Method for producing anhydrous nickel chloride powder

Abstract

To provide a method for producing anhydrous nickel chloride powder having a particle size distribution suitable for producing nickel fine powder without pulverization after production by adjusting the particle size in a process for heating nickel chloride hydrate.SOLUTION: There is provided a method for producing anhydrous nickel chloride powder comprising a step of obtaining anhydrous nickel chloride powder by heating nickel chloride hydrate. In the step of obtaining anhydrous nickel chloride powder, the pressure is controlled to 80 torr or less and to a saturated water vapor pressure or less at the product temperature of nickel chloride hydrate until the product temperature of nickel chloride hydrate reaches 65°C or nickel chloride hexahydrate becomes nickel chloride dihydrate while vibrating the nickel chloride hydrate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing anhydrous nickel chloride powder, and more particularly to a method for producing anhydrous nickel chloride powder that is suitable for use in producing nickel fine powder. [Background technology]

[0002] Nickel fine powder is suitably used as a raw material for forming electrodes of electronic components such as multilayer ceramic capacitors, etc. Such nickel fine powder is usually produced by reducing vaporized nickel chloride with hydrogen gas.

[0003] Nickel chloride is highly deliquescent, so nickel chloride hydrate is stable in the atmosphere. When nickel chloride hydrate is heated to a high temperature to vaporize it, the water in the hydrate dissociates and generates water vapor. This water vapor oxidizes the nickel chloride and reduces the quality of the vaporized nickel chloride. Therefore, it is preferable that the nickel chloride be anhydrous nickel chloride.

[0004] Examples of methods for producing anhydrous nickel chloride include those described in Patent Documents 1 and 2.

[0005] Patent Document 1 discloses a method for producing anhydrous nickel chloride by dehydrating and drying an aqueous solution of nickel chloride to obtain nickel chloride hydrate, and then dehydrating and drying the obtained nickel chloride hydrate. Patent Document 2 discloses a method for producing anhydrous nickel chloride by heating nickel chloride hexahydrate to 160°C or higher and 200°C or lower.

[0006] Furthermore, Patent Document 3 specifically describes the particle size and properties of anhydrous nickel chloride, which is the raw material for ultrafine nickel powder for multilayer ceramic capacitors. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-274854 [Patent Document 2] Japanese Patent Application Publication No. 11-263625 [Patent Document 3] Japanese Patent Application Laid-Open No. 2002-348122 Summary of the Invention [Problem to be solved by the invention]

[0008] When anhydrous nickel chloride is produced by heating nickel chloride hydrate, the resulting anhydrous nickel chloride tends to aggregate and form lumps. Such lumps of anhydrous nickel chloride are not powder-like as they are and are not suitable as a raw material for nickel fine powder. Therefore, unless the produced anhydrous nickel chloride is pulverized, anhydrous nickel chloride having a particle size distribution suitable for producing nickel fine powder cannot be obtained.

[0009] Patent Documents 1 and 2 do not describe the form of anhydrous nickel chloride obtained by the methods disclosed therein. Therefore, it is presumed that the anhydrous nickel chloride obtained by heating nickel chloride hydrate in these methods is in a lumpy form.

[0010] Furthermore, Patent Document 3 describes that the particle size of the recovered anhydrous nickel chloride is inappropriate, and therefore the particle size and other properties of the anhydrous nickel chloride described in Patent Document 3 are characteristics after crushing.

[0011] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing anhydrous nickel chloride powder having a particle size distribution suitable for producing nickel fine powder, by adjusting the particle size in the step of heating nickel chloride hydrate, without the need for pulverization after production. [Means for solving the problem]

[0012] From the above, the aspects of the present invention are as follows.

[0013] [1] A method for producing anhydrous nickel chloride powder, comprising the step of heating nickel chloride hydrate to obtain anhydrous nickel chloride powder, In the step of obtaining anhydrous nickel chloride powder, the pressure is controlled to 80 torr or less and to the saturated water vapor pressure at the product temperature of the nickel chloride hydrate while vibrating the nickel chloride hydrate, until the product temperature of the nickel chloride hydrate reaches 65°C.

