Nickel slurry

Abstract

To provide a nickel slurry that has a low environmental impact and excellent crushing properties. [Solution] The solution contains nickel powder, quaternary ammonium hydroxide, and a solvent containing water, and the absolute value of the zeta potential measured is 2mV or more.

Description

[Technical Field]

[0001] This disclosure relates to a nickel slurry consisting of an aqueous solvent used as a material for forming electrodes and wiring in electronic devices, and in particular as a material for forming internal electrodes in multilayer ceramic capacitors. [Background technology]

[0002] Slurries and pastes containing metal powders or ceramic powders have traditionally been used as materials for forming electrodes and wiring in many electronic devices such as semiconductor devices, solar cells, multilayer ceramic capacitors (MLCCs), and displays, particularly for forming the internal electrodes of multilayer ceramic capacitors. Electrodes and wiring in electronic devices are formed by pattern printing these slurries and pastes using methods such as screen printing, followed by firing.

[0003] Methods using slurries and pastes have advantages over vacuum process methods such as PVD (sputtering, vacuum deposition, etc.) and CVD, which require expensive vacuum equipment, including lower costs, the ability to handle non-planar shapes, and the ability to process large areas. However, because these slurries and pastes contain many organic components, methods using slurries and pastes inherently have environmental impact issues.

[0004] Specifically, for example, multilayer ceramic capacitors have a structure in which internal electrode layers and dielectric layers are alternately stacked, but currently they are obtained by the following manufacturing process. That is, a green sheet which will become the dielectric layer is formed from a ceramic dielectric slurry containing barium titanate powder as the ceramic powder, an internal electrode paste containing nickel powder as the metal powder is printed onto the obtained green sheet by a method such as screen printing, the green sheets printed with the internal electrode paste are alternately stacked and laminated, and the resulting laminate is heat-treated to form a laminated structure consisting of a sintered film of ceramic powder and metal powder.

[0005] Ceramic dielectric slurries and pastes for internal electrodes contain not only particulate components such as barium titanate powder and nickel powder, which are constituent materials of the dielectric layer and internal electrodes, but also large amounts of organic components such as resin binders, organic solvents, and dispersants, which are necessary to maintain a smooth and dense film structure from the printing process to the heat treatment process.

[0006] These organic components must ultimately be removed from the film structure, and current electronic device manufacturing processes incorporate steps to thermally decompose these organic components. Therefore, current electronic device manufacturing processes, including those for multilayer ceramic capacitors, require not only the cost of organic components contained in the slurry or paste, but also a significant amount of thermal energy for removing these organic components in addition to the thermal energy required for powder sintering. This presents a major challenge in reducing environmental impact in a society where carbon neutrality is increasingly demanded.

[0007] From the perspective of reducing environmental impact, the application of aqueous slurries and pastes containing metal powders and ceramic powders, with the use of organic components minimized as much as possible, is being considered.

[0008] However, the application of aqueous slurries and pastes presents challenges, particularly in the case of non-precious metal powders such as nickel powder. These challenges include degradation of particle components due to oxidation and leaching, and coarsening of particle components due to increased aggregation. Therefore, their realization is not easy. In particular, particles that have coarsened due to degradation of particle components become firmly bound together, making them extremely difficult to break down. Consequently, the application of aqueous slurries and pastes requires practical properties, such as the ability to easily break down aggregated particles during the process.

[0009] While it is possible to suppress the degradation and aggregation of particle components by applying a protective film to the particle surface with a large amount of organic components beforehand, this not only reduces the particle properties due to the replacement of constituent elements on the particle surface, but also necessitates a process to remove the large amount of organic components.

[0010] Investigations are also underway regarding aqueous slurries and pastes that can easily break down aggregated particles during the process. For example, Japanese Patent Publication No. 2006-028320 discloses an aqueous electrode ink in which metal powder such as nickel powder is contained in an amount of 25% to 40% by weight relative to the total weight of the aqueous electrode ink, at least two water-soluble resins with different average molecular weights selected from water-soluble resins are contained in an amount of 3 to 6 parts by weight per 100 parts by weight of metal powder, an aqueous plasticizer is contained in an amount of 1.5 to 1.9 times the weight of the water-soluble resins, and the remainder is water, wherein the average molecular weight of one water-soluble resin is 5,000 to 10,000 and the average molecular weight of the other water-soluble resin is 150,000 to 360,000.

[0011] Japanese Patent Publication No. 2006-210301 discloses a conductive ink comprising nickel powder having an average primary particle size of 100 nm or less dispersed in a dispersion medium mainly composed of water, alcohols, glycols, and saturated hydrocarbons having a boiling point of 300°C or less at atmospheric pressure, wherein the dispersion medium contains one or more metal salts or metal oxides selected from those containing Ti, V, Ni, Cu, Zn, Y, Nb, Mo, Ag, In, Sn, Ta, and W as film density improving agents for improving the film density of a conductor formed using the conductive ink.

