JP2007302485A - Indium oxide powder and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide inexpensive indium oxide powder exhibiting high sinterability in spite of low specific surface area even when sintered under normal pressure. <P>SOLUTION: The indium oxide powder is obtained by heat-treating indium hydroxide powder obtained by a neutralization precipitation method, with a hydrogen-containing gas at ≤800°C and calcining the heat-treated powder in the atmosphere. The obtained indium oxide powder has 5.0-9.0 m<SP>2</SP>/g BET specific surface area, ≤35% coefficient of variation of the primary particle diameter which is calculated by SEM observation and is the ratio (σ/SEM diameter) of the standard deviation σ of the primary particle diameter to the average particle diameter (SEM diameter) thereof, 70-150 nm average particle diameter, ≤300 nm maximum particle diameter, <90 nm crystallite diameter calculated by a Scherrer method and ≥80% relative density when a molding of the indium oxide powder is sintered at 1,500°C under normal pressure. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an indium oxide powder that is a raw material of a sputtering target containing indium used when forming a transparent conductive thin film by a sputtering method and a method for producing the same.

  Indium oxide powder is widely used as a raw material for a sputtering target material for forming a transparent conductive thin film. For example, when producing a composite oxide target containing indium such as an ITO (indium tin oxide) target, raw materials such as indium oxide powder and tin oxide powder are wet-mixed and pulverized with a bead mill or the like to form a slurry, which is then sprayed. Granulate by dry. After molding the granulated powder, the obtained molded body is sintered to produce a target material.

  The density at the time of target sintering, so-called sintered body density, is important with respect to the quality of the target. When the sintered body density is low, abnormal discharge due to the generation of nodules becomes a problem, resulting in a problem that the usage rate of the target is reduced. Therefore, the relative density of the target containing indium is usually required to be 98% or more.

  The indium oxide powder used as a raw material for these targets is made into indium hydroxide by adding a basic aqueous solution such as ammonia or sodium hydroxide to an indium salt aqueous solution to neutralize it, which is washed, dried and calcined. Can be obtained.

In Patent Document 1, a BET specific surface area is obtained by calcining acicular indium hydroxide obtained by mixing an indium salt aqueous solution and a basic aqueous solution and adjusting the pH to 7 or more, followed by aging, filtration and drying. Is 15-30 m ² / g, the ratio of the BET diameter to the crystallite diameter is 2 or less, and the average particle diameter of primary particles determined by particle size distribution measurement is 0.1 μm or less. Yes. By using this indium oxide powder, the density of the ITO target is 6.0 g / cm ³ and the relative density is 84% or more.

In Patent Document 2, indium and tin hydroxide are coprecipitated by mixing a mixed aqueous solution of indium chloride and tin chloride with ammonium carbonate, and the precipitate is thermally decomposed in the range of 400 to 950 ° C. Describes that the BET specific surface area of the coprecipitated powder for ITO target is 10 m ² / g or more.

Increasing the BET specific surface area to 10 m ² / g or more is effective for improving the surface activity and improving the sinterability, but increasing the BET specific surface area is a new technique that the strength of the molded product is reduced. Problems arise. This is considered because the weight of the molding binder per particle interface, for example, polyvinyl alcohol (PVA) is reduced. When the strength of the molded body decreases, the yield decreases due to cracks in the molded body and cracks during sintering.

  When the BET specific surface area increases, the density of the molded body decreases, and thus the shrinkage ratio during sintering increases to about 17 to 19%. However, the larger the BET specific surface area, the more remarkable deformation such as bending. As a result, in order to obtain a target having a predetermined size, the molded body must be manufactured in a large amount that can correct the deformation by processing, the processing yield is as low as about 70%, and the yield during processing is low. Productivity was reduced.

As a method for solving these problems, Patent Document 3 discloses that the BET specific surface area is 10 m ² / g or less, and the ratio of the average secondary particle size to the maximum secondary particle size is 3 times or less. An indium oxide powder having a crystallite diameter of 90 nm or more is disclosed.

  In Patent Document 3, hot press sintering is performed to obtain a high-density target using this indium oxide powder. The hot press sintering has a problem that the apparatus is complicated and the sintering becomes expensive as compared with the normal pressure sintering.

