors.

SUBSTANCE: proposed method for producing single-core and multicore superconductors for critical current density includes production of hollow metal ampoule, its filling with powder in the form of mixture of stoichiometric composition incorporating homogeneous granulated magnesium having clean passivated surface obtained by centrifugal spraying of magnesium heated to 650-850 °C from crucible revolving at speed of 1000-6000 rpm, as well as crystallization of sprayed magnesium in helium environment and amorphous boron powder, deformation of ampoule-powder element by extrusion at temperature of 450-500 °C and extrusion coefficient of 3-6, followed by drawing with deformation degree of 5-10% per pass, and heat treatment at 800-900 °C for 1-10 in vacuum or argon environment.

EFFECT: improved quality of superconductor core due to higher quality of magnesium powder and especially improved condition of magnesium powder surface.

5 cl

FIELD: electrochemistry.

SUBSTANCE: proposed method involves filling of cylindrical bag with auxiliary parts which are then removed from bag and replaced by bar assemblies placed in definite sequence affording maximal filling density; sectional area of each auxiliary member differs from that of its substituting bar; central regular-hexagon shaped auxiliary member has face width A1 found from expression where a is hexagonal bar width, M is number of bars in diametric direction; second row around central member is alternately filled with auxiliary members of which three ones are regular-hexagon shaped members having face width A2 found from expression and three other hexagon-shaped auxiliary members have face width found from set of expressions all next rows are alternately filled with auxiliary hexagon-shaped members whose face width is found from set of expressions and remaining free space between hexagon-shaped auxiliary members, as well as cylindrical bags are filled with additional auxiliary members whose cross-sectional area provides for maximal filling of bags.

EFFECT: facilitated procedure, ability of filling billet with thousands of bars during its single assembly process.

3 cl, 7 dwg

FIELD: electrical engineering.

SUBSTANCE: proposed superconducting device has superconducting oxide wire made of superconducting oxide material whose post-sintering density is 93% and more, best 95% and more, or most preferably 99% or more, which is attained by heat treatment of wire in enhanced pressure environment of at least 1 MPa and below 50 MPa. Heat treatment of wire at enhanced pressure prevents formation of gaps and bubbles. Stable superconducting oxide phase of Bi2223 is formed in the process.

EFFECT: enhanced critical current density of superconducting device and superconducting cable.

6 cl, 27 dwg, 4 tbl, 6 ex

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