Ni alloy powder

Abstract

This invention provides a Ni alloy powder that yields multilayer ceramic capacitors (MLCCs) with excellent capacitance. In the aforementioned Ni alloy powder, the Si content is 0.05% by mass or more and less than 0.50% by mass, and the particle size D... 50 The nm size is 40–250 nm. In the above Ni alloy powder, the ratio of Ni-OH bonds to Ni-Ni, Ni-O, and Ni-OH bonds is preferably less than 40 mol%. In the above Ni alloy powder, the S content is preferably less than 200 ppm by mass.

Description

Technical Field

[0001] This invention relates to a Ni alloy powder. Background Technology

[0002] Multilayer ceramic capacitors (MLCCs) have a stacked structure consisting of alternating layers of dielectric and internal electrodes. Previously, Ni alloy powder was used as the material for forming the internal electrodes of MLCCs (Patent Document 1).

[0003] To manufacture MLCCs, firstly, the internal electrode paste (a paste containing Ni alloy powder and binder) is printed in any pattern on a ceramic green sheet that has been calcined to become a dielectric.

[0004] Next, multiple ceramic green sheets printed with internal electrode paste are stacked and pressed together to obtain an uncalcined laminate (capacitor blank).

[0005] The resulting laminate is cut into arbitrary shapes, heated at a low temperature (to remove the binder), and then calcined at a high temperature. In this way, the dielectric material (such as barium titanate) contained in the ceramic green sheet is sintered to become the dielectric. Additionally, the Ni alloy powder contained in the internal electrode paste is sintered to become the internal electrode.

[0006] Patent Document 1: Japanese Patent Application Publication No. 11-189802 Summary of the Invention

[0007] In the manufacture of MLCCs, alternating layers of ceramic green sheets and internal electrode paste are calcined simultaneously.

[0008] At this point, compared to the dielectric material contained in the ceramic green sheet, the Ni alloy powder contained in the internal electrode paste is sintered at a low temperature first.

[0009] If the Ni alloy powder of the internal electrode paste is sintered first, voids are created in the formed internal electrode. In this case, the area ratio (coverage ratio) of the internal electrode of the coated dielectric decreases, and the number of effectively working internal electrodes is reduced. To obtain the desired capacitance, the coverage ratio needs to be increased.

[0010] However, in recent years, from the perspective of increasing the capacity of MLCCs, there has been a demand to thin the internal electrodes and dielectrics (e.g., to make the thickness less than 0.5 μm).

[0011] If fine particles of Ni alloy powder are used, the internal electrode can be formed in a thin layer.

[0012] However, by increasing the proportion of highly active particle surfaces, the sintering temperature is lowered, and the coating rate is reduced.

[0013] By including an appropriate amount of Si in Ni alloy powder, the decrease in sintering temperature can be suppressed. That is, a sintering suppression effect can be achieved.

[0014] However, compared to Ni, Si is a metal that is very easily oxidized. Therefore, Si in Ni alloy powder is easily precipitated as SiO2 in the calcination atmosphere (an atmosphere with low oxygen partial pressure) during the manufacture of MLCCs.

[0015] Therefore, if the Ni alloy powder in the internal electrode paste contains Si, a SiO2 layer may sometimes form between the internal electrode and the dielectric.

[0016] A dielectric stores electricity when a voltage is applied. If a SiO2 layer is present between the internal electrode and the dielectric, the applied voltage is distributed between the SiO2 layer and the dielectric, reducing the voltage applied to the dielectric. That is, the capacitance decreases.

[0017] The effect of this distribution caused by the SiO2 layer is negligible when the dielectric is thick, but cannot be ignored when the dielectric is thin.

[0018] Patent Document 1 does not describe the increase in capacitance of MLCCs by thinning the internal electrodes and dielectric (e.g., making the thickness less than 0.5 μm).

[0019] The inventors used the Ni alloy powder described in Patent Document 1 to fabricate an MLCC with an internal electrode and dielectric thickness of 0.5 μm, but sometimes the capacitance was insufficient.

[0020] Therefore, the object of the present invention is to provide a Ni alloy powder that can produce multilayer ceramic capacitors (MLCCs) with excellent capacitance.

[0021] In particular, the aim is to obtain MLCCs with excellent capacitance even when the internal electrodes and dielectrics are thin.

