WO2015107287A1

WO2015107287A1 - Method for manufacturing an electrical conductor made of copper and carbon nanotubes

Info

Publication number: WO2015107287A1
Application number: PCT/FR2015/050016
Authority: WO
Inventors: Guy-Marie VALLET; Michel Dunand; Jean-François SILVAIN
Original assignee: Labinal Power Systems; Centre National De La Recherche Scientifique
Priority date: 2014-01-17
Filing date: 2015-01-06
Publication date: 2015-07-23
Also published as: FR3016727B1; FR3016727A1

Abstract

The invention relates to a method for manufacturing an electrical conductor from a carbon nanotube powder and a copper salt powder. The method comprises the following steps: - mixing the carbon nanotube powder in a solution; - dispersing the carbon nanotubes in the solution; - adding the copper salt to the solution; - heat treatment making it possible to convert the copper salt into copper oxide; - heat treatment making it possible to convert the copper oxide into copper; - densification by hot-pressing; and - hot extrusion.

Description

PROCESS FOR PRODUCING AN ELECTRIC COPPER CONDUCTOR

AND CARBON NANOTUBES

TECHNICAL AREA

The present invention relates to a method of manufacturing an electrical conductor of copper and carbon nanotubes having improved electrical conductivity, and an electrical conductor obtained by this method.

STATE OF THE PRIOR ART

Good electrical, thermal and mechanical properties make copper a widespread element in the fields of aeronautics, aerospace and rail. Currently, the electrical systems embedded in aircraft are mainly composed of copper in areas where the environment is severe and aluminum in the rest of the vehicle. The increase in electrical power distributed on board aircraft, due to the electrification of hydraulic and pneumatic systems, also leads to an increase in electrical connectivity. This has the main drawback of increasing the mass of the onboard electrical distribution network.

To reduce the mass of the network, it is possible to improve the electrical conductivity of the conductors which then allows, at current and constant voltage, to also reduce the cross section of the conductors. The usual conductors in this network are particularly wired conductors (cables) and flat conductors (bus-bus).

Various methods have been proposed to improve the electrical conductivity of copper. However, none of the processes of the prior art actually makes it possible to significantly increase the electrical conductivity of copper.

SUMMARY OF THE INVENTION The invention aims to overcome the disadvantages of the state of the art by proposing a method that significantly increases the electrical conductivity of copper.

To do this, the method according to the invention proposes the development of a new material from copper powder and carbon nanotubes.

More specifically, a first aspect of the invention relates to a method of manufacturing an electrical conductor made of copper and carbon nanotubes from a powder of carbon nanotubes and a copper salt powder, the process comprising the following steps:

(a) mixing the carbon nanotube powder in a solution;

(b) Dispersion of carbon nanotubes in the solution;

(c) adding the copper salt to the solution;

(d) heat treatment for converting copper salt to copper oxide;

(e) heat treatment for converting copper oxide to copper;

(f) densification by hot pressing;

(g) Hot extrusion.

This method makes it possible to obtain materials with a higher conductivity than copper, in particular thanks to the step of dispersing the carbon nanotubes in the solution and at the hot extrusion stage, which makes it possible to align the nanotubes in the sense of their greater conductivity, that is to say along the axis of extrusion.

The method according to the invention may also have one or more of the following characteristics taken individually or in any technically possible combination.

The method is preferably a method for manufacturing electrical conductors for a turbomachine, and more preferably wire conductors, or Flat conductors of the bar type.

According to various embodiments, the carbon nanotubes may be multi-walled single wall. According to a preferred embodiment, the nanotubes are multi-walled.

In order to obtain optimized results, the process preferably uses multi-walled carbon nanotubes with between 10 and 20 walls. Advantageously, the carbon nanotubes each have a length of between 1 μιτι and 20 μιτι, and preferably between 1 μιτι and 2 μιη, which makes it possible to significantly increase the electrical conductivity of the material obtained.

The initial solution used is preferably an aqueous solution, and more preferably water, more preferably still distilled water.

In order to effectively disperse the nanotubes in solution without damaging them, the step of dispersing the nanotubes preferably comprises one or more of the following sub-steps:

a step of passing the solution under ultrasound, preferably for a time of between 30 minutes and 1 h 30 so as to sufficiently disperse the nanotubes without damaging them. Ultrasounds preferably have a frequency of 20 KHz. Ultrasounds preferably have a power of 1 W.ml ^-1 ;

a step of adding to the solution a surfactant making it possible to disperse the carbon nanotubes in solution. According to various embodiments, this surfactant may be sodium dodecyl sulphate or sodium dodecylbenzenesulphonate. Advantageously, the method further comprises a heat treatment step between steps (c) and (d), for evaporating at least partially the water of the solution. During this heat treatment step, the solution is preferably heated to a temperature of between 70 ° C. and 100 ° C. and preferentially between 90 ° C and 100 ° C, which allows to evaporate at least partially the solution, without damaging the nanotubes.

