JP2008056514A - Tin oxide powder and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tin oxide powder having a uniform particle diameter and good dispersibility, and to provide a method for manufacturing the tin oxide powder. <P>SOLUTION: In the method for manufacturing the tin oxide powder by dissolving metal tin in nitric acid, recovering formed metastannic acid precipitate, and washing/filtering and firing the precipitate, the tin oxide powder having a degree of compaction of ≤35% is produced by gradually adding nitric acid to the metal tin under heating to dissolve the metal tin, and then washing/filtering the recovered metastannic acid precipitate until the electric conductivity of the filtrate becomes 5-100 mS/cm. Since the tin oxide powder has good dispersibility and a uniform particle diameter, for example, when an ITO sintered compact is produced by mixing the tin oxide powder and an indium powder, a uniform mixed powder can be obtained, and a high density ITO sintered compact can be obtained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a tin oxide powder having a uniform particle size and good dispersibility, and a method for producing the same. Since the tin oxide powder of the present invention has a good dispersibility and a uniform particle size, for example, when mixed with indium powder to produce an ITO sintered body, a uniform mixed powder can be obtained. A sintered body can be obtained.

When forming an ITO film by sputtering, in order to form a high-quality ITO film, a high-density ITO sintered body is required as a sputtering target. There is a need for a tin oxide powder having a uniform particle size.

As a method for producing a tin oxide powder used as a raw material for a high density ITO target, the following production method is conventionally known.
(B) A method in which metal tin is dissolved in nitric acid to precipitate metastannic acid, and the precipitate is collected by filtration, dried, and baked to obtain tin oxide powder.
(B) Method of precipitating metastannic acid by tin electrolysis using tin as an anode and an ammonium nitrate solution as an electrolyte, collecting the precipitate by filtration, drying, and firing to produce tin oxide powder (Patent Document 1) .
(C) A method in which an alkaline solution is added to a tin salt aqueous solution containing tetravalent tin ions to produce a tin-containing precipitate, which is separated and recovered, and baked after drying to obtain a tin oxide powder (Patent Document 2).
(D) A method in which tin metal is added to a heated ammonium nitrate solution, nitric acid is further added to precipitate metastannic acid, and this is collected by filtration and fired to obtain tin oxide powder. (Patent Document 3).

In the above method (a) (d), the dissolution rate of metal tin is not controlled when metal tin is dissolved in nitric acid to form a metastannic acid precipitate. There is a problem. In particular, when metal tin is charged into a dissolution tank containing nitric acid at once and dissolved, the dissolution of metal tin proceeds rapidly, and the tin oxide powder obtained by collecting this precipitate has a large variation in particle size. There is a problem that it is difficult to increase the density of the sintered body as a raw material.

The tin oxide powder produced by the method (b) also has a large variation in particle size, and it is difficult to increase the density of the sintered body using this as a raw material. Further, the tin oxide powder obtained by the production method (c) also has irregular particle sizes, and this method has a problem that the filterability is very poor because the produced tin-containing precipitate is colloidal. is there.

On the other hand, a method for producing tin oxide powder having a uniform particle size by controlling the dissolution temperature of metal tin and the amount of nitric acid added has been proposed as an improved method of (A) (Patent Document 4). According to this method, it is possible to obtain a tin oxide powder having a single particle diameter in the range of 1 μm to 100 μm and having a uniform particle size. However, when the dehydrated and recovered metastannic acid precipitate is washed with water, the washing is too much. And metastannic acid may bind to each other and become difficult to dehydrate, resulting in a pebbles-sized lump.
Japanese Patent No. 2829557 JP 2002-29744 A Japanese Patent No. 3173440 JP 2005-272186 A

The present invention overcomes the above-mentioned problems in the conventional production method, and provides a method for producing a tin oxide powder having good filterability, thus having a uniform particle size, good dispersibility, and low compressibility, and its A tin oxide powder is provided.

