WO2014102188A1 - Method and device for the formation of a continuous layer on the inner and outer surfaces of a hollow part and part thus produced - Google Patents

Abstract

The invention relates to a method for forming, on the inner surface (101) of a hollow part (10) open at two opposing ends (103, 104) and consisting of a first material, a surface layer (70) of a second material extending continuously over at least part of the outer surface (102) of said part, especially at least over the surface of the end segments (107, 108) thereof. Said surface layer (70) is formed by chemical vapor deposition, from a precursor compound of the second material.

Description

 METHOD AND DEVICE FOR FORMATION OF A CONTINUOUS LAYER ON

 INTERNAL AND EXTERNAL SURFACES OF A HOLLOW PIECE AND PIECE SO OBTAINED

The present invention is in the field of the formation of surface coatings on hollow parts. More particularly, it relates to a method and a device for forming, on the inner surface of a hollow part open at two opposite ends, a surface layer extending continuously over at least a portion of the outer surface. of the piece, as well as a piece that can be obtained by such a method.

A particularly preferred field of application of the invention, although in no way limiting, is the metallization of the inner surface, and at least part of the outer surface, of electromagnetic wave conductors, commonly called waveguides. , in particular implemented in the spatial field for the transfer of signals between different devices such as receivers, amplifiers, antennas, etc. Another field of application of the invention is, for example, the metallization of antennas, in particular horn antennas.

At present, the waveguides used in the space sector are formed of aluminum or brass tubes, the internal and external surfaces of which can be coated with a material having a high electrical conductivity, such as silver, by so-called wet techniques, in particular by electrochemical treatment. Such techniques, applied for the metallization of internal surfaces of the tubes, however, have the disadvantage of inducing large variations in the thickness of the surface coating obtained, due to a great inhomogeneity of the local concentrations of reagents, or of the field. electric inside the tubes. By way of example, to ensure that a silver coating of at least 5 μιτι of thickness is obtained on the entire internal surface of an aluminum tube, these techniques require forming on this surface internal coating of thickness of 10 μιτι, the variation in thickness between different surface units of the room being 5 μιτι. In addition, these techniques are limited in terms of the particular geometry of the hollow parts that can be treated: they indeed require the introduction of an electrode and the flow of a liquid solution inside the room, which proves very complex to achieve for parts of small dimensions, or report length on high section.

In addition, in the particular case of the space domain, the waveguides equipping the satellites placed in orbit are connected to satellite structure elements formed from a composite material based on mechanically resistant fibers dispersed in an organic polymer matrix, via metal / composite junctions. Satellites being subjected to very large temperature variations, ranging between -150 and +200 ° C, during the life of the satellite, and the metallic and composite materials behaving differently under the thermomechanical stresses, this induces a fragility at the junctions, thus reducing the lifespan of the satellites. It would thus be advantageous to have waveguides also formed of composite material based on mechanically strong fibers dispersed in an organic polymer matrix, and all the more so since such composite materials have the advantage of a gain in large mass compared to metals such as aluminum, a significant advantage in the field of space.

However, so-called wet coating techniques are applicable only to pieces formed of electrically conductive material or rendered conductive by pretreatment, and not to composite materials based on mechanically resistant fibers dispersed in an organic polymer matrix, which does not are not electrically conductive. In addition, the implementation of such non-electrically conductive materials for the manufacture of waveguides would require a metallization extending continuously on the inner surface of the tube, and on at least a portion of its outer surface, for the electrical connection to cooperating elements to ensure the transmission of signals.

It has been proposed by the prior art, as illustrated by the documents US 2004/250772, US 2009/31 1443 and DE 198 09 675, coating the inner surface and a portion of the outer surface of a hollow part by the chemical vapor deposition technique. However, the methods proposed by this prior art do not make it possible to obtain a good uniformity of thickness of the coating thus formed on the surface of the part, in particular for the small thicknesses of coating.

There remains therefore a need for a method of forming, on the inner surface of a waveguide, and more generally of a hollow part open at two opposite ends, a surface coating extending continuously over at least a part of the outer surface of the part, which is simple to implement, which is applicable regardless of the nature of the material constituting said part, including for materials with little or no electrically conductive, and which also allows to obtain a surface coating with only slight variations in thickness, and this even for low coating thicknesses of less than 10 μιτι. The present invention aims to provide a method that meets such objectives.

For this purpose, it is proposed according to the present invention a forming method, on the inner surface of a hollow part open at two opposite ends and made of a first material, a surface layer of a second material s continuously extending over at least a portion of the outer surface of the workpiece. According to this method, the surface layer is formed by chemical vapor deposition from a precursor compound of the second material.

The present inventors have indeed discovered that, quite surprisingly, the implementation of the chemical vapor deposition technique, commonly known as CVD, under particular conditions makes it possible to form a surface layer of substantially constant thickness. extending over the inner surface of a hollow piece and continuously on at least a portion of its outer surface, i.e. without discontinuities between the inner surface and the outer surface of the piece . Such an advantageous result is obtained whatever the basic material constituting the piece, and whatever the geometry of the latter, and in particular its dimensions. The method according to the invention is thus applicable to all hollow parts, including complex geometry, including angles or curves, of any cross section, and profile closed as well as semi-closed.

