JP3265597B2 - Method for producing zirconia fine powder - Google Patents

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 ceramics, and more particularly to a method for producing zirconia fine powder having good formability.

[0002]

2. Description of the Related Art Conventionally, as a method for producing zirconia powder by calcining a hydrated zirconia sol, an aqueous solution of a zirconium salt is hydrolyzed, and then dried.
A method in which a hydrated zirconia sol having a thickness of 1 to 0.3 μm is separated by a sedimentation method or the like, and calcined to obtain a zirconia powder (Japanese Patent Laid-Open No. 58-1983).
A method in which aqueous ammonia is added to a suspension of hydrated zirconia fine particles in which a stabilizer is dissolved, followed by filtration, washing with water, and calcination to obtain zirconia powder (JP-A-63-129017). Etc. are known.

[0003]

In the meanwhile, specifically, hydrated zirconia sol having a crystallite diameter of 4.3 nm is calcined to obtain zirconia powder. In order to obtain a zirconia powder in which the stabilizer is fully dissolved using the zirconia sol, the calcination temperature must be increased, and if the calcination temperature is increased, strong coagulation occurs between particles. And sintering at a low temperature becomes difficult. Further, in the above, a hydrated zirconia sol having an average particle size of 1 μm is calcined at 800 ° C. to obtain a zirconia powder having a BET specific surface area of 29 m ² / g. The powder thus obtained has pores inside,
When this powder is molded and sintered, pores remain inside the particles, so that the characteristics of the sintered body are low. Further, since the BET specific surface area is large as described above, molding is difficult. In the present invention, such disadvantages in the conventional method are solved, that is, a zirconia powder having good dispersibility and good dispersibility, in which the stabilizing agent is well-dissolved, and thus, has good moldability is produced by a simple process. It is intended to provide a method capable of performing such operations.

[0004]

Means for Solving the Problems The present inventors calcinated a mixture of a hydrated zirconia sol and a stabilizer such as yttria, calcia, magnesia, and ceria, which are commonly used in the production of zirconia-based ceramics, to obtain zirconia. Focusing on the crystallite size and average particle size of the hydrated zirconia sol when obtaining the powder, as a result of examining in detail the solid solution reaction during calcination and the change in the particle structure of the hydrated zirconia sol, at a low temperature A dense, well-dispersed zirconia powder having a BET specific surface area of 5 to 25 m ² / g, which is sufficiently dissolved in a stabilizer, can be obtained. It has been found that the powder is zirconia powder that sinters at a temperature, and the present invention has been completed.

That is, the present invention provides an average particle size of 0.05 to
Method for producing fine zirconia powder by calcining a mixture of hydrated zirconia sol having a diameter of 0.3 μm and a crystallite diameter of 3 nm or less and at least one compound among Y, Ca, Mg and Ce at a temperature of 500 to 1200 ° C. It is the gist. Hereinafter, the present invention will be described in more detail. In the present specification, the "average particle size" related to the hydrated zirconia sol,
It is obtained by particle size measurement using an electron microscope or a particle size distribution analyzer, and is given by, for example, a photon correlation method. The “crystallite diameter” is obtained from powder X-ray diffraction. When the crystal structure of the hydrated zirconia sol is monoclinic, the diffraction line is (11-1), and when the crystal structure is tetragonal or cubic, Focusing on the diffraction line of (111), it is calculated by applying Scherrer's formula to the half width of each diffraction line.

In the present invention, the hydrated zirconia sol used when calcining a mixture of the hydrated zirconia sol and a stabilizer or the like has a crystallite size of 3 nm or less and an average particle size of 0.05 to 0.05 nm. It needs to be 0.3 μm. If the crystallite diameter is larger than 3 nm, the solid solubility with the stabilizer decreases, so that the calcination temperature must be set high. If the calcination temperature is high, strong agglomeration due to sintering between particles may occur. This is because the desired zirconia fine powder having good dispersibility cannot be obtained. However, it is not preferable that the crystallite is too small and a crystallization peak is observed by differential thermal analysis, that is, a substantially amorphous one is likely to cause aggregation between particles during calcination. Further, when the average particle size of the hydrated zirconia sol is smaller than 0.05 μm, strong aggregation due to sintering between the particles occurs during calcination, so that the dispersibility of the zirconia powder deteriorates,
If it is larger than μm, the particle size of the powder also becomes large, so that the sinterability becomes low and it is not suitable for ceramic raw material powder.

