WO2005024965A1

WO2005024965A1 - A method and apparatus for making a layer of coating material on a tape substrate, in particular for making superconductive tapes

Info

Publication number: WO2005024965A1
Application number: PCT/IB2004/002984
Authority: WO
Inventors: Alberto Baldini; Andrea Botarelli; Andrea Gauzzi; Sergio Zannella
Original assignee: Edison SpA; Outokumpu Copper Superconductors Italy SpA
Current assignee: Edison SpA; Outokumpu Copper Superconductors Italy SpA
Priority date: 2003-09-11
Filing date: 2004-09-10
Publication date: 2005-03-17
Anticipated expiration: 2006-03-11
Also published as: WO2005024965A8; ITTO20030691A1

Abstract

Provided herein are a method and an apparatus (1) for making a layer (2) of coating material (3) on a tape substrate (4), in particular for making superconductive tapes. A precursor (12) of the coating material (3) is evaporated so as to form an evaporation area (13), and the substrate (4) is carried through the evaporation area (13) to enable deposition of the evaporated coating material (3) on one face (17) of the substrate (4); the substrate (4) is carried through the evaporation area (13) along a curved path (60), in particular with a stretch (27) wound on a rotating carousel (25), in such a way that the deposition of the coating material (3) to form the layer (2) will be performed on a non-planar portion (16) of the substrate (4).

Description

"A METHOD AND APPARATUS FOR MAKING A LAYER OF COATING MATERIAL ON A TAPE SUBSTRATE, IN PARTICULAR FOR MAKING SUPERCONDUCTIVE TAPES"

TECHNICAL FIELD

The present invention relates to a method and an apparatus for making a layer of coating material on a tape substrate, in particular for making superconductive tapes.

BACKGROUND ART

It is known in the art the technique of obtaining high- critical-temperature superconductors by depositing suitable superconductive layers (for example YBCO or REBCO) on monocrystalline substrates of finite dimensions (in particular YSZ and AI2O3) , possibly with interposition of appropriate intermediate buffer layers, via co-evaporation or other deposition techniques. In this way, however, only elements of relatively small dimensions can be obtained, in the region of 100 cm².

In order to obtain superconductive tapes there are, instead, known methods which envisage moving the tape substrate (typically a flexible metallic tape) by means of rollers or other drawing members. The tape is brought into a vacuum chamber and is maintained tensioned in a planar configuration above an evaporation area, where the deposition of the buffer layers and of the superconductive layer is performed.

Known methods of this type are not, however, free from drawbacks. In the first place, these methods enable only low processing rates, above all because, to obtain efficient deposition, it is necessary to associate to the deposition step a step of in si tu oxygenation, which, with currently available systems, is relatively slow. In the second place, the mechanisms for moving the tape envisaged by known methods are relatively complex and involve the use of drawing members that subject the tape to dangerous stresses, which may cause damage and failure of the tape and/or of the deposition layers, or defects in the end product. The tape itself, during the deposition step, on account of the combined effect of its own weight, friction with the drawing members, and high temperature (typically above 600-700°C) , may undergo deformation, thus jeopardizing the final result. Furthermore, the planar configuration of the tape during the deposition step does not enable an optimal exploitation of the evaporation area, which typically has a divergent shape (evaporation cone) .

DISCLOSURE OF INVENTION

Consequently, it is an object of the present invention to provide a method and an apparatus for making a layer of coating material on a tape substrate that are free from the drawbacks of the known art highlighted herein. In particular, it is an object of the invention to provide a method and an apparatus that enable continuous operation at a high processing rate, ensuring at the same time an effective deposition.

In accordance with said objects, the present invention relates to a method and an apparatus for making a layer of coating material on a tape substrate as defined in the annexed Claims 1 and 13, respectively.