  In addition, as an indium oxide powder production method, an electrolytic method capable of producing uniform particles is used. However, the electrolysis method is inferior to the neutralization precipitation method in that the equipment cost is expensive and electric energy is also required. Although it is also disclosed to select and use indium oxide powder synthesized by the neutralization precipitation method, it is expensive and expensive to select one suitable for the conditions.

In Patent Document 4, an indium oxide powder having an average particle diameter of 0.8 to ² μm and a BET specific surface area of 3 to 5 m ² / g obtained from the particle size distribution is used and the gauge pressure is 0.9 atm. It is disclosed that sintering is performed in a pressurized oxygen atmosphere to obtain a high-density ITO sintered body. However, in general, it is known that sintering is easy in a pressurized oxygen atmosphere. Therefore, even if an indium oxide powder having such a low BET specific surface area is used, a high-density sintered body is used. However, the pressure sintering is more expensive than the normal pressure sintering, and the apparatus is complicated.

Further, Patent Document 5 discloses indium oxide powder from which a high-density ITO sintered body can be obtained by atmospheric pressure sintering. According to this, the indium salt aqueous solution is neutralized with a basic aqueous solution, and the obtained slurry is washed, dried, and calcined at 600 to 1000 ° C. so that the average particle diameter / specific surface area equivalent diameter is 1 to 10. Indium oxide powder having a specific surface area equivalent diameter / crystallite diameter of 2 or less is obtained. In a wide specific surface area range of 5 to 30 m ² / g, the secondary particle diameter and the primary particle diameter are set to specific values, that is, the aggregated state of the primary particles is controlled, so that a high-density ITO sintered body is obtained. Is supposed to be obtained. However, the relative density of the sintered body obtained varies greatly from 95.0 to 99.7%, and it is difficult to obtain a high-density sintered body having a relative density of 98% or more under all conditions.

Patent Document 6 also discloses a method for producing indium oxide powder from which a high-density ITO sintered body can be obtained by atmospheric pressure sintering. After calcining the indium oxide powder at 500 to 1200 ° C., the BET diameter is 10 m ² / g or less, the average crystallite diameter by dissolving and recrystallizing indium hydroxide by hydrothermal treatment in acid or alkali. An indium oxide powder having a diameter of 90 nm or more and a secondary particle diameter of 3 μm or less is obtained. By using this indium oxide powder, it is said that a high-density ITO sintered body can be obtained by atmospheric pressure sintering. However, even in this case, the relative density varies greatly as 95 to 100%, and it is difficult to obtain an ITO sintered body of 98% or more under all conditions. Furthermore, hydrothermal treatment is expensive and requires special equipment.

  On the other hand, Patent Document 7 discloses a method for producing a low-resistance ITO powder that can be easily crushed and an ITO powder for a target. This is because ITO hydroxide can be obtained by aging ITO hydroxide at a certain temperature or more during neutralization and then firing in a reducing atmosphere to obtain low-resistance ITO powder, and using an emulsifier during neutralization. The ITO powder for the target can be obtained by decomposing the object in high-temperature air. The ITO powder obtained by firing in a reducing atmosphere is easy to crush and has low resistance, but is not for targets but for forming conductive films. This document does not describe the sinterability, and hardly discloses the powder characteristics. Rather, ITO powder obtained by firing in a high temperature atmosphere is preferred for high density targets.

In Patent Document 8, as a method for producing an ITO target, high density firing is performed using indium oxide powder having a specific surface area of 3 to 15 m ² / g and an average particle size of 0.1 to 0.5 μm. A method for obtaining a ligation has been proposed. However, embodiments having a specific surface area using a 10 m ² / g or less of indium oxide powder is not, how specific surface area density of the sintered body by using a 10 m ² / g or less of indium oxide powder obtained is disclosed I cannot say that.

  As described above, a target having high strength of a molded body and a high sintered body density even by atmospheric pressure sintering is obtained, and indium oxide obtained by a low-cost method such as a neutralization precipitation method Powder is desired.

JP-A-5-193939

Japanese Patent Laid-Open No. 5-201731

JP-A-10-95615

Japanese Patent Laid-Open No. 9-228036

JP-A-7-188912

Japanese Patent Laid-Open No. 10-17324

JP 2003-40620 A

JP 2004-323877 A

  An object of the present invention is to provide an indium oxide powder having a low specific surface area and exhibiting high sinterability even by atmospheric pressure sintering at a low cost.

