JP5668879B1 - Nickel powder - Google Patents

Abstract

The present invention provides a nickel powder capable of quantifying the reactivity of the surface of nickel powder used in multilayer ceramic capacitors and the like and preventing the occurrence of defects. At 30 ° C. to 600 ° C., temperature rising desorption measurement of carbon dioxide adsorbed by detecting the amount of carbon dioxide desorbed by continuously increasing the temperature of nickel powder adsorbed with carbon dioxide. Nickel powder in which the total desorption amount of carbon dioxide at 100 ° C. to 600 ° C. is 130 μmol / g or less in the temperature rising process. [Selection] Figure 1

Description

  The present invention relates to nickel powder, and more particularly, to nickel powder whose reactivity on the surface of nickel powder is controlled and used for an internal electrode of a multilayer ceramic capacitor, for example.

  Nickel powder is used as a material of a conductive paste for producing a thick film conductor. Thick film conductors are used in the formation of electric circuits, electrodes of multilayer ceramic components such as multilayer ceramic capacitors and multilayer ceramic substrates.

  The multilayer ceramic capacitor has a structure in which a multilayer body in which dielectrics and internal electrodes are alternately overlapped is arranged, and external electrodes are attached to both ends of the multilayer ceramic capacitor so as to face the outside of the multilayer body. Yes.

  The manufacturing method of the multilayer ceramic capacitor is as follows. First, a conductive paste obtained by kneading nickel powder, a resin such as ethyl cellulose and an organic solvent such as terpineol is screen-printed on a dielectric green sheet. Dielectric green sheets are laminated so that the printed conductive pastes are alternately stacked, and pressure-bonded.

  The manufacturing method of the multilayer ceramic capacitor then cuts the multilayer body into a predetermined size, performs a binder removal process for burning and removing a resin such as ethyl cellulose used as an organic binder, and firing at a high temperature of 1000 ° C. or higher. . Then, an external electrode is attached to the ceramic body to form a multilayer ceramic capacitor.

  In the binder removal process of the multilayer ceramic capacitor manufacturing process, when nickel powder whose powder surface reactivity is not controlled is used, the resin is decomposed near the nickel powder at a temperature lower than the temperature at which the resin is normally decomposed. The This is because nickel itself has an action of promoting thermal decomposition of the resin.

  However, since a resin such as a dielectric layer that does not use nickel powder is not decomposed at this low temperature, the gas generated by partial resin decomposition is trapped inside the capacitor, and the internal electrode discontinuity or Separation between the dielectric layer and the internal electrode layer occurs. Therefore, it is important to control the reactivity of the nickel powder surface in order to prevent problems in the binder removal process.

  Moreover, in electronic devices typified by mobile phones and digital devices, the electronic components used are becoming lighter, thinner, and shorter year by year. Chip ceramic multilayer capacitors are also becoming smaller and larger in capacity. Along with this, since the internal electrode layer is thinned, the strength of the internal electrode layer is lowered. Therefore, it is more important to prevent the above problems in the binder removal process.

JP 2007-157563 A

  Various methods have been studied in order to prevent problems in the binder removal process as described above. In Patent Document 1, the oxygen content, carbon content, and sulfur content of nickel powder are controlled. Since this method suppresses the reactivity of the nickel powder surface, it is effective in preventing the occurrence of problems in the binder removal process. However, this method requires pasting to measure the resin decomposability, and it takes time to evaluate the reactivity of the nickel powder surface.

  Patent Document 1 describes that it is preferable that the amount of hydroxyl groups bonded to the surface of the nickel powder is as small as possible. From this description, it can be said that not only the oxygen content but also the form of its presence is affected. That is, the elements contained in the nickel powder and the presence forms affect the reactivity of the nickel powder surface, and oxygen, carbon and sulfur element contents and oxygen present as hydroxyl groups are disclosed. However, no mention is made of the strength and amount of the reactivity of the nickel powder surface itself. Therefore, it is unclear to what extent the reactivity of the nickel powder surface affects the decomposition behavior of the resin.

  Therefore, the present invention quantifies the reactivity of the surface of the nickel powder that affects the decomposition behavior of the resin in the binder removal process, and by setting the value below the reference value, the discontinuity of the partial internal electrodes and the dielectric An object of the present invention is to provide nickel powder capable of preventing problems such as peeling between the body layer and the internal electrode layer.

