TW202539827A - Nickel-containing particles, method for producing nickel-containing particles, and slurry - Google Patents

Abstract

This invention provides nickel-containing particles, a method for manufacturing nickel-containing particles, and a slurry for manufacturing nickel-containing particles, wherein the nickel-containing particles effectively suppress thermal shrinkage at a specific temperature upon heating. The nickel-containing particles of this invention have nickel-containing particles and a silicon-containing coating layer covering at least a portion of the surface of the nickel particles. The nickel particles contain sulfur, and in the Si-Kα spectrum obtained by soft X-ray emission spectroscopy analysis, the peak apex position is above 1735 eV, and the full width at half maximum (FWHM) of the peak is below 10.5 eV.

Description

Nickel-containing particles, methods for manufacturing nickel-containing particles, and slurries

This invention relates to nickel-containing particles, a method for manufacturing nickel-containing particles, and a slurry for manufacturing nickel-containing particles.

Nickel powder, which mainly contains nickel, is sometimes used as an electrode material for multilayer ceramic chip capacitors (MLCCs) in electronic computers, including multifunction mobile phones, as well as for nickel-hydrogen batteries or lithium-ion batteries due to its excellent heat dissipation and electrical properties.

Multilayer ceramic chip capacitors (MLCs) are constructed by alternately stacking dielectric layers and internal electrode layers, with external electrodes at both ends. The dielectric layers can be ceramic powders with high dielectric constants, such as barium titanium oxide, as the main component. The internal electrode layers can be powders of various metals or alloys. In recent years, the industry has been developing MLCs that use fine nickel powder in the internal electrode layers.

Regarding the technology of nickel powder, there are technologies described in patent documents 1 to 5, etc.

In patent document 1, as "nickel-containing particles that are difficult to shrink during sintering", it is proposed that "a nickel-containing particle has a core particle containing Ni and a covering layer on the surface of the particle containing at least one element selected from Si, Al, Zr and Sn, and in thermomechanical analysis in a mixed environment of 99% nitrogen and 1% hydrogen at a heating rate of 10℃/min from 25℃ to 800℃, the shrinkage rate at 400℃ is less than 3.0% and the shrinkage rate at 800℃ is less than 15.0%, and in thermogravimetric analysis in an atmospheric environment, the temperature at which the mass increases by 0.5% relative to 25℃ is between 250℃ and 350℃".

The purpose of Patent 2 is to "provide a composite Ni microparticle, its manufacturing method and manufacturing apparatus, wherein even ultrafine particles with an average particle size of less than 0.2 μm, particularly less than 0.1 μm, can prevent delamination during the sintering process and can achieve thin-layer production of ultrafine particle application products such as multilayer ceramic capacitors". Furthermore, Patent 2 discloses "a composite Ni microparticle characterized in that a material selected from the group consisting of Si, _Si3N4 and _SiO2 is coated on the surface of Ni or Ni alloy microparticles with a thickness of 1 to ₅ nm, and the average particle size of the composite Ni microparticle is 0.07 to 0.50 μm".

Patent document 3 describes "a nickel fine powder, characterized in that the average particle size is 0.05 to 0.3 μm, the crystallite diameter relative to the specific surface area diameter is 60 to 90%, the sulfur content is 0.1 to 0.5% by mass, and the oxygen content is 0.4 to 1.5% by mass, and the surface has a coating layer containing oxygen with a thickness of 2 to 15 nm, at least the outermost part of the coating layer contains a mixture of nickel sulfur compounds and nickel oxide compounds". According to this "nickel powder," it has "high purity and excellent crystallinity, making it suitable as a material for electronic devices and components. Especially when used as nickel powder for forming the internal electrodes of MLCCs, it can increase the shrinkage initiation temperature and suppress shrinkage accompanying sintering, thus preventing structural defects such as cracks or peeling." Furthermore, by controlling the surface compound layer, the decomposition temperature of the resin adhesive can be made the same as that of the original resin adhesive, thus further preventing discontinuity or peeling of the internal electrodes. "In addition, the above-mentioned method for manufacturing nickel powder is simple and can be realized on an industrial scale, so its industrial value is extremely high."

Patent document 4 describes "a nickel powder characterized by containing 1.0 to 5.0% by mass of sulfur, and 50% of the particles having a diameter of less than 0.09 μm".