According to the present invention, a tin oxide powder having the following characteristics and a method for producing the same are provided.
(1) Metal tin is dissolved in nitric acid, and the metastannic acid precipitate produced is recovered, washed, filtered, and baked to produce tin oxide powder. Under heating, nitric acid is gradually added to metal tin and dissolved. The method for producing a tin oxide powder, wherein the recovered metastannic acid precipitate is washed and filtered until the electric conductivity of filtered water reaches 5 mS / cm to 100 mS / cm.
(2) Metal tin is added to water and heated to 60 ° C. to 100 ° C., and nitric acid is converted into the above metal tin-containing water under the condition that the amount of nitric acid per hour (HNO _{3 /} Sn) is 0.2 to 10. And then adding metal water to adjust the pH to 2 to 6, and then dehydrating to recover the precipitate, and further adding the precipitate to filtered water. A method of producing a tin oxide powder by washing and filtering until the electrical conductivity reaches 5 mS / cm to 100 mS / cm, collecting and drying, crushing, and firing at 700 to 900 ° C. for 2 to 6 hours.
(3) The method for producing a tin oxide powder as described in (1) or (2) above, wherein a tin oxide powder having a compressibility of 35% or less is produced.
(4) Tin oxide powder produced by dissolving metal tin in nitric acid, recovering the generated metastannic acid precipitate, and calcining, and having a single distribution in the particle size frequency distribution curve in the range of 1 μm to 100 μm A tin oxide powder having a peak and a compressibility of 35% or less.

The production method of the present invention is a method in which tin metal is dissolved in nitric acid, and the produced metastannic acid precipitate is collected, washed, filtered and fired to produce tin oxide powder. In addition, the metastannic acid precipitate that has been dissolved and recovered is washed and filtered until the electrical conductivity of the filtered water reaches 5 mS / cm to 100 mS / cm. By this washing filtration, the compressibility is low and the dispersibility is good. Tin oxide powder can be obtained.

Specifically, for example, metallic tin is added to water and heated to 60 ° C. to 100 ° C., and nitric acid is added under the condition of an amount of nitric acid per hour (HNO _{3 /} Sn) of 0.2 to 10. Add metal tin-containing water to dissolve metal tin to form a metastannic acid precipitate, add aqueous ammonia to this solution to adjust the pH to 2-6, dehydrate to recover the precipitate, and further add the precipitate The filtered water was washed and filtered until the electric conductivity of the filtered water reached 5 mS / cm to 100 mS / cm, recovered, dried, crushed, and calcined at 700 to 900 ° C. for 2 to 6 hours to produce tin oxide powder. By doing so, it is possible to obtain a tin oxide powder having a single distribution peak in the particle size range of 1 μm to 100 μm in the frequency distribution curve of the particle size and having a compressibility of 35% or less.

The production method of the present invention is a method in which tin metal is dissolved in nitric acid, and the produced metastannic acid precipitate is collected, washed, filtered and fired to produce tin oxide powder. In addition, the metastannic acid precipitate that has been dissolved and recovered is washed and filtered until the electric conductivity of filtered water reaches 5 mS / cm to 100 mS / cm, thereby producing a tin oxide powder having a low compressibility and good dispersibility. Is the method.

In the conventional manufacturing method, when the collected metastannic acid precipitate is washed with water, the remaining salts are sufficiently removed. For example, washing with water is repeated until the electrical conductivity of the washing filtrate reaches about 20 μS / cm. Is going. In the production method of the present invention, this water washing is moderately suppressed, and the water washing is finished in a state where the electrical conductivity of the washing filtrate becomes 5 mS / cm to 100 mS / cm. By performing such water washing, a tin oxide powder having a low compressibility can be obtained.

A specific manufacturing process for the manufacturing method of the present invention is shown in FIG.
As shown in the figure, metallic tin is put into water and heated to 60 ° C. to 100 ° C., and nitric acid is added thereto to dissolve the metallic tin, thereby generating a metastannic acid precipitate. When hydrochloric acid or a mixed acid of hydrochloric acid and nitric acid is used, metastannic acid precipitation does not occur, all the metal tin dissolves and turns into tin ions. If alkali is added to this, tin hydroxide precipitates, but this precipitation is filterable. There is a problem that is very bad. In addition, sulfuric acid hardly dissolves metal tin.

