Nickel alloy-containing powder and method for producing same

Abstract

A nickel alloy-containing powder according to the present invention contains an alloy of Ni and Cu, and in an X-ray diffraction profile, has a highest peak within a 2θ range of 44.38° to 44.46°, wherein the half-width of said peak ranges from 0.120° to 0.200°.

Description

Nickel alloy-containing powder and method for producing nickel alloy-containing powder

[0001] The present invention relates to a nickel alloy-containing powder containing an alloy of Ni and Cu, and a method for producing the nickel alloy-containing powder.

[0002] Metal powders such as nickel powder and copper powder are sometimes used as electrode materials for multilayer ceramic chip capacitors (MLCCs) for electronic computers including multifunction mobile phones, and as materials for nickel-metal hydride batteries and lithium-ion batteries, due to their excellent heat dissipation and electrical properties.

[0003] Among these, multilayer ceramic chip capacitors have a structure in which dielectric layers and internal electrode layers are alternately laminated, with external electrodes provided on both ends. The dielectric layers may be made of a material primarily composed of a ceramic with a high dielectric constant, such as barium titanate, and the internal electrode layers may be made of the above-mentioned metal powder.

[0004] To use metal powder in the manufacture of multilayer ceramic chip capacitors, the metal powder is mixed with an organic binder or the like to form a paste, and then the paste containing the metal powder and a green sheet made of ceramic powder are laminated together and heated simultaneously to sinter the ceramic powder and metal powder, respectively, to form internal electrode layers and dielectric layers.

[0005] Here, when nickel powder consisting essentially of Ni or copper powder consisting essentially of Cu is used to form the internal electrode layers, when the paste and green sheet stacked together as described above are heated simultaneously, the nickel powder or copper powder may sinter at a temperature different from that of the ceramic powder, resulting in differences in their shrinkage behavior during sintering, which may result in defects such as delamination and cracks in the multilayer ceramic chip capacitor.

[0006] To address this issue, it may be possible to use a metal powder containing two or more metals, such as Ni and Cu, instead of the metal powder consisting of a single metal element, such as Ni or Cu.

[0007] As technologies relating to this type of powder, for example, Patent Document 1 describes "nickel-copper alloy powder, characterized in that the copper content is 5% by weight or more and 60% by weight or less and the average particle size is 0.1 μm or more and 5 μm or less" and "a method for producing nickel-copper alloy powder, the copper content being 5% by weight or more and 60% by weight or less and the average particle size being 0.1 μm or more and 5 μm or less, characterized in that an alkaline earth metal salt, a nickel salt, and a copper salt are mixed, the mixture is roasted in a stream of hydrogen alone, or in a mixed gas stream of hydrogen and nitrogen, or in a stream of hydrogen and argon, and after the roasting, the alkaline earth metal salt is dissolved and removed with an acid."

[0008] Furthermore, Patent Document 2 aims to "provide metal fine particles having an average particle diameter of 150 nm or less, uniform particle diameter with small variation, and excellent dispersibility," and describes nickel particles having a metal element component content of 85 to 99 mass %, a content of components other than the metal element of 1 to 12 mass %, and containing 80 mass % or more of nickel element in the metal element component and further containing 20 mass % or less of one or more metal elements selected from copper, silver, gold, platinum, and palladium, the average particle diameter D of the primary particles of the nickel particles being measured by observation with a scanning electron microscope. 50 is 20 nm to 150 nm, the coefficient of variation of the primary particle diameter is 0.2 or less, and the average particle diameter D 50 Patent Document 2 also describes a wet method for producing nickel particles, in which seed particles, which are copper particles with a nickel coating formed on the surface thereof, are mixed with a nickel complex solution, nickel ions in the mixture are heated and reduced, and nickel particles are grown using the seed particles as nuclei.

[0009] JP-A-11-124606 Patent No. 6799936

[0010] In applications such as the internal electrode layers of multilayer ceramic chip capacitors described above, the metal powder may be required to initiate sintering at a relatively high temperature when heated. A promising metal powder is a nickel alloy-containing powder, which contains Ni and Cu as an alloy and has a higher sintering initiation temperature than nickel powder or copper powder. The "nickel particles" described in Patent Document 2 are core copper particles or the like with a nickel coating formed on their surfaces, and are presumed not to be particles in which Ni and Cu are alloyed.

[0011] In order to effectively increase the sintering initiation temperature, it is necessary to adjust the particle size distribution of the nickel alloy-containing powder in detail to some extent. Patent Documents 1 and 2 do not consider at all the particle size distribution that can increase the sintering initiation temperature.