Patent document 5 describes "a metal powder comprising metal particles containing a metal and sulfur at a bulk concentration of 0.01% to 1.0% by weight, wherein the local concentration of sulfur at a position 4 nm away from the surface of the metal particles is 2 atoms or more, and the bulk concentration and the local concentration are estimated by means of an inductively coupled plasma emission spectrometry (ICP-ESI) analyzer and an energy-dispersive X-ray spectrometer of a scanning transmission electron microscope," and "the metal is nickel, copper, or silver." [Prior Art Documents][Patent Documents]

[Patent Document 1] International Publication No. 2021/199694 [Patent Document 2] Japanese Patent Application Publication No. 2004-232036 [Patent Document 3] International Publication No. 2011/037150 [Patent Document 4] International Publication No. 2015/156080 [Patent Document 5] International Publication No. 2020/004105

[Problem to be Solved by the Invention] However, when nickel powder is used to manufacture products such as the aforementioned multilayer ceramic chip capacitors, sometimes the nickel powder is contained in an organic binder or the like to form a paste. Then, a blank formed from ceramic powder for the dielectric layer and a nickel powder paste for the inner electrode layer are stacked, and they are heated simultaneously to sinter the ceramic powder and nickel powder separately.

If the nickel powder shrinks significantly at a relatively low temperature during sintering, the difference in shrinkage behavior compared to ceramic powder may lead to product defects such as internal electrode layer breakage. To prevent this, nickel powder is sometimes required to have heat resistance to the point that it does not shrink significantly at a specific temperature when heated. From the perspective of improving heat resistance, the inventions described in Patents 1-5 still have room for further improvement.

The present invention addresses the problems described above, aiming to provide nickel-containing particles that effectively suppress thermal shrinkage at specific temperatures during heating, a method for manufacturing nickel-containing particles, and a slurry for manufacturing nickel-containing particles. [Technical Means for Solving the Problem]

Through dedicated research, the inventors discovered that if nickel-containing particles, whose surface is covered by a silicon-containing coating, further contain sulfur, then the heat resistance may be improved. Furthermore, through further research, they found that if the peaks of the Si-Kα spectrum obtained by soft X-ray emission spectroscopy in these nickel-containing particles have a specific shape, then higher heat resistance is observed.

The nickel-containing particles of the present invention comprise nickel particles containing nickel and a covering layer containing silicon covering at least a portion of the surface of the nickel particles. The nickel particles contain sulfur, and in the Si-Kα spectrum obtained by analysis using soft X-ray emission spectroscopy, the peak apex position is above 1735 eV, and the full width at half maximum (FWHM) of the peak is below 10.5 eV.

The silicon content of the nickel-containing particles is preferably 0.05% to 1.5% by mass.

The sulfur content of the nickel-containing particles is preferably 0.01% to 1.0% by mass.

The particle size of the nickel-containing particles mentioned above is sometimes 50 nm to 300 nm.

In the method for manufacturing nickel-containing particles of the present invention, the nickel-containing particles have nickel particles containing nickel and a covering layer containing silicon covering at least a portion of the surface of the nickel particles. The method for manufacturing nickel-containing particles includes a coating step of coating the nickel particles with silicon. As the nickel particles, nickel particles with a concentration ratio of 5 times or more between the local concentration (atm%) of sulfur at a position 2 nm away from the surface in the depth direction and the local concentration (atm%) of sulfur at a position 5 nm away from the surface in the depth direction are used.

The slurry of the present invention is used to manufacture nickel-containing particles as described above, the nickel-containing particles having nickel-containing nickel particles and a covering layer containing silicon covering at least a portion of the surface of the nickel particles, the slurry comprising sulfur-containing nickel particles and silicon additives.

The aforementioned silicon additive preferably comprises granular silicon dioxide and/or organosilicon compounds. [Effects of the Invention]

The nickel-containing particles of this invention are nickel-containing particles that effectively suppress thermal shrinkage at a specific temperature when heated.

The embodiments of the present invention are described below. One embodiment of the present invention comprises nickel particles (core particles) and a covering layer covering at least a portion of the surface of the nickel particles. The covering layer contains silicon. The nickel particles primarily contain nickel, and importantly, further contain sulfur.