In the present description, the term "surface layer" refers to a layer matching the geometry of the part, over the entire surface covered.

The chemical vapor deposition technique is herein understood to encompass all types of chemical vapor deposition processes, such as ALD (Atomic Layer Deposition), MOCVD (for English MetalOrganic Chemical Vapor Deposition), DLICVD (for Direct Liquid Injection Chemical Vapor Deposition), etc. These techniques are well known in themselves, and widely described in the literature, for the formation of coatings on the outer surface of parts. The general principle of the chemical vapor deposition technique is in particular described in Hitchman and Jensen, 1993, Chemical Vapor Deposition Principles and Applications, London Academy Press.

The first material, said base material of the part, can be of any type, in particular aluminum, or a composite material based on mechanically resistant fibers dispersed in an organic polymer matrix, or a polymeric material such as polytetrafluoroethylene (PTFE, known as teflon), or polyether ether ketone (PEEK).

The second material, forming the surface layer, may be a metallic material as well as a ceramic or polymer, or even an architectural one, combining two or three of these families of materials. The second material may equally well be formed by a substantially pure element, or by a mixture of elements, so as to form in the part a so-called mixed surface layer, of an alloy or solid solution of a plurality of elements. . The precursor compound of the second material, or the mixture of precursor compounds in the case where the surface layer of the second material is mixed, is chosen, quite conventional manner in itself, depending on the second particular material to obtain. It may be for example an organometallic compound, for the formation of a metal surface layer on the part, by chemical reaction, activated by a supply of energy, especially thermal, decomposition of the precursor, and release of one or more atoms of the metal of interest, which are deposited on the surface of the piece.

In particular embodiments of the invention, the second material is more electrically conductive than the first material forming the part.

The method according to the invention may comprise successive steps of depositing, on the surface of the part, successive surface layers of a second material, then a third material, etc., each step being carried out under similar conditions the above, and as described in the present description, to the operating variations related to the nature of the materials, in particular to the nature of the particular material deposited.

Preferably, the surface layer is continuous over the entire internal surface of the part.

In particular embodiments of the invention, the surface layer extends continuously over the surface of only one of the slices of the part, at one end to which it has an opening. Such a characteristic is particularly advantageous for the preferential application of the method to the metallization of a horn antenna, which must be connected to an end with a cooperating element in the overall structure in which it is placed. the other end remains free.

In other particular embodiments of the invention, the surface layer extends continuously at least on the surface of the slices of the part at the two opposite ends to which it has openings. Such a characteristic is particularly advantageous for the preferential application of the method to the metallization of waveguides, the connection with the cooperating elements in the overall structure in which these waveguides are implemented taking place at the level of the end portions waveguides, generally at their end slices.

The outer surface layer may be formed only on these end wafers, as on a larger part of the outer surface of the workpiece. Preferably, it also extends over at least the outer surface of two opposite end portions of the workpiece, or even the entire outer surface of the workpiece.

The method according to the invention comprises:

introducing a first end portion of the piece into a first closed chamber, and a second end portion of the piece, opposite the first end portion, into a second closed chamber; maintaining the workpiece at a temperature greater than the vaporization temperature of the precursor compound, this temperature being a function of the pressure conditions applied in the workpiece, so as to avoid any liquefaction of the precursor compound in the workpiece,

introducing a stream of gas containing the precursor compound of the second material in the gaseous state into the first chamber, preferably towards the opening situated at the first end of the part, and preferably substantially according to the axis of the workpiece at said first end,

- the contribution at the surfaces of the part to be coated with the surface layer, with an energy greater than the activation energy of the decomposition reaction of the precursor compound, more generally greater than the activation energy of the overall deposition reaction from the precursor compound,

and evacuating the gas flow from the second enclosure. By the choice of the dimensions of the speakers, and the room lengths introduced into each of them, it is thus possible to easily adjust the extent of the external areas of the room on which the surface layer is deposited. In this respect, the process according to the invention is particularly advantageous from an economic point of view since it makes it possible to coat the surface layer only with the part of the outer surface of the part strictly necessary, and this very easily.

In particular embodiments of the invention, the energy supply is achieved by moving along the workpiece a localized energy supply front, from one of the opposite ends of the workpiece to the workpiece. other. Such displacement along the workpiece of a localized energy supplying front advantageously makes it possible to precisely control the variations in thickness of the surface layer formed inside and outside the workpiece. The displacement of the energy supply front along the workpiece can in particular be made several times in succession.

Preferably, the energy supply is achieved by heating the room to a temperature above the decomposition temperature of the precursor compound under the pressure conditions applied in the room. This heating can in particular be achieved by moving a heating zone around the workpiece, one of its ends opposite to the other.

The objective that the present invention has set itself, which is to reduce the thickness variations of the surface layer, is all the more attained in particular embodiments of the invention in which the temperature of the the deposition zone of the second material is set to lie within the range of temperatures where the deposition rate is controlled by the surface reactions, and preferably close to the boundary between this domain and the neighboring temperature range where the deposition rate is controlled by the input of the precursor compound into the gas stream. It is within the competence of a person skilled in the art to determine this temperature as a function of the particular characteristics of the precursor compound used and of the various operating conditions, in particular the concentration of compound precursor in the gas flow, the pressure applied inside the room, etc.

