JP6119622B2 - Method for producing indium hydroxide powder and cathode - Google Patents

Description

  The present invention relates to a method for producing indium hydroxide powder by an electrolytic method and a cathode used in a method for producing indium hydroxide powder.

  In recent years, the use of transparent conductive films has increased for solar cell applications and touch panel applications, and accordingly, demand for transparent conductive film forming materials such as sputtering targets has increased. For these transparent conductive film forming materials, indium oxide-based sintered materials are mainly used, and indium oxide powder is used as the main raw material.

In Patent Document 1, as a method for producing indium oxide powder, there is a method of producing indium oxide powder by precipitating indium hydroxide powder by electrolytic treatment of metal indium and so-called electrolytic method. Have been described.

  In the electrolysis method, as described in Patent Document 2, a method of increasing the electrode area by arranging a plurality of anode plates and cathode plates alternately may be used.

  In patent document 2, in the Example, the distance between electrodes is defined as 25 mm-50 mm. However, the distance between the electrodes and the electrolytic voltage are closely related, and it is desirable that the distance between the electrodes is as close as possible from the viewpoint of the liquid temperature between the electrodes and the pH control due to the voltage increase.

The chemical reaction formula of the cathode and the anode in the electrolytic crystallization method of In (OH) ₃ is as shown in Formula 1-1, Formula 1-2, and Formula 2.

Cathode: (Main) 6NO ₃ ⁻ + 24H ⁺ + 18e ⁻ → 6NO + 12H ₂ O (Formula 1-1)
(Sub) 18H ₂ O + 18e ⁻ → 9H ₂ + 18OH ⁻ (Formula 1-2)
Anode: 6In + 18OH ⁻ → 6In (OH) ₃ + 18e ⁻ (Formula 2)

In the main reaction in the vicinity of the cathode, the pH is increased due to consumption of H ⁺ , but in the vicinity of the anode, the pH is decreased because of consumption of OH ⁻ . For this reason, the H ⁺ concentration, that is, the pH value increases from the cathode toward the anode. In order to make the pH value between the electrodes uniform, it is necessary to stir the electrolyte to make the H ⁺ concentration uniform. However, since the movement of ions becomes more difficult as the distance between the electrodes increases, there is a problem that the effect cannot be obtained unless the stirring is sufficiently strong.

On the other hand, when the distance between the electrodes is shortened, the ions are easily moved, so that the H ⁺ concentration becomes more uniform even if the stirring intensity is the same. For this reason, it becomes easier to control the pH value uniformly by shortening the distance between the electrodes.

  However, if the distance between the electrodes is too short, contact or short-circuit between the electrodes is likely to occur, and the electrolyte solution between the electrodes stays without being sufficiently stirred, resulting in an increase in pH between the electrodes. There is a risk.

  Further, when the distance between the electrodes is increased, the voltage between the electrodes increases, so that the liquid temperature increases due to the liquid resistance. Since chemical reaction formula 1-2 at the cathode has a lower standard electrode potential than the reaction of formula 1-1, the rate at which the reaction of formula 1-2 occurs is lower than the reaction of formula 1-1. However, when the voltage between the electrodes rises, the surface potential of the cathode shifts in the negative direction, so that the rate at which the reaction of Formula 1-2 occurs increases.

For this reason, the pH value in the vicinity of the cathode tends to increase. On the other hand, the consumption amount of OH ^{− in} Formula 2 does not change, and as a result, the pH value of the entire liquid increases.

  That is, by increasing the distance between the electrodes, the liquid temperature and the pH are increased, and the cost of a large-capacity chiller facility or the like is required to cope with the liquid temperature control.

  Generally, in crystallization of hydroxide particles, the higher the pH, the easier the particle nucleation. However, in the crystallization reaction in a region having a high pH value, nucleation is likely to occur, but once formed nuclei are hardly dissolved or recrystallized. For this reason, many fine particles that tend to aggregate remain, and the particle size and particle size distribution of the secondary particles become coarse, and the width of the particle size distribution becomes wide.