[0022] The inventors discovered that the above-mentioned objectives can be achieved by adopting the following configuration, thereby completing the present invention.

[0023] That is, the present invention provides the following [1] to [3].

[0024] [1] A Ni alloy powder having a Si content of 0.05% by mass or more and less than 0.50% by mass, and a particle size D 50 The wavelength range is 40–250 nm.

[0025] [2] According to the Ni alloy powder described in [1] above, the proportion of Ni-OH bonds to Ni-Ni bonds, Ni-O bonds and Ni-OH bonds is less than 40 mol%.

[0026] [3] The Ni alloy powder according to [1] or [2] above, wherein the S content is less than 200 ppm by mass.

[0027] According to the present invention, a Ni alloy powder that can produce multilayer ceramic capacitors with excellent capacitance can be provided. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the reactor used to manufacture Ni alloy powder. Detailed Implementation

[0029] [Ni alloy powder]

[0030] The Ni alloy powder (nickel alloy powder) of this embodiment is generally a NiSi alloy powder containing nickel (Ni) and silicon (Si).

[0031] More specifically, in the Ni alloy powder of this embodiment, the Si content is 0.05% by mass or more and less than 0.50% by mass, and the particle size D 50 The wavelength range is 40–250 nm.

[0032] <Si content>

[0033] As mentioned above, by including Si in the Ni alloy powder, a sintering inhibition effect can be obtained.

[0034] However, when the Si content in Ni alloy powder is too low, it tends to sinter faster than dielectric materials. That is, it cannot achieve sufficient sintering inhibition.

[0035] Based on the reasons of excellent sintering suppression effect and excellent capacitance of the obtained MLCC, the Si content is 0.05% by mass or more, preferably 0.10% by mass or more, and more preferably 0.15% by mass or more.

[0036] On the other hand, if the Si content in the Ni alloy powder is too high, the capacitance of the resulting MLCC will also decrease. This is because a large amount of SiO2 layer is formed at the interface between the internal electrode and the dielectric in the resulting MLCC.

[0037] Based on the reason that the obtained MLCC has excellent capacitance, the Si content is less than 0.50% by mass, preferably 0.48% by mass or less, and more preferably 0.45% by mass or less.

[0038] Ideally, the Si content in each particle of the Ni alloy powder should not have extreme deviations.

[0039] When Si accumulates near the surface of the particles, a thick Si oxide film forms on the outermost surface of the particles. The Si oxide film has a lower coefficient of thermal expansion compared to the particles (NiSi alloy), and therefore peels off from the particle surface during calcination. The peeled Si oxide film moves along the grain boundaries as the particles sinter (grain growth), precipitating as a SiO2 layer at the interface between the internal electrode and the dielectric, leading to a decrease in the capacitance of the MLCC.

[0040] On the other hand, when Si is enriched in the center of the particles, not enough Si oxide film is formed on the particle surface, which cannot suppress sintering.

[0041] Therefore, relative to the overall Si content of the Ni alloy powder, the Si content of the portion excluding the surface layer of the particles (the portion from the surface to a depth of 5 nm) is preferably 30 to 300%.

[0042] <particle size D> 50 >

[0043] When the particle size of Ni alloy powder is too small, the surface area of ​​each particle is too large, and even if it contains Si, it cannot achieve sufficient sintering inhibition effect.

[0044] Based on the reasons of excellent sintering inhibition effect and excellent capacitance of the resulting MLCCs, the particle size D of Ni alloy powder... 50 The size is 40nm or larger, preferably 60nm or larger.

[0045] When the particle size of Ni alloy powder is too large, the number of particle layers formed by the coating of internal electrode paste decreases, making it easier for interparticle gaps to form and reducing the coverage rate. In addition, due to the increase in coarse particles, short circuit defects or reduced voltage withstand capability are more likely to occur in the resulting MLCC.

[0046] Therefore, the particle size D of Ni alloy powder 50 The wavelength is 250nm or less, preferably 220nm or less, and more preferably 200nm or less.

[0047] <S content>

[0048] Ni alloy powder may contain sulfur (S).

[0049] However, if the sulfur content in the Ni alloy powder is too high, the sintering inhibition effect may sometimes be reduced. Based on the consideration of superior sintering inhibition effect and thus superior capacitance of the resulting MLCC, the sulfur content of the Ni alloy powder is preferably 200 ppm by mass or less, more preferably 150 ppm by mass or less, even more preferably 100 ppm by mass or less, and particularly preferably 50 ppm by mass or less. The lower limit of the sulfur content is not particularly limited; for example, it can be 1 ppm by mass, 3 ppm by mass, or 5 ppm by mass.

