JPH05155622A - Production of fine zirconia powder - Google Patents

Abstract

PURPOSE:To produce fine zirconia powder having satisfactory compactibility by an easy process in the form of dense particles contg. a stabilizing agent in a uniform solid soln. and having satisfactory dispersibility. CONSTITUTION:When a mixture contg. a zirconia hydrate sol and a compd. of at least one among Y, Ca, Mg and Ce is calcined to produce fine zirconia powder, a layer of the mixture having a thickness H (cm) is calcined at a temp. T ( deg.C) satisfying an inequality 120H<0.5>+500<=T<=1200.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing zirconia powder, which is a raw material for zirconia-based ceramics, and more particularly to a method for producing fine zirconia powder which enables the raw material powder to have good moldability. ..

[0002]

2. Description of the Related Art Conventionally, as a method for producing zirconia powder, ammonia water is added to a suspension of hydrated zirconia fine particles in which a stabilizer is dissolved, and the zirconia powder is filtered, washed with water, and calcined. Method for Obtaining (JP-A-63-129017) Method for adding a stabilizer consisting of chloride to zirconium hydroxide raw material and calcining to obtain zirconia powder (JP-A-61-266307) Zirconyl ammonium carbonate A method in which hydrogen peroxide is added to a mixed aqueous solution of a salt and a stabilizer, and the resulting solid is dried and calcined to obtain a zirconia powder (JP-A-61-447).
17 gazette) etc. are known.

[0003]

By the way, the zirconia powder obtained by the above method is a fine powder having a very large BET specific surface area, that is, a small particle size. Since the adhesive force between them is remarkably increased, the obtained zirconia powder becomes a strong agglomerated powder, which makes it difficult to form. In the zirconia powder obtained by the method of 1, the gel-like precipitate of zirconium hydroxide is calcined at 1100 ° C. When the gel-like precipitate is calcined at a high temperature, strong agglomeration between particles occurs violently. , The dispersibility is inferior. In the method of (1), hydrogen peroxide is added to a mixed aqueous solution of a zirconyl ammonium carbonate salt and a stabilizer, and the gel coprecipitate obtained is calcined to obtain a zirconia powder. The precipitate has a non-uniform composition, and the powder obtained by calcination of the gel-like precipitate has poor dispersibility as described above. Further, the hydrogen peroxide used in the coprecipitation is a substance having a high risk, which makes industrial mass production difficult and impractical.

In the present invention, such a drawback of the conventional method is solved, that is, fine particles having good dispersibility in which a stabilizer is well solid-dissolved, that is, zirconia powder having good moldability is produced by a simple process. The purpose is to provide a possible method.

[0005]

The present inventors have calcined a mixture of a hydrated zirconia sol and a stabilizer such as yttria, calcia, magnesia, and ceria, which is commonly used in the production of zirconia-based ceramics, to form zirconia. According to a detailed study focusing on the calcination atmosphere and the solid solution reaction when obtaining the powder, according to a stabilizer by controlling the thickness of the mixture layer when the mixture is charged into the calcination furnace. Dense particles that are sufficiently solid-dissolved, and therefore fine zirconia powder with good dispersibility, can be produced, and the fine powder obtained in this way has good moldability and can be sintered at a relatively low temperature. The present invention was completed by finding out that it was a powder.

The present invention relates to a hydrated zirconia sol and Y, C.
In a method for producing a zirconia fine powder by calcination of a mixture containing at least one compound of a, Mg and Ce, the mixture having a layer thickness H (cm) is 120H ^0.5 +50.
The gist is a method for producing fine zirconia powder by calcining at a temperature T (° C.) satisfying the condition of 0 ≦ T ≦ 1200. Hereinafter, the present invention will be described in more detail.

In the present specification, the "solid solution reaction rate" relating to the solid solution reaction between the hydrated zirconia sol and the stabilizer is calculated by the following formula, paying attention to the diffraction line of powder X-ray diffraction. What is done.