The method and the apparatus according to the invention enable continuous operation at high processing rates, at the same time ensuring excellent results in terms of product quality (in particular, of the electromagnetic characteristics) and absence of defects. The method and apparatus according to the invention are hence fully suitable for industrial application and enable superconductive tapes to be obtained at competitive costs. In particular, moving of the tape substrate is performed in a simple way, in so far as it requires simple and functional mechanical elements. There is not envisaged the use of drawing members which subject the tape to dangerous stresses, and the sliding friction between the substrate and drawing members that can lead to damage and defects is substantially eliminated. Furthermore, the optimal exploitation of the entire evaporation area is ensured. Clearly, the method and apparatus according to the invention are suited to the deposition both of the superconductive layer and of the buffer layers.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the present invention emerge clearly from the ensuing description of a non-limiting example of embodiment thereof, with reference to the annexed drawings, in which:

- Figure 1 is a schematic view in a side elevation, with parts removed for reasons of clarity, of an apparatus according to the invention; and

- Figure 2 is a partially cross-sectional view of the apparatus of Figure 1.

BEST MODE FOR CARRYING OUT THE INVENTION In the attached figures, designated as a whole by 1 is a continuous-treatment apparatus for making a layer 2 of coating material 3 on a substrate 4 in the form of a continuous tape and designed specifically for obtaining superconductive tapes (so-called "coated conductors") .

The apparatus 1 comprises a casing 5, which delimits on the inside a vacuum chamber 6 and is provided with at least one suction pump 7 (known and represented only schematically in Figure 1) for bringing the internal pressure of the chamber 6 to pre-set values, in the region of 10^-5 mbar. The casing 5 has an inlet 8 and an outlet 9 for the substrate 4. The inlet 8 and the outlet 9 are formed through opposite walls of the casing 5 and are provided with suitable seal members (known and not illustrated) . According to a variant (not illustrated) , the substrate 4 is wound off a supply reel and wound onto a gathering reel, both of which are housed inside the chamber 6.

The apparatus 1 comprises evaporation means 11 for evaporating a precursor 12 of the coating material 3 so as to form an evaporation area 13 within the chamber 6, and feed means 14 for feeding the substrate 4 into the chamber 6 through the evaporation area 13. The feed means 14 in turn comprise, according to the invention, supporting means 15 for supporting the substrate 4 in a non-planar configuration through the evaporation area 13 and with the concavity of the substrate 4 facing the evaporation area 13. Specifically, the supporting means 15 support a non-planar portion 16 of the substrate 4 above the evaporation area 13 and with a substantially concave face 17 of the substrate 4 facing the evaporation means 11. The evaporation means 11 comprise a source 20, of any known type, capable of releasing the coating material 3 into the evaporation area 13. For example, the source 20 comprises a crucible 21, which contains the precursor 12 and is associated to an evaporation device 22, for instance, a device for electrical heating of the crucible 21, to evaporate the precursor 12. As an alternative to thermal evaporation, any other evaporation system can be used. It remains understood that a number of elements or substances necessary to the formation of the layer 2 can be evaporated simultaneously and that a number of crucibles 21 may be envisaged.

The feed means 14 comprise a return assembly 24 and a carousel 25 provided with the aforesaid supporting means 15. The carousel 25 is a substantially cylindrical motor-driven carousel, which is able to rotate about a central axis A and has a radially external side surface 26, on which a longitudinal stretch 27 of the substrate 4 including the portion 16 is wound. The surface 26 is provided with a circumferential slit 28, set substantially along a diametral plane of the carousel 25 for intercepting the evaporation area 13 and on which there extends a central longitudinal strip 29 of the substrate 4.