[0050] <Proportion of Ni-OH bonds>

[0051] In Ni alloy powder, the bonding states of Ni can be exemplified by, for example, Ni-Ni bonds, Ni-O bonds, and Ni-OH bonds.

[0052] If the Ni alloy powder has too many Ni-OH bonds, water will be generated from the OH groups of the Ni-OH bonds during calcination. This water reacts with the Si in the Ni alloy powder particles, sometimes forming a large amount of SiO2 layer at the interface between the internal electrode and the dielectric in the resulting MLCC. In this case, as mentioned above, the capacitance of the MLCC may decrease.

[0053] Furthermore, the temperature at which water detaches from the Ni-OH bond and transforms into the Ni-O bond is approximately 230°C. Therefore, when debinding is performed, for example, at approximately 250°C, the Ni-OH bond transforms into the Ni-O bond. During this transformation, the individual particles of the Ni alloy powder undergo volume shrinkage.

[0054] In Ni alloy powder containing Si, a Si oxide film forms and stabilizes the surface of each particle. However, due to volume shrinkage, the Si oxide film on the particle surface sometimes peels off. The heating atmosphere for debinding is usually air, so in each particle of the Ni alloy powder, Si oxidation begins from the surface where the Si oxide film has peeled off. Furthermore, due to volume shrinkage, strain is generated on the particle surface, making it easier for oxygen to diffuse, and the Si inside the particle is oxidized.

[0055] Furthermore, the thermal expansion coefficients of the individual Ni alloy powder particles and the Si oxide film differ significantly. During subsequent calcination, for example, at temperatures reaching 1200°C, the Si oxide film peels off. In this case, with Si remaining inside the particles, sintering can be suppressed by forming a new Si oxide film. However, during debinding, the Si inside the particles oxidizes, reducing the amount of Si and preventing the formation of a new Si oxide film. Therefore, the sintering suppression effect is weakened, and the area ratio (coverage) of the internal electrodes in the coated dielectric decreases. Consequently, this leads to a reduction in the capacitance of the MLCC.

[0056] Furthermore, the Si oxide film stripped during the debinding process moves along the grain boundaries along with the sintering of the particles, and is easily deposited as a SiO2 layer at the interface between the internal electrode and the dielectric. In this case, it leads to a decrease in the capacitance of the MLCC.

[0057] Therefore, based on the reason that the resulting MLCC has better capacitance, the proportion of Ni-OH bonds to Ni-Ni bonds, Ni-O bonds and Ni-OH bonds (also referred to as "the proportion of Ni-OH bonds") in Ni alloy powder is, for example, 40 mol% or less, preferably 35 mol% or less, and more preferably 33 mol% or less.

[0058] There is no specific lower limit; for example, it could be 5 mol%, 10 mol%, 15 mol%, or 20 mol%.

[0059] The bonding state of Ni in Ni alloy powder (and the proportion of Ni-OH bonds) was determined by X-ray photoelectron spectroscopy (XPS).

[0060] More specifically, using an XPS apparatus, the Ni2p spectrum of the Ni alloy powder was first obtained. Next, the obtained Ni2p spectrum was subjected to waveform separation using peak fitting, and the areas of the Ni peak, NiO peak, and Ni(OH)2 peak were calculated. The area ratios of the Ni peak, NiO peak, and Ni(OH)2 peak were considered as the molar ratios of Ni-Ni bonds, Ni-O bonds, and Ni-OH bonds, respectively, and the proportion of Ni-OH bonds (in moles%) was determined.

[0061] [Method for manufacturing Ni alloy powder]

[0062] Next, the method for manufacturing the Ni alloy powder of this embodiment will be described.

[0063] Methods for manufacturing Ni alloy powder with small particle size include CVD (Chemical Vapor Deposition) and PVD (Physical Vapor Deposition), but CVD is preferred because it can easily narrow the particle size distribution.

[0064] The following is based on Figure 1 The preparation of Ni alloy powder using the CVD method is explained.

[0065] <Composition of the Reactor>

[0066] Figure 1 This is a schematic diagram of the reactor 1 used in the manufacture of Ni alloy powder.

