JPH04325415A - Indium hydroxide and oxide - Google Patents

Abstract

PURPOSE:To obtain a high density ITO sintered body by using acicular indium hydroxide of a specified particle length as a starting material. CONSTITUTION:An aq. indium nitrate soln. is heated to 70-95 deg.C, an aq. alkali soln. is added to the heated soln. to form an indium hydroxide slurry and this slurry is filtered and dried to obtain acicular indium hydroxide of 0.03-0.3mum average length. Indium oxide powder of 200-500Angstrom crystallite diameter and <=0.5mum average particle diameter calculated from the particle size distribution is obtd. by calcining the acicular indium hydroxide powder. An ITO sintered body having >=5.3g/cm<3> density can be obtd. by mixing the indium oxide powder with tin oxide, molding and sintering the mixture.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to indium hydroxide, indium oxide powder, and a method for producing the same.

[0002] In recent years, ITO has been used as a transparent conductive film for use in solar cells, liquid crystal displays, transparent electrodes, touch panels, etc.
Demand for thin films is rapidly increasing. Methods for forming such an ITO thin film include a method of applying ITO fine particles to a base material;
Ion is applied to the substrate surface by sputtering an IT alloy target or ITO sintered target, or by vacuum evaporation.
Although methods for forming TO films are known, sputtering of an ITO sintered body is currently particularly popular because it yields a high-performance film.

The indium oxide powder according to the present invention has extremely excellent performance as a raw material powder for producing an ITO sintered sputtering target used in producing a transparent conductive film by such a sputtering method. be.

0004

[Prior Art] Conventionally, indium oxide, tin oxide powder, or ITO powder has been produced by heat dehydration or Precipitation can be produced by thermal decomposition or by adding a precipitant to a mixed solution of indium and tin salts (
JP-A-62-7627, JP-A-60-186416),
Or produced by hydrolysis (Japanese Patent Application Laid-open No. 58-36925)
A method of thermally decomposing the resulting product is known.

[0005] Normally, ITO sintered bodies are manufactured by press-molding a mixed powder of indium oxide and tin oxide (ITO powder) and then sintering it.
It sinters from around 0°C and is relatively easy to sinter, but ITO
In the powder, tin oxide, which is difficult to sinter, acts as a sintering alienating agent, making it difficult to sinter, and it has been extremely difficult to obtain a high-density sintered body using conventional methods.

When conventional powder is used, most of the ITO sintered bodies have a sintered density of about 65% of the theoretical density (~4.6 g/
cm3), it is a sintered body with a low density, and also has high electrical resistance. The sintered density of the ITO sintered body is 100
% is 7.1 g/cm3.

[0007] Such a low-density ITO target has low electrical conductivity, low thermal conductivity, and low transverse rupture strength, and during sputtering,
The film formation rate was slow, the target surface was easily reduced, and furthermore, the discharge was unstable.

[0008] In order to solve these problems, several methods have been proposed for producing raw material powders that make it possible to produce high-density ITO sintered bodies. For example, there is a method in which indium oxide powder is calcined to produce indium oxide or tin oxide having an average particle size of 3 to 6 μm (Japanese Unexamined Patent Publication No. 62-21751).

[0009] However, the ITO sintered body obtained from such a raw material powder with a relatively large particle size is at most 5 g/c.
m3, which cannot be said to be sufficiently high density. Furthermore, a method has been proposed in which coprecipitated ITO powder using a precipitant is used as a raw material for a sintered body. (Japanese Patent Application Laid-Open No. 62-12009). However, the sintered density of the sintered body obtained by this method is about 70% (5 g/cm3) of the theoretical density, which cannot be said to be a sufficiently high density.

0010

SUMMARY OF THE INVENTION An object of the present invention is to provide an indium oxide powder and its precursor, an indium hydroxide powder, which can produce a high-density sintered body with a theoretical density of 5.3 g/cm3 or more. Furthermore, the present invention provides a method for producing the indium oxide powder and indium hydroxide powder, and uses thereof.

[0011]

[Means for Solving the Problems] The present inventors have developed a high-density I
As a result of intensive studies regarding the raw material powder for manufacturing TO sintered bodies, it was discovered that the powder physical properties of indium oxide powder are affected by its precursor, indium hydroxide, and the present invention was completed.