  As a result of earnest research and development on the characteristics of indium oxide powder relating to sinterability, the present inventors have obtained knowledge that the influence of the primary particle size of the indium oxide powder and its surface state greatly affects the sinterability. It was. Furthermore, by controlling the calcining atmosphere and temperature, it was found that highly sinterable indium oxide powder can be obtained even with a low specific surface area, and the present invention has been achieved.

  In order to produce the indium oxide powder according to the present invention, the indium hydroxide powder is calcined in a hydrogen-containing gas atmosphere after washing. More preferably, it is preferable that the indium hydroxide powder is calcined in an air atmosphere after being washed and heat-treated in a hydrogen-containing gas atmosphere. The calcination step or the heat treatment and calcination steps are preferably performed at a temperature of 800 ° C. or lower.

The indium oxide powder of the present invention obtained by such a production method has a BET specific surface area of 5.0 to 9.0 m ² / g, a standard deviation σ of the primary particle diameter determined by SEM observation, and an average primary particle diameter (SEM diameter). ) Ratio (σ / SEM diameter) is 35% or less.

  Moreover, the average primary particle diameter calculated | required from SEM observation is 70-150 nm, the maximum primary particle diameter is 300 nm or less, and the crystallite diameter calculated | required by the Scherrer method is less than 90 nm, It is characterized by the above-mentioned.

  Further, the indium oxide powder of the present invention has a relative density of 80% or more when the molded body is sintered under normal pressure at 1500 ° C.

  According to the present invention, indium oxide powder having high sinterability even at a low specific surface area can be obtained at low cost. By using the indium oxide powder, the strength of the molded body can be increased, and a sputtering target having a high sintered body density can be obtained even by atmospheric pressure sintering. Therefore, during sputtering, abnormal discharge due to generation of nodules is suppressed, and a target having a high usage rate is provided at low cost.

  The indium oxide powder and the production method thereof according to the present invention will be described in detail. In the production of a complex oxide target containing indium, in a normal process, indium oxide powder is mixed and pulverized together with other raw material powders using a ball mill or bead mill, and after adding a binder and mixing, Granulated using a spray dryer or the like.

  This indicates that in the mixing and pulverization step, the secondary particles of the raw material powder are pulverized to a state close to the primary particles, and newly form secondary particles in the granulation step. That is, unless the connection is very strong, the state of the secondary particles is not so important for the target indium oxide powder, and the state of the primary particles is considered to have a great influence on the target to be finally obtained.

Therefore, in order to achieve the above object, in the indium oxide powder of the present invention, the BET specific surface area is set to 5.0 to 9.0 m ² / g, and the standard deviation σ of the primary particle diameter obtained from SEM observation and the average primary particle diameter The coefficient of variation, which is the ratio (σ / SEM diameter) of (SEM diameter), is 35% or less.

  The BET specific surface area is an index that integrates the particle diameter and the surface state. The large BET specific surface area means that the primary particle diameter is fine and the surface has many irregularities, that is, a so-called bulky state.

When the BET specific surface area is greater than 9.0 m ² / g, the primary particle surface has high sintering activity and excellent sinterability. However, since the density of the molded body is reduced, cracking and firing during molding and sintering are performed. Yield decreases due to an increase in machining allowance due to deformation during ligation. On the other hand, if the BET specific surface area is smaller than 5.0 m ² / g, the surface sintering activity is low, the sintered density of the target is lowered, and the connection between primary particles is strengthened, and the composite oxide containing indium Crushing in the pulverization step in the production of the target becomes insufficient, and desired secondary particles cannot be obtained even if granulation is performed.

  The coefficient of variation is an index of the variation in particle diameter obtained from SEM observation, and is the fluctuation (σ / SEM diameter) of the standard deviation σ of the primary particle diameter obtained from SEM observation and the average primary particle diameter (SEM diameter). When the coefficient exceeds 35%, voids between particles in the molded body increase, and the density of the sintered body of the target does not increase. The lower limit of the coefficient of variation is not particularly limited, but is usually not less than 5%.

  Moreover, in this invention, the average primary particle diameter calculated | required by SEM observation is 70-150 nm, and the largest primary particle is 300 nm or less.

