Nickel nanowires and methods of making the same

Abstract

The present invention provides a nickel nanowire which is less likely to break due to stress. The present invention relates to a nickel nanowire having a face-centered cubic lattice structure and a crystallite size of 10 nm or less in the direction of (111) lattice plane.

Description

Technical Field

[0001] This invention relates to nickel nanowires and methods for manufacturing the same. Background Technology

[0002] Because nickel nanowires are strongly magnetic, they can be used not only as conductive materials such as transparent conductive films and high dielectric constant materials, but also as magnetic materials such as electromagnetic wave absorbing materials. Nanowires are characterized by percolation and magnetic anisotropy due to the anisotropy of their fiber shape (high aspect ratio), enabling them to achieve properties that are unattainable with particles (Patent Document 1).

[0003] For example, the nickel nanowires disclosed in Patent Document 1 are manufactured by reducing a nickel salt, (111) with a crystallite size exceeding 10 nm and less than 15 nm in the lattice plane direction.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: International Publication No. 2019 / 073833 Summary of the Invention

[0007] The inventors of this invention discovered that conventional nickel nanowires are prone to breakage due to stress.

[0008] Specifically, to apply the properties of nickel nanowires to industrial products, they need to be molded into various shapes such as sheets and shells. Molding nickel nanowires requires mixing them with other substances, but like other metallic nanowires such as silver nanowires, nickel nanowires have weak resistance to stress. Therefore, when mixing and molding them with other substances through processes such as compounding, the following problems arise: they break into particles due to stress, anisotropy is lost, and the expected properties (such as magnetic anisotropy) cannot be achieved.

[0009] The present invention addresses the above-mentioned problems and aims to provide nickel nanowires that are not easily broken due to stress.

[0010] The inventors discovered that by controlling the crystallite size within a specific range, the above-mentioned objective can be achieved, thus completing this invention.

[0011] That is, the main idea of ​​this invention is as follows.

[0012] <1> A nickel nanowire with a face-centered cubic lattice structure, (111) the crystallite size in the lattice plane direction is less than 10 nm.

[0013] <2> According to <1>, the crystallite size in the (111) lattice plane direction is larger than the crystallite size in the (110) lattice plane direction.

[0014] <3> According to <2>, the nickel nanowires have a crystallite size in the direction of the (110) lattice plane that is larger than the crystallite size in the direction of the (100) lattice plane.

[0015] <4> The nickel nanowires according to any one of <1> to <3>, wherein the average diameter is 50 nm or more and less than 1 μm.

[0016] <5> The nickel nanowires according to any one of <1> to <4>, wherein the average length is 5 μm or more.

[0017] <6> The nickel nanowires according to any one of <1> to <5>, wherein the saturation magnetic susceptibility is 20 emu / g or more.

[0018] <7> The nickel nanowires according to any one of <1> to <6>, wherein the crystallite size in the direction of the (111) lattice plane is 1 to 8 nm.

[0019] <8> A dispersion comprising any one of <1> to <7> nickel nanowires.

[0020] <9> A molded body comprising any one of <1> to <7> nickel nanowires.

[0021] <10> A method for manufacturing nickel nanowires, wherein two or more nickel salts are reduced in a reaction solution while a magnetic field is applied, to obtain nickel nanowires as described in any one of <1> to <7>.

[0022] <11> According to the method for manufacturing nickel nanowires described in <10>, the two or more nickel salts mentioned above include nickel chloride and nickel sulfate.

[0023] The ratio of the nickel chloride to the total of the nickel chloride and nickel sulfate is 70–98 mol%.

[0024] <12> According to the method for manufacturing nickel nanowires described in <10>, wherein the two or more nickel salts mentioned above comprise nickel chloride and nickel acetate.

[0025] The ratio of the nickel chloride to the total of the nickel chloride and nickel acetate is 70–98 mol%.

[0026] <13> According to the method for manufacturing nickel nanowires described in <10>, wherein the two or more nickel salts mentioned above include nickel acetate and nickel sulfate.

[0027] The ratio of the nickel acetate to the total of the nickel acetate and nickel sulfate is 70–98 mol%.

[0028] According to the present invention, nickel nanowires that are not easily broken due to stress can be provided. Even when mixed with other substances and molded through processes such as compounding, the nickel nanowires of the present invention are not easily broken due to stress, and therefore can be applied to various purposes. Attached Figure Description

[0029] Figure 1 This is the WAXD (wide-angle X-ray diffraction) diffraction pattern of the nickel nanowires prepared in Example 1.

