WO2015156080A1

WO2015156080A1 - Nickel powder

Info

Publication number: WO2015156080A1
Application number: PCT/JP2015/057325
Authority: WO
Inventors: 広介六角; 浅井　剛
Original assignee: 東邦チタニウム株式会社
Priority date: 2014-04-08
Filing date: 2015-03-12
Publication date: 2015-10-15
Also published as: JP6559118B2; JPWO2015156080A1; TW201542832A; KR102292897B1; CN106457379A; CN106457379B; TWI638051B; KR20160142842A

Abstract

Provided is a nickel powder having excellent sintering properties in a manufacturing process for laminated ceramic capacitors, and capable of preventing the occurrence of defects in laminated ceramic capacitors such as cracking in an electrode layer and separating between the electrode layer and a dielectric layer. The nickel powder contains 1.0-5.0 mass% of sulfur, and 50% of particles therein have a size of less than or equal to 0.09 µm.

Description

Nickel powder

The present invention relates to a nickel powder suitable for use as a conductive paste used in electronic parts and the like, and more particularly to a nickel powder suitable for use as a conductive paste for internal electrodes of multilayer ceramic capacitors.

Mobile communication terminals represented by smartphones and tablet terminals increase power consumption and increase battery capacity with multifunctionality and high functionality, so the main substrate on which electronic components are mounted in a limited case Tends to be smaller. On the other hand, the number of electronic components mounted on the main substrate tends to increase. Therefore, the multilayer ceramic capacitor mounted on the main substrate is required to be small and have a large capacity.

With the miniaturization and increase in capacity of multilayer ceramic capacitors, thinning of internal electrodes of multilayer ceramic capacitors and reduction in resistance are required. For this reason, as for the nickel powder used for the internal electrode, ultrafine powder having a number of 50% primary particles of 0.3 μm or less as well as 0.2 μm or less, and further 0.1 μm or less is demanded.

In general, nickel powder has a lower sintering start temperature and larger thermal contraction than ceramic powders used for dielectrics of multilayer ceramic capacitors. For this reason, there is a problem that defects such as peeling between the electrode layer and the dielectric layer and generation of cracks in the electrode layer are easily generated when firing in the manufacturing process of the multilayer ceramic capacitor. In addition, when coarse particles exceeding 3 times the number 50% diameter of primary particles or agglomerated particles in which particles are coagulated exist in the nickel powder, the irregularities on the surface of the electrode layer become large, and shorts between electrode layers and resistance to multilayer ceramic capacitors It causes a drop in voltage.

For example, Patent Document 1 discloses a nickel powder having a sulfur content of 0.02 to 1.0% by weight as a means for coping with the occurrence of defects as described above. Further, Patent Document 2 discloses a nickel powder in which a coating film of nickel sulfide or nickel sulfate is formed on the surface.

However, in the prior art as described above, when the number 50% diameter of the nickel powder is smaller than 0.1 μm, the effect of preventing the occurrence of defects at the time of firing of the nickel powder is not sufficient, and further improvement is required.

JP-A-11-80817 (claims) JP 2008-223145 A (claims)

Therefore, the present invention has excellent sintering characteristics in the manufacturing process of the multilayer ceramic capacitor, and can prevent generation of defects such as peeling between the electrode layer and the dielectric layer of the multilayer ceramic capacitor and cracks in the electrode layer. The object is to obtain a nickel powder having a number 50% diameter smaller than 0.1 μm.

Furthermore, the present invention can suppress the occurrence of agglomerated particles in the manufacturing process of the multilayer ceramic capacitor, can prevent the occurrence of defects such as a short between electrode layers and a reduction in withstand voltage, and the number 50% diameter is 0.1 μm The aim is to provide a smaller nickel powder.

The nickel powder of the present invention is characterized by containing 1.0 to 5.0% by mass of sulfur and having a number 50% diameter of not more than 0.09 μm.

According to the present invention, by containing 1.0 to 5.0% by mass of sulfur, the sintering behavior of the nickel powder can be improved even if the number 50% diameter is not more than 0.09 μm. It is possible to solve the problems such as the characteristic deterioration of the multilayer ceramic capacitor due to the bonding.

The sintered powder is superior to the nickel powder of the present invention in the manufacturing process of the multilayer ceramic capacitor, and the occurrence of defects such as peeling between the electrode layer and dielectric layer of the multilayer ceramic capacitor and cracks in the electrode layer is prevented. Can. Furthermore, the nickel powder of the present invention can suppress the generation of agglomerated particles, and can suppress the generation of defects such as a short between electrode layers and a reduction in withstand voltage.

