WO2017122689A1

WO2017122689A1 - Nickel powder

Info

Publication number: WO2017122689A1
Application number: PCT/JP2017/000660
Authority: WO
Inventors: 雅人大栗; 浅井　剛; 貢吉田
Original assignee: 東邦チタニウム株式会社
Priority date: 2016-01-12
Filing date: 2017-01-11
Publication date: 2017-07-20
Also published as: CN108430673B; KR20180101504A; JP6876001B2; TWI716526B; CN108430673A; JPWO2017122689A1; KR102589697B1; TW201736617A

Abstract

[Problem] To provide a nickel powder suitable for use in electroconductive pastes which exhibits excellent sintering behavior and dispersibility and, as a result, can prevent delamination. [Solution] The nickel powder has a coating film comprising nickel oxide and nickel hydroxide and has an average particle diameter of 250 nm or smaller. In analysis by X-ray photoelectron spectroscopy (XPS) for the chemically bonded states of the nickel contained in the surface layer of the nickel powder, the areal proportion of the peak assigned to nickel/oxygen bonding to the whole Ni2p3/2 spectrum is 55.0-80.0%, the areal proportion of the peak assigned to nickel metal to the whole Ni2p3/2 spectrum is 5.0-15.0%, and the areal proportion of the peak assigned to nickel/hydroxy group bonding to the whole Ni2p_3/2 spectrum is 5.0-40.0%. The coating film has an average thickness of 3.0-5.0 nm.

Description

Nickel powder

The present invention relates to a nickel powder suitable for use in a conductive paste, and more particularly to a nickel powder excellent in sintering characteristics and dispersibility used for an internal electrode of a multilayer ceramic capacitor.

Conventionally, noble metal powders such as silver, palladium, platinum, and gold, or base metal powders such as nickel, cobalt, iron, molybdenum, and tungsten are used as conductive pastes for electronic materials, particularly for internal electrodes of multilayer ceramic capacitors. . In general, in a multilayer ceramic capacitor, dielectric ceramic layers and metal layers used as internal electrodes are alternately stacked, and external electrodes connected to the metal layers of the internal electrodes are connected to both ends of the dielectric ceramic layers. It has a configuration. Here, as a material constituting the dielectric, a material mainly composed of a material having a high dielectric constant such as barium titanate, strontium titanate, yttrium oxide or the like is used. On the other hand, as the metal constituting the internal electrode, the above-mentioned noble metal powder or base metal powder is used, but recently, a cheaper electronic material is required, so the development of a multilayer ceramic capacitor using the latter base metal powder has been developed. In particular, metallic nickel powder is typical.

Incidentally, a multilayer ceramic capacitor using metallic nickel powder as an internal electrode is generally manufactured by the following method. That is, a dielectric powder such as barium titanate is mixed and suspended with an organic binder, and this is formed into a sheet by a doctor blade method to produce a dielectric green sheet. On the other hand, metallic nickel powder for internal electrodes is mixed with an organic compound such as an organic solvent, a plasticizer, and an organic binder to form a metallic nickel powder paste, which is printed on the green sheet by a screen printing method. Next, after drying, laminating and pressure bonding, removing organic components by heat treatment, the temperature is further raised in a reducing atmosphere of hydrogen gas and baked at a temperature of 1000 to 1300 ° C. or higher. External electrodes are baked on both ends of the body ceramic layer to obtain a multilayer ceramic capacitor.

In the method for manufacturing a multilayer ceramic capacitor as described above, a heat treatment in which a metal paste is printed on a dielectric green sheet, laminated and pressure-bonded, and then an organic component is removed by heat treatment is usually performed in the atmosphere at 250 to 400. Done at ℃. Since the heat treatment is performed in the oxidizing atmosphere in this manner, the metallic nickel powder is oxidized, thereby causing volume expansion. At the same time, the metallic nickel powder begins to sinter and volume shrinkage begins to occur.

Thus, in the process of manufacturing a multilayer ceramic capacitor, a volume change due to expansion / contraction occurs in the metallic nickel powder by a redox / sintering reaction from a low temperature region around 300 ° C. At this time, if the oxidation behavior or sintering behavior of the metallic nickel powder is unstable at a low temperature stage, the dielectric layer and the electrode layer are likely to be distorted, resulting in the destruction of the layered structure called cracking or delamination. There was a problem of getting up.