In addition, in the Si-Kα spectrum obtained by analyzing the nickel-containing particles using soft X-ray emission spectroscopy (SXES), the peak apex position is above 1735 eV and the full width at half maximum (FWHM) of the peak is below 10.5 eV.

While the exact reason may not be clear, if a silicon-containing coating layer exists on the surface of nickel particles that contain both nickel and sulfur, resulting in the aforementioned peak shape in the Si-Kα spectrum, then these nickel-containing particles would possess excellent heat resistance. These particles do not undergo significant thermal shrinkage within a specific temperature range when heated. Therefore, when using nickel-containing particles in the manufacture of multilayer ceramic chip capacitors, it is possible to achieve shrinkage behavior consistent with that of ceramic powder during sintering, thereby suppressing product defects.

In particular, when nickel-containing particles are manufactured by coating nickel particles containing a relatively large amount of sulfur near their surface, it is believed that during the sintering of the nickel-containing particles, the liquefaction of the sulfur component in the surface layer is hindered by the silicon of the coating layer. Consequently, the diffusion of nickel deep within the nickel-containing particles between adjacent nickel-containing particles is further suppressed. As a result, it is speculated that sintering is delayed, thereby further effectively suppressing thermal shrinkage.

(Composition) Nickel particles, which constitute a part of nickel-containing particles, mainly contain nickel (Ni), but also contain sulfur (S). Therefore, nickel-containing particles containing nickel particles contain sulfur.

The sulfur content of the nickel particles is preferably 0.01% to 1.0% by mass. If the sulfur content is too low, sintering may have to be carried out at a low temperature. On the other hand, if the sulfur content is too high, there is a concern that oxidation may occur during firing, generating gases and causing interlayer peeling. The sulfur content is determined according to JIS K0116 using ICP emission spectroscopy. The sulfur content of the nickel particles described below can also be determined in the same manner.

At least a portion of the coating layer present on the surface of the nickel particles contains silicon (Si). The silicon content of the nickel-containing particles is preferably 0.05% to 1.5% by mass, more preferably 0.08% to 1.2% by mass. By ensuring that the nickel-containing particles contain a relatively high amount of silicon, heat resistance is improved. On the other hand, if the silicon content of the nickel-containing particles is too high, the improvement in heat resistance may be diminished. The silicon content is determined by X-ray diffraction (XRD). The silicon content is calculated as a value converted to the weight ratio of _SiO₂ .

(Particle size) The particle size of nickel-containing particles is, for example, 50 nm to 300 nm, typically 80 nm to 300 nm, but not limited to this. Nickel powder containing such fine nickel particles is particularly suitable for applications such as the above-mentioned multilayer ceramic chip capacitors.

The particle size referred to here is the number average diameter. When measuring the particle size of nickel-containing particles, the diameter of 500 to 1000 particles in the SEM image obtained by photographing each particle at a specific magnification is measured, and the average number of these particles is taken as the particle size.

(Si-Kα spectrum of SXES) When silicon contained in nickel-containing particles is analyzed by soft X-ray emission spectroscopy, the Si-Kα spectrum illustrated in Figure 1 is obtained as the energy distribution of characteristic X-rays (Kα lines) emitted from the Si element in the nickel-containing particles due to X-ray irradiation.

In the aforementioned Si-Kα spectrum of nickel-containing particles according to the embodiment of the present invention, the peak apex position Pt is 1735 eV or higher. Furthermore, the full width at half maximum (WHM) of this peak, i.e., the full width at half the intensity Sp of the peak apex (Sp/2), is 10.5 eV or lower. Here, the peak apex position Pt refers to the value of x when the function f(x) fitted as a linear synthesis of complex Gaussian functions in the Si-Kα spectrum reaches its maximum value Sp. The full width at half maximum (WHM) refers to the width of the range of x for which the value of the function f(x) is Sp/2 or higher.

If the peak position Pt and the full width at half maximum (WHM) of the Si-Kα spectrum are within the above ranges, then the nickel-containing particles will not undergo significant thermal shrinkage at a specific heating temperature and will exhibit excellent heat resistance.

In Si-Kα spectra, the higher the energy value of Pt at the peak position within the aforementioned range, and the smaller the full width at half maximum (FWHM) Wh within the same range, the higher the heat resistance tends to be. Therefore, the peak position Pt is preferably in the range of 1736 eV to 1740 eV. Furthermore, the FWHM Wh is preferably in the range of 8.0 eV to 10.5 eV.