  When the average primary particle diameter is smaller than 70 nm, the powder is bulky, the density of the molded body does not increase, and the above-described problems occur. On the other hand, if it is larger than 150 nm, the surface sintering activity is lowered, and the density of the sintered body of the target is not increased. When the maximum primary particle diameter exceeds 300 nm, voids between particles in the molded body increase, and the sintered body density of the target does not increase. The maximum primary particle size is not theoretically smaller than the average primary particle size, and in the present invention, the maximum primary particle size is 70 nm or more.

  Furthermore, the crystallite diameter determined by the Scherrer method is set to less than 90 nm. The Scherrer method is a method for estimating the size of the crystallite because the powder X-ray diffraction peak becomes broader as the crystallite becomes smaller. The crystallite diameter D is obtained by the Scherrer equation shown in Equation 1.

Formula 1: D = 4λ / (3 (Δ2θ) cosθ)
Here, λ is the wavelength, and Δ2θ is the integral width (in radians) of the diffraction peak when the X-ray scattering angle is taken on the horizontal axis.

  The crystallite diameter is an index of crystallinity, and is an index representing the activation state of the primary particles depending on the size of the interface of the primary particles. In other words, the interface in the primary particles plays an important role in sintering, and the heat treatment at higher temperatures reduces the interface in the primary particles, including the interface near the surface, which is particularly important, and reduces the sintering activity. I think that. Therefore, when the crystallite diameter is 90 nm or more, a target having a sufficiently high sintered body density cannot be obtained. The lower limit of the crystallite diameter is not particularly limited, and may be a minimum crystallite diameter obtained when indium hydroxide is converted into indium oxide by calcination, and is usually 20 nm or more.

  The indium oxide powder of the present invention has a relative density of 80% or more when the compact is sintered at 1500 ° C. under normal pressure. The concentration of indium oxide in a composite oxide containing indium such as ITO is generally as high as about 90%, and the sinterability of the composite oxide target containing indium is greatly influenced by the sinterability of indium oxide powder. Further, in the production of a complex oxide target containing indium, the optimum secondary particles corresponding to the sintering conditions are formed by the pulverization step and the granulation step, and the obtained target is a sintered body of unground indium oxide powder. In general, a large sintered body density can be obtained.

  Therefore, when the indium oxide powder of the present invention has a relative density of 80% or higher when the molded body is sintered at 1500 ° C. under normal pressure, a composite oxide target containing indium, for example, an ITO target is manufactured. A target having a sintered body density of 98% or more is obtained. This relative density is preferably higher, and even if it is equal to the theoretical density, that is, the relative density is 100%, there is no problem.

The density of the sintered body of indium oxide powder can be easily measured by sintering the molded body by an ordinary method. For example, 0.5 g of indium oxide powder is applied to a mold having a diameter of 10 mm and a pressure of 500 kgf / cm ² is applied. A uniaxial molding is performed, and a sintered body is obtained by sintering at 1500 ° C. for 3 hours in an atmospheric pressure oxidizing atmosphere, preferably in an air atmosphere, and the relative density thereof may be measured. In the present specification, this relative density is calculated with the true density of indium oxide (In ₂ O ₃ ) being 7.04 g / cm ³ .

  The indium oxide powder according to the present invention is prepared by neutralizing an indium salt aqueous solution with a basic aqueous solution and then calcining in a hydrogen-containing gas atmosphere at 400 ° C. or higher and 800 ° C. or lower after washing. Is obtained. Preferably, the indium hydroxide powder is obtained by calcining in an air atmosphere at 400 to 800 ° C. after heat treatment in a hydrogen-containing gas atmosphere at 400 ° C. or higher and 800 ° C. or lower.

  Indium hydroxide powder synthesized by neutralizing an aqueous solution of indium salt containing indium chloride with a basic aqueous solution is preferably calcined after repeated washing until the chlorine quality is 70 ppm or less in terms of indium oxide. . If the chlorine quality exceeds 70 ppm, the sintered density of the target will not increase. A lower chlorine grade is preferred, with 25 ppm or less being particularly preferred. There is no particular lower limit on the chlorine quality, but the quality that results in an analysis error even if the material does not substantially contain chlorine, that is, about 5 ppm is the lower limit.