[0014] [2] The method for producing anhydrous nickel chloride powder according to [1], wherein in the step of obtaining anhydrous nickel chloride powder, the product temperature of the nickel chloride hydrate is kept in the range of 250°C or less, and the pressure is controlled to be equal to or less than the saturated water vapor pressure at the product temperature of the nickel chloride hydrate.

[0015] [3] A method for producing anhydrous nickel chloride powder, comprising a step of heating nickel chloride hydrate to obtain anhydrous nickel chloride powder, In the step of obtaining anhydrous nickel chloride powder, the pressure is controlled to 80 torr or less and to the saturated water vapor pressure at the product temperature of nickel chloride hydrate while vibrating the nickel chloride hydrate, until nickel chloride hexahydrate is converted to nickel chloride dihydrate.

[0016] [4] A method for producing anhydrous nickel chloride powder according to [3], wherein in the step of obtaining anhydrous nickel chloride powder, the pressure is controlled to be equal to or lower than the saturated water vapor pressure at the product temperature of nickel chloride hydrate until nickel chloride dihydrate becomes anhydrous nickel chloride.

[0017] [5] A method for producing anhydrous nickel chloride powder according to any one of [1] to [4], wherein when the anhydrous nickel chloride powder obtained in the step of obtaining anhydrous nickel chloride powder is sieved through a sieve with 2 mm openings conforming to JIS Z8801-1, the amount of powder that does not pass through the sieve is 2.0% by weight or less of the input amount.

[0018] [6] The method for producing anhydrous nickel chloride powder according to any one of [1] to [5], wherein the nickel chloride hydrate is heated using a vibration dryer having a container for storing the nickel chloride hydrate and a vibration mechanism for vibrating the container. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide a method for producing anhydrous nickel chloride powder having a particle size distribution suitable for producing nickel fine powder, by adjusting the particle size in the step of heating nickel chloride hydrate, without the need for pulverization after production. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a graph showing the relationship between the set temperature of the vibration dryer, the product temperature, and the pressure inside the can, and the drying time, in relation to Example 1. [Figure 2] FIG. 2 is a graph showing the relationship between the set temperature of the vibration dryer, the product temperature, and the pressure inside the can, and the drying time, in relation to Example 2. [Figure 3] FIG. 3 is a graph showing the relationship between the set temperature of the vibration dryer, the product temperature, and the pressure inside the can, and the drying time, in relation to Example 3. [Figure 4] FIG. 4 is a graph showing the relationship between the set temperature of the vibration dryer, the product temperature, and the pressure inside the can, and the drying time, in relation to Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention will be described in detail below based on specific embodiments in the following order.

[0022] (Method of manufacturing anhydrous nickel chloride powder) The anhydrous nickel chloride powder produced by the method according to this embodiment is suitable for use as a raw material for nickel fine powder used as an electrode material for electronic components such as multilayer ceramic capacitors. The moisture content of the anhydrous nickel chloride powder is 1.0% by weight or less. A moisture content of 1.0% by weight or less makes the anhydrous nickel chloride powder less susceptible to oxidation, thereby suppressing the formation of nickel oxide. As a result, the purity of the nickel fine powder can be maintained at a high level.

[0023] Anhydrous nickel chloride powder is produced by heating nickel chloride hydrate to remove the water of crystallization of the nickel chloride hydrate. Examples of nickel chloride hydrate include nickel chloride hexahydrate, nickel chloride tetrahydrate, and nickel chloride dihydrate. In this specification, nickel chloride hydrate is used either as a general term for each nickel chloride hydrate, such as nickel chloride hexahydrate, or as a hydrate containing at least one of the nickel chloride hydrates.

