COPPER MICROPARTICLES IN THE FORM OF FIBER BUNDLES, THEIR PREPARATION AND USES

Abstract

The present invention relates to microparticles made of or comprising copper, in the form of fiber bundles, as well as their preparation, particularly by irradiation, notably with a gamma radiation source, and their uses. The invention also relates to said microparticles bearing on their surface a layer of metal other than copper, as well as their preparation and uses, particularly for making conductive pastes or adhesives in the photovoltaic, electronics, and other industries, but also in catalysis or for their bactericidal properties. (no figure)

Description

Title of the invention: COPPER MICROPARTICLES IN THE FORM OF FIBER BUNDLES, THEIR PREPARATION AND THEIR USES

[0001] The present invention relates to microparticles made of or comprising copper, which are in the form of fiber bundles, as well as their preparation, in particular by irradiation, notably with a gamma radiation source, and their uses. The invention also relates to said microparticles bearing on their surface a layer of metal other than copper, as well as their preparation and uses, in particular for making conductive pastes or adhesives in the photovoltaic, electronics, and other industries, but also in catalysis or for their bactericidal properties.

[0002] Currently, most conductive coatings are silver-based. This metal has excellent electrical conductivity and good oxidation resistance. For example, regarding the interconnection of photovoltaic modules, the conductive adhesives currently used are pastes based on micron-sized silver particles. Examples of leading products include Henkel's Loctite Ablestik ICP 8282 and Loctite Ablestik ICP 8311, Protavic's Ace 10720, Kyoto Elex's DD-1960S-101, and Namics' XH9489E-808 and XH9489E-807.

[0003] However, the cost of this metal is high. A key issue in the field of conductive coatings is therefore to replace silver with less expensive materials such as copper, aluminum, nickel, etc. Such a substitution is often problematic because of the oxidation of these materials, which can however be protected by adding a protective layer of a more precious material (gold, silver, platinum, etc.) to the surface.

[0004] In this context, Cu@Ag core-shell particles have been obtained by traditional chemical synthesis methods. However, these particles contain oxidized copper before the addition of the noble metal, thus requiring an additional step to remove copper oxides in favor of copper(0), and / or generally do not possess an advantageous shape factor, particularly for enabling good electrical properties. Furthermore, these syntheses require the use of reducing agents and / or heating steps, which are undesirable from a safety, environmental, and economic standpoint.

[0005] Irradiation synthesis (or radiolytic synthesis) has been used in this context, but still without success in obtaining particles with an advantageous shape factor.

[0006] The invention aims to avoid the aforementioned drawbacks.

[0007] The invention therefore aims to provide micron-sized nanostructured copper metal particles (copper (0)) with a form factor that allows for better electrical properties.

[0008] Another object of the invention is to provide such particles via a simple production process, not requiring heating or the use of reducing agents, while being possible on a large scale.

[0009] Yet another object of the invention is to provide particles of metallic copper (copper (0)), bearing on their surface a layer of another metal, which are less expensive than the particles of said other pure metal, while allowing the stability of the copper, in particular resistance to oxidation and diffusion in silicon.

[0010] Thus, according to a first aspect, the invention relates to a microparticle made of or comprising copper, which is in the form of a bundle of fibers.

[0011] By "fiber bundle", we mean in particular fibers (which can also be called "needles") aggregated together.

[0012] By "aggregated together," it is understood in particular that each fiber is in contact with at least one other fiber, for example a plurality of fibers, and this in particular in the middle zone of said fibers. The ends of the fibers are not necessarily in contact.

[0013] The fiber bundle shape can also be called a hay bale shape, a faggot shape, an apple core shape, or a bow tie shape.

[0014] According to a particular embodiment, the fiber bundle comprises more than 100 fibers, for example more than 200, 300, 400, 500, 600, 700, 800, 900 or 1000 fibers.

[0015] According to a particular embodiment, the fibers have a diameter less than or equal to 20 nm, which diameter being in particular greater than or equal to 1 nm.

[0016] According to a particular embodiment, the largest dimension of the microparticle, in particular obtained by the aggregation of fibers, is between 0.1 and 50 pm, in particular between 0.5 and 5 pm, in particular between 1 and 3 pm.