That is, the present invention suppresses agglomeration in the indium hydroxide state by forming indium hydroxide into needle-like crystals, and furthermore, by controlling the particle size of the needle-like crystals, calcining is performed. The basic idea is to control the agglomeration and particle size of the indium oxide powder obtained.

[0013] The indium hydroxide of the present invention must be in the form of needle-like crystals. The needle-like crystals make it possible to suppress aggregation compared to spherical particles. The average length of the acicular shape is 0.03 to 0.3 μm, and if the length is longer than this, the crystallite diameter of the indium oxide powder obtained by calcination becomes large and the sinterability deteriorates. If it is smaller than this,
The agglomeration of the powder becomes intense, the dispersibility of the powder decreases, and the sinterability decreases.

The size of the acicular crystals can be determined using a transmission electron microscope (
This can be confirmed by TEM) observation.

The diameter of the acicular crystal is not particularly limited, but since it is acicular, it is preferably smaller than the length direction and the diameter to length ratio is in the range of 0.4 to 0.05.

In addition, the indium hydroxide of the present invention is a crystal oriented in the (200) plane according to the Miller index of X-ray diffraction, and the peak intensity of the (220) plane is higher than that of the (200) plane. It is preferable that the peak intensity is 20% or less. Crystal orientation can be determined by X-ray diffraction patterns and Hanawalt in
dex (ASTM), (20
The diffraction peak of 0) appears around 2θ=22.28 degrees, and the (220) diffraction peak appears around 31.71 degrees. Depending on the hydroxide, in addition to the (200) diffraction peak, 2θ=
5 for the diffraction peak intensity of (200) at 23-26 degrees.
% or more may appear, but such indium hydroxide powder becomes a cohesive powder, probably due to disordered crystals, and is not suitable for high-density IT.
This is not preferable because it does not give an O sintered body.

Indium hydroxide, in which an X-ray diffraction peak of the (222) plane of indium oxide appears at 2θ=30.99 degrees, is also not preferred. The dehydration reaction of hydroxide to oxide occurs at around 270°C, but the fact that indium oxide is contained in indium hydroxide at a drying temperature below this temperature means that reactive fine particles are contained in the hydroxide. Indium oxide obtained by calcining such indium hydroxide tends to become a cohesive powder,
It is difficult to use as a powder for high-density ITO sintered bodies.

Next, a method for producing such indium hydroxide will be explained.

Such indium hydroxide is synthesized by adding an alkaline aqueous solution to an indium nitric acid aqueous solution. When an indium nitric acid aqueous solution is added to an alkaline aqueous solution, the resulting indium hydroxide becomes a fine powder, with severe agglomeration, and the indium oxide powder obtained by calcination also has poor dispersibility, making it a raw material powder for high-density ITO sintered bodies. It is not.

As the alkaline aqueous solution to be added, aqueous solutions of sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonia, etc. can be used, but an ammonia aqueous solution in which no metal ions remain in indium hydroxide is particularly preferred.

The temperature of the indium nitric acid aqueous solution is 70
It is necessary to add the alkaline aqueous solution while maintaining the temperature at ~95°C. When the reaction temperature is lower than 70° C., needle-like crystals are difficult to grow, resulting in agglomerated powder. On the other hand, at temperatures higher than 95° C., a pressurizing device is required, making production equipment expensive and impractical.

When adding the alkaline aqueous solution to the indium nitric acid aqueous solution, the addition time is preferably 30 minutes to 3 hours. If the addition time is too short, needle-shaped crystals will not grow, and furthermore, the amount of fine powder will increase, resulting in agglomerated powder. On the other hand, if the addition time is significantly long, grain growth will occur;
Since the average length of the needle crystals is longer than 0.3 μm,
The crystallite size of the indium oxide powder obtained by calcining becomes large, resulting in a powder with poor sinterability.

It is preferable to add the alkaline aqueous solution until the final pH of the indium nitric acid aqueous solution reaches 7-9. If the addition of the alkaline aqueous solution is terminated outside this range, the resulting indium hydroxide slurry will have poor filterability.

[0024] Furthermore, the neutralization reaction by addition of an aqueous alkali solution is preferably carried out while stirring. If stirring is not performed, the added alkaline aqueous solution will be non-uniform within the reaction tank. The stirring speed is preferably from several revolutions/minute to several hundred revolutions/minute, particularly preferably from 30 to 150 revolutions/minute.

The obtained slurry is left to stand until it reaches room temperature, separated into solid and liquid, and then dried.