[0012] Japanese Patent Publication No. 2002-317201 discloses an aqueous nickel slurry comprising water, nickel fine powder in which an insoluble inorganic oxide, which is an oxide or complex oxide containing silicon, aluminum, or zirconium, is fixed to the surface of individual nickel fine particles, polyacrylic acid, its ester or a salt thereof, and organic group-substituted ammonium hydroxide. [Prior art documents] [Patent Documents]

[0013] [Patent Document 1] Japanese Patent Publication No. 2006-028320 [Patent Document 2] Japanese Patent Publication No. 2006-210301 [Patent Document 3] Japanese Patent Publication No. 2002-317201 [Overview of the project] [Problems that the invention aims to solve]

[0014] Although Japanese Patent Publication No. 2006-028320 and Japanese Patent Publication No. 2006-210301 enable sufficient dispersion of particles such as nickel powder in an aqueous slurry, they have the problem that it is difficult to reduce the energy required to separate the particles from the dispersion aids because large amounts of resins, organic salts, inorganic salts, etc., must be used as dispersion aids.

[0015] On the other hand, Japanese Patent Publication No. 2002-317201 describes a method in which an insoluble inorganic oxide, rather than an organic component, is fixed to the surface of nickel powder particles. However, because the surface of the nickel powder particles is covered with an insoluble inorganic oxide, there is a problem in that the particle properties and applications are severely limited unless the oxide is decomposed and removed by heating or other means.

[0016] This disclosure aims to provide an environmentally friendly aqueous nickel slurry that can easily break down aggregated particles during the process without requiring a protective film to be applied to the particle surface with a large amount of organic components, without limiting particle properties and applications, and without using insoluble non-electrolytes that adhere to the particle surface. [Means for solving the problem]

[0017] The nickel slurry according to one aspect of the present disclosure contains nickel powder, quaternary ammonium hydroxide, and a solvent containing water, and is characterized in that the absolute value of the zeta potential is 2 mV or more in zeta potential measurement.

[0018] In the nickel slurry according to one aspect of the present disclosure, it is preferable that the quaternary ammonium hydroxide has 16 or less carbon atoms.

[0019] In this case, the quaternary ammonium hydroxide is preferably at least one selected from tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

[0020] In the nickel slurry according to one aspect of the present disclosure, it is preferable that the pH based on a liquid temperature of 25 °C is 8 or more.

[0021] In the nickel slurry according to one aspect of the present disclosure, it is preferable that the solvent contains an organic solvent having a relative permittivity of 20 or more.

[0022] In this case, the organic solvent is preferably at least one selected from methanol, ethanol, and 1-propanol.

[0023] The nickel slurry according to one aspect of the present disclosure contains a polyelectrolyte, and it is preferable that the absolute value of the zeta potential is 15 mV or more.

[0024] In this case, the polyelectrolyte is preferably at least one selected from polydiallyldimethylammonium chloride, sodium polystyrene sulfonate, polyethyleneimine, sodium polyacrylate, and ammonium polyacrylate.

[0025] In the nickel slurry according to one aspect of the present disclosure, it is preferable that the number average particle diameter in terms of the equivalent circle diameter of the nickel powder is 10 nm or more and 250 nm or less.

[0026] In a nickel slurry according to one aspect of the present disclosure, the content of the nickel powder is preferably 0.5% by mass or more and 40% by mass or less, and more preferably 1% by mass or more and 20% by mass or less, based on the total amount of the nickel slurry. [Effects of the Invention]

[0027] Nickel slurry according to one aspect of this disclosure has a low environmental impact, excellent pulverizability, and can be applied to the manufacturing process of electronic devices such as multilayer ceramic capacitors, in line with a carbon-neutral society. [Modes for carrying out the invention]

[0028] The inventors of this disclosure diligently studied means for realizing an easily cleavable aqueous nickel slurry without using insoluble non-electrolytes that adhere to the particle surface. They found that including a quaternary ammonium hydroxide in the aqueous nickel slurry is effective, and thus completed this disclosure.

[0029] A nickel slurry according to one aspect of the present disclosure comprises nickel powder, a quaternary ammonium hydroxide, and a solvent containing water, and is characterized in that the absolute value of the zeta potential measured is 2 mV or more.

[0030] The components and characteristics of a nickel slurry relating to one aspect of this disclosure will be described below.

[0031] (1) Nickel powder Nickel powder is used as an internal electrode in multilayer ceramic capacitors (MLCCs), among other applications.

[0032] While precious metals such as platinum, palladium, and silver-palladium can be used as metal materials for internal electrodes, nickel, a non-precious metal, is being used as a substitute for these precious metal materials from the standpoint of cost reduction. When non-precious metal powders such as nickel powder are applied to aqueous slurries, it is more difficult to suppress the deterioration and aggregation of particle components due to oxidation and elution, making the nickel slurry used in this example advantageous.