[0067] The main body of the reactor 1 is divided into a reaction section 2, a cooling section 6, and a collection section 8.

[0068] The reaction section 2 is the upstream part in the gas flow direction. The raw material gas supply pipe 3 and the reducing gas supply pipe 4, which will be described later, are provided in the reaction section 2.

[0069] The collection section 8 is the downstream part in the gas flow direction, and has a filter 9 inside for collecting the Ni alloy powder produced.

[0070] 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 to the collection section 8. A cooling gas supply pipe 7, which will be described later, is provided in the cooling section 6.

[0071] A valve 10 and an oxidizing gas supply pipe 11, described later, are provided at the connection 12 connecting the cooling section 6 and the collection section 8.

[0072] <Manufacturing of Ni Alloy Powder>

[0073] When using reactor 1 to manufacture Ni alloy powder, for example, the raw material gas is reacted with a reducing gas in the reaction section 2.

[0074] The raw material gas is supplied to the reaction section 2 through the raw material gas supply pipe 3.

[0075] The raw material gas contains Ni and Si raw materials as chlorides.

[0076] Examples of nickel-based raw materials include chlorides such as nickel chloride (NiCl2).

[0077] Examples of silicon-containing raw materials include silicon tetrachloride (SiCl4), dichlorosilane (H2SiCl2), and trichlorosilane (HSiCl3).

[0078] In the manufacture of Ni alloy powder containing sulfur (S), the sulfur raw material is mixed in a raw material gas. Examples of sulfur raw materials include sulfur dioxide (SO2), sulfur trioxide (SO3), and hydrogen sulfide (H2S).

[0079] Furthermore, the dilution gas, together with the raw material gas, is supplied to the reaction section 2 through the raw material gas supply pipe 3. Examples of dilution gases include inactive gases such as nitrogen (N2) and argon (Ar).

[0080] Regarding the raw material gas and dilution gas, by adjusting their respective flow rates (volume flowing per unit time), the residence time in the reaction section 2 where grain growth occurs is adjusted, thereby controlling the particle size of the manufactured Ni alloy powder.

[0081] Excessive flow will increase the pressure loss of the filter 9 in the collection section 8, causing pressure fluctuations in the reaction section 2, so it is not preferred.

[0082] For example, the flow rate ratio of dilution gas to feed gas (dilution gas / feed gas) is preferably 200 or less, more preferably 160 or less, and even more preferably 100 or less.

[0083] On the other hand, if the flow ratio (dilution gas / raw material gas) is too low, condensation of the raw material gas is likely to occur. Therefore, a flow ratio of 2 or higher is preferred, 5 or higher is more preferred, and 8 or higher is even more preferred.

[0084] The reducing gas is supplied to the reaction section 2 through the reducing gas supply pipe 4.

[0085] Reducing gases include, for example, hydrogen (H2).

[0086] Regarding the flow rate ratio of the reducing gas (hydrogen) to the chlorides (Ni and Si raw materials) contained in the feed gas, for example, the flow rate ratio of hydrogen to nickel chloride and silicon tetrachloride (H2 / (NiCl2+SiCl4)) is 2 or more, or 3 or more. The upper limit is, for example, 12, or 8.

[0087] An electric furnace 5 is installed on the outside of the reaction section 2. By driving the electric furnace 5 to generate heat, the reaction section 2 is controlled at an arbitrary temperature (reaction temperature), causing the raw material gas to react with the reducing gas.

[0088] Based on the reason that the raw material gas is not easy to condense, the reaction temperature is preferably above 900°C, and more preferably above 1000°C.

[0089] On the other hand, from an economic point of view, the reaction temperature is preferably below 1300°C, and more preferably below 1200°C.

[0090] The reactants obtained by reacting the raw material gas with the reducing gas are rapidly cooled in the cooling section 6 by cooling gas supplied from the cooling gas supply pipe 7. For example, the same gas as the dilution gas described above is used as the cooling gas.

[0091] The rapidly cooled reactant (Ni alloy powder) is collected via the filter 9 attached to the collection section 8 through the connecting part 12. In this way, Ni alloy powder is obtained.

[0092] <Oxidation Treatment>

[0093] The obtained Ni alloy powder can be subjected to oxidation treatment.

