WO2015132719A1 - Nanometric copper formulations - Google Patents
Nanometric copper formulations Download PDFInfo
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- WO2015132719A1 WO2015132719A1 PCT/IB2015/051536 IB2015051536W WO2015132719A1 WO 2015132719 A1 WO2015132719 A1 WO 2015132719A1 IB 2015051536 W IB2015051536 W IB 2015051536W WO 2015132719 A1 WO2015132719 A1 WO 2015132719A1
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- formulation
- dispersion
- particulate matter
- dispersant
- particles
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/05—Metallic powder characterised by the size or surface area of the particles
- B22F1/054—Nanosized particles
- B22F1/0545—Dispersions or suspensions of nanosized particles
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
- B22F1/102—Metallic powder coated with organic material
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F1/16—Metallic particles coated with a non-metal
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/16—Making metallic powder or suspensions thereof using chemical processes
- B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
- B22F9/24—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from liquid metal compounds, e.g. solutions
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82B—NANOSTRUCTURES FORMED BY MANIPULATION OF INDIVIDUAL ATOMS, MOLECULES, OR LIMITED COLLECTIONS OF ATOMS OR MOLECULES AS DISCRETE UNITS; MANUFACTURE OR TREATMENT THEREOF
- B82B1/00—Nanostructures formed by manipulation of individual atoms or molecules, or limited collections of atoms or molecules as discrete units
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/02—Elements
-
- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
- C30B29/60—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape characterised by shape
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- C—CHEMISTRY; METALLURGY
- C30—CRYSTAL GROWTH
- C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
- C30B7/00—Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions
- C30B7/14—Single-crystal growth from solutions using solvents which are liquid at normal temperature, e.g. aqueous solutions the crystallising materials being formed by chemical reactions in the solution
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K1/00—Printed circuits
- H05K1/02—Details
- H05K1/09—Use of materials for the conductive, e.g. metallic pattern
- H05K1/092—Dispersed materials, e.g. conductive pastes or inks
- H05K1/097—Inks comprising nanoparticles and specially adapted for being sintered at low temperature
Definitions
- the present invention relates to nanometric copper formulations and stable dispersions containing single-crystal metallic copper particles, and to methods of producing such formulations and dispersions.
- a formulation including particulate matter including nanometric metallic copper particles, at least 10% of the particulate matter being single-crystal metallic copper particles, the particulate matter having an average secondary particle size (d 5 o) within a range of 20 to 200 nanometers (nm), the nanometric metallic copper particles being at least partially covered by at least one dispersant; a concentration ratio of crystalline cuprous oxide to the nanometric metallic copper particles, within the particulate matter, being at most 0.4.
- a process including the steps of: (a) adding a borohydride to cupric ions in an acidic aqueous medium, in a presence of a dispersant, to reduce the cupric ions and to produce the nanometric metallic copper particles in a first dispersion; and (b) providing the nanometric metallic copper particles in a product dispersion.
- a process for producing a formulation containing nanometric metallic copper particles including: (a) adding a borohydride to cupric ions in an aqueous medium, at an acidic pH, to reduce the cupric ions, in a presence of a first dispersant, and to produce the nanometric metallic copper particles in a first dispersion; and (b) separating off at least a portion of the aqueous medium from the nanometric metallic copper particles.
- the process further includes curtailing the incremental addition when a pH of the aqueous medium is at most 7, or when a pH of the aqueous medium is within a range of 2.5 to 7, within a range of 2.5 to 6.5, or within a range of 2.5 to 6.
- the process further includes treating the first dispersion so as to provide the nanometric metallic copper particles in a product dispersion.
- the concentration ratio is at most 0.35, at most 0.30, at most 0.25, at most 0.20, at most 0.15, at most 0.12, at most 0.10, at most 0.08, at most 0.06, at most 0.05, at most 0.04, or at most 0.035.
- the average secondary particle size is at most 180 nm, at most 150 nm, at most 120 nm, at most 100 nm, or at most 80 nm.
- the average secondary particle size is at least 25 nm, at least 30 nm, at least 35 nm, at least 40 nm, at least 45 nm, or at least 50 nm.
- At least 15%, at least 20%, at least 25%, at least 30%, at least 40%, at least 50%, at least 60%), at least 70%, or at least 80% of the particulate matter are single-crystal metallic copper particles.
- a majority of the particles in the particulate matter may be single-crystal metallic copper particles.
- a specific electrical resistivity of the copper particles, after standard thermal sintering is at most 5 x 10 "3 ohm » cm, at most 2 x 10 "3 ohm » cm, at most 1 x 10 "3 ohm » cm, at most 5 x 10 "4 ohm » cm, at most 2 x 10 "4 ohm » cm, or at most 1 x 10 "4 ohm » cm.
- a specific electrical resistivity of the copper particles, after standard thermal sintering is within a range of 5 x 10 "5 to 5 x 10 "3 ohm » cm, within a range of 8 x 10 "5 to 2 x 10 "3 ohm » cm, or within a range of 1 x 10 "4 to 1 x 10 "3 ohm » cm.
- the dispersant includes, primarily includes, or consists essentially of polyvinylpyrrolidone (PVP) or pure polyvinylpyrrolidone.
- the dispersant includes, or primarily includes, at least one dispersant selected from the group consisting of polyvinylpyrrolidone (PVP), gum arabic, polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyallylamine (PAAm), polysodium styrene sulfonate (PSS), 3-(aminopropyl)trimethoxysilane (APS), a fatty acid, lauryl amine, cetyltrimethylammonium bromide (CTAB), and tetraoctylammonium bromide (TOAB).
- PVP polyvinylpyrrolidone
- PVA polyvinyl alcohol
- PAAm polyacrylic acid
- PAAm polyallylamine
- PSS polysodium styrene sulfonate
- a weight average molecular weight of the dispersant is within a range of 8,000 to 500,000, 10,000 to 500,000, 15,000 to 500,000, 20,000 to 500,000, 30,000 to 500,000, 15,000 to 300,000, 15,000, to 200,000, 15,000 to 150,000, or 30,000 to 150,000.
- the formulation further includes at least a first solvent, the particulate matter and the solvent forming a dispersion.
- the concentration of the particulate matter within the dispersion is within a range of 5% to 90%, 5% to 85%, 5% to 80%, 5% to 75%, 5% to 70%, 5% to 65%, 10% to 75%, 10% to 70%, 10% to 65%, 15% to 80%, 15% to 70%, 15% to 65%, 20% to 75%, 25% to 75%, 30% to 75%, 20% to 65%, 25% to 65%, 25% to 60%, 25% to 55%, 30% to 60%, 30% to 55%, or 30% to 65%, by weight.
- the concentration of the particulate matter within the dispersion is at least 35%, at least 40%, at least 45%, or at least 50%, by weight.
- the first solvent includes, or primarily includes, an alcohol.
- the alcohol includes at least one alcohol selected from the group consisting of methanol, ethanol, isopropanol, benzyl alcohol, and terpineol.