Various methods have been proposed as means for solving the above delamination problem. For example, Patent Document 1 discloses a metallic nickel powder having a tap density with respect to a specific particle size having a certain limit value or more. By using such a metallic nickel powder, a nickel powder dispersed in a paste and a dielectric are used. It is described that delamination hardly occurs when the capacitor is baked.

However, although Patent Document 1 has a certain effect for improving the sintering behavior, it is not always sufficient as a method for preventing delamination, and further improvement has been desired.

Patent Document 2, Patent Document 3, and Patent Document 4 disclose nickel powder that can prevent delamination. Specifically, it is a nickel powder obtained by heat treatment in an oxidizing atmosphere at 200 to 400 ° C. and a heat treatment time of 1 minute to 10 hours.

However, in this method, rapid oxidation occurs at a particle size smaller than 250 nm, the oxygen content increases, and the aggregation of nickel powder increases. For this reason, when firing in a reducing atmosphere, gas generation and volume change due to reduction of the nickel powder oxide become large, so that a dense electrode film cannot be obtained, and problems such as cracking and delamination of laminated electronic components The agglomerated nickel powder results in insufficient mixing with the co-material and causes delamination.

JP-A-8-246001 JP 2000-0500001 A Japanese Patent Laid-Open No. 2000-045002 International Publication No. WO2004 / 020128

Therefore, in view of the above-mentioned problems of the prior art, the present invention exhibits excellent sintering behavior and dispersibility in nickel powder having an average particle size of 250 nm or less used in the production process of a multilayer ceramic capacitor, resulting in delamination. An object of the present invention is to provide a nickel powder suitable for a conductive paste that can be prevented. More specifically, the volume change or weight change due to the oxidation-reduction reaction is small during the heat treatment, and the sintering start temperature is higher than that of the conventional nickel powder, so that the dielectric used for manufacturing the multilayer ceramic capacitor is used. The object is to provide a nickel powder for a conductive paste that is closer to the sintering start temperature of the body and, as a result, can prevent delamination.

As described above, in the process of manufacturing the multilayer ceramic capacitor, a volume change due to expansion / contraction occurs in the nickel powder due to the oxidation-reduction reaction, thereby causing delamination. Therefore, if a dense and thick oxide film is formed on the surface of the nickel powder, the progress of oxidation from the nickel powder surface to the inside is suppressed.

Therefore, as a result of intensive research on metallic nickel powders, the present inventors belonged to the binding state of nickel and oxygen in the analysis of the chemical bonding state of nickel on the surface layer of nickel powder by X-ray photoelectron spectroscopy (XPS). The sintering behavior varies depending on the area ratio of the peak to the entire Ni2p _3/2 spectral peak, and it has been found that metallic nickel powder produced by a specific method and having a specific oxide film has excellent sintering characteristics. The invention has been completed.

That is, the nickel powder of the present invention has a coating containing nickel oxide and nickel hydroxide, has an average particle size of 250 nm or less, and analyzes the chemical bonding state of nickel on the surface layer of the nickel powder by X-ray photoelectron spectroscopy (XPS). , The area ratio of the peak attributed to the bonding state of nickel and oxygen to the entire Ni2p _3/2 spectrum is 55.0 to 80.0%, and the area ratio of the peak of metallic nickel to the entire Ni2p _3/2 spectrum is 5. The area ratio of the peak attributed to the bonding state of nickel and hydroxyl group to 0 to 15.0% with respect to the entire Ni2p _3/2 spectrum is 5.0 to 40.0%, and the average thickness of the coating is 3 0.0 to 5.0 nm.

According to the nickel powder of the present invention, it is possible to provide a nickel powder suitable for a conductive paste that exhibits excellent sintering behavior and dispersibility, and as a result can prevent delamination.

It is a graph which shows the sintering behavior of the nickel powder obtained in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 of the present invention.

The number average particle diameter of the nickel powder of the present invention is 250 nm or less. Further, it is preferably 30 to 250 nm, more preferably fine particles in the range of 50 to 250 nm, and more preferably fine particles in the range of 140 to 250 nm. In addition, the average particle diameter of the nickel powder of the present invention was obtained by taking a photograph of the primary particles of the nickel powder with a scanning electron microscope and measuring the particle diameter of 500 or more particles using image analysis software from the photograph. The number average particle size is calculated from the particle size distribution of the obtained nickel powder. At this time, the particle diameter is the diameter of the smallest circle that encloses the particles.

