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• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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  • Y10S505/00—Superconductor technology: apparatus, material, process
  • Y10S505/725—Process of making or treating high tc, above 30 k, superconducting shaped material, article, or device
  • Y10S505/739—Molding, coating, shaping, or casting of superconducting material
  • Y10S505/74—To form wire or fiber

Definitions

• the present invention relates to a method of manufacturing an electrically insulating and mechanically structuring sheath on an electrical conductor.
• the precursor is, according to a variant of the invention, in the form of a flexible impregnated fabric, allowing the shaping of the conductor which one wants to isolate and, in certain cases, ensures the control of the thickness and determines the geometric precision of windings produced by means of the conductor.
• the precursor is sintered and the electrical insulation thus formed " absorbs the mechanical forces exerted on the conductor during subsequent phases of assembly and
• the ceramic nature of the insulation produced allows operating temperatures ranging from 1.8 K to 1270 K.
• materials with superconductive properties and the ability to circulate high current densities require heat treatment at a high temperature (above 600 ° C for Nb 3 Sn and 700 ° C for Nb 3 Al), of long duration (more than 100 hours for Nb 3 Sn and of the order of a few tens of hours for Nb 3 Al) and in the presence of 'an inert or vacuum atmosphere.
• the temperature conditions mentioned above prohibit the use of conventional electrical insulations, made from organic products, during the heat treatment.
• the superconductive material obtained at the end of this heat treatment is fragile and any mechanical stresses which are likely to be applied to it can easily deteriorate its superconductive properties.
• Winding transfer operations are particularly delicate and, to date, have never allowed mass production of complex windings (of the dipole or quadrupole type), of large size (in particular of length greater than 1 meter), using Nb 3 Sn superconductors.
• the cost of the superconductive materials used (of the order of 750 € / g to 2000 € / kg depending on the production methods used) as well as the processing time and the duration of the winding operations represent more than 30% of the manufacturing cost.
• superconductive electromagnets The risk associated with transferring the reaction mold (in which the superconductor precursor is transformed into a superconductor) to the impregnation mold is therefore very significant.
• EP-A-0044144 (invention of G.R. Sutcliffe, S.J. arden and D. Humpherson), corresponding to US-A- 4,407,062.
• the present invention aims to remedy the drawbacks of known techniques for manufacturing electrically insulating sheaths on electrical conductors, particularly those made of superconductive materials.
• the subject of the invention is a method of manufacturing an electrical insulator which can be deposited on an electrical conductor or with which one can wrap this conductor, in particular in the case of a conductor intended to be wound, the method allowing to wrap the conductor with the insulation or to deposit the latter, before the conductor is wound.
• This method also aims to leave a certain flexibility to the conductor thus coated, this flexibility making it possible to bend, in particular to wind, this conductor.
• this process allows the synthesis of a ceramic material during a heat treatment.
• the invention leads to the following results, in particular in the case of a superconductive conductor: - the electrical insulation of the conductor is adequate,
• the winding advantageously has a certain porosity to liquid helium.
• the ceramic insulation produced in accordance with the invention has no organic phase after the heat treatment and does not require the addition of an organic phase to obtain its electrical insulation properties.
• this insulator is formed from a ceramic matrix reinforced with short ceramic fibers.
• the subject of the present invention is a method of manufacturing an electrically insulating and mechanically structuring sheath on an electrical conductor, in particular a non-superconductive metal conductor or a superconductor precursor conductor, this method being characterized in that that it includes the steps of:
• this heat treatment being able to form the ceramic from the ceramic precursor in gelled form.
• the ceramic precursor is a liquid constituted by a solution comprising water, a mineral component, chosen from boehmite and clays of the kaolin family, and an organic binder and reacting the mineral component with an acid to gel the solution and thus obtain the ceramic precursor in gel form.
• the acid can be chosen from the group comprising boric acid, citric acid, hydrochloric acid, nitric acid and carboxylic acids, preferably formic acid.
• the solution may further comprise glass frit and / or at least one additional mineral oxide.
• the solution comprises, in percentage by mass, 35% to 45% of water, 8% to 30% of the mineral component, 1% to 10% of organic binder, 0% to 15 % of one or a plurality of additional mineral oxides and an optional complement of glass frit, this optional addition of glass frit ranging, of course, from 0% to 56%.
