Ni alloy powder

Abstract

Provided is an Ni alloy powder that makes it possible to obtain a multilayer ceramic capacitor (MLCC) that exhibits excellent capacitance. The Ni alloy powder has an Si content of not less than 0.05 mass% but less than 0.50 mass% and a particle size D50 of 40-250 nm. In the Ni alloy powder, the proportion of Ni-OH bonds with respect to Ni-Ni bonds, Ni-O bonds, and Ni-OH bonds is preferably not more than 40 mol%. The Ni alloy powder preferably has a S content of not more than 200 mass ppm.

Description

Ni alloy powder

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

[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 (see Patent Document 1).

[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 ceramic green sheets that will become a dielectric upon firing. Next, multiple ceramic green sheets with the printed internal electrode paste are stacked and pressed together to obtain an unfired laminate (capacitor element). The resulting laminate is cut into a 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. Furthermore, the Ni alloy powder contained in the internal electrode paste is sintered to form an internal electrode.

[0004] Japanese Patent Application Publication No. 11-189802

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

[0006] Recently, in order to increase the capacity of MLCCs, it has become necessary to thin the internal electrodes and dielectrics (for example, to reduce the thickness to 0.5 μm or less). The use of fine Ni alloy powder particles allows for the formation of thin internal electrodes. However, the increased proportion of highly active particle surfaces leads to a decrease in the sintering temperature and a decrease in 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. In other words, a sintering suppression effect can be obtained. However, since Si is a metal that is more easily oxidized than Ni, Si in the Ni alloy powder is likely to be converted into SiO in the firing atmosphere (an atmosphere with a slight oxygen partial pressure) when manufacturing MLCC. ２ Therefore, if Si is contained in the Ni alloy powder of the internal electrode paste, SiO ２ A layer may be formed. The dielectric stores electricity when a voltage is applied. In this case, SiO ２ When the layer is present between the internal electrode and the dielectric, the applied voltage is ２ The SiO2 is distributed in both the layer and the dielectric, reducing the voltage applied to the dielectric, i.e., reducing the capacitance. ２ The effect of layer partitioning is negligible for thick dielectrics, but not for thin dielectrics.

[0008] Patent Document 1 does not mention that the capacitance of an MLCC in which the internal electrodes and dielectrics are thinned (for example, the thickness is set to 0.5 μm or less) is increased. When the present inventors fabricated an MLCC in which the internal electrodes and dielectrics are 0.5 μm thick 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 multilayer ceramic capacitors (MLCCs) with excellent capacitance, particularly when the internal electrodes and dielectric are thin.

[0010] The present inventors have found that the above object can be achieved by adopting the following constitution, and have completed the present invention. That is, the present invention provides the following [1] to [3]. [1] A silicon dioxide powder having a Si content of 0.05 mass % or more and less than 0.50 mass %, and a particle size D ５０[2] The Ni alloy powder according to the above item [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 the above item [1] or [2], wherein the S content is 200 ppm by mass or less.

[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.

[0012] FIG. 2 is a schematic diagram showing a reactor used for producing Ni alloy powder.

[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 is too low, the Ni alloy powder tends to sinter faster than the dielectric material. In other words, a sufficient sintering suppression effect cannot be obtained. Because the sintering suppression effect is excellent and the resulting MLCC has excellent capacitance, the Si content is 0.05 mass% or more, preferably 0.10 mass% or more, and more preferably 0.15 mass% or more.

[0015] On the other hand, if the Ni alloy powder contains too much Si, the capacitance of the resulting MLCC also decreases. This is because SiO ２ In order to obtain an MLCC with excellent capacitance, the Si content is less than 0.50 mass %, preferably 0.48 mass % or less, and more preferably 0.45 mass % or less.