In particular embodiments of the invention, the speed of the constant gas flow is maintained at the entry into the room. Such a characteristic advantageously improves the homogeneity of the layer of the second material on the internal surface of the part.

The process according to the invention can be carried out at atmospheric pressure or under reduced pressure. Preferably, a reduced pressure is applied in the room, as well as in the first and second chambers, preferably a pressure of less than or equal to 950 mbar.

When the part has a semi-closed profile, the method comprises a prior step of reversibly sealing the opening, so as to temporarily form a closed profile piece.

By way of example, the method according to the invention can be applied for forming, on a hollow part open at two opposite ends, in particular a waveguide, made of aluminum or a fiber-based composite material. mechanically resistant dispersed in a polymeric organic matrix, and more particularly on the inner surface and on the surface of the end wafers of this piece, and optionally on the outer surface of its opposite end portions, of a layer continuous surface of an electrically conductive material, for example silver or copper.

According to another aspect, the present invention relates to a forming device, on the inner surface of a hollow part open at two opposite ends and made of a first material, a surface layer of a second material extending continuously on at least a portion of the outer surface of this part, this device being particularly suitable for the implementation of a method meeting one or more of the above characteristics. Such a device comprises, besides the hollow part: a first closed enclosure containing a first part end of the room,

a second closed enclosure, preferably separate from the first enclosure, containing a second end portion of the part, opposite to the first end portion; means for introducing a gas flow, containing a precursor compound; of the second material in the gaseous state, in the first chamber, preferably in the direction of the opening located at the first end of the part, and preferably substantially along the axis of the part at said first end, - means for evacuating the gas flow from the second chamber,

means for holding the part at a temperature higher than the vaporization temperature of the precursor compound,

and a system for supplying energy, in particular heat, capable of providing, at the surfaces of the part to be coated with the surface layer, an energy greater than the activation energy of the decomposition reaction of the precursor compound .

The energy supply system can be of any conventional type in itself, in particular of the thermal type (resistive, convective and / or radiative), plasma, photonic or electronic.

In particular embodiments of the invention, it is a heating system capable of forming on the surface of the part a heating zone at a temperature above the decomposition temperature of the precursor compound. This heating system may be constituted by the holding means of the workpiece at a temperature greater than the vaporization temperature of the precursor compound, or be distinct from it. Preferably, this heating system is an infrared emitter system, particularly suitable for heating composite materials based on carbon fibers and epoxy-type polymer matrix, which are arranged around the circumference of the part. In particular embodiments of the invention, the device comprises means for moving the energy supply system along the part, one of its ends opposite to the other.

In the particular case where the energy supply system is of the infrared emitter type arranged around the workpiece, the latter are mounted on a linear guide module for moving them along the workpiece at an adjustable speed. In other particularly advantageous variants of the invention, the heating system comprises a set of infrared emitters arranged around the piece along the entire length of the latter, and means for switching on, extinguishing and adjusting the the radiation power of each of these emitters independently of each other.

During the implementation of the device according to the invention, the flow of gas introduced into the first chamber enters the hollow part by the first end of the latter, and circulates there until it reaches the level of the opposite end, in the second enclosure, from where it is evacuated. At the level of the first enclosure, part of the gas flow also spreads around the outer surface of the first end portion of the part, in particular at the end edge, making it possible to form a layer of surface of the second material in the continuity of the inner surface layer. At the level of the second enclosure, a part of the gas flow escaping from the part is brought back, by recirculation loops, around the outer surface of the second end portion of the part contained in the second enclosure, comprising the end wafer, to form, under the effect of the energy supply, a surface layer of the second material also continuous with the inner surface layer.

The device may comprise means for applying a reduced pressure in the room and, where appropriate, in the first and second chambers.

In variants of the invention, the first enclosure and the second enclosure are separate parts. In other advantageous variants of the invention, the first chamber and the second chamber are constituted by two separate chambers of the same reactor containing the part. These two reaction chambers are preferably separated by a so-called intermediate chamber, containing the central part of the part located between the two opposite end portions.

All of these chambers are separated by partitions which are preferably capable of allowing the balancing of the pressures between the chambers, so as to obtain an identical pressure inside and around the hollow part, along the entire length of this chamber. last. These partitions may for example be formed by bodies of heat-resistant material, for example glass with a low coefficient of thermal expansion, such as a borosilicate glass marketed under the name Pyrex®.

The reactor preferably comprises a glass wall, transparent to infrared radiation, preferably glass with a low coefficient of thermal expansion, such as borosilicate glass marketed under the name Pyrex®.

