JP2002285201A - Fluorine-containing nickel powder and production method for the fluorine-containing nickel powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nickel powder which is hardly oxidized even in a high temperature air atmosphere, and to provide a production method therefor. SOLUTION: The fluorine-containing nickel powder contains, by weight, 0.01 to 1.0% fluorine. The fluorine-containing nickel powder is produced by bringing the nickel powder into contact with a fluorine-containing gas, and heating the nickel powder at 100 to 400%oC.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nickel powder and a method for producing the nickel powder. In particular, the present invention relates to a nickel powder suitable for manufacturing a heat-fired electrode for a chip component as an electronic material component.

[0002]

2. Description of the Related Art Conventionally, nickel powder has been widely and generally used as an electrode material for chip parts and the like. In such a case, the nickel powder is once processed into a nickel paste using a binder resin or the like, and the nickel paste is applied to a predetermined portion of a component for manufacturing a nickel electrode, and the binder resin is oxidized from the nickel paste applied in the air. After being decomposed, high-temperature heating such as sintering is generally performed.

[0003] After the above-described steps, the surface of the nickel powder is also oxidized. If the oxidized nickel layer is left as it is, the resistance value increases and the conductive performance deteriorates. Therefore, in order to reduce the oxidized nickel layer, a reduction treatment is generally performed in a high-temperature reducing atmosphere gas.

[0004]

However, it has been found that even if the above-described reduction treatment is performed in a high-temperature reducing atmosphere gas, oxygen cannot be sufficiently removed. That is, the high-temperature heat applied during the reduction treatment may cause thermal diffusion in the dielectric layer before some of the nickel oxide formed on the surface undergoes reduction, and the electrodes may disappear.

[0005] Therefore, since such a phenomenon occurs, there is a certain limit in adopting a method of reducing nickel particles once having undergone surface oxidation, and it has been desired to solve this problem. It is.

[0006]

The inventors of the present invention have conducted intensive studies on nickel powder which is hardly oxidized even in high-temperature heating, and as a result, the nickel powder corresponds to the following nickel powder.

In the first aspect, the fluorine content is 0.01 to 1.0.
It is a fluorine-containing nickel powder characterized by containing by weight%. The reason for expressing the fluorine-containing nickel powder in this manner is as follows. The inventors of the present invention have studied the surface modification of nickel particles so as to prevent the formation of an oxide film on the surface of the nickel particles and to have no adverse effect on the conductive performance when processed into an electrode material of an electronic component. I thought. For that purpose, they conceived that if the surface of nickel powder particles is modified using fluorine, it is possible to obtain nickel powder of high quality for the purpose.

At this stage, it is desirable to employ a method for modifying the surface of nickel powder particles using fluorine as described later at this stage. When these production methods are considered, the method of existence of fluorine used for the surface modification of the nickel particles exists on the surface of the nickel particles. A nickel layer containing fluorine is formed in the near-surface layer. The elemental fluorine is diffused and uniformly distributed in the nickel powder particles. And so on. And
It is considered that at least the above-mentioned state is formed as a minimum necessary condition.

The method of existence of fluorine in the nickel particles should be clarified through research. However, it is necessary to accurately confirm the shape and the size of the nickel particles because they are small. Is difficult. Therefore, the present inventors prepared a fluorine-containing nickel powder exhibiting good oxidation resistance against atmospheric oxidation at a high temperature at a temperature of 145 ° C. in a sulfuric acid solution (98 wt% sulfuric acid: water =
1: 1), the effluent was dissolved in a constant volume, and quantitatively determined by an ion chromatograph (IC-7000 ion chromatograph) to determine the ratio of fluorine to the total weight of the fluorine-containing nickel powder. It is used after conversion.