The carousel 25 comprises a pair of wheels 31, 32, which are set parallel alongside one another and are axially separated by the slit 28 (in Figure 1 only the wheel 32 is shown, for reasons of clarity) . The wheels 31, 32 are aligned along the axis A and can rotate about a common axis of rotation defined by the axis A. The wheels 31, 32 have respective cylindrical side surfaces 33 that extend axially in cantilever fashion towards one another from respective radially external peri etral edges 34 of the wheels 31, 32 and define an internal cavity 35 of the carousel 25. The perimetral edges 34 are connected to respective hubs 36 via spokes 37. The hubs 36 are coupled in rotation, via bearings 38, to respective supports 39 set at axially opposite ends of the carousel 25. The supports 39 comprise respective brackets 40 fixed to the casing 5 and from which there axially project respective cylindrical sleeves 41 housed so that they pass through the hubs 36. Respective end portions of the surfaces 33 define a pair of curved resting surfaces 45, which are set alongside one another, for supporting respective opposite side edges 46 of the substrate 4 and are separated from one another by the slit 28. The substrate 4 rests, via the edges 46, on the wheels 31, 32, whilst the strip 29 extends between the wheels 31, 32 and hence on the slit 28.

The wheels 31, 32 are moved synchronously by a common motor shaft 47 parallel to the axis A, said shaft in turn being actuated by a motor (known and not illustrated) and being provided with a pair of gears 48 set axially spaced apart from one another, which engage respective ring gears 49 carried radially on the outside by the surfaces 33.

The carousel 25 also determines advance of the substrate 4, which is driven by friction by the resting surfaces 45, without requiring any other drawing member.

The return assembly 24 comprises two rollers 51 set parallel to the carousel 25, one upstream and one downstream of the carousel 25 in the direction of advance of the substrate 4, so as to define the stretch 27 of the substrate 4 wound on the carousel 25. In particular, the rollers 51 are set in such a way that the stretch 27 will extend on a winding sector 52 of the carousel 25 having an angular amplitude substantially equal to the angular amplitude of the evaporation area 13. Clearly, the geometry of the evaporation area 13 can vary according to the applications. Indicatively, the winding sector 52 is comprised between approximately 90° and approximately 130° and preferably is around 120°.

The apparatus 1 also comprises a heating device 55 for heating the substrate 4. The heating device 55 comprises heating elements 56, for example infrared lamps, set above the winding sector 52 in such a way as to define a heating front 57 shaped like the winding sector 52 (i.e., having the same curvature as the surfaces 33 of the wheels 31, 32) .

The crucible 21 is carried by a bracket 58 which projects in cantilever fashion parallel to the axis A within the cavity 35 from a front end of the sleeve 41a, which supports the wheel 31 and is hence set radially on the inside of the carousel 25. The supply and control wires of the evaporation device 22 are not shown for reasons of simplicity, but it may be appreciated that they can advantageously be housed so that they pass through the sleeve 41a, without interfering with rotation of the carousel 25. If a number of crucibles 21 is envisaged, these are set aligned to one another on the bracket 58 along a diameter of the carousel 25 so that they will all be aligned to the slit 28.

The supporting means 15 define a substantially curved path 60 of the substrate 4 through the evaporation area 13, and the source 20 of the coating material 3 is set radially internal to the path 60. In particular, the path 60 is shaped like the arc of circle and develops about a centre of curvature 61 constituted by the geometrical centre of the carousel 25, and the source 20 is set preferably in a position corresponding to, or in the proximity of, the centre of curvature 61.

The apparatus 1 then comprises at least one gas diffuser 70 for assisting growth of the layer 2 on the substrate 4, and moving means 71 for bringing the diffuser 70 into the proximity of the substrate 4 and within the evaporation area 13 along a curved path and, specifically, a circular one.

The moving means 71 comprise at least one motor-driven rotating arm 72 set within the cavity 35; the arm 72 extends radially from a head end 73 of a rotating shaft 74, which is housed so that it can rotate and is supported via bearings 75 in a cylindrical seat 76 formed centrally so that it passes through the sleeve 41b that supports the wheel 32. The head end 73 is axially set at a distance from the bracket 58, i.e., it does not reach the centre of curvature 61, nor does it intercept the evaporation area 13. The diffuser 70 projects axially in cantilever fashion from one free end 77 of the arm 72 so as to be aligned with the slit 28.

The shaft 74 has an axis of rotation coincident with the axis of rotation of the carousel 25 and, hence, with the axis A. The moving means 71 are hence rotatable about an axis of rotation (axis A) that is substantially parallel to the substrate 4 and in a plane substantially perpendicular to the substrate 4.