On the other hand, in the crystallization reaction in a low pH region, the OH ⁻ around the nucleus is consumed by nucleation, so the pH value is lowered, and this causes dissolution of small nuclei and promotes the growth of the remaining nuclei. The

  As described above, in the crystallization reaction, it is desirable to perform the reaction in a region where the liquid temperature and the pH value are low, but it is difficult to suppress the increase in the liquid temperature and the pH while maintaining an appropriate distance between the electrodes.

Japanese Patent No. 2829556 JP 2013-36074 A

  The present invention has been proposed in view of the above-described conventional situation, suppresses the increase in the liquid temperature and pH between the electrodes, the indium hydroxide powder has excellent uniformity in particle size, and the particle size distribution width. The present invention provides a method for producing indium hydroxide powder capable of obtaining a narrow indium hydroxide powder, and a cathode used in the method for producing indium hydroxide powder.

In the method for producing indium hydroxide powder according to the present invention, a plurality of cathodes are alternately arranged and electrolyzed in an electrolytic solution, and used for electrolysis in a method for producing indium hydroxide powder by producing indium hydroxide powder. The main surface part of the cathode where the electrolytic reaction occurs is formed in a net shape, and the net shape is one in which a hole by lath processing is formed in the main surface portion of the cathode or a hole by punching processing is formed in the main surface portion of the cathode. Features.

Further, in the method for producing indium hydroxide powder according to the present invention, the liquid temperature between the anode and the cathode is controlled within a range of ± 2 ° C. with respect to the set temperature of the electrolyzer, and the pH of the electrolyte between the anode and the cathode is controlled. It is preferable to control within the range of 3.2 to 4.0. Furthermore, in the method for producing indium hydroxide powder according to the present invention, the distance between the anode and the cathode is preferably 10 to 25 mm.

The cathode according to the present invention, there is provided a cathode for use in the method of manufacturing the indium hydroxide powder, Ri Na form a main surface of the cathode mesh, braided, hole by lath machining on the main surface of the cathode Or a hole in which a hole is formed by punching in the main surface portion of the cathode.

  In the present invention, an increase in liquid temperature and pH between electrodes can be suppressed, and indium hydroxide powder having excellent particle size uniformity and a narrow particle size distribution width can be obtained.

It is the figure which showed the example of the shape of the net-like cathode to which this invention is applied. FIG. 1A is a diagram illustrating an example of a net-like cathode when lath processing is performed, and FIG. 1B is a diagram illustrating an example of a net-like cathode when punching is performed. is there. It is a figure showing transition of the liquid temperature between the anode and cathode at the time of the electrolysis in an Example and a comparative example. It is a figure showing transition of pH of the electrolyte solution between the anode and the cathode at the time of electrolysis in an Example and a comparative example. It is a figure showing the particle size of the indium hydroxide powder obtained by the Example and the comparative example.

Below, the manufacturing method of the indium hydroxide powder to which the present invention is applied and the cathode used in the manufacturing method of the indium hydroxide powder will be described in the following order.
1. Method for producing indium hydroxide powder2. Cathode structure

<1. Method for producing indium hydroxide powder>
In the method for producing indium hydroxide, indium hydroxide is obtained by utilizing an electrolytic reaction using an electrolytic solution whose concentration, pH, solubility and the like are adjusted. In this manufacturing method, metal indium as a raw material is used as an anode, and a conductive metal is used for a cathode (cathode) as a counter electrode, and both are immersed in an electrolytic solution to generate a potential difference between both electrodes to generate a current. As a result, dissolution of the metal proceeds at the anode. Furthermore, in the method for producing indium hydroxide, the indium hydroxide slurry crystallizes and precipitates by adjusting the pH so that the solubility of the produced indium hydroxide is low in the electrolytic solution.

The metal indium used for the anode is not particularly limited, but a high-purity metal is desirable in order to suppress the mixing of impurities into the indium oxide powder obtained by calcining the indium hydroxide powder . As metal indium, a purity of 99.9999% (commonly called 6N product) can be mentioned as a suitable product.