[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 is formed on the outermost surface of the particle. The Si oxide film has a lower thermal expansion coefficient than the particle (NiSi alloy), so it peels off from the particle surface during firing. The peeled Si oxide film moves along the grain boundary as the particles are sintered (grain growth), and SiO is formed at the interface between the internal electrode and the dielectric. ２ The resulting layer precipitates, resulting in 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, making it impossible to suppress sintering. For these reasons, the Si content in the part excluding the surface layer of the particle (the part up to a depth of 5 nm from the surface) 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 area of ​​each particle becomes large, and even if Si is contained, a sufficient sintering suppression effect cannot be obtained. In order to obtain an excellent sintering suppression effect and an excellent capacitance of the obtained MLCC, the particle size D of the Ni alloy powder is ５０ is 40 nm or more, and 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 are likely to occur, and the coverage rate decreases. Also, the increase in coarse particles makes it easier for short circuits to occur and for the withstand voltage to decrease in the resulting MLCC. For this reason, the particle size D of the Ni alloy powder is 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 Ni alloy powder has too much S content, the sintering suppression effect may be reduced. For reasons such as a better sintering suppression effect and a better electrostatic capacity 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 Ni alloy powder, examples of bonding states of Ni include Ni-Ni bonds, Ni-O bonds, and Ni-OH bonds. 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 Si in the particles of the Ni alloy powder, resulting in the formation of SiO at the interface between the internal electrode and the dielectric in the resulting MLCC. ２ In some cases, too many layers are formed, which can reduce the capacitance of the MLCC, as described above.

[0021] Furthermore, the temperature at which water is released from Ni—OH bonds and converted to Ni—O bonds is around 230°C. Therefore, when binder removal is performed at, for example, approximately 250°C, the Ni—OH bonds are converted to Ni—O bonds. During this conversion, each particle of the Ni alloy powder undergoes volumetric contraction. In Ni alloy powder containing Si, an Si oxide film is formed on the surface of each particle, stabilizing the particle. However, this volumetric contraction may cause the Si oxide film to peel off from the particle surface. Since the heating atmosphere for binder removal is usually an air atmosphere, oxidation of Si progresses from the surface from which the Si oxide film peeled off in each particle of the Ni alloy powder. Furthermore, volumetric contraction generates strain 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. At this time, if Si remains inside the particles, a new Si oxide film is formed, suppressing sintering. However, if the oxidation of Si inside the particles progresses during binder removal and the amount of Si is reduced, a new Si oxide film is not formed, reducing the sintering suppression effect and reducing the area ratio (coverage rate) of the internal electrodes covering the dielectric. As a result, the capacitance of the MLCC decreases. Furthermore, the Si oxide film peeled off during binder removal migrates along the grain boundaries as the particles are sintered, forming SiO ２ It is prone to deposit as a layer, which in this case leads to a decrease in the capacitance of the MLCC.

[0022] For this reason, in the Ni alloy powder, the ratio of Ni-OH bonds to Ni-Ni bonds, Ni-O bonds, and Ni-OH bonds (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, because the resulting MLCC has a better capacitance. The lower limit is not particularly limited, and may be, for example, 5 mol %, 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 device is used to first obtain a Ni2p spectrum of the Ni alloy powder. Then, the obtained Ni2p spectrum is subjected to waveform separation by peak fitting to obtain Ni peaks, NiO peaks, and Ni(OH) peaks. ２ The areas of the Ni peak, NiO peak, and Ni(OH) peak are calculated. ２ The area ratios of the peaks 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 for producing Ni alloy powder] Next, a method for producing the Ni alloy powder of the present embodiment described above 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 CVD is preferred because it is easy to narrow the particle size distribution. Hereinafter, the production of Ni alloy powder by CVD will be described 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 the upstream section in the gas flow direction. The reaction section 2 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 the downstream section 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 section 12 connecting the cooling section 6 and the collection section 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 the raw material gas supply pipe 3. The raw material gas contains a Ni raw material and a Si raw material, which are chlorides. The Ni raw material is nickel chloride (NiCl ２ ) and other chlorides. Examples of silicon raw materials include silicon tetrachloride (SiCl ４ ), dichlorosilane (H ２ SiCl ２ ), trichlorosilane (HSiCl ３ When producing Ni alloy powder containing sulfur (S), an S raw material is mixed with the raw material gas. The S raw material is sulfur dioxide (SO ２ ), sulfur trioxide (SO ３ ), hydrogen sulfide (H ２ S) and the like.

