JPH0632615A - Production of hydrated zirconia gel and zirconia powder - Google Patents

Abstract

(57) [Abstract] [Purpose] Hydrated zirconia gel that can form zirconia powder with fast grain growth during calcination and good formability at a relatively low calcination temperature, and formability and sinterability. Provided is a method capable of producing excellent zirconia powder by a simple process. [Structure] 50 to 100 alkali metal to ZrO ₂
Hydrated zirconia gel containing 0 ppm by weight. A method for producing zirconia powder by drying this hydrated zirconia gel and then calcining it at 500 to 1200 ° C.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a zirconia thin film material,
The present invention relates to a hydrated zirconia gel used for producing zirconia-based ceramic raw material powder and the like, and a method for producing zirconia powder that can be used as a raw material powder having good moldability.

[0002]

2. Description of the Related Art Conventionally, as a method for producing hydrated zirconia gel and zirconia powder, ammonia water is added to a suspension of hydrated zirconia fine particles in which a stabilizer is dissolved, followed by filtration, washing with water, and calcination. (JP-A-63-129017) A method for obtaining a zirconia-based raw material powder by neutralizing a hydrated zirconia sol obtained by hydrolyzing an aqueous zirconium salt solution with urea or an ammonia-based compound (special Kaihei 4-3
1359) and the like are known.

[0003]

By the way, the zirconia powder obtained by any of the above methods and
It is a fine powder having a very large ET specific surface area, that is, a small particle size. When the particle size is extremely small, the adhesive force between particles remarkably increases, so that the zirconia powder becomes a strong agglomerated powder. Resulting in poor dispersibility. Further, in these methods, since the hydrated zirconia gel is obtained by neutralizing with ammonia or urea, only those with a slow grain growth rate during calcination can be obtained. It has been difficult to obtain a zirconia powder having good formability at a relatively low calcination temperature.

The present invention solves the above-mentioned drawbacks of the conventional method, that is, water capable of forming a zirconia powder having fast grain growth during calcination and good moldability at a relatively low calcination temperature. It is an object of the present invention to provide a method capable of producing a Japanese zirconia gel and a zirconia powder having excellent moldability and sinterability by a simple process.

[0005]

The present inventors have SUMMARY OF THE INVENTION may, according to was examined in detail by focusing on the microstructure of the hydrated zirconia gel and the calcination behavior, 50 the alkali metal relative to ZrO ₂ When hydrated zirconia gel containing 1000 ppm by weight or a mixture of the gel and a stabilizer such as yttria, calcia, magnesia, and ceria which is commonly used for producing zirconia-based ceramics is calcined, zirconia powder is obtained at a relatively low temperature. The powder has good moldability, and
They have found that they have excellent sinterability, and have reached the present invention.

That is, according to the present invention, a hydrated zirconia gel containing an alkali metal in an amount of 50 to 1000 ppm by weight with respect to ZrO ₂ b dried zirconia gel, and then 500 to 1
The gist is a method for producing a zirconia powder, which comprises calcining at 200 ° C. Hereinafter, the present invention will be described in more detail.

In the present specification, the "average particle size" relating to the hydrated zirconia gel shows a value substantially the same as that measured by an electron microscope, although it depends on the photon correlation method. Also,
The "BET specific surface area" of the zirconia powder is measured using nitrogen as an adsorbed molecule.

The zirconia powder has a BET specific surface area of 3.5.
If it is smaller than m ² / g, strong agglomeration due to sintering between particles occurs, resulting in poor dispersibility, resulting in a powder that is difficult to sinter on the low temperature side, and if it is larger than 25 m ² / g, particles Since the adhesive force between them becomes remarkably increased, it becomes a strong agglomerated powder, which makes it difficult to mold and becomes unsuitable as a ceramic raw material powder. According to the above method b, the BET specific surface area is 3.5 to 25 m ² / g, the cohesiveness is poor, the dispersibility is good, and the moldability is excellent.
In addition, a zirconia powder that can be sintered at a relatively low temperature is obtained. A more preferable range of the BET specific surface area is 5 to ²⁰ m ² / g.