[0033] Furthermore, with the increasing miniaturization of electronic devices such as multilayer ceramic capacitors, there is a demand for thinner ceramic dielectric layers and internal electrode layers.

[0034] Therefore, in the nickel slurry of this example, the number-average particle size of the nickel powder contained in the nickel slurry in terms of the equivalent circular diameter is preferably 10 nm or more and 250 nm or less, and more preferably 20 nm or more and 100 nm or less.

[0035] If the number-average particle diameter at the equivalent circle diameter is less than 10 nm, problems such as powder re-aggregation may occur. On the other hand, if the number-average particle diameter at the equivalent circle diameter exceeds 250 nm, problems such as difficulty in achieving uniform thickness may occur when forming internal electrodes using nickel slurry or conductive paste containing said nickel slurry.

[0036] The number-average particle diameter in terms of the equivalent circle diameter is obtained by selecting 100 observable primary nickel powder particles arbitrarily using image analysis of observation images captured with a scanning electron microscope (SEM), measuring their equivalent circle diameters (diameters of circles with equal area), and calculating the number-average value.

[0037] The nickel powder content in the nickel slurry in this example can be any amount depending on the intended use of the nickel slurry. For example, the nickel powder content is not limited to this, but can be within a concentration range that can be crushed by a crusher. More specifically, the nickel powder content is preferably 0.5% by mass or more and 40% by mass or less, and more preferably 1% by mass or more and 20% by mass or less, relative to the total amount of nickel slurry.

[0038] The nickel powder applicable to the nickel paste in this example is not particularly limited, and any nickel powder can be used. For example, it may be either an experimentally synthesized product or a commercially available product.

[0039] For example, nickel powder can be produced by known granulation methods using reactions in the liquid or gas phase. Examples of granulation methods using reactions in the gas phase include the CVD method, the evaporative quenching method, and the hydrogen reduction method using nickel salts or nickel hydroxide. Examples of granulation methods using reactions in the liquid phase include the electroless reduction method, in which nickel powder is deposited in a nickel salt solution using a reducing agent such as hydrazine, and the electrolytic reduction method, in which nickel powder is deposited by placing electrodes in an aqueous nickel salt solution and passing an electric current between the electrodes.

[0040] Furthermore, the particle size of the nickel powder can be appropriately controlled by known methods depending on the granulation method.

[0041] (2) Quaternary ammonium hydroxide The nickel slurry of this disclosure contains a quaternary ammonium hydroxide. Quaternary ammonium hydroxide has the general formula: [R 1 , R 2 , R 3 , R 4 N + ][OH - It has the composition represented by [ ]. In the general formula, R represents an alkyl group.

[0042] Quaternary ammonium hydroxide almost completely ionizes in an aqueous solution to simultaneously generate hydroxide ions and ammonium ions. The hydroxide ions make the pH of the aqueous solution alkaline, that is, the pH becomes 7 or higher, and it becomes possible to suppress the progress of aggregation due to the elution of nickel in an acidic atmosphere. Furthermore, the quaternary ammonium ions charged between the particles constituting the nickel powder intervene, so that the aggregability of the nickel powder is alleviated, and its disintegration treatment can be facilitated.

[0043] In order to effectively exhibit such an effect, it is preferable that it has a high degree of dissociation in an aqueous solution and at the same time the length of the alkyl group is such that the action of the positive charge of the nitrogen atom is not inhibited by steric hindrance.

[0044] From this point of view, the quaternary ammonium hydroxide preferably has 16 or less carbon atoms. When the carbon number is in the range of 4 or more and 16 or less, due to the synergistic effect of forming an alkaline environment in an aqueous solution and the interposition of charged quaternary ammonium ions between particles, the aggregability of nickel particles in the nickel slurry is significantly alleviated. Therefore, even if the addition amount of quaternary ammonium hydroxide with respect to the total amount of the solvent is very small, it becomes possible to provide an aqueous nickel slurry that is easily disintegratable.

[0045] General formula representing quaternary ammonium hydroxide: [R 1 , R 2 , R 3 , R 4 [[ID=XX]]N + [OH - In this formula, R 1 , R 2 , R 3 , R 4 are each preferably an alkyl group having 1 or more and 4 or less carbon atoms, and are preferably composed of alkyl groups that are the same or different from each other.

[0046] Examples of quaternary ammonium hydroxides with such a structure include tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, trimethylethylammonium hydroxide, trimethylpropylammonium hydroxide, dimethyldipropylammonium hydroxide, monomethyltriethylammonium hydroxide, and monomethyltripropylammonium hydroxide. These quaternary ammonium hydroxides may be used individually or in combination of two or more.