Further, the ratio (d / D) of the number average particle diameter D and the specific surface area diameter d of the nickel powder of the present invention is preferably 0.7 or more. The specific surface area diameter of the present invention is calculated from the specific surface area of the nickel fine powder assuming that the particles are true spheres. If d / D is 0.7 or more, it is easy to obtain a good paste, the film density of the film obtained by applying the paste is improved, and good sinterability is obtained in the MLCC manufacturing process.

The specific surface area of the nickel powder by BET is preferably 2 to 30 m ² / g.

Furthermore, the particle shape of the nickel powder of the present invention is preferably spherical in order to improve the sintering characteristics and dispersibility. The spherical shape of the present invention means that the aspect ratio is 1.2 or less and the circularity coefficient is 0.675 or more. The aspect ratio is the ratio of the major axis to the minor axis of the smallest ellipse that encloses the particles. The circularity coefficient is a value defined by 4πS / (L × L), where S is the area of the smallest ellipse surrounding the particle and L is the circumference. Further, since the shape of the nickel powder is spherical, when the MLCC is processed into an internal electrode of the MLCC, the filling rate is increased and the flatness is improved, and cracks and delamination can be suppressed.

In the nickel powder of the present invention, the area of the peak attributed to the bonding state of nickel and oxygen with respect to the entire Ni2p _3/2 spectrum in the analysis of the chemical bonding state of nickel on the surface layer of the nickel powder by X-ray photoelectron spectroscopy (XPS). The ratio of the area of the nickel metal peak to the entire Ni2p _3/2 spectrum is 5.0 to 15.0%, and the peak of the Ni2p _{3 / The} area ratio with respect to the entire _two spectra is 5.0 to 40.0%. In other words, it has a coating film containing nickel oxide and nickel hydroxide formed on the surface of the nickel powder of the present invention. The average thickness of the coating is 3.0 to 5.0 nm.

Furthermore, the nickel powder of the present invention has an absorption peak with a wave number of 3600 to 3700 cm ⁻¹ due to the OH group chemically bonded to metallic nickel when infrared absorption spectrum analysis is performed.

By forming a dense nickel oxide and nickel hydroxide film having a specific thickness in this way, when heat treatment is performed, particularly at 300 to 400 ° C. for removing organic components in the production process of the multilayer ceramic capacitor. When heated in this temperature range, changes in volume and weight due to oxidation and reduction of nickel can be minimized.

Since the nickel powder of the present invention has a strong nickel oxide and nickel hydroxide coating on the surface, the sintering start temperature is higher than that of the conventional nickel powder, and the dielectric powder used when manufacturing the multilayer ceramic capacitor is used. It is closer to the sintering start temperature of the body. Therefore, the nickel powder of the present invention is superior in oxidation behavior and sintering behavior during heating as compared with conventional nickel powder, so that delamination can be effectively prevented.

Further, the nickel powder of the present invention has good dispersibility in a solvent such as pure water.

The entire Ni2p _3/2 spectrum of the present invention is the peak attributed to metallic nickel, the combined state of nickel and oxygen in the analysis of the chemical bonding state of nickel on the surface layer of nickel powder by X-ray photoelectron spectroscopy (XPS). It is the spectrum resulting from the peak attributed to and the peak attributed to the bonding state of nickel and a hydroxyl group. The area ratio of each spectrum is obtained by peak-separating the obtained Ni2p _3/2 spectrum, calculating the area of each spectrum, and determining the area ratio of each spectrum relative to the sum.

The thickness of the coating of the present invention is obtained by observing a lattice image of a nickel powder sample with a transmission electron microscope, measuring the film thickness of the nickel powder surface at six points, and calculating the average.

More preferably, in the analysis of the chemical bonding state of nickel on the surface layer of nickel powder by X-ray photoelectron spectroscopy (XPS), the area ratio of the peak attributed to the bonding state of nickel and oxygen to the entire Ni2p _3/2 spectrum is 60. 0.0 to 75.0%, the area ratio of the peak of nickel metal to the entire Ni2p _3/2 spectrum is 7.0 to 13.0%, and the entire Ni2p _3/2 spectrum of the peak attributed to the bonding state between nickel and a hydroxyl group The area ratio with respect to the thickness is 12.0 to 33.0%, and the average thickness of the nickel oxide and nickel hydroxide coatings is 3.5 to 4.5 nm.

