Ni alloy powder

Abstract

To provide a Ni alloy powder capable of forming a multilayer ceramic capacitor (MLCC) excellent in electrostatic capacity.SOLUTION: Provided is a Ni alloy powder having an Si content of 0.05 mass% or more and less than 0.50 mass%, and a particle diameter D50 of 40-250 nm. In the Ni alloy powder, the proportion of Ni-OH bonds relative to Ni-Ni bonds, Ni-O bonds, and Ni-OH bonds is preferably about 40 mol% or less. The Ni alloy powder preferably has an S content of 200 ppm by mass or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a Ni alloy powder. [Background technology]

[0002] Multilayer ceramic capacitors (MLCCs) have a laminated structure in which dielectrics and internal electrodes are alternately stacked. Conventionally, Ni alloy powder has been used as a material for forming the internal electrodes of MLCCs (Patent Documents 1 to 3).

[0003] To manufacture an MLCC, first, an internal electrode paste (a paste containing Ni alloy powder and a binder) is printed in a desired pattern on a ceramic green sheet that will become a dielectric when fired. Next, a plurality of ceramic green sheets on which the internal electrode paste has been printed are stacked and pressure-bonded to obtain an unfired laminate (capacitor element). The resulting laminate is cut into any desired shape, heated at a low temperature (to remove the binder), and then fired at a high temperature. This sinters the dielectric material (such as barium titanate) contained in the ceramic green sheets to form a dielectric. The Ni alloy powder contained in the internal electrode paste also sinters to form an internal electrode. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-189802 Summary of the Invention [Problem to be solved by the invention]

[0005] When manufacturing an MLCC, alternately stacked ceramic green sheets and internal electrode paste are fired simultaneously. At this time, the Ni alloy powder contained in the internal electrode paste is sintered at a lower temperature earlier than the dielectric material contained in the ceramic green sheets. If the Ni alloy powder in the internal electrode paste sinters first, voids will form in the formed internal electrode. In this case, the area ratio of the internal electrode that covers the dielectric (coverage rate) will decrease, and less of the internal electrode will function effectively. In order to obtain the desired capacitance, it is necessary to improve the coverage rate.

[0006] In recent years, in order to increase the capacitance of MLCCs, there has been a demand for thinner internal electrodes and dielectrics (for example, a thickness of 0.5 μm or less). By using fine particles of Ni alloy powder, the internal electrodes can be formed thinly. However, the increased proportion of highly active particle surface reduces the sintering temperature and reduces the coverage.

[0007] By adding an appropriate amount of Si to the Ni alloy powder, it is possible to suppress the decrease in sintering temperature, that is, to obtain the effect of suppressing sintering. However, since Si is a metal that is much more easily oxidized than Ni, the Si in the Ni alloy powder is likely to precipitate as SiO2 in the firing atmosphere (an atmosphere with a slight oxygen partial pressure) when manufacturing MLCCs. Therefore, if Si is contained in the Ni alloy powder of the internal electrode paste, an SiO2 layer may be formed between the internal electrode and the dielectric. Dielectrics store electricity when a voltage is applied. When an SiO2 layer is present between the internal electrode and the dielectric, the applied voltage is distributed to both the SiO2 layer and the dielectric, reducing the voltage applied to the dielectric. This reduces the capacitance. The effect of such partitioning due to the SiO2 layer can be ignored when the dielectric is thick, but cannot be ignored when the dielectric is thin.

[0008] Patent Document 1 does not mention that the capacitance of an MLCC is increased when the internal electrodes and dielectric are thinned (for example, the thickness is reduced to 0.5 μm or less). When the present inventors produced MLCCs with internal electrodes and dielectrics each having a thickness of 0.5 μm using the Ni alloy powder described in Patent Document 1, the capacitance was sometimes insufficient.