[0030] Figure 2 This is the WAXD diffraction pattern of the nickel nanowires fabricated in Comparative Example 2.

[0031] Figure 3 This is the WAXD diffraction pattern of the nickel nanowires fabricated in Comparative Example 4. Detailed Implementation

[0032] Nickel nanowires

[0033] The nickel nanowires of this invention require an fcc structure (i.e., face-centered cubic lattice structure) as their crystal structure. The lattice structure (or crystal structure) can be analyzed using WAXD.

[0034] Nickel nanowires exhibiting an fcc structure refer to the presence of one or more (especially three) principal peaks characteristic of a so-called fcc-type crystal structure at a specified incident angle during X-ray diffraction under the following conditions. Examples of principal peaks characteristic of the fcc structure include the peak at 2θ = 44.4° (111), the peak at 2θ = 51.6–51.9° (200), and the peak at 2θ = 76.3° (220).

[0035] condition: 50kV, 300mA, 2θ / θ method.

[0036] The nickel nanowires of the present invention may include other crystal structures (e.g., hcp structure, i.e., hexagonal close-packed structure) as crystal structures, rather than strictly having only an fcc structure. For example, the nickel nanowires of the present invention mainly have an fcc structure, but may include an hcp structure.

[0037] The hcp structure content (hcp / fcc) of the nickel nanowires of the present invention is typically 0.15 or less, preferably 0.1 or less, and more preferably 0, from the viewpoint of magnetic properties. The hcp structure content (hcp / fcc) is the ratio of the hcp structure to the fcc structure in the nickel nanowire. Specifically, the hcp structure content is determined using WAXD (wide-angle X-ray diffraction). The value is calculated based on the ratio of the integral value of the peak (010) at 2θ = 37.2° in the hcp structure to the integral value of the peak (200) at 2θ = 51.6~51.9° in the fcc structure (hcp(010) / fcc(200)) in the diffraction pattern of 50kV, 300mA, 2θ / θ method.

[0038] The smaller the crystallite size of nickel nanowires, the easier it is for them to slide at the crystallite boundaries, thus easing the stress applied to them. Conversely, the larger the crystallite size, the more difficult it is for them to slide at the crystallite boundaries, making it harder for the applied stress to be eased. Therefore, to prevent nickel nanowires from breaking due to stress, it is sufficient to increase the number of regions at the crystallite boundaries where stress can be eased by sliding. Thus, the crystallite size of nickel nanowires is preferably small. Specifically, the crystallite size in the (111) lattice plane direction needs to be less than 10 nm. From the viewpoint of more adequate stress easing and excellent magnetic properties, it is preferably 1 to 10 nm, more preferably 1 to 9 nm, further preferably 1 to 8 nm, particularly preferably 5 nm to 8 nm, and most preferably more than 5 nm but less than 8 nm. If the crystallite size in the (111) lattice plane direction is too large, the stress cannot be adequately eased, thus making them prone to breakage due to stress. In addition, the magnetic properties may sometimes decrease. It should be noted that, considering the process of generating tiny nickel nuclei from nickel ions and growing them into nanowires, it is impractical for the crystallite size to be less than 1–5 nm. To achieve a crystallite size of less than 10 nm along the (111) lattice plane, as described later, in the reaction solution, while applying a magnetic field, two or more nickel salts are used to adjust the dissociation constant of each nickel salt, the size of the counterion, the coordination state, the amount of crystal nuclei, the generation time of the nanowires, and the timing of nanowire growth, while simultaneously obtaining nickel nanowires through reduction. It should be noted that the direction of the (111) lattice plane is perpendicular to the (111) lattice plane.

[0039] The magnetic properties of nickel nanowires vary depending on the orientation of their lattice planes. For nickel, the (111) lattice plane is the easiest to magnetize, the (110) lattice plane is the next easiest, and the (100) lattice plane is the least easy. For use as a magnetic material, a larger crystallite size in the (111) lattice plane direction is more advantageous. Therefore, for nickel nanowires to be used as a magnetic material, it is preferable that the crystallite size in the (111) lattice plane direction is larger than that in the (110) lattice plane direction, and even more preferably that the crystallite size in the (110) lattice plane direction is larger than that in the (100) lattice plane direction.