- the first solvent includes, or primarily includes, at least one solvent selected from the group consisting of a glycol and a glycol ether.
- the glycol is selected from the group of glycols consisting of an ethylene glycol, a propylene glycol, a butylene glycol, a pentylene glycol, and a hexylene glycol.
- the glycol includes, or primarily includes, at least one of diethyleneglycol and triethyleneglycol.
- the glycol ether is selected from the group of glycol ethers consisting of an ethylene glycol ether and a propylene glycol ether.
- the glycol ether includes at least one glycol ether selected from the group of glycol ethers consisting of propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene glycol mono-t-butyl ether, propylene glycol monophenyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, propylene glycol mono-t-butyl ether, tripropylene glycol monopropyl ether, and tripropylene glycol monobutyl ether.
- the glycol ether includes at least one glycol ether selected from the group of glycol ethers consisting of ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, diethylene glycol mono-t-butyl ether, triethylene glycol monopropyl ether, and triethylene glycol monobutyl ether.
- a weight ratio of the at least one dispersant to the particulate matter is at least 0.015, at least 0.016, at least 0.017, at least 0.018, at least 0.019, or at least 0.020.
- the weight ratio of the dispersant to the particulate matter is at most 0.2, at most 0.16, at most 0.12, at most 0.08, at most 0.05, at most 0.04, at most 0.03, at most 0.025, at most 0.022, or at most 0.020.
- the particulate matter is disposed within a dispersion, a concentration of the particulate matter within the dispersion being within a range of 20% to 65%, or a range of 20% to 60%, an amount of the dispersant being at most 4%, by weight, of a weight of the copper particles, a viscosity of the dispersion being at most 70cP, at most 60cP, at most 50cP, or at most 45cP at 25°C.
- the concentration of the particulate matter within the dispersion is at least 25% or at least 30%), and more typically, at least 35%, at least 40%, at least 45%, or at least 50%.
- the particulate matter is adapted, and the dispersant and the solvent are selected, such that a cuprous oxide concentration is substantially maintained over the course of at least 2 months, at least 3 months, at least 4 months, at least 6 months, or at least 12 months.
- the particulate matter is adapted, and the dispersant and the solvent are selected, such that a cuprous oxide concentration is maintained, on an absolute percentage basis, within 2 percent, within 1.5 percent, or within 1 percent, over the course of at least 2 months, at least 3 months, at least 4 months, at least 6 months, or at least 12 months.
- the crystalline cuprous oxide has a particular cuprous oxide concentration (Cu 2 0 conc.(i)) within the formulation, at an initial time, and the particulate matter is adapted and the dispersant and the solvent are selected such that within the formulation, an increase in crystalline cuprous oxide concentration after the initial time, normalized by a total initial concentration of copper (% Cu total), is maintained within a value (V) of the particular cuprous oxide concentration, the value expressed as a percentage and defined by:
- V 100 » (Cu 2 O conc(t) - Cu 2 0 conc.(i))/ (% Cu total), Cu 2 0 conc.(t) being a concentration of crystalline Cu 2 0 evaluated at an elapsed time (t), with respect to the initial time; the value (V) being at most 3%, the elapsed time (t) being at least 2 months.
- the value (V) is at most 2%, at most 1.5%, at most 1%, at most 0.8%, at most 0.6%, at most 0.5%, or at most 0.4%.
- the elapsed time is at least 3 months, at least 4 months, at least 6 months, or at least 12 months.
- the formulation is produced according to a process including the steps of: (a) adding a borohydride to cupric ions in an acidic aqueous medium, in a presence of a dispersant, to reduce the cupric ions and to produce the nanometric metallic copper particles in a first dispersion; and (b) providing the nanometric metallic copper particles in the product dispersion.
- the process further includes curtailing the incremental addition when a pH of the aqueous medium is at most 7.
- the process further includes: curtailing the incremental addition when a pH of the aqueous medium is within a range of 2.5 to 7, within a range of 2.5 to 6.5, or within a range of 2.5 to 6.
- the borohydride includes, primarily includes, or consists substantially of, sodium borohydride or potassium borohydride.
- the process further includes introducing a second dispersant within the product dispersion.
- the second dispersant includes, primarily includes, or consists essentially of polyvinylpyrrolidone (PVP)
- the adding of the borohydride is performed over the course of at least 15 minutes, at least 30 minutes, or at least 60 minutes.
- step (a) subsequent to step (a), the nanometric metallic copper particles are washed and concentrated.
- the aqueous medium achieves a pH below 1.5, below 1.0, or below 0.5 during step (a).
- the process subsequent to step (a), includes exchanging at least a portion of the aqueous medium from the particles to produce the product dispersion.
- the exchanging includes concentrating the particulate matter to form the product dispersion, the product dispersion being concentrated in the particulate matter, with respect to the first dispersion.
- the process further includes aging the dispersion for at least 6 months, at least 9 months, at least 12 months, at least 18 months, or at least 24 months, while maintaining at least 10% of the particulate matter as single-crystal metallic copper particles, and while maintaining the average secondary particle size of the particulate matter within the product dispersion within a range of 20 to 200 nm.
- Figure 1 is a schematic block diagram of a process for producing a nanometric copper product, according to one aspect of the present invention
- Figure 2 is a High-Resolution Scanning Electron Microscopy (HRSEM) image showing a typical field containing nanometric copper particles produced according to an embodiment of the present invention, described in Example 3;
- HRSEM High-Resolution Scanning Electron Microscopy
- Figure 3 is a Transmission Electron Microscopy (TEM) image showing a typical field containing nanometric copper particles produced according to an embodiment of the present invention, described in Example 4;
- TEM Transmission Electron Microscopy
- Figure 4 is an Electron Back Scattered Diffraction (EBSD) pattern of the nanometric copper particles produced according the embodiment described in Example
- Figure 5 provides identifications of various diffraction patterns characteristic of crystalline copper metal, based on the EBSD pattern provided in Figure 4;
- Figure 6 provides a powder X-Ray diffraction pattern of a nanometric copper product, according to one aspect of the present invention
- Figure 7 provides a thermal gravimetric analysis (TGA) plot for a sample of copper nanoparticles in an inert atmosphere
- Figure 8 is a conceptual representation of a copper nanoparticle enveloped by a dispersant layer. DESCRIPTION OF THE PREFERRED EMBODIMENTS
- nanometric copper particles in which a large fraction of the particles are single-crystal particles.
- stable dispersions of these nanometric copper particles may be particularly problematic when producing such dispersions directly in various organic solvents that may be used in the final product dispersions.
- stable dispersions from pre-made (e.g., commercially available) nanometric copper particles has also been found to be extremely difficult and unpredictable.
- the inventive method may advantageously produce — without agglomeration — concentrated dispersions containing particulate matter including mostly or predominantly single-crystal copper particles, the particulate matter (and typically, the single-crystal copper particles) being characterized by an average secondary particle size of at least 20 nm, at least 25 nm, at least 30 nm, at least 35 nm, at least 40 nm, at least 45 nm, or at least 50 nm.