[0012] The present invention has been made to address the above-mentioned problems, and an object of the invention is to provide a nickel alloy-containing powder having a relatively high sintering initiation temperature, and a method for producing the nickel alloy-containing powder.

[0013] As a result of extensive research, the inventors have found that when a nickel alloy-containing powder is analyzed by X-ray diffraction (XRD), if a predetermined peak appears, the sintering start temperature increases significantly.

[0014] The nickel alloy-containing powder of the present invention contains an alloy of Ni and Cu, and in its X-ray diffraction profile, the highest peak has a peak top within a 2θ range of 44.38° to 44.46°, and the half-value width of the peak is 0.120° to 0.200°.

[0015] The nickel alloy-containing powder preferably has an average crystallite size of 40 nm to 150 nm.

[0016] The nickel alloy-containing powder preferably has a Cu content of 30 mass % or less.

[0017] The method for producing a nickel alloy-containing powder of the present invention includes a reduction step in which a mixed gas of nickel chloride gas and copper chloride gas is contacted with a reducing gas in a reduction furnace to produce nickel alloy particles containing an alloy of Ni and Cu.

[0018] In the above manufacturing method, the temperature inside the reduction furnace is preferably set to 1000°C to 1150°C.

[0019] The above-mentioned production method preferably includes a copper chlorination step of heating a copper raw material under a supply of chlorine gas in a copper chlorination furnace connected to the reduction furnace to generate the copper chloride gas, and a nickel chlorination step of heating a nickel raw material under a supply of chlorine gas in a nickel chlorination furnace connected to the reduction furnace to generate the nickel chloride gas.

[0020] In the above production method, the ratio of the supply rate of the copper chloride gas to the supply rate of the nickel chloride gas is preferably 1% by mass to 30% by mass.

[0021] The nickel alloy-containing powder of the present invention has a relatively high sintering initiation temperature, and the manufacturing method of the present invention is suitable for manufacturing such a nickel alloy-containing powder.

[0022] The nickel alloy-containing powder and the method for producing the nickel alloy-containing powder according to the present invention are described in detail below. The nickel alloy-containing powder according to one embodiment of the present invention contains an alloy of Ni and Cu, and in an X-ray diffraction profile, the highest peak has a peak top within a 2θ range of 44.38° to 44.46°, and the half-width of the peak is 0.120° to 0.200°.

[0023] A nickel alloy-containing powder exhibiting the above peaks in its X-ray diffraction profile is believed to have a high crystallinity of the Ni-Cu alloy contained therein. This is presumably why the sintering initiation temperature is high. To produce such a nickel alloy-containing powder, for example, a reduction step may be performed in a reduction furnace, in which a mixed gas of nickel chloride gas and copper chloride gas is brought into contact with a reducing gas to produce nickel alloy particles containing an alloy of Ni and Cu.

[0024] (Nickel alloy-containing powder) The nickel alloy-containing powder may contain nickel alloy particles containing an alloy of Ni and Cu, and may also contain particles other than nickel alloy particles, such as copper particles or nickel particles.

[0025] The nickel alloy-containing powder may contain Cu in an amount of, for example, 30% by mass or less, typically 1% by mass or more and 30% by mass or less. The nickel alloy-containing powder may contain Ni in an amount of, for example, 70% by mass or more, typically 70% by mass to 99% by mass. The nickel alloy-containing powder may contain Cu in the above amount, with the remainder consisting of Ni and unavoidable impurities.

[0026] The nickel alloy particles contain Ni and Cu as an alloy (Ni-Cu alloy). The alloying of Ni and Cu in the nickel alloy particles prevents the segregation of the individual components when the particles are fired and used as an electrode. The presence of a Ni-Cu alloy in the nickel alloy particles can be confirmed by the presence of a peak appearing at a position between the diffraction angle of the Ni peak and the Cu peak in an X-ray diffraction profile obtained by X-ray diffraction (XRD). Specifically, this can be confirmed by measuring the nickel alloy-containing powder using an XRD device (SmartLab) manufactured by Rigaku Corporation, with a step width of 0.02° and a scan speed of 20° / min, over an angle of 43-45°.

[0027] In the X-ray diffraction profile of the nickel alloy-containing powder of this embodiment obtained by X-ray diffraction analysis, the highest peak has a peak top within the 2θ range of 44.38° to 44.46°, and the half-width of the peak is 0.120° to 0.200°. If the highest peak has a peak top within the 2θ range of less than 44.38°, the copper particles may be excessively incorporated into the nickel particles, resulting in poor oxidation resistance. If the highest peak has a peak top within the 2θ range of greater than 44.46°, the copper particles may be insufficiently incorporated into the nickel particles, resulting in the formation of single nickel particles. If the half-width of the highest peak is greater than 0.200°, the crystallinity may be poor, resulting in a lower sintering start temperature. Typically, the highest peak may be within the 2θ range of 44.40° to 44.46°, and / or the half-width of the highest peak may be 0.140° to 0.160°.