In particular embodiments of the invention, the device comprises means for maintaining a constant flow rate of the gas flow at the entrance to the room. These means preferably comprise a gas flow guide member to a first open end of the workpiece, in particular arranged in the first chamber, having substantially the same cross section as the workpiece at said first end, and capable of conditioning the flow of gas such that 95 to 99% of the gas streams of this stream entering the piece enter the latter substantially parallel to its axis at its first end. The other gas lines are distributed around the outer surface of the room. This member, placed upstream of the room in the direction of the gas flow, in the immediate vicinity of the room, that is to say a few millimeters from its first end, can channel the flow of gas and avoid that he undergoes an acceleration as he enters the room. Another aspect of the invention relates to a hollow part, open at two opposite ends, made of a first material, and obtainable by a process corresponding to one or more of the above characteristics. This part comprises, on its inner surface and at least a portion of its outer surface, preferably on at least the surface of one of its slices, preferably of its two slices at said two opposite ends, and where appropriate on the outer surface of its two opposite end portions, a continuous surface layer of a second material, of thickness less than or equal to 100 μιτι. The thickness of this surface layer is preferably less than or equal to 25 μιτι, a range in which the uniformity of the layer, both along the length of the part and at its cross-section, is advantageously particularly important. . Preferably, the continuous surface layer has a thickness less than or equal to 20 μιτι, preferably less than 15 μιτι. A surface layer with a thickness of less than or equal to 10 μιτι is particularly preferred in the context of the invention, in particular because the adhesion of the layer to the surface of the part is particularly good in such a range of thicknesses. Preferably, the thickness variation of this surface layer is, as a function of the thickness of the layer, less than or equal to 2 μιτι, preferably less than or equal to 0.5 μιτι.

The first material forming the part may be of any type, especially metal, such as aluminum, composite, ceramic or polymer, such as teflon or PEEK. The second material may also be of any type, for example metallic, such as copper, silver or nickel, ceramic, polymer, etc., including a mixture of different elements.

In particularly preferred embodiments of the invention, the second material is more electrically conductive than the first material. In particular embodiments of the invention, the part consists of a first non-electronically conductive material, in particular a composite material based on mechanically strong fibers distributed in an organic polymer matrix, and the surface layer is made of a second electrically conductive material, for example silver or copper.

In particular embodiments of the invention, the part comprises, on its inner surface and at least a part of its external surface, several successive continuous layers of a second material, a third material, etc. Such an embodiment is particularly advantageous from an economic point of view, since it makes it possible in particular to obtain a surface coating of total thickness and predetermined surface properties, by several successive layers, for example comprising a first layer of low cost and greater thickness, and a final layer of small thickness and desired properties. It may also allow for example to obtain a coating having good adhesion to the surface of the part, by inserting a layer of a material having better adhesion properties, under a layer of a material having minus good adhesion properties. For example, a waveguide of metallized composite material may comprise, on the surface of the part, a first layer of nickel, inexpensive material, and a second copper layer, material having the properties required for the application.

The part according to the invention is in particular a waveguide, made of composite material or metallized aluminum, in particular for an application in the spatial field. It may also be for example the cone of a horn antenna.

The features and advantages of the invention will emerge more clearly in the light of the following embodiments, provided for illustrative purposes only and in no way limitative of the invention, with the support of FIGS. 1 to 12, in which: - Figure 1 shows schematically a device according to a first particular embodiment of the invention;

FIG. 2 shows a partial view of the device of FIG. 1, illustrating a first end portion of the hollow part and the associated enclosure;

- Figure 3 shows a sectional view along the plane A-A of the device of Figure 2;

FIG. 4 schematically represents a device according to a second particular embodiment of the invention; - Figure 5 shows a partial view of the device of Figure 4, illustrating the hollow part disposed in the reactor of the device;

- Figure 6 shows a partial view of a variant of the device of Figure 4, comprising a gas flow guide member disposed upstream of the hollow part; - Figure 7 shows a sectional view along the plane B-B of the device of Figure 4;

FIG. 8a illustrates a heating system of a device according to one particular embodiment of the invention;

FIG. 8b illustrates a heating system of a device according to a different embodiment of the invention;

- Figure 9 shows schematically, in sectional view along a longitudinal plane, a hollow part according to the invention, coated with a continuous surface layer on its inner surface and a portion of its outer surface; FIG. 10 represents a spectrum obtained by X-ray energy dispersion spectroscopy on the inner surface of a hollow part according to the invention, coated with a copper surface layer approximately 5 μιτι thick; FIG. 11 represents a scanning electron microscope image of a portion of a transverse section of a hollow part according to the invention, coated with a copper surface layer approximately 5 μm thick. ; and FIG. 12 represents a scanning electron microscopy image of the inner surface of a hollow part according to the invention, coated with a copper surface layer approximately 5 μm thick.

An example of a device according to a first particular embodiment of the invention, for forming, on the inner surface 101 and at least a part of the outer surface 102 of a hollow part 10 open at two opposite ends 103, 104, and made of a first material, a continuous surface layer of a second material, is illustrated in FIG.

The hollow part 10 can have any shape and any dimensions. In the exemplary embodiment shown in FIGS. 1 to 7, it is a rectangular section tube, particularly adapted to the formation of a waveguide, open at its two opposite longitudinal ends 103, 104, and having a longitudinal axis 109. This part may be made of any material, especially a composite material based on mechanically resistant fibers, such as carbon fibers, glass, aramid, or a mixture thereof, which are distributed in a matrix of an organic polymer, for example of the epoxy type.