The analysis of nickel-containing particles using soft X-ray emission spectroscopy is performed as follows: A dried sample containing nickel particles is pressed onto an indium foil and then fixed to the experimental stage of the soft X-ray emission spectroscopy apparatus using a carbon ribbon for analysis. Here, the accelerating voltage can be set to 3 kV, the current to 45–50 nA, the magnification to 30,000x, the measurement time to 15 minutes per field of view, and the cumulative number of fields of view to 50–100.

(Manufacturing method) In order to manufacture the nickel-containing particles as described above, nickel particles containing sulfur must first be prepared.

Nickel powder can be commercially available or produced using methods such as gas-phase or liquid-phase methods. For ease of particle size control and efficient production of spherical nickel particles, the following methods are particularly preferred: gas-phase reduction method, which involves contacting nickel chloride gas with a reducing gas, or spray thermal decomposition method, which involves thermally decomposing a thermally decomposable nickel compound.

In gas-phase reduction processes, a chlorination step and a reduction step are typically performed. The chlorination step involves heating a solid feedstock containing elemental nickel to evaporate it, which then comes into contact with chlorine gas to generate nickel chloride gas. The reduction step involves reacting the nickel chloride gas with a reducing gas such as hydrogen. Specifically, for example, chlorine gas can be introduced into the nickel in the chlorination step to continuously generate nickel chloride gas, while simultaneously supplying this nickel chloride gas to the reduction step to allow it to come into contact with a reducing gas, thereby continuously reducing the nickel chloride gas. Furthermore, if the nickel chloride gas used in the reduction step can be obtained through other means, the chlorination step can be omitted.

The solid feedstock used in the chlorination step can be in granular, block, or plate form with a particle size of approximately 5 mm to 20 mm, and its nickel purity is preferably 99.5% by mass or higher. In the chlorination step, the solid feedstock is heated while simultaneously contacting it with chlorine gas. The temperature can be set above 800°C and below the melting point of nickel (1453°C) to fully promote the reaction. Considering the reaction rate and the durability of the chlorination furnace, a range of 900°C to 1100°C is preferred. This generates nickel chloride gas.

In the reduction step, the nickel chloride gas is brought into contact with a reducing gas such as hydrogen to carry out the reaction. At this time, an inert gas such as nitrogen or argon can also be mixed in at an amount of 1 mol% to 30 mol% relative to the nickel chloride gas. Alternatively, chlorine gas can be supplied separately from the nickel chloride gas in the reduction step. When an inert gas or chlorine gas is supplied in the reduction step, the partial pressure of the nickel chloride gas can be adjusted, which can control the particle size of the nickel particles and suppress particle size inhomogeneity. Furthermore, in the reduction step, other sulfur-containing gases such as hydrogen sulfide, sulfur dioxide, sulfur halides ( _SnCl₂ (n is an integer greater than or equal to 2), _SF₆ , _SF₅Cl , _{SF₅Br ,} etc.) can be supplied. Thus, nickel particles containing sulfur are obtained after the reduction step. The temperature of the reduction reaction can be above the temperature required for the reduction reaction, but in order to generate easily handleable solid nickel particles, it can be set below the melting point of nickel, for example, preferably 900℃～1100℃.

In the reduction step, nickel atoms are generated instantaneously upon contact between nickel chloride gas and the reducing gas. These nickel atoms collide with each other, thereby generating ultrafine particles that then grow. Furthermore, nickel particles of a specific particle size are obtained based on other conditions such as the partial pressure or temperature of the nickel chloride gas in the reduction step. Because the amount of nickel chloride gas produced in the chlorination step corresponds to the amount of chlorine supplied, the supply of nickel chloride gas to the reduction step can be adjusted by controlling the amount of chlorine supplied. Therefore, the particle size of the nickel particles can be effectively controlled.

The nickel particles obtained in the reduction step can be cooled. Ideally, this is done by blowing in an inert gas such as nitrogen to rapidly cool the airflow, which has completed the reduction reaction and is around 1000°C, to about 400–800°C. This prevents the formation of secondary particles from the agglomeration of primary particles in the powder generated in the reduction step, thus allowing the acquisition of nickel particles of the desired particle size. The nickel particles are then separated and recovered, for example, using a filter bag.