[0010] In claim 1, the fluorine content is 0.01 to
1.0% by weight. At this time, the fluorine content is
If the content is less than 0.01% by weight, the effect of adding fluorine to the nickel powder does not contribute to improving the oxidation resistance. On the other hand, when the content of elemental fluorine exceeds 1.0% by weight, the electrical conductivity starts to deteriorate. Among them, 0.05 to 0.5% by weight of fluorine
Within this range, there is no variation in product quality, and in particular, the oxidation resistance of nickel powder in a high-temperature atmosphere is stabilized. In particular, if it exceeds 0.5% by weight, the surface of the nickel powder particles tends to be rough instead of smooth. Since the fluorine-containing nickel powder according to claim 1 is hard to be oxidized, it is useful in the production of electrodes for heating and firing used in electronic components, for example, the external electrodes of a multilayer ceramic capacitor, and effectively prevents the disappearance of the electrodes. That is what you do.

First, in claim 2, 100 ° C. to 400 ° C.
The method according to claim 1, wherein the nickel powder and the fluorine-containing gas are brought into contact with each other at an ambient temperature. According to a third aspect of the present invention, there is provided the method for producing a fluorine-containing nickel powder according to the first aspect, wherein the nickel powder is brought into contact with a fluorine-containing aqueous solution, and the nickel powder is heated at a temperature of 100 ° C to 600 ° C. . The fluorine-containing solid compound according to claim 1, wherein the nickel powder is brought into contact with a fluorine-containing solid compound, and the nickel powder is heated at a temperature not lower than the decomposition temperature of the fluorine-containing solid compound and not higher than 600 ° C. It is a method for producing nickel powder.

According to the second aspect of the present invention, first, 100
It begins by bringing the nickel powder into contact with a fluorine-containing gas at an ambient temperature of from 400C to 400C. That is, the nickel powder is placed in a stream of a high-temperature fluorine-containing gas. The fluorine-containing gas at this time is such as a hydrogen fluoride gas. The contacting method at this time is not particularly limited, as long as the fluorine-containing gas and the nickel powder can be efficiently contacted and the fluorine-containing gas can be adsorbed on at least the surface of the nickel powder particles. For example, nickel powder is placed in an atmosphere replaced by a fluorine-containing gas, and the frequency of contact between the fluorine-containing gas and the nickel powder is increased by rocking or stirring the nickel powder. At this time, in order to increase the number of collisions of the fluorine-containing gas with the surface of the nickel powder and to cause the surface to be efficiently adsorbed, the contact can be performed by raising the temperature to a certain level. Thus, the reaction between the nickel powder and the fluorine is caused to modify the surface of the nickel powder.

The temperature of the atmosphere at which the nickel particles and the fluorine-containing gas are brought into contact with each other is a temperature of 100 ° C. to 400 ° C. Adopting this temperature range
Fluorine-containing gas adsorbed on the surface of nickel particles reacts to diffuse and fix elemental fluorine to the surface of nickel particles and the layer near the surface of nickel particles, and is most suitable for surface modification of nickel particles -ing If the atmosphere temperature at this time is lower than 100 ° C., the reactivity with the fluorine-containing gas on the surface of the nickel particles is poor, and the industrial production efficiency is significantly impaired. And, even if the ambient temperature exceeds 400 ° C., the reaction rate does not increase any more.

According to a third aspect of the present invention, a fluorine-containing aqueous solution is used for the adsorption of fluorine on the surface of nickel powder. Here, a method of adsorbing a fluorine compound on the surface of nickel powder using a fluorine-containing aqueous solution will be described. The fluorine-containing aqueous solution is an aqueous solution in which a fluorine compound is dissolved, specifically, a solution in which ammonium fluoride, potassium hydrofluorate, or the like as a fluorine compound is dissolved in water.

The adsorption of the fluorine compound on the surface of the nickel particles is performed by charging the nickel powder into a fluorine-containing aqueous solution and stirring for a certain period of time to adsorb the fluorine compound on the surface of the nickel particles. Then, by heating at a predetermined temperature, the moisture and the fluorine compound adsorbed on the surface of the nickel particles are decomposed, and only the elemental fluorine is diffused and fixed to the surface of the nickel particles and a layer near the surface of the nickel particles. Then, a fluorine fixing process for modifying the surface of the nickel particles is performed (hereinafter, this heating operation is referred to as a “fluorine fixing process”).