The content of alkali metal in the hydrated zirconia gel of the present invention must be 50 to 1000 ppm by weight based on ZrO ₂ . If it is less than 50 ppm by weight, the grain growth rate during calcination becomes slow and BET
A zirconia powder having a large specific surface area can be obtained, and
When it is more than 00 ppm by weight, the content of alkali metal in the obtained zirconia powder is naturally high, and abnormal grain growth and segregation due to the alkali metal occur during molding and sintering, thus causing uneven shrinkage. To do. A more preferable alkali metal content is 80 to 500 ppm by weight, preferably 50 to 400 ppm by weight. There is no limitation on the kind of the alkali metal, and sodium and potassium which are easily available may be used, and two or more kinds may be contained. Anions such as chlorine ion, sulfate ion, and nitrate ion derived from the raw material are 200 wtpp with respect to ZrO ₂ .
If it is m or less and the molar ratio to the alkali metal is 2.6 or less, its presence is allowed. These anions inhibit the sinterability of zirconia, and reduce the action of the alkali metal by making alkali metal present as a counter ion and making its distribution non-uniform, but if the amount in the above range, This is because the undesired effects of these anions can be ignored. The hydrated zirconia gel is preferably crystalline and its crystallite size is preferably 4 nm or less. When the crystallite size becomes larger than 4 nm, yttria, calcia,
This is because when a zirconia powder stabilized with magnesia, ceria, etc. is obtained, the solid solubility with these stabilizers becomes poor and it becomes difficult to obtain a powder having a uniform composition. The average particle size measured with hydrated zirconia gel as a sol is 0.
The range of 05 to 0.3 μm is preferable. This average particle size 0.05
When a gel smaller than μm is calcined, strong agglomeration is likely to occur due to sintering between particles because the particle size is extremely small. On the other hand, when a gel larger than 0.3 μm is calcined, the particles of the zirconia powder obtained are calcined. This is because the diameter becomes large and the sinterability tends to be poor.

The hydrated zirconia gel of the present invention hydrolyzes an aqueous zirconium salt solution to obtain a hydrated zirconia sol,
It can be manufactured by adding an alkali metal compound to this and dissolving it, or mixing an aqueous solution of the compound to form a suspension, filtering and washing with water. The pH of the mixed suspension of the hydrated zirconia sol and the alkali metal compound must be 8 or higher. When the pH is lower than 8, the binding amount of Zr-O ^- M ⁺ formed by the hydroxyl group (Zr-OH) and the alkali metal ion (M ⁺ ) on the surface of the hydrated zirconia particles is decreased, and the anion is negative. Because the amount of Zr—OH ₂ ⁺ X ⁻ formed by the ion (X ⁻ ) increases,
The obtained hydrated zirconia gel has an alkali metal content of 5
It is lower than 0 ppm and the content of anions is 20
This is because it becomes larger than 0 ppm. Also, the pH is 8
When it is lower than the above range, the hydrated zirconia sol is less likely to aggregate, the gel separation property by the filtration operation is reduced, and the production efficiency is deteriorated. More preferably, the pH is 10 or higher, especially 12 or higher. Examples of the zirconium salt used for producing the hydrated zirconia sol include zirconium oxychloride, zirconium nitrate, zirconium sulfate, zirconyl chloride, and the like, but in addition to these, a mixture of zirconium hydroxide and an acid may be used. When zirconium hydroxide is used, various methods can be selected as its production method. For example, zirconium hydroxide can be obtained by neutralizing a water-soluble zirconium salt aqueous solution with an alkali. Examples of the alkali metal compound include hydroxides such as sodium hydroxide and potassium hydroxide, and carbonates such as sodium carbonate and potassium carbonate.

The hydrated zirconia sol may be obtained under any reaction condition. When the zirconium salt aqueous solution is hydrolyzed, the average particle size of the obtained hydrated zirconia sol can be controlled by adjusting the pH of the reaction solution at the end of the reaction. For example, a hydrated zirconia sol having an average particle size of 0.05 to 0.3 μm is prepared by adding an alkali or an acid to an aqueous zirconium salt solution and adjusting the pH at the end of the reaction to 0.1 to 1.5. Is obtained. On the other hand, the crystallite size can be controlled by adjusting the anion concentration of the zirconium salt aqueous solution, and when the anion concentration is 0.8 g ion / l or more and hydrolyzed, the crystallite size is 4 nm or less. A hydrated zirconia sol is obtained. Therefore, a desired hydrated zirconia sol can be obtained by controlling the anion concentration and pH of the zirconium salt aqueous solution within the above ranges.

In the present invention, when the suspension obtained above is filtered to wash the separated solid, that is, the hydrated zirconia gel, with water until the pH of the filtrate becomes 9 or less. I need. If it is not washed with water until the pH of the filtrate becomes 9 or less, the alkali metal salt will not be sufficiently removed, and the alkali metal content of the obtained hydrated zirconia gel will be larger than 1000 ppm, and the desired hydrated zirconia gel will be obtained. Is no longer obtained, and the content of anions is more than 200 ppm. More preferable p
H is 8 or less. Alternatively, the hydrated zirconia gel separated by filtration may be washed with an aqueous solution of an alkali metal compound and then washed with water. Washing with an alkali metal compound easily removes anions contained in the hydrated zirconia gel.