[0047] For reasons unknown, among these, those in which the charge is easily distributed isotropically when ionized in a solvent are preferred. More specifically, the quaternary ammonium hydroxide is preferably at least one selected from tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

[0048] In this example, the amount of quaternary ammonium hydroxide in the nickel slurry is restricted to an amount that can set the absolute value of the zeta potential to 2 mV or higher, preferably an amount that can set the absolute value of the zeta potential to 2 mV or higher and the pH to 8 or higher based on a liquid temperature of 25°C.

[0049] In other words, when producing the nickel slurry in this example, a quaternary ammonium hydroxide is added to a solvent containing water until the absolute value of the zeta potential is 2 mV or more, preferably until the absolute value of the zeta potential is 2 mV or more and the pH is 8 or more.

[0050] Specifically, although it varies depending on factors such as the amount of carbon dioxide dissolved in the solvent from the atmosphere, the concentration of quaternary ammonium hydroxide in nickel slurry is approximately several tens of millimol / L.

[0051] (3) pH The nickel slurry in this example contains quaternary ammonium hydroxide, and therefore its pH is 7 or higher at a liquid temperature of 25°C.

[0052] The pH of the nickel slurry at a liquid temperature of 25°C is preferably 8 or higher. If the pH is below 8, the nickel powder will oxidize and dissolve due to acidification by dissolved carbon dioxide in the water and reaction with dissolved oxygen, and aggregation will progress more easily. The aggregated and coarse particles, accompanied by degradation of the particulate components, will bind together firmly, making it difficult to break them up. However, depending on the application and storage period of the nickel slurry, the pH of the nickel slurry at a liquid temperature of 25°C can be 8 or lower.

[0053] While there is no particular upper limit to the pH of nickel slurry at a liquid temperature of 25°C, a pH above 13 is undesirable because it may increase the measurement error (alkalinity error) when using a pH meter with a typical glass electrode.

[0054] (4) Solvent The solvent used in the nickel slurry in this example is an aqueous solution of water mixed with a quaternary ammonium hydroxide. For the quaternary ammonium hydroxide to dissociate sufficiently, the solvent must be a polar solvent with a remarkably high dielectric constant, such as water.

[0055] In the nickel slurry of this example, the solvent may include an organic solvent with a relative permittivity of 20 or higher. That is, from the viewpoint of not excessively inhibiting the ionization of electrolytes in aqueous solution, a mixed solution containing an organic solvent with lower polarity than water can be used as the solvent. However, in order for the solvent to retain the properties of water, it is preferable to use an organic solvent whose volume ratio to the total solvent is less than 50% and which has a relative permittivity of 20 or higher.

[0056] Examples of organic solvents with a relative permittivity of 20 or higher include methanol, ethanol, and 1-propanol. These organic solvents may be used individually or in combination of two or more.

[0057] (5)Polymer electrolyte The nickel slurry in this example may contain a polymer electrolyte. By adding a polymer electrolyte that is highly dissociable in aqueous solution and carries a positive or negative charge, the coagulation relaxation effect due to interparticle mediation can be enhanced together with the charged quaternary ammonium ions, thereby further improving the ease of disintegration of the nickel slurry.

[0058] Examples of polymer electrolytes include polydiallyldimethylammonium chloride, sodium polystyrene sulfonate, polyethyleneimine, sodium polyacrylate, and ammonium polyacrylate. These polymer electrolytes may be used individually or in combination of two or more types.

[0059] The amount of polymer electrolyte added is preferably in the range of 0.01% to 10% by mass relative to the nickel powder, and more preferably 0.1% to 5% by mass.

[0060] Furthermore, inorganic bases such as sodium hydroxide may promote aggregation by increasing the ionic strength of the aqueous solution simply by making the pH alkaline; therefore, it is preferable that the nickel slurry in this example does not contain inorganic bases.

[0061] (6) Absolute value of the zeta potential In this example, the nickel slurry has an absolute value of 2mV or higher in zeta potential measurement. The zeta potential is the potential of the slip surface where liquid flow begins to occur in the electric double layer formed around particles in an aqueous solution. When the zeta potential approaches zero, the repulsive force between particles weakens and the particles aggregate. In other words, if the interparticle mediation of quaternary ammonium hydroxide is normal, the absolute value of the zeta potential of the nickel slurry will be 2mV or higher, and if it is less than 2mV, there is a possibility that the interparticle mediation of quaternary ammonium hydroxide is not being performed normally.

[0062] In this example, if the nickel slurry contains a polymer electrolyte, the interparticle interaction of the polymer electrolyte also contributes to making it possible to achieve an absolute value of 15 mV or higher for the zeta potential.

[0063] The zeta potential can be measured using any known method, such as electrophoresis, electroacoustics, or colloidal vibrational current spectroscopy.