[0040] The crystallite size in the (110) lattice plane direction of the nickel nanowires of the present invention is generally 8.0 nm or less (especially 1.0 to 8.0 nm), and from the viewpoint of more adequate stress relief and excellent magnetic properties, it is preferably 4.0 to 7.8 nm, more preferably 4.8 nm to 7.8 nm, and even more preferably 5.3 nm to 6.0 nm.

[0041] The crystallite size in the (100) lattice plane direction of the nickel nanowires of the present invention is generally 7.0 nm or less (especially 0.8 to 7.0 nm), and from the viewpoint of more adequate stress relief and excellent magnetic properties, it is preferably 2.0 to 6.4 nm, more preferably 3.0 nm to 5.4 nm, and even more preferably 3.0 nm to 4.5 nm.

[0042] In this specification, the crystallite size for each lattice plane direction is the value calculated from the peak of WAXD. In the case of nickel with fcc, since the extinction law cannot directly observe the reflection of the (100) lattice plane and the (110) lattice plane, the values ​​are set to the values ​​calculated from the peaks of the (200) lattice plane and the (220) lattice plane, respectively.

[0043] Typically, nanowires are fibrous materials with an average diameter on the nanometer scale. Furthermore, the average diameter of the nickel nanowires of this invention is necessarily larger than the crystallite size along each lattice plane. In this invention, from the viewpoints of operability, more adequate stress relief, and excellent magnetic properties, the average diameter of the nickel nanowires is preferably 50 nm or more and less than 1 μm, more preferably 50–500 nm, further preferably 70–200 nm, particularly preferably 90–200 nm, and most preferably 90–150 nm.

[0044] In this specification, the average diameter of the nickel nanowires is used as the average of the nickel nanowire diameters at any 100 points in 10 fields of view measured by transmission electron microscopy (600,000x).

[0045] From the viewpoints of mixing with other substances through compounding, as well as from the viewpoints of operability, stress relief and magnetic properties, the average length of nickel nanowires is preferably 5 μm or more (especially 5 to 50 μm), and more preferably 10 to 30 μm.

[0046] In this specification, the average length of the nickel nanowires is the average of the lengths of any 200 nickel nanowires measured by scanning electron microscopy (2000–6000x).

[0047] The aspect ratio (average length / average diameter) of the nickel nanowires of the present invention is typically 50 or more, preferably 100 or more from the viewpoint of magnetic properties, more preferably 150 or more, further preferably 200 or more, and particularly preferably 250 or more. There is no particular upper limit to this aspect ratio, which is typically 400 or less, and particularly 300 or less.

[0048] The nickel nanowires of the present invention are strongly magnetic materials with a saturation magnetic susceptibility of 20 emu / g or higher. From the viewpoint of further improving magnetic properties, the saturation magnetic susceptibility of the nickel nanowires of the present invention is preferably 30 emu / g or higher, more preferably 40 emu / g or higher, and even more preferably 45 emu / g or higher. There is no particular limitation on the upper limit of this saturation magnetic susceptibility; it is typically 60 emu / g or lower, and particularly 55 emu / g or lower.

[0049] In this specification, the saturation magnetic susceptibility, as described below, can be determined using a VSM (vibrating sample magnetometer). In particular, nickel nanowires with an hcp structure containing a proportion exceeding 0.1 (especially exceeding 0.15) do not possess sufficient magnetic properties and have a saturation magnetic susceptibility of less than 20 emu / g.

[0050] [Manufacturing Method of Nickel Nanowires]

[0051] The nickel nanowires of this invention can be obtained by performing reduction in a reaction solution while applying a magnetic field and using two or more nickel salts to adjust the dissociation constant of the nickel salts, the size of the counterions, the amount of crystal nuclei, the generation time of the nanowires, and the timing of nanowire growth. Previously, techniques for controlling the crystallite size of nickel nanowires were unknown. In this invention, by using two or more nickel salts, compared to using a single nickel salt, nickel nanowires with smaller crystallite sizes can be obtained, and the crystallite size can be controlled over a wide range.