[0028] The nickel alloy-containing powder may contain oxygen (O) as an unavoidable impurity in the form of oxides, etc. However, when the nickel alloy-containing powder is used as an electrode material, the remaining oxides are undesirable because they increase the resistance value. 2 / g), it is preferable that the content is 0.3% or less.

[0029] The nickel alloy-containing powder may contain chlorine (Cl) due to its manufacturing method, etc. However, since chlorine may cause deterioration of other metals in the electrode material, it is preferable that the chlorine content in the nickel alloy-containing powder is small. The Cl content of the nickel alloy-containing powder is preferably less than 0.005 mass%.

[0030] The nickel and copper in the nickel alloy-containing powder are measured by ICP atomic emission spectroscopy, and the oxygen content is measured by inert gas fusion-infrared absorption spectroscopy. The O content can be measured using an oxygen and nitrogen simultaneous analyzer (an EMGA-920 manufactured by Horiba, Ltd., or a device substantially equivalent thereto). The Cl content is measured by combustion-coulometric titration.

[0031] The nickel alloy-containing powder has a 10% particle size D10 of 0.10 μm to 0.20 μm, a 50% particle size D50 of 0.20 μm to 0.40 μm, and D50 / D10<2.00. This reduces the number of fine particles that are easily sintered, thereby increasing the sintering initiation temperature of the nickel alloy-containing powder. From this perspective, it is preferable that the nickel alloy-containing powder has a 10% particle size D10 of 0.10 μm to 0.25 μm, a 50% particle size D50 of 0.20 μm to 0.40 μm, and a D50 / D10 ratio of 1.0 to 1.8.

[0032] If the 10% particle size D10 is too small, the number of fine particles that are easily sintered may increase. If the 50% particle size D50 is too small, the number of fine particles that are easily sintered may increase. If the D50 / D10 ratio is too large, the number of fine particles that are easily sintered may increase.

[0033] The SPAN value of the nickel alloy-containing powder is preferably 140% or less, and more preferably 50% to 120%. If the SPAN value is large, there is a concern that the particle size distribution will be wide and that this will hinder the formation of a smooth coated electrode.

[0034] The 10% particle size D10, 50% particle size D50, and 90% particle size D90 refer to particle sizes at which the cumulative volumetric frequency is 10%, 50%, or 90%, respectively, in a particle size distribution obtained by visually analyzing images taken at 30,000x magnification with a scanning electron microscope (JSM-7900F) using image analysis software (Macview). The SPAN value of the nickel alloy-containing powder can be calculated using the formula: SPAN value = (D90 - D10) / D50.

[0035] When the nickel alloy-containing powder described above is subjected to thermomechanical analysis (TMA), the temperature at which the shrinkage rate reaches 2% (also referred to as the "sintering initiation temperature") is high. Specifically, the nickel alloy-containing powder may have a sintering initiation temperature of, for example, 300°C to 400°C, typically 330°C to 370°C. Note that for nickel powder consisting essentially of Ni, the same temperature may be approximately 210°C, and for copper powder consisting essentially of Cu, the same temperature may be approximately 280°C. For this reason, the nickel alloy-containing powder described above is expected to begin sintering at a relatively high temperature when heated compared to the nickel powder and copper powder.

[0036] To determine the temperature at which a nickel alloy-containing powder exhibits a shrinkage rate of 2% by thermomechanical analysis, the nickel alloy-containing powder is first subjected to uniaxial pressing with a surface pressure of 1 ton for 10 seconds to produce a press-molded body of φ5×10 mmh, and the temperature is measured using a thermomechanical analyzer (Rigaku Thermo Plus EVO2 TMA8311 or an equivalent device) in a 2% H-N atmosphere at a continuous temperature increase rate of 5°C / min. During this heating, the temperature at which the shrinkage rate in the height direction reaches 2% is confirmed.

[0037] The nickel alloy-containing powder preferably has an average crystallite diameter of 40 nm to 150 nm. If the average crystallite diameter is too small, the powder may be easily sintered, which may lower the sintering initiation temperature. To measure the average crystallite diameter, the full width at half maximum of the peak corresponding to the 111 plane (2θ: 44° to 44.5°) is measured using an X-ray diffractometer, such as a SmartLab manufactured by Rigaku Corporation, and the value can be calculated using the Scherrer equation.