[Production method of nickel powder]
The nickel powder of the present invention can be produced by a known method such as a gas phase method or a liquid phase method. In particular, the vapor phase reduction method in which nickel powder is produced by bringing nickel chloride gas into contact with a reducing gas, or the spray pyrolysis method in which a thermally decomposable nickel compound is sprayed to thermally decompose is used to produce fine metal powder. It is preferable in that the particle size can be easily controlled, and spherical particles can be efficiently produced. In particular, the vapor phase reduction method in which nickel chloride gas is brought into contact with a reducing gas is preferable from the viewpoint that the particle diameter of the produced nickel powder can be precisely controlled and the generation of coarse particles can be prevented.

In the vapor phase reduction method, vaporized nickel chloride gas is reacted with a reducing gas such as hydrogen. In this case, nickel chloride gas may be generated by heating and evaporating solid nickel chloride. However, in consideration of nickel chloride oxidation or moisture absorption prevention and energy efficiency, the metal chloride is brought into contact with chlorine gas to continuously generate nickel chloride gas, and this nickel chloride gas is directly supplied to the reduction process and then reduced. It is advantageous to produce nickel fine powder by contacting nickel chloride gas and continuously reducing nickel chloride gas. The vapor phase reduction method can obtain nickel powder having a ratio of the number average particle diameter D to the crystallite diameter d (d / D) of 0.40 or more with a high yield.

Metal chloride gases other than nickel chloride gas when used in a method for producing an alloy powder containing nickel as a main component are silicon trichloride (III) gas, silicon tetrachloride (IV) gas, monosilane gas, copper chloride (I ) Gas, copper chloride (II) gas, silver chloride gas, molybdenum chloride gas (III) gas, molybdenum chloride (V) gas, iron chloride (II) gas, iron chloride (III) gas, chromium chloride (III) gas, Chromium chloride (VI) gas, tungsten chloride (II) gas, tungsten chloride (III) gas, tungsten chloride (IV) gas, tungsten chloride (V) gas, tungsten chloride (VI) gas, tantalum chloride (III) gas, chloride Tantalum (V) gas, cobalt chloride gas, rhenium chloride (III) gas, rhenium chloride (IV) gas, rhenium chloride (V) gas, Borangasu include phosphine gas or the like, and a mixed gas thereof.

Further, examples of the reducing gas include hydrogen gas, hydrogen sulfide gas, ammonia gas, carbon monoxide gas, methane gas, and a mixed gas thereof. Particularly preferred are hydrogen gas, hydrogen sulfide gas, ammonia gas, and mixed gas thereof.

In the production process of nickel powder by vapor phase reduction reaction, nickel atoms are generated at the moment when the nickel chloride gas and the reducing gas come into contact with each other, and nickel particles collide and agglomerate to generate and grow nickel particles. The particle diameter of the nickel powder to be generated is determined by conditions such as the partial pressure and temperature of the nickel chloride gas in the reduction step. According to the nickel powder manufacturing method as described above, an amount of nickel chloride gas corresponding to the supply amount of chlorine gas is generated. Therefore, the amount of nickel chloride gas supplied to the reduction process is controlled by controlling the supply amount of chlorine gas. The amount can be adjusted, thereby controlling the particle size of the nickel powder produced.

Furthermore, since nickel chloride gas is generated by the reaction of chlorine gas and metal, unlike the method of generating nickel chloride gas by heating evaporation of solid nickel chloride, not only can the use of carrier gas be reduced. Depending on the manufacturing conditions, it is possible not to use them. Therefore, in the gas phase reduction reaction, the production cost can be reduced by reducing the amount of carrier gas used and the accompanying reduction in heating energy.

Moreover, the partial pressure of nickel chloride gas in the reduction process can be controlled by mixing an inert gas with the nickel chloride gas generated in the chlorination process. Thus, by controlling the supply amount of chlorine gas or the partial pressure of nickel chloride gas supplied to the reduction process, the particle size of nickel powder can be controlled, and variation in particle size can be suppressed, The particle size can be arbitrarily set.