In the fluorine fixing treatment, the fluorine-containing aqueous solution adsorbed on the surface of the nickel particles reacts to diffuse and fix the elemental fluorine on the surface of the nickel particles and the layer near the surface of the nickel particles, thereby fixing the nickel particles. The surface of the nickel powder is made less likely to be oxidized. As the heating temperature at this time, a temperature of 100 ° C. to 600 ° C. is adopted. Heating at a temperature of less than 100 ° C. did not allow fluorine alone to stably remain on the surface of the nickel powder particles or on the layer near the surface, and was adsorbed on the surface of the nickel powder particles without lowering the productivity. In order to sufficiently remove water, a temperature of at least about 100 ° C. is required. This is because, when heating is performed in a temperature range exceeding 600 ° C., the nickel powder particles are sintered and aggregated easily by the heating operation at this stage.

Here, the fluorine-containing aqueous solution used for adsorbing the fluorine compound on the surface of the nickel powder using the fluorine-containing aqueous solution is an aqueous solution in which the fluorine compound is dissolved. A solution in which ammonium, potassium hydrofluorate, or the like is dissolved in water is used.

The invention according to claim 4 is different from claim 3 only in that fluorine is adsorbed on the nickel powder surface by using a fluorine-containing solid compound, and the fluorine fixing treatment is the same. Therefore, here, a method of using a fluorine-containing solid compound to react with a fluorine compound on the surface of nickel powder will be described. The fluorine-containing solid compound is an ammonium fluoride crystal, a potassium hydrofluoride crystal, a nickel fluoride crystal, or the like. These fluorine-containing solid compound and nickel powder are mixed, and the fluorine-containing solid compound and nickel powder are mixed. In contact with the surface.
The mixing method at this time is not particularly limited, as long as the fluorine-containing solid compound and the nickel powder can be uniformly mixed.

In the fluorine fixing treatment, the fluorine-containing solid compound is decomposed in a state where the nickel powder particles and the fluorine-containing solid compound are mixed by heating at a temperature not lower than the decomposition temperature of the fluorine-containing solid compound and not more than 600 ° C. Then, a fluorine fixing treatment for modifying the surface of the nickel particles is performed by diffusing and fixing only the fluorine element to the surface of the nickel particles and the layer near the surface of the nickel particles. The decomposition temperature of the fluorine-containing solid compound at this time is a value determined for each selected compound. For example, the decomposition temperature of ammonium fluoride is about 220 ° C. in a nitrogen atmosphere.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a case where a fluorine-containing nickel powder is produced by the production method according to the present invention and the oxidation initiation temperature is measured to compare with a conventional nickel powder will be described.

First Embodiment: First, 15 g of ammonium fluoride was dissolved in 200 cc of water to produce a fluorine-containing aqueous solution. 150 g of nickel powder (average particle size 0.2 μm by SEM observation) was added to the fluorine-containing aqueous solution, and the mixture was stirred for 20 minutes to perform a fluorine adsorption treatment on the surface of the nickel powder. Thereafter, this was filtered to separate a nickel powder, and the nickel powder was dried in an air atmosphere at 70 ° C.

Next, this nickel powder was subjected to a heat treatment at 250 ° C. for 1 hour in a stream of nitrogen gas to carry out a fluorine fixing treatment. The nickel powder having been subjected to the fluorine fixing treatment was washed with water and dried at a temperature of 100 ° C. to obtain a fluorine-containing nickel powder. The fluorine content in the fluorine-containing nickel was 0.16% by weight.

The inventors of the present invention confirmed the performance of the fluorine-containing nickel powder obtained in the first embodiment,
20 mg of the fluorine-containing nickel powder obtained in the present embodiment was heated at 5 ° C./min in the air and subjected to thermogravimetric analysis (TG-DT).
A; Seiko Denshi Kogyo TG / DTA6300). Further, as a comparative sample, a similar nickel powder having an average particle size of 0.2 μm observed by SEM and having not been subjected to any treatment (hereinafter referred to as “Comparative Example 1”) was used. A gravimetric analysis was performed. As a result, as can be seen from the results shown in Table 1, in Comparative Example 1, 300 ° C.
A weight increase due to oxidation occurs from around, resulting in a weight increase of approximately 27% at 600 ° C. This means
Nickel (atomic weight 58.7) is converted to nickel oxide (molecular weight 7
If it is considered that the weight increases by 4.7% at 4.7), it means that complete oxidation has occurred at a temperature near 600 ° C. On the other hand, in comparison with Comparative Example 1, the weight increase in the case of the fluorine-containing nickel powder according to the present embodiment is delayed, and it can be seen that the oxidation resistance is excellent.