Alternatively, the nickel after the reduction step can be contacted with sulfur-containing compounds such as thiourea in a dry or wet manner, either based on or replacing the supply of sulfur-containing gas in the reduction step. By contacting with the sulfur-containing compound, the surface of the nickel particles is coated with the sulfur-containing compound, or a layer of nickel and sulfur compounds is formed, thereby obtaining sulfur-containing nickel particles (core particles). In the wet case, specifically, a sulfur-containing compound can be added to the nickel particles in the liquid, or an aqueous solution of the sulfur-containing compound or an alcohol solution such as ethanol or isopropanol can be mixed. At this time, stirring can be performed using ultrasound or the like. The amount of sulfur-containing compound used can be adjusted such that the sulfur content of the nickel particles after contact is, for example, 0.01 to 1.0% by mass, preferably 0.05 to 0.5% by mass. The contact time is sometimes set to 10-60 minutes, or even 15-30 minutes.

If a sulfur-containing gas is supplied during the reduction step, the resulting nickel particles tend to contain sulfur from the surface to relatively deep locations. On the other hand, when the nickel particles are brought into contact with sulfur-containing compounds after the reduction step, the local concentration of sulfur near the surface of the inner part of the nickel particles tends to increase.

In the spray thermal decomposition method, a thermally decomposable nickel compound is used as a raw material. A solution of the raw material is sprayed to form fine droplets, and then heated at a high temperature to cause the nickel compound to thermally decompose and generate nickel particles. Specifically, the raw material can include at least one selected from the group consisting of nitrates, sulfates, nitrate oxysalts, sulfate oxysalts, chlorides, ammonium complexes, phosphates, carboxylates, and alkoxy compounds. Water, alcohols, acetone, ethers, etc., can be used as solvents when spraying the raw material to form droplets. The spraying method sometimes utilizes ultrasound or dual nozzles. The temperature of the heated droplets is preferably set above the temperature at which the specific nickel compound used as the raw material undergoes thermal decomposition and near the melting point of the metal.

In the liquid-phase method, a nickel aqueous solution containing nickel sulfate, nickel chloride, or nickel complexes is brought into contact with an alkaline metal hydroxide such as sodium hydroxide by means of addition, thereby generating nickel hydroxide. Then, the nickel hydroxide is reduced using a reducing agent such as hydrazine to obtain nickel particles. The nickel particle powder generated in this way is sometimes subjected to pulverization as needed to form a uniform particle size.

The nickel particles obtained by the methods described above ideally contain sulfur. Therefore, the nickel particles containing nickel particles produced through the following coating steps become sulfur-containing nickel particles. The sulfur content of the nickel particles is preferably 0.01% to 1.0% by mass, and more preferably 0.05% to 0.2% by mass. The sulfur content of the nickel particles can be adjusted by changing the flow rate of the sulfur-containing gas supplied to the reduction step.

Furthermore, the nickel particles are preferably such that, when the sulfur concentration (atm%) is measured from the surface of the nickel particles toward the depth direction, the local sulfur concentration (atm%) at a position 2 nm away from the surface in the depth direction is at least 5 times higher than the local sulfur concentration (atm%) at a position 5 nm away from the surface in the depth direction. In this way, by ensuring a relatively high amount of sulfur is present near the surface of the nickel particles, and interacting with the silicon of the coating layer formed in the following coating step, the diffusion of nickel between the nickel-containing particles is suppressed, thereby further improving heat resistance.

The localized sulfur concentration of nickel particles can be observed, for example, using an energy-dispersive X-ray spectroscopy (STEM-EDS) analyzer within a scanning transmission electron microscope. A specific measurement method is described as follows: First, nickel particles are dispersed in resin, and the resin is cured. Then, a cross-section is exposed using a section polisher (CP), and a thin film sample based on planar sampling is prepared using focused ion beam (FIB). By setting the sample thickness to approximately 100 nm, the nickel particles are shaped into a thin film of that thickness. Then, EDS measurement is performed on the obtained thin film along a straight line passing through the center of the nickel particles, thereby obtaining the localized concentration. As conditions for EDS measurement, for example, the following conditions can be selected: accelerating voltage 200 kV, probe diameter 1 nm, spacing width 3 nm, and measurement time of 15 seconds per point.

