JP4707448B2 - Method for producing indium oxide powder - Google Patents

Description

  The present invention relates to a method for producing indium oxide powder used as a sputtering target material when forming an ITO film (Indium Tin Oxide film).

Since ITO film has both high conductivity and visible light transmission, it is widely used for various transparent conductive film applications such as solar cells, liquid crystal display devices, touch panels, and anti-condensation heating films for window glass.
Examples of the method for producing such an ITO thin film include sputtering, vacuum deposition, sol-gel method, cluster beam deposition, and PLD. Among them, the sputtering method uses a relatively low resistance film on a large area substrate. Since it can be produced at a low temperature, it is widely used industrially.

Thus, when manufacturing an ITO thin film by sputtering method, an ITO sintered body is used as a sputtering target. This ITO sintered body is generally manufactured by press-molding a mixed powder (premix powder) of indium oxide powder and tin oxide powder and then sintering.
Since the performance of the ITO thin film thus produced is greatly influenced by the physical properties of the indium oxide powder as a raw material for the ITO sintered body, various proposals have conventionally been made regarding the indium oxide powder and its production method.

  A conventional method for producing indium oxide powder is to synthesize indium hydroxide by adding an alkaline solution to an indium salt solution, and calcine the obtained indium hydroxide to obtain an indium oxide powder. However, in order to obtain a higher performance ITO sintered body, various proposals have been made for the manufacturing method.

  For example, in Patent Document 1, in order to obtain fine and highly dispersed indium oxide powder, an indium salt aqueous solution and an alkaline aqueous solution are mixed, and the pH of the mixed solution is set to 7 or higher, followed by aging, filtration, and drying treatment. A method for producing an indium oxide powder by calcining acicular indium hydroxide obtained in this manner is disclosed.

In Patent Document 2, in order to obtain an indium oxide powder capable of producing a high-density ITO sintered body having a sintered density of 6.0 g / cm ³ or more, an indium salt aqueous solution having a temperature of 60 ° C. to 100 ° C. The alkaline aqueous solution is mixed so that the [OH] / [In] ratio is in the range of 3 to 5, and the mixing rate is specified to obtain the desired indium hydroxide, and the indium hydroxide is washed and filtered. A method for producing an indium oxide powder, characterized by being produced by drying, calcining, and the like, is disclosed.

In Patent Document 3, in order to obtain an indium oxide powder capable of producing a high-density sintered body having a theoretical density of 5.3 g / cm ³ or more, an indium nitric acid aqueous solution is kept at 70 ° C. to 95 ° C. for 30 minutes to By adding an alkaline aqueous solution until the final pH of the indium nitric acid aqueous solution becomes 7 to 9 over 3 hours, the average length is 0.03 μm to 0.3 μm, the crystallite diameter is 200 μm to 500 μm, and the average particle size is 0.5 μm or less. The obtained slurry is solid-liquid separated and dried at 90 ° C. to 260 ° C., lightly crushed and then fired at 500 ° C. to 900 ° C. to obtain indium oxide powder. A manufacturing method is disclosed.

JP-A-5-193939 (Patent No. 3289335) Japanese Patent Laid-Open No. 6-191846 (Japanese Patent No. 3324164) JP 2002-316818 A

By the way, it has been found that if there is a pinhole in the ITO sintered body, nodules are easily generated when sputtering, and the life that can be used for sputtering is shortened.
Accordingly, the present invention is intended to provide a production method capable of obtaining an indium oxide powder capable of producing an ITO sintered body that can be used for a long time in sputtering by suppressing generation of pinholes and generating nodules. .

  In the present invention, an indium salt solution and an alkaline aqueous solution are mixed to synthesize indium hydroxide, and the obtained indium hydroxide is first baked at 700 ° C. to 800 ° C. in the air, and then 1070 ° C. in the air. A method for producing indium oxide powder, characterized in that the second baking is performed at ˜1300 ° C.

  In the synthesis of indium hydroxide, it is preferable that the mixed solution of the indium salt solution and the alkaline aqueous solution is controlled so as to have a liquid temperature of 50 to 90 ° C. and a pH of 7 to 8. At this time, an alkaline aqueous solution may be added to the indium salt solution, an indium salt solution may be added to the alkaline aqueous solution, or it may be supplied to the reaction vessel at the same time, but the alkaline aqueous solution is added to the indium salt solution. It is preferable to do so.