[0052] Examples of nickel salts include nickel chloride, nickel sulfate, nickel nitrate, and nickel acetate. These salts can be hydrates or acid anhydrides. Among these nickel salts, two or more (especially two) nickel salts with different dissociation constants and / or counterions are used. As combinations of nickel salts, combinations of nickel salts with large differences in dissociation constants and / or large differences in the size of counterions are preferred. Examples of such combinations include the combination of nickel chloride and nickel sulfate (hereinafter sometimes referred to as combination A), the combination of nickel chloride and nickel acetate (hereinafter sometimes referred to as combination B), and the combination of nickel acetate and nickel sulfate (hereinafter sometimes referred to as combination C). Among these, combination A of nickel chloride and nickel sulfate is more preferred from the viewpoint of reducing crystallite size (especially crystallite size in the (111) lattice plane direction) and improving magnetic properties.

[0053] The preferred total concentration of nickel salts in the reaction solution varies greatly depending on the type of nickel salt used, the type of solvent, and the reaction temperature. If the total concentration is too high, nanowires cannot be formed; if the concentration is too low, the manufacturing efficiency tends to decrease. From the viewpoint of reducing crystallite size (especially crystallite size in the (111) lattice plane direction) and improving magnetic properties, the total concentration of nickel salts in the reaction solution is preferably 0.01 to 1 mmol / g, more preferably 0.015 to 0.25 mmol / g, and even more preferably 0.015 to 0.030 mmol / g.

[0054] The preferred concentration ratio of each nickel salt in the reaction solution varies greatly depending on the dissociation constant of the nickel salt used. Among the various combinations of nickel salts, the following concentration ratios are preferred from the viewpoint of reducing crystallite size (especially crystallite size in the (111) lattice plane direction) and improving magnetic properties.

[0055] (1A) When the nickel salt used is a combination of nickel chloride and nickel sulfate (A), the ratio of nickel chloride to the total of nickel chloride and nickel sulfate is preferably 70-98 mol%, preferably 70-95 mol%, and more preferably 85-95 mol%. When the above ratio is 50 mol% or more but less than 70 mol%, sometimes nanowires are not formed and particles are formed instead. When the above ratio is less than 50 mol%, the crystallite size in the (111) lattice plane direction of the nanowires increases.

[0056] (1B) When the nickel salt used is a combination of nickel chloride and nickel acetate (B), the ratio of nickel chloride to the total of nickel chloride and nickel acetate is preferably 70-98 mol%, preferably 70-95 mol%, and more preferably 85-95 mol%. When the above ratio is 50 mol% or more but less than 70 mol%, sometimes nanowires are not formed and particles are formed instead. When the above ratio is less than 50 mol%, the crystallite size in the (111) lattice plane direction of the nanowires increases.

[0057] (1C) When the nickel salt used is a combination of nickel acetate and nickel sulfate (C), the ratio of nickel acetate to the total of nickel acetate and nickel sulfate is preferably 70-98 mol%, preferably 70-95 mol%, and more preferably 85-95 mol%. When the above ratio is 50 mol% or more but less than 70 mol%, sometimes nanowires are not formed and particles are formed instead. When the above ratio is less than 50 mol%, the crystallite size in the (111) lattice plane direction of the nanowires increases.

[0058] There are no particular limitations on the solvents used in the reaction solution, but from the viewpoint of easily dissolving nickel salts, highly polar solvents such as water, alcohol, and NMP, and diol solvents such as ethylene glycol and propylene glycol with high boiling points and high polarity are preferred.

[0059] There are no particular limitations on the reducing agent used to reduce nickel salts, but from the viewpoint of reducing crystallite size (especially crystallite size in the (111) lattice plane direction) and improving magnetic properties, hydrazine monohydrate (hydrazine) is preferred. For phosphorus-based and borane-based reducing agents such as hypophosphorous acid and dimethylamine borane, which are commonly used for electroless nickel plating, phosphorus and boron become impurities in the metal, reducing the metal's own crystallinity. Therefore, sometimes nanowires cannot be formed or the magnetic properties of the obtained nickel nanowires are reduced, making them less desirable. Furthermore, organic reducing agents such as glycols and ascorbic acid require high temperatures above 200°C, and the magnetic field and solvent state (temperature, boiling, etc.) used in the reaction are unstable, making them less desirable.