In the present invention, in view of the problems of the prior art, the reactivity of the nickel powder surface is greatly influenced by the base strength and the amount of base on the nickel powder surface, and carbon dioxide is attached to the nickel powder, and then the temperature is continuously raised. Te Atsushi Nobori measurement of carbon dioxide to detect the amount of carbon dioxide that release heat removal (hereinafter, may be referred to as a CO ₂ -TPD) found that quantifiable at, and completed the present invention based on this finding It is a thing.

That is, the nickel powder according to the present invention has a temperature rise of carbon dioxide that detects the amount of carbon dioxide desorbed and the desorption temperature by continuously heating the nickel powder adsorbed with carbon dioxide and thermally desorbing it. The total desorption amount of carbon dioxide at 100 ° C. to 600 ° C. is 130 μmol / g or less in the temperature rising process at 30 ° C. to 600 ° C. by desorption measurement.

  In the present invention, the reactivity of the nickel powder surface is reduced so that the total desorption amount of carbon dioxide in the range of 100 ° C. to 600 ° C. is 130 μmol / g or less in the temperature-programmed desorption measurement of carbon dioxide. , Rapid decomposition of the resin at the time of temperature rise can be suppressed. Moreover, in this invention, suppression of rapid decomposition | disassembly of resin is accelerated | stimulated by reducing the reactivity so that the total desorption amount of the carbon dioxide in the range of 200 degreeC-400 degreeC may also be 80 micromol / g or less. be able to. Therefore, in this invention, even if it uses nickel powder for the internal electrode layer of a multilayer ceramic capacitor, for example, it can prevent generating a malfunction by a binder removal process.

In Examples 1-3 and Comparative Examples 1 and 2 _is a diagram showing the relationship between the temperature -CO ₂ desorption amount of CO 2 -TPD measurement.

  The nickel powder to which the present invention is applied will be described below. Note that the present invention is not limited to the following detailed description unless otherwise specified. The nickel powder to which the present invention is applied will be described in the following order.

1. Nickel powder 2. Manufacturing method of nickel powder Surface treatment of nickel powder

<1. Nickel powder>
The nickel powder to which the present invention is applied has surface reactivity controlled based on the base strength and amount of the surface. The nickel powder quantifies the surface reactivity and suppresses the surface reactivity by setting the value below a desired reference value.

  Nickel powder is used for an internal electrode layer of a multilayer ceramic capacitor, for example. When used for an internal electrode layer of a multilayer ceramic capacitor, it is necessary to make the surface reactive enough to suppress the decomposition of the resin and further suppress the promotion of the decomposition during the binder removal process. Therefore, the reactivity which can suppress decomposition | disassembly is quantified, and decomposition | disassembly of resin can be suppressed if it is below the reference | standard by making it into the reference | standard. In other words, if the reactivity of the surface of the nickel powder that can suppress the decomposition of the resin can be quantified in advance, there is no need to paste to measure the resin decomposability, and the time for evaluating the reactivity of the surface of the nickel powder can be shortened. Can do.

The surface reactivity is quantified by a temperature programmed desorption method (CO ₂ -TPD method) of carbon dioxide. Specifically, the reactivity of the nickel powder surface is determined by temperature rising desorption of carbon dioxide that detects the amount of carbon dioxide desorbed by continuously heating the nickel powder with carbon dioxide adsorbed and thermally desorbing it. In the temperature rising process at 30 ° C. to 600 ° C., the total desorption amount of carbon dioxide at 100 ° C. to 600 ° C. is set to 130 μmol / g or less.

(Measured by _CO 2 -TPD method)
The resin decomposition reaction involves an electrophilic reaction or a nucleophilic reaction to the resin, and the decomposition proceeds via an intermediate compound. In addition to the surface free energy, this reaction on the metal surface is influenced by the basicity of the metal surface in the case of a nucleophilic substitution reaction and the acidity of the metal surface in the case of an electrophilic substitution reaction. Therefore, the reactivity of the metal surface is indicated by high basicity or acidity.

The basicity and acidity of the metal surface can be measured by the amount of gas adsorbed on the metal surface and the temperature at which the gas desorbs when the temperature is raised. That is, by adsorbing gas on the metal surface and measuring the amount of gas desorbed during the temperature rising process, the amount of basicity or acidity (adsorption point = number of reaction points) can be measured. Moreover, if the desorption temperature of the adsorbed gas is measured, the strength of basicity or acidity can be measured. The basicity can be measured by acid gas adsorption and thermal desorption, and the acidity can be measured by basic gas adsorption and thermal desorption. Carbon dioxide (CO ₂ ) is used for the basicity measurement, and ammonia (NH ₃ ) is used for the acidity measurement.