- the particulate matter (and typically, the single crystal copper particles) in the dispersions may have an average secondary particle size of at most 200 nm or at most 180 nm, and more typically, at most 150 nm, at most 120 nm, at most 100 nm, or at most 80 nm.
- the single-crystal structure of the copper particles is a decisive factor in attaining, after sintering, low specific electric resistivity values.
- the single-crystal structure of the copper particles enables the formulation of highly concentrated dispersions of copper nanoparticles, without undergoing appreciable agglomeration.
- the dispersions of the present invention may be distinguished in at least one of several ways, including:
- the nanometric copper particles having an average secondary particle size (d 5 o) within a range of 20 to 200 nm.
- the particulate matter in these dispersions may contain more than 10% single-crystal metallic copper particles, and more typically, mostly or predominantly single-crystal metallic copper particles.
- the concentration of nanometric copper particles within the concentrated dispersions of the present invention is typically within a range of 5% to 90%, by weight.
- the production of the nanoparticles is typically performed whereby a relatively dilute dispersion is obtained.
- the workup of the dilute dispersion which may include washing, solvent addition and/or replacement, etc., may be a major contributor to the agglomeration of copper nanoparticles.
- the inventive process described hereinbelow, produces a high percentage of single crystal copper nanoparticles in the reaction stage, and largely preserves that high percentage by averting, to a large degree, the agglomeration of the copper nanoparticles.
- the nanometric copper particles may be partially, mostly or predominantly single crystal copper particles, on a weight basis, on a particle number basis, or on a cross-sectional basis.
- the presence of single crystal particles was qualitatively demonstrated by means of Electron Back Scattered Diffraction (EBSD). Quantification of the results was achieved by performing a plurality of scans at randomly chosen points, as described in greater detail hereinbelow.
- EBSD Electron Back Scattered Diffraction
- the concentrated dispersions of the present invention may contain a small percentage of cuprous oxide (Cu 2 0), resulting from reaction of copper nanoparticles with oxygen.
- cuprous oxide was qualitatively demonstrated by means of Powder X-Ray Diffraction (Powder XRD).
- the concentration ratio of crystalline cuprous oxide to nanometric crystalline metallic copper is at most 0.4, at most 0.35, or at most 0.30, and typically, at most 0.25, at most 0.20, at most 0.15, at most 0.12, at most 0.10, at most 0.08, at most 0.06, or at most 0.03.
- the particulate matter, and particularly of the copper particles, following thermal sintering may be characterized by specific ranges of electrical resistivity.
- the electrical resistivity of the particulate matter was measured using Four Point Probe (4PP) method.
- the electrical resistivity is at most 5xlO "3 ohm » cm, and more typically, at most 2xl0 "3 ohm » cm, at most lxlO "3 ohm » cm, at most 8xl0 "4 ohm » cm, at most 5xl0 "4 ohm » cm, at most 2xl0 "4 ohm » cm, or at most lxlO "4 ohm » cm.
- the specific electrical resistivity of the sintered particulate matter may be within a range of 5 x 10 "5 to 5 x 10 "3 ohm » cm, within a range of 8 x 10 "5 to 2 x 10 "3 ohm•cm, or within a range of 1 x 10 "4 to 1 x 10 "3 ohm » cm.
- the viscosity of the dispersion may greatly affect the possible applications for which the dispersion may be used.
- dispersions suitable for inkjet printing may require a viscosity of about 5-60cP, and more typically, 5-40cP, at the jetting temperature.
- Various aspects of the materials and process used to produce the dispersion influence the viscosity of the resulting dispersion, including the type of dispersant used and its concentration in the dispersion, the type of solvent used and its concentration in the dispersion, and the concentration of solids in the dispersion.
- the particulate matter in the inventive formulations may contain a high percentage of relatively smooth-sided nanoparticles, and more particularly, single-crystal copper nanoparticles.
- the particulate matter in the inventive formulations may require less dispersant per unit weight of the particulate matter, with respect to various other nanometric copper particles.
- this structural feature contributes to the ability of the inventive dispersions to require relatively small concentrations of dispersant (or dispersant-layer thickness), while maintaining physical and chemical stability over at least six months, at least twelve months, or at least eighteen months of storage.
- use of the inventive particulate matter within various dispersions may appreciably reduce the viscosity of these dispersions, relative to similar dispersions employing nanometric copper particles of the prior art.
- the viscosity of the dispersion was measured for various concentrations of copper particles, as described hereinbelow.
- the viscosity at 25°C is at most 10000 cP, at most 5000 cP, or at most 2000 cP, and more typically, at most 1000 cP, at most 600 cP, at most 300 cP, at most 200 cP, at most 120cP, at most 80 cP, at most 60 cP, at most 45 cP, at most 35 cP, at most 25 cP, or at most 20 cP.
- Figure 1 is a schematic block diagram of a method of producing a nanometric copper product, according to one aspect of the present invention.
- the method may include the following steps:
- Step 1 reducing cupric ions in an aqueous medium using a borohydride, in a presence of a first dispersant, to produce nanometric metallic copper particles, the copper particles having an average secondary particle size within a range of 20 to 200 nm;
- Step 2 purifying the copper particles of Step 1; the aqueous medium may also be partially removed from the particles, to form a concentrate containing most of the copper particles;
- Step 3 introducing, to the purified copper particles, at least one solvent, and replacing most or all of the aqueous medium therewith.
- At least one soluble copper compound is dissolved in an aqueous solvent to form a first, aqueous solution containing dissolved cupric ions.
- the reducing agent, an alkaline borohydride e.g., sodium borohydride or potassium borohydride
- an alkaline borohydride e.g., sodium borohydride or potassium borohydride
- An anti-foaming agent may be introduced to control, prevent, or reduce foaming in any of the process steps, as necessary.
- the anti-foaming agent may be added prior to introduction of the alkaline borohydride to the first solution.
- an inert gas such as argon, may be constantly blown or bubbled through the solution, in order to reduce oxidation of the copper particles within the dispersion.
- the vigorous mechanical mixing may be applied, and may begin within an ambient temperature range (typically between 10°C and 35°C).
- Various dispersants may be used within the reaction mixture, most notably, polyvinylpyrrolidone (PVP).
- PVP polyvinylpyrrolidone
- the presence of such a dispersant may reduce or substantially inhibit agglomeration of the particles during the reaction and prior to subsequent processing.
- PVP has been found to be particularly advantageous. While the average molecular weight of PVP may be in the range of about 2,000 to about 3,000,000 gram/mole, the inventors have found to be particularly effective, in most cases, PVP molecules having a weight average molecular weight of about 8,000 to 700,000 gram/mole, 10,000 to 500,000 gram/mole, 10,000 to 350,000 gram/mole, 10,000 to 250,000 gram/mole, 10,000 to 200,000 gram/mole, 10,000 to 150,000 gram/mole, or 10,000 to 100,000 gram/mole.
