JP3878867B2 - Indium hydroxide and oxide - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to indium hydroxide and indium oxide powder and a method for producing the same.
[0002]
In recent years, the demand for an ITO thin film as a transparent conductive film used for a solar cell, a liquid crystal display transparent electrode, a touch panel or the like has increased rapidly. Methods for forming such an ITO thin film include a method of applying ITO fine particles to a substrate, a method of forming an ITO film on the surface of a substrate by sputtering of an IT alloy target or an ITO sintered body target, or a vacuum deposition method, etc. However, at present, the sputtering method of the ITO sintered body is generally used because a high-performance film can be obtained.
[0003]
The indium oxide powder according to the present invention has extremely excellent performance as a raw material powder for producing an ITO sintered body sputtering target used when producing a transparent conductive film by such a sputtering method.
[0004]
[Prior art]
Conventionally, indium oxide, tin oxide powder, or ITO powder is a method of dehydrating or thermally decomposing metal hydroxide, oxide hydrate, organic metal salt or inorganic metal salt powder, or each sol or gel, respectively. Precipitation agent added to a mixed solution of indium salt and tin salt to form a precipitate (JP-A-62-2627, JP-A-60-186416), or a product produced by hydrolysis (JP-A 58-36925) There is known a method of thermally decomposing the above.
[0005]
Usually, ITO sintered body is manufactured by pressing and sintering a mixed powder of indium oxide and tin oxide (ITO powder), but indium oxide alone sinters from around 1000 ° C, Although it is easy to sinter, ITO powder is difficult to sinter due to the sintering sinter of tin oxide as a sintering alienating agent, and it was very difficult to obtain a high-density sintered body by the conventional method. .
[0006]
When conventional powders are used, most of the ITO sintered bodies are low-density sintered bodies whose sintered density is about 65% of theoretical density (˜4.6 g / cm ³ ), and also have high electric resistance. . The sintered density of the ITO sintered body is 7.1 g / cm ³ at 100%.
[0007]
Such a low-density ITO target has low conductivity, thermal conductivity, and bending strength, the film formation rate is low during sputtering, the target surface is easily reduced, and discharge is unstable.
[0008]
Thus, in order to solve such problems, several methods for producing raw material powders that enable the production of a high-density ITO sintered body have been proposed. For example, there is a method in which indium oxide powder is calcined to form indium oxide or tin oxide having an average particle size of 3 to 6 μm (Japanese Patent Laid-Open No. 62-21751).
[0009]
However, the ITO sintered body obtained from such a relatively large particle size raw material powder is at most 5 g / cm ³ and cannot be said to have a sufficiently high density. In addition, a method has been proposed in which coprecipitated ITO powder using a precipitant is used as a raw material for the sintered body. (JP-A-62-12009). However, the sintered density of the sintered body obtained by this method is about 70% (5 g / cm ³ ) of the theoretical density, and cannot be said to be sufficiently high.
[0010]
[Problems to be solved by the invention]
An object of the present invention is to provide 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 hydroxide powder as a precursor thereof, and the indium oxide powder and indium hydroxide powder. The manufacturing method and its use are provided.
[0011]
[Means for Solving the Problems]
As a result of intensive studies on the raw material powder for producing a high-density ITO sintered body, the present inventors have found that the powder physical properties of the indium oxide powder are influenced by its precursor, indium hydroxide. The invention has been completed.
[0012]
That is, the present invention provides indium hydroxide as needle-like crystals to suppress aggregation in the state of indium hydroxide, and further, calcined by controlling the particle diameter of the needle-like crystals. It is based on controlling the agglomeration and particle size of the resulting indium oxide powder.
[0013]
The indium hydroxide of the present invention must be a needle crystal. By being acicular crystals, aggregation can be suppressed compared to spherical particles. The average length of the needle shape is 0.03 to 0.3 μm, and if it is longer than this, the crystallite diameter of the indium oxide powder obtained by calcination becomes large, and the sinterability decreases. When it is smaller than this, the agglomeration of the powder becomes intense, the dispersibility of the powder is lowered, and the sinterability is lowered.
[0014]
The size of the needle crystal can be confirmed by observation with a transmission electron microscope (TEM).
[0015]
The diameter of the acicular crystal is not particularly limited, but since it is acicular, it is smaller than the length direction and the ratio of the diameter to the length is preferably in the range of 0.4 to 0.05.