The reactivity of the nickel powder surface with respect to the resin is determined by temperature programmed desorption (CO ₂ -TPD) of carbon dioxide in the nickel powder because the resin is decomposed by a nucleophilic substitution reaction.

  The reference value is a total desorption amount of 130 μmol / g from 100 ° C. to 600 ° C. when carbon dioxide is adsorbed on nickel powder and the temperature is raised from 30 ° C. to 600 ° C. Therefore, the nickel powder has a total desorption amount from 100 ° C. to 600 ° C. of 130 μmol / g or less. More preferably, the total desorption amount from 200 ° C. to 400 ° C. is 80 μmol / g or less. When the total desorption amount exceeds 130 μmol / g, the decomposition of the resin by the nucleophilic substitution reaction is promoted, the internal electrode becomes discontinuous, or the dielectric layer and the internal electrode layer are separated by the binder removal treatment of the multilayer ceramic capacitor. Peeling may occur and cracks may be generated.

  The higher the basicity and the stronger the base, the higher the reactivity of the nickel powder with an acidic compound.

  In particular, in the decomposition reaction between the surface and the organic compound found in the metal powder, it has been found that there is a correlation between the reactivity and the adsorption / desorption characteristics of the ammonia gas or carbon dioxide gas of the metal powder. In the actual decomposition reaction, as described above, in addition to the surface free energy, the basicity of the metal surface affects the nucleophilic substitution reaction. The higher the basicity, the higher the reactivity.

  In such a decomposition reaction, a reaction intermediate is once formed. Then, charge and electrons move in the reaction intermediate, the reaction intermediate is mutated and eliminated, and shifts to the reaction with the next organic compound, thereby expressing the catalytic action on the surface of the metal powder. Become. However, when the interaction between the reaction intermediate and the surface of the metal powder is strong, charges and electrons cannot be desorbed, the decomposition reaction is stopped, and the catalyst does not act as a catalyst.

  The strength of this interaction has a correlation with the desorption temperature of carbon dioxide gas or ammonia gas. It has been found that a desorption amount in a temperature range from about 200 ° C. to about 400 ° C. means that the decomposition reaction proceeds. Further, it has been found that the desorption amount in the temperature range of 400 ° C. or higher means that the interaction between the reaction intermediate and the metal powder surface is strong and the decomposition reaction does not proceed.

  That is, for example, in the case of a nucleophilic substitution reaction, an electron is donated from a base to form a reaction intermediate, and if the basicity is moderately strong, the reaction intermediate is mutated and decomposed to form a metal surface. Can be desorbed from. Therefore, by analyzing the basicity and the strength of the base, it is possible to evaluate the decomposition reactivity between the metal powder and the resin without producing a metal paste.

  Therefore, in the nickel powder, the total desorption amount of carbon dioxide at 100 ° C. to 600 ° C. is 130 μmol / g or less, more preferably the total amount of carbon dioxide at 200 ° C. to 400 ° C. in the temperature rising process at 30 ° C. to 600 ° C. By making the desorption amount 80 μmol / g or less, the decomposition reaction with the resin can be suppressed without producing a metal paste.

(Surface coating)
The nickel powder is subjected to a surface treatment to be described later in order to set the decomposition reaction with the resin to a reference value or less. The surface of the nickel powder is coated with at least one of a sulfur-containing substance, a silicon-containing substance, and a titanium-containing substance on the particle surface by surface treatment. The nickel powder is preferably coated with a sulfur-containing substance, and the sulfur content is preferably 0.1 to 1.0% by mass.

(Shape, average particle size)
The nickel powder is preferably spherical and has an average particle size of 0.05 to 1.0 μm. Thus, it can be suitably used as a conductive paste material for forming an electric circuit or a multilayer ceramic capacitor.

  That is, by making the nickel powder spherical, when a thick film conductor serving as an internal electrode layer is obtained using a conductive paste, the nickel particles in the thick film conductor can be uniformly dispersed and the nickel particles The density of can be improved.