  Compared with primary firing only, secondary firing is followed by secondary firing, so there is less unevenness in firing and the particle size is uniform, and there is no unevenness in the distribution of components after firing. Holes can be suppressed, and as a result, it is possible to produce an ITO sintered body that can be used for a long time in sputtering with less generation of nodules.

  In the present invention, the expression “X to Y” means a range from X to Y unless otherwise specified.

  Hereinafter, although this invention is demonstrated based on embodiment, this invention is not limited to the following embodiment.

In the method for producing indium oxide powder according to the present embodiment, indium hydroxide is synthesized by adding an alkaline aqueous solution to an indium salt solution to react, and the obtained indium hydroxide is first fired at 700 ° C. to 800 ° C. in the atmosphere. Then, second firing is performed at 1070 ° C. to 1300 ° C.
Details will be described below.

(Indium hydroxide synthesis process)
In the synthesis of indium hydroxide, an alkaline aqueous solution is added to an indium salt solution to control the temperature of the mixed solution (reaction solution) to a predetermined temperature, and the alkaline aqueous solution is added until the pH of the mixed solution (reaction solution) reaches a predetermined range. In addition, it is preferable that the mixture is stirred for a predetermined time and allowed to react sufficiently.

The liquid temperature of the mixed solution (reaction solution) of the indium salt solution and the alkaline aqueous solution is preferably controlled and managed so as to maintain a temperature of 50 ° C to 90 ° C, particularly 60 ° C to 85 ° C, particularly 70 ° C to 85 ° C. .
Moreover, it is preferable to add alkaline aqueous solution so that pH of a liquid mixture (reaction liquid) may be 7-8, especially 7.4-7.6.
At this time, the addition rate of the aqueous alkali solution is preferably adjusted so as to reach the target pH over 40 to 60 minutes. After reaching the target pH, an appropriate time (for example, about 30 minutes) is set so that the reaction proceeds sufficiently. ) It is preferable to make it react, stirring. However, it is not necessary to carry out an aging treatment for several hours.

  As the alkaline aqueous solution, for example, an aqueous solution of sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonia or the like can be used, and among them, an aqueous ammonia solution is particularly preferable.

Examples of the indium salt solution include a solution obtained by dissolving indium in an acid such as an indium nitrate solution and an indium sulfate solution. Among them, indium nitrate is preferable.
For this indium nitrate solution, for example, indium shot is put into pure water, an appropriate amount of nitric acid is added and dissolved in an oil bath (for example, immersed at 110 to 150 ° C. for about 9 to 20 hours), and dissolution is completed. Thereafter, an indium nitrate solution having a predetermined indium ion concentration can be used by diluting with pure water.

When the indium salt solution and the alkaline aqueous solution are mixed and reacted as described above, indium hydroxide is precipitated and the reaction solution becomes a slurry. Therefore, it is preferable that after standing to about room temperature if necessary, solid-liquid separation is performed to recover a solid (cake), which is washed and dried to obtain indium hydroxide.
The drying temperature at this time is not particularly limited, but is preferably 90 ° C. to 260 ° C. After drying, the drying temperature may be lightly crushed as necessary.

(First firing step)
Next, the indium hydroxide obtained by synthesis as described above is fired at 600 ° C. to 900 ° C. in the atmosphere. That is, baking is performed so that indium hydroxide is held in a furnace set to 600 ° C to 900 ° C. Here, setting the inside of the furnace to 600 ° C. to 900 ° C. means that the atmospheric temperature in the furnace is set to the temperature.