[0009] Therefore, an object of the present invention is to provide a Ni alloy powder that can be used to obtain a multilayer ceramic capacitor (MLCC) with excellent capacitance. In particular, the object is to obtain an MLCC that has excellent capacitance even when the internal electrodes and dielectric are thin. [Means for solving the problem]

[0010] The present inventors have found that the above object can be achieved by employing the following configuration, and have completed the present invention. That is, the present invention provides the following [1] to [3]. [1] The Si content is 0.05 mass% or more and less than 0.50 mass%, and the particle size D 50 Ni alloy powder having a particle size of 40 to 250 nm. [2] The Ni alloy powder according to the above [1], wherein the ratio of Ni-OH bonds to Ni-Ni bonds, Ni-O bonds and Ni-OH bonds is 40 mol % or less. [3] The Ni alloy powder according to [1] or [2] above, wherein the S content is 200 mass ppm or less. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a Ni alloy powder that can be used to obtain a multilayer ceramic capacitor having excellent capacitance. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a schematic diagram showing a reactor used for producing Ni alloy powder. DETAILED DESCRIPTION OF THE INVENTION

[0013] [Ni alloy powder] The Ni alloy powder (nickel alloy powder) of this embodiment is generally a powder of a NiSi alloy containing nickel (Ni) and silicon (Si). More specifically, the Ni alloy powder of this embodiment has a Si content of 0.05 mass % or more and less than 0.50 mass % and a particle size D 50 is 40 to 250 nm.

[0014] <Si content> As described above, the inclusion of Si in the Ni alloy powder provides a sintering suppression effect. However, if the Si content of the Ni alloy powder is too low, it tends to sinter faster than the dielectric material, meaning that a sufficient sintering suppression effect cannot be obtained. The Si content is 0.05 mass % or more, preferably 0.10 mass % or more, and more preferably 0.15 mass % or more, because this provides an excellent sintering suppression effect and the resulting MLCC has excellent capacitance.

[0015] On the other hand, if the Ni alloy powder contains too much Si, the capacitance of the resulting MLCC will also decrease because a large amount of SiO2 layer will be formed at the interface between the internal electrode and the dielectric in the resulting MLCC. The Si content is less than 0.50 mass %, preferably 0.48 mass % or less, and more preferably 0.45 mass % or less, because the resulting MLCC has excellent capacitance.

[0016] It is preferable that there is no extreme bias in the Si content within each particle of the Ni alloy powder. When Si is concentrated near the surface of a particle, a thick Si oxide film forms on the outermost surface of the particle. Because the Si oxide film has a lower thermal expansion coefficient than the particle (NiSi alloy), it peels off from the particle surface during sintering. As the particles sinter (grain growth), the peeled Si oxide film migrates along the grain boundaries and precipitates as an SiO2 layer at the interface between the internal electrode and the dielectric, causing a decrease in the capacitance of the MLCC. On the other hand, if Si is concentrated in the center of the particle, a sufficient Si oxide film is not formed on the particle surface, and sintering cannot be suppressed. For these reasons, the Si content in the part excluding the surface layer of the particle (part from the surface to a depth of 5 nm) is preferably 30 to 300% of the total Si content of the Ni alloy powder.

[0017] 〈Particle size D 50 〉 If the particle size of the Ni alloy powder is too small, the proportion of the surface of each particle becomes large, and even if Si is contained, a sufficient sintering suppression effect cannot be obtained. The particle size of Ni alloy powder D is chosen because it has an excellent effect of suppressing sintering and the capacitance of the resulting MLCC is excellent. 50 is 40 nm or more, preferably 60 nm or more.

[0018] If the particle size of the Ni alloy powder is too large, the number of particle layers formed by applying the internal electrode paste decreases, particle gaps tend to occur, and the coverage rate decreases. In addition, the increase in coarse particles tends to cause short circuits and a decrease in the withstand voltage of the resulting MLCC. Therefore, the particle size D of the Ni alloy powder 50 is 250 nm or less, preferably 220 nm or less, and more preferably 200 nm or less.

[0019] <S content> The Ni alloy powder may contain sulfur (S). However, if the S content of the Ni alloy powder is too high, the sintering suppression effect may be reduced. For reasons such as a better sintering suppression effect and a better capacitance of the resulting MLCC, the S content of the Ni alloy powder is preferably 200 mass ppm or less, more preferably 150 mass ppm or less, even more preferably 100 mass ppm or less, and particularly preferably 50 mass ppm or less. The lower limit of the S content is not particularly limited, and may be, for example, 1 mass ppm, 3 mass ppm, or 5 mass ppm.