For example, nickel chloride as a starting material is made by reacting metallic nickel having a purity of 99.5% or more in the form of particles, lumps, plates, etc. with chlorine gas to generate nickel chloride gas. In this case, the temperature is set to 800 ° C. or higher for sufficient progress of the reaction, and 1453 ° C. or lower, which is the melting point of nickel. Considering the reaction rate and the durability of the chlorination furnace, the range of 900 ° C. to 1100 ° C. is preferable for practical use.

Next, this nickel chloride gas is directly supplied to the reduction process and brought into contact with a reducing gas such as hydrogen gas. At that time, the partial pressure of the nickel chloride gas can be controlled by appropriately diluting the nickel chloride gas with an inert gas such as argon or nitrogen. By controlling the partial pressure of the nickel chloride gas, the quality such as the particle size distribution of the metal powder produced in the reducing part can be controlled. Thereby, while being able to set arbitrarily the quality of the metal powder to produce | generate, quality can be stabilized. The temperature of the reduction reaction may be at least the temperature sufficient for completion of the reaction, preferably below the melting point of nickel, and practically 900 ° C. to 1100 ° C. in view of economy.

When the nickel powder subjected to the reduction reaction is generated in this way, the generated nickel powder is cooled. During cooling, in order to prevent the formation of secondary particles due to aggregation of primary particles of the generated nickel and obtain nickel powder with a desired particle size, a reduction reaction is performed by blowing an inert gas such as nitrogen gas. It is desirable to rapidly cool the finished gas flow around 1000 ° C. to about 400 to 800 ° C. Thereafter, the produced nickel powder is separated and collected by, for example, a bag filter or the like.

In the method for producing nickel powder by the spray pyrolysis method, a heat decomposable nickel compound is used as a raw material. Specifically, one or more of nitrate, sulfate, oxynitrate, oxysulfate, chloride, ammonium complex, phosphate, carboxylate, alkoxy compound and the like are included. The solution containing the nickel compound is sprayed to form fine droplets. As the solvent at this time, water, alcohol, acetone, ether or the like is used. The spraying method is performed by a spraying method such as ultrasonic or double jet nozzle. In this way, fine droplets are formed and heated at a high temperature to thermally decompose the metal compound to produce nickel powder. The heating temperature at this time is equal to or higher than the temperature at which the specific nickel compound used is thermally decomposed, and is preferably near the melting point of the metal.

In the method for producing nickel powder by the liquid phase method, nickel hydroxide containing nickel sulfate, nickel chloride or a nickel complex is brought into contact by adding it to an alkali metal hydroxide such as sodium hydroxide. Then, the nickel hydroxide is reduced with a reducing agent such as hydrazine to obtain metallic nickel powder. The nickel metal powder thus produced is crushed as necessary to obtain uniform particles.

The nickel powder obtained by the above method is preferably dispersed and washed in the liquid phase in order to remove the remaining raw material. For example, the nickel powder obtained by the above method is suspended in a carbonic acid aqueous solution under specific conditions with controlled pH and temperature. By treating with an aqueous carbonate solution, impurities such as chlorine adhering to the surface of the nickel powder are sufficiently removed, and oxides such as nickel oxide and nickel hydroxide such as nickel hydroxide existing on the surface of the nickel powder are removed. Fine particles formed away from the surface due to friction between objects and particles are removed, and a thin and uniform film made of nickel oxide and nickel hydroxide can be re-formed by dissolved oxygen in water. As a treatment method with a carbonic acid aqueous solution, a method in which nickel powder and a carbonic acid aqueous solution are mixed, or carbon dioxide gas is blown into a water slurry after the nickel powder is once washed with pure water, or the nickel powder is once washed with pure water. The aqueous slurry can be treated by adding an aqueous carbonate solution.

The method for incorporating sulfur into the nickel powder of the present invention is not particularly limited, and for example, the following method can be employed.
(1) Method of adding sulfur-containing gas during the reduction reaction (2) Method of contacting nickel powder with sulfur-containing gas (3) Method of mixing nickel powder and solid sulfur-containing compound in a dry process (4) Nickel Method of adding sulfur-containing compound solution in slurry in which powder is dispersed in liquid phase (5) Method of bubbling sulfur-containing gas in slurry in which nickel powder is dispersed in liquid phase

In particular, the methods (1) and (4) are preferable from the viewpoint that the sulfur content can be precisely controlled and sulfur can be added uniformly. The sulfur-containing gas used in the methods (1), (2), and (5) is not particularly limited, and is a gas at the temperature of the reduction process, such as sulfur vapor, sulfur dioxide gas, and hydrogen sulfide gas. A certain gas can be used as it is or after being diluted. Of these, sulfur dioxide gas and hydrogen sulfide gas are advantageous because they are gases at room temperature and the flow rate can be easily controlled and impurities are less likely to be mixed.