- the average molecular weight of the PVP is at least 15,000 gram/mole, at least 20,000 gram/mole, at least 25,000 gram/mole, at least 30,000 gram/mole, or at least 35,000 gram/mole.
- the inventors have found it to be advantageous to form single-crystal metallic copper particles, without these particles undergoing agglomeration or appreciable agglomeration.
- the copper nanoparticle formation reaction described in detail hereinbelow, may advantageously be effected in an acidic solution containing at least one dissolved copper salt.
- the pH of the solution may be monitored throughout the reaction.
- the inventors have observed that the pH may first decrease, as the borohydride is incrementally added to the reaction mixture. As the incremental addition of the borohydride is continued, the pH may subsequently rise in a largely monotonic fashion, from a highly acidic pH, that may be close to zero, to a pH of at least 2, and up to about 10.
- water or an aqueous solvent may be used to purify the resulting dispersion of Step 1 in a suitable purification system.
- the introduction of water or aqueous solvent to the purification system may be controlled to replace the spent aqueous liquor, while maintaining the concentration of the particulate matter (or copper particles), at any time, below a preset value (below 90%, by weight, and preferably below 80%, below 70%, or below 60%), to ensure that disadvantageous agglomeration does not occur, or is appreciably reduced.
- a preset value below 90%, by weight, and preferably below 80%, below 70%, or below 60%
- the aqueous solvent may contain, in addition to water, an organic solvent such as a polar organic solvent.
- the streams produced in Step 2 typically include a concentrate containing most of the nanometric copper particles, and a relatively dilute stream containing a lower concentration of the copper nanoparticles, and preferably, containing substantially none of the copper nanoparticles.
- Step 2 substantially all of the salts, part of the dispersant, unreacted materials, by-product impurities and part of the liquid present with the formed copper particles, are removed.
- Step 2 is considered finished when these preset values are met.
- Step 2 may advantageously be carried out under constant flow of an inert gas, such as argon.
- Step 2 can be conducted in a microfiltration system such as a membrane purification system having at least one membrane capable of separating the copper particles from the aqueous liquor, without losing a fraction of the copper particles in the aqueous phase that would make the process economically unviable.
- a microfiltration system such as a membrane purification system having at least one membrane capable of separating the copper particles from the aqueous liquor, without losing a fraction of the copper particles in the aqueous phase that would make the process economically unviable.
- Step 2 may be conducted using a centrifugation system.
- this method of purification is less preferable, because the centrifugation procedure may cause appreciable agglomeration of the copper metal particles.
- the centrifuged nanoparticles must be re-dispersed to form the product dispersion, and the additional operations and handling may cause additional oxidation of the copper metal.
- At least one membrane of the membrane purification system should be capable of filtering off the nanometric copper particles in the dispersion.
- the characteristic pore size of this membrane may be within a range that is suitable to retain the nanometric copper particles.
- the membranes may be made of a metallic material, ceramic material, polymeric material, or of other materials that may be known to those of ordinary skill in the art.
- At least one organic solvent may replace most of the aqueous liquor of the purified dispersion obtained in Step 2, in a method similar to the method utilized in Step 2.
- the same purification system may be used. In displacing the aqueous liquor, a further purification of the copper particles is achieved, which may be essential for various products and applications.
- the organic solvent may replace the aqueous liquor in an evaporation system in which the aqueous liquor is evaporated, with a concomitant addition of the desired organic solvent, in order to maintain a concentration of the particulate matter (or copper particles) below a particular, desired value.
- concentration of the solids is at most 90%, at most 85%, or at most 80%, by weight.
- an additional decantation step may be added between washing the dispersion in Step 2 and changing the solvent of the dispersion in Step 3, in order to separate out large particles from the dispersion.
- the organic solvent may advantageously be soluble in water, and may readily dissolve the dispersant or dispersants remaining from Step 2.
- Various solvents may be appropriate as solvents for Step 3 of the process, either alone or mixed with at least one additional solvent.
- These solvents include, but are not limited to glycols such as ethylene glycol, diethylene glycol, propylene glycol, and hexylene glycol; alcohols such as methanol, ethanol, propanol, isopropanol, butanol such as 1-butanol, benzyl alcohol, and terpineol; glycol ethers. These solvents may also be used as co-solvents.
- Suitable glycol ethers which may be used for solvents include, but are not limited to, ethylene or propylene glycol monomethyl ether, ethylene or propylene glycol monoethyl ether, ethylene or propylene glycol monopropyl ether, ethylene or propylene glycol monobutyl ether, ethylene or propylene glycol mono-t-butyl ether, ethylene or propylene glycol monophenyl ether, diethylene or dipropylene glycol monomethyl ether, diethylene or dipropylene glycol monoethyl ether, diethylene or dipropylene glycol monopropyl ether, diethylene or dipropylene glycol monobutyl ether, tri ethylene glycol methyl ether or tripropylene glycol methyl ether (TPM), triethylene or tripropylene glycol monopropyl ether, and triethylene or tripropylene glycol monobutyl ether.
- TPM tripropylene glycol methyl ether
- Various solvents may be less suitable or unsuitable for use in Step 3, including acetates such as propylene glycol methyl ether acetate (PMA), or acetone.
- PMA propylene glycol methyl ether acetate
- the nanometric copper dispersions of the present invention may achieve exceptional stability (having a guaranteed shelf-life of at least 6 months, and more typically, at least 12 months, at least 18 months or at least 24 months).
- the inventive dispersions may be characterized by very low specific resistivity values (at most 5xlO "3 ohm » cm, at most 2xl0 "3 ohm » cm, at most lxlO "3 ohm » cm, at most 8xl0 "4 ohm » cm, at most 5xl0 "4 ohm » cm, at most 2xl0 "4 ohm » cm, at most lxlO "4 ohm » cm, at most 8xl0 "5 ohm » cm, at most 5xl0 "5 ohm » cm, at most 2xl0 "5 ohm » cm, or at most lxlO "5 ohm » cm), as measured using Four Point Probe (4PP) method.
- 4PP Four Point Probe
- the inventive dispersions may be characterized by the particulate matter having an average secondary particle size (d 5 o) within a range of 20 to 200 nm.
- the particulate matter in these dispersions may primarily contain single-crystal metallic copper particles.
- the solids fraction (or "particulate matter") within the inventive dispersions may contain at least 10%, at least 15%, at least 20%, at least 25%, at least 30%>, at least 40%), at least 50%, at least 60%, or at least 70% single-crystal metallic copper particles, as measured by EBSD.
- the inventors have found that in producing the dispersion of nanometric copper particles of the present invention, partial oxidation of the metallic copper particles to cuprous oxide may be observed.
- a concentration ratio of cuprous oxide to metallic copper within the particulate matter may be at most 0.4 or at most 0.35, and more typically, at most 0.30, at most 0.25, at most 0.20, at most 0.15, at most 0.12, or at most 0.10.