• the mass percentage of the mineral component ranges from 15% to 30% in this solution, the possible addition of glass frit then going, of course, from 0% to 49%.
• Each additional mineral oxide can be chosen from the group comprising alumina, zirconia, silica and silico-aluminous clays.
• this process further comprises a step of removing the organic binder after the step of forming the coating, this removal step starting before the heat treatment step suitable to form the ceramic but ending during this heat treatment step, so that these two steps overlap partially in time.
• the method further comprises a step of removing the organic binder by reaction with oxygen, after the step of forming the coating.
• the conductor is a precursor of the superconductor Nb 3 Sn or Nb 3 Al and an overall heat treatment of this conductor provided with the coating is carried out, this heat treatment overall being carried out in a neutral atmosphere and capable of forming the superconductor Nb 3 Sn or Nb 3 Al, remove the organic binder and form the ceramic.
• the driver is the precursor of a copper oxide superconductor, in particular YBa 2 Cu 3 0 7 , Bi 2 Sr 2 CaCu 2 0 2 or Bi 2 Sr 2 Ca 2 Cu 3 O ⁇ 0 , and the organic binder is removed by heating, in the air, of the conductor provided with the coating then an overall heat treatment is carried out, in the air, of the conductor provided with the coating, this overall heat treatment being able to form the superconductor based on copper oxide and to form the ceramic .
• a copper oxide superconductor in particular YBa 2 Cu 3 0 7 , Bi 2 Sr 2 CaCu 2 0 2 or Bi 2 Sr 2 Ca 2 Cu 3 O ⁇ 0
• the organic binder is removed by heating, in the air, of the conductor provided with the coating then an overall heat treatment is carried out, in the air, of the conductor provided with the coating, this overall heat treatment being able to form the superconductor based on copper oxide and to form the ceramic .
• the conductor is made of a non-superconductive metal and an overall heat treatment of this conductor provided with the coating is carried out, this overall heat treatment being carried out in a neutral atmosphere and capable of removing the organic binder and to form the ceramic.
• the step of forming the coating may include a step of depositing the ceramic precursor in gelled form on a fabric of ceramic fibers previously desensed (that is to say a fabric of ceramic fibers from which the size has been previously removed). , then a step of placing the fabric provided with the ceramic precursor around the conductor.
• the ceramic fibers can be made of a material chosen from glass E, glass C, glass R, glass S2, silica, alumina and mullite.
• the ceramic fiber fabric can be previously desensed thermally or chemically.
• the conductor provided with the coating is shaped, in particular a coil, before the heat treatment step capable of forming the ceramic.
• This conductor is for example an electric wire or cable.
• a glass ribbon impregnated with a ceramic precursor is used.
• This ceramic precursor is obtained from a liquid solution and it is without sedimentation because the liquid solution contains boehmite or a clay of the family of kaolin, which has been reacted with an acid to obtain a gelation of this liquid solution.
• This property of homogeneity of the ceramic precursor facilitates its use during its deposition on the conductor, in particular in the case where this deposition is carried out by passage of the conductor in a bath of this precursor of ceramic, this bath serving to form a flexible sheath which allows the subsequent shaping (in particular the winding) of the conductor.
• the sheath After baking of the conductor thus treated and shaped, the sheath is rigid and the conductor (in particular the superconductor) is electrically isolated and taken in a ceramic matrix.
• the resistance to mechanical stress is considerably increased compared to the prior art.
• the electrical insulation is very good and the porosity of the sheath is low due to the vitrification. It should be noted that the invention applies in particular to the manufacture of high-field electromagnets and of windings for electric motors.
• the ceramic precursor is manufactured in the form of a liquid solution, more or less viscous and without sedimentation.
• the composition of this solution in percentage by mass is: - 35% to 40% of water, - 1% to 10% of an organic binder (commercially available),
• boehmite or of a clay of the kaolin family, - 0% to 15% of other mineral oxides such as alumina, zirconia, silica, a silico-aluminous clay (for example mica), which form a mineral filler, and
• the acid is added to obtain the gelation of the solution in the presence of boehmite or clay of the kaolin family .
• boehmite or clay of the kaolin family For example, formic acid is used with a mass percentage of 0.3% to 2%. This eliminates sedimentation.