It is the schematic which shows the nickel powder manufacturing apparatus used by the Example and the comparative example.

The nickel powder of the present invention includes nickel powder produced by various production methods and nickel alloy powder containing nickel as a main component. As a nickel alloy powder, there is an alloy powder in which chromium is added with chromium, silicon, boron, phosphorus, a rare earth element, a noble metal element or the like in order to impart oxidation resistance or the like and improve the electric conductivity.

The number 50% diameter of the nickel powder of the present invention is 0.09 μm or less. The lower limit of the number 50% diameter of the nickel powder of the present invention is not particularly limited, but is preferably 0.01 μm or more from the viewpoint of the production cost and use of the usual nickel powder.

The number 50% diameter of the nickel powder of the present invention can be obtained by taking a picture of the nickel powder with a scanning electron microscope and measuring the particle size of about 1,000 particles from the picture using image analysis software. From the particle size distribution of the nickel powder, the number 50% of the number is calculated. In this case, the particle size is the diameter of the smallest circle that encloses the particle.

The nickel powder of the present invention contains 1.0 to 5.0% by weight of sulfur. By making the sulfur concentration 1.0% by weight or more, the sintering behavior of the nickel powder can be improved. On the other hand, if the sulfur concentration exceeds 5.0% by weight, problems such as generation of corrosive gas at the time of sintering to deteriorate the characteristics of the laminated ceramic capacitor occur. The sulfur concentration in the nickel powder is more preferably 1.2 to 4.0% by weight, still more preferably 1.5 to 3.0% by weight.

In the nickel powder of the present invention, among the sulfur present on the surface of the powder, the molar ratio of sulfur present as sulfate ion to sulfur present as sulfide (sulfate ion / sulfide ion ratio) is 0.10 or less Is preferable, and 0.05 or less is more preferable. By setting the molar ratio of the sulfur present as sulfate ion to the sulfur present as sulfide ion in the above-mentioned range, it is possible to prevent the generation of agglomerated particles during the production of the nickel powder paste. The ratio of sulfur present as sulfate ion to sulfur present as sulfide ion (sulfate ion / sulfide ion ratio) of the nickel powder surface is 168 eV of the S _2p spectrum measured using an X-ray photoelectron spectrometer. Calculated from the intensity ratio of the peak to the peak of 162 eV.

Further, in the nickel powder of the present invention, the abundance ratio of particles having a particle diameter three times or more the number of 50% diameter in the nickel powder (hereinafter sometimes referred to as "coarse particles") is on a number basis. 100 ppm or less is preferable, and 50 ppm or less is more preferable. By setting the particle size distribution in this range, the electrode layer can be smoothed in the production of the multilayer ceramic capacitor. In addition, the evaluation of the abundance ratio of coarse particles is carried out by taking a picture of the nickel powder with a scanning electron microscope in the same manner as described above, and using the image analysis software from the picture, the particle size is about 100,000 particles. The number of particles exceeding 3 times the number 50% diameter obtained above is counted and calculated.

The nickel powder of the present invention can be produced, for example, by a known method such as a gas phase method or a liquid phase method. In particular, a vapor phase reduction method in which nickel powder is produced by contacting nickel chloride gas with a reducing gas, or a spray pyrolysis method in which a pyrolytic nickel compound is sprayed and pyrolyzed It is preferable in that the particle size can be easily controlled, and spherical particles can be produced efficiently. In particular, the gas phase reduction method by bringing nickel chloride gas into contact with a reducing gas is preferable from the viewpoint of being able to precisely control the particle size of the nickel powder to be produced and of preventing the generation of coarse particles.

In the gas phase reduction method, the vaporized nickel chloride gas is reacted with a reducing gas such as hydrogen. In this case, solid nickel chloride may be heated and evaporated to produce nickel chloride gas. However, considering oxidation or moisture absorption prevention of nickel chloride and energy efficiency, metal nickel is brought into contact with chlorine gas to continuously generate nickel chloride gas, and this nickel chloride gas is directly supplied to the reduction step and then reduced. A method of producing nickel fine powder by continuously reducing nickel chloride gas by contacting with a hydrogen chloride gas is preferred.