[0017] This larger dimension is in particular in the direction of the fibers, at least in the median zone of said fibers.

[0018] According to a particular embodiment, the smallest dimension of the microparticle is between 0.05 and 25 pm, in particular between 0.1 and 2.5 pm, in particular between 0.2 and 1 pm.

[0019] This smallest dimension is in particular orthogonal to the direction of the fibers in the median zone of said fibers.

[0020] According to a particular embodiment, the microparticle of the invention further comprises a compound A selected from polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyoxazoline and mixtures thereof.

[0021] It should be noted that traces of compound A can be eliminated, if desired, by any technique well known to a person skilled in the art.

[0022] According to a more particular embodiment, compound A is present in the microparticle at most at a mass of 5%.

[0023] According to a particular embodiment, the invention relates to a microparticle as described above, carrying, on at least a part of its surface, a layer comprising or made up of a metal M chosen from Ag, Au, Pt, Pd.

[0024] According to a particular embodiment, said layer has a thickness between 10 and 1000 nm, in particular between 50 and 300 nm.

[0025] This embodiment corresponds in particular to a "core-shell" type microparticle, in which the core corresponds to the fibers and the shell to the layer made of or comprising the metal M. Thus, in particular, said fibers carry, on at least a part of their surface, a layer made of or comprising the metal M.

[0026] According to another aspect, the invention also relates to a powder made up of or comprising a plurality of microparticles as defined above.

[0027] According to another aspect, the invention also relates to a method for preparing microparticles as described above, comprising a step of irradiating a reaction medium consisting of or comprising a copper source.

[0028] By "copper source" is meant in particular a solution, in particular an aqueous solution, containing copper ions.

[0029] According to a particular embodiment, the irradiation is a y irradiation.

[0030] According to a particular embodiment, the irradiation is carried out at a dose comprising between 25 and 200 kGv, in particular between 45 kGy and 55 kGy.

[0031] According to a particular embodiment, the irradiation is carried out at a dose rate of between 0.5 and 2 kGy / h.

[0032] According to a particular embodiment, the irradiation is carried out in the absence of a reducing agent, and the process is thus carried out in the absence of a step of washing away such a reducing agent.

[0033] According to a particular embodiment, the irradiation is carried out in the absence of heating.

[0034] According to a particular embodiment, the irradiation is an irradiation [3, said irradiation being in particular carried out continuously.

[0035] According to a particular embodiment, the reaction medium is liquid, in particular an aqueous reaction medium, more particularly an aqueous solution.

[0036] According to a more particular embodiment, the aqueous reaction medium further comprises a co-solvent, in particular chosen from ethylene glycol and isopropanol.

[0037] According to a particular embodiment, the reaction medium is degassed, in particular with argon or nitrogen, prior to and possibly during the irradiation step.

[0038] According to a particular embodiment, the reaction medium is present in a container in a vertical position relative to its largest dimension.

[0039] According to a particular embodiment, the copper source is a copper(II) salt, in particular soluble in water.

[0040] According to a particular embodiment, the copper source is chosen from copper nitrate, copper sulfate, copper formate, copper acetate.

[0041] According to a particular embodiment, the reaction medium further comprises a compound A selected from polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyoxazoline and mixtures thereof.

[0042] According to a particular embodiment, wherein the molar mass of PVP and / or PVA is from 20000 to 70000 or 80000 g / mol, for example about 29000 g / mol.

[0043] According to a more particular embodiment, compound A is present in the reaction medium at a level of 0.01 to 1% by mass, in particular from 0.05 to 0.5% by mass.

[0044] According to a particular embodiment, the reaction medium further comprises an oxidizing radical scavenger, in particular selected from 2-propanol, formate ions.

[0045] It is also possible, without wanting to restrict ourselves to any particular theory, that other compounds such as those described above may play the role of scavenger of oxidizing radicals, such as copper formate or ethylene glycol.

[0046] According to a particular embodiment, the invention relates to a process for preparing microparticles as described above, bearing, on at least a part of their surface, a layer comprising or made up of a metal M chosen from Ag, Au, Pt, Pd, said process comprising after the irradiation step a step of depositing said layer, in particular by galvanic reaction, more particularly from silver nitrate salt, silver formate, silver lactate or silver acetate.