  On the other hand, when the average particle size is less than 0.05 μm, aggregation is severe, nickel particles cannot be sufficiently dispersed in the conductive paste, and handling of the nickel powder is not easy. On the other hand, when the average particle size exceeds 1.0 μm, the surface of the thick film conductor obtained using the conductive paste has a large unevenness, and when it is laminated as an internal electrode using a multilayer ceramic capacitor or the like, there is a gap between the electrodes. There is a risk of short circuit.

  More preferably, the nickel powder has an average particle size of 0.05 to 0.3 μm. Nickel powder having an average particle size of 0.05 to 0.3 μm is suitable for a multilayer ceramic capacitor having a thin internal electrode layer. In addition, the average particle diameter of nickel powder can obtain | require the diameter of each particle | grain from observation with a scanning electron microscope (SEM), and can obtain | require it from the average value.

<2. Manufacturing method of nickel powder>
The nickel powder described above can be produced by a known method such as a wet method, a PVD method, a CVD method, or a plasma method. As an example, a method for producing nickel powder by a wet method will be described below.

  In the wet method, first, a water-soluble nickel salt is dissolved in water, and the nickel salt is reduced to nickel particles with a reducing agent such as hydrazine. Then, after the reduction, the nickel particles are washed in order to remove the residual reaction solution, followed by solid-liquid separation, and the nickel particles are dried to obtain nickel powder.

  The reducing agent is not particularly limited, but it is preferable to use at least one selected from hydrazine, a hydrazine compound, sodium borohydride, a polyol, a saccharide, and the like. Of these reducing agents, hydrazine is most preferred because it has particularly few impurities. Further, when hydrazine or the like is used, it is preferable to add an alkaline substance since the reduction reaction rate increases when the pH is 10 or more.

  Furthermore, in order to obtain spherical and monodispersed nickel powder, it is preferable to add a metal salt, complexing agent, colloidal agent or the like that is nobler than nickel.

  As an example of a metal salt more noble than nickel, water-soluble gold salt, silver salt, platinum salt, palladium salt, rhodium salt, iridium salt and copper salt can be mentioned. Examples of complexing agents include ammonium or formic acid having a carboxyl group, acetic acid, tartaric acid, citric acid, malic acid, and ascorbic acid. Examples of colloid agents include gelatin, polyvinyl pyrrolidone, gum arabic, sodium hexametaphosphate, and polyvinyl alcohol.

<3. Nickel powder surface treatment>
The nickel powder is subjected to a surface treatment to reduce the surface reactivity. A known method may be used as the surface treatment method and the substance used therefor.

  Examples of the surface treatment method include the following methods. Nickel powder is added to a solution in which at least one of a sulfur-containing substance, a silicon-containing substance, and a titanium-containing substance is dissolved, and a surface coating treatment is performed. Alternatively, the surface coating treatment is performed by bringing vapor or gas containing at least one of sulfur-containing material, silicon-containing material, and titanium-containing material into contact with the surface of the nickel powder. Furthermore, the nickel powder is exposed to an oxidizing or reducing atmosphere to control the oxidation state of the nickel powder surface. By such a method, the nickel powder is subjected to a surface treatment to control the surface reactivity.

  Specifically, examples of the sulfur-containing substance include inorganic sulfides such as sodium hydrogen sulfide, ammonium hydrogen sulfide, sodium sulfide, ammonium sulfide, and hydrogen sulfide, 2-mercaptobenzothiazole, 2-mercaptobenzimidazole, triazine thiol, and thiourea. Organic sulfur compounds such as are preferred.

  Silicon-containing materials include alkoxysilanes such as methyltriethoxysilane, dimethyldiethoxysilane and tetraethoxysilane, silane cups such as vinyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane and 3-aminopropyltrimethoxysilane. A ring agent or the like is preferable.

  As the titanium-containing substance, for example, titanate coupling agents such as isopropyl triisostearoyl titanate, isopropyl trioctanoyl titanate, isopropyl dimethacrylisostearoyl titanate, isopropyl tridodecylbenzenesulfonyl titanate, and isopropyl isostearoyl diacryl titanate are preferable.