The nickel powder slurry is dried after the aforementioned washing step and sulfur addition step. The drying method is not particularly limited, and a known method can be used. Specific examples include air-flow drying, drying by heating, and vacuum drying that are brought into contact with a high-temperature gas to dry. Among these, air drying is preferable because there is no destruction of the sulfur-containing layer due to collision between particles.

The nickel powder obtained as described above is subjected to an oxidation treatment under specific conditions. As a specific method of the oxidation treatment, an atmosphere containing an oxidizing gas (for example, oxygen gas or ozone gas) (for example, in an air or oxygen gas atmosphere, an inert gas containing oxygen gas (nitrogen, argon, etc.)) And the like, and a method of performing a heat treatment. The optimum heat treatment temperature at this time varies depending on the particle diameter, but is preferably 140 to 180 ° C. when the average particle diameter is 250 nm or less used in the production process of the multilayer ceramic capacitor, and particularly in the air when the average particle diameter is 140 to 250 nm. In this case, the temperature is preferably maintained at 160 to 180 ° C for 1 minute to 4 hours. In analysis of the chemical bonding state of nickel on the surface layer of nickel powder by X-ray photoelectron spectroscopy (XPS), the area ratio of the peak attributed to the bonding state of nickel and oxygen to the entire Ni2p _3/2 spectrum is 55.0 to 80 The heat treatment conditions (temperature, time) are adjusted as appropriate so that the area ratio of the nickel nickel peak to the entire Ni2p _3/2 spectrum is 5.0 to 15.0%. In this way, a stronger nickel oxide film is formed by oxidizing nickel powder.

The nickel powder of the present invention can be used as a paste raw material. More preferably, it is a nickel paste containing the nickel powder and an organic solvent. Further, if necessary, an organic binder such as ethyl cellulose, a dispersant, and an unfired powder of the ceramic to be coated may be included.

This nickel paste is added to the above nickel powder, for example, an organic solvent such as terpineol, an organic binder such as ethyl cellulose, a dispersant, and an unfired ceramic powder to be applied, if necessary, and kneaded with three rolls. Thus, a nickel paste having desirable characteristics can be easily produced by a known method. Organic solvents include alcohol, acetone, propanol, ethyl acetate, butyl acetate, ether, petroleum ether, mineral spirit, other paraffinic hydrocarbon solvents, or butyl carbitol, terpineol, dihydroterpineol, butyl carbitol acetate, dihydro Propionate solvents such as terpineol acetate, dihydrocarbyl acetate, carbyl acetate, terpinyl acetate, linalyl acetate, etc., dihydroterpinyl propionate, dihydrocarbyl propionate, isobornyl propionate, Examples include cellosolves such as ethyl cellosolve and butyl cellosolve, aromatics, and diethyl phthalate.

The organic binder is preferably a resin binder, and examples thereof include ethyl cellulose, polyvinyl acetal, acrylic resin, alkyd resin, and the like.

As the dispersant, a known appropriate one can be used, and for example, a vinyl polymer, a polycarboxylic acid amine salt, a polycarboxylic acid type, or the like can be used.

Since the nickel powder of the present invention obtained as described above has a coating film containing nickel oxide and nickel hydroxide having a certain thickness and density on the surface, the production process of the multilayer ceramic capacitor Exhibits excellent sintering behavior and prevents the occurrence of delamination. More specifically, when the heat treatment is performed, the volume change or weight change due to the oxidation-reduction reaction is small, and the sintering start temperature is higher than that of the conventional nickel powder, so that a multilayer ceramic capacitor is manufactured. It becomes closer to the sintering start temperature of the dielectric used at the time, and as a result, generation of delamination can be effectively prevented.

Next, the present invention will be described more specifically with reference to examples and comparative examples. However, this is merely an example and does not limit the present invention.