[0064] (7) Decomposition In the nickel slurry of this example, known methods can be used to crush the nickel powder. Examples of crushing methods include ultrasonic homogenizers, ball mills, bead mills, automatic mortars, and thin-film swirling high-speed mixers.

[0065] (8) Applications of nickel slurry The nickel slurry in this example can be used in the same way as slurry and paste materials for electronic materials.

[0066] When manufacturing a conductive paste using the nickel slurry in this example, the nickel powder in the nickel slurry is crushed by any method, and then a binder such as cellulose resin (ethylcellulose, nitrocellulose, etc.), acrylic resin, or phenolic resin is added to form a paste.

[0067] The nickel slurry of this example and the nickel paste manufactured using this nickel slurry can be used, for example, as internal electrode material for multilayer ceramic capacitors, electrode material for electronic devices including multilayer ceramic capacitors, wiring formation material, printed circuit boards, internal wiring for semiconductors, and bonding between printed circuit boards and electronic components.

[0068] In these applications, known methods can be used to apply the nickel slurry of this example and the nickel paste produced using this nickel slurry to various substrates. Such application methods include, for example, gravure printing, screen printing, spray coating, spin coating, dip coating, bar coating, knife coating, offset printing, flexographic printing, inkjet printing, and dispenser printing. Of these, dip coating or spin coating is preferred from the viewpoint of efficiently forming a coated film. [Examples]

[0069] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0070] First, the evaluation methods used in this embodiment and comparative example will be described.

[0071] (1) Method for measuring the number-average particle size The "number-average particle diameter" was obtained by performing image analysis using observation images captured with a scanning electron microscope (SEM (JEOL Ltd., model: JSM-7200F)), arbitrarily selecting 100 observable primary nickel powder particles, measuring their equivalent circle diameters (diameters of circles with equal area), and calculating the number-average value.

[0072] (2) Method for measuring zeta potential The "zeta potential" was measured using an electroacoustic zeta potential meter (Colloidal Dynamics LLC, model: ZetaProbe) while stirring the slurry at 250 rpm.

[0073] (3) Method for evaluating disintegration ability The nickel powder in the nickel slurry was crushed using a thin-film swirling high-speed mixer (Primix Corporation, model: Filmix 30-L) at a rotation speed of 22,000 rpm for 5 minutes.

[0074] Ten mL of the slurry after crushing was filtered through a membrane filter with a pore size of 0.5 μm or 1.0 μm (both manufactured by Merck KGaA). Undisintegrated particles larger than the pore size of each membrane filter were captured on the filter, and the amount of these undisintegrated particles was calculated by ICP emission spectrometry (inductively coupled plasma emission spectrometry) of a solution containing all of the undisintegrated particles dissolved in acid.

[0075] For a 1.0 μm pore size filter, if the content of undisintegrated particles in the nickel slurry was less than 100 ppm, the disintegration performance was judged to be good. For both 1.0 μm and 0.5 μm pore size filters, if the content of undisintegrated particles in the nickel slurry was less than 100 ppm, the disintegration performance was judged to be excellent. For both 1.0 μm and 0.5 μm pore size filters, if the content of undisintegrated particles in the nickel slurry was 100 ppm or more, the disintegration performance was judged to be poor.

[0076] [Example 1] A nickel slurry was prepared containing water as the solvent and tetraethylammonium hydroxide, which has eight carbon atoms, as the quaternary ammonium hydroxide.

[0077] (1) Preparation of nickel powder 405 g of nickel chloride hexahydrate (NiCl2·6H2O) as a nickel source, 1.271 g of L-methionine (CH3SC2H4CH(NH2)COOH) and 1.024 g of ethylenediamine (H2NC2H4NH2) as stabilizers, 40.0 mg of palladium(II) ammonium chloride (also known as tetrachloropalladium(II)ate) ((NH4)2PdCl4) as a nucleating agent, and 230 g of sodium hydroxide (NaOH) as a pH adjuster were added to 2570 g of distilled water and stirred to prepare a 3 L reaction aqueous solution. The pH of the prepared reaction aqueous solution was measured at a liquid temperature of 25°C using a pH meter (Horiba, Ltd., model: LAQUAact D-73), and the pH was found to be approximately 13.

[0078] Next, 207 g of commercially available industrial-grade 60% by mass hydrated hydrazine (manufactured by MGC Otsuka Chemical Co., Ltd.) was gradually added to the above reaction aqueous solution as a reducing agent. The reaction aqueous solution was then heated to a bath temperature of 85°C while stirring, and the electroless reduction reaction was continued for 60 minutes. As a result, nickel powder precipitated in the solution.

[0079] The nickel powder precipitated in the reaction aqueous solution was washed by decantation with distilled water, and then dried under reduced pressure to obtain 100 g of nickel powder.