Tetragonal crystal ratio (%) = It / (It + Ic + Im) × 100 Cubic crystal ratio (%) = Ic / (It + Ic + Im) × 100 where It is the intensity of the tetragonal (111) diffraction line, I
c is the cubic (111) strength, and Im is the monoclinic (11).
It is the sum of the intensities of 1) and (11-1). The “average particle size” of the hydrated zirconia sol is obtained by particle size measurement using an electron microscope or a particle size distribution measuring device, and is given by, for example, photon correlation method.

The zirconia fine powder obtained by the present invention is B
The ET specific surface area is 5 to 25 m ² / g. When the BET specific surface area is smaller than 5 m ² / g, zirconia powder having good dispersibility cannot be obtained because of strong agglomeration due to sintering between particles, and when the BET specific surface area is larger than 25 m ² / g, the adhesion between particles is increased. Since the cohesive force is remarkably increased, it becomes a strong agglomerated powder, which makes it difficult to mold and becomes unsuitable as a ceramic powder. Further, the calcined powder obtained by calcining the mixture of the hydrated zirconia sol and the stabilizer preferably has a solid solution reaction rate of 90% or more, and when the solid solution reaction rate becomes lower than 90%, the zirconia fine particles become fine. The composition of the powder becomes non-uniform, and if such powder is molded and fired, non-uniform shrinkage due to abnormal grain growth is likely to occur, which is not preferable. More preferably, it is 95% or more. By the way, the above-mentioned hydrated zirconia sol has an average particle size of 0.0
It is preferable that the crystallite diameter is 5 to 0.3 μm and the crystallite diameter is 4 nm or less. The average particle size of hydrated zirconia sol is 0.0
If it is less than 5 μm, strong agglomeration due to sintering between particles is likely to occur during calcination, and if it is more than 0.3 μm, the particle size of the powder is large and the sinterability tends to be low. It is not preferable as a powder. Further, if the crystallite size is larger than 4 nm, the solid solubility with the stabilizer decreases, which is not preferable.

In the present invention, when the mixture of the hydrated zirconia sol and the stabilizer is calcined, the layer thickness H (cm) and the calcining temperature T (° C.) of the mixture are 120H ^0.5 +500. The relationship of ≦ T ≦ 1200 must be satisfied. Calcination temperature is 120H
^When it is lower than ^0.5 + 500, the solid solution reaction rate of the calcined powder is lower than 90%, and a solid solution with the stabilizer cannot be sufficiently obtained, and when it is lower than 500 ° C, BET
The specific surface area becomes larger than 25 m ² / g and the desired zirconia fine powder cannot be obtained. On the other hand, 120
If the temperature is higher than 0 ° C., strong agglomeration due to sintering between particles occurs, so that the BET specific surface area becomes smaller than 5 m ² / g and zirconia powder having good dispersibility cannot be obtained. Further, at such a high calcination temperature, industrial mass production is difficult, so that it is not practical. A more preferable calcination temperature T (° C.) is (120H ^0.5 +5).
00) to 1200 ° C., and the relationship between the average particle diameter φ (μm) of the hydrated zirconia sol satisfies T ≧ 1000φ + 400, and more preferably 1000φ + 400 ≦ T ≦ 3000φ + 600. Is satisfied. Various gases can be selected as the atmosphere gas at the time of calcination. It is better that the gas used at this time contains water vapor, and the water vapor partial pressure is 30 mm.
It is better to use a gas of Hg or higher. If it is lower than 30 mmHg, grain growth of the hydrated zirconia sol during calcination is suppressed, and it becomes difficult to obtain dense particles at a low temperature, which is not preferable. The more preferable partial pressure of water vapor is 40 to 760 mmHg. 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 0.5 to 10 ° C /
min is preferred. If the holding time is shorter than 0.5 hours, it is difficult to uniformly calcine, and if it is longer than 10 hours, productivity is lowered, which is not preferable. If the heating rate is less than 0.5 ° C / min, it takes longer to reach the set temperature, and if the heating rate is more than 10 ° C / min, the powder will be severely scattered during the calcination, resulting in poor operability. Sex decreases.