In the present invention, it is necessary to calcine a mixture of a hydrated zirconia sol and a stabilizer at a temperature of 500 to 1200 ° C. When the calcination temperature is lower than 500 ° C., the BET specific surface area is larger than 25 m ² / g, and zirconia powder sufficiently dissolved with the stabilizer cannot be obtained. BET specific surface area is 5m due to strong aggregation due to sintering
² / g, and a zirconia powder having good dispersibility cannot be obtained. Furthermore, at such a high calcination temperature, industrial mass production is difficult and therefore impractical. The calcination temperature T ° C is in the above range of 500 to 1200 ° C.
Within the box, the average particle diameter of the hydrated zirconia sol
Relationship between is one which satisfies the 1000φ + 400 ≦ T ≦ 3000 φ +600.

Various gases can be selected as the atmosphere gas during calcination. The gas used at this time preferably contains water vapor, and it is better to use a gas having a water vapor partial pressure of 30 mmHg or more. If the pressure is lower than 30 mmHg, the grain growth of the hydrated zirconia sol during calcination is suppressed, so that it is difficult to obtain dense particles at a low temperature, which is not preferable. More preferred water vapor partial pressure is 40 mm
Hg or more. Examples of the type of gas include air, carbon dioxide, nitrogen, oxygen, argon, and helium. The holding time of the calcination temperature is preferably 0.5 to 10 hours, and the heating rate is preferably 0.5 to 10 ° C / min. If the holding time is shorter than 0.5 hour, it is difficult to uniformly calcine, and if the holding time is longer than 10 hours, the productivity is undesirably reduced. On the other hand, if the heating rate is lower than 0.5 ° C./min, the time required to reach the set temperature becomes longer. Is reduced.

The above-mentioned hydrated zirconia sol may be obtained under any reaction conditions as long as the average particle size and the crystallite size are obtained within the above ranges. In the case of a hydrolysis reaction of an aqueous zirconium salt 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, by adjusting the pH at the end of the reaction to be 0.1 to 1.5, a hydrated zirconia sol having an average particle size of 0.05 to 0.3 μm can be obtained. On the other hand, the crystallite diameter can be controlled by adjusting the anion concentration of the zirconium salt aqueous solution. When the anion concentration is increased to 0.8 g ion / l or more and the hydrolysis is performed, the crystallite diameter becomes 4 n.
m or less hydrated zirconia sol is obtained. Therefore,
A desired hydrated zirconia sol can be obtained by controlling the anion concentration and pH of the aqueous zirconium salt solution within the above ranges. As a method for controlling the pH and the anion concentration, that is, the average particle size and crystallite of the hydrated zirconia sol, for example, an acid, an alkali or a metal salt is added to an aqueous solution of a zirconium salt; A method of adjusting the pH by removing a part of the anions constituting the salt to effect hydrolysis; a mixed slurry of zirconium hydroxide and an acid, a metal salt added to the mixed slurry, and p
A method of adjusting the concentration of H and anions to carry out hydrolysis is exemplified. Here, examples of the zirconium salt used in the production of the hydrated zirconia sol include zirconium oxychloride, zirconyl nitrate, zirconium chloride, zirconyl sulfate, and the like. In addition, a mixture of zirconium hydroxide and an acid is used. Is also good. Examples of the alkali added to control the average particle size of the hydrated zirconisol include ammonia, sodium hydroxide, potassium hydroxide, and the like. In addition, the alkali decomposes like urea to show basicity. It may be a compound. Examples of the acid include hydrochloric acid, nitric acid, sulfuric acid and the like, and in addition, organic acids such as acetic acid and citric acid may be used. Further, examples of the metal salt to be added to control the anion concentration of the aqueous zirconium salt solution, that is, the crystallite size of the hydrated zirconia sol, include salts of alkali metals or alkaline earth metals such as sodium salts, aluminum salts and the like. However, an ammonium salt may be added. When a raw material of zirconium hydroxide is used, various methods can be selected for its production method. For example, zirconium hydroxide can be obtained by neutralizing an aqueous solution of zirconium salt with an alkali.