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

[0029] By adjusting the flow rates (volume flowing per unit time) of the source gas and diluent gas, the residence time in the reaction section 2 where grain growth occurs is adjusted, thereby controlling the particle size of the produced Ni alloy powder. An excessive flow rate is not preferable because it increases the pressure loss in the filter 9 of the collection section 8, leading to pressure fluctuations in the reaction section 2. For example, the flow rate ratio of the diluent gas to the source gas (diluent gas / source 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 (diluent gas / source gas) is too low, condensation of the source 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 (H ２Regarding the flow rate ratio of the reducing gas (hydrogen gas) to the chlorides (Ni raw material and Si raw material) contained in the source gas, for example, the flow rate ratio of hydrogen gas to nickel chloride and silicon tetrachloride (H ２ / (NiCl ２ +SiCl ４ )) 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 disposed 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. The reaction temperature is preferably 900°C or higher, and more preferably 1000°C or higher, because the raw material gas is less likely to condense. On the other hand, from an economical viewpoint, the reaction temperature is preferably 1300°C or lower, and more preferably 1200°C or lower.

[0032] The reaction product obtained by the reaction between the raw material gas and the reducing gas is quenched in the cooling unit 6 by a cooling gas supplied from a cooling gas supply pipe 7. The cooling gas may be, for example, the same gas as the dilution gas described above. The quenched reaction product (Ni alloy powder) passes through the connection unit 12 and adheres to the filter 9 of the collection unit 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 the 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 the 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 of the oxidation treatment are adjusted depending on, for example, the desired ratio 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 (for example, nitrogen gas).

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

[0036] From the viewpoint of preventing excessive oxidation due to heat generation by oxidation, 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 lower.

[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] <Washing> The obtained Ni alloy powder is preferably washed with water or the like because unreacted Ni raw materials (such as nickel chloride) 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. This allows the proportion of Ni—OH bonds in the Ni alloy powder after washing to be maintained at a low value. One method for reducing the amount of dissolved oxygen in the washing water is, for example, to pass nitrogen gas through the washing water.

[0040] The Ni alloy powder after washing is preferably dried. For drying, a known drying device 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 preferably dried in an inert gas or in vacuum.

[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> Ni alloy powder was produced by reacting a raw material gas with a reducing gas according to the production method described above using the reaction furnace 1 described with reference to Fig. 1 . That is, raw material gas and diluent gas were supplied to the reaction section 2 from the raw material gas supply pipe 3, and reducing gas was supplied from the reducing gas supply pipe 4 to the reaction section 2. The electric furnace 5 was driven to raise the temperature (reaction temperature) of the reaction section 2 to 1100°C, and the raw material gas and reducing gas were reacted. The reaction product obtained by the reaction of the raw material gas and reducing gas was quenched in the cooling section 6 using a cooling gas (diluent gas) supplied from the cooling gas supply pipe 7, and then collected by the filter 9 of the collection section 8. In this way, Ni alloy powder was obtained.

[0043] The Ni raw material contained in the raw material gas is nickel chloride (NiCl ２ The silicon source gas contained silicon tetrachloride (SiCl ４ The flow rates of nickel chloride and silicon tetrachloride were adjusted so that the Si content of the resulting Ni alloy powder would be the values ​​shown in Tables 1 to 4 below. The raw material gas contained sulfur dioxide (SO ) as the 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. ２ As a reducing gas, hydrogen gas (H ２ As a dilution gas, nitrogen gas (N ２ The flow rate ratio of the dilution gas to the raw material gas (dilution gas / raw material gas) was determined based on the particle size D of the resulting Ni alloy powder. ５０ was adjusted between 5 and 100 so that the values ​​shown in Tables 1 to 4 below were obtained. ２ / (NiCl ２ +SiCl ４ )) was given a score of 4.