Next, the hydrated zirconia gel obtained above is dried and then calcined. There is no limitation on the method for drying the hydrated zirconia gel, and the drying temperature is usually 100 to 150.
It may be ℃. In addition, calcination of hydrated zirconia gel is
Calcination is required within the range of 500 to 1200 ° C. When the calcination temperature is lower than 500 ° C., the BET specific surface area becomes larger than 25 m ² / g, and when a stabilizer is further used, zirconia powder sufficiently dissolved with it cannot be obtained. On the other hand, when the temperature is higher than 1200 ° C, strong agglomeration occurs due to sintering between particles, so that BE
If the T specific surface area is smaller than 3.5 m ² / g, the dispersibility will be reduced and zirconia powder with good sinterability will not be obtained. Furthermore, at such a high calcination temperature, industrial mass production is difficult, which makes it impractical. A more preferable calcination temperature T (° C.) is in the range of 500 to 1100 ° C., and the average particle diameter φ (μ) of hydrated zirconia is
The relationship with m) satisfies T ≧ 1000φ + 400, and more preferably satisfies 1000φ + 400 ≦ T ≦ 3000φ + 600. Various gases can be selected as the atmosphere gas at the time of calcination. The gas used at this time should contain water vapor, and the water vapor partial pressure is 30 m.
It is better to use a gas of mHg or more. If it is lower than 30 mmHg, grain growth of the hydrated zirconia gel during calcination is suppressed, and it becomes difficult to obtain dense particles at a low temperature. More preferable steam partial pressure is 40 to 760 mmH.
It is g. Air, carbon dioxide, nitrogen, oxygen, argon, helium, etc. can be mentioned as a kind of gas. The holding time of the calcination temperature is preferably 0.5 to 10 hours, and the temperature rising rate is preferably 0.5 to 10 ° C / min. If the holding time is less than 0.5 hours, it is difficult to calcine evenly,
If it is longer than 10 hours, the productivity is lowered, which is not preferable. If the heating rate is less than 0.5 ° C / min, it takes a long time to reach the set temperature.
If it is higher than ° C / min, the powder will be violently scattered during calcination, resulting in poor operability and reduced productivity. Moreover, the alkali metal contained in the zirconia powder can be easily removed by washing the calcined powder with water depending on the application.

When obtaining a zirconia powder solid-dissolved with the stabilizer, the stabilizer may be added to the suspension after hydrolysis, and the stabilizer may be added in advance at the time of hydrolysis. May be. Further, the addition amount is preferably 1 to 30 mol% as the zirconia conversion amount of the hydrated zirconia gel, and the kind thereof may be any compound such as Y, Ca, Mg and Ce. Especially, water-soluble salts, hydroxides and oxides are preferable. If necessary, compounds such as aluminum and transition elements may be added before drying.

The calcined powder obtained as described above is pulverized into a zirconia powder having good dispersibility.

[0016]

[Function] Although the fine structure of the hydrated zirconia gel obtained by mixing the hydrated zirconia sol and the alkali metal compound is not clear, a part of the protons of the hydroxyl groups on the surface of the hydrated zirconia particles is converted to alkali metal cations. When the hydrated zirconia gel having such a structure is considered to be exchanged, and the hydrated zirconia gel having such a structure is calcined, the alkali metal on the particle surface promotes particle growth, whereby the zirconia particles become more compact, and the moldability and It is presumed that the zirconia powder has excellent sinterability.

[0017]

As described above, the hydrated zirconia gel of the present invention can be made into a zirconia powder having fast grain growth during calcination and good moldability at a relatively low calcination temperature.

[0018]

EXAMPLES The present invention will be specifically described below with reference to examples. In the examples, the crystal structure of hydrated zirconia is a monoclinic system, and the Scherrer's formula was applied to the half width of the diffraction line of (11-1) to calculate the crystallite size. Here, the Scherrer constant is 0.9. The average particle size was measured by the photon correlation method. The zirconia powder was compacted by a die press at a compaction pressure of 700 kgf / cm ² , and the compact was sintered at 1500 ° C. for 2 hours.