[0024] In this embodiment, nickel chloride hexahydrate, which is a hydrate that is usually obtained at room temperature, is used as the raw material for the anhydrous nickel chloride powder.

[0025] In this embodiment, in the step of heating nickel chloride hydrate, the pressure is controlled to be 80 torr (10665.8 Pa) or less and the saturated vapor pressure at the product temperature of the nickel chloride hydrate while vibrating the nickel chloride hydrate until the product temperature of the nickel chloride hydrate reaches 65° C. Note that the product temperature of the nickel chloride hydrate does not refer to the set temperature during heating, but refers to the actual temperature of the nickel chloride hydrate.

[0026] That is, in the step of heating the nickel chloride hydrate to 65°C, it is important to reduce the pressure to within the above range and vibrate the nickel chloride hydrate.

[0027] When nickel chloride hexahydrate, the raw material, is heated from room temperature under atmospheric pressure, it transforms into nickel chloride tetrahydrate and then nickel chloride dihydrate at a temperature of around 100°C. In other words, when nickel chloride hexahydrate is heated from room temperature to around 100°C, four water molecules separate from the nickel chloride hydrate. Because these separated water molecules are liquid or gas under atmospheric pressure, the separated water is immediately absorbed by the nickel chloride hydrate, increasing the water content of the nickel chloride hydrate and promoting its aggregation. As a result, after drying, the nickel chloride anhydrous is in a strongly aggregated state, and it must be crushed.

[0028] On the other hand, in this embodiment, the pressure when heating nickel chloride hexahydrate is controlled within the above range. By controlling the pressure within the above range, the water molecules separated from nickel chloride hexahydrate exist as gas (water vapor) rather than liquid. Some of this water vapor comes into contact with nickel chloride hydrate. At this time, the product temperature of nickel chloride hydrate is maintained at 100°C or less, for example, about 65°C, due to the latent heat generated when nickel chloride hydrate changes from hexahydrate to dihydrate. Therefore, the water vapor that comes into contact with nickel chloride hydrate is cooled and condensed to become liquid.

[0029] Because the evaporation and condensation of the water vapor are repeated locally in the nickel chloride hydrate, the absorption of the liquid water molecules into the nickel chloride hydrate gradually progresses, and the accompanying aggregation of the nickel chloride hydrate also gradually progresses. Furthermore, in this embodiment, the nickel chloride hydrate is vibrated until the nickel chloride hexahydrate is converted into nickel chloride dihydrate. The crushing effect due to this vibration and the aggregation effect caused by the condensation of water vapor occur within appropriate ranges, so that the particle size of the nickel chloride hydrate becomes uniform, and a particle size distribution with few coarse particles is obtained.

[0030] Therefore, the drying of nickel chloride hydrate from the hexahydrate to the dihydrate can proceed smoothly while preventing excessive aggregation of the nickel chloride hydrate.

[0031] In this embodiment, it is preferable to control the pressure within the above range until the product temperature of the nickel chloride hydrate reaches 80° C. By controlling the pressure within the above range until the product temperature of the nickel chloride hydrate reaches 80° C., the fluidity of the nickel chloride hydrate during drying can be improved. As a result, aggregation of the nickel chloride hydrate is further suppressed.

[0032] On the other hand, if the pressure exceeds 80 torr (10665.8 Pa), the balance between the agglomeration effect and the crushing effect is lost, and the agglomeration of nickel chloride hydrate proceeds excessively, making it difficult to obtain the stirring effect of vibration.

[0033] In this embodiment, the pressure is preferably 60 torr (7999.3 Pa) or less until the product temperature of the nickel chloride hydrate reaches 65°C, and more preferably 40 torr (5332.9 Pa) or less until the product temperature of the nickel chloride hydrate reaches 55°C.