Gases other than nickel chloride gas when used in a method of producing an alloy powder containing nickel as a main component include silicon trichloride (III) gas, silicon tetrachloride (IV) gas, monosilane gas, copper (I) chloride 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, tantalum chloride (V) ) Gas, cobalt chloride gas, rhenium chloride (III) gas, rhenium chloride (IV) gas, rhenium chloride (V) gas, diborane gas Include phosphine gas or the like, and a mixed gas thereof.

Further, as the reducing gas, hydrogen gas, hydrogen sulfide gas, ammonia gas, carbon monoxide gas, methane gas and a mixed gas thereof can be mentioned. Particularly preferred are hydrogen gas, hydrogen sulfide gas, ammonia gas, and a mixed gas thereof.

In the process of producing nickel powder by vapor phase reduction reaction, nickel atoms are formed at the moment of contact between nickel chloride gas and reducing gas, and nickel particles are formed and grown by collision and aggregation of nickel atoms. Then, the particle diameter of the nickel powder to be produced is determined by the conditions such as the partial pressure of nickel chloride gas and the temperature in the reduction step. According to the above-described nickel powder production method, an amount of nickel chloride gas corresponding to the amount of chlorine gas supplied is generated. Therefore, by controlling the amount of chlorine gas supplied, the amount of nickel chloride gas supplied to the reduction step is The amount can be adjusted, which can control the particle size of the nickel powder produced.

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

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

The production conditions of the nickel powder by the above-mentioned vapor phase reduction method are arbitrarily set so that the number 50% diameter becomes 0.09 μm or less, for example, the particle diameter of the starting material metallic nickel is about 5 to Granules, lumps, plates and the like of 20 mm are preferable, and the purity thereof is generally preferably 99.5% or more. This metallic nickel is first reacted with chlorine gas to produce nickel chloride gas, the temperature at that time is made 800 ° C. or more to sufficiently proceed the reaction, and 1453 ° C. or less, which is the melting point of nickel. In consideration of the reaction rate and the durability of the chlorination furnace, the range of 900 ° C. to 1100 ° C. is practically preferable.

Next, the nickel chloride gas is directly supplied to the reduction step, and is brought into catalytic reaction with a reducing gas such as hydrogen gas. At this time, the partial pressure of the nickel chloride gas can be controlled by diluting the nickel chloride gas with an inert gas such as argon or nitrogen as appropriate. By controlling the partial pressure of the nickel chloride gas, it is possible to control the quality such as the particle size distribution of the metal powder produced in the reducing portion. While being able to set arbitrarily the quality of the metal powder produced | generated by this, quality can be stabilized. Usually, in order to obtain a nickel powder having a number of 50% diameter of 0.09 μm or less, the partial pressure of nickel chloride gas is controlled to 30 kPa or less. The temperature of the reduction reaction may be a temperature sufficient to complete the reaction. It is preferable that the solid nickel powder is produced, because it is easy to handle, so the melting point or less of nickel is preferable, and 900 ° C. to 1100 ° C. is practical in consideration of economics.

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

In the method of producing a nickel powder by a spray pyrolysis method, a pyrolytic nickel compound is used as a raw material. Specifically, one or more kinds 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 a solvent at this time, water, alcohol, acetone, ether or the like is used. Moreover, the method of spraying is performed by the spraying methods, such as an ultrasonic wave or a double jet nozzle. In this way, it is made into fine droplets and heated at high temperature to pyrolyze the metal compound to form nickel powder. The heating temperature at this time is equal to or higher than the temperature at which the specific nickel compound to be used is thermally decomposed, and is preferably near the melting point of the metal.

In the method of producing nickel powder by the liquid phase method, nickel hydroxide is obtained by contacting nickel sulfate, nickel chloride or nickel aqueous solution containing nickel complex by adding to 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 metallic nickel powder thus produced is subjected to a crushing treatment as necessary to obtain uniform particles.

The nickel powder obtained by the above method is preferably dispersed in a liquid phase and washed to remove the remaining raw material. For example, the nickel powder obtained by the above method is suspended in a carbonated aqueous solution under specific conditions of controlled pH and temperature for treatment. By treating with a carbonic acid aqueous solution, impurities such as chlorine adhering to the surface of the nickel powder are sufficiently removed, and at the same time, the friction between hydroxides and particles such as nickel hydroxide present on the surface of the nickel powder As a result, fine particles formed away from the surface are removed, so that a uniform nickel oxide film can be formed on the surface. As a treatment method with a carbonic acid aqueous solution, a method of mixing nickel powder and carbonic acid solution, carbon dioxide gas is blown into an aqueous slurry after the nickel powder is once washed with pure water, or the nickel powder is once washed with pure water. It is also possible to treat by adding an aqueous solution of carbonic acid to the water slurry after the treatment.