The device comprises a first closed enclosure 301 whose wall is pierced by a window 303 within which is inserted a first end portion 105 of the hollow part 10, as illustrated in FIG. piece introduced into the first chamber 301 is variable, and chosen according to the length of the part which it is desired to coat the outer surface 102. It is for example equal to about 1 cm. The tightness at the interface of the enclosure 301 and the part 10 is provided by a seal 304, made of heat-resistant material, interposed between the wall defining the part 10 and the peripheral edges of the window 303, as illustrated in Figure 3.

The device comprises a second closed enclosure 302, visible in FIG. 1, of identical constitution to the first enclosure 301, and inside which is disposed a second end portion 106 of the part 10. The interface of the second enclosure 302 and the part 10 is provided in the same manner as for the first enclosure 301. The length of the coin introduced into the second chamber 302 is variable, and may be substantially identical to, or different from, that introduced into the first chamber 301. The device comprises, in addition to the hollow part 10 and the enclosures 301,

302, conventional means in themselves for generating a flow of a neutral gas, for example nitrogen, containing a precursor compound of the second material in the gaseous state. These means may for example comprise sources of gas or gas mixtures 201, 202, connected by pipes 203 equipped with valves 204 to means, not visible in FIG. 1, for introducing the stream of gas thus generated in the first pregnant 301. These means for introducing the flow of gas into the first enclosure are conventional in themselves, and are constituted in particular by an injector. The injection is preferably made towards the first end 103 of the part 10, substantially along the axis of the latter.

The device also comprises means for evacuating the flow of gas out of the second enclosure 302, which are conventional in themselves, for example a vacuum pump connected to the second enclosure 302 via a pipe 205. This vacuum pump realizes at the same time time the reduced pressure of the part 10 and the speakers 301, 302, which are in hydraulic communication with each other.

It further comprises means for maintaining the workpiece at a temperature greater than the vaporization temperature of the precursor compound, so as to avoid any liquefaction of said precursor compound in or around the workpiece. The device finally comprises a power supply system 206. This system may in particular be a heating system, examples of which will be described below in detail, with reference to FIGS. 8a and 8b, and which is example adapted to generate a localized heat zone movable along the part 10, from one end 103, 104 to the other, so as to ensure that each surface unit of the part 10 is exposed to the same amount of heat .

Such a device is particularly suitable for implementing a process for deposition under reduced pressure of a coating on the surface of hollow parts which are sufficiently rigid at high temperature so as not to undergo geometric deformation under the effect of a pressure difference between their internal volume and the outside, which is at atmospheric pressure, for example aluminum wall parts with a thickness greater than or equal to 0.5 mm. An example of a device according to a different embodiment of the invention is shown in FIG. 4. This device comprises means 201, 202, 203, 204 for generating a gas containing the precursor compound of the second material, means for introduction of a flow of this gas into the first chamber, means 205 for evacuating the gas flow out of the second chamber, and a system for supplying energy, in particular for heating 206, which are similar to those described above with reference to FIG.

It differs from the first device described above in that the first chamber 401 and the second chamber 402 are constituted by separate chambers formed in the same reactor 40 containing the hollow part 10. These so-called reaction chambers 401, 402 are separated by an intermediate chamber 403, containing the central part of the part 10.

The reactor is in particular in the form of a glass tube, preferably borosilicate glass resistant to temperature variations and pressure differences between its internal volume and the outside, large enough to contain the piece 10 in its entirety. The chambers 401, 402 and 403 are delimited relative to each other by partitions 404, formed for example by glass members, occupying the entire internal cross section of the reactor 40, and pierced at their center with a window 405 of shape and dimensions of the part 10, allowing the insertion of the latter through it, as illustrated in Figure 7. These partitions 404, which further realize the support of the part 10 in the reactor 40, are configured to allow balancing the pressures between the different chambers, without allowing the passage of a significant amount of the gas flow introduced into the reactor 40. They may in particular be pierced with a plurality of small orifices.

At least two such partitions 404 are provided in the reactor, so as to form a first reaction chamber 401 receiving the first end portion 105 of the workpiece 10, and a second reaction chamber 402, receiving the second end portion. 106 of the room, separated by an intermediate chamber 403, as shown in Figure 5.

Such an embodiment of the device according to the invention is advantageously suitable for all types of hollow parts, including those formed of thermosensitive composite material. Indeed, it ensures the establishment and maintenance of substantially equal pressure conditions inside and around the part 10.

Preferably, the device further comprises, as illustrated in FIG. 6, a guiding member for the gas flow introduced into the first reaction chamber 401 towards the first end 103 of the part 10, having substantially the same cross section as the piece 10 at this first end 103 and able to condition the flow of gas so that most of the gas lines reaching the piece 10 penetrate substantially parallel to its axis 109. This organ is for example in the form of a tube 406 having the same cross section as the piece 10 at its first end 103, disposed in the first chamber 401 upstream of the piece 10 with respect to the direction of the gas flow, illustrated at 407 in FIG. 6, and so as to lead substantially in vis-à-vis the first end 103 of the piece. This tube 406 has a length sufficient to channel the flow of gas. It is disposed in the immediate vicinity of the piece 10, that is to say at a distance of a few millimeters from it. Such a distance is advantageously low enough not to induce a change in the speed of the gas flow between the outlet of the tube 406 and the entry into the room 10, and sufficiently high to allow a small portion of the gas flow to be distribute around the first end portion 105 of the piece 10, to form the surface layer of the second desired material.