The firing temperature in the first firing step may be 600 ° C to 900 ° C as described above, more preferably 700 ° C to 800 ° C, particularly 720 ° C to 780 ° C, and the firing time is 80 minutes to 200 minutes. Preferably, it is 100 minutes to 180 minutes, and for example, firing performed at 600 ° C. for 200 minutes and 900 ° C. for 80 minutes can be exemplified.
At this time, it is possible to put the material to be fired into a furnace heated to 600 ° C. to 900 ° C., but instead of suddenly putting the material to be fired in such a high temperature atmosphere, gradually, the temperature is gradually increased to the temperature range. Heating is preferred. For example, the initial temperature at the time when the object to be fired is put into the firing furnace is set to 20 ° C. to 80 ° C., particularly preferably 20 ° C. to 60 ° C., and the temperature rising rate from the initial temperature is 4 ° C./min to 8 ° C. / Min, particularly preferably 4.5 ° C./min to 6 ° C./min, and particularly preferably 4.5 ° C./min to 5.5 ° C./min to 700 ° C. to 800 ° C., and then 700 ° C. to 800 ° C. It is preferable to keep the temperature at a predetermined time.
As the firing furnace, either a continuous furnace or a batch furnace can be used.

(Crushing process)
After the first firing, it is preferable to cool to a predetermined temperature and pulverize to a predetermined particle size.

  At this time, it is preferable to gradually cool until the product temperature reaches 20 ° C. to 100 ° C. over 8 hours to 15 hours, and in particular, the product temperature reaches 40 ° C. to 70 ° C. over 8 hours to 15 hours. It is more preferable to cool slowly until it does.

Subsequent grinding, Dmax12myuemu below by using a hammer mill, among others Dmax10μm below, enters Dmax8μm within the range Among them, (hereinafter also referred to as "AD") bulk density of the milled powder is 0.2 g / cm ³ It is preferable to grind so that it may become the range of -0.5g / cm < ³ >.

(Second firing step)
What passed through the 1st baking process is baked at 1000 to 1300 degreeC in air | atmosphere. That is, the material to be fired is fired in a furnace set at 1000 ° C. to 1300 ° C. so as to be held for a predetermined time. Here, setting the inside of the furnace to 1000 ° C. to 1300 ° C. means setting the atmospheric temperature in the furnace to the temperature.

In the second firing, firing is performed at a temperature of at least 1000 ° C. to 1300 ° C., preferably 1070 ° C. to 1300 ° C., particularly preferably 1130 ° C. to 1240 ° C. for 110 minutes to 240 minutes, preferably 150 minutes to 210 minutes. It is important to do. For example, 1000 ° C. may be held for 210 minutes, or 1300 ° C. may be held for 110 minutes.
At this time, it is possible to put the object to be fired in a furnace heated to 1000 ° C. to 1300 ° C., but instead of suddenly putting the object to be fired in such a high temperature atmosphere, gradually the temperature is gradually increased to the temperature range. Heating is preferred. That is, the initial temperature at the time when the article to be fired is put into the firing furnace is set to 20 ° C. to 80 ° C., particularly preferably 20 ° C. to 60 ° C., and the temperature rising rate from the initial temperature is 4 ° C./min to 8 ° C. / Min, particularly preferably 4.5 ° C./min to 6 ° C./min, and particularly preferably 4.5 ° C./min to 5.5 ° C./min. It is preferable to hold 1000 ° C. to 1300 ° C. for a predetermined time.
The firing furnace used for the second firing may be either a continuous furnace or a batch furnace.

  In both the first firing and the second firing, it is also possible to use a continuous furnace in which the object to be fired moves in the tunnel furnace. In this case, the tunnel furnace is divided into a plurality of blocks in the transfer length direction. The set temperature can be changed for each block. For example, in the case of the second firing furnace, the heating temperature is gradually increased from the entrance, the temperature of the predetermined block is set to a temperature range of 1000 ° C. to 1300 ° C., and the temperature of each block is set so that the subsequent blocks are used for cooling. You only have to set it.

After the second baking, it is preferable to cool to a predetermined temperature. For example, it is preferable to cool gradually until the product temperature of indium oxide reaches 20 ° C to 150 ° C, and it is more preferable to cool gradually until the product temperature reaches 20 ° C to 50 ° C.
After cooling, if necessary, it may be crushed so as to loosen dama-like indium oxide, or dama may be removed by classification.
The slow cooling can be performed outside the furnace, although the tunnel furnace can be divided into a plurality of blocks in the transfer length direction as described above and the final block can be designed as a cooling block.