Example 1 A 0.4 mol / l zirconium oxychloride aqueous solution 10
28 g of yttrium oxide was added to 1 liter, and the hydrolysis reaction was carried out at the boiling temperature for 160 hours while stirring in a flask equipped with a reflux condenser. The obtained hydrated zirconia sol had an average particle diameter of 0.1 μm, and the gel obtained by collecting the sol and drying it in the air had a crystallite diameter of 2.
It was 5 nm. To the suspension containing the hydrated zirconia sol, 10 liter of a 1N aqueous sodium hydroxide solution was added and mixed to obtain a suspension having a pH of 12. The suspension was filtered, washed with 1N sodium hydroxide, further washed with water until the pH of the filtrate became 9 or less, and dried.
The sodium content and the chlorine content of the obtained hydrated zirconia gel were each 27% as a weight ratio to zirconia.
0 and 150 ppm.

Next, the hydrated zirconia gel dried as described above was calcined at 850 ° C. for 2 hours in air having a water vapor partial pressure of 100 mmHg. The obtained calcined powder was washed with water and then pulverized. The BET specific surface area of the obtained zirconia powder is
It was 20 m ² / g. When a compact was created using this powder, the compact density was 2.80 g / cm ³ , and the density of the sintered compact obtained by firing this compact was:
6.07 g / cm ³ , flexural strength 120 kgf / mm ²
Met.

Example 2 Example 2 was repeated except that the calcination temperature was set to 1000 ° C.

The BET specific surface area of the obtained zirconia powder was 10 m ² / g, and when a molded body was prepared using this powder, the density of the molded body was 2.75 g / cm ³ . The density of the sintered body obtained by firing this molded body is 6.
The bending strength was 04 g / cm ³ and the bending strength was 105 kgf / mm ² .

Example 3 The procedure of Example 1 was repeated, except that 4 g of aluminum chloride was added when the reaction solution was prepared.

The BET specific surface area of the obtained zirconia powder was 19 m ² / g, and when a molded body was prepared using this powder, the density of the molded body was 2.79 g / cm ³ . The density of the sintered body obtained by firing this molded body is 6.
The bending strength was 08 g / cm ³ and the bending strength was 125 kgf / mm ² .

Example 4 2.0 mol / l zirconium oxychloride aqueous solution 2.
3.6 liters of 1 mol / l ammonia water was mixed with 0 liters, and distilled water was added to prepare 10 liters of 0.4 mol / l zirconium oxychloride aqueous solution. 28 g of yttrium oxide was added to this reaction solution, and the hydrolysis reaction was carried out at the boiling temperature for 120 hours while stirring in a flask equipped with a reflux condenser. The average particle size of the obtained hydrated zirconia sol was 0.25 μm, and the crystallite size of the gel obtained by collecting the sol and drying it in the atmosphere was 2.
It was 7 nm. To the suspension containing the hydrated zirconia sol, 5 liter of 1N aqueous sodium hydroxide solution was added and mixed. The pH of the suspension at this time was 12. The suspension was filtered, washed with 1N aqueous sodium hydroxide solution, washed with water until the pH of the filtrate was 9 or less, and dried. The sodium and chlorine contents of the resulting hydrated zirconia gel were 380 and 150 ppm, respectively, as a weight ratio to zirconia.

Next, the hydrated zirconia gel dried as described above was calcined at 1000 ° C. for 2 hours in the air having a steam partial pressure of 30 mmHg. The obtained calcined powder was washed with water and then pulverized. The BET specific surface area of the obtained zirconia powder is
It was 8 m ² / g. When a molded body was prepared using this powder, the molded body had a density of 2.82 g / cm ³ ,
The density of the sintered body obtained by firing this molded body is 6.06.
The bending strength was g / cm ³ , and the bending strength was 118 kgf / mm ² .

Comparative Example 1 The procedure of Example 1 was repeated except that sodium hydroxide was changed to aqueous ammonia.

The BET specific surface area of the obtained zirconia powder was 28 m ² / g, and when a molded body was prepared using this powder, the density of the molded body was 2.55 g / cm ³ . The density of the sintered body obtained by firing this molded body is 5.
The bending strength was 95 g / cm ³ , and the bending strength was 70 kgf / mm ² .

Comparative Example 2 The procedure of Example 1 was repeated except that urea was used instead of sodium hydroxide.

The BET specific surface area of the obtained zirconia powder was 29 m ² / g, and when a molded body was prepared using this powder, the density of the molded body was 2.56 g / cm ³ . The density of the sintered body obtained by firing this molded body is 5.
The bending strength was 97 g / cm ³ , and the bending strength was 80 kgf / mm ² .

Claims (2)

[Claims] 1. An alkali metal is added to ZrO _{2 in} an amount of 50 to 1.
A hydrated zirconia gel containing 000 ppm by weight. 2. A method for producing a zirconia powder, which comprises drying the hydrated zirconia gel according to claim 1 and then calcining it at 500 to 1200 ° C.