Second Embodiment: First, 2 g of solid ammonium fluoride crystals and 200 g of nickel powder (average particle diameter of 0.6 μm by SEM observation) are mixed by stirring, and the surface of the nickel powder particles and the ammonium fluoride crystals are mixed. Is in contact with.

Next, the mixture of the ammonium fluoride crystal and the nickel powder was placed in a nitrogen gas stream at 250 ° C.
For 1 hour to decompose the ammonium fluoride crystal and perform a fluorine fixing treatment. The fluorine content in this fluorine-containing nickel was 0.43% by weight.

Then, the present inventors confirmed that the performance of the fluorine-containing nickel powder obtained in the second embodiment was
The same thermogravimetric analysis as performed in the first embodiment was performed. Further, as a comparative sample, a similar nickel powder having an average particle size of 0.6 μm as observed by SEM and having not been subjected to any treatment (hereinafter referred to as “Comparative Example 2”) was used. A gravimetric analysis was performed. As a result, as can be seen from the results shown in Table 1, in the case of Comparative Example 2, a weight increase due to oxidation was clearly observed at around 300 ° C.
As a result, the weight increased by almost 27%. On the other hand, in comparison with Comparative Example 2, it can be seen that the weight increase in the case of the fluorine-containing nickel powder according to the present embodiment is delayed and the oxidation resistance is excellent.

Third Embodiment: In this embodiment, 200
g of nickel powder (average particle diameter 0.6 μm by SEM observation)
m) was placed in a gas-flow rotary electric furnace. While rotating and mixing, at a temperature of 200 ° C., 1 liter of nitrogen /
And a mixed gas of 0.05 l / min of hydrogen fluoride for 30 minutes
The nickel powder and the mixed gas were brought into contact with each other to cause a reaction between the nickel powder and the fluorine-containing gas.

Then, the inventors of the present invention confirmed the performance of the fluorine-containing nickel powder obtained in the third embodiment,
The same thermogravimetric analysis as performed in the first embodiment was performed. As a result, as can be seen from the results shown in Table 1, Comparative Example 2
In the case of (1), an increase in weight due to oxidation was clearly observed from around 300 ° C., and the result was that the weight increased by approximately 27% at 600 ° C. On the other hand, in comparison with Comparative Example 2, it can be seen that the weight increase in the case of the fluorine-containing nickel powder according to the present embodiment is delayed and the oxidation resistance is excellent.

[0029]

[Table 1]

[0030]

The fluorine-containing nickel powder according to the present invention exhibits oxidation resistance performance that is incomparable to conventional nickel powder. Therefore, high-temperature heating processing when nickel powder is used as a nickel paste as an electrode material for chip parts and the like. When the binder resin is oxidized and decomposed, the nickel particles are less susceptible to oxidation, and as a result, diffusion into the dielectric is suppressed, and the loss of the electrode can be effectively prevented. Further, the fluorine-containing nickel powder can achieve high productivity efficiently and efficiently by using the production method according to the present invention.

Claims (4)

[Claims] 1. A fluorine-containing nickel powder containing 0.01 to 1.0% by weight of fluorine. 2. The method for producing a nickel powder containing fluorine according to claim 1, wherein the nickel powder is brought into contact with a fluorine-containing gas at an ambient temperature of 100 ° C. to 400 ° C. 3. The method according to claim 1, wherein the nickel powder is brought into contact with a fluorine-containing aqueous solution, and the nickel powder is heated at a temperature of 100 ° C. to 600 ° C. 4. The fluorine-containing solid compound according to claim 1, wherein the nickel powder is brought into contact with a fluorine-containing solid compound, and the nickel powder is heated at a temperature not lower than the decomposition temperature of the fluorine-containing solid compound and not higher than 600 ° C. Method for producing nickel powder.