[0026] The drying temperature is preferably 90 to 260°C. If the drying temperature is too high, some oxides will be produced and the powder will be non-uniform; if the drying temperature is too low, the drying efficiency will be poor.

[0027] The dry cake is preferably slightly crushed before calcining. Crushing before calcination improves the dispersibility of the resulting indium oxide powder, making it possible to produce a higher density ITO sintered body.

The crushing method is not particularly limited, but for example, an automatic mortar, hammer mill, etc. are sufficient.

The crushed indium hydroxide is calcined to produce indium oxide. The calcination temperature is 500-900℃,
Particularly preferred is 600 to 800°C. If the calcination temperature is too low, the density of the molded body will not increase and a high-density sintered body will not be obtained. On the other hand, if it is too high, the crystallite diameter of the indium oxide powder is too large, resulting in poor sinterability.

The indium oxide powder thus obtained has a crystallite diameter of 200 to 500 angstroms, and the difference between the crystallite diameter and the BET diameter is 100 angstroms.
and the average particle diameter determined from the particle size distribution is within 0.5mm.
It is 5 μm or less.

If the crystallite size is smaller than 200 angstroms, the particle size is too small and becomes agglomerated particles, and a high-density ITO sintered body cannot be obtained. On the other hand, if the particle size is larger than 500 angstroms, the particle size is too large, resulting in poor sinterability and failure to produce a high-density ITO sintered body.

[0032] Also, the difference between the crystallite diameter and the BET diameter is 200
If larger than angstroms, the primary particle size of the powder is
Since the powder is polycrystalline and highly agglomerated, the ITO sintered body does not have high density in this case as well.

The crystallite diameter is (222) of indium oxide.
It can be determined from the half width of the X-ray diffraction peak. Further, the BET diameter is a value obtained by measuring the BET value of the powder and approximating the particles to a sphere.

[0034] The average particle diameter determined from the particle size distribution is 0.5μ.
m or less. If the average particle size is larger than this, the indium oxide powder is tightly agglomerated;
Does not give a high density ITO sintered body. Particle size distribution is generally measured using a centrifugal sedimentation type particle size distribution measuring device.

By using the indium oxide powder according to the present invention, a high-density, low-resistance ITO sintered body having a sintered density of 5.3 g/cm 3 or more can be produced by the following method.

ITO powder for producing an ITO sintered body is made by adding 5 to 15 wt of tin oxide powder to the indium oxide powder of the present invention.
% by mixing. For this mixing, equipment such as a ball mill or a vibration mill is used.

The obtained ITO powder is molded into a desired shape.

[0038] Molding is carried out using a mold press or cold isostatic press (
CIP) may be used, and slip cast molding or the like is used for complex shapes.

Finally, the obtained molded body is heated to 1350°C
Sinter at a temperature of 1600°C.

[0040]

[Examples] The present invention will be explained below based on Examples, but the present invention is not limited thereto.

Example 1 2.2 liters of an aqueous indium nitrate solution containing 0.5 mol/liter of indium ions and 1.53 mol/liter of nitrate ions was placed in a 3-liter separable flask equipped with a stirrer, and heated to 85° C. while refluxing. 14% ammonia aqueous solution at 8.62/min. It was added to the indium nitrate aqueous solution at a rate of 1 hour. pH at the end of addition
was 8.1. Produced indium hydroxide slurry
was filtered, washed with 6 liters of pure water, dried at 110°C, and ground in a mortar. The obtained acicular indium hydroxide had an average length of 0.09 μm. A transmission electron micrograph showing the particle structure of the acicular indium hydroxide is shown in FIG.

[0042] The indium oxide obtained by calcining this indium hydroxide at 700°C for 4 hours has a crystallite diameter of 380°C.
angstrom, the BET diameter is 410 angstroms, and the average particle diameter determined from the particle size distribution is 0.32 angstroms.
It was μm.

135 g of this indium oxide powder was mixed with 15 g of tin oxide in a mortar, molded under pressure in a mold, and then sintered at 1400° C. in atmospheric pressure. Temperature increase rate during sintering is 100°C/hour, held at 1400°C for 10 hours,
The temperature decreasing rate was 100°C/hour. Under these sintering conditions, the sintered density was 5.8 g/cm3, and the specific resistance was 3 x 10-
A sintered body of 4 Ω·cm was obtained.