[0047] According to a particular embodiment, the removal step is carried out protected from light.

[0048] According to another aspect, the invention also relates to the use of microparticles as described above for the production of conductive pastes or adhesives, particularly in the photovoltaic field, or in electronics, said

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[0058] microparticles being present for example in said conductive pastes or glues at more than 50% by mass. According to another aspect, the invention also relates to the use of microparticles as previously described in catalysis. According to another aspect, the invention also relates to the use of microparticles as described above in insertion into composite materials, for example as mechanical reinforcements. According to another aspect, the invention also relates to the use of microparticles as described above for disinfection. FIGURES Figure [1] presents a TEM characterization of copper particles synthesized by y irradiation, obtained according to example 1. Figure 2 shows A: a TEM image of a silver-coated copper particle in the shape of a hay bale according to the invention (example 2); B: an EDX map of a Cu@Ag particle in the shape of a hay bale according to the invention (example 2). Figure [Fig. 3] illustrates a characterization by TEM (A) and SEM (B) of copper particles synthesized by y irradiation according to example 3. EXAMPLES Example 1: Synthesis of microparticles of the invention. Precursors and solvents used: - Copper nitrate hemipentahydrate (Sigma-Aldrich, CAS 19004-19-4) - Polyvynilpyrrolidone (PVP, Fluka Analytical, CAS 9003-39-8) - Ethylene glycol (EG) - 2-propanol (IPA) - Deionized water (EDI) - Technical ethanol Protocol: Three solutions A, B and C are prepared as follows: - Solution A: 468 mg of copper nitrate are dissolved in 1.2 mL of EDI - Solution B: 7.7 mL of ethylene glycol are taken - Solution C: 17.2 mg of PVP are dissolved in 1.1 mL of IPA The solutions are mixed (without heating) until complete dissolution is achieved. Then, solutions A and B are mixed. Once mixture AB is homogeneous, solution C is added. The final concentrations are 0.194 mol / L of copper nitrate and 4.31 × 10⁵ mol / L of PVP. The resulting stock solution ABC is mixed, transferred to a test tube, and bubbled with argon. Finally, it is irradiated at a dose of 50 kGy.

[0059] After the reaction, the suspension is centrifuged three times at 8500 rpm for 10 min and washed with ethanol between centrifugations. The synthesis product is diluted in ethanol. After 10 min in an ultrasonic bath, 5 pL of the suspension is taken and deposited onto nickel grids (Agar Scientific, AGS166N3), then allowed to evaporate in open air for a few minutes.

[0060] The particles obtained are characterized by Transmission Electron Microscope (S / TEM FEI Tecnai Osiris) ([Fig.1]).

[0061] Example 2: Synthesis of silver-encapsulated microparticles according to the invention Precursors and solvents used:

[0062] - Copper nitrate hemipentahydrate (Sigma-Aldrich, CAS 19004-19-4) - Polyvynilpyrrolidone (PVP, Fluka Analytical, CAS 9003-39-8) - Silver nitrate (Sigma-Aldrich, CAS 7761-88-8) # - Ethylene glycol (EG) - 2-propanol (IPA) - Deionized water (EDI) - Technical ethanol

[0063] Copper particles were synthesized in a test tube as described in the previous section. After irradiation, 5 mL of the suspension was taken, centrifuged three times at 8500 rpm for 10 min, and washed with ethanol between centrifugations. Approximately 5 mL of suspension was obtained after centrifugation. Twenty-five days later, the washed suspension had settled. The decantation was taken (V ~ 1 mL, containing almost all of the particles produced by 5 mL of irradiated solution). 0.304 g of PVP and 4 mL of EG were added to it. After stirring to ensure thorough solubilization, 0.066 g of silver nitrate and 1 mL of EG were added to the suspension. The additions of PVP and silver nitrate represent 60.8 mg of PVP added per mL of irradiated solution, and 13.2 mg of silver nitrate added per mL of irradiated solution.