[0060] When using hydrazine monohydrate as a reducing agent, the molar amount of hydrazine monohydrate relative to the total amount of nickel salt is preferably 1.1 to 2.0 times, more preferably 1.2 to 1.8 times. When the molar amount of hydrazine monohydrate relative to the total amount of nickel salt is less than 1.1 times, unreacted nickel salt remains, resulting in poor efficiency. On the other hand, when the molar amount exceeds 2.0 times, the reaction activity sometimes becomes too high, causing the reaction solution to foam and hindering the formation of nanowires.

[0061] In the reduction of nickel salts with hydrazine monohydrate, the reaction temperature and liquid properties are crucial. If the reaction temperature is too high, the reaction system becomes unstable due to foaming caused by gas production; if the reaction temperature is too low, the reduction reaction itself may not occur. The preferred reaction temperature is below the boiling point of hydrazine at atmospheric pressure (114°C), and from the viewpoints of adjusting the reaction temperature, the amount of gas produced, and convection diffusion, 80–100°C is preferred, and particularly 80–95°C. When the reaction is carried out at a temperature of 80–100°C, especially 80–95°C, the liquid properties are preferably alkaline. To achieve an alkaline liquid properties, hydroxide salts such as sodium hydroxide are preferred. However, depending on the concentration of the hydroxide salt, insoluble nickel hydroxide precipitates may sometimes form. In such cases, precipitation can be suppressed by using sodium hydroxide and ammonia in combination. When using sodium hydroxide, the concentration of sodium hydroxide in the reaction solution is preferably 0.020–1 mmol / g (particularly 0.025–1 mmol / g), more preferably 0.020–0.5 mmol / g (particularly 0.025–0.5 mmol / g). Ammonia complexes the nickel hydroxide precipitate with ammonia, causing it to redissolve. The amount of ammonia added is not particularly limited, but redissolving requires an excess relative to nickel hydroxide. On the other hand, excess ammonia can destabilize the reaction system due to the endothermic effect of vaporization heat. Therefore, relative to 1 mol of sodium hydroxide, a range of 3–30 mol is generally preferred. From the viewpoint of reducing crystallite size (particularly crystallite size in the (111) lattice plane direction) and improving magnetic properties, a range of 10–30 mol is more preferred, and a range of 10–20 mol is even more preferred. From the viewpoint of obtaining and managing, ammonia is preferably added in the form of ammonia water. The above-mentioned amount of ammonia relative to 1 mol of sodium hydroxide is sufficient as long as it is within the above range in the reaction solution.

[0062] Complexing agents such as citrate can be added to the reaction solution. Adding a complexing agent tends to increase the amount of crystal nuclei and decrease the crystallite size of the nickel nanowires. From the viewpoint of reducing crystallite size (especially crystallite size in the (111) lattice plane direction) and improving magnetic properties, the concentration of the complexing agent relative to the total moles of the nickel salt is preferably 1–20 mol%, more preferably 5–15 mol%, and even more preferably 5–10 mol%. If the concentration of the complexing agent is too high, the reduction reaction may not occur easily, reducing manufacturing efficiency.

[0063] The reaction takes place within a magnetic field. The central magnetic field is preferably 10–200 mT, more preferably 80–180 mT. Nickel nanowires cannot be manufactured without applying a magnetic field during the reaction.

[0064] The reduction time for the reduction reaction is not particularly limited as long as nickel nanowires are produced, and is usually less than 1 hour, preferably around 10 to 40 minutes. Crystal nuclei, which affect the crystallite size, form within a few minutes, and grow into nanowires from the crystallites in about 10 minutes. It is speculated that the size of the crystal nuclei is determined by multiple factors, such as the structure and concentration of the salt in the raw material.

[0065] After the reduction reaction, nickel nanowires are obtained through purification and recovery via centrifugation, filtration, and magnetic adsorption. Ammonia can be added before recovering the nickel nanowires after the reaction. This dissolves the byproduct nickel hydroxide precipitate, facilitating the removal of impurities.