The tube 406 can be supported in the reactor 40 by members 408 similar to the support members 404 of the part 10.

A first example of a heating system of the device according to the invention is illustrated in FIG. 8a. This system comprises a set of infrared emitters 501 disposed around the workpiece 10 and fixed to the same structure 502 mounted on a linear conveyor 503, able to move it from one end 103, 104 of the workpiece 10 to the other in the directions indicated at 504, 505 in FIG. 8a, including around the enclosures 301, 302 or the reactor 40, as the case may be. Such a system is associated with separate means for holding the entire part at a temperature above the vaporization temperature of the precursor compound, under the pressure conditions applied in the part.

A second particularly advantageous embodiment of this heating system is illustrated in FIG. 8b. It comprises a plurality of infrared emitters 601, for example of annular shape, arranged one after the other around the piece 10 and the enclosures 301, 302, or the reactor 40 as appropriate, at regular intervals over the entire length of the room. These emitters 601 are individually controllable by control means 602 shown schematically in FIG. 8b, so that their radiation power can be individually adjusted. The displacement of the heating zone is then effected by increasing, then decreasing, the radiation power of the successive emitters 601. Such an embodiment advantageously makes it possible at the same time to move the localized heat front inducing the decomposition reaction of the precursor compound, and keeping the workpiece at a temperature always higher than the vaporization temperature of this precursor compound, throughout the implementation of the formation process of the precursor compound; surface, by a proper adjustment of the power of each transmitter.

Such a method of forming a continuous surface layer of the second material on the inner surface 101 and a portion of the outer surface 102 of the part 10, comprises preliminary steps of introduction of the first end portion 105 of the piece 10 in the first chamber 301, 401, and the second end portion 106 in the second chamber 302, 402.

It is then established a reduced pressure, for example less than or equal to 100 mbar, in the room 10 and the speakers, then it is introduced into the first chamber 301, 401 a gas stream containing a precursor compound of the second material to the gaseous state.

The heating system may optionally have been previously implemented to bring the room to a temperature above the vaporization temperature of the precursor compound at the pressure applied in the room. Otherwise, this step may have been performed by any other conventional heating means in itself.

It is then generated a heating zone located at one of the ends 103, 104 of the part 10, at a temperature above the decomposition temperature of the precursor compound of the second material at the pressure applied in the room. This zone is displaced at a controlled and constant speed, for example between 0.5 and 500 cm / min, to the opposite end 104, 103 of the part 10.

Alternatively, the energy supply front can be moved from a first end 103 of the workpiece 10 to a central part thereof, so as to form the surface layer, then the process of forming the layer can be interrupted, and the piece 10 returned so position the second end 104 at the initial location of the first end 103. The method of forming the surface layer can then be applied to the part of the part not yet covered, so as to form a continuous layer extending over the entire inner surface of the workpiece and at least a portion of its outer surface.

There is then obtained on the part a surface layer 70 of the second material, which extends continuously on the inner surface 101 and on a part of the outer surface 102, in particular on the surface of the end wafers 107, 108, corresponding to the wall thickness of the peripheral part of the end openings, and on the outer surface of the end portions 105, 106 of the workpiece, as shown schematically in Figure 9. In this figure, For the sake of clarity, the surface layer 70 is slightly spaced from the surface of the part 10. In reality, this surface layer is pressed against the surface of the part and perfectly matches the geometry.

Detailed examples of implementation of a method according to the invention respectively meet the following operating conditions.

EXAMPLE 1 Formation of a Copper Surface Layer in a Tube of Composite Material The hollow part 10 is a tube made of composite material based on epoxy matrix and carbon fibers, of a shape and dimensions particularly suited to the production of a waveguide, more particularly of rectangular section, internal dimensions 9.53 mm x 19.05 mm, and length 6 cm. The day before the implementation of the method according to the invention, the tube is subjected to a preliminary cleaning, comprising the friction of its inner and outer surfaces with a soft brush, detergent and water; rinsing with water for 30 seconds under a tap, then with deionized water; rinsing with acetone for 30 s; and drying under argon flow. The reactor 40, and the guide member 406, when they are put in work, are subject to the same preparation steps.

The next day, the tube is placed in the device, a length of about 1 cm of each of its end portions being introduced into the corresponding chamber. Depending on the device used, the seal 304 is formed at the level of the pregnant / tube interfaces, or the support members 404 are put in place in the reactor 40. Where appropriate, the guide member 406 and its supports 408 are arranged in the reactor, a few millimeters upstream of the tube to be coated. The entire device is placed in a thermostatically controlled chamber at a temperature to bring the outer surface of the tube to a constant temperature of about 90 ° C.