[0094] In this situation, for example, with Ni alloy powder adhering to the filter 9 of the collection section 8, valve 10 is closed, and oxidizing gas (containing oxygen gas) is supplied from the oxidizing gas supply pipe 11 through the connection 12 to the collection section 8. This brings the oxidizing gas into contact with the Ni alloy powder adhering to the filter 9, performing an oxidation treatment. In the oxidized Ni alloy powder, the proportion of the aforementioned Ni-OH bonds decreases.

[0095] The conditions for oxidation treatment are adjusted, for example, according to the desired proportion of Ni-OH bonds.

[0096] The oxidizing gas supplied from the oxidizing gas supply pipe 11 may be, for example, a mixture of oxygen and an inactive gas (e.g., nitrogen).

[0097] The oxygen content in the oxidizing gas is, for example, 0.1% by volume or more, or 0.3% by volume or more.

[0098] On the other hand, if there is too much oxygen, it will generate heat through oxidation, and Ni alloy powder may sometimes be over-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.

[0099] From the viewpoint of preventing excessive oxidation caused by oxidative heating, the flow rate of the oxidizing gas through filter 9 is preferably 1 cm / s or more, more preferably 3 cm / s or more. There is no particular upper limit; for example, it can be 15 cm / s or 10 cm / s.

[0100] The temperature of the oxidizing gas used in the oxidation process is preferably 10°C or higher, more preferably 15°C or higher. On the other hand, from the viewpoint of preventing over-oxidation, the temperature of the oxidizing gas is preferably 40°C or lower, more preferably 35°C or lower.

[0101] In addition, the temperature of the oxidizing gas may sometimes rise after passing through filter 9, but the rise is preferably less than 10°C.

[0102] The oxidation treatment time can be 10 minutes or more, or 30 minutes or more. There is no specific upper limit; for example, it can be 90 minutes or 60 minutes.

[0103] <Cleaning>

[0104] Since unreacted Ni raw materials (such as nickel chloride) may remain in the obtained Ni alloy powder, it is preferable to clean it with water or the like.

[0105] At this point, it is preferable that the dissolved oxygen content of the water used for cleaning (cleaning water) is low, specifically, preferably less than 0.01 mg / L. This ensures that the proportion of Ni-OH bonds in the cleaned Ni alloy powder remains low.

[0106] One method to reduce the dissolved oxygen content in the cleaning water is to circulate nitrogen gas through it.

[0107] It is preferable to dry the cleaned Ni alloy powder.

[0108] Drying can be performed using known drying equipment such as box dryers, rotary dryers, airflow dryers, fluidized bed dryers, and vacuum dryers. Since Ni alloy powder is easily oxidized, drying in an inert gas or under vacuum is preferred.

[0109] Example

[0110] The present invention will be specifically described below with examples. However, the present invention is not limited to the examples described below.

[0111] <Manufacturing of Ni Alloy Powder>

[0112] Use based on Figure 1 The described reactor 1, manufactured according to the above method, reacts the raw material gas with the reducing gas to produce Ni alloy powder.

[0113] That is, the raw material gas and dilution gas are supplied to the reaction section 2 from the raw material gas supply pipe 3, and the reducing gas is supplied to the reaction section 2 from the reducing gas supply pipe 4. The electric furnace 5 is driven to make the temperature (reaction temperature) of the reaction section 2 reach 1100°C, so that the raw material gas reacts with the reducing gas.

[0114] The reactants obtained by reacting the raw material gas with the reducing gas are rapidly cooled in the cooling section 6 using cooling gas (diluent gas) supplied from the cooling gas supply pipe 7, and then collected using the filter 9 of the collection section 8. In this way, Ni alloy powder is obtained.

[0115] Nickel chloride (NiCl2) is used as the Ni raw material in the feed gas. Silicon tetrachloride (SiCl4) is used as the Si raw material in the feed gas. The flow rates of nickel chloride and silicon tetrachloride are adjusted so that the Si content of the resulting Ni alloy powder is as shown in Tables 1 to 4 below.

[0116] Sulfur dioxide (SO2) gas is mixed into the raw material gas as S raw material so that the S content of the obtained Ni alloy powder is as shown in Tables 1 to 4 below.

[0117] Hydrogen (H2) is used as a reducing gas.

[0118] Nitrogen (N2) is used as a diluent gas.