[Example 1]
After the gas phase reaction method in which nickel chloride and hydrogen are reacted, washing is performed in pure water and an aqueous carbonate solution, and a sulfur-containing compound solution is added to a slurry in which nickel powder is dispersed in a liquid phase, followed by drying. Nickel powder was prepared. It was confirmed that the obtained nickel powder was a spherical nickel powder having a number average particle diameter of 191 nm, an average aspect ratio of 1.2, and an average circularity coefficient of 0.68. Moreover, the specific surface area was 4.0 m < ² > / g and the specific surface area diameter was 168 nm. Further, the ratio d / D of the number average particle diameter d and the specific surface area diameter was 0.88.

The nickel powder was oxidized at 175 ° C. for 4 hours in an oxidizing atmosphere to obtain nickel powder. Oxygen content, average particle size, X-ray photoelectron spectroscopy (XPS) measurement, dispersibility evaluation, nickel oxide and nickel hydroxide coating thickness, 2% heat shrinkage temperature, specific surface area diameter, number average particle size and ratio The measurement results of the ratio of the surface area diameters are shown in Table 1, and the results of the sintering behavior are shown in FIG.

Further, when the nickel powder of Example 1 was subjected to infrared absorption spectrum analysis, an absorption peak having a wave number of 3600 to 3700 cm ⁻¹ due to the OH group chemically bonded to metallic nickel was observed.

[Comparative Example 1]
A sample was prepared in the same manner as in Example 1 except that the oxidation treatment was performed at 155 ° C. for 2 hours in an oxidizing atmosphere to obtain nickel powder. Oxygen content, average particle size, X-ray photoelectron spectroscopy (XPS) measurement, dispersibility evaluation, nickel oxide and nickel hydroxide coating thickness, 2% heat shrinkage temperature, specific surface area diameter, number average particle size and ratio The measurement results of the ratio of the surface area diameters are shown in Table 1, and the results of the sintering behavior are shown in FIG.

[Comparative Example 2]
A sample was prepared in the same manner as in Example 1 except that the oxidation treatment was not performed to obtain nickel powder. Oxygen content, average particle size, X-ray photoelectron spectroscopy (XPS) measurement, dispersibility evaluation, nickel oxide and nickel hydroxide coating thickness, 2% heat shrinkage temperature, specific surface area diameter, number average particle size and ratio The measurement results of the ratio of the surface area diameters are shown in Table 1, and the results of the sintering behavior are shown in FIG.

[Comparative Example 3]
A sample was prepared in the same manner as in Example 1 except that the oxidation treatment was performed at 230 ° C. for 2 hours in an oxidizing atmosphere to obtain nickel powder. Oxygen content, average particle size, X-ray photoelectron spectroscopy (XPS) measurement, dispersibility evaluation, nickel oxide and nickel hydroxide coating thickness, 2% heat shrinkage temperature, specific surface area diameter, number average particle size and ratio The measurement results of the ratio of the surface area diameters are shown in Table 1, and the results of the sintering behavior are shown in FIG.