A reduced pressure, equal to 7 mbar, is applied in the tube and the enclosures, then a stream of nitrogen of 320 sccm (standard cubic centimeters per minute) is established in the tube.

The heating system 206 is placed around the tube and the speakers. It is an infrared oven, regulated so as to obtain, on the internal surfaces of the tube, and at a longitudinal coordinate corresponding to the center of the oven, a temperature of about 195 ° C. The tube is heated in this way for a few tens of minutes until the temperature is stabilized.

The precursor used is a precursor of copper, more particularly a solution of (hexafluoroacetylacetonato) Cu (2-methyl-1-hexen-3-yne), known commercially under the name Gigacopper®, prepared conventionally in itself. same and diluted in octane to obtain a concentration of 60 g / l.

For the deposition of the copper layer on the surface of the tube, the pressure, the temperatures and the flow rates are regulated in the manner

Next . Spray ⁼ 80 ° C, Gas T ⁼ 90 ° C, total P in the reactor ⁼ 5 ΤθΓΓ, nitrogen flow of 320 sccm. The precursor solution in the octane is diffused in the nitrogen stream, then the whole is vaporized at 80 ° C. before being introduced into the first chamber, according to the following parameters: solution volume flow rate of 0.9 mL / min, equivalent to a flow rate of about 130 sccm of precursor solution in the gas phase; gas flow rate of 320 sccm.

At the end of the process, the assembly is brought back under atmospheric pressure and at room temperature, and the tube is removed from the device.

It emerges from a visual observation that on the inner surface of the tube, on its end edges and on the outer surface of its end portions, a continuous layer of thickness measured at 5 μιτι ± was formed on the inside surface of the tube. 0.5 μιτι, having a metallic coppery appearance. The internal angles are well coated, and the outer edges and edges also.

A chemical composition measurement carried out by energy dispersive X-ray spectroscopy (EDX) shows that the surface layer consists of pure copper. The spectrum obtained on the inner surface of the tube is shown in FIG. 10. In this spectrum, the peaks corresponding to carbon (C) and oxygen (O) are very weak, and reflect a very minimal pollution of the surface. , due to exposure to ambient air. The morphology of the copper surface layer is illustrated by the scanning electron microscopy images shown in FIGS. 11 to 12, obtained at different magnifications. FIG. 11, obtained from a transverse section of the tube, shows that the layer covers the angles of the tube, with a constant thickness and without discontinuity. Figure 12 shows the surface morphology of the copper layer. It is observed that this layer is homogeneous and slightly rough.

The X-ray diffraction spectra show that the copper has its stable face-centered cubic structure, without obvious texturing (preferred orientation of crystallites). Finally, the electrical resistivity, which is the essential property for evaluating the performance of the surface layer in terms of RF signal transmission, is measured using a 4-point resistivity meter, at a value of approximately 3- 4 μΩ.ατι, quite satisfactory for a waveguide application.

Example 2 - Formation of a copper surface layer in an aluminum tube

The hollow part 10 is an aluminum tube, of shape and dimensions particularly suitable for the production of a waveguide, more particularly of rectangular section, of internal dimensions 9.53 mm × 19.05 mm, and length 50 cm.

The operating conditions are the same as those described above with reference to Example 1 except for the parameters specified below.

The heating system is here a heating cord placed around the room. The temperature is adjusted so as to obtain a temperature of about 180 ° C at the inner surface of the workpiece.

The precursor used is a precursor of copper, more particularly a solution of (hexafluoroacetylacetonato) Cu (2-methyl-1-hexen-3-yne), known commercially under the name Gigacopper®, prepared conventionally in itself. same and diluted in octane to obtain a concentration of 40 g / l.

For the deposition of the copper layer on the surface of the tube, the pressure, the temperatures and the flow rates are regulated in the manner

Next . Spray ⁼ 80 ° C, Gas T ⁼ 90 ° C, total P in the reactor ⁼ 5 ΤθΓΓ, nitrogen flow of 320 sccm.

Two experiments were carried out with two different durations, respectively of 1 h 41 min. and 42 min.

At the end of these experiments, the tubes obtained were cut lengthwise by means of a small diamond disk. We observe for both of them have formed on the inner surface and a part of the outer surface of the piece a continuous copper coating having a metallic appearance. SEM and EDS analyzes show that this coating contains negligible traces of oxygen and carbon, and that it has a uniform thickness. For the tube of the first experiment, this average thickness is 5 μιτι.

Example 3 - Formation of a silver surface layer in a PEEK tube

The hollow part 10 is a PEEK tube, of internal dimensions 10 mm × 3 mm, and length 10 cm.

The operating conditions are the same as those described above with reference to Example 1 except for the parameters specified below.

The precursor is hexafluoroacetylacetonato-α-vinyltriethylsilane ((hfac) Ag (VTES)) at a concentration of 0.1 mol / L in toluene. The part is treated by degassing, and polishing with SiC P4000 paper, then treated with UV under air for 2 h 40 min.

The deposit duration is 39 min.

The deposition temperature is 220 ° C.

At the end of this experiment, it is observed that a continuous silver coating of homogeneous thickness, of about 900 nm, has formed on the inner surface and a part of the external surface of the part.