- the inventive dispersion may be characterized by a low concentration ratio of crystalline cuprous oxide to nanometric crystalline metallic copper of at most 0.4 or at most 0.35, and more typically, at most 0.3, at most 0.2, at most 0.15, at most 0.2 at most 0.10, at most 0.09, at most 0.08, at most 0.06, or at most 0.03, as measured using powder X-ray diffraction (XRD).
- XRD powder X-ray diffraction
- single-crystal metallic copper particles have a distinct geometrical shape, and have smoother surfaces than agglomerates or multi-crystal metallic copper particles.
- the smooth surfaces of the single-crystal metallic copper nanoparticles of the inventive formulations and dispersions may contribute to the low concentration of oxidized surface area.
- the inventors believe that due to the smooth surfaces of the single- crystal copper nanoparticles, oxygen and water molecules may be poorly adsorbed onto the crystal surface, and may easily desorb, appreciably reducing the opportunity for reacting with adjacent copper atoms to produce the copper oxide.
- the copper nanoparticle agglomerates or multi-crystal metallic copper nanoparticles may characteristically have a relative abundance of stabilized adsorption sites, leading to accelerated rates of attack on the copper surface, and higher ratios of copper oxide to copper.
- the smooth surfaces of the single-crystal copper nanoparticles, and the reduced formation of cuprous oxides, as disclosed hereinabove, additionally contribute to the stability of the inventive dispersions disclosed herein.
- the inventive dispersions may remain stable for at least 12 months, during which time the concentration of cuprous oxide or crystalline cuprous oxide in the dispersion increases by less than 7 percent, less than 5 percent, less than 3 percent, and more typically, less than 1.5 percent.
- the concentration of cuprous oxide or crystalline cuprous oxide in the dispersion does not increase at all, even over periods of 15 months or 18 months.
- the concentration of the inventive dispersions is greatly dependent on the volume of solvent added at Step 3, and on the specific application for which the dispersion will be used. That said, the inventive dispersions may be characterized by fairly low viscosity values (at most 10000 cP, and more typically, at most 5000 cP, at most 2000 cP, at most 1000 cP, at most 600 cP, at most 300 cP, at most 200 cP, at most 120cP, at most 80 cP, at most 60 cP, at most 45 cP, at most 35 cP, at most 25 cP, or at most 20 cP) as measured at 25 °C.
- fairly low viscosity values at most 10000 cP, and more typically, at most 5000 cP, at most 2000 cP, at most 1000 cP, at most 600 cP, at most 300 cP, at most 200 cP, at most 120cP, at most 80 cP, at most 60 cP, at most
- the purifying step may advantageously be effected by crossflow microfiltration, using micro-separation membranes.
- Such processes may be excessively and impractically slow when the size of the filtrate species approaches that of the membrane pore or opening.
- microfiltration membrane processes may even be substantially impossible when the size of the filtrate species equals, or exceeds, the size of the membrane opening.
- a further, perhaps even more significant determent to using such separation processes relates to the relative size between the particles or species impeded by the micro-separators (such as micro-membranes), and the species that are supposed to pass through the micro-separators.
- certain dispersants such as PVP, are effective to implement microfiltration purification.
- the PVP dispersant has at least one narrow characteristic dimension/diameter with respect to the copper particles and with respect to the characteristic diameter of the membrane openings.
- This narrow characteristic dimension/diameter of the dispersant is preferably less than half the average secondary particle size of the copper particles.
- the average molecular weight of the polyvinylpyrrolidone should typically have a weight average molecular weight (MW) of less than 1,000,000, in order to pass through various suitable micro-membranes, the MW of the polyvinylpyrrolidone should preferably exceed about 8,000 to avoid reactivity and/or compatibility issues in either or both of the reaction steps.
- the PVP it is generally preferable for the PVP to have a MW of at least 20,000, at least 30,000, at least 40,000, or at least 50,000,.
- Hollow-fiber microfiltration membranes have been advantageously employed, but other ceramic, polymeric and/or metallic microfiltration membranes may also be fundamentally suitable.
- the membrane systems may be static or dynamic (e.g., having a vibrational mechanism for facilitating the separation).
- Typical microseparation or microfiltration membranes for use in conjunction with the method of the present invention have one or more pores that are typically cylindrical, with a high length to width aspect ratio, through which the water/solvent and fine matter can pass.
- the membrane is typically shaped like a long cylinder, but other geometries may be practical.
- membranes having a pore diameter of less than 200 nm may be suitable for use in the process of the present invention.
- the preferred pore diameter is less than 100 nm.
- the pore diameter or nominal pore diameter of the membrane may be at least 20 nm, and often, at least 40 nm, so as to enable various species to pass through the membrane openings, and so that the separation kinetics are not prohibitively slow.
- the dispersant size and shape and the size of the membrane openings may be selected such that the dispersant molecules pass through the openings, while passage of the copper nanoparticles through the openings is hindered or substantially prevented.
- PVP polyvinylpyrrolidone
- tripropylene glycol mono methyl ether (TPM) - Sigma-Aldrich
- Aqueous solutions were prepared by using deionized water using an Ionex water purification system (PuriTech, Dessel, Belgium). All reagents and solvents were used without further purification.
- HRSEM High Resolution Scanning Electron Microscopy
- EBSD Electron Back Scattered Diffraction
- OIM orientation image microscopy
- Typical working conditions for EBSD: E 20 kV, working distance - 15 mm, the resolution of the beam is approximately 30-40nm, the spot size is 4.5, the probe current is about 0.5 nA, the collection time for EBSD pattern - 300 msec, integration - 50.
- EBSD image was taken using back electrons.
- Samples for SEM measurements were prepared by placing 1 drop of diluted (1% w/w) Cu dispersion on a small piece of Si-wafer with following drying under vacuum (0.1 mbar) at room temperature.
- HRTEM images were generally obtained using JEOL JEM- 2100 (LaB6) at 200 kV, integrated with a digital Scanning device (STEM) comprising annular Dark-Field (DF) and Bright-Field (BF) detectors and with a Thermo Scientific energy-dispersive X-ray spectrometer (EDS) system for elemental analysis.
- STEM digital Scanning device
- DF Dark-Field
- BF Bright-Field
- EDS Thermo Scientific energy-dispersive X-ray spectrometer
- SAED selected area electron diffraction
- Samples for TEM measurements were prepared by placing a drop of diluted Cu dispersion (by factor of -25,000) on a 400-mesh carbon-coated nickel grid.
- Samples for XRD measurements were prepared as follows: copper nanoparticles (about 0.5-1 grams) were precipitated from dispersion using an excess of acetone and centrifugation under argon, rinsed several times with acetone, and dried by argon blow; then the obtained powder was mixed with apizone-M grease to prevent possible oxidation during following handling.
- TGA Thermal Gravimetric Analysis
- Example 1 The dispersion produced in Example 1 was used, and additional quantities of solution B were gradually added to the dispersion.
- the pH of the dispersion solution reached 10.0. At this pH the metallic copper particles were highly agglomerated.
