COPPER-SILVER COMPOSITE MATERIAL

Abstract

The invention relates to a solid composite material comprising copper and an amount by volume of silver of less than about 5% by volume, relative to the total volume of said material, a process for manufacturing said material, and the uses of said material in various applications.

Claims

1. Material comprising copper and silver, whrerein said material is a solid composite material and in that it comprises an amount by volume of silver of less than about 5% by volume, relative to the total volume of said material.

2. Material according to claim 1, wherein the copper and silver are in the form of grains having at least one of their dimensions less than or equal to 500 nm.

3. Material according to claim 1, wherein said material has a conductivity of at least 80% IACS.

4. Material according to claim 1, wherein said material has a tensile strength of at least 1 GPa.

5. Material according to claim 1, wherein said material comprises at most 1.5% by volume of silver, relative to the total volume of said material.

6. Material according to any one of the preceding claim1, wherein the copper and the silver represent at least 99.9% by volume, relative to the total volume of said material.

7. Material according to any one of the preceding claim1, characterized in that wherein the silver and the copper are in the form of grains having a filament form.

8. Material according to claim 7, wherein the copper grains have: a length, extending along a main direction of elongation, two dimensions and, referred to as orthogonal dimensions, extending along two transverse directions that are orthogonal to one another and that are orthogonal to said main direction of elongation, said orthogonal dimensions being smaller than said length and ranging from 50 to 400 nm, and two ratios and, referred to as shape factors, between said length and each of the two orthogonal dimensions and, said shape factors being greater than or equal to 75, and the silver grains have: a length, extending along a main direction of elongation, two dimensions and, referred to as orthogonal dimensions, extending along two transverse directions that are orthogonal to one another and that are orthogonal to said main direction of elongation, said orthogonal dimensions being smaller than said length and ranging from 50 to 400 nm, and two ratios and, referred to as shape factors, between said length and each of the two orthogonal dimensions and, said shape factors being greater than or equal to 75.

9. Process for preparing a solid composite material as defined in claim 1, wherein said process comprises at least the following steps: i) a step of dispersing micrometric copper particles and micrometric or submicrometric silver particles, in a non-solvent medium, ii) a drying step in order to form a composite powder comprising said copper and silver particles, said powder comprising an amount of less than 5% by volume of silver particles, relative to the total volume of said powder, iii) a step of flash sintering at a temperature of at most 600° C., in order to obtain a composite solid mass, and iv) at least one cold-drawing step, in order to shape the composite solid mass from step iii).

10. Process according to claim 9, wherein the non-solvent medium of step i) is chosen from alcohols, water, ketones, and a mixture thereof.

11. Process according to claim 9, wherein the micrometric copper particles have at least one of their dimensions ranging from 0.5 to 20

12. Process according to any one of claim 9, wherein the micrometric or submicrometric silver particles are filiform particles having: a length, extending along a main direction of elongation, two dimensions and, referred to as orthogonal dimensions, extending along two transverse directions that are orthogonal to one another and that are orthogonal to said main direction of elongation, said orthogonal dimensions being smaller than said length, and two ratios and, referred to as shape factors, between said length and each of the two orthogonal dimensions and, and being characterized by at least one of the following features: the two orthogonal dimensions, of the filiform particles range from 50 nm to 400 nm; the length ranges from 1 μm to 150 μm; the shape factors are greater than or equal to 75.

13. Process according to claim 9, wherein step iii) is carried out at a temperature ranging from 375° C. to 525° C.

14. Process according to claim 9, wherein the composite solid mass obtained at the end of step iii) has a relative density ranging from 85% to 97%.

15. Process according to claim 9, wherein said process further comprises a step ii′) of reducing the dried composite powder from step ii), in the presence of dihydrogen.

16. An electrical conductor, as a conductor for continuous- or pulsed-field magnets, in the field of intense field installations, or in the field of industrial electromagnetic forming, wherein said electrical conductor includes a composite material of claim 1.

Description

EXAMPLES

[0134] The raw materials used in the examples are listed below:

[0135] copper powder, 0.5-1.5 μm, Alfa-Aesar,

[0136] AgNO.sub.3, Aldrich

[0137] ethylene glycol, Aldrich,

[0138] polyvinyl/pyrrolidinone PVP, 55000 g/mol, Aldrich.

[0139] Unless otherwise indicated, all these raw materials were used as received from the manufacturers.

Example 1

[0140] Preparation of a composite material in accordance with the invention

[0141] Silver nanowires were prepared according to a growth process in solution from silver nitrate (AgNO.sub.3), PVP, and ethylene glycol, as described by Sun Y. G. et al.,“Crystalline silver nanowires by soft solution processing”, Nano Letters, 2002. 2(2): p. 165-168, with a PVP/AgNO.sub.3 ratio of 1.53. The silver nanowires obtained have a length ranging from about 30 to 60 μm, and a diameter ranging from about 200 to 300 nm.

[0142] A suspension comprising 0.178 g of silver nanowires and 9 ml of ethanol was prepared.