  The calcination step is performed in a hydrogen-containing gas atmosphere. Furthermore, it is more preferable to calcine in an air atmosphere after heat treatment in a hydrogen-containing gas atmosphere. As the hydrogen-containing gas atmosphere, it is preferable to use a mixed gas of hydrogen and nitrogen.

  By receiving the thermal history in the hydrogen-containing gas atmosphere in this way, the specific surface area is reduced at a low temperature compared to the calcining in the air atmosphere, and the calcining conditions can be lowered. Compared with the indium oxide powder having the same specific surface area, the target subjected to the thermal history in the hydrogen-containing gas atmosphere has a higher relative density of the target than the one calcined in the air atmosphere. This is presumably because the sintering activity of the indium oxide powder is maintained because there is no high-temperature thermal history.

  Furthermore, since heat treatment at a low temperature is possible in a hydrogen-containing gas atmosphere, there is no abnormal grain growth, and the dispersion of primary particles is smaller than that obtained by calcination in an air atmosphere. That is, indium oxide powder having a coefficient of variation of 35% or less, which is a ratio (σ / SEM diameter) of the standard deviation σ of the primary particle diameter and the average primary particle diameter (SEM diameter), is obtained, and the average primary particle diameter is 70 to 150 nm and the maximum primary particle size is 300 nm or less.

For the above reasons, indium oxide powder that has undergone a thermal history in a hydrogen-containing gas atmosphere has a lower BET specific surface area than that calcined in the air atmosphere, that is, 5 m ² / g or more, after sintering. A relative density of 80% or more can be achieved.

  In order to obtain the indium oxide powder according to the present invention, it may be simply calcined in a hydrogen-containing gas atmosphere, but in the bead mill pulverization in the production process of the composite oxide target containing indium, the dispersant used in this process In order to improve the compatibility, it is desirable to perform calcination in an air atmosphere as a post process. By calcination in an air atmosphere, indium metal or lower indium oxide slightly reduced on the primary particle surface can be reoxidized to indium oxide.

  Furthermore, calcination in the air atmosphere in the post-process can be performed at low temperature, there is no history of high temperature, and abnormal grain growth is unlikely to occur, so the powder characteristics obtained by heat treatment in a hydrogen-containing gas atmosphere can be obtained. It is thought that this contributes to higher sinterability.

The calcination temperature (heat treatment temperature) in the hydrogen-containing gas atmosphere and the calcination temperature in the air atmosphere after the heat treatment in the hydrogen-containing gas atmosphere are preferably 800 ° C. or lower. The calcining temperature may be determined so that the indium oxide powder obtained has a BET specific surface area of 5 to 9.0 m ² / g in consideration of the state, amount, calcining time, and the like of indium hydroxide to be calcined. . However, in order to avoid a high temperature heat history and to suppress variations in the primary particle size, it is further preferably set to 700 ° C. or lower. Further, in order to thermally decompose indium hydroxide into indium oxide, it is necessary to set the temperature to 250 ° C. or more. However, in order to make the BET specific surface area 9.0 or less, the temperature is preferably 400 ° C. or more, and more desirably 500 ° C. It is preferable to set the temperature to be at least ° C.

  The hydrogen concentration in the hydrogen-containing gas is not particularly limited. According to the ISO international standard, a mixed gas of hydrogen and nitrogen containing less than 5.7% by volume of hydrogen is incombustible regardless of air. From the viewpoint of safety, it is desirable to make it less than 5.7% by volume. The lower limit of the hydrogen concentration is preferably 0.4% by volume or more because a reducing action is required during firing.

The indium oxide powder obtained by such a method has a specific surface area as low as 5.0 to 9.0 m ² / g, but has a relative density of 80% or more when the molded body is sintered at 1500 ° C. under normal pressure. Thus, an indium oxide powder excellent in sinterability can be obtained.

  Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples of the present invention, but the present invention is not limited to these Examples. The particle observation method and the crystallite diameter evaluation method used in Examples and Comparative Examples are as follows.

(1) BET specific surface area: The specific surface area was measured by a BET one-point method using a specific surface area measuring device (manufactured by Yuasa Ionics Co., Ltd., Countersorb QS-10).