[0020] <Ratio of Ni-OH bonds> In the Ni alloy powder, examples of the bonding state of Ni include Ni-Ni bonding, Ni-O bonding, and Ni-OH bonding. If the Ni alloy powder has too many Ni-OH bonds, water is generated from the OH groups of the Ni-OH bonds during firing, and this water reacts with the Si in the Ni alloy powder particles, which may result in the formation of a large SiO2 layer at the interface between the internal electrode and the dielectric in the resulting MLCC. In this case, the capacitance of the MLCC may decrease, as described above.

[0021] The temperature at which water is released from Ni-OH bonds and they change to Ni-O bonds is around 230°C. Therefore, when binder removal is performed at, for example, about 250°C, the Ni-OH bonds change to Ni-O bonds. During this change, each particle of the Ni alloy powder undergoes volumetric shrinkage. In Ni alloy powder containing Si, an Si oxide film is formed on the surface of each particle, providing stability, but this volume shrinkage can cause the Si oxide film to peel off from the particle surface. Because the heating atmosphere for binder removal is typically an air atmosphere, oxidation of Si progresses from the surface where the Si oxide film has peeled off in each particle of the Ni alloy powder. Furthermore, volume shrinkage causes distortion on the particle surface, which facilitates oxygen diffusion and oxidizes the Si inside the particle. Furthermore, because there is a large difference in the thermal expansion coefficient between each Ni alloy particle and the Si oxide film, the Si oxide film peels off during subsequent firing, for example, when the temperature is raised to 1200°C. If Si remains inside the particles at this time, a new Si oxide film will form, suppressing sintering. However, if the oxidation of Si inside the particles progresses during binder removal and the Si content decreases, a new Si oxide film will not form, reducing the sintering suppression effect and the area ratio (coverage rate) of the internal electrode covering the dielectric. This results in a decrease in the capacitance of the MLCC. Furthermore, the Si oxide film that peels off during binder removal tends to migrate along grain boundaries as the particles are sintered and precipitate as an SiO2 layer at the interface between the internal electrode and the dielectric, which in this case leads to a decrease in the capacitance of the MLCC.

[0022] Therefore, in order to obtain a MLCC with a better capacitance, the ratio of Ni-OH bonds to Ni-Ni bonds, Ni-O bonds, and Ni-OH bonds in the Ni alloy powder (also simply referred to as the "ratio of Ni-OH bonds") is, for example, 40 mol % or less, preferably 35 mol % or less, and more preferably 33 mol % or less. The lower limit is not particularly limited, and is, for example, 5 mol %, but may be 10 mol %, 15 mol %, or 20 mol %.

[0023] The bonding state of Ni in the Ni alloy powder (and the proportion of Ni-OH bonds) is determined by X-ray photoelectron spectroscopy (XPS). More specifically, an XPS apparatus is used to first obtain the Ni2p spectrum of the Ni alloy powder. The obtained Ni2p spectrum is then subjected to waveform separation using peak fitting to calculate the areas of the Ni peak, NiO peak, and Ni(OH)2 peak. The area ratios of the Ni peak, NiO peak, and Ni(OH)2 peak are regarded as the molar ratios of Ni-Ni bonds, Ni-O bonds, and Ni-OH bonds, respectively, and the proportion of Ni-OH bonds (unit: mol%) is calculated.

[0024] [Method of manufacturing Ni alloy powder] Next, a method for producing the Ni alloy powder of the present embodiment will be described. Methods for producing Ni alloy powder with a small particle size include CVD (Chemical Vapor Deposition) and PVD (Physical Vapor Deposition), but the CVD method is preferred because it is easy to narrow the particle size distribution. The production of Ni alloy powder by the CVD method will be described below with reference to FIG.

[0025] <Configuration of reactor> FIG. 1 is a schematic diagram showing a reactor 1 used for producing Ni alloy powder. The main body of the reactor 1 is divided into a reaction section 2 , a cooling section 6 and a collection section 8 . The reaction section 2 is located on the upstream side in the gas flow direction and is provided with a raw material gas supply pipe 3 and a reducing gas supply pipe 4, which will be described later. The collection section 8 is a portion on the downstream side in the gas flow direction, and has a filter 9 therein for collecting the produced Ni alloy powder. The cooling section 6 is part of the section connecting the reaction section 2 and the collection section 8, and its diameter gradually decreases from the reaction section 2 toward the collection section 8. The cooling section 6 is provided with a cooling gas supply pipe 7, which will be described later. A connection part 12 connecting the cooling part 6 and the collection part 8 is provided with a valve 10 and an oxidizing gas supply pipe 11, which will be described later.