[0034] By controlling the pressure and applying vibration to the nickel chloride hydrate as described above, the particle size of the nickel chloride hydrate becomes more uniform, which has a favorable effect on the particle size distribution of the finally obtained anhydrous nickel chloride powder. That is, aggregation of the nickel chloride hydrate is suppressed until nickel chloride hexahydrate is converted into nickel chloride dihydrate, so that the finally obtained anhydrous nickel chloride has few coarse particles (for example, particles with a particle size of 2000 μm or more) even without a pulverization treatment, and can be obtained as a powder suitable for producing nickel fine powder. The finally obtained anhydrous nickel chloride will be described later.

[0035] Heating after nickel chloride hexahydrate is converted to nickel chloride dihydrate may be continued until the water content reaches a level at which the nickel chloride finally obtained can be determined to be anhydrous nickel chloride. That is, heating is continued until two molecules of water are separated from nickel chloride dihydrate. In this embodiment, it is determined that anhydrous nickel chloride has been obtained when the water content is 1% by weight or less. As with the heating until nickel chloride hexahydrate is converted to nickel chloride dihydrate, the pressure during heating is controlled to be equal to or less than the saturated water vapor pressure at the product temperature of the nickel chloride hydrate in order to prevent aggregation of the nickel chloride hydrate. Furthermore, the nickel chloride hydrate is subsequently vibrated.

[0036] The temperature at which two molecules of water separate from nickel chloride dihydrate is 120°C or higher. Therefore, in this embodiment, nickel chloride hydrate is heated to 120°C or higher while controlling the pressure and applying vibration to the nickel chloride hydrate as described above.

[0037] At this stage, the nickel chloride hydrate is vibrated while drying, making it less likely to aggregate. As a result, the nickel chloride hydrate becomes a powder with good fluidity. As the drying proceeds further, the water content of the nickel chloride hydrate powder becomes 1.0 wt % or less, and anhydrous nickel chloride powder is obtained.

[0038] In order to shorten the time (drying time) required for the water content of nickel chloride hydrate to reach 1% by weight or less, nickel chloride hydrate may be heated to an even higher temperature. In this embodiment, it is preferable to heat the nickel chloride hydrate so that the product temperature of the nickel chloride hydrate reaches 250°C or less. If the product temperature of the nickel chloride hydrate exceeds 250°C, the nickel chloride hydrate is likely to be oxidized, and nickel oxide, an impurity, is likely to be produced.

[0039] As described above, the resulting anhydrous nickel chloride powder has a very low content of coarse particles (for example, particles with a particle size of 2000 μm or more). Specifically, when sieved through a sieve with 2 mm openings conforming to JIS Z8801-1, the amount of powder that does not pass through the sieve is 2.0 wt % or less of the input amount. In other words, 98.0 wt % or more of the resulting anhydrous nickel chloride powder is composed of particles with a particle size of less than 2000 μm.

[0040] Conventionally, nickel chloride hydrate has been dried by placing it in a tray and drying it at a high temperature of about 450°C under atmospheric pressure. This type of drying method allows heat to escape easily and has a low insulating effect. Therefore, it consumes a lot of energy. Furthermore, as mentioned above, the anhydrous nickel chloride obtained by this type of drying method is strongly agglomerated and requires a crushing process. In other words, an extra step is required.

[0041] On the other hand, the anhydrous nickel chloride powder obtained by the above-described method is already in a powder form with few coarse particles at the time of becoming anhydrous nickel chloride, and does not require further pulverization treatment. In other words, there is no need to perform any extra steps. Therefore, from the viewpoint of particle size distribution, the method for producing anhydrous nickel chloride powder according to this embodiment is more advantageous than the conventional method for producing anhydrous nickel chloride powder.

[0042] Furthermore, as described above, conventional drying of nickel chloride hydrate is carried out at high temperatures, and therefore the resulting anhydrous nickel chloride is also exposed to high temperatures, which easily decomposes the anhydrous nickel chloride and generates highly toxic and corrosive hydrogen chloride gas. Therefore, it is necessary to take measures against hydrogen chloride gas from various aspects, such as ensuring the safety of workers, taking measures against corrosion of equipment, and providing equipment for recovering hydrogen chloride gas.