When surfactant has been added to the solution, the method further comprises a heat treatment step for removing the surfactant. This heat treatment step is preferably carried out at a temperature of between 200 ° C. and 300 ° C., which makes it possible to burn the surfactant and to evaporate the remainder of solution that has not been evaporated during the previous step. Following step (d) of heat treatment for transforming the copper salt into copper oxide, the method preferably comprises a grinding step of the copper oxide powder and carbon nanotubes obtained at the end of step (d), in order to dissociate the copper oxide grains from each other. The material obtained at the end of the process preferably comprises a volume fraction of carbon nanotubes of between 0.25 and 5% and preferably between 0.25% and 1.5%, and more preferably equal to 0.5%. , which makes it possible to obtain the best possible results in terms of electrical conductivity. When the amounts of copper salt and carbon nanotubes initially used by the process do not directly make it possible to obtain this volume fraction, the process further comprises, following step (e), a step (h) of adding a dendritic copper powder so as to obtain a mixture of copper powder and carbon nanotubes comprising a percentage by volume of carbon nanotubes of between 0.01 and 5%, and preferably of between 0.25% and 1, 5%, more preferably equal to 0.5%.

Advantageously, the method further comprises, following step (h), a step of three-dimensional mixing of the powders, which makes it possible to obtain a homogeneous mixture between the carbon nanotubes and the copper.

DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT The method first comprises a step of adding a carbon nanotube powder, preferably multi-wall, in a solution. The nanotubes preferably comprise between 10 and 20 walls and they preferably measure between 1 μιτι and 2 μιτι. The solution is preferably an aqueous solution, and more preferably water, preferably distilled. In this embodiment, 80 mg of carbon nanotubes are added to 100 ml of distilled water.

A surfactant for dispersing the nanotubes in water is also added to the solution. In this embodiment, this surfactant is sodium dodecyl sulphate. The amount of sodium dodecyl sulphate added is substantially equal to 1 g.

The solution is then subjected to ultrasound for a time of between 30 minutes and 1 hour 30 minutes, preferably equal to 1 hour, so as to disperse the nanotubes. These ultrasounds preferably have a frequency of 20 KHz and a power of 1 W.ml ^-1 .

The process then comprises a step of adding a copper salt to the solution. This copper salt may be copper sulfate or copper acetate. According to a preferred embodiment, the copper salt is copper nitrate trihydrate (Cu (NO ₃ ) ₂ , 3H ₂ O).

The method then comprises a heat treatment step for evaporating a large part of the water of the solution. For this, the solution is preferably heated to a temperature between 90 ° C and 100 ° C, and preferably at 95 ° C for a time between 30 minutes and 1 h 30, preferably for one hour.

The method then comprises a heat treatment step for removing the surfactant used. When the surfactant used is sodium dodecyl sulphate, the heat treatment is preferably carried out at a temperature of between 200 and 300 ° C., and more preferably at 250 ° C., for a time of between 30 minutes and 1 hour 30 minutes, and preferably equal to one hour. The process then comprises a heat treatment step for converting copper nitrate to copper oxide. For this, the heat treatment is preferably carried out at a temperature between 300 ° C and 500 ° C, preferably equal to 400 ° C for a durationecomprise between 1 hour and three hours, preferably of the order of two hours.

At the end of this step, a composite powder composed of copper oxide and carbon nanotubes is obtained. This composite powder is then milled, for example in a mortar so as to obtain a homogeneous composite powder between the carbon nanotubes and the copper.