[0066] [Dispersions, coatings, pastes, and molded articles]

[0067] The nickel nanowires of the present invention can be dispersed in a medium such as water, an organic solvent, or a mixture thereof, and / or a curable resin to form a dispersion. As the organic solvent, all organic solvents conventionally used as media for nanowire dispersions can be used, for example, acetone, isobutanol, isopropanol, isoamyl alcohol, ethanol, diethyl ether, ethylene glycol, ethylene glycol monoethyl ether, ethylene glycol monoethyl ether acetate, ethylene glycol mono-n-butyl ether, ethylene glycol monomethyl ether, dichlorobenzene, xylene, cresol, chlorobenzene, isobutyl acetate, isopropyl acetate, isoamyl acetate, ethyl acetate, n-butyl glycol acetate, n-propyl acetate, n-amyl acetate, methyl acetate, cyclohexanol, cyclohexanone, N,N-dimethylformamide, tetrahydrofuran, 1,1,1-trichloroethane, toluene, n-hexane, propylene glycol, 1-butanol, 2-butanol, methanol, methyl ethyl ketone, methyl cyclohexanol, methyl cyclohexanone, methyl n-butyl ketone, etc. Examples of curable resins include acrylic resins, epoxy resins, silicone resins, and phenolic resins.

[0068] The content of nickel nanowires in the dispersion is not particularly limited, for example, it can be 0.01 to 50 parts by mass relative to 100 parts by mass of the medium, especially 0.1 to 10 parts by mass.

[0069] By mixing the dispersion containing the nickel nanowires of the present invention with an adhesive resin or with a curing agent that cures a curable resin, it can be used as a coating, adhesive, or molding material. Leveling agents, wetting agents, defoamers, and inorganic fillers for purposes such as heat conduction can also be added to the dispersion.

[0070] Examples of adhesive resins and curing resins include acrylic resins, polyurethane resins, epoxy resins, silicone resins, and phenolic resins. Examples of curing agents include aldehydes, amines, isocyanates, imidazoles, carboxylic acids, acid anhydrides, hydrazides, and formaldehyde compounds.

[0071] The dispersions, coatings, and pastes containing the nickel nanowires of this invention can be used for coating and other applications as before. The coating film is a conductor or a high dielectric constant material, suitable for wires, electrode materials, electromagnetic wave shielding materials, antenna substrates, electromagnetic wave absorbing materials, etc.

[0072] Because the nickel nanowires of the present invention are less prone to breakage due to stress compared to conventional methods, it is also possible to produce molded articles by mixing, melting, and compounding the nickel nanowires of the present invention with other substances (e.g., polymers) and then molding them. Examples of other substances include polymers (especially thermoplastic polymers) similar to the aforementioned adhesive resin. The method of mixing, melting, and compounding with other substances is not particularly limited; for example, methods using a mixer and a screw extruder can be used. Furthermore, the molding method is not particularly limited; for example, compression molding and injection molding can be used.

[0073] In particular, the sheet-like molded body obtained by mixing, melting, kneading and molding the nickel nanowires of the present invention with the binder resin is useful as an electric wire, electrode material, electromagnetic wave shielding material, antenna substrate, electromagnetic wave absorbing material and the like.

[0074] Example

[0075] The present invention will now be described through examples, but the invention is not limited thereto. It should be noted that the physical properties of the nickel nanowires were determined using the following methods.

[0076] (1) Average diameter

[0077] The obtained nanowires were dispersed in ethanol, thinly coated onto a grid with a support film, and dried. The resulting sample was imaged using a transmission electron microscope at 600,000x magnification. The diameter of the nickel nanowires at any 100 points in 10 fields of view was measured, and the average value was calculated.

[0078] (2) Average length

[0079] The sample, which was coated on the sample stage in the same manner as (1) and dried, was photographed using a scanning electron microscope at 2000–6000x magnification. The lengths of any 200 nickel nanowires were measured and the average value was calculated.

[0080] (3) Crystal structure

[0081] The obtained nickel nanowires were filled into a glass sample plate and subjected to WAXD (wide-angle X-ray diffraction). The crystal structure was identified by the diffraction pattern. The measurement conditions were CuKα rays, 50 kV, 300 mA, 2θ / θ method.

[0082] Specifically, in the diffraction pattern, the presence of peaks at 2θ = 44.4°, 2θ = 51.6–51.9°, and 2θ = 76.3° identifies the face-centered cubic (fcc) lattice structure (e.g., Figure 1 and Figure 2 ). Figure 1 and Figure 2 These are the WAXD (wide-angle X-ray diffraction) diffraction patterns of the nickel nanowires prepared in Example 1 and Comparative Example 2, respectively.

[0083] On the other hand, the presence of peaks at 2θ = 37.2°, 2θ = 43.2°, and 2θ = 62.8° identifies hexagonal close-packed structures (hcp) (e.g. Figure 3 ). Figure 3 This is the WAXD (wide-angle X-ray diffraction) pattern of the nickel nanowires fabricated in Comparative Example 4. Given the presence of peaks representing both crystal structures, it is assumed that these two crystal structures have been formed.

