JP3257094B2 - Method for producing zirconia powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for removing anionic impurities from zirconia powder obtained by a hydrolysis method.
The present invention relates to a method for producing a zirconia powder having excellent sintered body characteristics.

[0002]

2. Description of the Related Art A general method for producing zirconia powder by hydrolysis is to obtain a zirconia powder by hydrolyzing an aqueous solution containing a water-soluble zirconium salt alone or a metal salt having Ca, Mg or a valence of three or more. An organic solvent is added to the hydrated zirconia sol, dried by heating distillation, and then the dried powder is calcined to obtain zirconia fine powder (Japanese Patent Publication No. 59-39).
366) After hydrolyzing unreacted substances, ungrown zirconium hydroxides and zirconia hydrates, and coexisting salts, etc., they are filtered and washed using an ultrafiltration membrane. There is known a method of adding a hydroxide of a metal selected from lanthanide elements such as Ca, Mg, Y, and Ce and performing a dehydration heat treatment (Japanese Patent Application Laid-Open No. 63-185821).

[0003]

However, in the zirconia powder obtained by the production method described above, the unreacted product of the water-soluble zirconium salt as a raw material and the metal salt which becomes a stabilizer by firing, and by-products during calcination, are contained. Anion components such as chloride ions due to the generation of acidic components
000 ppm remain. The anion component decreases when the calcination temperature is increased. However, when the calcination temperature is increased, the aggregation of the powder is promoted and a very hard zirconia powder is obtained. Further, by performing water washing after calcination, the anion component can be reduced, but it cannot be sufficiently reduced. In addition, when washing is performed, elution of metal salts in unreacted substances also occurs.

[0004] In the production method, unreacted substances or coexisting salts are removed using an ultrafiltration membrane while circulating pure water before calcination. Is low. It is also difficult to completely remove unreacted substances adhering to the surface of the zirconia sol. In addition, the surface pH of the zirconia sol is low, and the zirconia sol is concentrated by dehydration and heating after filtration. As the pH further decreases, the hydroxide dissolves to form a water-soluble salt. And part of the salt remains in the zirconia powder after calcination as salt.

In any case, in the method for producing zirconia powder by the above method, it is difficult to prevent zirconium and a metal element to be a stabilizing agent from being eluted in the form of a salt, thereby reducing anionic components of impurities. The sintered body obtained by molding using the zirconia powder according to these production methods does not have sufficiently satisfactory characteristics.

The present invention solves such a problem, that is, when zirconium or a stabilizer is contained from zirconia powder obtained by a hydrolysis method, anionic impurities are removed without eluting the metal element and sintering is performed. An object of the present invention is to provide a method for producing zirconia powder having excellent body characteristics.

[0007]

According to the present invention, a hydrated zirconia sol obtained by hydrolysis of a water-soluble zirconium compound is dried, calcined, and the calcined powder obtained is washed with an aqueous alkali solution. A method for producing a zirconia powder comprising:

Hereinafter, the present invention will be described in more detail.

As the water-soluble zirconium compound used in the present invention, zirconium oxychloride, zirconium nitrate, zirconium chloride, zirconium sulfate and the like are used, but generally zirconium oxychloride is mainly used. These concentrations are not particularly limited, but are suitably 0.1 to 1 mol / l from the relationship between the reaction time and the reaction rate. In the case of producing a zirconia powder containing a stabilizer, Mg, Ca, a salt of a metal having a valency of 3, etc. is hydrolyzed together with water-soluble zirconium, and then supplied to a hydrated zirconia sol slurry or the like. I just need. Hydrolysis may be performed by a known method,
Usually, the heating is performed at a boiling point or near the boiling point for 3 to 6 days.

An organic solvent such as acetone or octanol is added to the hydrated zirconia sol obtained by hydrolysis with or without addition, and the mixture is heated or concentrated under reduced pressure.
Gel powder can be obtained by drying with a spray dryer or the like.

Next, the obtained gel powder is supplied to a calciner.