(Indium oxide powder)
The indium oxide powder obtained as described above can be suitably used as a sputtering target raw material when forming an ITO film (Indium Tin Oxide film) obtained by mixing and firing with a tin oxide powder. An ITO sintered body that does not generate holes can be manufactured.
Among these, in particular, a predetermined tin oxide powder, for example, a primary particle observed when observed with a TEM photograph (magnification: 300,000 times) has an average particle size of 1 μm or less, preferably 0.01 μm to 0.2 μm, and BET measurement. specific surface area according to the 1m ² / g~20m ² / g, preferably 2m ² / g~5m if ² / g and is mixed with tin oxide powder producing ITO sintered body, more uniform and tin oxide powder The ITO sintered body that does not generate pinholes can be manufactured with higher yield.

As a manufacturing method of the ITO sintered body, for example, tin oxide powder is added to indium oxide powder, for example, 5 wt% to 20 wt%, and mixed with a ball mill or a vibration mill to form an ITO powder. If sintered under conditions, an ITO sintered body can be produced.
Also, indium oxide powder, tin oxide powder and ion-exchanged water are mixed in a ball mill, and further added with a dispersant and a binder to form a slurry, which is poured into a structural mold and drained under reduced pressure to form a molded body. After performing drying and degreasing treatment, an ITO sintered body can be produced by sintering.
However, it is not limited to these manufacturing methods.

As a molding means of the ITO powder, a molding method such as a die press, a casting molding, a cold isostatic pressing (CIP), a slip cast molding or the like can be employed.
The sintering may be performed at a temperature of 1450 ° C. to 1650 ° C., for example, but is not limited to this temperature. The sintering time is generally several hours to several tens of hours, but is not limited to this time. The sintering atmosphere is not particularly limited, and can be performed in air, oxygen, inert gas, or the like.

Examples of the present invention will be described below. However, the present invention is not limited to the following examples.
In addition, each sample obtained by the Example and the comparative example evaluated by the following method.

<BET measurement>
The BET (specific surface area) of the indium oxide powders obtained in Examples and Comparative Examples was measured using Monosorb manufactured by Yuasa Ionics Co., Ltd.
As shown in FIG. 1, the indium oxide used for the measurement was sampled by about 20 g each from a total of nine locations on the diagonal, center, and bottom of the SiC firing container, and BET measurement was performed on each of the nine samples. The average value, standard deviation and CV value were calculated from the following formula.
The BET measurement was started within 1 hour immediately after sampling of indium oxide.

<TEM diameter measurement>
As for the tin oxide TEM, 200 particles were randomly extracted, the TEM diameter was measured by TEM photograph observation (magnification: 300,000 times), and the average value was obtained.

<AD measurement>
The apparent density (AD) of the pulverized powder was measured using a Kasa specific gravity measuring instrument manufactured by Kuramotsu Scientific Instruments in accordance with JIS K-5101. At that time, measurement was started within 3 hours after any powder was pulverized.

<Pinhole evaluation>
For the ITO sintered compacts obtained in the examples and comparative examples, 10 arbitrarily selected visual fields were observed with a stereomicroscope (magnification 100 times), and the presence or absence of a pinhole having a diameter of 50 μm or more was evaluated.

Example 1
After controlling the indium nitrate solution with an indium ion concentration of 3.4 mol / L to 70 ° C. to 80 ° C. with an oil bath and adjusting the pH to 7.6 by adding 28% aqueous ammonia over 55 minutes with stirring, Stirring was continued for 30 minutes to deposit indium hydroxide to obtain a slurry.
The obtained slurry was subjected to solid-liquid separation with a filter press to recover a solid (cake), which was sufficiently washed with pure warm water and then dried in an atmosphere at 140 ° C. for 22 hours. After drying, put it in a SiC firing container (contents 300 mm x 300 mm x 200 mm), raise the temperature from the initial temperature of 40 ° C to 750 ° C at a heating rate of 5.0 ° C / min, and keep 750 ° C for 150 minutes. First firing was performed.
The obtained powder was cooled to 40 ° C. while being put in a SiC baking vessel, and then pulverized using a hammer mill having a mesh opening of 1 mmφ (powder supply amount: 7.4 kg / min, rotation speed: 5800 rpm). The apparent density (AD) of the obtained powder was 0.33 g / cm ³ .
Next, the pulverized powder is put in a SiC firing container (internal capacity: 300 mm × 300 mm × 200 mm), heated from an initial temperature of 40 ° C. to 1175 ° C. at a heating rate of 5.0 ° C./min, and then 1175 ° C. is 180 ° C. The second baking was performed so as to hold for a minute, and the obtained powder was cooled to a product temperature of 40 ° C. while being put in a SiC baking container to obtain an indium oxide powder.
When the BET of the obtained indium oxide powder was measured as described above, the BET average value was 2.42 m ² / g, the standard deviation was 0.10 m ² / g, and the CV value (coefficient of variation) was 0.04. Met. In addition, Table 2 shows BET measurement values, average values, standard deviations, and CV values at the upper, middle, and lower nine locations of the diagonal and center of the SiC firing container after the second firing, respectively.