  In order to make the total desorption amount of carbon dioxide on the surface of the nickel powder below the reference value, it is necessary to subject the nickel powder to surface treatment. However, the amount of adsorption on the surface depends on the surface treatment method and the substance adsorbed on the surface. Even if they are the same, the effect of suppressing the surface decomposition reaction is different, and the surface reactivity is different. For this reason, it is necessary to change the amount to be adsorbed depending on which surface treatment method is used to treat at least one of the sulfur-containing material, silicon-containing material, and titanium-containing material. Accordingly, the surface treatment method, the substance to be adsorbed, and the amount of adsorption are appropriately determined so that the surface treatment of the nickel powder is less than the reference value.

  For example, when nickel powder is surface-treated with an aqueous solution of sodium hydrogensulfide, the surface is obtained by adjusting the sodium hydrogensulfide concentration so that the sulfur content in the nickel powder after the surface treatment is 0.15% by mass or more. Process.

  When surface treatment is performed by bringing hydrogen sulfide gas into contact with nickel powder, the surface treatment is performed by adjusting the concentration of hydrogen sulfide gas so that the sulfur content in the nickel powder after the surface treatment is 0.1% by mass or more. I do.

Therefore, when performing the surface coated with the sulfur-containing _material, CO 2 in -TPD measurement, the total desorption amount and the CO ₂ from 100 ° C. to 600 ° C., total disengagement of CO ₂ from 200 ° C. to 400 ° C. It is preferable that the separation amount is equal to or less than the above-described reference value, and the sulfur content in the nickel powder is 0.1 to 1.0% by mass. More preferably, the sulfur content is 0.1 to 0.5% by mass.

  When the sulfur content of the nickel powder is less than 0.1% by mass, the reactivity of the nickel powder surface cannot be suppressed, and cracks often occur in the binder removal process during the production of the multilayer ceramic capacitor. On the other hand, if the sulfur content exceeds 1.0% by mass, the effect of suppressing the reactivity of the nickel powder surface will not be improved, and there may be another problem due to excessive sulfur during the production of the multilayer ceramic capacitor. There is a possibility that the sulfur-containing gas generated in the binder process or the subsequent firing process corrodes the capacitor manufacturing apparatus.

  The nickel powder as described above has a total desorption amount of carbon dioxide at 100 ° C. to 600 ° C. of 130 μmol / g or less in the temperature rising process at 30 ° C. to 600 ° C. by temperature rising desorption measurement of carbon dioxide, The reactivity of the nickel powder to the resin is quantified. Thereby, even if it does not actually produce a metal paste and confirm generation | occurrence | production of a malfunction, it can be set as the nickel powder which does not generate a malfunction. Therefore, when this nickel powder is used, time for evaluating the reactivity with the resin is not required, and therefore the manufacturing time of the multilayer ceramic capacitor or the like can be shortened. Further, when such nickel powder having a reference value or less is used for the internal electrode of the multilayer ceramic capacitor, it is possible to prevent the discontinuity of the internal electrode and the generation of cracks due to the separation between the dielectric layer and the internal electrode.

Specific examples to which the present invention is applied will be described below, but the present invention is not limited to these examples. The average particle diameter, the evaluation method of the CO ₂ -TPD measurement and nickel powder of the catalytic activity of the nickel powder of the nickel powder used in Examples and Comparative Examples are as follows.

(1) Average particle diameter of nickel powder Using a scanning electron microscope (manufactured by JEOL Ltd., JSM-5510), a photograph at a magnification of 20,000 times (corresponding to a range of 19.2 μm long × 25.6 μm wide) The area of the particles in which the entire shape of the particles in the photograph can be seen was measured, the diameter of each particle was determined from the area, and the average value was determined.

(2) Sulfur content of nickel powder The sulfur concentration of nickel powder was measured using a carbon and sulfur simultaneous analyzer (LECO, CS-600).

(3) _CO 2 -TPD measurement of nickel powder fully automatic temperature-programmed desorption spectrum apparatus (manufactured by BEL Japan Inc., TPD-1-ATw) using, after the CO ₂ adsorbed on the nickel powder, 600 from room temperature The temperature was continuously raised to 0 ° C., and the desorption temperature and desorption amount of CO ₂ were measured with a quadrupole mass spectrometer. From the obtained results, the total desorption amount (integral value) of CO ₂ from 100 ° C. to 600 ° C. and the total desorption amount (integral value) of CO _{2 from} 200 ° C. to 400 ° C. were determined.

(4) Presence or absence of cracks After the nickel powder obtained in each example and comparative example was made into a paste, it was applied on a dielectric sheet containing BaTiO ₃ as a main component, and 100 layers were laminated. Thereafter, the laminate was treated to remove the binder in a weak oxidizing atmosphere and fired in a weak reducing atmosphere to obtain a sintered body. By observing the cross section of the obtained sintered body with a microscope, the presence of cracks was observed.