[0080] When the obtained nickel powder was observed using a scanning electron microscope (SEM), the particle shape was found to be approximately spherical. Image analysis of the observed image revealed that the number mean of the equivalent circle diameter was 60 nm.

[0081] (2) Preparation of nickel slurry A 10% by mass nickel slurry was prepared by adding tetraethylammonium hydroxide to water used as a solvent until the pH reached 12, while measuring the pH at a liquid temperature of 25°C using a pH meter. 12.6 g of this aqueous solution was then mixed with 1.4 g of roughly spherical nickel powder obtained in the nickel powder preparation process. The mixture was then subjected to crushing treatment using a thin-film swirling high-speed mixer (Primix Corporation, Filmix 30-L model) to prepare a 10% by mass nickel slurry. The amount of tetraethylammonium hydroxide added to the water was 17 mmol / L. The amount of slurry required for evaluation was repeatedly prepared using the above procedure.

[0082] (3) Evaluation (a) Zeta potential measurement of nickel slurry The zeta potential of the nickel slurry obtained during the nickel slurry preparation process was analyzed using an electroacoustic zeta potential meter and found to be -2.0 mV.

[0083] (b) Evaluation of the disintegration properties of nickel slurry using a 1.0 μm pore size filter Analysis of the disintegration properties of the nickel slurry, obtained by filtering through a membrane filter with a pore size of 1.0 μm, revealed that the content of undisintegrated particles was less than 100 ppm.

[0084] (c) Evaluation of the disintegration properties of nickel slurry using a 0.5 μm pore size filter Analysis of the disintegration properties of the nickel slurry, obtained by filtering through a 0.5 μm pore size membrane filter, revealed that the content of undisintegrated particles was 100 ppm or more.

[0085] Table 1 shows the preparation conditions for the nickel slurry, and Table 2 shows the evaluation results of the obtained nickel slurry. The same applies to Examples 2-11 and Comparative Examples 1-5.

[0086] [Example 2] Nickel powder was prepared in the same manner as in Example 1, except that the amount of 0.134 mg of ammonium palladium(II) chloride added as a nucleating agent in the nickel powder preparation process was used. The number average value of the equivalent circle diameter of the obtained nickel powder was 250 nm.

[0087] A nickel slurry was prepared in the same manner as in Example 1, except that tetrabutylammonium hydroxide, which has 16 carbon atoms, was added as a quaternary ammonium hydroxide during the preparation of the nickel slurry. The amount of tetrabutylammonium hydroxide added to water was 17 mmol / L.

[0088] The zeta potential of the nickel slurry was -2.4 mV. Analysis after filtration with a 1.0 μm pore size filter showed that the content of undisintegrated particles in the nickel slurry was less than 100 ppm, while analysis after filtration with a 0.5 μm pore size filter showed that the content of undisintegrated particles in the nickel slurry was 100 ppm or more.

[0089] [Example 3] Nickel powder was prepared in the same manner as in Example 1, except that the amount of palladium(II) ammonium chloride added as a nucleating agent in the nickel powder preparation process was 5.3 mg. The number average value of the equivalent circle diameter of the obtained nickel powder was 100 nm.

[0090] In the nickel slurry preparation process, water and 1-propanol were mixed as solvents in a volume ratio of 9:1, and then tetrapropylammonium hydroxide, a quaternary ammonium compound with 12 carbon atoms, was added until the pH reached 8. The nickel slurry was prepared in the same manner as in Example 1, except that the amount of tetrapropylammonium hydroxide added relative to the water was 0.1 mmol / L.

[0091] The zeta potential of the nickel slurry was -4.5 mV. Analysis after filtration with a 1.0 μm pore size filter showed that the content of undisintegrated particles in the nickel slurry was less than 100 ppm, while analysis after filtration with a 0.5 μm pore size filter showed that the content of undisintegrated particles in the nickel slurry was 100 ppm or more.

[0092] [Example 4] Five g of nickel powder was prepared in the same manner as in Example 1, except that 20.2 g of nickel chloride hexahydrate was used as the nickel source, 5.084 g of L-methionine and 1.024 g of ethylenediamine were used as stabilizers, and 53.4 mg of palladium(II) ammonium chloride was used as a nucleating agent. The number average value of the equivalent circle diameter of the obtained nickel powder was 10 nm.

[0093] In the nickel slurry preparation process, water and methanol were mixed as solvents in a volume ratio of 6:4, and then tetramethylammonium hydroxide, a quaternary ammonium compound with 4 carbon atoms, was added until the pH reached 13. The nickel slurry was prepared in the same manner as in Example 1, except that the solvent was mixed with tetramethylammonium hydroxide in a volume ratio of 6:4. The amount of tetramethylammonium hydroxide added relative to the water was 90 mmol / L.