(2) Particle observation: The shape and size of the particles were observed using an FE scanning electron microscope (SEM) system (manufactured by Hitachi, Ltd., S-4700). The average primary particle diameter (SEM diameter), the maximum primary particle diameter, and the standard deviation σ were determined by measuring arbitrary 250 particles of the obtained SEM image.

(3) Crystallite size measurement: Using an X-ray diffraction (XPD) system (X'pert PRO, manufactured by PANalytal), a powder X-ray diffraction pattern was obtained, and the crystallite size was determined by the Scherrer method. . Lanthanum hexaboride (LaB ₆ ) powder (NIST: 660a) was used as a standard for determining the breadth of the half width due to systematic errors in the apparatus.

[Example 1]
Indium metal was dissolved in 11.6N hydrochloric acid, pure water was added, and a 0.88 mol / L indium chloride aqueous solution was prepared. This indium chloride aqueous solution was heated to 40 ° C., and 1.05 equivalent of a 25 mass% ammonia aqueous solution was supplied by a pump at a rate of 4.2 L / min to synthesize indium hydroxide powder. The obtained indium hydroxide was filtered, washed with water, dispersed in a 0.1 mol / L aqueous ammonia solution to form a suspension, which was kept at 80 ° C. with stirring for 1 hour, then filtered, washed with water, dried, 0.01 mol This was washed with an aqueous / L ammonium nitrate solution, washed with water and dried. The chlorine quality of the obtained indium hydroxide was 17 ppm by mass.

The obtained indium hydroxide was heat-treated at 550 ° C. for 60 minutes in a 4% hydrogen / nitrogen mixed gas stream at 10 L / min, and then 550 ° C. in a stream (atmosphere) with an air flow rate of 10 L / min. And calcined by holding for 60 minutes. The calcined sample was hand pulverized for 5 minutes in an agate mortar to obtain indium oxide powder. It was 7.4 m < ² > / g when the BET specific surface area of the obtained indium oxide powder was measured.

About 0.5 g of this indium oxide powder was uniaxially molded in a mold having a diameter of 10 mm at 500 kgf / cm ² and fired in an air stream of 10 L / min for 3 hours at 1500 ° C. to obtain a sintered body. When the relative density of the obtained sintered body was measured, a high relative density of 96% was obtained. The relative density was calculated with the true density of indium oxide (In ₂ O ₃ ) being 7.04 g / cm ³ .

  When the primary particle diameter was measured from the SEM image, the average particle diameter (SEM diameter): 89 nm, the maximum particle diameter: 165 nm, the minimum particle diameter: 46 nm, the standard deviation σ: 24 nm, and the coefficient of variation (σ / SEM diameter): 27% Met. The crystallite diameter was 68 nm. Table 1 and FIG. 3 show the results of this example.

[Example 2]
Using indium hydroxide obtained in Example 1, indium oxide powder was obtained in the same manner as in Example 1 except that the heat treatment temperature and the calcining temperature were 600 ° C.

When evaluated in the same manner as in Example 1, the BET specific surface area was 6.2 m ² / g, but the sintered body had a high relative density of 89%. FIG. 1 shows an SEM image of the sample after calcination. The primary particle size is larger than that obtained by calcining in an air atmosphere (Comparative Example 1), but none of the primary particle size has grown extremely, and the particle size distribution is more uniform. Primary particles having a primary particle diameter exceeding 300 nm were not recognized.

  When the primary particle diameter was measured from the SEM image, the average particle diameter (SEM diameter): 109 nm, the maximum particle diameter: 235 nm, the minimum particle diameter: 55 nm, the standard deviation σ: 32 nm, and the coefficient of variation (σ / SEM diameter): 29% Met. The crystallite diameter was 85 nm. Table 1 and FIG. 3 show the results of this example.

[Example 3]
Indium metal was dissolved in 11.6N hydrochloric acid, pure water was added, and a 0.88 mol / L indium chloride aqueous solution was prepared. This indium chloride aqueous solution was heated to 40 ° C., and 1.05 equivalent of 25 mass% ammonia (NH ₄ OH) aqueous solution was supplied to this with a pump at a rate of 3.3 L / min. Was synthesized. The obtained indium hydroxide was filtered, washed with water, dispersed in a 0.1 mol / L aqueous ammonia solution to form a suspension, which was kept at 80 ° C. with stirring for 1 hour, then filtered, washed with water, dried, 0.01 mol Washing, rinsing and drying were performed with an / L ammonium nitrate (NH ₄ NO ₃ ) aqueous solution. The chlorine quality of the obtained indium hydroxide was 19 ppm. Using the obtained indium hydroxide, indium oxide powder was obtained in the same manner as in Example 2.