[0026] <Production of Ni alloy powder> When Ni alloy powder is produced using the reactor 1, for example, a raw material gas and a reducing gas are reacted in the reaction section 2.

[0027] The raw material gas is supplied to the reaction section 2 through a raw material gas supply pipe 3 . The source gas contains a Ni source and a Si source, which are chlorides. Ni raw materials include chlorides such as nickel chloride (NiCl2). Examples of Si raw materials include chlorides such as silicon tetrachloride (SiCl4), dichlorosilane (H2SiCl2), and trichlorosilane (HSiCl3). When producing Ni alloy powder containing sulfur (S), S raw materials such as sulfur dioxide (SO2), sulfur trioxide (SO3), and hydrogen sulfide (H2S) are mixed into the raw material gas.

[0028] Furthermore, together with the raw material gas, a diluent gas is supplied to the reaction section 2 through the raw material gas supply pipe 3. Examples of the diluent gas include inert gases such as nitrogen gas (N2) and argon gas (Ar).

[0029] By adjusting the flow rates (volumes flowing per unit time) of the raw material gas and diluent gas, the residence time in the reaction section 2 where grain growth occurs is adjusted, thereby controlling the grain size of the Ni alloy powder produced. An excessive flow rate is not preferable because it increases the pressure loss in the filter 9 of the collection section 8 and leads to pressure fluctuations in the reaction section 2. For example, the flow rate ratio of the dilution gas to the raw material gas (dilution gas / raw material gas) is preferably 200 or less, more preferably 160 or less, and even more preferably 100 or less. On the other hand, if this flow rate ratio (dilution gas / raw material gas) is too low, condensation of the raw material gas is likely to occur, so it is preferably 2 or more, more preferably 5 or more, and even more preferably 8 or more.

[0030] The reducing gas is supplied to the reaction section 2 through a reducing gas supply pipe 4 . The reducing gas is, for example, hydrogen gas (H2). Regarding the flow rate ratio of the reducing gas (hydrogen gas) to the chlorides (Ni raw material and Si raw material) contained in the raw material gas, for example, the flow rate ratio of hydrogen gas to nickel chloride and silicon tetrachloride (H2 / (NiCl2+SiCl4)) is, for example, 2 or more, and may be 3 or more. The upper limit is, for example, 12, and may be 8.

[0031] An electric furnace 5 is arranged outside the reaction section 2. By driving the electric furnace 5 to generate heat, the reaction section 2 is controlled to a desired temperature (reaction temperature), and the raw material gas and the reducing gas are reacted with each other. The reaction temperature is preferably 900° C. or higher, more preferably 1000° C. or higher, because the raw material gas is less likely to condense. On the other hand, from an economical point of view, the reaction temperature is preferably 1300°C or lower, more preferably 1200°C or lower.

[0032] The reaction product obtained by the reaction between the raw material gas and the reducing gas is rapidly cooled in the cooling section 6 by a cooling gas supplied from a cooling gas supply pipe 7. As the cooling gas, for example, the same gas as the dilution gas described above is used. The quenched reaction product (Ni alloy powder) passes through the connection part 12 and adheres to the filter 9 of the collection part 8, where it is collected. In this way, the Ni alloy powder is obtained.

[0033] <Oxidation treatment> The obtained Ni alloy powder may be subjected to an oxidation treatment. In this case, for example, with Ni alloy powder adhering to the filter 9 of the collection unit 8, the valve 10 is closed and an oxidizing gas (oxygen-containing gas) is passed from the oxidizing gas supply pipe 11 through the connection part 12 to the collection unit 8. In this way, the Ni alloy powder adhering to the filter 9 is brought into contact with the oxidizing gas, and an oxidation treatment is performed. The Ni alloy powder that has been subjected to the oxidation treatment has a reduced proportion of the Ni-OH bonds described above.