Then, a silicon coating step is performed on the nickel particle powder. By means of the coating step, at least a portion of the surface of the nickel particles (core particles) is covered by a silicon-containing coating layer, thereby obtaining nickel particle-containing powder.

In the coating step, any specific method used will suffice as long as it allows the nickel particles to come into contact with silicon and form a coating layer on its surface. For example, powdered nickel particles can be added to a slurry containing silicon additives suspended in a liquid such as water, and the mixture can be stirred and stirred together.

The silicon additive included in the slurry is preferably a granular silicon additive containing silicon dioxide ( _SiO2 ) and/or an organosilicon with carbon-silicon bonds. Specific examples of organosilicon include Si resinates and silicone oils. The average particle size of the granular silicon additive is preferably set to 20 nm to 50 nm.

The mass percentage of silicon additives in the slurry can be set from 1% to 75%. This makes it easy to adjust the silicon content of nickel-containing particles to a specific range. In addition, dispersants are sometimes included in the slurry.

Sometimes the stirring speed during mixing is set to 3000 rpm to 5000 rpm, the stirring time is set to 1 hour to 20 hours, and the liquid temperature is set to 10℃ to 60℃.

It is believed that when nickel particles are mixed into the slurry, the nickel particles come into contact with the silicon additives in the slurry, and a coating reaction occurs. As a result, a silicon-containing coating layer is formed on the surface of the nickel particles.

After mixing the nickel particles with the slurry, the slurry is dried. At this point, the slurry can be heated to a temperature of 60°C to 80°C, for example, in an argon atmosphere. If the temperature is too low, drying will take a long time; if it is too high, there is a concern about the formation of unwanted hydroxides, etc.

After drying, a nickel-containing powder is obtained, in which at least a portion of the surface of the nickel particles (core particles) is covered by a silicon-containing coating. The nickel-containing particles exhibit the following tendency: the peak positions and full width at half maximum (FWHM) of the peaks in the Si-Kα spectrum obtained by soft X-ray emission spectroscopy are respectively within specific ranges. It is concluded that when the nickel-containing particles are heated, thermal shrinkage at relatively low temperatures is suppressed by the reaction products of sulfides and silicon components on the particle surface. [Example]

Next, the nickel-containing particles of this invention were prototyped and their effects were confirmed, which will be explained below. However, the explanation here is merely illustrative and is not intended to be limiting.

(Examples 1 and 2) Nickel particles (core particles) with a particle size of 180 nm were produced by performing the chlorination and reduction steps described above, followed by contact with a sulfur-containing compound, using a gas-phase reduction method. The contact with the sulfur-containing compound was performed by adding an ethanol solution of the sulfur-containing compound to a liquid containing the nickel particles and then subjecting it to ultrasonic treatment at room temperature (20°C) for 30 minutes. Then, drying was carried out using an airflow dryer and heated at 200°C in the atmosphere for 30 minutes. Here, by varying the amount of sulfur-containing compound added, several types of nickel particles with different sulfur contents were obtained, as shown in Table 1. Furthermore, the ratio (C2/C1) of the local sulfur concentration C2 (atm%) at a position 2 nm away from the surface of the nickel particles in the depth direction to the local sulfur concentration C1 (atm%) at a position 5 nm away from the surface of the nickel particles in the depth direction is 5.5 times in Example 1 and 7.8 times in Example 2.

Then, the nickel particle powder is coated with a silicon-containing coating layer to cover at least a portion of the surface of the nickel particles (core particles), thereby producing nickel-containing particles. Specifically, nickel particle powder is added to a slurry containing the silicon additives shown in Table 1 and mixed, and the slurry is stirred for 1 hour. Thus, nickel-containing particles are obtained.

(Comparative Example 1) Nickel particles manufactured by another company were obtained. The concentration ratio (C2/C1) of sulfur at a location 2 nm away from the surface of the nickel particles in the depth direction (C2(atm%)) relative to the local concentration of sulfur at a location 5 nm away from the surface of the nickel particles in the depth direction (C1(atm%)) was 1.9 times. Nickel-containing particles were obtained by coating in the same manner as in Example 1.