The diffuser 70 comprises a box 78 closed by a radially external perforated cup 79, out of which there flows gas. The cup 79 is curved and reproduces the profile of the substrate 4 in the evaporation area 13 (and hence has substantially the same curvature as that of the surfaces 33) . The gas is supplied to the box 78 through a pipe 80, which is made inside the arm 72 and the shaft 74. For reasons of simplicity, not shown in the figures are the gas-supply source to which the pipe 80 is connected and the motor drive of the shaft 74.

As illustrated in the figures, preferably the apparatus 1 comprises a plurality of diffusers 70 carried by respective arms 72, which are able to rotate fixedly about the axis A and are set circu ferentially at a distance from one another, for example three arms 72 set at 120° apart from one another.

Operation of the apparatus 1 embodying the method according to the invention is described in what follows.

The substrate 4 in the form of a tape is supplied continuously through the chamber 6. Advance of the substrate 4 along the path 60 is ensured by rotation of the carousel 25. While the substrate 4 traverses the chamber 6, an evaporation step is performed, in which the precursor 12 is evaporated to form the evaporation area 13. The substrate 4 traverses the evaporation area 13 resting on the carousel 25, with its face 17 facing the evaporation area 13 and being substantially concave, and with the strip 29 set on top of the slit 28 and consequently exposed to the evaporation area 13.

The coating material 3 is deposited on the face 17 and, in particular, on the portion 16 of the substrate 4 in a deposition step performed while the substrate 4 is traversing the evaporation area 13 in a non-planar configuration and with the concavity facing the evaporation area 13. The deposition step can be aimed at the formation of a layer of superconductive material, or else of an intermediate buffer layer.

The deposition step is assisted by a step of gas delivery performed by cyclically bringing the diffusers 70 into the proximity of the face ,17 of the substrate 4 along the winding sector 52 and hence along a curved path (in the case in point circular) radially internal to the concavity of the substrate 4. The gas-delivery step can perform different functions of assistance to the growth of the layer 2 and, according to the function, is performed before, during, or else after the deposition step.

For example, the gas-delivery step is a step of in si tu oxygenation, performed by bringing the diffusers 70 cyclically into the proximity of the face 17 of the substrate 4 within the evaporation area 13 during the deposition step for sending oxygen onto the layer 2 being grown, or else is a step of delivery of reactive gases, in particular forming gases (for example, an argon/hydrogen mixture) .

Claims

C L A I M S

1. A method for making a layer (2) of coating material (3) on a tape substrate (4), in particular for making superconductive tapes, comprising: a step of evaporation of a precursor (12) of the coating material so as to form an evaporation area (13) ; a step of feeding the substrate through the evaporation area; and a deposition step, in which the evaporated coating material deposits on one face (17) of the substrate; the method being characterized in that the substrate (4) traverses the evaporation area (13) in a non-planar configuration and has a concavity facing the evaporation area (13) .

2. The method according to Claim 1, characterized in that the deposition of the coating material (3) to form said layer (2) is made on a non-planar portion (16) of the substrate (4) and on a substantially concave face (17) of the substrate (4) .

3. The method according to Claim 1 or Claim 2, characterized in that the substrate (4) traverses the evaporation area (13) along a substantially curved path (60), and the evaporation area (13) is radially internal to said path (60).

4. The method according to Claim 3, characterized in that said path (60) develops about a centre of curvature (61), and the evaporation step is performed substantially in a position corresponding to, or in the proximity of, said centre of curvature (61) .

5. The method according to any one of the preceding claims, characterized in that, in the deposition step, the substrate (4) is supported via opposite side edges (46) of the substrate, and a central longitudinal strip (29) of the substrate is exposed to the evaporation area (13) .

6. The method according to Claim 5, characterized in that the substrate (4) is fed to the evaporation area (13) on a rotating carousel (25) .