Measurement Oxygen content, average particle diameter, nickel metal and surface oxide by surface X-ray photoelectron spectroscopy (XPS), surface hydroxide ratio, dispersibility evaluation, oxidation The method for measuring the thickness of the nickel and nickel hydroxide coatings and the 2% heat shrinkage temperature is shown below.
1) Oxygen content The nickel powder of the sample is filled in a nickel capsule, put in a graphite crucible, heated to 500 ° C. in an argon atmosphere, and the carbon monoxide generated at this time is Fourier-transform infrared spectrophotometric. It quantified with the meter and calculated | required the oxygen content rate in nickel powder.
2) Average particle diameter A photograph of the sample was taken with an electron microscope, and using the image analysis software, the particle diameter of 900 powders was measured and the number average particle diameter was calculated. At this time, the particle diameter is the diameter of the smallest circle that encloses the particles.
3) X-ray photoelectron spectroscopic analysis (XPS) measurement Using an X-ray photoelectron spectroscopic analyzer (manufactured by Thermo Fisher Scientific Co., Ltd., K-ALPHA ⁺ ), the Ni2p _3/2 spectrum of the powder surface is measured and the analyzer is used. Using the attached analysis software “Avantage Ver. 5.951”, the spectrum is peak-separated, the peak of metallic nickel with respect to the entire Ni2p _3/2 spectrum, the peak attributed to the combined state of nickel and oxygen, nickel and water The area ratio of peaks attributed to the oxide bonding state was calculated.
4) Dispersibility evaluation 0.05 g of nickel powder was put in 100 g of pure water, and dispersed for 1 minute with an ultrasonic disperser (Sonic Technology Co., Ltd., GSD600AT). After sample dispersion treatment, vacuum filtration was performed using a 3 μm membrane filter. If the time taken for the slurry to pass through the membrane filter was within 30 seconds (◯), it took more than 30 seconds. In the case, it was regarded as defective (x).
5) Thickness of nickel oxide and nickel hydroxide film Nickel powder was directly sprinkled on a copper sheet mesh covered with a collodion film, and then carbon was deposited to prepare a measurement sample. Next, using a transmission electron microscope (manufactured by JEOL Ltd., JEM-2100F), the lattice image of the measurement sample was observed under the condition of an acceleration voltage of 200 kV, and the film thicknesses of nickel oxide and nickel hydroxide on the surface of the nickel powder were measured. Six points were measured and the average was calculated.
6) 2% heat shrinkage temperature and sintering behavior 1 g of nickel powder, 3% by weight of camphor and 3% by weight of acetone are mixed and filled into a cylindrical mold having an inner diameter of 5 mm and a length of 10 mm. A test piece was prepared by applying a load of tons. Using this test piece, a thermal dilatometry measuring device (TMA, 8310, manufactured by Rigaku Co., Ltd.), under a nitrogen gas atmosphere (containing 2% hydrogen gas), a temperature rising rate of 10 ° C./min. The measurement was performed. Further, the temperature of 2% heat shrinkage measured by a thermal expansion / shrinkage behavior measuring apparatus (TMA) was defined as 2% heat shrinkage temperature.
7) Specific surface area Using a BET specific surface area measuring device (manufactured by Mountec Co., Ltd.), a specific surface area is measured after pretreatment at 160 ° C. for 1 hour under a nitrogen stream. The specific surface area diameter d was calculated using 1). Here, ρ is the true density of nickel. Furthermore, the ratio of the number average particle diameter D and the specific surface area diameter d was calculated.

As is apparent from Table 1, the nickel powder of Example 1 having a higher surface oxide ratio than the nickel powders of Comparative Examples 1 and 2 is more dispersed than the nickel powder of Comparative Example 3 having a higher surface oxide ratio. The sex evaluation was excellent. From this, since the nickel powder of Example 1 is excellent in dispersibility, it is presumed that mixing of the nickel powder and the common material becomes sufficient when the multilayer ceramic capacitor is manufactured, and delamination is prevented. The

It can also be seen that the thickness of the nickel powder coating of Example 1 is larger than that of Comparative Examples 1 and 2.

Furthermore, at 2% heat shrinkage temperature, the nickel powder of Example 1 is higher than the nickel powders of Comparative Examples 1 and 2, and the volume change in the low temperature region of 300 to 400 ° C. is completely observed in the sintering behavior of FIG. Sintering behavior is stable.

From the above results, it is estimated that the nickel powder of the present invention exhibits excellent sintering behavior in the production process of the multilayer ceramic capacitor and is excellent in dispersibility, and as a result, prevention of delamination can be achieved. The

As described above, according to the nickel powder of the present invention, the sintering behavior is very stable as compared with the conventional nickel powder at an average particle size of 250 nm or less, and the shrinkage and expansion of the nickel powder in the low temperature region. In addition, the paste using the nickel powder of the present invention has an effect of preventing the occurrence of delamination in the manufacturing process of the multilayer ceramic capacitor.

According to the present invention, the sintering behavior is very stable compared to the conventional nickel powder, there is no shrinkage and expansion of the nickel powder in the low temperature region, and the dispersibility is excellent. A suitable nickel powder can be provided.

Claims

In the analysis of the chemical bonding state of nickel in the surface layer of nickel powder by X-ray photoelectron spectroscopy (XPS) having a coating containing nickel oxide and nickel hydroxide and having an average particle size of 250 nm or less, the bond between nickel and oxygen The area ratio of the peak attributed to the state to the entire Ni2p 3/2 spectrum is 55.0 to 80.0%, the area ratio of the peak of metallic nickel to the entire Ni2p 3/2 spectrum is 5.0 to 15.0%, The area ratio of the peak attributed to the bonded state of nickel and hydroxyl group to the entire Ni2p 3/2 spectrum is 5.0 to 40.0%, and the average thickness of the coating is 3.0 to 5.0 nm. Nickel powder characterized by being.