The method of incorporating sulfur into the nickel powder of the present invention is not particularly limited, and, for example, the following method can be adopted.
(1) Method of adding sulfur-containing gas during the reduction reaction (2) Method of contacting nickel powder with sulfur-containing gas (3) method of dry mixing nickel powder and solid sulfur-containing compound (4) nickel Method of adding sulfur-containing compound solution to 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 the sulfur can be uniformly added. The sulfur-containing gas used in the methods (1), (2) and (5) is not particularly limited, and sulfur vapor, sulfur dioxide gas, hydrogen sulfide gas, etc. are gases at the temperature of the reduction step. A certain gas can be used as it is or after dilution. Among these, sulfur dioxide gas and hydrogen sulfide gas are advantageous from the point of being gas at normal temperature and easy to control the flow rate and low in the possibility of mixing of impurities.

In the method (1), sulfur can be uniformly contained in the nickel powder produced by the reduction reaction by mixing these gases with any of nickel chloride gas, inert gas and reducing gas. In addition, the sulfur content of the nickel powder can be controlled by controlling the flow ratio of the nickel chloride gas and the sulfur-containing gas.

The sulfur-containing compound used in the methods (3) and (4) is not particularly limited, and sulfur-containing compounds such as triazine thiol, 2-mercaptobenzothiazole, thiourea and the like can be used. Among them, the method using thiourea is most effective.

In the method (4), after the nickel slurry and the solution of the sulfur-containing compound are mixed, stirring, ultrasonic treatment or the like is performed. The liquid temperature range in the above treatment is 20 to 60.degree. C., more preferably 20 to 40.degree. The sulfur content of the nickel powder can be arbitrarily adjusted by adjusting the addition amount of the sulfur-containing compound. When applying the method of (4) to the nickel powder obtained by a vapor-phase reduction method, it is preferable to perform a sulfur addition process after the above-mentioned washing | cleaning process.

After the aforementioned washing and sulfur addition steps, the nickel powder slurry is dried. The drying method is not particularly limited, and known methods can be used. Specific examples thereof include flash drying, heating and drying, vacuum drying, etc., which are brought into contact with a high temperature gas for drying. Among these, flash drying is preferable because there is no destruction of the sulfur-containing layer due to collision of particles.

The nickel powder of the present invention is subjected to heat treatment under atmosphere control after the above-mentioned drying step. The heat treatment is performed at a temperature of 100 to 400 ° C., preferably 100 to 250 ° C., more preferably 150 to 250 ° C. in a reducing atmosphere for 0.5 to 10 hours. The reducing atmosphere may be, for example, an atmosphere of a mixed gas of an inert gas such as nitrogen and argon and hydrogen gas. The hydrogen partial pressure in the reducing atmosphere is 0.001 to 0.01 MPa. By this treatment, the sulfate ion present on the surface of the nickel powder is converted to sulfide ion, and the sulfur present as sulfate ion on the surface of the nickel powder and the molar ratio of sulfur present as sulfide ion (sulfate ion / sulfide ion ratio ) Can be made stable to 0.10 or less.

FIG. 1 is a view showing an apparatus for producing nickel powder. In FIG. 1, reference numeral 10 is a reduction furnace. The reduction furnace 10 has a bottomed cylindrical shape, and a nickel chloride gas nozzle 11 is attached on the upstream side thereof, and the reduction furnace 10 is supplied with nickel chloride gas, sulfur dioxide gas, and nitrogen gas for concentration adjustment. It has become so. Further, a hydrogen gas nozzle 12 is attached to the upstream side wall of the reduction furnace 10. The nickel chloride is reduced by the hydrogen gas supplied from the hydrogen gas nozzle 12 into the reduction furnace 10 to produce nickel powder P. A cooling gas nozzle 13 is attached to the downstream side wall of the reduction furnace 10, and the nickel powder P generated by the inert gas such as nitrogen gas supplied from the cooling gas nozzle 13 into the reduction furnace 10 is rapidly cooled. The coarsening of the nickel powder P is prevented. A recovery pipe 14 is attached to the downstream side of the reduction furnace 10, and the nickel powder P flows through the recovery pipe 14 and is sent to a recovery device.

(Examples 1 and 2, Comparative Examples 1 to 3)
A nickel powder having a 50% diameter diameter of about 0.03 μm and variously changed sulfur contents was manufactured by a vapor phase reduction method using the nickel powder manufacturing apparatus shown in FIG.