[0044] Next, the Ni alloy powder collected on the filter 9 of the collection unit 8 was subjected to an oxidation treatment (except for Example 8). That is, with the Ni alloy powder attached to the filter 9 of the collection unit 8, the valve 10 was closed, and an 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 containing 0.5% by volume of oxygen (the remainder being nitrogen gas) was passed through the filter 9 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 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 passed through oxidizing gas supply pipe 11 to collection unit 8 was 20°C. Furthermore, the temperature of the oxidizing gas after passing through filter 9 was at most 21°C (i.e., the temperature increase was 1°C or less).

[0045] Next, the Ni alloy powder collected on the filter 9 was collected in the atmosphere, washed with cleaning water (pure water), and then dried in nitrogen gas at 100°C. The cleaning water used had a dissolved oxygen content of less than 0.01 mg / L by passing nitrogen gas through it in advance. However, in Example 9, 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 particle size D of the obtained Ni alloy powder was ５０ The values ​​of the Si content and the S content were determined. The results are shown in Tables 1 to 4 below.

[0047] <<Measurement Methods>> Particle size D of Ni alloy powder ５０ was determined as follows. First, the Ni alloy powder was observed using a scanning electron microscope (SU5000, manufactured by Hitachi High-Technologies Corporation) to obtain an SEM photograph. At this time, a 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 major axis of each particle was defined as the particle diameter, and the particle diameter D ５０ asked for.

[0048] The Si content of the Ni alloy powder was determined using the silicon dioxide gravimetric method. When the value determined using the silicon dioxide gravimetric method was less than 0.10 mass%, it was determined using molybdosilicic acid blue absorptiometry. 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 device (VersaProbe II, manufactured by ULVAC-PHI, Inc.).

[0049] In each of the Ni alloy powders of the examples, the Si content in the portion excluding the surface layer of the particle (the portion 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 particle was determined by observing the composition of the cross section of the Ni alloy powder particle 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 heterophase other than Ni is detected in the X-ray diffraction (XRD) pattern obtained by measurement using an X-ray diffractometer (D8 ADVANCE, manufactured by BRUKER). In the Ni alloy powder of each example, no heterophase other than Ni was detected in the XRD pattern.

[0051] Sintering Characteristics of Ni Alloy Powder (600°C Shrinkage) 5 g of the obtained Ni alloy powder and 0.25 mL of a 10% by mass aqueous solution of PVA (polyvinyl alcohol) were kneaded for 10 minutes using a tabletop Ishikawa-type mixing and crushing machine (manufactured by Ishikawa Kogyo Co., Ltd.) with the rotary dial set to the maximum setting to obtain a kneaded mixture. The resulting kneaded mixture was dried at 100°C for 10 minutes. 0.58 g of the dried kneaded mixture was placed in a 7 mm diameter mold and subjected to a pressure of 6 kN for 30 seconds to prepare a sample. The sintering behavior of the prepared sample was investigated using a thermomechanical analyzer (TMA4000SE, manufactured by NETZCH). Specifically, the sample was heated at a heating rate of 5°C / min under a 10 g load in an atmosphere of 1200 ppm hydrogen by volume.

[0052] The volumetric shrinkage at 600°C (600°C shrinkage) was determined from the results of thermomechanical analysis. The following criteria are listed in Tables 1 to 4 below: "A" if the 600°C shrinkage was less than 5%, "B" if it was 5% or more but less than 10%, "C" if it was 10% or more but less than 15%, and "D" if it was 15% or more. If it is rated "A", "B", or "C", it can be evaluated as having an excellent sintering suppression effect.

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

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

[0055] <<Preparation of Ceramic Green Sheets>> Next, 50 parts by mass of barium titanate (dielectric material) with a specific surface area of ​​120 nm, 26.5 parts by mass of organic solvent, and 0.5 parts by mass of dispersant were mixed and dispersed using a ball mill. The organic solvent used was a toluene / ethanol mixed solvent with a mass ratio (toluene / ethanol) of 1 / 1. An organic binder (21.5 parts by mass) and a plasticizer (1.5 parts by mass) were then added and mixed to obtain a ceramic slurry. An ethanol solution containing 18% by mass of polyvinyl butyral (PVB) was used as the organic binder. The resulting ceramic slurry was applied to a polyethylene terephthalate (PET) film using a doctor blade method to a thickness of 0.5 μm after firing. The mixture was then dried to obtain a ceramic green sheet.