[0016]
The indium hydroxide of the present invention is a crystal oriented in the (200) plane, which is a mirror index of X-ray diffraction, and the (220) plane peak intensity is 20% or less with respect to the (200) plane peak intensity. It is preferable that The crystal orientation can be confirmed by an X-ray diffraction pattern and Hanawat index (ASTM). The diffraction peak of (200) is around 2θ = 2.28 degrees, and the (220) plane is 31.71 degrees. Appears nearby. Depending on the hydroxide, in addition to the diffraction peak of (200), a crystalline peak having an intensity of 5% or more with respect to the diffraction peak intensity of (200) may appear at 2θ = 23 to 26 degrees. Such indium hydroxide powder is not preferable because the crystal is disordered or becomes a coherent powder and does not give a high-density ITO sintered body.
[0017]
Further, indium hydroxide in which an X-ray diffraction peak of the (222) plane of indium oxide appears at 2θ = 30.99 degrees is not preferable. 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 the reactive fine particles are contained in the hydroxide. Indium oxide obtained by calcining such indium hydroxide is likely to be an agglomerated powder and is not likely to be a powder for a high-density ITO sintered body.
[0018]
Next, a method for producing such indium hydroxide will be described.
[0019]
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 water-soluble wave, the resulting indium hydroxide becomes a fine powder, agglomeration is intense, and the indium oxide powder obtained by calcining is also poorly dispersible, which is a raw material for high-density ITO sintered bodies It will not be a powder.
[0020]
An aqueous solution of sodium hydroxide, potassium hydroxide, calcium hydroxide, ammonia or the like can be used as the alkaline aqueous solution to be added, but an aqueous ammonia solution in which metal ions do not remain in indium hydroxide is particularly preferable.
[0021]
It is necessary to add an alkaline aqueous solution while maintaining the temperature of the indium nitric acid aqueous solution at 70 to 95 ° C. When the reaction temperature is lower than 70 ° C., acicular crystals are difficult to grow and become agglomerated powder. On the other hand, at a temperature higher than 95 ° C., a pressurizing device is required, and the production equipment becomes expensive, which is not realistic.
[0022]
When adding alkaline aqueous solution to indium nitric acid aqueous solution, as the addition time, 30 minutes-3 hours are preferable. When the addition time is short, needle-like crystals do not grow, and more fine powders increase, resulting in an agglomerated powder. On the other hand, when the addition time is remarkably long, grain growth occurs, and the average length of the acicular crystals becomes longer than 0.3 μm, so that the crystallite diameter of the indium oxide powder obtained by calcination becomes large, and sintering The powder becomes inferior.
[0023]
The addition of the alkaline aqueous solution is preferably performed until the final pH of the indium nitric acid aqueous solution becomes 7-9. Outside this range, when the addition of the alkaline aqueous solution is terminated, the resulting indium hydroxide slurry has poor filterability.
[0024]
Moreover, it is preferable to perform the neutralization reaction by addition of aqueous alkali solution, stirring. When stirring is not performed, the added aqueous alkali solution becomes uneven in the reaction vessel. The stirring speed is preferably from several revolutions / minute to several hundred revolutions / minute, and particularly preferably from 30 to 150 revolutions / minute.
[0025]
The obtained slurry is allowed to stand until it reaches room temperature, and after solid-liquid separation, it is dried.
[0026]
The drying temperature is preferably 90 to 260 ° C. If the drying temperature is too high, some oxides are generated and the powder becomes non-uniform, and if it is too low, the drying efficiency is poor.
[0027]
The dried cake is preferably lightly crushed before calcining. The dispersibility of the indium oxide powder obtained by pulverizing before calcination is improved, and a higher density ITO sintered body can be produced.
[0028]
Although the crushing method is not particularly limited, for example, an automatic mortar or a hammer mill is sufficient.
[0029]
The crushed indium hydroxide is calcined to form indium oxide. The calcination temperature is preferably 500 to 900 ° C, particularly preferably 600 to 800 ° C. If the calcining 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, so that the sinterability decreases.
[0030]
The indium oxide powder thus obtained has a crystallite diameter of 200 to 500 angstroms, the difference between the crystallite diameter and the BET diameter is within 100 angstroms, and the average particle diameter determined from the particle size distribution is 0.00. 5 μm or less.
[0031]
When the crystallite size is smaller than 200 angstroms, the particle size is too small to be agglomerated particles and do not give a high-density ITO sintered body. On the other hand, those larger than 500 angstroms are too large in particle size, so that the sinterability is lowered and a high-density ITO sintered body is not provided.
[0032]
In addition, when the difference between the crystallite diameter and the BET diameter is larger than 200 angstroms, the primary particle diameter of the powder is polycrystalline and is a highly agglomerated powder. Not.
[0033]
The crystallite diameter can be determined from the half width of the (222) X-ray diffraction peak of indium oxide. The BET diameter is a value obtained by measuring the BET value of the powder and approximating the particle to a sphere.