[0038] The nickel alloy-containing powder can be mixed with an organic solvent, a plasticizer, an organic binder, etc. to prepare a paste, which can be used to form the internal electrode layers of a multilayer ceramic chip capacitor.

[0039] (Production Method) The nickel alloy-containing powder as described above can be produced, for example, by the vapor phase reduction method described below. However, the nickel alloy-containing powder of the present invention is not limited to those produced by the following method.

[0040] In the gas-phase reduction method, nickel chloride gas and copper chloride gas are mixed to form a mixed gas, and a reduction step is performed in which the mixed gas is brought into contact with a reducing gas in a reduction furnace to reduce the chlorides while alloying the nickel and copper contained therein. Nickel alloy particles containing an alloy of Ni and Cu are obtained by the reduction step.

[0041] Typically, a copper chlorination step in which a copper raw material is heated under the supply of chlorine gas in a copper chlorination furnace connected to the reduction furnace to generate copper chloride gas, and a nickel chlorination step in which a nickel raw material is heated under the supply of chlorine gas in a nickel chlorination furnace connected to the reduction furnace to generate nickel chloride gas, may be carried out. However, if the copper chloride gas and / or nickel chloride gas used in the reduction step is separately available, the copper chlorination step and / or nickel chlorination step may be omitted.

[0042] In the copper chlorination step, a solid raw material containing metallic copper is heated to, for example, 850°C to 1000°C in a copper chlorination furnace to evaporate it, and then contacted with chlorine gas to produce a copper chloride gas such as copper chloride gas. In the nickel chlorination step, a solid raw material containing metallic nickel is heated to, for example, 900°C to 1100°C in a nickel chlorination furnace to evaporate it, and then contacted with chlorine gas to produce a nickel chloride gas such as nickel chloride gas. The copper chloride gas obtained in the copper chlorination step and the nickel chloride gas obtained in the nickel chlorination step are each sent to a reduction furnace, where they are subjected to the reduction step.

[0043] In the reduction step, the mixed gas of copper chloride gas and nickel chloride gas is brought into contact with a reducing gas such as hydrogen to reduce the chlorides in the mixed gas, while copper and nickel are alloyed and precipitated. By connecting each of the copper chlorination furnace and the nickel chlorination furnace to a reduction furnace, copper chloride gas and nickel chloride gas are generated in the copper chlorination step and the nickel chlorination step, respectively, and then supplied to the reduction step to cause reduction and alloying, so that the copper chlorination step, nickel chlorination step, and reduction step can be carried out continuously.

[0044] In the reduction step, an inert gas such as nitrogen or argon can be further supplied to the reduction furnace. The supply of the inert gas adjusts the partial pressure of the copper chloride gas and the nickel chloride gas, thereby controlling the particle size and alloy composition of the nickel alloy-containing powder obtained thereafter. The supply ratio of hydrogen gas as the reducing gas supplied to the reduction furnace is preferably 100 mol % or more, and more preferably 200 mol % to 50,000 mol %, of the theoretical value required for the gas-phase reduction reaction.

[0045] In the above-described manufacturing method, the ratio of the supply rate of the copper chloride gas to the nickel chloride gas into the reduction furnace is preferably 1% by mass to 30% by mass, and more preferably 5% by mass to 29% by mass. If the supply rate ratio of the copper chloride gas to the nickel chloride gas is too low, nickel element particles may be generated, lowering the sintering start temperature. If the supply rate ratio is too high, copper element particles may be generated, lowering the sintering start temperature. Note that when the nickel chlorination furnace or copper chlorination furnace is connected to the reduction furnace, the supply rate of the nickel chloride gas or copper chloride gas may be approximately the same as the supply rate of chlorine gas to the nickel chlorination furnace or copper chlorination furnace.

[0046] The temperature in the reduction furnace is preferably 1000° C. to 1150° C., more preferably 1000° C. to 1100° C., and particularly preferably 1050° C. to 1100° C. From the viewpoint of obtaining a nickel alloy-containing powder with a small particle size, it is better not to set the temperature too high, but if the temperature is too low, chlorides may precipitate.

[0047] After the nickel alloy-containing powder is obtained in the reduction step, it is preferable to rapidly cool the nickel alloy-containing powder to about 400°C to 800°C, for example, by supplying an inert gas such as low-temperature nitrogen, in order to suppress the generation of secondary particles due to aggregation. The nickel alloy-containing powder can then be recovered using a bag filter or the like. The nickel alloy-containing powder recovered in this manner can be washed, dried, or otherwise treated as necessary.