[0043] On the other hand, in the method for producing anhydrous nickel chloride powder according to this embodiment, heating is performed under reduced pressure, so the generation of hydrogen chloride gas resulting from the decomposition of anhydrous nickel chloride is suppressed. Although a small amount of hydrogen chloride gas resulting from the raw material nickel chloride hydrate is also generated, the generated hydrogen chloride gas comes into contact with the water vapor separated from the nickel chloride hydrate, is condensed in a condenser as exhaust gas, and is recovered as dilute hydrochloric acid. Therefore, the burden on the environment is small. Therefore, from the environmental perspective, the method for producing anhydrous nickel chloride powder according to this embodiment is more useful than conventional methods for producing anhydrous nickel chloride powder.

[0044] Furthermore, the method for producing anhydrous nickel chloride powder according to this embodiment has a high heat insulating effect, and drying is completed at a relatively low temperature, thereby realizing energy savings. Moreover, since oxidation of nickel chloride is suppressed, the amount of nickel oxide in the anhydrous nickel chloride powder can be reduced.

[0045] The method for producing the anhydrous nickel chloride powder is preferably carried out using a dryer capable of heating under the above-mentioned conditions. As such a dryer, it is preferable to use a vibration dryer having a container capable of reducing the pressure inside and a vibration mechanism for vibrating the container. In particular, it is more preferable to use a vibration mechanism that generates circular vibrations in the circumferential direction.

[0046] By using such a vibration dryer, the nickel chloride hydrate is fluidized and dried while being agitated to some extent, so that aggregation of the nickel chloride hydrate can be suppressed.

[0047] As for the conditions of the vibration dryer, the vibration amplitude and the like may be set to the conditions set for the vibration dryer. Furthermore, by changing the vibration frequency or drying time, or by performing the vibration continuously or intermittently, the drying of the nickel chloride hydrate can be controlled, and the particle size distribution of the resulting anhydrous nickel chloride powder can be controlled. Furthermore, the temperature rise rate and temperature rise pattern during heating are preferably set based on the product temperature of the nickel chloride hydrate so that the set temperature and the product temperature do not differ too much. If the set temperature and the product temperature differ too much, the drying of the nickel chloride hydrate may proceed too rapidly, which may result in aggregation of the nickel chloride hydrate.

[0048] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and may be modified in various ways within the scope of the present invention. [Example]

[0049] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0050] Example 1 Nickel chloride hexahydrate (equivalent to JIS K8152:2018 nickel (II) chloride hexahydrate (reagent)) was prepared as nickel chloride hydrate. 10.05 kg of the prepared nickel chloride hexahydrate was placed in a vibration dryer (Chuo Kakoki, VH-25) and dried under the conditions shown in Table 1. The set temperature of the vibration dryer, the product temperature of the nickel chloride hexahydrate, and the internal pressure of the vibration dryer are shown in Figure 1.

[0051] [Table 1]

[0052] As shown in Figure 1, the pressure inside the vessel was 80 torr (10,665.8 Pa) or less, and was below the saturated vapor pressure of the nickel chloride hydrate at its product temperature, until it reached the temperature (near 65°C) at which the nickel chloride hydrate changed from hexahydrate to dihydrate. Furthermore, when the product temperature of the nickel chloride hydrate reached approximately 80°C, the nickel chloride hydrate was well agitated and fluidized, suppressing aggregation of the nickel chloride hydrate. Furthermore, even after the nickel chloride hydrate changed to dihydrate, the pressure inside the vessel was controlled to 50 torr (6,666.1 Pa) or less, and below the saturated vapor pressure of the nickel chloride hydrate at its product temperature, while the nickel chloride dihydrate was dried until its product temperature reached 239°C.