[0084] Based on the diffraction pattern, the ratio of the hexagonal close-packed structure (hcp) to the face-centered cubic (fcc) lattice structure was calculated. Specifically, the integral value of the peak (010) at 2θ = 37.2° in the hexagonal close-packed structure was calculated relative to the integral value of the peak (200) at 2θ = 51.6–51.9° in the face-centered cubic lattice structure (hcp(010) / fcc(200)).

[0085] (4) Crystal size

[0086] Based on the diffraction pattern obtained from WAXD, multiple peaks were separated using JADE software. The corrected half-peak width β (rad) of the peaks corresponding to (111), (220), and (200) was calculated using equation (1). The crystallite size in each lattice direction was calculated using the Scherrer formula (2). Specifically, the corrected half-peak width β was obtained using equation (1) with a deconvolution constant of 1.3 and a device constant of 0.1. The crystallite size was obtained using equation (2) with a constant K of 0.9, λ of 1.5406 (the wavelength of the CuKα1 X-rays used), β as the corrected half-peak width, and θ as the diffraction angle.

[0087] The measurement conditions based on WAXD are as follows:

[0088] 50kV, 300mA, 2θ / θ method.

[0089] [Mathematical Expression 1]

[0090] β 1.3 = (Measured half-peak width) 1.3 -0.1 1.3 (1)

[0091] Crystallite size (nm) = 0.1 × (K × λ) / (β × cosθ) (2)

[0092] ◎: Below 8nm (excellent);

[0093] ○: Exceeding 8nm but below 9nm (Good);

[0094] △: Exceeding 9nm but below 10nm (qualified);

[0095] ×: Exceeding 10nm (unacceptable).

[0096] (5)Magnetic properties

[0097] The obtained nanowires were filled into a sample holder, and the saturation magnetic susceptibility (emu / g) was measured using a VSM (vibrating sample magnetometer).

[0098] ◎◎: Above 45 emu / g (optimal);

[0099] ◎: 40 μg / g or higher and less than 45 μg / g (excellent);

[0100] ○: Above 30mu / g and less than 40mu / g (good);

[0101] △: Above 20mu / g and less than 30mu / g (qualified);

[0102] ×: Less than 20mu / g (unqualified).

[0103] (6) Ease of cutting relative to stress

[0104] One g of the obtained nickel nanowires was dispersed in 50 g of ethylene glycol and treated with ultrasound at 42 kHz for 2 minutes. The ease of cutting (fracture) of the nanowires under this stress was evaluated. The retention rate was calculated from the average length of the treated nickel nanowires and evaluated according to the following criteria.

[0105] In this invention, a mark of "△" or higher is considered acceptable, and "◎" is preferred.

[0106] ◎: Over 90% (Excellent);

[0107] ○: 70% or more but less than 90% (Good);

[0108] △: 50% or more but less than 70% (qualified);

[0109] ×: Less than 50% (unacceptable).

[0110] Example 1

[0111] 3.61 g (15.2 mmol) of nickel chloride hexahydrate, 0.442 g (1.68 mmol) of nickel sulfate hexahydrate, and 0.375 g (1.27 mmol) of trisodium citrate dihydrate were added to ethylene glycol, for a total volume of 500 g. The solution was heated to 90 °C to dissolve the nickel chloride.

[0112] In another container, 1.00 g (25.0 mmol) of sodium hydroxide was added to ethylene glycol, bringing the total amount to 499 g. The solution was heated to 90 °C and allowed to dissolve completely, then 1.00 g (20.0 mmol) of hydrazine monohydrate was added.

[0113] The two solutions were mixed and placed in a magnetic circuit in which a magnetic field of 150 mT could be applied. The reduction reaction was carried out for 15 minutes at a temperature of 90–95°C.

[0114] After the reaction, 25g of 28% ammonia water (7g of ammonia (=411.8mmol)) was added, and the nickel nanowires were recovered by filtration.

[0115] Examples 2-6 and Comparative Examples 1-4

[0116] The nickel nanowires were recovered by changing the type and amount of nickel salt used to those listed in Table 1, except that the same operation as in Example 1 was performed.