Example 4 - Formation of a Silver Surface Layer in a Tube of Composite Material

The hollow part 10 is a composite material tube based on epoxy matrix and carbon fibers, of internal dimensions 10 mm × 3 mm, and length 10 cm.

The operating conditions are the same as those described above with reference to Example 3. At the end of this experiment, it is observed that on the inner surface and a part of the external surface of the part, a continuous silver coating with a uniform thickness of approximately 1 μιη has been formed.

Claims

A method of forming, on the inner surface (101) of a hollow piece (10) open at two opposite ends (103, 104) and made of a first material, a surface layer (70) of a second material extending continuously over at least a portion of the outer surface (102) of said workpiece, wherein said surface layer (70) is formed by chemical vapor deposition from a precursor compound said second material, characterized in that it comprises: - introducing a first end portion (105) of said workpiece (10) into a first closed enclosure (301, 401) and a second end portion (106) of said workpiece opposed to said first end portion, in a second closed chamber (302, 402), maintaining said piece (10) at a temperature greater than the vaporization temperature of said precursor compound, introducing a gas stream containing said precursor compound in the gaseous state into said first chamber (301, 401), - the contribution at the surfaces of said part (10) to be coated with the surface layer, with an energy greater than the activation energy of the decomposition reaction of said precursor compound, and evacuating said gas stream from said second enclosure (302, 402). A method according to claim 1, wherein the surface layer (70) extends continuously over the surface of the wafers (107, 108) of the workpiece at said two opposite ends, and preferably on the outer surface of two opposed end portions (105, 106) of said workpiece (10). 3. Method according to any one of claims 1 to 2, according to wherein the energy input is achieved by moving an energy supplying edge (206) along said workpiece, from one of said opposite ends (103, 104) to the other. 4. Method according to any one of claims 1 to 3, wherein the supply of energy is achieved by heating said room to a temperature above the decomposition temperature of said precursor compound. 5. Method according to any one of claims 1 to 4, wherein a reduced pressure is applied in said part (10), preferably a pressure less than or equal to 950 mbar. 6. Method according to any one of claims 1 to 5, wherein the speed of said constant gas flow is maintained at the entrance to said room (10). 7. A formation device, on the inner surface (101) of a hollow part (10) open at two opposite ends (103, 104) and made of a first material, a surface layer (70) of a second material extending continuously over at least a portion of the outer surface (102) of said part, characterized in that it comprises: said hollow part (10), a first closed enclosure (301, 401) containing a first end portion (105) of said part, a second closed enclosure (302, 402) containing a second end portion (106) of said part opposite to said first end portion; means for introducing a gas stream, containing a precursor compound of said second material in the gaseous state, in said first chamber (301, 401), means for evacuating said flow of gas out of said second enclosure (302, 402), means for maintaining said part at a temperature higher than the vaporization temperature of said precursor compound, - and a power supply system (206) capable of providing at the surfaces of said part (10) to be coated with the surface layer, an energy greater than the activation energy of the decomposition reaction of said precursor compound. 8. Device according to claim 7, comprising means for moving said energy supply system along said part (10) of one of said opposite ends (103, 104) to the other. 9. Device according to any one of claims 7 to 8, wherein the energy supply system (206) is a heating system capable of forming at the surfaces of said part (10) to be coated with the layer surface, a heating zone at a temperature above the decomposition temperature of said precursor compound. 10. Device according to any one of claims 7 to 9, wherein said first chamber (401) and said second chamber (402) are constituted by two separate chambers of the same reactor (40) containing said piece (10), and are preferably separated by a so-called intermediate chamber (403). 11. Device according to claim 10, wherein said chambers (401, 402, 403) are separated by partitions (404) adapted to allow the balancing of the pressures between the chambers. 12. Device according to any one of claims 7 to 1 1, comprising means for ensuring the maintenance of a speed of said constant gas flow at the entrance to said piece (10), preferably a member (406) of guiding said gas flow to a first end (103) of said workpiece, having substantially the same cross section as said workpiece (10) to said first end, and able to condition said flow of gas so that 95 to 99% of the gas lines of said stream reaching the workpiece (10) penetrate therein parallel to the axis (109) of said workpiece at said first end (103). 13. Hollow part (10) open at two opposite ends (103, 104), made of a first material, and obtainable by a method according to any one of claims 1 to 6, characterized in that it comprises, on its inner surface (101) and at least a part its outer surface (102), preferably on at least the surface of its slices (107, 108) at said two opposite ends, a continuous surface layer (70) of a second material, of thickness less than or equal to 100 μιτι. 14. Part according to claim 13, wherein the continuous surface layer (70) of a second material is of thickness less than or equal to 25 μιτι, preferably less than or equal to 20 μιτι, and preferably less than or equal to 10 μιτι. μιτι. 15. Part according to any one of claims 13 to 14, wherein the second material is more electrically conductive than the first material. 16. Part according to claim 15, consisting of a nonelectronically conductive material, in particular a composite material based on mechanically resistant fibers distributed in an organic polymer matrix, and wherein the surface layer (70) consists of an electrically conductive material.