The calcination conditions are not particularly limited, and general conditions may be applied. Usually 700-1200
The calcination is performed at ℃ for several hours. If the calcination temperature is high, the residual ratio of unreacted substances decreases and the anion component of impurities can be reduced, but aggregation is promoted. Increase and the yield as an oxide tends to decrease.
It is desirable that the temperature be 1100 ° C.

The gist of the present invention is that the anion component of impurities is reduced by washing the powder obtained by calcining with an alkaline aqueous solution, and the elution of zirconium and metal elements constituting the stabilizer is prevented. It is in.

After calcination and washing with water, the remaining zirconium and the salt of the metal element constituting the stabilizer are eluted. However, by making the washing water alkaline, the zirconium and the metal element constituting the stabilizer of the above salt become water. Elution is prevented because the oxides become oxides and are stabilized, and the anionic components of impurities are washed and reduced.

[0015] The slurry concentration at the time of cleaning can be any concentration.

The alkaline aqueous solution used for washing is not particularly limited as long as it exhibits alkali in the state of an aqueous solution.
Alkali hydroxide such as OH and NH ₄ OH and urea are applied. However, it is preferable to use ammonia water from the viewpoint of suppressing the mixing of alkali metals and the reaction rate.

The concentration of the aqueous alkali solution at the time of washing is adjusted so that the pH of the zirconia slurry is 8.0 to 13.0, particularly 9.0 to 13.0.
It is better to adjust to 12.0.

If the pH is less than 8.0, the anion component of impurities is insufficiently reduced. Further, it is difficult to completely suppress the elution of the metal element. On the other hand, pH 1
If it exceeds 3.0, zirconium may elute as an anion.

The washing temperature is not particularly limited. However, when the temperature is increased, the dissolution concentration of the hydroxide is higher than the solubility equilibrium constant. Usually, it is desirable to carry out at normal temperature in consideration of operability. In addition, the time and frequency of washing should be set so that the anion component in the zirconia powder reaches a steady value.However, if stirring is performed, a relatively short time is used, and if stirring is not performed, the time is extended somewhat. In the case of the batch type, the above-mentioned steady value can be obtained by setting the number of times to 1 to 3 times, and in the case of the continuous type, setting to 1 to 3 steps.

After the zirconia powder thus obtained is washed with water, it is pulverized to a desired particle size distribution by using a general pulverizer, for example, a ball mill, a par mill or the like. It is dried by using a machine, for example, a spray dryer.

[0021]

[Function] By washing the powder obtained by calcination with an aqueous alkaline solution, the remaining unreacted metal element of the raw material zirconium salt and the stabilizer precursor in hydrolysis and calcination is converted to hydroxide. It is considered that it is stabilized and no longer eluted.

[0022]

According to the present invention, when zirconium and a stabilizing agent are contained from zirconia powder obtained by a hydrolysis method, anionic impurities are removed without eluting the metal element, thereby improving the characteristics of the sintered body. Zirconia powder can be produced.

[0023]

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

Example 1 A 0.4 mol / l aqueous solution of zirconium oxychloride was mixed with Y
Yttrium oxide was added so that the molar ratio in terms of ₂ O ₃ / ZrO _{2 was} 3/97, and hydrolysis was performed at the boiling temperature for 120 hours to synthesize a hydrated zirconia sol slurry. Octanol was added to the hydrated zirconia sol slurry, concentrated by heating with steam, spray-dried with a spray dryer, and then calcined at 950 ° C. for 2 hours.

After the calcined powder is made into a 60 wt% slurry with pure water, 1 mol / l ammonia water is added at room temperature and under stirring to adjust the slurry pH to about 10, and the slurry is adjusted to about 1%.
After an hour, the slurry was filtered, and then washed with water.

The calcination after the powder and after the ammonia washing powder Cl was analyzed. ^{_{- (ppm) Y 2 O 3}} (wt%) calcined powder 2000 5.30 ammonia washing powder 150 5.30 (Analysis Cl ^-: AAS, Y: an X-ray fluorescence), Cl ^- is was not observed elution of metal components of reduced stabilizer.

Next, the filtered powder was pulverized using a general par mill to obtain a zirconia powder having a BET specific surface area of 19 m ² / g and an average particle diameter of 0.64 μm. 35mm ×
After performing uniaxial press molding under a pressure of 1 Ton / cm ^{2 in} a 45 mm square mold, sintering was performed at 1400 ° C. for 2 hours. As a result, the sintered body density was 6.07. flexural strength ranged 110~130kgf / mm ^2.