[0119] The flow rate ratio of the dilution gas to the feed gas (dilution gas / feed gas) is adjusted between 5 and 100 to achieve the desired particle size D of the resulting Ni alloy powder. 50 It becomes the value shown in Tables 1 to 4 below.

[0120] The flow rate ratio of hydrogen to nickel chloride and silicon tetrachloride (H2 / (NiCl2+SiCl4)) is 4.

[0121] Next, the Ni alloy powder collected in the collection section 8 and the filter 9 is subjected to oxidation treatment (except for Example 8).

[0122] That is, with Ni alloy powder adhering to the filter 9 of the collection section 8, the valve 10 is closed, and the oxidizing gas is allowed to flow from the oxidizing gas supply pipe 11 through the connection 12 to the collection section 8. More specifically, the oxidizing gas with an oxygen content of 0.5% by volume (the remainder being nitrogen) is circulated at a flow rate of 100 NL / min for 30 minutes. The collection area of ​​the filter 9 is 2 m². 2Therefore, the flow rate of the oxidizing gas through filter 9 is 5 cm / s. Next, an oxidizing gas with an oxygen content of 1.0% by volume (the remainder being nitrogen) is passed through under the same conditions.

[0123] The temperature of the oxidizing gas flowing from the oxidizing gas supply pipe 11 to the collection section 8 is 20°C. In addition, the temperature of the oxidizing gas after passing through the filter 9 is at most 21°C (that is, the temperature rise is less than 1°C).

[0124] Next, the Ni alloy powder collected by filter 9 is recovered in the atmosphere, washed with cleaning water (pure water), and then dried in nitrogen at 100°C.

[0125] At this time, regarding the cleaning water, cleaning water with a dissolved oxygen content of less than 0.01 mg / L was used by pre-circulating nitrogen gas. However, in Example 9, cleaning water with a dissolved oxygen content of 10 mg / L without nitrogen gas circulation was used.

[0126] <Analysis of Ni alloy powder>

[0127] The particle size D of the obtained Ni alloy powder was determined. 50 The values ​​of Si and S content are shown in Tables 1 to 4 below.

[0128] Various Determination Methods

[0129] Ni alloy powder particle size D 50 The following steps will yield the results.

[0130] First, Ni alloy powder was observed using a scanning electron microscope (SU5000, manufactured by Hitachi High-Tech Corporation) to obtain SEM images. At this time, a magnification of 200 to 600 particles observed in a single field of view was selected, and a field of view with a total particle count of more than 10,000 particles was chosen.

[0131] Image analysis was performed on the obtained SEM images. For each particle, the major axis was defined as the particle size, and the particle size D was calculated based on the particle size of each particle. 50 .

[0132] The Si content of Ni alloy powder was determined using the silica gravimetric method. If the value obtained using the silica gravimetric method was less than 0.10% by mass, the Si content was determined using the blue spectrophotometric method.

[0133] The sulfur content of Ni alloy powder was determined using a carbon-sulfur measuring device (CS844, manufactured by LECO).

[0134] The proportion of Ni-OH bonds in the Ni alloy powder was determined using an XPS apparatus (VersaProbeII, manufactured by ULVAC PHI) via the method described above.

[0135] It should be noted that for the Ni alloy powder in each embodiment, the Si content in the portion excluding the surface layer of the particles (the portion from the surface to a depth of 5 nm) is in the range of 50% to 200% relative to the overall Si content of the Ni alloy powder.

[0136] The Si content in the particles was determined by observing the composition of the particle cross-section of the Ni alloy powder using a transmission electron microscope (Hitachi High Tech, HF2000).

[0137] When the Ni alloy powder is an alloy of Ni and Si, no heterogeneous phase other than Ni is detected in the X-ray diffraction (XRD) pattern obtained by measuring using an X-ray diffraction device (D8ADVANCE, manufactured by BRUKER).

[0138] No heterogeneous phases other than Ni were detected in the XRD patterns of the Ni alloy powders in each embodiment.

[0139] <Sintering characteristics of Ni alloy powder (shrinkage rate at 600℃)>

[0140] Using a benchtop Ishikawa-style mixing and chopping machine (manufactured by Ishikawa Corporation), with the rotary dial set to the maximum value, 5g of the obtained Ni alloy powder and 0.25mL of 10% by mass PVA (polyvinyl alcohol) aqueous solution were mixed for 10 minutes to obtain a mixture.