In order to dissolve metallic tin in nitric acid, it is preferable to add metallic tin to water in advance and add nitric acid to this metallic tin-containing water. The method of adding concentrated nitric acid directly to metal tin or the method of adding the total amount of metal tin to nitric acid is not preferable because the dissolution reaction proceeds rapidly and the reaction temperature boils and the reaction cannot be controlled. Moreover, it is preferable to add nitric acid by heating the water temperature of metal tin-containing water to 60 ° C. or higher and lower than 100 ° C. When the water temperature is less than 60 ° C., the dissolution reaction is slow.

The amount of nitric acid added to the metal tin-containing water is suitably such that the amount of nitric acid per hour (HNO ₃ / Sn) is in the range of 0.2 to 10 (dissolution time 10 to 12 minutes). 3 to 4 (dissolution time: 6 hours 40 minutes to 30 minutes) is preferable, and 0.5 to 2 (dissolution time: 4 hours to 1 hour) is most preferable. If the amount of nitric acid added per hour exceeds 10, the dissolution reaction proceeds rapidly and the reaction cannot be controlled, and the particle size of the finally obtained tin oxide powder is not stable. On the other hand, when the amount of nitric acid added is less than 0.2, the variation in particle size of the obtained tin oxide powder is small, but the reaction rate is extremely slow, which is industrially disadvantageous.

By controlling the amount of nitric acid added per hour in the range of 0.2 to 10, for example, a tin oxide powder having a single distribution peak in the particle size range of 1 μm to 100 μm in the frequency distribution curve of the particle size is obtained. be able to. Further, by controlling the amount of nitric acid added to 0.3 to 4, a tin oxide powder having a single distribution peak in a particle size range of 5 to 50 μm can be obtained, and the amount of nitric acid added is further 0.5. By controlling to ˜2, for example, a tin oxide powder having a single distribution peak in a particle size range of 5 μm to 50 μm can be obtained.

Nitric acid is added to metal tin-containing water to form a metastannic acid precipitate, and then ammonia water is added to the solution to adjust the pH to 2-6. Preferably, the pH is adjusted to 3.5 to 4.5. This pH adjustment ensures that tin can be metastannic acid, and the filterability of the precipitate is greatly improved. Furthermore, impurities such as nitrogen are greatly reduced by this pH adjustment. When washed with water without adjusting the pH, the filterability is poor and the washing effect is low, so that impurity ions remain in the precipitate, so that the purity of tin oxide is lowered. If the pH is lower than 2, the cleaning effect of the metastannic acid precipitate is not sufficient. If the pH is higher than 6, the cleaning effect is not changed, and ammonia is excessive and wasted.

After the metastannic acid precipitate is formed, it is decanted to recover the metastannic acid precipitate and washed with water. Washing with water is performed by, for example, using a centrifuge and washing and filtering while pouring pure water. Washing is performed until the electric conductivity of the washing filtrate reaches 5 mS / cm to 100 mS / cm, and the washing is finished before the electric conductivity reaches 5 mS / cm. Conventionally, water washing is performed until the electric conductivity is 100 μS / cm or less. However, when washing is performed until the electric conductivity is reached, metastannic acid is bonded to each other and is difficult to be dehydrated. Since it may become, it is not preferable.

By washing to an electrical conductivity of 5 mS / cm to 100 mS / cm, the filtered water is prevented from binding to each other and becoming difficult to dehydrate. A good tin oxide powder can be obtained, the washing step, the dehydration step, and the crushing step can be facilitated, and the yield can be improved. A small amount of alcohol may be sprayed during washing with pure water. By interposing alcohol between the particles of metastannic acid that are in close contact with each other, dispersibility is further improved and the crushing process becomes extremely easy.

The metastannic acid precipitate recovered by dehydration is dried and crushed, and then baked at 700 to 900 ° C. for 2 to 6 hours to produce tin oxide powder.

According to the above production method of the present invention, the particle size frequency distribution curve has a single distribution peak in the particle size range of 1 μm to 100 μm, and preferably a single distribution peak in the particle size range of 5 μm to 50 μm. In addition, a tin oxide powder having a degree of compression of 35% or less can be obtained.