The process then comprises a step of converting copper oxide to copper. For this, the composite powder is subjected to a heat treatment to reduce the copper oxide copper. This reduction is carried out under a reducing atmosphere. This reduction is preferably carried out at a temperature substantially equal to 400 ° C. for two hours. At the end of this step, a copper powder and carbon nanotubes are thus obtained. In order to improve the electrical conductivity properties of copper, the mixture of copper powder and carbon nanotubes preferably comprises a volume fraction of between 0.25% and 5% and preferably between 0.25% and 1.5%. and more preferably equal to 0.5%. Depending on the amounts of powders added initially, the powder mixture can at this stage have the right volume fraction. However, if this is not the case, the process may comprise at this stage a step of adding dendritic copper powder to the mixture so that the powder mixture comprises the desired volume fraction of carbon nanotubes. The method then comprises a step of mixing, preferably in the three dimensions of the space, the powder mixture. This mixing step is preferably carried out for a period of between 1 hour and three hours, preferably substantially equal to two hours. The method then comprises a step of densifying the powder mixture by pressing, preferably uni-axial, hot. During this step, the powder is preferably densified in a mold, under vacuum, at a temperature of between 600 ° C. and 700 ° C., preferably substantially equal to 650 ° C., for a period of between 10 and 30 minutes. preferably substantially equal to 20 minutes, and under a pressure of between 50 and 100 MPa, preferably equal to 70 MPa. At the end of this step, a copper-carbon nanotube pellet is obtained. The method then comprises a hot extrusion step to obtain the desired shape for the conductor and to align the carbon nanotubes in their direction of greater electrical conductivity. For this, the copper-carbon nanotube pellet is inserted into a die so as to be extruded into a blank wire at a temperature substantially equal to 400 ° C. The extrusion rate is preferably substantially equal to 1 mm per minute. The die has a section adapted according to the type of electrical conductor that one wants to obtain. Thus, when it is desired to obtain an electric wire, the die preferably has a cylindrical section. According to a preferred embodiment, the wire has a diameter section of between 5 mm and 10 mm, preferably equal to 6 mm. When one wants to obtain a conductor type bar, the die preferably has a rectangular section. Moreover, in the case of a bar, it will be possible to use during the densification step a matrix of the shape of the bar.

The method according to the invention thus makes it possible to obtain electrical conductors based on copper which have an electrical conductivity greater than that of copper. Indeed, the conductors obtained for a composite material comprising copper and a volume fraction of 0.5% of carbon nanotubes with 10 to 20 walls and a length of between 1 μιτι and 2 μιη have an electrical conductivity of 104% IACS (International Annealed Copper Standard), which corresponds to an electric conductivity of 6.031 S 10 ⁷ m ^-1 or an electric resistivity of 1, 658 10 ^"8 Ω.ιτι.

Thus, the addition of carbon nanotubes inside a copper matrix allows to improve the electrical conductivity of copper. During the unipolar hot densification, a first orientation of the carbon nanotubes within the matrix is observed, in the direction of their greater conductivity. The hot extrusion step reinforces this orientation in the direction parallel to the extrusion direction, which makes it possible to increase the electrical conductivity of the conductor obtained by this method.

Naturally, the invention is not limited to the embodiments described with reference to the figures and variants could be envisaged without departing from the scope of the invention.

Claims

A method of manufacturing an electrical conductor made of copper and carbon nanotubes from a carbon nanotube powder and a copper salt powder, the method comprising the steps of:

(a) mixing the carbon nanotube powder in a solution;

(b) Dispersion of carbon nanotubes in the solution;

(c) Addition of the copper salt to the solution;

(d) First heat treatment for converting the copper salt to copper oxide;

(e) Second heat treatment for converting copper oxide into copper;

(f) Densification by hot pressing;

(g) Hot extrusion.

Manufacturing method according to the preceding claim, wherein the carbon nanotubes are multi-walled.

The manufacturing method according to claim 1, wherein the carbon nanotubes are single-walled.

Manufacturing method according to one of the preceding claims wherein the carbon nanotubes each have a length between 1 μιτι and 20 μιτι.

Manufacturing method according to one of the preceding claims, further comprising a prior heat treatment step between steps (c) and (d), for evaporating at least partially the water of the solution. Manufacturing method according to one of the preceding claims, wherein the step (b) of dispersion of the carbon nanotubes in the solution comprises a step of passing under ultrasound.

Manufacturing method according to one of the preceding claims, wherein the step (b) for dispersing the carbon nanotubes in the solution comprises a step of adding a surfactant for dispersing the carbon nanotubes in solution.

Manufacturing method according to the preceding claim, wherein the surfactant is sodium dodecyl sulphate

Manufacturing method according to one of claims 7 or 8, further comprising a heat treatment step for removing the surfactant.

Manufacturing method according to one of the preceding claims, further comprising, following step (e), a step (h) of adding a copper dendritic powder so as to obtain a mixture of copper powder and carbon nanotubes having a volume percentage of carbon nanotubes of between 0.01 and 5%, and preferably between 0.25% and 1.5%.

Manufacturing method according to the preceding claim, further comprising, following step (h) a step of three-dimensional mixing of the powders.