[0064] The suspension is gently stirred for 1 hl / O at room temperature. It is then centrifuged twice for 10 min at 8500 rpm and washed with ethanol. After washing, the suspension is re-diluted in ethanol. After passing through an ultrasonic bath for 10 min, 5 µL of the suspension is taken and deposited on a nickel grid (Agar Scientific, AGS166N3).

[0065] This allows the obtaining of silver-coated copper particles (Cu@Ag), characterized by TEM (S / TEM FEI Tecnai Osiris) as illustrated in [Fig.2].

[0066] The advantages of the process of the invention are as follows: - Copper is protected from oxidation by silver - The silver coating is continuous on the surface of the particle - The hay bale shape is preserved - The successful use of a galvanic reaction is proof that the particles are indeed made of pure, unoxidized copper.

[0067] Example 3: Synthesis of copper particles in a large container (approximately 125 mL):

[0068] Precursors and solvents used: identical to those of the "standard" embodiment described above.

[0069] In the same manner as described in the preceding section, three solutions A, B, and C are prepared and mixed sequentially. The final solution contains 12.2 g of copper nitrate and 0.456 g of PVP dissolved in 201 mL of EG, 31 mL of EDI, and 28 mL of IPA. These concentrations and solvent ratios are identical to those used for the test-tube synthesis (0.194 mol / L copper nitrate and 4.33 × 10⁵ mol / L PVP). A portion of this solution is poured into a 125 mL flask, filling it to the neck. After bubbling with argon, the solution is irradiated at 55 kGy.

[0070] The washing protocol is the same:

[0071] After the reaction, the suspension is centrifuged three times at 8500 rpm for 10 min and washed with ethanol between centrifugations. The synthesis product is diluted in ethanol. After 10 min in an ultrasonic bath, 5 µL of the suspension is taken and deposited onto nickel grids (Agar Scientific, AGS166N3), then allowed to evaporate in air for a few minutes. In parallel, a few drops of the suspension are deposited onto a silicon wafer for observation by SEM.

[0072] The particles obtained are observed by Transmission Electron Microscope (S / TEM FEI Tecnai Osiris) as well as by SEM (Leo 1530, Zeiss) and exhibit the same structure as those synthesized in a volume of 10 mL of suspension ([Fig.3]).

[0073] Example 4: Irradiation of precursor solutions using a pumping system

[0074] A pumping system is installed in the chamber. This allows the injection of precursor solutions to be irradiated, while recovering the suspensions of synthesized particles as they are produced.

Claims

Demands

1. Microparticle made of or comprising copper, which is in the form of a bundle of fibers.

2. Microparticle according to claim 1, the largest dimension of which is between 0.1 and 50 pm, in particular between 0.5 and 5 pm, in particular between 1 and 3 pm.

3. Microparticle according to any one of the preceding claims, having, on at least a part of its surface, a layer comprising or made up of a metal M selected from Ag, Au, Pt, Pd.

4. Microparticle according to any one of the preceding claims, wherein said layer has a thickness between 10 and 1000 nm, in particular between 50 and 300 nm.

5. A method for preparing microparticles according to any one of the preceding claims, comprising an irradiation step, in particular y or [3, of a reaction medium consisting of or comprising a copper source.

6. A method according to claim 5, wherein the irradiation is an irradiation y carried out at a dose between 25 and 200 kGv, in particular between 45 kGy and 55 kGy, and / or at a dose rate between 0.5 and 2 kGy / h.

7. A method according to any one of claims 5 to 6, wherein the copper source is a copper(II) salt, in particular soluble in water.

8. A process according to any one of claims 5 to 7, wherein the reaction medium further comprises a compound A selected from polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyoxazoline and mixtures thereof.

9. A method according to any one of claims 5 to 8, for preparing microparticles according to claim 3, having, on at least a part of their surface, a layer comprising or made up of a metal M selected from Ag, Au, Pt, Pd, said method comprising after the irradiation step a step of depositing said layer, in particular by galvanic reaction, more particularly from silver nitrate salt, silver formate, silver lactate or silver acetate.

10. Use of microparticles according to any one of claims 1 to 4 for the production of conductive pastes or glues, in particular in the field of photovoltaics, electronics, catalysis, insertion in composite materials, for example as mechanical reinforcements, or for disinfection.

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