- Example 1 was repeated, using 4.62g of the PVP. Under these conditions, a significant portion of the metallic copper particles produced was agglomerated.
- EXAMPLE 2C
- Example 1 was repeated, using 9.25g of the PVP. Under these conditions, a portion of the metallic copper particles produced was agglomerated.
- EXAMPLE 2D
- Example 1 was repeated, using 55.5g of the PVP. Under these conditions, the metallic copper particles produced were found to be single crystals, but were much smaller than those obtained in Example 1. EXAMPLE 2E
- Example 1 was repeated, using 37. Og of the PVP. Under these conditions, the metallic copper particles produced were found to be single crystals, but were smaller than those obtained in Example 1.
- the washing process was continued until the salts in the dispersion were practically eliminated, and the dispersant was reduced to a preset concentration of 3% of the weight of the copper particles.
- the final color of the obtained washed dispersion sample was dark-red, which is the characteristic color of copper nanoparticle dispersion.
- the metal loading of the resulting washed dispersion of copper nanoparticles in water was about 5% w/w (calculated for Cu° metal).
- the % metal loading of the copper dispersion was determined by firing the small sample (0.5g) at 600°C; and was recalculated to metallic Cu, assuming that all Cu was converted to CuO during firing.
- a particle size analysis of the washed copper particles yielded an average particle size (d 5 o) of about 40 nm, using a Brookhaven 90Plus particle size analyzer.
- the inventors positively identified at least 25%, at least 35%, at least 40%, at least 50%, or at least 60% of the particles as having a clear single crystal geometry, on a per-particle basis.
- a particle size analysis of the copper dispersion after the water-ethylene glycol exchange yielded an average particle size (d 50 ) of about 40 nm.
- Figure 3 provides an exemplary HRTEM image of the nanometric copper particles obtained. These particles were stored ("aged") in ethylene glycol for over 18 months prior to undergoing characterization in the HRTEM. A majority of the particles were single crystalline FCC Cu having characteristic geometrical shapes, among them triangular and hexagonal particles (i.e., having triangular and hexagonal morphologies, respectively). Detailed analysis of HRTEM images showed that single-crystal particles remained almost entirely non-oxidized, and that a thin Cu oxide layer was mainly formed on the surface of non-single-crystal particles. The inventors have found that the particulate matter in the inventive formulations may require less dispersant per unit weight of the particulate matter, with respect to various other nanometric copper particles.
- the faces of the single crystals are extremely smooth, with a maximum deviation from flatness being only 1.54nm in the exemplary measured crystal.
- the inventors believe that this structural feature contributes to the ability of the inventive dispersions to require relatively small concentrations of dispersant, while maintaining physical and chemical stability over at least six months, at least twelve months, or at least eighteen months of storage.
- use of the inventive particulate matter within various dispersions may appreciably reduce the viscosity of these dispersions, relative to similar dispersions employing nanometric copper particles of the prior art.
- inventive reaction method and more particularly, the slow and gradual introduction of the borohydride into the acidic media, under vigorous stirring, appreciably contribute to the formation of the single crystals, and to the smoothness of the crystal faces.
- the inventors have observed the physical stability of dispersions such as that described in Example 4, and have found such dispersions to be both physically stable and stable from an oxidation standpoint. Such dispersions retain their dark-red color and show no evidence of agglomeration.
- this exemplary URTEM image frame may be observed 13 individual particles and one large agglomerate that are entirely or largely within the frame.
- 6 may be identified as single crystals by their definitive geometrical shapes (marked with x). Of these, at least 2 are triangular and at least one is hexagonal (truncated).
- the observed ratio of single-crystal copper particles to the total number of particles is 6/14, or over 40%.
- the observed ratio of single-crystal copper particles having a triangular or hexagonal morphology, to the total number of particles is 3/14, or over 20%.
- EBSD produces a diffraction pattern from the surface of the sample of particulate matter in the dispersion.
- the procedure which will be readily understood to those of ordinary skill in the art of EBSD, is as follows: 1. The sample is scanned using a focused electron beam, and the diffraction pattern is obtained.
- Example 5 Following the basic procedure of Example 5, we quantified the presence of single-crystal metallic copper nanoparticles within a sample of nanometric copper. Quantification was achieved by performing a plurality (at least 5, and preferably at least 10) of scans at randomly chosen points.
- Figure 4 is an Electron Back Scattered Diffraction (EBSD) pattern of the nanometric copper particles produced according the embodiment described in Example 4;
- Figure 5 provides identifications of various diffraction patterns characteristic of crystalline copper metal, based on the EBSD pattern provided in Figure 4.
- EBSD Electron Back Scattered Diffraction
- At least 10%, at least 20%, at least 30%> or at least 50% of the scans produce a substantially perfect match for a single crystal copper nanoparticle. More typically, at least 60%, at least 70%, at least 80%, or at least 90% of the scans produce a substantially perfect match for a single crystal copper nanoparticle.
- these quantitative EBSD scanning methods may provide a quantitative evaluation of a top layer or cross-section of the sample.
- this quantitative evaluation closely reflects the fraction of copper particles characterized as single-crystal copper particles, particularly for samples that do not have an extremely broad particle size distribution.
- Figure 2 is a SEM image of a sample containing nanometric copper particles, produced according to the present invention. Randomly chosen locations in the sample were scanned at six locations. Using EBSD as described above, a perfect match for a copper single crystal was obtained in five of the six locations.
- the dispersion was printed as narrow lines on a microscope glass slide, by means of an air-operating dispenser.
- the slide with Cu lines was pre-heated (in air) at 100°C for 10 minutes, followed by heating in oven at 300°C for 30 minutes in an argon atmosphere.
- the line width is about 1mm, and the thickness is about 10 micrometers.
- An inventive dispersion of copper particles in ethylene glycol (EG) was prepared for specific resistivity testing according to the procedure provided in Example 8.
- the sample had a metal loading of approximately 25-29%.
- the specific resistivity determined according to the procedure provided in Example 8, was about 9 x 10 "5 ohm » cm, (x50 of bulk resistivity)
- cuprous oxide within the copper nanoparticle formulations of the present invention was qualitatively and quantitatively demonstrated by means of Powder X-Ray Diffraction (XRD), using the copper dispersion produced in Example 4.
- XRD Powder X-Ray Diffraction
- the nanometric copper product was prepared for X-Ray diffraction analysis according to the procedure provided hereinabove.
- Figure 6 provides a powder X-Ray diffraction pattern of the inventive nanometric copper product.
- the peak positions and the full width at half maximum (FWHM), as a function of 2-theta, are provided in Table 1.
- cuprous oxide has a 2-theta value of approximately 36.8 degrees
- metallic copper has a 2-theta value of approximately 43.7 degrees
- the presence of two peaks in the XRD scan is indicative of the presence of cuprous oxide in the inventive dispersion; the relative intensity of these peaks is indicative of the relative concentration of copper metal and cuprous oxide in the dispersion.