Further, the indium oxide powder and tin oxide powder (average particle size 0.08 μm, specific surface area 2.6 m ² / g) obtained as described above were mixed at a mass ratio of 90:10 to obtain ZrO ₂ balls. Dispersion treatment was performed for 21 hours in a dry ball mill using Then, polyvinyl alcohol (binder) is added to the mixed powder after the dispersion treatment, mixed with a stirring crusher, molded with a press at a pressure of 200 kgf / cm ² , and then the molded body is hammered with 3 mmφ openings. The powder obtained was pulverized using a mill, and the obtained powder was press-molded at a pressure of 1000 kgf / cm ² to obtain a 300 mm × 300 mm × 7 mm rectangular shaped compact. Then, this molded body was dried at 80 ° C. for 15 hours, and then fired at 1550 ° C. for 8 hours in an oxygen atmosphere at atmospheric pressure to obtain five ITO sintered molded bodies.
Observation of the ITO sintered compacts thus obtained revealed no pinholes of 50 μmφ or more in all ITO sintered compacts.

(Example 2)
An indium oxide powder and an ITO sintered compact were obtained in the same manner as in Example 1 except that the temperature increase rate of the second firing was changed to 4.5 ° C./min. Table 1 shows the BET average value, standard deviation, and CV value of the obtained indium oxide. The apparent density (AD) of the powder obtained by pulverization after the first firing was 0.33 g / cm ³ .
Moreover, when observing about the obtained ITO sintered compact, the pinhole of 50 micrometer (phi) or more was 0 in all the ITO sintered compacts.

(Example 3)
An indium oxide powder and an ITO sintered compact were obtained in the same manner as in Example 1 except that the firing temperature of the second firing was changed to 1200 ° C. Table 1 shows the BET average value, standard deviation, and CV value of the obtained indium oxide. The apparent density (AD) of the powder obtained by pulverization after the first firing was 0.31 g / cm ³ .
Moreover, when observing about the obtained ITO sintered compact, the pinhole of 50 micrometer (phi) or more was 0 in all the ITO sintered compacts.

Example 4
An indium oxide powder and an ITO sintered compact were obtained in the same manner as in Example 1 except that the firing temperature of the second firing was changed to 1150 ° C. Table 1 shows the BET average value, standard deviation, and CV value of the obtained indium oxide. The apparent density (AD) of the powder obtained by pulverization after the first firing was 0.32 g / cm ³ .
Moreover, when observing about the obtained ITO sintered compact, the pinhole of 50 micrometer (phi) or more was 0 in all the ITO sintered compacts.

(Example 5)
An indium oxide powder and an ITO sintered compact were obtained in the same manner as in Example 1 except that the temperature increase rate of the second baking was changed to 4.5 ° C./min and the baking temperature was changed to 1150 ° C. Table 1 shows the BET average value, standard deviation, and CV value of the obtained indium oxide. The apparent density (AD) of the powder obtained by pulverization after the first firing was 0.32 g / cm ³ .
Moreover, when observing about the obtained ITO sintered compact, the pinhole of 50 micrometer (phi) or more was 0 in all the ITO sintered compacts.