[0117] Example 7

[0118] 3.61 g (15.2 mmol) of nickel chloride hexahydrate, 0.442 g (1.68 mmol) of nickel sulfate hexahydrate, and 0.375 g (1.27 mmol) of trisodium citrate dihydrate were added to ethylene glycol, for a total volume of 500 g. The solution was heated to 90 °C to dissolve the nickel chloride.

[0119] In another container, 1.00 g (25.0 mmol) of sodium hydroxide was added to ethylene glycol, bringing the total amount to 499 g. The solution was heated to 90 °C and allowed to dissolve completely. Then, 25 g of 28% ammonia solution (7 g ammonia (=411.8 mmol)) and 1.00 g (20.0 mmol) of hydrazine monohydrate were added sequentially.

[0120] The two solutions were mixed and placed in a magnetic circuit in which a magnetic field of 150 mT could be applied. The reduction reaction was carried out for 15 minutes at a temperature of 90–95°C.

[0121] After the reaction, the nickel nanowires are recovered by filtration.

[0122] Comparative Example 5

[0123] The amounts of nickel chloride hexahydrate and nickel sulfate hexahydrate were changed to those listed in Table 1. Otherwise, the same operation as in Example 1 was performed in order to obtain nickel nanowires. However, since the concentrations of nickel chloride hexahydrate and nickel sulfate hexahydrate were equimolar, nanowires could not be obtained.

[0124] [Table 1]

[0125]

[0126] The nickel nanowires in Examples 1-7 have an fcc crystal structure, with crystallites smaller than 10 nm in the (111) lattice plane direction. Therefore, even when stress is applied to the nanowires, the average length can be maintained, with a maintenance rate of more than 50%.

[0127] In particular, the crystallite size in the (111) lattice plane direction of the nickel nanowires in Examples 1 and 7 is more preferably in the range of 1 to 8 nm (especially more than 5 nm and less than 8 nm), so that even when stress is applied to the nanowires, the average length is basically maintained and the retention rate is more than 90%.

[0128] The nickel nanowires in Comparative Examples 1-4 were fabricated using a single nickel salt, resulting in a crystallite size exceeding 10 nm in the (111) lattice plane direction. Consequently, when stress was applied to the nanowires, the average length decreased, and the retention rate was less than 50%.

[0129] Industrial availability

[0130] The nickel nanowires of this invention are conductors or high dielectric constant materials, suitable for use as wires, electrode materials, electromagnetic wave shielding materials, antenna substrates, electromagnetic wave absorbing materials, etc.

Claims

1. A nickel nanowire having a face-centered cubic lattice structure, wherein the crystallite size in the (111) lattice plane direction is 1-10 nm; The crystallite size in the (111) lattice plane direction is larger than the crystallite size in the (110) lattice plane direction. The crystallite size in the (110) lattice plane direction is larger than the crystallite size in the (100) lattice plane direction; The nickel nanowires have an average diameter of 50 nm or more and less than 1 μm. The aspect ratio of the nickel nanowires is 50 to 400.

2. The nickel nanowire according to claim 1, wherein, The average length is over 5μm.

3. The nickel nanowire according to claim 1 or 2, wherein, The saturation magnetic susceptibility is above 20 emu / g.

4. The nickel nanowire according to claim 1 or 2, wherein, The crystallite size in the direction of the (111) lattice plane is 1 to 8 nm.

5. A dispersion comprising nickel nanowires according to any one of claims 1 to 4.

6. A molded body comprising nickel nanowires according to any one of claims 1 to 4.

7. A method for manufacturing nickel nanowires, comprising reducing two or more nickel salts in a reaction solution while applying a magnetic field to obtain nickel nanowires as described in any one of claims 1 to 4.

8. The method for manufacturing nickel nanowires according to claim 7, wherein, The two or more nickel salts include nickel chloride and nickel sulfate. The ratio of nickel chloride to the total of nickel chloride and nickel sulfate is 70–98 mol.

9. The method for manufacturing nickel nanowires according to claim 7, wherein, The two or more nickel salts include nickel chloride and nickel acetate. The ratio of nickel chloride to the total of nickel chloride and nickel acetate is 70–98 mol.

10. The method for manufacturing nickel nanowires according to claim 7, wherein, The two or more nickel salts include nickel acetate and nickel sulfate. The ratio of nickel acetate to the total of nickel acetate and nickel sulfate is 70–98 mol.

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