[0034] The conditions for the oxidation treatment are adjusted depending on, for example, the desired proportion of Ni—OH bonds. The oxidizing gas supplied from the oxidizing gas supply pipe 11 may be, for example, a mixed gas of oxygen and an inert gas (such as nitrogen gas).

[0035] The oxygen content in the oxidizing gas is, for example, 0.1% by volume or more, and may be 0.3% by volume or more. On the other hand, if there is too much oxygen, oxidation heat may occur and the Ni alloy powder may be excessively oxidized. Therefore, the oxygen content in the oxidizing gas is preferably 1.5% by volume or less, more preferably 1.2% by volume or less, and even more preferably 0.8% by volume or less.

[0036] From the viewpoint of preventing excessive oxidation due to oxidation heat generation, the flow rate of the oxidizing gas passing through the filter 9 is preferably 1 cm / s or more, more preferably 3 cm / s or more. The upper limit is not particularly limited, and may be, for example, 15 cm / s or 10 cm / s.

[0037] The temperature of the oxidizing gas when carrying out the oxidation treatment is preferably 10° C. or higher, more preferably 15° C. or higher. On the other hand, from the viewpoint of preventing excessive oxidation, the temperature of the oxidizing gas is preferably 40° C. or lower, more preferably 35° C. or lower. Furthermore, the temperature of the oxidizing gas may increase after passing through the filter 9, but the temperature increase is preferably 10° C. or less.

[0038] The time for which the oxidation treatment is carried out is, for example, 10 minutes or more, and may be 30 minutes or more. The upper limit is not particularly limited, and may be, for example, 90 minutes, or may be 60 minutes.

[0039] <Cleaning> The obtained Ni alloy powder is preferably washed with water or the like because unreacted Ni raw material (nickel chloride, etc.) may remain. In this case, the amount of dissolved oxygen in the water used for washing (washing water) is preferably low, specifically, less than 0.01 mg / L, which allows the proportion of Ni-OH bonds in the Ni alloy powder after washing to be maintained at a low value. An example of a method for reducing the amount of dissolved oxygen in the cleaning water is to pass nitrogen gas through the cleaning water.

[0040] After washing, the Ni alloy powder is preferably dried. For drying, a known drying apparatus such as a box dryer, rotary dryer, flash dryer, fluidized bed dryer, vacuum dryer, etc. Since the Ni alloy powder is easily oxidized, it is preferable to dry it in an inert gas or in vacuum. [Example]

[0041] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the examples described below.

[0042] <Production of Ni alloy powder> Using the reactor 1 explained based on FIG. 1, a raw material gas and a reducing gas were reacted with each other according to the above-mentioned production method to produce Ni alloy powder. That is, raw material gas and dilution gas were supplied from raw material gas supply pipe 3, and reducing gas was supplied from reducing gas supply pipe 4 to reaction section 2, and electric furnace 5 was driven to raise the temperature (reaction temperature) of reaction section 2 to 1100°C, thereby causing the raw material gas and reducing gas to react with each other. The reaction product obtained by the reaction between the raw material gas and the reducing gas was quenched in the cooling section 6 using a cooling gas (dilution gas) supplied from a cooling gas supply pipe 7, and then collected by a filter 9 in the collection section 8. In this way, a Ni alloy powder was obtained.

[0043] Nickel chloride (NiCl2) was used as the Ni raw material contained in the raw material gas. Silicon tetrachloride (SiCl4) was used as the Si raw material contained in the raw material gas. The flow rates of nickel chloride and silicon tetrachloride were adjusted so that the Si content of the obtained Ni alloy powder would be the values ​​shown in Tables 1 to 4 below. Sulfur dioxide (SO2) gas was mixed into the raw material gas as an S raw material so that the S content of the resulting Ni alloy powder would be the values ​​shown in Tables 1 to 4 below. Hydrogen gas (H2) was used as the reducing gas. Nitrogen gas (N2) was used as the dilution gas. The flow rate ratio of the dilution gas to the raw material gas (dilution gas / raw material gas) is determined by the particle size D of the resulting Ni alloy powder. 50 was adjusted between 5 and 100 so as to have the values ​​shown in Tables 1 to 4 below. The flow rate ratio of hydrogen gas to nickel chloride and silicon tetrachloride (H2 / (NiCl2+SiCl4)) was set to 4.