- Quantitative evaluation of the crystalline Cu 2 0 content using XRD was performed on many samples, including the dispersions described in Examples 4, 11, 12, 13, 14 and 15. Some of the results are provided in Table 2 hereinbelow.
- the concentration ratio of crystalline Cu 2 0 to metallic copper content was, for all examples, significantly below, 0.4, below 0.35, below 0.3, below 0.25, below 0.2, or below 0.15.
- the weight ratio of crystalline Cu 2 0 to total copper content was at most 0.12, at most 0.10, at most 0.08, at most 0.06, at most 0.05, at most 0.04, or at most 0.035.
- the Cu 2 0 concentration is defined as the area of peak 1 to the total area of peak 1 and peak 2.
- An estimate of the average grain sizes of crystallites in the particulate matter of the dispersion, and particularly, of copper nanoparticles in the dispersion, may be obtained from the XRD scan.
- the average grain size, in nm may be calculated using the data provided in Table 1, and using the Debye-Scherrer equation:
- ⁇ is the wavelength of the X-ray radiation, which, in the specific instrument used, was 0.1541nm;
- FWHM is the full width at half maximum of the peak (in rad), and is equal:
- Example 4 About 900 ml of a copper dispersion in water containing about 42g of the copper particles, which was prepared as in Example 3, was introduced to a 2L flask under a constant argon blow, and approximately 25 grams of ethylene glycol were added to the flask. The flask was then connected to the Rotavapor evaporator, and the water was distilled as in Example 4. The resulting 52 grams of copper dispersion ( ⁇ 20ml) contained 31 grams of nanometric copper, corresponding to a metal loading of about 60% (metallic copper). The viscosity was about 1400cP at 25°C.
- the applied washing mode was performed as follows: in each washing cycle 4L of "fresh" de-ionized water was added to 1.3L of concentrated dispersion; the dilution factor of each cycle was accordingly 5.3 : 1.3 ⁇ 4.
- the dispersant level was reduced only to a concentration of 10% of the weight of the copper particles.
- the final color of the obtained washed dispersion sample was dark-red, which is the characteristic color of copper nanoparticle dispersion.
- the final dispersion was concentrated to 600ml.
- the resulting 82 grams of copper dispersion ( ⁇ 60ml) contained 24 grams of nanometric copper, corresponding to a metal loading of about 29% (metallic copper).
- the viscosity was about 130cP at 25°C (comparing to 34cP of sample with 3% dispersant in Example 4), exceeding the maximum viscosity limit for ink-jet printing.
- washing cycles were applied, corresponding to about 32L of de-ionized water.
- 4L of "fresh” water was added to 1.3L of concentrated dispersion, similar to example 12A.
- the dispersant level was reduced to a concentration of 6% of the weight of the copper particles.
- the final color of the obtained washed dispersion was dark-red.
- the final dispersion was concentrated to 600ml.
- Dispersant (PVP)/Cu weight/weight ratio usually provided as w/w %PVP/Cu, can be measured by using Thermal Gravimetric Analysis (TGA).
- Figure 7 provides a thermal gravimetric analysis (TGA) plot for the nanodispersion from Example 12(B), conducted in an inert atmosphere (argon) to prevent oxidation of copper metal during analysis.
- TGA thermal gravimetric analysis
- copper nanoparticles were dried from solvent (under argon), and an 8.75mg sample of dried copper particles was analyzed. The sample was heated gradually to 600°C, with weight changes being monitored. The organic dispersant was totally decomposed between 300°C and 500°C, leaving only clean copper metal at 600°C. The corresponding weight loss in the temperature range between 300°C and 500°C, divided by the final weight of copper metal, yielded a dispersant/Cu ratio of approximately 5%.
- the copper nanoparticle is often represented as a spherical particle having a copper metal core coated by an outer organic, polymeric shell, as shown in Figure 8.
- the diameter of the copper core is d
- the thickness (width) of the dispersant (from now on, PVP as a non-limiting example) layer is S
- Vc u as the volume of the copper core
- V P V P as the volume of the PVP outer shell
- V D VC U +V P V P or, combining with (4):
- V D /Vc u l+7.4K
- Example 4 To 600 ml of a copper dispersion in water containing about 28 grams of the copper particles, which was prepared as in Example 3, were added 60 grams of hexylene glycol, under argon blow. The flask was then connected to the Rotavapor evaporator, and the water was distilled as in Example 4. The resulting 82 grams of copper dispersion ( ⁇ 60ml) contained 24 grams of nanometric copper, corresponding to a metal loading of about 29% (metallic copper). The viscosity was about 180cP at 25°C.
- the water-ethanol solvent exchange was performed using a crossflow membrane system.
- ethanol-TPM solvent exchange was performed.
- the resulting 80 grams of copper dispersion ( ⁇ 60ml) contained 23 grams of nanometric copper, corresponding to a metal loading of about 29% (metallic copper). The viscosity was about 15cP at 25°C.
- Example 15A The procedure of Example 15A was repeated, but using diethylene glycol monomethyl ether (DGME) in the second step.
- DGME diethylene glycol monomethyl ether
- the copper dispersion obtained (38 grams) contained 23 grams of nanometric copper, corresponding to a metal loading of about 60.5% (metallic copper).
- the viscosity was about 40cP at 25°C.
- Example 4 To 100 ml of a copper dispersion in water containing about 5 grams of the copper particles, which was prepared as in Example 3, were added 10 grams of benzyl alcohol, under argon blow. A two-phase mixture was formed. The water was then distilled in a Rotavapor evaporator, as in Example 4. The final dispersion obtained (12 grams) was of a dark-red to violet color (characteristic of Cu nanodispersions), and was found to be (including by visual inspection and by optical microscope observation) a stable nanodispersion.
- the exemplary dispersions described in Examples 4, 11, 12, and 15 were subjected to an oxidation stability ("aging") test at about 20°C.
- the results are provided in Table 3.
- the concentration of the crystalline cuprous oxide or “cuprous oxide concentration”—the area of peak 1 to the total area of peak 1 and peak 2, using powder XRD) was substantially maintained over the course of at least 1 month, at least 2 months, at least 3 months, or at least 12 months.
- the amount of dispersant was maintained at at least 2%, at least
- the particulate matter was produced according to the inventive method, in order to produce a high fraction of single crystals, as well as single crystals having particularly smooth faces.
- the amount of dispersant may be maintained at at most 5%, at most 4.5%, at most 4%, or at most 3.5%, of the weight of the copper particles.
- solvents contributing to achieve a low viscosity e.g., TPM may be preferred.
- the particulate matter was adapted, and the dispersant and solvent were selected such that the increase in cuprous oxide concentration over time, normalized by the total initial or previously measured concentration of copper (% Cu total), was maintained within a value V, the value V being expressed as a percentage and defined by:
- V 100-(Cu 2 O conc.(t) - Cu 2 0 cone, (i))/ (% Cu total), wherein:
- Cu 2 0 conc.(i) is the initial or previously measured concentration of Cu 2 0;
- Cu 2 0 conc.(t) is a concentration of Cu 2 0 evaluated at time t.