[0034]
The average particle size obtained from the particle size distribution is 0.5 μm or less. When the average particle size is larger than this, the indium oxide powder is tightly agglomerated and such powder does not give a high density ITO sintered body. The particle size distribution is generally measured by a centrifugal sedimentation type particle size distribution measuring device.
[0035]
If the indium oxide powder according to the present invention is used, a high-density and low-resistance ITO sintered body having a sintered density of 5.3 g / cm ³ or more can be produced by the following method.
[0036]
An ITO powder for producing an ITO sintered body can be obtained by mixing 5 to 15 wt% of tin oxide powder with the indium oxide powder of the present invention. For this mixing, a device such as a ball mill or a vibration mill is used.
[0037]
The obtained ITO powder is molded into a desired shape.
[0038]
Molding may be performed by a die press or a cold isostatic press (CIP), and slip casting or the like is used for complex shapes.
[0039]
Finally, the obtained molded body is sintered at a temperature of 1350 ° C to 1600 ° C.
[0040]
【Example】
Hereinafter, the present invention will be described based on examples, but the present invention is not limited thereto.
[0041]
Example 1
A 2.2 liter aqueous solution of indium nitrate containing indium ions: 0.5 mol / liter and nitrate ions: 1.53 mol / liter was placed in a 3 liter separable flask equipped with a stirrer and heated to 85 ° C. while refluxing, 14% Aqueous ammonia solution of 8.62 / min. Was added in an indium nitrate aqueous solution at a rate of 1 hour. The pH at the end of the addition was 8.1. The produced indium hydroxide slurry was filtered, washed with 6 liters of pure water, dried at 110 ° C., and then 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]
Indium oxide obtained by calcining this indium hydroxide at 700 ° C. for 4 hours has a crystallite diameter of 380 angstroms, a BET diameter of 410 angstroms, and an average particle diameter determined from the particle size distribution of 0.32 μm. Met.
[0043]
15 g of tin oxide was mixed with 135 g of this indium oxide powder in a mortar, pressed with a mold, and then sintered at 1400 ° C. in atmospheric pressure. The temperature increase rate in sintering was 100 ° C./hour, 10 hours at 1400 ° C., and the temperature decrease rate was 100 ° C./hour. Under such sintering conditions, a sintered body having a sintered density of 5.8 g / cm ³ and a specific resistance of 3 × 10 ⁻⁴ Ω · cm was obtained.
[0044]
Comparative Example 1
The temperature of the indium aqueous solution was set to 50 ° C., and indium hydroxide was obtained in the same manner as in Example 1. The obtained acicular indium hydroxide had an average length of 0.02 μm and was very fine. A transmission electron micrograph showing the particle structure of the fine acicular indium hydroxide is shown in FIG.
[0045]
The crystallite diameter 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 diameter 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 / cm ³ .
[0047]
Comparative Example 2
The addition rate of the aqueous ammonia solution was 34.48 ml / min. Indium hydroxide was obtained in the same manner as in Example 1 except that the addition was completed in 15 minutes. The obtained acicular indium hydroxide had an average length of 0.06 μm, but from the results of X-ray diffraction, 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 / cm ³ .
[0049]
Comparative Example 3
The addition rate of the aqueous ammonia solution was 2.16 ml / min. Indium hydroxide was obtained in the same manner as in Example 1 except that the addition was completed in 4 hours. 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 indium oxide obtained by calcining this indium hydroxide at 700 ° C. for 4 hours was 480 Å, the BET diameter was 700 Å, and the average particle size 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 / cm ³ .
[0051]
Comparative Example 4
The crystallite diameter of indium oxide obtained by calcining indium hydroxide obtained in the same manner as in Example 1 for 4 hours at 450 ° C. is 180 Å, and sintered in the same manner as in Example 13. The consolidation density was 4.7 g / cm ³ .
[0052]
Comparative Example 5
Indium oxide obtained by calcining indium hydroxide obtained in the same manner as in Example 1 at 1000 ° C. for 4 hours has a crystallite diameter of 810 Å, and was sintered in the same manner as in Example 1. The consolidation density was 4.8 g / cm ³ .
[0053]
【The invention's effect】
The indium hydroxide of the present invention gives a fine and highly dispersed indium oxide powder by calcination, and if the indium oxide powder is used as a raw material powder for an ITO sintered body, it has high density and low resistance. It is possible to produce an ITO sintered body.
[Brief description of the drawings]
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. FIG.

Claims (1)

The crystallite diameter determined from the half-value width of the (222) X-ray diffraction peak of indium oxide is 200 to 500 angstroms. An indium oxide powder having a difference within 100 angstroms and having an average particle size of 0.5 μm or less determined from a particle size distribution measured by a centrifugal sedimentation type particle size distribution analyzer .

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