[0044] Next, the Ni alloy powder collected in the filter 9 of the collection unit 8 was subjected to an oxidation treatment (except for Example 8). That is, with Ni alloy powder adhering to the filter 9 of the collection unit 8, the valve 10 was closed, and the oxidizing gas was passed from the oxidizing gas supply pipe 11 through the connection part 12 to the collection unit 8. More specifically, an oxidizing gas with an oxygen content of 0.5% by volume (the remainder being nitrogen gas) was passed through at a flow rate of 100 NL / min for 30 minutes. The collection area of ​​the filter 9 was 2 m 2 Therefore, the flow rate of the oxidizing gas passing through the filter 9 was 5 cm / s. Next, an oxidizing gas with an oxygen content of 1.0 vol % (the remainder being nitrogen gas) was passed through under the same conditions. The temperature of the oxidizing gas flowing from the oxidizing gas supply pipe 11 to the collection unit 8 was 20°C. Furthermore, the temperature of the oxidizing gas after passing through the filter 9 was at most 21°C (i.e., the temperature increase was 1°C or less).

[0045] Next, the Ni alloy powder captured on the filter 9 was recovered in the atmosphere, washed with washing water (pure water), and then dried at 100° C. in nitrogen gas. In this case, the cleaning water used had a dissolved oxygen content of less than 0.01 mg / L by passing nitrogen gas through it in advance, except for Example 9, in which cleaning water with a dissolved oxygen content of 10 mg / L was used without passing nitrogen gas through it.

[0046] <Analysis of Ni alloy powder> The obtained Ni alloy powder had a particle size D 50 The values ​​of the Si content and the S content were determined. The results are shown in Tables 1 to 4 below.

[0047] 《Various measurement methods》 Ni alloy powder particle size D 50 was asked as follows: First, the Ni alloy powder was observed using a scanning electron microscope (SU5000, manufactured by Hitachi High-Technologies Corporation) to obtain SEM photographs. At this time, the magnification was selected so that the number of particles observed in one field of view was 200 to 600, and the number of fields of view was selected so that the total number of particles was 10,000 or more. Image analysis was performed on the obtained SEM photograph, and the particle diameter of each particle was defined as the long diameter. 50 asked for.

[0048] The Si content of the Ni alloy powder was determined by the silicon dioxide gravimetric method. When the value determined by the silicon dioxide gravimetric method was less than 0.10 mass%, the Si content was determined by the molybdosilicic acid blue absorptiometry method. The S content of the Ni alloy powder was determined using a carbon / sulfur measuring device (CS844, manufactured by LECO Corporation). The proportion of Ni-OH bonds in the Ni alloy powder was determined by the above-mentioned method using an XPS apparatus (VersaProbe II, manufactured by ULVAC-PHI, Inc.).

[0049] In addition, for the Ni alloy powders of each example, the Si content in the part excluding the surface layer of the particle (the part from the surface to a depth of 5 nm) was in the range of 50 to 200% of the total Si content of the Ni alloy powder. The Si content in the particles was determined by observing the composition of the cross section of the Ni alloy powder particles using a transmission electron microscope (HF2000, manufactured by Hitachi High-Technologies Corporation).

[0050] When the Ni alloy powder is an alloy of Ni and Si, no other phases than Ni are detected in the X-ray diffraction (XRD) pattern obtained by measurement using an X-ray diffractometer (D8ADVANCE, manufactured by BRUKER). In the Ni alloy powder of each example, no other phases than Ni were detected in the XRD pattern.

[0051] <Sintering characteristics of Ni alloy powder (shrinkage rate at 600°C)> 5 g of the obtained Ni alloy powder and 0.25 mL of a 10 mass % aqueous solution of PVA (polyvinyl alcohol) were kneaded for 10 minutes using a tabletop Ishikawa-type stirring and crushing machine (manufactured by Ishikawa Factory Co., Ltd.) with the rotation dial set to the maximum value to obtain a kneaded product. The obtained kneaded product was dried for 10 minutes at 100° C. 0.58 g of the dried kneaded product was placed in a mold with a diameter of 7 mm, and a pressure of 6 kN was applied for 30 seconds to prepare a sample. The sintering behavior of the prepared samples was investigated using a thermomechanical analyzer (TMA4000SE, manufactured by NETZCH). Specifically, the samples were heated at a temperature increase rate of 5°C / min under a load of 10 g in an atmosphere of 1200 ppm hydrogen by volume.