  The cathode may be made of any material that does not corrode by the electrolytic solution, and a conductive metal or the like is used. As the cathode, for example, an insoluble titanium plate or the like can be used, and an insoluble electrode obtained by coating a titanium plate with platinum, a stainless steel (SUS) plate, an In plate, or the like can be used. The cathode has a main surface formed in a net shape.

The distance between the anode and the cathode is not particularly specified, but is preferably 10 to 25 mm. If it exceeds 25 mm, the voltage increases due to the liquid resistance, so the liquid temperature and pH between the electrodes increase, the particle size of the indium hydroxide powder becomes non-uniform, and the width of the particle size distribution becomes wider. In the case of less than 10 mm, contact between electrodes and short circuit are likely to occur.

  As the electrolytic solution, an aqueous solution of a general electrolyte salt such as a water-soluble nitrate, sulfate, or chloride salt can be used. Among them, an aqueous ammonium nitrate solution using ammonium nitrate in which nitrate ions and ammonium ions are removed as nitrogen compounds after precipitation of indium hydroxide powder and calcination is left as impurities is preferable.

The electrolytic solution preferably has a solubility of the produced indium hydroxide powder in the range of 10 ⁻⁶ to 10 ⁻³ mol / L. When the solubility of the indium hydroxide powder is lower than 10 ⁻⁶ mol / L, indium ions dissolved from the anode are easily nucleated, so that the primary particle diameter becomes too fine. When the primary particle diameter is too fine, it is not preferable because it becomes difficult to separate and recover the indium hydroxide powder in the subsequent step of recovering the indium hydroxide powder.

On the other hand, when the solubility of the indium hydroxide powder is higher than 10 ⁻³ mol / L, grain growth is promoted, so that the primary particle diameter becomes large. For this reason, the larger the particle is grown, the larger the difference in particle size between the growing particle and the non-growing particle. Since the difference in particle diameter affects the degree of aggregation, as a result, the width of the particle size distribution of the indium hydroxide powder becomes wide. If the width of the particle size distribution of the indium hydroxide powder becomes wider, the width of the particle size distribution of the indium oxide powder obtained by calcining the indium hydroxide powder also becomes wider, and the density of the sputtering target obtained by sintering this becomes higher. This is not preferable because it is difficult to achieve density.

Therefore, the electrolyte solution should just have the solubility of indium hydroxide powder in the range of 10 ^<-6 > ^-10 < ^-3 > mol / L, and can control solubility with the density | concentration, pH, liquid temperature, etc. of ammonium nitrate.

  Although it does not specifically limit about the density | concentration of electrolyte solution, 0.1-2.0 mol / L is preferable. If it is thinner than 0.1 mol / L, the voltage rise during electrolysis will increase, and the amount of heat generated will increase at places where the contact resistance is high, such as the contact portion of the electrode. As a result, problems such as an increase in the temperature of the electrolytic solution and an increase in power cost due to heat generation of the electrodes are not preferable. When the concentration is higher than 2.0 mol / L, the indium hydroxide particles are coarsened by electrolysis and the variation in the particle size becomes large, which is not preferable.

  Although it does not specifically limit about the pH of the electrolyte solution between an anode and a cathode, 3.2-4.0 are preferable. When the pH of the electrolyte is less than 3.2, hydroxide precipitation is difficult to occur, and when it is greater than 4.0, the precipitation rate of the hydroxide is too high and the concentration is not uniform. Is not preferable because the particle size is non-uniform and the particle size distribution width is widened. In addition, it is preferable that pH of the whole electrolyte solution is also 3.2-4.0. Since the main surface portion of the cathode is formed in a net shape, the electrolyte solution can be easily circulated through the cathode network holes, and the increase in pH between the electrodes can be suppressed by uniformly mixing the electrolyte solution as a whole. .