Examples of the present invention are shown below together with comparative examples. In addition, the compression degree of a tin oxide powder is a powder evaluation value given by a formula of compression degree = (tap density−bulk density) / tap density × 100.

〔Example〕
After putting 50g of metallic tin (shot shape: particle size 2 ~ 3mmφ) into 380ml of pure water and raising the temperature to 70 ° C, the concentration 61% nitric acid is 2ml / min (HNO ₃ /Sn=3.7) for 1 hour. A fixed amount (120 ml in total) was added and reacted for 3.5 hours from the start of addition of nitric acid to dissolve the metal tin, thereby obtaining a metastannic acid precipitate. After this solution was naturally cooled to 50 ° C., it was adjusted to pH 4 by adding a fixed amount of 25% ammonia water at a rate of 2 ml / min for 40 minutes (total 80 ml). This lysate was put into a centrifuge and dehydrated to recover the metastannic acid precipitate. Further, pure water was poured into metastannic acid, followed by washing with water and filtration. During the washing, the electric conductivity of the washing filtrate is continuously measured, and the washing filtration is finished before the electric conductivity reaches 1 mS / cm. The precipitate is collected, dried at 100 ° C., and lightly pulverized, and further 850 The tin oxide powder was obtained by calcination at 4 ° C. for 4 hours. The bulk specific gravity and tap density of this tin oxide powder were measured, and the degree of compression was determined based on the measured values. The results are shown in Table 1.

[Examples 2-3]
A tin oxide powder was produced in the same manner as in Example 1 except that the filtration and washing were performed so that the electric conductivity of the washing filtrate water was a value shown in Table 1. The results are shown in Table 1.

[Comparative Example 1]
A tin oxide powder was produced in the same manner as in Example 1 except that the filtration and washing were performed so that the electric conductivity of the washing filtrate water was a value shown in Table 1. The results are shown in Table 1.

As shown in Table 1, the tin oxide powders of Examples 1 to 3 each have a compressibility of 35% or less, a uniform particle size, and good dispersibility, so that a mixed powder for an ITO raw material is produced. In this case, a uniform mixed powder with the indium powder can be obtained. On the other hand, the tin oxide powder of Comparative Example 1 has a degree of compression larger than 35% (41.4%) and low dispersibility. Tin oxide powder with low dispersibility tends to be non-uniform when mixed with indium powder, and an ITO sintered body using non-uniform mixed powder as a raw material tends to cause cracks and poor characteristics.

Process diagram of the production method of the present invention

Claims (4)

Metal tin was dissolved in nitric acid, and the produced metastannic acid precipitate was recovered, washed, filtered, and baked to produce tin oxide powder. Under heating, nitric acid was gradually added to metal tin and dissolved and recovered. A method for producing a tin oxide powder, wherein the metastannic acid precipitate is washed and filtered until the electric conductivity of filtered water reaches 5 mS / cm to 100 mS / cm.
Metal tin is put into water and heated to 60 ° C. to 100 ° C., and nitric acid is added to the metal tin-containing water under the condition that the amount of nitric acid per hour (HNO _{3 /} Sn) is 0.2 to 10. Then, metal tin was dissolved to form a metastannic acid precipitate. After adjusting the pH to 2 to 6 by adding aqueous ammonia to the solution, the precipitate was recovered by dehydration, and the precipitate was further subjected to electric conductivity of filtered water. Is obtained by washing, filtering until it reaches 5 mS / cm to 100 mS / cm, collecting and drying, crushing, and firing at 700 to 900 ° C. for 2 to 6 hours to produce tin oxide powder.
The method for producing a tin oxide powder according to claim 1 or 2, wherein a tin oxide powder having a degree of compression of 35% or less is produced.
Tin oxide powder produced by dissolving metal tin in nitric acid, recovering the generated metastannic acid precipitate and calcining, and has a single distribution peak in the particle size range of 1 μm to 100 μm in the frequency distribution curve of particle size And a tin oxide powder having a compression degree of 35% or less.

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