[0052] From the results of thermomechanical analysis, the volumetric shrinkage rate at 600°C (600°C shrinkage rate) was determined. The following tables 1 to 4 list the shrinkage rates: "A" when the shrinkage rate at 600°C was less than 5%, "B" when it was 5% or more but less than 10%, "C" when it was 10% or more but less than 15%, and "D" when it was 15% or more. If it is rated as "A," "B," or "C," it can be evaluated as having an excellent sintering suppression effect.

[0053] <MLCC Fabrication> Using the prepared Ni alloy powder, a multilayer ceramic capacitor (MLCC) was fabricated as described below.

[0054] <<Preparation of Internal Electrode Paste>> Ni alloy powder (46 parts by mass), barium titanate powder (9 parts by mass) with a particle size of 30 nm as a co-material, ethyl cellulose resin (2 parts by mass) as a binder, and an organic vehicle (45 parts by mass) containing dihydroterpinyl acetate as a solvent were mixed, and the mixture was dispersed using a three-roll mill to obtain an internal electrode paste.

[0055] <<Preparation of ceramic green sheets>> Next, a dielectric material (barium titanate, specific surface area diameter 120 nm, 50 parts by mass), an organic solvent (26.5 parts by mass), and a dispersant (0.5 parts by mass) were mixed and dispersed using a ball mill. The organic solvent used was a mixed solvent of toluene and ethanol in a mass ratio (toluene / ethanol) of 1 / 1. Then, an organic binder (21.5 parts by mass) and a plasticizer (1.5 parts by mass) were further added and mixed to obtain a ceramic slurry. As the organic binder, an ethanol solution containing 18% by mass of polyvinyl butyral (PVB) was used. The obtained ceramic slurry was applied to a polyethylene terephthalate (PET) film by a doctor blade method so that the thickness after firing would be 0.5 μm, and then dried to obtain a ceramic green sheet.

[0056] <<Making the capacitor element>> The internal electrode paste was screen printed on the ceramic green sheets so that the thickness after firing would be 0.5 μm and the dimensions after firing would be 1.0 mm×0.5 mm. The ceramic green sheets on which the internal electrode paste was printed were peeled off from the PET film, and 100 sheets were stacked together without any misalignment, and then pressed together using a press to produce a capacitor element, which was a laminate. The capacitor element was cut to a predetermined size using a cutting machine.

[0057] <<Binder removal and firing>> The capacitor element was heated in an air atmosphere at 260° C. for 6 hours to remove the binder. The debindered capacitor element was heated to 1200°C over 4 hours in a moist nitrogen atmosphere containing 2% hydrogen by volume, and then fired at 1200°C for 2 hours. The temperature was then lowered to 1000°C over 1 hour, and the fired capacitor element was then held at 1000°C for 3 hours in moist nitrogen for reoxidation. It was then cooled to room temperature. This resulted in an MLCC with internal electrodes and a dielectric both 0.5 μm thick.

[0058] <MLCC evaluation> The fabricated MLCCs were evaluated as follows.

[0059] Coverage The fabricated MLCC was split with pliers and observed using a scanning electron microscope (SU5000, Hitachi High-Technologies Corporation) to find the surface where the internal electrode was exposed as the outermost surface. The SEM photograph of this surface was binarized, and the coverage rate (unit: %) was calculated by distinguishing between areas where the internal electrode covered the dielectric and areas where there were holes in the internal electrode and the dielectric was visible. For each example and comparative example, the average value of three measurements was taken as the coverage rate for that example. If the coverage rate was 96% or more, it was marked as "A", if it was 96% or more but less than 93%, it was marked as "B", if it was 90% or more but less than 93%, it was marked as "C", and if it was less than 90%, it was marked as "D". These are shown in Tables 1 to 4 below. In practice, "A", "B" or "C" are preferred.