A 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 particular limitation on the method for drying the liquid content. For example, the suspension or a method in which an organic solvent is added to the suspension to dry it, an alkali is added to the suspension, and the suspension is filtered, washed with water, and dried And the like. At this time, the composition of the mixture preferably contains at least 1 wt% of anions as impurities. If the anion content is lower than 1 wt%, the grain growth rate of the hydrated zirconia sol during calcination becomes slow, so that it is difficult to obtain dense particles at a low temperature. A more preferred anion content is 3 to 13 wt%. The stabilizer may be added to the suspension after hydrolysis, or may be added in advance at the time of hydrolysis. The amount of the stabilizer added is 1 to 30 mol% in terms of zirconia in the hydrated zirconia sol.
Is preferable, and any kind may be used as long as it is a compound of Y, Ca, Mg, and Ce. Preferably a water-soluble salt,
Hydroxides and oxides are preferred. Of course, if necessary, compounds such as aluminum and transition metals may be added before drying. The calcined powder obtained as described above becomes a zirconia fine powder having good dispersibility by pulverization.

[0011]

[Effect] The microstructure of the hydrated zirconia sol obtained by hydrolysis of the aqueous solution of zirconium salt is observed by an electron microscope to be composed of aggregated particles of ultrafine particles having good crystallinity. It almost coincides with the crystallite diameter determined from X-ray diffraction. From this fact, the smaller the size of the ultrafine particles, the better the uniformity with the stabilizer is obtained, and the reaction surface area of solid solution is also increased, so that dense particles sufficiently dissolved at low temperature are obtained. It is assumed that

[0012]

As described above, according to the present invention, according to the present invention, the stabilizer is well dissolved and has good dispersibility.
Zirconia powder having good moldability can be manufactured by a simple process.

[0013]

The present invention will be described below in detail with reference to examples. In the examples, the average particle size of the hydrated zirconia sol was determined by a photon correlation method. In addition, the crystallite diameter was calculated by calculating the half width of the diffraction line of (11-1) by wave processing, and applying the Scherrer equation to the half width (in each case, the tetragonal crystal was used). And cubic crystals were not included). Here, the Scherrer constant was set to 0.9. The zirconia powder was molded by a mold press at a molding pressure of 700 kg / cm ² , and the molded body was sintered under the firing conditions of 1500 ° C. and 2 hours.

Example 1 To 2 liters of a 2 mol / l aqueous solution of zirconium oxychloride, 250 ml of 1N ammonia water and 6 g of sodium chloride were added, and 0.4 mol of distilled water was further added.
Per liter of an aqueous zirconium oxychloride solution was prepared. The hydrolysis reaction was performed at the boiling temperature for 120 hours while stirring the raw material liquid. The resulting hydrated zirconia sol has an average particle size of 0.09 μm and a crystallite size of 2.
It was 5 nm. Next, 49 g of yttrium chloride was added to the suspension containing the hydrated zirconia sol, concentrated by heating, and spray-dried to prepare a dry powder of the hydrated zirconia sol. The chlorine content of this dry powder is 11 wt%
Met. The obtained dry powder has a steam partial pressure of 40 mmH.
The resultant was calcined at a temperature of 680 ° C. for 2 hours in the air controlled to g. When the obtained calcined powder was measured for powder X-ray diffraction, a tetragonal diffraction pattern was obtained, and almost no monoclinic diffraction line was observed. Next, the calcined powder obtained above was washed with water, and then pulverized with a ball mill for 50 hours to obtain a zirconia powder having a BET specific surface area of 23 m ² / g. When a compact was prepared using this zirconia powder, the compact had a density of 2.71 g / cm ³ , and the sintered compact obtained by firing this compact had a density of 6.08 g / cm ^3.
cm ³ , and the flexural strength was 119 kgf / mm ² .