[0141] The obtained mixture was dried at 100°C for 10 minutes. 0.58 g of the dried mixture was then placed into a metal mold with a diameter of 7 mm, and a pressure of 6 kN was applied for 30 seconds to prepare a sample.

[0142] The sintering behavior of the prepared samples was investigated using a thermomechanical analysis apparatus (TMA4000SE, NETZCH). Specifically, the samples were heated at a rate of 5 °C / min under a 10 g load in an atmosphere of 1200 ppm hydrogen by volume.

[0143] The volume shrinkage rate at 600℃ (shrinkage rate at 600℃) was determined based on the thermomechanical analysis results.

[0144] In Tables 1 to 4 below, the case with a shrinkage rate of less than 5% at 600℃ is marked as "A", the case with a shrinkage rate of more than 5% but less than 10% is marked as "B", the case with a shrinkage rate of more than 10% but less than 15% is marked as "C", and the case with a shrinkage rate of more than 15% is marked as "D".

[0145] If the result is "A", "B" or "C", it can be evaluated as having excellent sintering inhibition effect.

[0146] <MLCC Manufacturing>

[0147] Multilayer ceramic capacitors (MLCCs) were fabricated using the prepared Ni alloy powder according to the following instructions.

[0148] Preparation of Internal Electrode Paste

[0149] Ni alloy powder (46 parts by mass), barium titanate powder with a particle size of 30 nm as a common material (9 parts by mass), ethyl cellulose resin as a binder (2 parts by mass), and an organic carrier composed of dihydroterpineol acetate as a solvent (45 parts by mass) were dispersed using a three-roll mill to obtain an internal electrode paste.

[0150] The Making of Ceramic Raw Slices

[0151] Next, barium titanate (50 parts by mass) with a specific surface area diameter of 120 nm, used as a dielectric material, an organic solvent (26.5 parts by mass), and a dispersant (0.5 parts by mass) were mixed and dispersed using a ball mill. A mixed solvent with a toluene to ethanol mass ratio of 1:1 was used as the organic solvent.

[0152] Then, an organic binder (21.5 parts by weight) and a plasticizer (1.5 parts by weight) are added and mixed to obtain a ceramic slurry. An ethanol solution containing 18% by weight of polyvinyl butyral (PVB) is used as the organic binder.

[0153] The obtained ceramic slurry was coated onto a polyethylene terephthalate (PET) film with a thickness of 0.5 μm after calcination using a doctor blade method. Then, the ceramic green sheet was obtained by drying.

[0154] Fabrication of Capacitor Blanks

[0155] The internal electrode paste was screen-printed onto the ceramic green sheet with a thickness of 0.5 μm after calcination and a size of 1.0 mm × 0.5 mm after calcination.

[0156] After the ceramic green sheet printed with internal electrode paste is peeled off from the PET film, 100 sheets are overlapped without misalignment, and then pressed together using a press to produce a capacitor blank as a laminate.

[0157] The capacitor blank is cut into the specified size using a cutting machine.

[0158] Debinding and Calcination

[0159] Debinding was performed by heating the capacitor blank at 260°C for 6 hours in an air atmosphere.

[0160] The debinder-treated capacitor blank was heated to 1200°C in a moist nitrogen atmosphere containing 2% by volume hydrogen for 4 hours, and then calcined at 1200°C for 2 hours. Next, it was cooled to 1000°C for 1 hour, and then held at 1000°C in a moist nitrogen atmosphere for 3 hours for re-oxidation. Finally, it was cooled to room temperature. This yielded an MLCC with an internal electrode and dielectric thickness of 0.5 μm.

[0161] <Evaluation of MLCCs>

[0162] The following evaluation is given to the fabricated MLCCs.

[0163] "Cover rate"

[0164] The fabricated MLCCs were separated using pliers and observed using a scanning electron microscope (SU5000, Hitachi High Tech). The internal electrodes were identified as the outermost exposed surface. The SEM images of this surface were binarized, and the dielectric-coated portions of the internal electrodes were distinguished from the portions where the dielectric was visible through openings in the internal electrodes. The dielectric coverage (in %) was then calculated.

[0165] For each embodiment and comparative example, the average of three measurement results is taken as the coverage rate of that example.