• the gel is formed by the chemical reaction of the acid on boehmite or clay of the kaolin family and the rest of the solution is taken up in the gel. Gelation makes it possible to use much less organic binder compared to the traditional technique which consists in adding an organic dispersant which must then be eliminated.
• Formic acid is used in this example because the molecule of this acid contains only one carbon atom and gives advantageous gelling properties but other acids can be used, for example nitric acid, acid boric, hydrochloric acid, citric acid or another acid from the family of carboxylic acids.
• formic acid is a relatively strong acid among weak acids, but if a weaker acid is used more will be needed.
• the viscosity of the solution is adjusted as necessary, by dosing the various mineral fillers and water.
• fibrous fillers can be added to obtain a viscous or even pasty ceramic precursor. Between 5% and 40% of fibrous filler is used to have sufficient viscosity.
• the wire or cable can be coated directly by circulating the latter in a bath of this ceramic precursor in gelled form.
• This ribbon of ceramic fibers is first of all desensed.
• This ribbon is for example made of E glass, C glass, R glass, S2 glass, silica, alumina or mullite (which is a silicate forming an essential constituent of ceramics).
• This ribbon can be a commercial ribbon, for example E glass from Bourgeois or S2 glass from Hiltex or ceramic marketed under the Nextel brand from 3M. It is also possible to use silica fibers sold under the brand name Quartzel by the company Saint-Gobain, preferably woven with a thickness of 60 ⁇ m by the company Textile Bourguisanne.
• the desizing can be thermal (according to the prescriptions of the manufacturer of the tape), for example at 700 ° C for 1 minute or 350 ° C for 20 hours.
• chemical desizing is used with a suitable solvent.
• the solvent only serves to dissolve the size.
• the choice of solvent and the residence time in solution depend on the type of ribbon and the products used for its size. The solvent must therefore only dissolve polymers and must not attack the ceramic fiber.
• the desensed ribbon is then impregnated with the ceramic precursor in gelled form.
• the ribbon thus impregnated is placed around the conductive wire or cable, this ribbon then forming a flexible sheath, then the conductor is shaped. As an example, this conductor is wound. Then, three cases are to be distinguished.
• the conductor is made of a superconductor precursor, namely the precursor of Nb 3 Sn or Nb 3 Al (before this material has undergone the heat treatment which gives it its superconductive properties), both by temperature rise: - the reaction heat treatment of Nb 3 Sn or Nb 3 Al,
• the temperature is increased from ambient temperature (approximately 20 ° C.) to a plateau of the order of 600 ° C. to 700 ° C. (reaction temperature Nb 3 Sn) for a period of 100 hours to 300 hours, which is necessary for the transformation of the precursor of the superconductor into the Nb 3 Sn superconductor.
• the temperature is increased from ambient temperature to a plateau of the order of 700 ° C to 800 ° C (reaction temperature of Nb 3 Al) for a duration of a few tens of hours, duration which is necessary for the transformation of the precursor of superconductor into Nb 3 Al superconductor.
• the ceramic binder and precursor also react in the above temperature range. It is necessary to monitor the rise in temperature which must be very slow so that the driver
• the atmosphere is modified gradually by the introduction of a slightly reducing gaseous mixture (for example a mixture containing less than 5% of hydrogen and more than 95% of nitrogen because, if there were more hydrogen, the mixture would be explosive) at the start of the Nb 3 Sn or Nb 3 Al reaction heat treatment stage.
• a slightly reducing gaseous mixture for example a mixture containing less than 5% of hydrogen and more than 95% of nitrogen because, if there were more hydrogen, the mixture would be explosive
• This mixture replaces the atmosphere of argon or nitrogen and makes it possible to be sure that the conductor will not be oxidized by possible residues of oxygen.
• the reaction must take place at temperatures compatible with the sintering of the ceramic and with the reaction treatment of the superconductor and must also leave no residue of carbon (which is a good electrical conductor).
• Oxygen is used here with which it is certain to eliminate everything by the formation of gas. In addition, this reaction is very rapid as soon as it exceeds 350 ° C. The generated gas (CO or C0 2 ) must be evacuated. This is why the heat treatment takes place under a gas sweep. In addition, the removal of the binder and the sintering are carried out in the same operation by chaining and overlapping of the binder removal phase and the sintering phase. This is an essential characteristic of the example considered of the invention.