[0060] 《SiO2 layer》 An MLCC was fabricated in the same manner as described above, except that the internal electrode paste was printed so that the thickness after firing would be 0.8 μm. The fabricated MLCC was split with pliers to expose the cross section, which was then observed using a scanning microscope equipped with an energy dispersive X-ray analyzer to confirm the presence or absence of an SiO2 layer between the internal electrode and the dielectric. In Tables 1 to 4 below, "A" is given when no SiO2 layer was formed, and "D" is given when an SiO2 layer was formed. In practice, "A" is preferred.

[0061] Capacitance The capacitance of the MLCC was measured using an LCR meter (4263B, manufactured by Aglient) under conditions of an AC voltage of 1 Vrms and a frequency of 1 kHz. Measurements were performed on 10 MLCCs, and the average value was used as the capacitance of each example. The highest capacitance among the capacitances of each example was set as 100%, and the capacitance of each example was indexed. If the index was 98% or higher, it was marked with "A", if it was 95% or higher but less than 98%, it was marked with "B", if it was 90% or higher but less than 95%, it was marked with "C", and if it was less than 90%, it was marked with "D". These are shown in Tables 1 to 4 below. In practice, "A", "B" or "C" are preferred.

[0062] [Table 1]

[0063] [Table 2]

[0064] [Table 3]

[0065] [Table 4]

[0066] <Summary of evaluation results> As shown in Tables 1 to 4 above, the capacitance of the MLCC was good in Examples 1 to 10. In contrast, the particle size D 50 In Comparative Example 1, in which the Si content was outside the range of 40 to 250 nm, and in Comparative Examples 2 and 3, in which the Si content was outside the range of 0.05 mass % or more and less than 0.50 mass %, the capacitance of the MLCC was insufficient. In more detail, it was as follows:

[0067] 《Particle size D 50 》 See Table 1 above. The shrinkage rate at 600℃ is 50 The larger the value, the better the results were. On the other hand, the coverage and capacitance are related to the particle size D 50 As it increased, it decreased.

[0068] 《Si content》 See Table 2 above. The 600°C shrinkage rate and coverage rate tended to improve as the Si content increased. However, in Comparative Example 3, which had an excessive Si content, deposition of an SiO2 layer was confirmed between the internal electrode and the dielectric. This shows that the capacitance is affected not only by the coverage but also by the deposition of the SiO2 layer.

[0069] 《Ni-OH bond ratio》 See Table 3 above. Example 1, which underwent oxidation treatment and was washed with cleaning water having a low dissolved oxygen content, had a lower proportion of Ni-OH bonds than Example 8, which did not undergo oxidation treatment, and Example 9, which underwent oxidation treatment but was washed with cleaning water having a high dissolved oxygen content. In comparison with Examples 8 and 9, Example 1 was superior in 600° C. shrinkage rate, coverage rate, and capacitance.

[0070] 《S content》 See Table 4 above. Example 1, in which the S content was 10 ppm by mass, was better in 600° C. shrinkage, coverage, and capacitance than Example 10, in which the S content was 250 ppm by mass. [Explanation of symbols]

[0071] 1: Reactor 2: Reaction section 3: Raw material gas supply pipe 4: Reducing gas supply pipe 5: Electric furnace 6: Cooling section 7: Cooling gas supply pipe 8: Collection section 9: Filter 10: Valve 11: Oxidizing gas supply pipe 12: Connection part

Claims

1. A powder of a NiSi alloy containing nickel and silicon, The Si content is 0.05% by mass or more and less than 0.50% by mass, The S content is 250 ppm by mass or less, the balance being nickel, Particle size D ５０ The Ni alloy powder has a particle size of 40 to 250 nm. However, the Ni alloy powder is observed using a scanning electron microscope at a magnification such that the number of particles observed in one field of view is 200 to 600, and an SEM photograph is obtained with a number of fields of view such that the total number of particles is 10,000 or more, and the particle diameter D50 is determined by defining the major axis of each particle as the particle diameter.

2. The Ni alloy powder according to claim 1, wherein the ratio of Ni-OH bonds to Ni-Ni bonds, Ni-O bonds and Ni-OH bonds on the surface of the Ni alloy powder is 40 mol % or less.

3. The Ni alloy powder according to claim 1 or 2, wherein the S content is 200 mass ppm or less.

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