The hydrated zirconia sol may be obtained under any reaction condition. In the case of the hydrolysis reaction of the zirconium salt aqueous solution, 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 can be obtained by adjusting the pH at the end of the reaction to 0.1 to 1.5. On the other hand, the crystallite size can be controlled by adjusting the anion concentration of the zirconium salt aqueous solution, and the anion concentration is 0.8 g ion / l.
When hydrolyzed as described above, a hydrated zirconia sol having a crystallite size of 4 nm or less 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. As a method for controlling the pH and the anion concentration, that is, the average particle size and crystallites of the hydrated zirconia sol, for example, an acid, alkali or metal salt is added to the zirconium salt aqueous solution, or anion exchange is performed. A method of adjusting the pH to hydrolyze by removing a part of the anion constituting the zirconium salt with a resin,
Alternatively, a mixed slurry of zirconium hydroxide and an acid, a metal salt is added to the mixed slurry, and p of the mixed slurry is added.
Examples include a method of adjusting the H and anion concentrations to cause hydrolysis. Examples of the zirconium salt used for producing the hydrated zirconia sol include zirconium oxychloride, zirconyl nitrate, zirconium chloride, zirconyl sulfate, and the like. In addition to these, a mixture of zirconium hydroxide and an acid is used. Good. Examples of alkalis added to control the average particle size of hydrated zirconisols include ammonia, sodium hydroxide, and potassium hydroxide. In addition to these, they decompose to show basicity like urea. It may be a compound. Examples of the acid include hydrochloric acid, nitric acid, sulfuric acid and the like, but in addition to these, organic acids such as acetic acid and citric acid may be used. Furthermore, as the anion concentration of the zirconium salt aqueous solution, that is, as the metal salt added to control the crystallite size of the hydrated zirconisol, an alkali metal salt or an alkaline earth metal salt such as a sodium salt, an aluminum salt, or the like can be given. However, in addition to this, an ammonium salt may be added. When a zirconium hydroxide raw material is used, various methods can be selected as the production method, and for example, zirconium hydroxide can be obtained by neutralizing an aqueous zirconium salt solution with an alkali.

The mixture of the hydrated zirconia sol and the stabilizer obtained by this reaction can be obtained by drying the hydrated zirconia sol-containing liquid containing the stabilizer. There is no limitation on the method of drying the contained liquid, for example, the suspension or a method of adding an organic solvent to the suspension to dry, or adding an alkali to the suspension, filtering, washing with water and then drying. And the like. The bulk density of the mixture obtained at this time is preferably in the range of 0.5 to 2.1 g / cm ³ . When the bulk density is higher than 2.1, the atmosphere in the mixture becomes non-uniform during calcination, so that the solid solubility with the stabilizer is deteriorated, and when it is smaller than 0.5, the production efficiency is reduced. Not preferred because of A more preferable bulk density is 0.9 to 1.6 g / cm ³ . In addition, the mixture contains 1% by weight of zirconia.
It is better to include the above anions. If the anion content is lower than 1%, the particle growth rate of the hydrated zirconia sol will be slow during calcination, and it will be difficult to obtain dense particles at a low temperature. More preferable anion content is
3 to 33%. The stabilizer may be added to the suspension after the hydrolysis, or may be added in advance at the time of hydrolysis. The amount of the stabilizer added is 1 to zirconia equivalent of the hydrated zirconia sol.
30 mol% is preferable, and the types are Y, Ca, Mg,
Any compound such as Ce may be used. Water-soluble salts, hydroxides, oxides, etc. are particularly preferable. of course,
If necessary, compounds such as aluminum and transition metals may be added before drying.

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

[0014]

It is observed from an electron microscope that the fine structure of the hydrated zirconia sol obtained by hydrolysis of the aqueous solution of zirconium salt is composed of aggregated particles of ultrafine particles having good crystallinity. It is considered that the smaller the size of the ultrafine particles, the larger the reaction surface area with the stabilizer and the better the uniformity with the stabilizer. From this, it is speculated that the higher the layer thickness of the mixture due to calcination, the more the atmosphere in the vicinity of the particles changes, so that the reaction surface area is affected, and as a result, the solid solubility with the stabilizer changes.

[0015]

As described above, according to the present invention, dense particles having a good solid solution of a stabilizer and good dispersibility,
Therefore, zirconia powder having good moldability can be manufactured by a simple process.