(Example 6)
An indium oxide powder and an ITO sintered compact were obtained in the same manner as in Example 1 except that 28% ammonia water was added over 55 minutes to adjust to pH 7.3 to precipitate indium hydroxide to obtain a slurry. Table 1 shows the BET average value, standard deviation, and CV value of the obtained indium oxide. The apparent density (AD) of the powder obtained by pulverization after the first firing was 0.35 g / cm ³ .
Moreover, when observing about the obtained ITO sintered compact, the pinhole of 50 micrometer (phi) or more was 0 in all the ITO sintered compacts.

(Example 7)
An indium oxide powder and an ITO sintered compact were obtained in the same manner as in Example 1 except that 28% ammonia water was added over 55 minutes to adjust the pH to 8.0 to precipitate indium hydroxide to obtain a slurry. Table 1 shows the BET average value, standard deviation, and CV value of the obtained indium oxide.
The apparent density (AD) of the powder obtained by pulverization after the first firing was 0.33 g / cm ³ . When observing the obtained ITO sintered compact, pinholes of 50 μmφ or more were 0 in all ITO sintered compacts.

(Example 8)
An indium oxide powder and an ITO sintered compact were obtained in the same manner as in Example 1 except that the first firing temperature was changed to 650 ° C. and the second firing temperature was changed to 1070 ° C. Table 1 shows the BET average value, standard deviation, and CV value of the obtained indium oxide. The apparent density (AD) of the powder obtained by pulverization after the first firing was 0.25 g / cm ³ .
Moreover, when observing about the obtained ITO sintered compact, the pinhole of 50 micrometer (phi) or more was 0 in all the ITO sintered compacts.

Example 9
An indium oxide powder and an ITO sintered compact were obtained in the same manner as in Example 1 except that the first firing temperature was changed to 650 ° C. and the second firing temperature was changed to 1200 ° C. Table 1 shows the BET average value, standard deviation, and CV value of the obtained indium oxide. The apparent density (AD) of the powder obtained by pulverization after the first firing was 0.24 g / cm ³ .
Moreover, when observing about the obtained ITO sintered compact, the pinhole of 50 micrometer (phi) or more was 0 in all the ITO sintered compacts.

(Example 10)
An indium oxide powder and an ITO sintered compact were obtained in the same manner as in Example 1 except that the first firing temperature was changed to 850 ° C. and the second firing temperature was changed to 1070 ° C. Table 1 shows the BET average value, standard deviation, and CV value of the obtained indium oxide. The apparent density (AD) of the powder obtained by pulverization after the first firing was 0.43 g / cm ³ .
Moreover, when observing about the obtained ITO sintered compact, the pinhole of 50 micrometer (phi) or more was 0 in all the ITO sintered compacts.

(Example 11)
An indium oxide powder and an ITO sintered compact were obtained in the same manner as in Example 1 except that the first firing temperature was changed to 850 ° C. and the second firing temperature was changed to 1200 ° C. Table 1 shows the BET average value, standard deviation, and CV value of the obtained indium oxide. The apparent density (AD) of the powder obtained by pulverization after the first firing was 0.45 g / cm ³ .
Moreover, when observing about the obtained ITO sintered compact, the pinhole of 50 micrometer (phi) or more was 0 in all the ITO sintered compacts.

(Comparative Example 1)
After controlling the indium nitrate solution with an indium ion concentration of 3.4 mol / L to 70 ° C. to 80 ° C. with an oil bath and adjusting the pH to 7.5 by adding 28% aqueous ammonia over 55 minutes with stirring, Stirring was continued for 30 minutes to deposit indium hydroxide to obtain a slurry.
The obtained slurry was subjected to solid-liquid separation with a filter press to recover a solid (cake), which was sufficiently washed with pure warm water and then dried in an atmosphere at 140 ° C. for 22 hours. After drying, the obtained powder is put into a SiC baking container (internal capacity 300 mm × 300 mm × 200 mm), heated from an initial temperature of 40 ° C. to 750 ° C. at a heating rate of 5.0 ° C./min, and 750 ° C. is maintained for 150 minutes. Firing was performed so that the powder was held, and the resulting powder was cooled to 40 ° C. in an SiC firing container to obtain an indium oxide powder.
The obtained indium oxide was sampled in the same manner as in Example 1 and BET was measured. The BET average value was 13.47 m ² / g, its standard deviation was 3.41 m ² / g, and the CV value was It was 0.25. Moreover, the apparent density (AD) of the obtained powder was 0.32 g / cm ³ .
In addition, Table 3 shows BET measurement values, average values, standard deviations, and CV values at the upper, middle, and lower nine locations on the diagonal and center of the SiC firing container after the firing, respectively.