[Example 1]
In Example 1, surface treatment was performed using an aqueous solution in which sodium monosulfide was dissolved in nickel powder obtained by a wet method. It was 3000 mass ppm when the sulfur content of the obtained nickel powder was measured. Then, the average particle diameter of the obtained nickel _powder, CO 2 -TPD, were evaluated for the presence of cracks. The results are shown in Table 1 and FIG.

[Example 2]
In Example 2, 5000 mass ppm of sulfur was contained in the nickel powder in the same reaction as in Example 1 except that the concentration of sodium hydrogen monosulfide used for the surface treatment was changed. Thereafter, the same evaluation as in Example 1 was performed. The results are shown in Table 1 and FIG.

[Example 3]
In Example 3, 1000 mass ppm sulfur was contained in nickel powder with respect to nickel powder using hydrogen sulfide gas. Thereafter, the same evaluation as in Example 1 was performed. The results are shown in Table 1 and FIG.

[Comparative Example 1]
In Comparative Example 1, 1000 mass ppm of sulfur was included with respect to the nickel powder in the same reaction as in Example 1 except that the concentration of sodium hydrogen monosulfide used for the surface treatment was changed. Thereafter, the same evaluation as in Example 1 was performed. The results are shown in Table 1 and FIG.

[Comparative Example 2]
In Comparative Example 2, the same evaluation as in Example 1 was performed with the prepared nickel powder without performing the surface treatment with sodium hydrogen monosulfide. Table 1 and FIG.

From the results shown in Table 1 and FIG. 1, in Examples 1 to 3, the total desorption amount of CO ₂ from 100 ° C. to 600 ° C. of the nickel powder is 130 μmol / g or less, and further from 200 ° C. to 400 ° C. The total desorption amount of CO ₂ is 80 μmol / g or less. Therefore, it is considered that the reactivity of the nickel powder surface was suppressed, and as a result, no crack was generated even in the evaluation of reproducing the binder removal step of the sintered body.

In Comparative Examples 1 and 2, the total desorption amount of CO ₂ from 100 ° C. to 600 ° C. of the nickel powder exceeded 130 μmol / g, and the total desorption amount of CO ₂ from 200 ° C. to 400 ° C. was 80 μmol / g. It was over. Therefore, it is considered that the surfaces of the nickel powders of Comparative Example 1 and Comparative Example 2 had reactivity suitable for the decomposition of the resin, and as a result, cracks were generated even in the evaluation reproducing the binder removal step of the sintered body. .

Furthermore, when Example 3 and Comparative Example 1 are compared, the cracking at the time of binder removal cannot be controlled by the sulfur content, but cracks are caused by the difference in total CO ₂ desorption from 100 ° C to 600 ° C. It is found that the reactivity with the resin on the nickel powder surface is lowered when the total amount of CO ₂ desorbed from 100 ° C. to 600 ° C. is less than 130 μmol / g. Furthermore, when the total amount of CO ₂ desorbed from 200 ° C. to 400 ° C. is less than 80 μmol / g, it can be seen that the reactivity directly connected to the decomposition of the resin is low.

Claims (5)

30 ° C. to 600 ° C. by temperature-programmed desorption measurement of carbon dioxide for detecting the amount of desorbed carbon and the amount of desorbed carbon dioxide by continuously heating the nickel powder adsorbed with carbon dioxide and thermally desorbing it. Nickel powder, wherein the total desorption amount of carbon dioxide at 100 ° C. to 600 ° C. is not more than 130 μmol / g in the temperature raising process in FIG.   2. The nickel powder according to claim 1, wherein the total desorption amount of carbon dioxide at 200 ° C. to 400 ° C. is 80 μmol / g or less in the temperature raising process at 30 ° C. to 600 ° C. 3.   The nickel powder according to claim 1 or 2, wherein the surface is coated with at least one of a sulfur-containing substance, a silicon-containing substance, and a titanium-containing substance.   The nickel powder according to claim 3, wherein the surface is coated with the sulfur-containing substance, and the sulfur content is 0.1 to 1.0% by mass.   The nickel powder according to any one of claims 1 to 4, wherein an average particle diameter is 0.05 to 1.0 µm.

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