[0048] Next, a nickel alloy-containing powder according to the present invention was produced as a prototype, and its effects were confirmed. This description is provided for illustrative purposes only and is not intended to be limiting.

[0049] In a copper chlorination furnace, a copper raw material was heated while supplying chlorine gas to generate copper chloride gas, and in a nickel chlorination furnace, a nickel raw material was heated while supplying chlorine gas to generate nickel chloride gas. At the same time, in reduction furnaces connected to the copper chlorination furnace and the nickel chlorination furnace, the copper chloride gas and nickel chloride gas were fed and mixed, and the mixed gas was reduced with hydrogen gas to alloy nickel and copper. In this way, a nickel alloy-containing powder was obtained, which included nickel alloy particles containing an alloy of Ni and Cu.

[0050] Here, nickel alloy-containing powders of Examples 1 to 5 were produced under different conditions, such as the temperature inside the reducing furnace and the supply rate ratio of copper chloride gas to nickel chloride gas (Cu supply rate ratio), as shown in Table 1. When the nickel alloy-containing powders of Examples 1 to 5 were analyzed by X-ray diffraction, no peaks for Ni alone or Cu alone were detected, and a peak appeared at a diffraction angle between them, confirming that the powders contained nickel alloy particles in which Ni and Cu were alloyed.

[0051] In Comparative Example 1, nickel powder and copper powder were mixed and then molded to obtain a molded product, which was then melted and evaporated by arc plasma heating and then cooled to produce a nickel alloy-containing powder. In Comparative Example 2, a mixed powder was prepared by mixing nickel powder and copper powder. In Comparative Example 3, nickel powder was used. In Comparative Example 4, copper powder was used.

[0052] For each powder of Examples 1 to 5 and Comparative Examples 1 to 4, the Cu content, Cl content, 10% particle size D10, 50% particle size D50, 90% particle size D90, and average crystallite size were measured using the methods described above. The specific surface area was also measured using the BET method. The results are shown in Table 2. The 2θ position of the highest peak in the X-ray diffraction profile and the half-width of the peak are also shown in Table 2.

[0053] Furthermore, for each powder, the sintering initiation temperature, which is the temperature at which the shrinkage in the height direction reaches 2%, was measured using a thermomechanical analyzer (TMA, TMA8311 manufactured by Rigaku Corporation) according to the method described above. The results are also shown in Table 2.

[0054]

[0055]

[0056] As can be seen from Tables 1 and 2, the nickel alloy-containing powders of Examples 1 to 5 were produced by a vapor phase reduction method under predetermined conditions, and as a result, predetermined peaks appeared in the X-ray diffraction profile, and the sintering initiation temperature was significantly increased. On the other hand, the nickel alloy-containing powder of Comparative Example 1 had a large half-width of the highest peak in the X-ray diffraction profile, and a low sintering initiation temperature.

[0057] From the above, it is suggested that the nickel alloy-containing powder of the present invention may have a relatively high sintering initiation temperature.

Claims

1. A nickel alloy-containing powder containing an alloy of Ni and Cu, in which in an X-ray diffraction profile, the highest peak has a peak top within the 2θ range of 44.38° to 44.46°, and the half-width of the peak is 0.120° to 0.200°.

2. The nickel alloy-containing powder according to claim 1, wherein the average crystallite size is 40 nm to 150 nm.

3. The nickel alloy-containing powder according to claim 1 or 2, wherein the Cu content is 30 mass % or less.

4. A method for producing a nickel alloy-containing powder, comprising a reduction step of contacting a mixed gas of nickel chloride gas and copper chloride gas with a reducing gas in a reduction furnace to produce nickel alloy particles containing an alloy of Ni and Cu.

5. The method for producing a nickel alloy-containing powder according to claim 4, wherein the temperature in the reduction furnace is set to 1000°C to 1150°C.

6. A method for producing a nickel alloy-containing powder according to claim 4 or 5, comprising: a copper chlorination step of heating a copper raw material in a copper chlorination furnace connected to the reducing furnace while supplying chlorine gas to generate the copper chloride gas; and a nickel chlorination step of heating a nickel raw material in a nickel chlorination furnace connected to the reducing furnace while supplying chlorine gas to generate the nickel chloride gas.

7. A method for producing a nickel alloy-containing powder according to claim 4 or 5, wherein the ratio of the supply rate of the copper chloride gas to the supply rate of the nickel chloride gas is 1% by mass to 30% by mass.

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