Comparative Example 1 Indium hydroxide was obtained in the same manner as in Example 1, except that the temperature of the indium aqueous solution was set at 50°C. The obtained acicular indium hydroxide was very fine with an average length of 0.02 μm. A transmission electron micrograph showing the fine acicular indium hydroxide particle structure is shown in FIG.

[0045] The crystallite size of indium oxide obtained by calcining this indium hydroxide at 700°C for 4 hours was 190 angstroms, the BET diameter was 230 angstroms, and the average particle size determined from the particle size distribution. was 0.8 μm.

[0046] This indium oxide powder was sintered in the same manner as in Example 1, but the sintered density was 5.0 g/cm3.

Comparative Example 2 The rate of addition of ammonia aqueous solution was 34.48 ml/min. Example 1 except that the addition was completed in 15 minutes at
Indium hydroxide was obtained in the same manner as above. The obtained acicular indium hydroxide had an average length of 0.06 μm, but the results of X-ray diffraction showed that it contained indium oxide. The crystallite diameter of indium oxide obtained by calcining this powder at 700°C for 4 hours was 360 angstroms.
The BET diameter was 580 angstroms, and the average particle diameter determined from the particle size distribution was 0.8 μm.

[0048] This indium oxide powder was sintered in the same manner as in Example 1, but the sintered density was 5.1 g/cm3.

Comparative Example 3 The addition rate of ammonia aqueous solution was 2.16 ml/
min. Example 1 except that the addition was completed after 4 hours.
Indium hydroxide was obtained in the same manner as above. The obtained acicular indium hydroxide had an average length of 0.4 μm. A transmission electron micrograph showing the particle structure of the acicular indium hydroxide is shown in FIG. The crystallite diameter of the indium oxide obtained by calcining this indium hydroxide at 700°C for 4 hours was 480 angstroms, and the BET diameter was 700 angstroms.
angstrom, and the average particle diameter determined from the particle size distribution was 0.8 μm.

[0050] This indium oxide powder was sintered in the same manner as in Example 1, but the sintered density was 5.1 g/cm3.

Comparative Example 4 Indium hydroxide obtained in the same manner as in Example 1 was
The crystallite diameter of indium oxide obtained by calcination at 0° C. for 4 hours was 180 angstroms, and was sintered in the same manner as in Example 1, but the sintered density was 4.7 g/cm 3 .

Comparative Example 5 Indium hydroxide obtained in the same manner as in Example 1 was
The crystallite diameter of the indium oxide obtained by calcination at 00°C for 4 hours was 810 angstroms, and the indium oxide was sintered in the same manner as in Example 1, but the sintered density was 4.8 g/cm3. Ta.

[0053]

Effects of the Invention: By calcining the indium hydroxide of the present invention, a fine and highly dispersed indium oxide powder can be obtained, and if the indium oxide powder is used as a raw material powder for an ITO sintered body, Moreover, it is possible to produce an ITO sintered body with low resistance.

[Brief explanation of drawings]

FIG. 1 is a transmission electron micrograph showing the particle structure of indium hydroxide obtained in Example 1.

FIG. 2 is a transmission electron micrograph showing the particle structure of indium hydroxide obtained in Comparative Example 1.

FIG. 3 is a transmission electron micrograph showing the particle structure of indium hydroxide obtained in Comparative Example 3.

Claims (5)

[Claims] 1. Acicular indium hydroxide having an average length of 0.03 to 0.3 μm. 2. An average length characterized in that an indium nitrate aqueous solution is heated to 70 to 95°C, an alkali aqueous solution is added to the aqueous solution, an indium hydroxide slurry is produced, and then filtered and dried. A method for producing acicular indium hydroxide having a diameter of 0.03 to 0.3 μm. Claim 3: Crystallite diameter is 200 to 500 angstroms.
and the average particle diameter determined from the particle size distribution is 0.5μ.
Indium oxide powder having a particle size of less than m. 4. Acicular indium hydroxide obtained by heating an aqueous indium nitrate solution to 70 to 95°C, adding an alkali aqueous solution to the aqueous solution to produce an indium hydroxide slurry, and then filtering and drying the slurry. A method for producing indium oxide powder having a crystallite diameter of 200 to 500 angstroms and an average particle diameter of 0.5 μm or less as determined from particle size distribution, the method comprising calcining the powder. 5. A method for producing an ITO sintered body having a sintered density of 5.3 g/cm 3 or more, which comprises mixing tin oxide with the indium oxide powder according to claim 4, molding the powder, and sintering the mixture.