When evaluated in the same manner as in Example 1, the BET specific surface area was as small as 5.9 m ² / g, but the relative density was 84%. When the primary particle diameter was measured from the SEM image, the average particle diameter (SEM diameter): 114 nm, the maximum particle diameter: 248 nm, the minimum particle diameter: 64 nm, the standard deviation σ: 31 nm, and the variation coefficient (σ / SEM diameter): 30% Met. The crystallite diameter was 81 nm. Table 1 and FIG. 3 show the results of this example.

[Example 4]
Using the indium hydroxide obtained in Example 1, the hydrogen concentration in the hydrogen-nitrogen mixed gas was adjusted to 0.4% by volume, the time for the hydrogen-nitrogen heat treatment and the subsequent air calcining for 15 minutes each, An indium oxide powder was obtained in the same manner as in Example 1 except that the temperature was 700 ° C.

When evaluated in the same manner as in Example 1, the BET specific surface area was 6.6 m ² / g, and the sintered compact had a high relative density of 90%. When the particles are observed, the primary particle size is larger than that of the calcined sample in the air atmosphere (Comparative Example 1), but there is no extremely grown particle size and the particle size distribution is more uniform. Further, primary particles having a particle diameter exceeding 300 nm were not recognized.

  When the primary particle diameter was measured from the SEM image, the average particle diameter (SEM diameter): 119 nm, the maximum particle diameter: 227 nm, the minimum particle diameter: 55 nm, the standard deviation σ: 34 nm, and the coefficient of variation (σ / SEM diameter): 29% Met. The crystallite diameter was 76 nm. Table 1 shows the results of this example.

[Comparative Example 1]
The indium hydroxide obtained in Example 1 was calcined by being held for 200 minutes in an air current (atmosphere) at a temperature of 1050 ° C. and an air flow rate of 10 L / min. The calcined sample was hand pulverized for 5 minutes in an agate mortar to obtain indium oxide powder.

When the obtained indium oxide powder was evaluated in the same manner as in Example 1, the BET specific surface area was 6.4 m ² / g, and when the relative density of the sintered body was measured, the relative density was as low as 70%. Value. In FIG. 2, the SEM image of the sample after calcination is shown. Most of the primary particles are about 100 nm, but particles of 400 nm or more existed and were non-uniform.

  When the primary particle diameter was measured from the SEM image, the average particle diameter (SEM diameter): 107 nm, the maximum particle diameter: 429 nm, the minimum particle diameter: 26 nm, the standard deviation σ: 51 nm, and the coefficient of variation (σ / SEM diameter): 50% Met. The crystallite diameter was 96 nm. Table 1 and FIG. 3 show the results of this comparative example.

[Comparative Example 2]
The indium hydroxide obtained in Example 3 was calcined by being held for 200 minutes in an air current (atmosphere) at a temperature of 900 ° C. and an air flow rate of 10 L / min. The calcined sample was hand pulverized for 5 minutes in an agate mortar to obtain indium oxide powder.

  When the obtained indium oxide powder was evaluated in the same manner as in Example 1, the BET specific surface area was as large as 9.5 m 2 / g, but the relative density was 86%.

  When the particles were observed, the primary particle diameter was almost uniform, but the connection between the particles was observed.

  When the primary particle diameter was measured from the SEM image, the average particle diameter (SEM diameter): 82 nm, the maximum particle diameter: 170 nm, the minimum particle diameter: 33 nm, the standard deviation σ: 21 nm, and the coefficient of variation (σ / SEM diameter): 25% Met. The crystallite diameter was 68 nm. Table 1 and FIG. 3 show the results of this example.

[Comparative Example 3]
Using indium hydroxide obtained in Example 1, treatment was performed in the same manner as in Comparative Example 1 except that the calcining temperature was set to 850 ° C. to obtain indium oxide powder. The obtained indium oxide powder was evaluated in the same manner as in Example 1. Although the relative density of the sintered body was as high as 97%, the BET specific surface area of the indium oxide powder before sintering was further increased to 11.7 m ² / g.