[0056] <<Preparation of Capacitor Element>> The internal electrode paste was screen-printed onto a ceramic green sheet so that the thickness after firing would be 0.5 μm and the dimensions after firing would be 1.0 mm × 0.5 mm. After peeling the ceramic green sheets with the internal electrode paste printed thereon from the PET film, 100 sheets were stacked without misalignment and then pressed together using a press to prepare a laminated capacitor element. The capacitor element was then cut to a predetermined size using a cutter.

[0057] <<Binder Removal and Firing>> The capacitor element was debindered by heating it in an air atmosphere at 260°C for 6 hours. The debindered capacitor element was heated to 1200°C over 4 hours in a wet 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 held at 1000°C for 3 hours in wet nitrogen for reoxidation. It was then cooled to room temperature. In this way, an MLCC was obtained in which the internal electrodes and dielectric were both 0.5 μm thick.

[0058] <Evaluation of MLCC> The produced MLCC was evaluated as follows.

[0059] <<Coverage>> The fabricated MLCC was split with pliers and observed using a scanning electron microscope (SU5000, manufactured by Hitachi High-Technologies Corporation) to identify the surface where the internal electrode was exposed as the outermost surface. The SEM photograph of this surface was binarized, and the coverage (unit: %) was determined by distinguishing between the area where the internal electrode covered the dielectric and the area where holes in the internal electrode exposed the dielectric. For each example and comparative example, the average of three measurements was used as the coverage for that example. Tables 1 to 4 below show the following: "A" for coverage of 96% or more, "B" for coverage of less than 93% (96% or more), "C" for coverage of 90% or more but less than 93%, and "D" for coverage of less than 90%. From a practical perspective, "A," "B," or "C" is preferred.

[0060] <SiO ２An 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, and the cross section was observed using a scanning microscope equipped with an energy dispersive X-ray analyzer. ２ The presence or absence of a SiO layer was confirmed. ２ If no layer was formed, "A" was used, and SiO ２ If a layer was formed, "D" is recorded in the following Tables 1 to 4. In practice, "A" is preferred.

[0061] <<Capacitance>> Using an LCR meter (4263B, manufactured by Agilent), the capacitance of the MLCC was measured 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 to 100%, and the capacitance of each example was indexed. The following Tables 1 to 4 show the following: "A" if the index was 98% or more, "B" if the index was 95% or more but less than 98%, "C" if the index was 90% or more but less than 95%, and "D" if the index was less than 90%. In practical terms, "A", "B", or "C" is preferred.

[0062]

[0063]

[0064]

[0065]

[0066] <Summary of Evaluation Results> As shown in Tables 1 to 4 above, Examples 1 to 10 had good MLCC capacitance. ５０ In Comparative Example 1, in which the thickness 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.

[0067] 《Particle size D ５０See Table 1 above. The shrinkage rate at 600°C is ５０ On the other hand, the coverage and capacitance tended to improve as 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, SiO ２ From this, it was found that the capacitance is affected not only by the coverage but also by the SiO ２ It can be seen that the deposition of layers also has an effect.

[0069] <<Ratio of Ni—OH Bonds>> See Table 3 above. Example 1, which was subjected to oxidation treatment and washed with cleaning water having a low dissolved oxygen content, had a lower ratio of Ni—OH bonds than Example 8, which was not subjected to oxidation treatment, and Example 9, which was subjected to oxidation treatment but washed with cleaning water having a high dissolved oxygen content. Example 1 had better 600° C. shrinkage, coverage, and capacitance than Examples 8 and 9.

[0070] <<S Content>> See Table 4 above. Example 1, in which the S content was 10 ppm by mass, had better 600°C shrinkage, coverage, and capacitance than Example 10, in which the S content was 250 ppm by mass.

[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: Collector 9: Filter 10: Valve 11: Oxidizing gas supply pipe 12: Connection section

Claims

1. The Si content is 0.05 mass% or more and less than 0.50 mass%, and the particle size D ５０ The Ni alloy powder has a particle size of 40 to 250 nm.

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 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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