[0094] The zeta potential of the nickel slurry was -5.4 mV. Analysis after filtration with a 1.0 μm pore size filter showed that the content of undisintegrated particles in the nickel slurry was less than 100 ppm, while analysis after filtration with a 0.5 μm pore size filter showed that the content of undisintegrated particles in the nickel slurry was 100 ppm or more.

[0095] [Example 5] In each nickel slurry preparation step, the nickel slurry was prepared in the same manner as in Example 1, except that 0.05 g of polydiallyldimethylammonium chloride (molecular weight 8500) was added to the aqueous solution as a polymer electrolyte.

[0096] The zeta potential of the nickel slurry was +22.8 mV. Furthermore, analysis after filtration with a 1.0 μm pore size filter and a 0.5 μm pore size filter revealed that the content of undissolved particles was less than 100 ppm in both cases.

[0097] [Example 6] In each nickel slurry preparation step, the nickel slurry was prepared in the same manner as in Example 1, except that 0.05 g of sodium polystyrene sulfonate (molecular weight 10000) was added to the aqueous solution as a polymer electrolyte.

[0098] The zeta potential of the nickel slurry was -30.2 mV. Furthermore, analysis after filtration with a 1.0 μm pore size filter and a 0.5 μm pore size filter revealed that the content of undissolved particles was less than 100 ppm in both cases.

[0099] [Example 7] In the preparation of each nickel slurry, water and ethanol used as solvents were mixed in a volume ratio of 8:2, then tetraethylammonium hydroxide was added, and 0.05 g of polyethyleneimine (molecular weight 1200) was added to the aqueous solution as a polymer electrolyte. Otherwise, the nickel slurry was prepared in the same manner as in Example 1.

[0100] The zeta potential of the nickel slurry was +15.0 mV. Furthermore, analysis after filtration with a 1.0 μm pore size filter and a 0.5 μm pore size filter revealed that the content of undissolved particles was less than 100 ppm in both cases.

[0101] [Example 8] In each nickel slurry preparation step, the nickel slurry was prepared in the same manner as in Example 1, except that 0.05 g of sodium polyacrylate (molecular weight 3500) was added to the aqueous solution as a polymer electrolyte.

[0102] The zeta potential of the nickel slurry was -46.3 mV. Furthermore, analysis after filtration with a 1.0 μm pore size filter and a 0.5 μm pore size filter revealed that the content of undissolved particles was less than 100 ppm in both cases.

[0103] [Example 9] In each nickel slurry preparation step, the nickel slurry was prepared in the same manner as in Example 1, except that 0.05 g of ammonium polyacrylate (molecular weight 6000) was added to the aqueous solution as a polymer electrolyte.

[0104] The zeta potential of the nickel slurry was -47.4 mV. Furthermore, analysis after filtration with a 1.0 μm pore size filter and a 0.5 μm pore size filter revealed that the content of undissolved particles was less than 100 ppm in both cases.

[0105] [Example 10] In the preparation of each nickel slurry, 14.85 g of an aqueous solution prepared by adding tetraethylammonium hydroxide to water used as the solvent until the pH reached 12 was mixed with 0.15 g of the roughly spherical nickel powder obtained in the nickel powder preparation step, and then subjected to crushing treatment using a thin-film swirling high-speed mixer to prepare a 1% by mass nickel slurry. The nickel slurry was prepared in the same manner as in Example 1. The amount of tetraethylammonium hydroxide added to the water was 17 mmol / L.

[0106] The zeta potential of the nickel slurry was -2.1 mV. Analysis after filtration with a 1.0 μm pore size filter showed that the content of undisintegrated particles in the nickel slurry was less than 100 ppm, while analysis after filtration with a 0.5 μm pore size filter showed that the content of undisintegrated particles in the nickel slurry was 100 ppm or more.

[0107] [Example 11] In the preparation of each nickel slurry, 12 g of an aqueous solution was prepared by adding tetraethylammonium hydroxide to water used as the solvent until the pH reached 12. This aqueous solution was then mixed with 3 g of the roughly spherical nickel powder obtained in the nickel powder preparation step, and the mixture was subjected to crushing treatment using a thin-film swirling high-speed mixer to prepare a 20% by mass nickel slurry. The nickel slurry was prepared in the same manner as in Example 1, except that in the preparation step of each nickel slurry, 12 g of an aqueous solution was prepared by adding tetraethylammonium hydroxide to water until the pH reached 12. The amount of tetraethylammonium hydroxide added to the water was 17 mmol / L.

[0108] The zeta potential of the nickel slurry was -2.1 mV. Analysis after filtration with a 1.0 μm pore size filter showed that the content of undisintegrated particles in the nickel slurry was less than 100 ppm, while analysis after filtration with a 0.5 μm pore size filter showed that the content of undisintegrated particles in the nickel slurry was 100 ppm or more.