  In addition, five ITO sintered compacts were obtained in the same manner as in Example 1 using indium oxide obtained as described above. When the obtained ITO sintered compact was observed, several pinholes of 50 μmφ or more were observed in any ITO sintered compact.

(Comparative Example 2)
After adjusting an indium nitrate solution having an indium ion concentration of 3.4 mol / L to 70 ° C. to 80 ° C. with an oil bath and stirring, 28% aqueous ammonia is added over 55 minutes to adjust to pH 7.5. The stirring was continued for 30 minutes to deposit indium hydroxide to obtain a slurry.
The obtained slurry was subjected to solid-liquid separation with a filter press to recover a solid (cake), which was sufficiently washed with pure water and then dried in an atmosphere at 140 ° C. for 22 hours. After drying, the obtained powder is put in a SiC firing container (internal capacity 300 mm × 300 mm × 200 mm), heated from an initial temperature of 40 ° C. to 1185 ° C. at a heating rate of 5.0 ° C./min, and 1185 ° C. is increased for 150 minutes. Firing was performed so that the powder was held, and the resulting powder was cooled to 40 ° C. in an SiC firing container to obtain an indium oxide powder.
Table 1 shows the BET average value, standard deviation, and CV value of the obtained indium oxide. The apparent density (AD) of the obtained powder was 0.82 g / cm ³ .

  In addition, five ITO sintered compacts were obtained in the same manner as in Example 1 using the indium oxide obtained as described above. When the obtained ITO sintered compact was observed, several pinholes of 50 μmφ or more were observed in any ITO sintered compact.

  As shown in Table 1, the CV values of the indium oxide powders obtained in Examples 1 to 11 are in the range of 0.03 to 0.16, and all are indium oxide powders having uniform primary particle sizes. It was found that there was very little uneven baking. On the other hand, the CV values of the indium oxide powders of Comparative Examples 1 and 2 were 0.25 and 0.47, respectively, indicating that the particle size of the primary particles was not uniform and the baking unevenness due to firing was large.

Looking at the distribution of the BET measurement values in Example 1 shown in Table 2, since the fluctuation width of the BET value was small and the CV value was 0.04 in all the sampled locations, there was almost no unevenness in baking. I found out.
On the other hand, when the distribution of the BET measurement values in Comparative Example 1 shown in Table 3 is seen, the BET value fluctuation width is large depending on the sampled location, in particular, the BET value at the center of the SiC firing container is large. Since the value was 0.25, it was found that uneven baking occurred.
Considering the results in Table 1, in Example 1, since there is almost no unevenness in baking, when this indium oxide is used, more uniform mixing with tin oxide becomes possible, and an ITO sintered body without pinholes can be obtained. It is thought that it was possible to obtain.

It is a schematic diagram of the sampling location at the time of sampling the obtained indium oxide from a SiC baking container.

Claims (4)

  An indium salt solution and an aqueous alkali solution are mixed to synthesize indium hydroxide, and the obtained indium hydroxide is first baked at 600 ° C. to 900 ° C. in the atmosphere, and then 1000 ° C. to 1300 ° C. in the air. Second baking is performed, and the manufacturing method of the indium oxide powder characterized by the above-mentioned.   The indium hydroxide is synthesized by controlling the indium hydroxide so that the mixed solution of the indium salt solution and the alkaline aqueous solution has a liquid temperature of 50 ° C to 90 ° C and a pH of 7 to 8. Powder manufacturing method. The method for producing an indium oxide powder according to claim 1 or 2, wherein after the first baking, the pulverization is performed, and then the second baking is performed. After the first firing, and cooled until the product temperature is 20 ° C. to 100 ° C., then Dmax is according to any one of claims 1 to 3, characterized in that the ground to fall within the following 12μm Of producing indium oxide powder.