A mixed gas of nickel chloride gas, sulfur dioxide gas, and nitrogen gas is supplied from the nickel chloride gas nozzle 11 into the reduction furnace 10 at an atmosphere temperature of 1,100 ° C. by a heater at a flow rate of 2.8 m / sec (1,100 ° C. Introduced in At the same time, hydrogen gas was introduced from a hydrogen gas nozzle 12 into the reduction furnace 10 at a flow velocity of 2.2 m / sec (1,100 ° C. conversion), and nickel chloride gas was reduced in the reduction furnace 10 to obtain nickel powder P.

In this case, the sulfur content of the nickel powder was adjusted by controlling the flow ratio of nickel chloride gas and sulfur dioxide gas. During the nickel formation reaction, the nickel powder produced by the heat of reaction is heated to 1,200 ° C., and the gas flow containing the produced nickel powder is a combustion flame of gaseous fuel such as hydrocarbon by black body radiation of the nickel powder. It was observed as a similar luminous flame F. The produced nickel powder P is mixed with 25 ° C. nitrogen gas introduced from the cooling gas nozzle 13 at a mass flow rate of 200 times the amount of nickel powder produced per unit time, cooled to 400 ° C. or less, and then recovered. It led to the bag filter which is not shown in figure by 14, and isolate | separated and collect | recovered nickel powder. In Comparative Example 3, a nickel powder was prepared without adding sulfur dioxide gas to nickel chloride gas.

The recovered nickel powder was subjected to a washing step of dispersing and settling in water five times to remove the remaining nickel chloride, and then dried by means of a flash dryer so that the water content would be 0.5% or less. Next, heat treatment was performed at 150 ° C. for 3 hours under a reducing atmosphere of 2 vol% hydrogen-argon (hydrogen partial pressure: 2 kPa) to obtain nickel powders of Examples 1, 2 and Comparative Examples 1 to 3.

With respect to the obtained nickel powder, the number 50% diameter, the sulfur concentration, the sulfate ion / sulfide ion ratio on the surface of the nickel powder, the coarse particle ratio, the sintering behavior, and the aggregation behavior were evaluated by the following methods.

a. Photograph of metal nickel powder with a 50% diameter scanning electron microscope (made by Hitachi High-Technologies, Inc., trade name S-4700), and image analysis software (made by Mountech, Inc., trade name MacView 4.0) from the photograph The particle diameter of about 1,000 particles was measured to calculate the number 50% number of particles. The particle size is the diameter of the smallest circle that encloses the particles.

b. Sulfur concentration was measured using an inductively coupled plasma emission spectrometer (manufactured by SII Nano Technology Co., Ltd., trade name SPS3100).

c. Sulfate ion / sulfide ion ratio of the surface of nickel powder Nickel was obtained from the intensity ratio of the peak of 168 eV and the peak of 162 eV in the S 2 _p spectrum measured using an X-ray photoelectron spectrometer (manufactured by ULVAC-PHI, trade name QVuantum 2000) The sulfate ion / sulfide ion ratio of the powder surface was calculated.

d. Coarse particle rate Photograph a picture of metallic nickel powder with a scanning electron microscope (made by Hitachi High-Technologies, Inc., trade name S-4700), and use the image analysis software (made by Mt. Tech, trade name MacView 4.0) from the photograph Then, out of about 100,000 particles, the number of coarse particles having a particle size of 3 times or more of the number 50% diameter was measured to determine the ratio of coarse particles.

e. Sintering behavior 1 g of nickel powder, 3% by weight of camphor and 3% by weight of acetone were mixed, this mixture was filled in a cylindrical metal container with an inner diameter of 5 mm and a length of 10 mm and compressed at 500 MPa to prepare test pellets. The thermal shrinkage behavior of this test pellet was measured using a thermomechanical analyzer (Rigaku Co., Ltd., trade name TMA 8310) under a 1.5% by volume hydrogen-nitrogen reducing atmosphere at a heating rate of 5 ° C./min. It was measured. The 5% shrinkage temperature was determined from the measurement results, and the sintering behavior of the nickel powder was evaluated as shown in Table 1.

f. Agglomerated particles 100 g of a 5 wt% aqueous solution of a polycarboxylic acid-based dispersant is added to 0.5 g of nickel powder and dispersed for 60 seconds with an output of 600 W and an amplitude width of 30 μm using an ultrasonic dispersing machine did. After dispersion, suction filtration is performed at a suction pressure of 0.1 MPa using a membrane filter (pore diameter: 1 μm, filter diameter: 25 mm) (manufactured by GE Healthcare Bio-Sciences Co., Ltd., trade name Nucripore membrane). The aggregation behavior of the nickel powder was evaluated as shown in Table 2.