Example 2 Y was added to a 0.6 mol / l aqueous solution of zirconium oxychloride.
Yttrium oxide was added so that the molar ratio in terms of ₂ O ₃ / ZrO _{2 was} 3/97, and hydrolysis was performed at the boiling temperature for 130 hours to synthesize a hydrated zirconia sol. It was calcined for 2 hours.

After this calcined powder was made into a 50 wt% slurry with pure water, 2 mol / l aqueous ammonia was added at room temperature and under stirring to adjust the slurry pH to about 9.0, and about 1 hour. Thereafter, the slurry was filtered, and this operation of adding and filtering ammonia was repeated three times, followed by washing with water.

[0030] Cl was analyzed of the powder after the powder and ammonia water washing after calcination ^{_{- (ppm) Y 2 O 3}} (wt%) calcined powder 7000 5.19 ammonia washing powder 190 5.19 (Analysis Cl ⁻ : atomic absorption spectrometry, Y: fluorescent X-ray), Cl was reduced and no metal component of the stabilizer was eluted.

Next, the filtered powder was pulverized using a general ball mill to obtain a zirconia powder having a BET specific surface area of 15 m ² / g and an average particle diameter of 0.83 μm. 35mm ×
After performing uniaxial press molding under a pressure of 1 Ton / cm ^{2 in} a 45 mm square mold, sintering was performed at 1500 ° C. for 2 hours. As a result, the sintered body density was 6.06. The bending strength was 105 to 130 kgf / mm ² .

Comparative Example 1 The calcined zirconia powder obtained by the hydrolysis method of Example 1 was washed five times with pure water four times the weight of the powder. The slurry pH at the time of the last washing with water was 6.5.

The slurry for each washing - is filtered using an ultrafiltration membrane, it was subjected to analysis of the filtrate _{^{Cl - (ppm) Y 2 O}} 3 (wt%) water washing first 254 179 rinsing second 86 59 washing Third time 48 30 Washing 4th time 27 19 Washing time 5 23 As in the case of 23 15, Cl ⁻ decreased, but Y ³⁺ eluted simultaneously. Cl The analyzes of the powder after washing was compared with the powder after calcination ^{_{- (ppm) Y 2 O 3}} (wt%) a calcined powder 2000 5.30 washing powder 760 5.13, Cl ^- of The residual concentration was high, and Y ₂ O ₃ was reduced by elution.

Next, the filtered powder was pulverized under the same conditions using the same pulverizer as in Example 1 to obtain a powder having substantially the same specific surface area and average particle diameter as in Example 1.

Using this powder, uniaxial press molding was performed in a 35 mm × 45 mm square mold at a pressure of 1 Ton / cm ² , followed by sintering at 1400 ° C. for 2 hours. 6.01, and the bending strength of the sintered body is 70 to
It was 90 kgf / mm ² .

Comparative Example 2 A 0.8 mol / l aqueous solution of zirconium oxychloride was hydrolyzed at the boiling temperature for 130 hours to synthesize a hydrated zirconia sol, and an ultrafiltration membrane UF-3 manufactured by Tosoh Corporation was produced.
000 was used for filtration. This sol has Y ₂ O ₃ / Zr
After adding yttrium hydroxide so that the molar ratio in terms of O _{2 was} 3/97, a calcined powder was obtained in the same manner as in Example 1. Cl of the calcined powder ^- was about 1000ppm was analyzed for.

Using this calcined powder, pulverization, molding and sintering were performed under the same conditions as in Example 1. The sintered body density was 6.03 and the bending strength of the sintered body was 95 to 100 kg.
f / mm ² .

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C01G 25/00-47/00 WPI (DIALOG)

Claims (1)

(57) [Claims] 1. A method for producing zirconia powder, characterized in that a hydrated zirconia sol obtained by hydrolysis of a water-soluble zirconium compound is dried and calcined, and the calcined powder obtained is washed with an aqueous alkali solution. Method.