[0053] After drying, nickel chloride powder having a moisture content of 1.0% by weight or less was obtained, as shown in Table 1. In other words, anhydrous nickel chloride powder was obtained. When the obtained anhydrous nickel chloride powder was sieved through a sieve with 2 mm openings in accordance with JIS Z8801-1, the amount of powder that did not pass through the sieve was less than 0.1% by weight of the amount added.

[0054] From the above, it was confirmed that in Example 1, by using a vibration dryer to vibrate nickel chloride hydrate while controlling the pressure inside the dryer within the above-mentioned range and heating until the product temperature reached a predetermined temperature, anhydrous nickel chloride powder having a low moisture content, suppressed aggregation, and few coarse particles can be obtained.

[0055] (Examples 2 to 4) The nickel chloride hydrate was dried in the same manner as in Example 1, except that the conditions shown in Table 1 and the conditions shown in FIG. 2 were used, to obtain anhydrous nickel chloride powder.

[0056] It was also confirmed that in Examples 2 to 4, anhydrous nickel chloride powders having a low moisture content, suppressed aggregation, and few coarse particles were obtained.

[0057] Furthermore, the oxygen concentration in the anhydrous nickel chloride powder of Example 1 and the oxygen concentration in a commercially available reagent of anhydrous nickel chloride powder were measured, and the oxygen concentration in the anhydrous nickel chloride powder of Example 1 was found to be about half of the oxygen concentration in the commercially available reagent of anhydrous nickel chloride powder. In other words, it was confirmed that the amount of nickel oxide in the anhydrous nickel chloride powder of Example 1 was low. [Industrial Applicability]

[0058] The method for producing anhydrous nickel chloride powder according to the present invention can produce anhydrous nickel chloride powder suitable for producing nickel fine powder used as a raw material for the material constituting the electrodes of electronic components. It is expected that the same effects as those of the present invention can be obtained by drying other metal chloride crystalline hydrates in the same manner.

Claims

1. 1. A method for producing anhydrous nickel chloride powder, comprising the step of heating nickel chloride hydrate to obtain anhydrous nickel chloride powder, In the step of obtaining anhydrous nickel chloride powder, the pressure is controlled to 80 torr or less and to a saturated water vapor pressure at the product temperature of the nickel chloride hydrate while vibrating the nickel chloride hydrate until the product temperature of the nickel chloride hydrate reaches 65°C.

2. 2. The method for producing anhydrous nickel chloride powder according to claim 1, wherein in the step of obtaining anhydrous nickel chloride powder, the product temperature of the nickel chloride hydrate is kept in a range of 250°C or less, and the pressure is controlled to be equal to or less than the saturated water vapor pressure at the product temperature of the nickel chloride hydrate.

3. 1. A method for producing anhydrous nickel chloride powder, comprising the step of heating nickel chloride hydrate to obtain anhydrous nickel chloride powder, In the step of obtaining anhydrous nickel chloride powder, the pressure is controlled to 80 torr or less and to a saturated water vapor pressure at the product temperature of the nickel chloride hydrate while vibrating the nickel chloride hydrate until nickel chloride hexahydrate is converted to nickel chloride dihydrate.

4. 4. The method for producing anhydrous nickel chloride powder according to claim 3, wherein in the step of obtaining anhydrous nickel chloride powder, the pressure of the nickel chloride dihydrate is controlled to be equal to or lower than the saturated water vapor pressure at the product temperature of the nickel chloride hydrate until the nickel chloride dihydrate becomes anhydrous nickel chloride.

5. 5. The method for producing anhydrous nickel chloride powder according to claim 1, wherein when the anhydrous nickel chloride powder obtained in the step of obtaining anhydrous nickel chloride powder is sieved through a sieve having a mesh size of 2 mm in accordance with JIS Z8801-1, the amount of powder that does not pass through the sieve is 2.0% by weight or less of the input amount.

6. 5. The method for producing anhydrous nickel chloride powder according to claim 1, wherein the nickel chloride hydrate is heated using a vibration dryer having a container for accommodating the nickel chloride hydrate and a vibration mechanism for vibrating the container.

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