The measurement results and the evaluation results of Examples 1 and 2 and Comparative Examples 1 to 3 are shown in Table 3. In Comparative Example 3, the sulfur concentration was below the detection limit, and it was not possible to evaluate the state of sulfur on the surface of the nickel powder.

(Examples 3 to 5)
A nickel powder was produced in which the state of sulfur on the surface was variously changed so that the number 50% diameter was about 0.09 μm, and the sulfur content was about 1.5%. Using the nickel powder production apparatus shown in FIG. 1, the washing step of dispersing and settling in water is repeated five times for the sulfur-free nickel powder produced without adding sulfur dioxide gas to nickel chloride gas. The nickel chloride was removed. Thereafter, an ethanol solution of thiourea was added so that the sulfur content was 1.5% with respect to the nickel powder, and the mixture was stirred at 35 ° C. for 30 minutes. Then, after performing a drying treatment so that the water content is 0.5% or less with a flash dryer, heat treatment at 200 ° C. in a reducing atmosphere of 2 vol% hydrogen-argon (hydrogen partial pressure: 2 kPa), In order to change the state of sulfur on the surface of the nickel powder, the treatment time was changed to 0.5 to 3 hours to obtain nickel powders of Examples 3 to 5. The measurement results and the evaluation results of Examples 3 to 5 are shown in Table 3.

(Comparative example 4)
Step after the stirring process in the ethanol solution of thiourea after the washing process of Example 3 is subjected to a drying process so that the water content becomes 0.5% or less by the flash drying apparatus after the washing process Sulfurization treatment was performed at 230 ° C. for 10 minutes in a quartz reaction tube under a 1.5 vol% hydrogen-5 vol% hydrogen sulfide-nitrogen atmosphere (hydrogen partial pressure: 1.5 kPa, hydrogen sulfide partial pressure: 5 kPa) Nickel powder was obtained in the same manner as in Example 3 except for the above. The measurement results and the evaluation results of Comparative Example 4 are shown in Table 3.

With respect to the obtained nickel powder, the number 50% diameter, the sulfur concentration, the sulfate ion / sulfide ion ratio on the surface of the nickel powder, the coarse particle ratio, the sintering behavior, and the aggregated particles were evaluated by the aforementioned method. The results are shown in Table 3.

As is clear from Table 3, the nickel powders of Examples 1 and 2 have a sulfur concentration of 1.0 to 5 in spite of the 50% number diameter being comparable as compared with Comparative Examples 1 to 3. Since it is in the range of 0% by weight, it can be seen that the sintering behavior is excellent. In addition, the nickel powders of Examples 3 and 4 have the same sulfur concentration as the above-mentioned range despite the fact that the number 50% diameter is similar to that of Example 5 and Comparative Example 4, and the sulfate ion is As the sulfide ion ratio is 0.10 or less, it can be seen that the generation of agglomerated particles is small. In addition, although the evaluation of the aggregation behavior was “Δ” in Example 5, the evaluation of the more important sintering behavior was “o”, which is sufficient as the performance of the present invention.

From the above results, the nickel powder of the present invention has excellent sintering characteristics in the manufacturing process of the multilayer ceramic capacitor, and as a result, defects such as peeling between the electrode layer and dielectric layer of the multilayer ceramic capacitor and cracks in the electrode layer Was proven to be effective in preventing the occurrence of Furthermore, it was proved to be effective in preventing generation of defects such as shorts between electrode layers and a reduction in withstand voltage as it has an effect of preventing the generation of aggregated particles.

The present invention is useful as a nickel powder for a conductive paste in internal electrode applications of multilayer ceramic capacitors.

Claims

A nickel powder comprising 1.0 to 5.0% by mass of sulfur and having a number 50% diameter of not more than 0.09 μm.
2. The nickel powder according to claim 1, wherein the molar ratio of sulfur present as sulfate ion to sulfur present as sulfide ion among sulfur present on the surface of said nickel powder is 0.10 or less.
The nickel powder according to claim 1 or 2, wherein the abundance ratio of coarse particles having a particle diameter three or more times the number 50% diameter of the nickel powder is 100 ppm or less on a number basis.