(Comparative Example 2) Except that the nickel particle powder was not coated, nickel particle powder was prepared by the methods of Examples 1 and 2. The concentration ratio (C2/C1) of the local sulfur concentration C2 (atm%) at a position 2 nm away from the surface of the nickel particles in the depth direction to the local sulfur concentration C1 (atm%) at a position 5 nm away from the surface of the nickel particles in the depth direction was 9.9 times.

(Evaluation) The sulfur content (S content) and silicon content (Si content) of each nickel-containing particle obtained in the above manner were measured using the method described above, and the results are shown in Table 1. The analysis results of the sulfur concentration in the depth direction of the nickel particles of Example 1 and Comparative Example 1 obtained by STEM-EDS are shown in Figure 2. In addition, the particle size of the nickel-containing particles is 180 nm.

Furthermore, following the order and conditions described above, each nickel-containing particle was analyzed using soft X-ray emission spectroscopy (SXES) to obtain the Si-Kα spectrum. The peak positions and full width at half maximum (FWHM) of the Si-Kα spectrum were then confirmed. The results are shown in Table 1.

In addition, tests were conducted to confirm the heat resistance of each nickel-containing particle. In this test, the nickel-containing particles were heated to 800°C to create a sintered film, and images of the sintered film were visually verified by photographing. The heat resistance was then evaluated according to the following criteria: ○ Maintaining particle shape △ Partially maintaining particle shape × Not maintaining particle shape

[Table 1] Nickel particles (core particles) Cover Nickel-containing particles Silicone Additives Mixed conditions S content [mass ppm] Si content (converted from _SiO2 weight ratio) [mass %] SXES Heat resistance evaluation S content [mass ppm] S concentration ratio C2/C1 [times] Stirring speed [rpm] Stirring time [hours] Liquid temperature [℃] Peak position [eV] The full width of the peak at half its peak [eV] Implementation Example 1 800 5.5 Silicon dioxide 4000 8 25 800 1.0 1736.9 10.5 ○ Implementation Example 2 1200 7.8 Silicon dioxide 4000 8 25 1200 1.0 1736.3 8.8 ○ Comparative example 1 1300 1.9 Silicon dioxide 4000 8 25 1300 1.0 1734.6 8.9 △ Comparative example 2 1600 9.9 - - - - 1600 - Unable to measure Unable to measure ×

The above suggests that the nickel-containing particles of this invention may effectively suppress thermal shrinkage at a specific temperature during heating.

Sp: Peak intensity; Pt: Peak position; Wh: Half-peak width of the peak.

[Figure 1] is a chart showing an example of the Si-Kα spectrum obtained by analyzing nickel-containing particles using soft X-ray emission spectroscopy. [Figure 2] is a chart showing the analysis results of sulfur concentration in the depth direction of nickel particles (core particles) of Example 1 and Comparative Example 1 obtained by STEM-EDS.

Claims (7)

A nickel-containing particle comprising nickel particles and a covering layer containing silicon covering at least a portion of the surface of the nickel particles, wherein the nickel particles contain sulfur and, in a Si-Kα spectrum obtained by analysis using soft X-ray emission spectroscopy, the peak apex position is above 1735 eV and the full width at half maximum (FWHM) of the peak is below 10.5 eV. For example, in the nickel-containing particles of Request 1, the silicon content is 0.05% to 1.5% by mass. For example, the nickel-containing particles in request item 1 or 2, wherein the sulfur content is 0.01% by mass to 1.0% by mass. For example, the nickel-containing particles in claim 1 or 2 have a particle size of 50 nm to 300 nm. A method for manufacturing nickel-containing particles, wherein the nickel-containing particles have nickel-containing nickel particles and a covering layer containing silicon covering at least a portion of the surface of the nickel particles, the method for manufacturing nickel-containing particles includes a coating step of coating the nickel particles with silicon, and the nickel particles used are nickel particles in which the concentration ratio of local sulfur concentration (atm%) at a position 2 nm away from the surface in the depth direction to the concentration ratio of local sulfur concentration (atm%) at a position 5 nm away from the surface in the depth direction is more than 5 times. A slurry for manufacturing nickel-containing particles having nickel-containing particles and a covering layer of silicon covering at least a portion of the surface of the nickel particles, and comprising sulfur-containing nickel particles and a silicon additive. The slurry of claim 6, wherein the aforementioned silicon additive comprises granular silicon dioxide and/or organosilicones.