The electrolyte solution between the anode and the cathode is adjusted, for example, to a concentration of ammonium nitrate of 0.1 to 2.0 mol / L, a pH of 3.2 to 4.0, and a liquid temperature between the electrodes of 20 to 60 ° C. Thereby, the solubility of indium hydroxide powder can be controlled in the range of 10 ^<-6 > ^-10 < ^-3 > mol / L. The pH can be adjusted by the amount of ammonium nitrate added.

When the temperature of the electrolyte solution between the anode and the cathode is lower than 20 ° C., the deposition rate is too slow, and when it is higher than 60 ° C., the deposition rate is too high and precipitates are formed with non-uniform concentration. Therefore, the particle size becomes non-uniform and the particle size distribution width of the indium hydroxide powder is widened, which is not preferable. Moreover, it is preferable to control the liquid temperature between electrodes in the range of +/- 2 degreeC with respect to the preset temperature of an electrolyzer. When the temperature range of the electrolyte solution between the electrodes becomes wider than ± 2 ° C., the particle size distribution width of the indium hydroxide powder becomes wide . By controlling the temperature of the electrolyte between the electrodes within a range of ± 2 ° C with respect to the set temperature of the electrolyzer, it is possible to obtain indium hydroxide powder having excellent particle size uniformity and a narrow particle size distribution range. it can. The main surface of the cathode is formed in a net-like shape, which makes it easier for the electrolyte to circulate through the cathode-like holes in the cathode, and prevents the increase in the liquid temperature between the electrodes by mixing the electrolyte uniformly. it can.

In addition, an oxygen-containing chelate compound such as citric acid, tartaric acid or glycolic acid or a nitrogen-containing chelate such as EDTA may be added to the electrolytic solution as necessary in order to improve the dissolution stability of the indium hydroxide powder. .

The electrolysis conditions are not particularly limited, but the current density is preferably 3 A / dm ^{2 to} 24 A / dm ² . When the current density is lower than 3 A / dm ² , the production efficiency of indium hydroxide powder is lowered. When the current density is higher than 24 A / dm ² , the electrolysis voltage increases, so that the liquid temperature and pH between the electrodes increase, the particle size of the indium hydroxide powder becomes uneven, and the width of the particle size distribution is wide. Become.

  As described above, in the method for producing indium hydroxide powder, the main surface portion of the cathode used for electrolysis is formed in a net shape, so that the electrolytic solution is easily circulated through the net holes of the cathode. As a result, in the method for producing indium hydroxide powder, the electrolytic solution is uniformly mixed as a whole, the rise in the temperature and pH between the electrodes is suppressed, the particle size is excellent in uniformity, and the particle size distribution width is narrow. Indium powder can be obtained. Furthermore, the temperature of the liquid between the electrodes is controlled within a range of ± 2 ° C. with respect to the set temperature of the electrolysis apparatus, and the pH of the electrolytic solution between the electrodes is controlled within the range of 3.2 to 4.0. An indium hydroxide powder having excellent diameter uniformity and a narrow particle size distribution width can be obtained.

<2. Structure of cathode>
In the above-described method for producing indium hydroxide powder, the cathode described below is used. The cathode has a main surface formed in a net shape. The cathode is mainly an insoluble electrode.

  For example, a cathode 1A as shown in FIG. Cathode 1A has a contact portion 2A that is electrically connected to a power supply portion of a power source, and a main surface portion 3A that is mainly in contact with an electrolytic solution and undergoes an electrolytic reaction. The cathode 1A has a net-like shape by forming holes 4A by lath processing on the main surface portion 3A of the cathode.

The cathode 1A is formed into a net by lath processing in which a large number of slits are alternately formed in a 1.0 mm thick Ti plate and the plate material is stretched in a direction perpendicular to the slits. By processing the cathode 1A into a net shape , the electrolyte existing between the electrodes is circulated between the electrodes without stagnation.

  In the case of lath processing, the net shape is not particularly limited, but when a 1.0 mm thick Ti plate is used, a net shape with rhombus holes having a vertical dimension of 3 mm to 4 mm and a horizontal dimension of 6 mm to 7 mm is preferable.