[0143] The suspension of silver nanowires was mixed with 15 g of copper powder, then the resulting mixture was homogenized using ultrasound, then evaporated using a rotary evaporator at 80° C. A composite powder PC.sub.1 comprising 1% by volume of silver, relative to the total volume of the powder was thus obtained.

[0144] The composite powder was reduced in the presence of dihydrogen for 1 h at 160° C. in order to reduce the copper oxide formed on the surface of the copper particles.

[0145] The resulting powder was then sintered by SPS using a device sold under the trade name Dr Sinter 2080®, by the company Syntex Inc.

[0146] To do this, the composite powder was placed in a die made of tungsten carbide and cobalt (WC/Co) alloy with an internal diameter of 8 mm, the interior of which was protected by a graphite film. The die was then closed by symmetrical pistons then introduced into the chamber of the SPS machine. The sintering was carried out under vacuum (residual pressure of the chamber<10 Pa) using defined pulsed direct currents over 14 periods of 3.2 ms, including 12 periods of pulses and 2 periods of no pulses. The temperature was controlled using a thermocouple introduced into an orifice (depth of 5 mm) drilled through the outer surface of the die. A temperature of 500° C. was reached in two steps: a ramp of 25° C.min.sup.−1 for 13 minutes in order to go from ambient temperature to 350° C., then a ramp of 50° C.min.sup.−1 for 3 minutes in order to go from 350° C. to 500° C. This temperature was then maintained for 5 minutes. These temperature ramps were obtained by applying defined pulsed direct currents over 14 periods of 3.2 ms, including 12 periods of pulses and 2 periods of no pulses. A pressure of 25 MPa was reached in 1 minute and maintained for the remainder of the sintering. The die was then cooled within the chamber of the SPS. The composite 25 solid mass MSC.sub.A obtained is in the form of a cylinder with a diameter of 8 mm and a length of 33 mm.

[0147] The composite solid mass obtained was then drawn at ambient temperature using a tungsten carbide die. After 40 passes, a composite material in the form of a wire FC.sub.1 with a diameter of 0.29 mm and a length of 25 m was obtained. No rupture of the wires was observed.

[0148] The composite powders and the composite wires were analysed by scanning electron microscopy (SEM) using a field-emission gun, sold under the trade name JEOL JSM 6700F by the company JEOL, and operating at 200 kV.

[0149] The density of the composite solid masses and of the composite wires was determined by the Archimedes method.

[0150] The electrical resistivity of the composite wires was determined at 77K (liquid nitrogen) using the four-point method with a maximum current of 100 mA in order to avoid heating of the wires.

[0151] The tensile strength was measured using a device sold under the trade name INSTRON 1195 by the company INSTRON, at 77K (liquid nitrogen) and at 293K on composite wires with a length of 170 mm. The specific tensions encountered were measured with a force sensor (1000 N or 250 N; 1.6×10.sup.−5 m.s.sup.−1).

[0152] By way of comparison, a process identical to the one as described above (identical operating conditions) was used, replacing the volume proportion of silver which was about 1% by volume, with an amount by volume of about 10% by volume. A composite powder PCA comprising 10% by volume of silver, relative to the total volume of the powder was thus obtained at the end of step i). The composite powder PCA is not part of the invention. A composite solid mass MSCA and a composite wire FCA which are not part of the invention, were also obtained.

[0153] The density of the composite solid masses MSCI and MSCA is about 94% (±2%).

[0154] FIG. 1 is an SEM image of the composite powder PC1 in accordance with the invention (cf. FIG. 1a: 10 μm scale, and FIG. 1b: 2 μm scale), and of the composite powder PCA not in accordance with the invention (cf. FIG. 1c: 10 μm scale, and FIG. 1d: 2 μm scale). FIG. 1 shows the uniform dispersion of the silver nanowires within the copper powder, leading to a homogeneous powder. In contrast, the use of a volume amount of silver of about 10% by volume does not make it possible to obtain a homogeneous powder.

[0155] FIG. 2 shows the resistivity (in μΩ.cm) at 77K of a composite material in the form of a wire FC.sub.1 in accordance with the invention (curve with solid triangles) and of a composite material in the form of a wire FC.sub.A not in accordance with the invention (curve with solid circles), as a function of their respective diameter (in mm).

[0156] FIG. 3 shows the tensile strength (in MPa) at 77K of a composite material in the form of a wire FC.sub.1 in accordance with the invention (curve with solid triangles) and of a composite material in the form of a wire FC.sub.A not in accordance with the invention (curve with solid circles), as a function of their respective diameter (in mm).

[0157] The tensile strength at 77K of a composite wire in accordance with the invention is two times greater than that of a pure copper wire at equivalent diameters, while guaranteeing low electrical resistivity (0.38-0.50 μΩ.cm). These electrical resistivity values are in particular lower than those obtained for alloys or composites from the prior art having a similar tensile strength, but comprising 20 times more silver.