  When the primary particle diameter was measured from the SEM image, the average particle diameter (SEM diameter): 68 nm, the maximum particle diameter: 190 nm, the minimum particle diameter: 25 nm, the standard deviation σ: 24 nm, and the coefficient of variation (σ / SEM diameter): 35% Met. The crystallite diameter was 62 nm. Table 1 and FIG. 3 show the results of this comparative example.

As is apparent from FIG. 3, the relative density of the indium oxide sintered body decreases as the BET specific surface area decreases. In the calcination in an air stream (atmosphere), this tendency is remarkable. As described in Comparative Example 1, the calcination at 1050 ° C. reduces the BET specific surface area to 6.4 m ² / g. The relative density after firing of the sample is only 70%, and in order to make the relative density 80% or more, it is necessary to increase the BET specific surface area as 9.5 m ² / g as described in Comparative Example 2. is there.

However, by performing heat treatment in a 4% by volume hydrogen-nitrogen mixed gas atmosphere, the BET specific surface area is 9.0 m ² / g or less by heat treatment and calcining at 550 ° C. or 600 ° C. as in Examples 1 to 3. Even so, the relative density of the sample after firing is 80% or more. For example, the indium powder of Example 2 and 3, even BET surface area 6.2m ² /g,5.9m ² / g, I coupled with a variation in the primary particle diameter is small, the relative density Compared to the calcination in the air atmosphere described in Comparative Example 1 as 89% and 84%, the relative density after firing the sample is 20% or more.

  Furthermore, as described in Example 4, after heat treatment at a temperature of 700 ° C. in a 0.4% by volume hydrogen-nitrogen mixed stream, the obtained oxidation was also performed by calcination in an air atmosphere at the same temperature. Although the indium powder has a small BET specific surface area as in Comparative Example 1, a high relative density can be obtained. It can be seen that heat treatment in a hydrogen-containing gas stream reduces the BET specific surface area even at low temperatures, maintains high sinterability even at a small BET specific surface area, and provides a high relative density.

It is a SEM image of the sample in Example 2 of this invention. 3 is a SEM image of a sample in Comparative Example 1. It is a graph which shows the relationship between the BET specific surface area of the obtained indium oxide powder, and the relative density after the baking of the molded object in the Example and comparative example of this invention.

Claims (10)

Indium oxide having a BET specific surface area of 5.0 to 9.0 m ² / g and a coefficient of variation which is a ratio of the standard deviation of the primary particle diameter and the average primary particle diameter determined by SEM observation is 35% or less powder.   2. The indium oxide powder according to claim 1, wherein the average primary particle diameter determined by SEM observation is 70 to 150 nm, and the maximum primary particle diameter is 300 nm or less.   The indium oxide powder according to claim 1 or 2, wherein the crystallite diameter determined by the Scherrer method is less than 90 nm.   4. The indium oxide powder according to claim 1, wherein a relative density when the molded body is sintered under normal pressure at 1500 ° C. is 80% or more. 5.   Indium oxide powder obtained by calcination in a hydrogen-containing gas atmosphere after washing indium hydroxide powder synthesized by neutralizing an indium salt aqueous solution with a basic aqueous solution.   An indium oxide powder obtained by washing an indium hydroxide powder synthesized by neutralizing an indium salt aqueous solution with a basic aqueous solution, heat treating it in a hydrogen-containing gas atmosphere, and calcining in an air atmosphere.   A method for producing indium oxide powder, characterized in that indium hydroxide powder synthesized by neutralizing an indium salt aqueous solution with a basic aqueous solution is calcined in a hydrogen-containing gas atmosphere after washing.   The method for producing indium oxide powder according to claim 7, wherein the calcination is performed at a temperature of 800 ° C. or less.   Production of indium oxide powder characterized in that indium hydroxide powder synthesized by neutralizing indium salt aqueous solution with basic aqueous solution is washed, heat-treated in a hydrogen-containing gas atmosphere, and calcined in air atmosphere Method.   The method for producing indium oxide powder according to claim 9, wherein the heat treatment and calcination are performed at a temperature of 800 ° C. or less.