[0016]

EXAMPLES The present invention will be specifically described below with reference to examples. In the examples, the crystal structure of the hydrated zirconia sol is a monoclinic system, and its crystallite size was calculated by applying the Scherrer's formula to the half width of the diffraction line of (11-1). Here, the Scherrer constant is 0.9. The zirconia fine powder was compacted by a die press at a compacting pressure of 700 kg / cm ² , and the compact was sintered at 1500 ° C. for 2 hours.

Example 1 To 2.5 liters of a 2 mol / l zirconium oxychloride aqueous solution, 2 liters of 1N ammonia water, 36 g of yttrium oxide and 7.5 g of sodium chloride were added,
Further, distilled water was added to prepare 10 liters of a 0.5 mol / l zirconium oxychloride aqueous solution. The hydrolysis reaction was carried out at the boiling temperature for 120 hours while stirring this raw material liquid. The obtained hydrated zirconia sol had an average particle size of 0.1 μm and a crystallite size of 2.4 n according to the photon correlation method.
It was m. The hydrated zirconia sol-containing liquid is concentrated by heating and further spray-dried to have a bulk density of 1.3 g / cm.
^{3. A} hydrated zirconia dry powder having a chlorine content of 15% (weight ratio to zirconia, the same applies hereinafter) was prepared. This dry powder was charged into a calcining furnace with a layer thickness of 6 cm, and the steam partial pressure was 10
It was calcined at a temperature of 850 ° C. for 2 hours in air of 0 mmHg (120 × 6 ^0.5 + 500 = 794). As a result of measuring the powder X-ray diffraction of the obtained calcined powder, it was found to be a tetragonal diffraction pattern, and the solid solution reaction rate was 97%.

Next, the calcined powder obtained above was washed with water and then pulverized with a ball mill for 50 hours. The BET specific surface area of the obtained zirconia fine powder was 15 m ² / g. When a molded body was produced using this powder, the molded body had a density of 2.67 g / cm ³ , and the sintered body obtained by firing this molded body had a density of 6.07 g / cm ³ ,
The bending strength was 115 kgf / mm ² .

Example 2 The same procedure was carried out as in Example 1 except that the calcination temperature was 700 ° C. and the dry powder layer thickness was 2.5 cm (120 × 2.5).
^0.5 + 500 = 690).

The solid solution reaction rate of the obtained calcined powder was 92%, and the BET specific surface area of the zirconia fine powder after washing with water and pulverization was 23 m ² / g. With this powder,
When a molded product was produced, the density of the molded product was 2.75 g / c.
m ³ , the sintered body obtained by firing this molded body had a density of 6.08 g / cm ³ and a bending strength of 120 kgf /
It was mm ² .

Example 3 To 2 liters of a 2 mol / l zirconium oxychloride aqueous solution, 1.9 liters of 1N ammonia water and 36 g of yttrium oxide were added, and distilled water was further added to the mixture.
10 l of a 4 mol / l zirconium oxychloride aqueous solution was prepared. The hydrolysis reaction was carried out at the boiling temperature for 120 hours while stirring this raw material liquid. The average particle size of the obtained hydrated zirconia sol measured by the photon correlation method is 0.15μ.
m, and the crystallite diameter was 2.6 nm. The hydrated zirconia sol-containing solution was concentrated by heating and further spray-dried to prepare a hydrated zirconia dry powder having a bulk density of 1.2 g / cm ³ and a chlorine content of 14%. 8c of this dry powder
Charged in a calcining furnace with a layer thickness of m, steam partial pressure 100 mmHg
In air for 2 hours at 900 ℃ (120 ×
8 ^0.5 + 500 = 839). When powder X-ray diffraction was measured on the obtained calcined powder, only a tetragonal diffraction pattern was obtained, and the solid solution reaction rate was 98%.

Next, the calcined powder obtained above was washed with water and then pulverized with a ball mill for 50 hours. The BET specific surface area of the obtained zirconia fine powder was 15 m ² / g. When a molded body was produced using this powder, the molded body had a density of 2.75 g / cm ³ , and the sintered body obtained by firing this molded body had a density of 6.09 g / cm ³ ,
The bending strength was 125 kgf / mm ² .