[0166] In Tables 1 to 4 below, cases with a coverage rate of 96% or higher are marked as “A”, cases with a coverage rate of less than 93% but more than 96% are marked as “B”, cases with a coverage rate of 90% or higher but less than 93% are marked as “C”, and cases with a coverage rate of less than 90% are marked as “D”.

[0167] In practical terms, "A", "B" or "C" are preferred.

[0168] SiO2 layer

[0169] The internal electrode paste was printed to a thickness of 0.8 μm after calcination. Otherwise, the process was the same as described above to fabricate MLCCs.

[0170] The fabricated MLCC was cut open with pliers to expose the cross-section. The cross-section was then observed using a scanning microscope equipped with an energy dispersive X-ray analyzer to confirm whether there was a SiO2 layer between the internal electrodes and the dielectric.

[0171] In Tables 1 to 4 below, the case where no SiO2 layer is formed is denoted as "A", and the case where a SiO2 layer is formed is denoted as "D".

[0172] In practical terms, "A" is the preferred choice.

[0173] "capacitance"

[0174] The capacitance of MLCCs was measured using an LCR meter (4263B, Aglient) at 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 for each example.

[0175] Set the highest capacitance in each example to 100%, and exponentialize the capacitance of each example.

[0176] In Tables 1 to 4 below, cases with an index of 98% or higher are denoted as “A”, cases with an index of 95% or higher but less than 98% are denoted as “B”, cases with an index of 90% or higher but less than 95% are denoted as “C”, and cases with an index of less than 90% are denoted as “D”.

[0177] In practical terms, "A", "B" or "C" are preferred.

[0178]

[0179]

[0180]

[0181]

[0182] <Summary of Evaluation Results>

[0183] As shown in Tables 1-4 above, the MLCCs in Examples 1-10 exhibited good capacitance. In contrast, the particle size D... 50 The capacitance of the MLCCs in Comparative Example 1 (outside the 40-250nm range) and Comparative Examples 2-3 (outside the Si content range of 0.05% by mass and less than 0.50% by mass) is insufficient.

[0184] More details are as follows.

[0185] Particle size D 50 》

[0186] Refer to Table 1 above.

[0187] Shrinkage at 600℃ varies with particle size D 50 The trend is towards increasing and improving.

[0188] On the other hand, coverage and capacitance increase with particle size D 50 Increases and decreases.

[0189] Si content

[0190] Refer to Table 2 above.

[0191] For shrinkage rate and coverage rate at 600℃, there is a trend that they improve with increasing Si content.

[0192] However, in Comparative Example 3 with excessive Si content, a SiO2 layer was found to be deposited between the internal electrode and the dielectric. This indicates that capacitance is affected not only by the coating ratio but also by the deposition of the SiO2 layer.

[0193] The proportion of Ni-OH bonds

[0194] Refer to Table 3 above.

[0195] Compared to Example 8, which did not undergo oxidation treatment, and Example 9, which underwent oxidation treatment but used cleaning water with low dissolved oxygen content, Example 1, which performed oxidation treatment and used cleaning water with low dissolved oxygen content, had a lower proportion of Ni-OH bonds.

[0196] Compared with Examples 8-9, Example 1 showed good shrinkage rate, coverage and capacitance at 600°C.

[0197] S content

[0198] Refer to Table 4 above.

[0199] Example 1, with an S content of 10 ppm by mass, showed better shrinkage, coverage, and capacitance at 600°C compared to Example 10, with an S content of 250 ppm by mass.

[0200] Symbol Explanation

[0201] 1: Reactor

[0202] 2: Reaction Section

[0203] 3: Raw material gas supply pipe

[0204] 4: Reducing gas supply pipe

[0205] 5: Electric furnace

[0206] 6: Cooling section

[0207] 7: Cooling gas supply pipe

[0208] 8: Collection Department

[0209] 9: Filter

[0210] 10: Valves

[0211] 11: Oxidizing gas supply pipe

[0212] 12: Connecting part

Claims

1. A Ni alloy powder having a Si content of 0.05% by mass or more and less than 0.50% by mass, and a particle size D 50 The wavelength range is 40–250 nm.

2. The Ni alloy powder according to claim 1, wherein, The proportion of Ni-OH bonds relative to Ni-Ni bonds, Ni-O bonds, and Ni-OH bonds is less than 40 mol%.

3. The Ni alloy powder according to claim 1 or 2, wherein, The sulfur content is below 200 ppm by mass.

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