  The cathode may be a cathode 1B as shown in FIG. 1B, for example. Cathode 1B has a contact portion 2B that is electrically connected to a power supply portion of the power source, and a main surface portion 3B that is mainly in contact with the electrolyte and undergoes an electrolytic reaction. The cathode 1B has a net-like shape by forming holes 4B by punching in the main surface portion 3B of the cathode.

  In addition, since the cathode only needs to circulate without the electrolyte solution between the electrodes staying, punching board or hole processing by etching is also effective.

  Note that the cathodes 1A and 1B shown in FIG. 1 are examples, and the shape, size, number, interval, and the like of the holes are not limited to these.

  For example, a plurality of reticulated cathodes as described above are electrolyzed together with an anode made of metallic indium in an electrolytic solution. In this electrolysis, the shape of the cathode is made reticulated so that the electrolyte circulates through the reticulated cathode without staying between the anode and the cathode. As a result, the electrolytic solution is uniformly mixed as a whole, the rise in the temperature and pH between the electrodes can be suppressed, and indium hydroxide powder having excellent particle size uniformity and a narrow particle size distribution width can be obtained. it can.

  Specific examples to which the present invention is applied will be described below, but the present invention is not limited to these examples.

As conditions common to the examples and comparative examples, a 1 mol / L ammonium nitrate aqueous solution was used as the electrolyte. In addition, the liquid temperature between the electrodes was set to 40 ° C., the pH was set to 3.5, and 14 sheets of metal indium (size 30 cm × 30 cm × 4 mm thickness) were electrolyzed as an anode by an electrolysis method with a current density of 12 A / dm ² An indium hydroxide slurry was prepared. The temperature between the electrodes is measured by immersing a thermometer in the electrolyte between the electrodes. The pH between the electrodes is obtained by collecting the electrolyte between the electrodes and immediately adjusting the pH of the electrolyte to a pH meter. Measured with

Example 1
In Example 1, as a cathode with respect to the anode, a 1 mm thick Ti plate was subjected to lath processing with a mesh pitch of 1 mm to form rhombic holes having a longitudinal dimension of 3.2 mm and a lateral dimension of 6 mm, and a mesh shape of 30 cm × 30 cm × 1 mm thickness The cathode plate was used. The distance between electrodes of the anode and the cathode performs electrolysis as 17 mm, transition and the liquid temperature and pH between electrodes at the time of electrolytic, check the particle size distribution of the obtained indium hydroxide powder was performed.

  As a result, the liquid temperature between the electrodes was substantially constant at about 40 ° C. Further, the pH of the electrolytic solution was almost constant at about 3.5.

In the cumulative distribution of the particle size of the obtained indium hydroxide powder , 10% particle size (D10): 0.626 μm, 50% particle size (D50): 1.176 μm, 90% particle size (D90): 1.864 μm Met.

(Example 2)
In Example 2, as a cathode with respect to the anode, a 1 mm thick Ti plate was subjected to lath processing with a mesh pitch of 1 mm to form rhomboid holes having a longitudinal dimension of 3.2 mm and a lateral dimension of 6 mm, and a mesh shape of 30 cm × 30 cm × 1 mm thickness The cathode plate was used. The distance between electrodes of the anode and the cathode performs electrolysis as 25 mm, the transition of the liquid temperature and pH between poles during electrolytic, check the particle size distribution of the obtained indium hydroxide powder was performed.

  As a result, the liquid temperature between the electrodes was substantially constant at about 40 ° C. Further, the pH of the electrolytic solution was almost constant at about 3.5.

In the cumulative distribution of the particle size of the obtained indium hydroxide powder , 10% particle size (D10): 0.647 μm, 50% particle size (D50): 1.345 μm, 90% particle size (D90): 2.204 μm Met.

(Comparative Example 1)
In Comparative Example 1, a flat plate having a thickness of 30 cm × 30 cm × 1 mm was used as a cathode for the anode, not a net-like cathode. The distance between electrodes of the anode and the cathode performs electrolysis as 17 mm, the transition of the liquid temperature and pH between poles during electrolytic, check the particle size distribution of the obtained indium hydroxide powder was performed.