Example 4 To 2 liters of a 2 mol / l zirconium oxychloride aqueous solution, 3.6 liters of 1N ammonia water and 28.5 g of yttrium oxide were added, and distilled water was further added to the mixture to give 0.4 mol / l oxychloride. Zirconium solution 10
1 liter was prepared. The hydrolysis reaction was carried out at the boiling temperature for 120 hours while stirring this raw material liquid. The average particle size of the obtained hydrated zirconia sol is 0.2 by the photon correlation method.
It was 6 μm and the crystallite size was 2.9 nm. The hydrated zirconia sol-containing liquid is heated and concentrated, and further spray-dried to obtain a bulk density of 1.0 g / cm3 and a chlorine content of 13
% Dry zirconia dry powder was prepared. The dry powder was charged into a calcining furnace with a layer thickness of 10 cm, and the steam partial pressure was 40 mm.
Calcination in Hg air at a temperature of 1000 ° C. for 2 hours (1
20 × 10 ^0.5 + 500 = 879). When powder X-ray diffraction was measured on the obtained calcined powder, only a tetragonal diffraction pattern was obtained, and the solid solution reaction rate was 97%.

Next, the calcined powder obtained above was washed with water and then pulverized with a ball mill for 50 hours. The BET specific surface area of the obtained zirconia fine powder was 8 m ² / g. When a molded body was produced using this powder, the molded body had a density of 2.70 g / cm ³ , and the sintered body obtained by firing this molded body had a density of 6.08 g / cm ³ . The bending strength was 120 kgf / mm ² .

Example 5 To 3 liters of a 2 mol / l zirconium oxychloride aqueous solution, 4 liters of 1N ammonia water and 36 g of yttrium oxide were added, and distilled water was further added to obtain 0.6 mol.
10 liter of an aqueous solution of zirconium oxychloride of 1 / l was prepared. The hydrolysis reaction was carried out at the boiling temperature for 120 hours while stirring this raw material liquid. The average particle size of the obtained hydrated zirconia sol by the photon correlation method is 0.1 μm,
The crystallite size was 2.5 nm. The hydrated zirconia sol-containing liquid was heated and concentrated, and further spray-dried to prepare a hydrated zirconia dry powder having a bulk density of 1.3 g / cm ³ and a chlorine content of 15%. This dry powder was charged into a calcining furnace with a layer thickness of 6 cm, and the dry powder was mixed with air in a steam partial pressure of 30 mmHg for 9
It was calcined at a temperature of 00 ° C. for 2 hours (120 × 6 ^0.5 +5
00 = 794). As a result of measuring the powder X-ray diffraction of the obtained calcined powder, it was found to be a tetragonal diffraction pattern, and the solid solution reaction rate was 98%.

Next, the calcined powder obtained above was washed with water and then pulverized with a ball mill for 50 hours. The BET specific surface area of the obtained zirconia fine powder was 20 m ² / g. When a molded body was produced using this powder, the density of the molded body was 2.88 g / cm ³ , and the density of the sintered body obtained by firing this molded body was 6.08 g / cm ³ ,
The bending strength was 125 kgf / mm ² .

Comparative Example 1 The same procedure as in Example 1 was carried out (120 × 6 ^0.5 +5) except that the calcining temperature was 700 ° C. and the layer thickness of the dry powder was 6 cm.
00 = 794).

The solid solution reaction rate of the obtained calcined powder was 80%, and the BET specific surface area of the zirconia fine powder after washing with water and pulverization was 23 m ² / g. With this powder,
When a molded product was produced, the density of the molded product was 2.59 g / c.
m ^3, the density of the sintered body obtained by firing the molded body, 5.95 g / cm ^3, flexural strength 96Kgf / m
It was m ² .

Claims (1)

[Claims] 1. A hydrated zirconia sol and Y, Ca, Mg, C
In the method for producing fine zirconia powder by calcining a mixture containing at least one compound of e, the layer thickness H
(Cm) of the mixture 120H ^0.5 + 500 ≦ T ≦ 1
A method for producing zirconia fine powder, which comprises calcining at a temperature T (° C.) satisfying the condition of 200.