[0109] [Comparative Example 1] A nickel slurry was prepared in the same manner as in Example 1, except that, in the nickel slurry preparation step, only water was used as the solvent, without adding a quaternary ammonium hydroxide.

[0110] The zeta potential of the nickel slurry was +1.0 mV. Furthermore, analysis after filtration with a 1.0 μm pore size filter and a 0.5 μm pore size filter revealed that the content of undissolved particles was 100 ppm or more in both cases.

[0111] [Comparative Example 2] A nickel slurry was prepared in the same manner as in Comparative Example 1, except that an aqueous solution of water with sodium hydroxide added to adjust the pH to 12 was used as the solvent in the nickel slurry preparation process.

[0112] The zeta potential of the nickel slurry was -1.5 mV. Furthermore, analysis after filtration with a 1.0 μm pore size filter and a 0.5 μm pore size filter revealed that the content of undissolved particles was 100 ppm or more in both cases.

[0113] [Comparative Example 3] In the nickel slurry preparation process, a nickel slurry was prepared in the same manner as in Example 2, except that trioctylmethylammonium chloride, a quaternary ammonium compound but not a quaternary ammonium hydroxide, with 25 carbon atoms, was added to water at a concentration of 17 mmol / L without pH adjustment.

[0114] The zeta potential of the nickel slurry was +1.8 mV. Furthermore, analysis after filtration with a 1.0 μm pore size filter and a 0.5 μm pore size filter revealed that the content of undissolved particles was 100 ppm or more in both cases.

[0115] [Comparative Example 4] A nickel slurry was prepared in the same manner as in Example 3, except that quaternary ammonium hydroxide was not added during the nickel slurry preparation process.

[0116] The zeta potential of the nickel slurry was +1.2 mV. Furthermore, analysis after filtration with a 1.0 μm pore size filter and a 0.5 μm pore size filter revealed that the content of undissolved particles was 100 ppm or more in both cases.

[0117] [Comparative Example 5] A nickel slurry was prepared in the same manner as in Example 4, except that quaternary ammonium hydroxide was not added during the nickel slurry preparation process.

[0118] The zeta potential of the nickel slurry was +0.7 mV. Furthermore, analysis after filtration with a 1.0 μm pore size filter and a 0.5 μm pore size filter revealed that the content of undissolved particles was 100 ppm or more in both cases.

[0119] [Table 1]

[0120] [Table 2]

[0121] [Discussion on the evaluation results] Table 2 shows that the examples satisfying the composition of the nickel slurry according to one aspect of this disclosure exhibit superior disintegration properties compared to the comparative examples. The reason why the examples, despite being aqueous nickel slurries, exhibit such excellent disintegration properties is understood from the comparison between Examples 1, 3, and 4 and Comparative Examples 1, 4, and 5. This is thought to be because the synergistic effect of the formation of an alkaline environment in the aqueous solution of quaternary ammonium hydroxide and the interparticle interposition of charged quaternary ammonium ions significantly reduces the aggregation of nickel particles in the nickel slurry, resulting in an easily disintegrable aqueous nickel slurry.

[0122] It is understood that the effects of this disclosure cannot be obtained when simply making the pH alkaline with a typical inorganic salt, as in Comparative Example 2, or when the quaternary ammonium compound has 25 carbon atoms and does not contain a hydroxide, as in Comparative Example 3.

Claims

1. A nickel slurry comprising nickel powder, quaternary ammonium hydroxide, and a solvent containing water, wherein the absolute value of the zeta potential measured is 2 mV or greater.

2. The nickel slurry according to claim 1, wherein the quaternary ammonium hydroxide has 16 or fewer carbon atoms.

3. The nickel slurry according to claim 2, wherein the quaternary ammonium hydroxide is at least one selected from tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide.

4. The nickel slurry according to claim 1, wherein the pH is 8 or higher based on a liquid temperature of 25°C.

5. The nickel slurry according to claim 1, wherein the solvent comprises an organic solvent with a relative dielectric constant of 20 or more.

6. The nickel slurry according to claim 5, wherein the organic solvent is at least one selected from methanol, ethanol, and 1-propanol.

7. The nickel slurry according to claim 1, comprising a polymer electrolyte, wherein the absolute value of the zeta potential is 15 mV or more.

8. The nickel slurry according to claim 7, wherein the polymer electrolyte is at least one selected from polydiallyldimethylammonium chloride, sodium polystyrene sulfonate, polyethyleneimine, sodium polyacrylate, and ammonium polyacrylate.

9. The nickel slurry according to claim 1, wherein the number-average particle diameter of the nickel powder in the equivalent circular diameter is 10 nm or more and 250 nm or less.

10. The nickel slurry according to claim 1, wherein the content of the nickel powder is 0.5% by mass or more and 40% by mass or less with respect to the total amount of the nickel slurry.

Images