• the sheath does not crumble thanks to this overlapping, or partial recovery over time, of the step of removing the binder and of the sintering step. Without nesting, there would be a risk of obtaining a very fragile pulverulent sheath and the shaped conductor should not be disturbed. However, in the prior art, these steps are separated and this requires resin impregnation.
• the conductor is made of a precursor of a copper oxide-based superconductor such as:
• the step of complete elimination of the organic binder is carried out by air cooking according to the parameters of temperature, duration and rise in temperature which depend on the chosen binder and are indicated by the supplier of the latter.
• both the reaction heat treatment of the superconductor and the sintering of the ceramic take place.
• the parameters of this treatment thermal which is carried out in air, are a plateau temperature of the order of 800 ° C to 900 ° C and a plateau time of 10 minutes to 3 hours.
• the conductor is made of a metal or of a non-superconductive metallic compound
• the step of thermal elimination of the organic binder takes place in a neutral atmosphere, with the introduction of a controlled amount of oxygen, corresponding to complete carbonization of the binder. Indeed, in air the metal would be completely oxidized, unless this metal is gold.
• This figure shows a wire 2 on which a coating 3 of ceramic precursor in gel form is formed by passing this wire 2 through this ceramic precursor in gel form 4 contained in a container 6.
• the wire passes over a succession of pulleys 8, 10, 12 and 14 and also passes through a series of thickness control devices 16 and 18 to remove the excess quantities of the coating 3 formed on the wire.
• the wire is then dried by passing through a drying oven 20 and then wound on a suitable spool 22.
• the wire thus wound can then be subjected to the heat treatments mentioned above, which allow the elimination of the organic binder, the formation of ceramic and the formation of the superconductor when the wire 2 is superconductive.
• the wire 2 is thus provided with an electrically insulating and mechanically structuring sheath.
• quadrupole electromagnets are manufactured, each comprising four identical windings. Each of these requires approximately 75 m of superconducting cable.
• the latter of slightly trapezoidal section, consists of 36 strands based on Nb 3 Sn. These strands have a diameter of 0.825 mm and are twisted together and distributed in two layers.
• the dimensions of the cross section of this cable are: 1.362 mm for the short side, 1.598 mm for the long side and 15.1 mm for the width.
• Each length (75 m) of cable is wrapped around 400 m with a 15 mm wide ribbon.
• This ribbon consists of ceramic fibers and impregnated with a solution containing boehmite and mica as mineral fillers, a glass frit sold under the reference VN 821 by the company Cerdec, a dispersant and a binder respectively sold under the references D-3005 and B-1000 by the company Rohm and Haas and water as a solvent.
• a cable 24 before treatment
• This cable is a Rutherford type flat cable, with two layers of strands 26.
• the cable 24 is wrapped: we see a first ribbon 28 of glass fibers, which is impregnated with ceramic precursor and which surrounds the cable 24.
• Each of these ribbons 28 and 30 is wound around the cable so that the edge of one turn of the ribbon is against the edge of the adjacent turn, but, with a view to ensuring the continuity of the electrical insulation, the second ribbon 30, which is wound over the first, is offset by half a step with respect to this first ribbon 28.
• glass frits and / or binders can be used.
• the latter After having formed the windings, the latter are subjected to a heat treatment comprising heating at 6 ° C / hour to 660 ° C. This heating is followed by a 240 hour plateau at 660 ° C and a slow cooling in the enclosure of the oven used for heat treatment.
• each winding is cooled to the temperature of liquid helium (4.2 K at atmospheric pressure) or to that superfluid helium (less than or equal to 2.1 K at atmospheric pressure).
• the invention also applies to the manufacture of small compact superconductive solenoids, devoid of metallic structuring elements.
• the invention can also be used for windings of rotating superconductive electrical machines.
• the invention can also be used for the windings of non-superconductive rotating electrical machines intended to operate at high temperature (above 300 ° C).
• the invention can also be used for the manufacture of electrical insulations resistant to high heat, for example that of a flame, or to projections of very hot liquids due to the low porosity of the structuring insulator.

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• 2001
  • 2001-07-20 FR FR0109741A patent/FR2827699B1/fr not_active Expired - Fee Related
• 2002
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