Example 2 To 2.5 liters of a 2 mol / l aqueous solution of zirconium oxychloride, 1 liter of 1N aqueous ammonia and 7 g of sodium chloride were added, and distilled water was added to obtain 0.5 m
10 liters of an aqueous solution of zirconium oxychloride of ol / l was prepared. The hydrolysis reaction was performed at the boiling temperature for 120 hours while stirring the raw material liquid. The average particle size of the obtained hydrated zirconia sol was 0.08 μm, and the crystallite size was 2.2 nm. Next, 61 g of yttrium chloride was added to the suspension containing the hydrated zirconia sol, heated and concentrated, and then spray-dried to prepare a dry powder of the hydrated zirconia sol. The chlorine content of this dry powder is 10w
t%. The obtained dry powder has a steam partial pressure of 40 m.
Calcination was performed at a temperature of 650 ° C. for 2 hours in air controlled to mHg. When the obtained calcined powder was measured for powder X-ray diffraction, a tetragonal diffraction pattern was obtained, and almost no monoclinic diffraction line was observed. Next, the calcined powder obtained above was washed with water, and then pulverized with a ball mill for 50 hours to obtain a zirconia powder having a BET specific surface area of 23 m ² / g. When a compact was prepared using this zirconia powder, the compact density was 2.70 g / cm ³ , and the density of the sintered compact obtained by firing this compact was 6.08 g.
/ Cm ³ , and the flexural strength was 120 kgf / mm ² .

Example 3 To 2 liters of a 2 mol / l zirconium oxychloride aqueous solution, 250 ml of 1N ammonia water, 6.5 g of sodium chloride and 28.5 g of yttrium oxide were added.
Distilled water was further added to prepare 10 liters of a 0.4 mol / l zirconium oxychloride aqueous solution. The hydrolysis reaction was performed at the boiling temperature for 120 hours while stirring the raw material liquid. The average particle size of the obtained hydrated zirconia sol was 0.1 μm, and the crystallite size was 2.4 nm. The obtained hydrated zirconia sol-containing liquid was heated and concentrated, and further spray-dried to prepare a dried powder of the hydrated zirconia sol. The chlorine content of this dry powder was 10% by weight. The obtained dry powder was calcined at 850 ° C. for 2.5 hours in air controlled at a partial pressure of steam of 100 mmHg. When the obtained calcined powder was measured for powder X-ray diffraction, a tetragonal diffraction pattern was obtained, and almost no monoclinic diffraction line was observed. Next, the calcined powder obtained above was washed with water, and then pulverized with a ball mill for 50 hours to obtain a zirconia powder having a BET specific surface area of 15 m ² / g. When a compact was prepared using this zirconia powder, the compact density was 2.65 g / cm ³ , and the sintered compact obtained by firing this compact had a density of 6.07 g / cm ^3.
cm ³ , and the bending strength was 115 kgf / mm ² .

Comparative Example 1 The same procedure as in Example 1 was carried out except that the calcination temperature was set at 400 ° C.

The obtained calcined powder was analyzed by powder X-ray diffraction, and was found to be a monoclinic diffraction pattern. The specific surface area of the obtained zirconia powder was 150 m ^2.
/ G.

Claims (1)

(57) [Claims] 1. A hydrated zirconia sol having an average particle diameter of 0.05 to 0.3 μm and a crystallite diameter of 3 nm or less, and Y, Ca, Mg
And a mixture of at least one compound of Ce is calcined at a temperature of 500 to 1200 ° C., the calcination temperature and water
The relationship between the average particle diameter φμm of the sum zirconia sol is given by the following formula:
A method for producing zirconia fine powder, characterized by being represented by the following formula: 1000φ + 400 ≦ T ≦ 3000φ + 600