  As a result, the liquid temperature between the electrodes increased with time. Moreover, the pH of the electrolyte also increased with the passage of time.

In the cumulative distribution of the particle size of the obtained indium hydroxide powder , 10% particle size (D10): 0.796 μm, 50% particle size (D50): 2.023 μm, 90% particle size (D90): 3.624 μm Met.

(Comparative Example 2)
In Comparative Example 2, a flat plate having a thickness of 30 cm × 30 cm × 1 mm was used as a cathode for the anode, not a net-like cathode. The distance between electrodes of the anode and the cathode performs electrolysis as 25 mm, the transition of the liquid temperature and pH between poles during electrolytic, check the particle size distribution of the obtained indium hydroxide powder was performed.

  As a result, the liquid temperature between the electrodes increased with time. Moreover, the pH of the electrolyte also increased with the passage of time.

In the cumulative distribution of the particle size of the obtained indium hydroxide powder , 10% particle size (D10): 0.814 μm, 50% particle size (D50): 2.369 μm, 90% particle size (D90): 4.432 μm Met.

  A summary of these results is shown in FIGS. FIG. 2 shows the transition of the liquid temperature between the electrodes, FIG. 3 shows the transition of the pH in the electrolyte solution between the electrodes, and FIG. 4 shows the particle size of the obtained indium hydroxide powder.

  In FIG. 2, in Examples 1 and 2 using a mesh cathode, the liquid temperature between the electrodes is almost constant at about 40 ° C., whereas in Comparative Examples 1 and 2 using a flat cathode, the time is The liquid temperature increases with the passage of time. Therefore, it can be seen that an increase in the liquid temperature between the electrodes can be suppressed by using the net-like cathode.

  Also, in FIG. 3, the pH of the electrolyte solution is substantially constant at about 3.5 in Examples 1 and 2, whereas in Comparative Examples 1 and 2, the pH value increases with time. I'm stuck. Therefore, it can be seen that an increase in pH between the electrodes can be suppressed by using a net-like cathode.

  Further, in FIG. 4, the 10% particle size is not so different from Examples 1 and 2 and Comparative Examples 1 and 2, whereas the 90% particle size is Comparative Example 1 and 2 in Example 1. Compared to 2, it is about twice as large. That is, indium hydroxide powder having excellent particle size uniformity and a narrow particle size distribution width is obtained when Example 1 or 2 is applied, compared with the case where Comparative Example 1 or 2 is applied. I understand.

  As described above, by applying the present invention, it is possible to obtain an indium hydroxide powder that suppresses an increase in liquid temperature and pH between electrodes, is excellent in particle size uniformity, and has a narrow particle size distribution width.

1A, 1B cathode, 2A, 2B contact part, 3A, 3B main surface part, 4A, 4B hole

Claims (4)

In the method for producing indium hydroxide powder in which a plurality of anodes made of metal indium and cathodes are alternately arranged and indium hydroxide powder is produced by electrolysis in an electrolytic solution,
The main surface portion where the electrolytic reaction of the cathode used for the electrolysis occurs is formed in a net shape ,
The method for producing indium hydroxide powder, wherein the mesh is formed by forming a hole by lath processing on the main surface portion of the cathode or by forming a hole by punching processing on the main surface portion of the cathode .   The liquid temperature between the anode and the cathode is controlled within a range of ± 2 ° C. with respect to the set temperature of the electrolysis device, and the pH of the electrolyte between the anode and the cathode is set within a range of 3.2 to 4.0. The method for producing indium hydroxide powder according to claim 1, wherein the method is controlled. The method for producing indium hydroxide powder according to claim 1 or 2, wherein an interelectrode distance between the anode and the cathode is 10 to 25 mm. In the cathode used in the method for producing indium hydroxide powder according to any one of claims 1 to 3 ,
The main surface portion of the cathode Ri greens formed reticulated,
The net is a cathode in which holes are formed by lath processing on the main surface portion of the cathode, or holes are formed by punching processing on the main surface portion of the cathode.

Images