- cuprous oxide concentration over time was maintained within a value V of 3%, 2%, 1.5%, 1%, 0.8%, 0.6%, 0.5%, or 0.4% over the course of at least 2 months, at least 3 months, or at least 12 months.
- the weight ratio of the PVP to the particulate matter in the dispersion may be within the range of 0.01 to 0.5, 0.015 to 0.4, 0.015 to 0.4, 0.015 to 0.3, or 0.015 to 0.2. More typically, the weight ratio of the PVP to the particulate matter is at most 0.18, at most 0.16, at most 0.12, at most 0.08, at most 0.05, at most 0.04, at most 0.03, at most 0.025, at most 0.022, or at most 0.020.
- the formulations of the present invention typically are free or substantially free of organometallic materials such as metal carboxylates.
- organometallic materials such as metal carboxylates.
- such materials make up at most 8%, at most 6%, at most 4%, at most 2%, or at most 0.5% of the total weight of the particulate matter.
- the term “average secondary particle size”, with respect to particulate matter, refers to a mean diameter of the particulate matter, and is specifically meant to include the diameters of agglomerated particles as well as the diameters of single crystals.
- mean diameter used with regard to dry particulate matter, refers to the mean diameter of the particulate matter, as determined by size measurements using a representative HRSEM image containing at least 50 particles, and according to robust techniques used by those of skill in the art.
- mean diameter used with regard to particulate matter within a dispersion, refers to an equivalent spherical particle size (d 5 o), calculated using the Stokes-Einstein equation, by a Brookhaven 90Plus particle size analyzer (Brookhaven Instruments Corporation, Holtsville, New York), or if unavailable, by a functionally-equivalent particle size analyzer suited for measuring equivalent spherical particle size throughout the range of 5 to 2000 nm.
- the particle size analysis is performed in a professional and reproducible manner using the particle size analyzer, by personnel trained and qualified to operate the particle size analyzer, and under the following conditions:
- polyvinylpyrrolidone also known as PVP, refers to a water-soluble polymer having or including the following molecular structure:
- PVP is typically made from the vinyl pyrrolidone monomer, which has the following structure:
- PVP dispersants include polymers produced by attaching (e.g., grafting) PVP onto other moieties.
- polyvinylpyrrolidone includes such dispersants.
- pure polyvinylpyrrolidone is meant to exclude such dispersants.
- single-crystal refers to (unless designated otherwise) a single-crystal copper particle as determined by the standard Electron Back Scattered Diffraction (EBSD) method described in Example 5 hereinabove.
- EBSD Electron Back Scattered Diffraction
- the term “majority”, with respect to metallic copper particles refers to at least one of the following: at least 30% of the randomly-selected EBSD scans produce a substantially perfect match for a copper single crystal, according to the procedure described in Example 6, or more than 50% of the copper particles, based on the number of copper particles.
- the term “% Cu total”, “total concentration of copper”, “total initial concentration of copper”, and the like, with respect to a formulation or dispersion refers to the total amount of copper, in metallic and oxide forms, in the formulation or dispersion, and quantitatively expressed as %Cu° in the formulation or dispersion.
- standard sintering or “standard thermal sintering” refers to the sintering procedure described in Example 8.
- concentration ratio refers to the area ratio of the crystalline cuprous oxide and the metallic copper, using powder XRD, as described in Example 10A.
- Cu 2 0 concentration or “cuprous oxide concentration” refers to the area of peak 1 to the total area of peak 1 and peak 2, using powder XRD, as described in Example 10A.
- the term "primary” or “primarily”, with respect to a phase, dispersant or solvent within a formulation or dispersion, refers to the largest component, by weight, within that phase, dispersant or solvent.
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Abstract
Description
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CN201580014550.1A CN106102970A (en) | 2014-03-03 | 2015-03-03 | Nanometer copper preparation |
JP2016554873A JP2017514988A (en) | 2014-03-03 | 2015-03-03 | Nano copper preparation |
US15/122,185 US10166602B2 (en) | 2014-03-03 | 2015-03-03 | Nanometric copper formulations |
IL247528A IL247528B (en) | 2014-03-03 | 2015-03-03 | Nanometric copper formulations |
KR1020167026792A KR20160128370A (en) | 2014-03-03 | 2015-03-03 | Nanometric copper formulations |
BR112016020056-0A BR112016020056B1 (en) | 2014-03-03 | 2015-03-03 | production process of nanometric copper formulations |
RU2016137018A RU2730285C2 (en) | 2014-03-03 | 2015-03-03 | Compositions containing nanometric copper |
EP15758302.2A EP3113897B1 (en) | 2014-03-03 | 2015-03-03 | Nanometric copper formulations |
US16/202,135 US11590567B2 (en) | 2014-03-03 | 2018-11-28 | Nanometric copper formulations |
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CN (1) | CN106102970A (en) |
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GB (1) | GB201403731D0 (en) |
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WO2017115330A1 (en) * | 2015-12-30 | 2017-07-06 | Universidad De Chile | Method for producing copper nanoparticles and use of said particles |
EP3287499A1 (en) | 2016-08-26 | 2018-02-28 | Agfa-Gevaert | A metallic nanoparticle dispersion |
CN114054746A (en) * | 2021-10-14 | 2022-02-18 | 华南理工大学 | Copper powder with particle size in nanometer to micrometer trimodal distribution, and one-time synthesis method and application thereof |
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CN106029261A (en) * | 2014-02-27 | 2016-10-12 | 学校法人关西大学 | Copper nanoparticles and production method for same, copper nanoparticle fluid dispersion, copper nanoink, copper nanoparticle preservation method, and copper nanoparticle sintering method |
GB201403731D0 (en) * | 2014-03-03 | 2014-04-16 | P V Nano Cell Ltd | Nanometric copper formulations |
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CN111868977A (en) * | 2018-05-25 | 2020-10-30 | 本田技研工业株式会社 | Composite electrode material for fluoride ion electrochemical cells |
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Also Published As
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US11590567B2 (en) | 2023-02-28 |
BR112016020056B1 (en) | 2021-06-08 |
US20160368048A1 (en) | 2016-12-22 |
RU2016137018A (en) | 2018-03-20 |
EP3113897B1 (en) | 2019-10-09 |
EP3113897A1 (en) | 2017-01-11 |
RU2730285C2 (en) | 2020-08-21 |
US10166602B2 (en) | 2019-01-01 |
GB201403731D0 (en) | 2014-04-16 |
IL247528A0 (en) | 2016-11-30 |
US20190291180A1 (en) | 2019-09-26 |
IL247528B (en) | 2022-09-01 |
KR20160128370A (en) | 2016-11-07 |
EP3113897A4 (en) | 2017-11-08 |
RU2016137018A3 (en) | 2018-11-06 |
JP2017514988A (en) | 2017-06-08 |
US20230191486A1 (en) | 2023-06-22 |
CN106102970A (en) | 2016-11-09 |
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