7. The method according to any one of the preceding claims, characterized in that the deposition step is assisted by a step of gas delivery.

8. The method according to Claim 7, characterized in that said gas-delivery step is performed before, after, or during said deposition step.

9. The method according to Claim 7 or Claim 8, characterized in that said gas-delivery step is performed by bringing at least one diffuser (70) into the proximity of the substrate (4) along a curved path that is radially internal to the concavity of the substrate.

10. The method according to Claim 9, characterized in that said gas-delivery step is performed cyclically by moving said diffuser (70) along a circular path.

11. The method according to Claim 9 or Claim 10, characterized in that said gas-delivery step is performed via a plurality of diffusers (70) set circumferentially spaced from one another and carried cyclically in the proximity of the substrate (4) .

12. The method according to any one of Claims 7 to 11, characterized in that the gas-delivery step is performed by bringing at least one diffuser (70) into the proximity of the substrate (4) and inside the evaporation area (13) during the deposition step so as to deliver a flow of oxygen, or a reactive gas such as a forming gas, for example an argon/hydrogen mixture.

13. An apparatus (1) for making a layer (2) of coating material (3) on a tape substrate (4) , in particular for making superconductive tapes, said apparatus comprising: a chamber (6); evaporation means (11) for evaporating a precursor (12) of the coating material so as to form an evaporation area (13) within the chamber; and feed means (14) for feeding the substrate (4) through the evaporation area; the apparatus being characterized in that it comprises supporting means (15) for supporting the substrate (4) in a non-planar configuration through the evaporation area (13) with a concavity of the substrate (4) facing the evaporation area (13) .

14. The apparatus according to Claim 13, characterized in that the supporting means (15) support a non-planar portion (16) of the substrate (4) above the evaporation area (13) and with a substantially concave face (17) of the substrate (4) facing the evaporation area (13) .

15. The apparatus according to Claim 13 or Claim 14, characterized in that the supporting means (15) define a substantially curved path (60) of the substrate (4) through the evaporation area (13), and the evaporation means (11) comprise a source (20) of the coating material (3) set radially internal to said path (60) .

16. The apparatus according to any one of Claims 13 to 15, characterized in that the supporting means (15) have a pair of curved resting surfaces (45) set alongside one another for supporting respective opposite side edges (46) of the substrate (4) , said resting surfaces (45) being separated by a slit (28), which intercepts the evaporation area (13) and on which a central strip (29) of the substrate (4) extends.

17. The apparatus according to any one of Claims 13 to 16, characterized in that the supporting means (15) comprise a rotating carousel (25) , which is able to rotate about an axis (A) and has a radially external side surface (26), on which a stretch (27) of the substrate (4) is wound, said surface (26) being provided with a circumferential slit (28), which intercepts the evaporation area (13) and on which a central strip (29) of the substrate (4) extends.

18. The apparatus according to Claim 17, characterized in that said stretch (27) extends on a winding sector (52) of the carousel (25) having an angular amplitude substantially equal to the angular amplitude of the evaporation area (13) .

19. The apparatus according to Claim 17 or Claim 18, characterized in that the carousel (25) comprises a pair of wheels (31, 32), which rotate synchronously about said axis (A) and are set alongside one another and separated by said slit (28).

20. The apparatus according to any one of Claims 13 to 19, characterized in that it comprises at least one gas diffuser (70) and moving means (71) for bringing said diffuser (70) into the proximity of the substrate (4) and defining, for said diffuser (70) , a curved path that is radially internal to the concavity of the substrate.

21. The apparatus according to Claim 20, characterized in that the moving means (71) rotate about an axis (A) of rotation so as to carry said diffuser (70) along a circular path.

22. The apparatus according to Claim 21, characterized by comprising a plurality of diffusers (70) set circumferentially spaced from one another and carried by respective arms (72) , which arms rotate fixedly to one another about said axis (A) of rotation.

23. The apparatus according to any one of Claims 20 to 22, characterized in that said diffuser (70) is a diffuser for oxygen or for a reactive gas, for example a forming gas.