JPH06171945A - Production of zirconia powder - Google Patents

Abstract

PURPOSE:To obtain zirconia powder giving a sintered compact excellent in characteristics by removing anionic impurities from zirconia powder obtd. by hydrolysis without causing elution of metallic elements in the case where the powder contains zirconium and a stabilizing agent. CONSTITUTION:A zirconia hydrate sol obtd. by hydrolyzing a water-soluble zirconium compd. is dried and calcined and the resulting calcined powder is washed with an aq. alkali soln. to produce the objective zirconia powder.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention removes anionic impurities from zirconia powder obtained by a hydrolysis method,
The present invention relates to a method for producing a zirconia powder having excellent properties of a sintered body.

[0002]

2. Description of the Related Art As a general method for producing zirconia powder by hydrolysis, a water-soluble zirconium salt alone or an aqueous solution containing Ca, Mg or a metal salt having a valence of 3 or more is obtained by hydrolysis. An organic solvent is added to the hydrated zirconia sol, the mixture is heated and distilled to be dried, and then the dried powder is calcined to obtain fine zirconia powder (JP-B-59-39).
366) Hydrolyzing unreacted substances, ungrown zirconium hydroxide and zirconia hydrate, and coexisting salts and the like, and then filtering and washing with an ultrafiltration membrane to obtain a hydrated zirconia sol. A method of adding a hydroxide of a metal selected from lanthanide series elements such as Ca, Mg, Y, or Ce and performing a dehydration heat treatment (JP-A-63-185821) is known.

[0003]

However, in the zirconia powder obtained by the above production method, the water-soluble zirconium salt as a raw material and the unreacted metal salt which becomes a stabilizer by firing and by-products during calcination are used. The number of anion components, such as chloride ions, generated by the generation of acidic components
000 ppm remains. This anion component is reduced when the calcination temperature is raised, but when the calcination temperature is raised, agglomeration of the powder is promoted and a very hard zirconia powder is obtained. Further, washing with water after calcination can reduce the anion component, but cannot sufficiently reduce it. Moreover, when washing is performed with water, the metal salt in the unreacted material is eluted at the same time.

In the production method (1), unreacted substances or coexisting salts are removed by using an ultrafiltration membrane while circulating pure water before the calcination. However, the method using the ultrafiltration membrane is productive. Is low. Further, it is difficult to completely remove the unreacted material attached to the surface of the zirconia sol. Moreover, since the surface pH of the zirconia sol is low and it is concentrated by being dehydrated and heated after filtration, the pH is further lowered, and the hydroxide is dissolved to form a water-soluble salt. And some of the salt remains in the zirconia powder even after calcination.

In any case, in the method for producing zirconia powder by the above-mentioned method, it is difficult to prevent zirconium or a metal element serving as a stabilizer from being eluted in the form of a salt and reduce the anion component of impurities. Therefore, the sintered body obtained by molding using the zirconia powder by these manufacturing methods does not have sufficiently satisfactory characteristics.

The present invention solves such problems, that is, when zirconium powder obtained by the hydrolysis method contains zirconium or a stabilizer, it removes anionic impurities without elution of the metal element and sinters them. An object of the present invention is to provide a method for producing a zirconia powder having excellent body properties.

[0007]

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

The present invention will be described in more detail below.

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 applied. The concentration of these is not particularly limited, but it is suitable to be 0.1 to 1 mol / l in view of the relationship between the reaction time and the reaction rate. Further, in the case of producing a zirconia powder containing a stabilizer, Mg, Ca, a salt such as a metal having a trivalent valence is hydrolyzed with water-soluble zirconium and then supplied to a hydrated zirconia sol slurry or the like. Good. The hydrolysis may be carried out by a known method,
Usually, the heating is performed for 3 to 6 days under the boiling point or a state close to the boiling point.

The hydrated zirconia sol obtained by hydrolysis is heated or concentrated under reduced pressure with or without addition of an organic solvent such as acetone or octanole.
Gel powder can be obtained by drying with a spray dryer or the like.

Next, the gel powder obtained is supplied to a calcining furnace.

The calcination conditions are not particularly limited, and general conditions may be applied. Usually 700-1200
Calcination is carried out at ℃ for several hours, but if the calcination temperature is high, the residual rate of unreacted materials decreases and the anion component of impurities can be reduced, but aggregation is promoted. Tends to decrease, and the yield as an oxide tends to decrease.
It is desirable to set the temperature to 1100 ° C.

The main point of the present invention is to reduce the anion component of impurities by washing the powder obtained by the calcination with an alkaline aqueous solution, and to prevent the elution of zirconium and metal elements constituting the stabilizer. Especially.

After calcination, washing with water causes elution of the remaining zirconium and the salt of the metal component of the stabilizer, but by making the washing water alkaline, the zirconium of the salt and the metal element of the stabilizer are dissolved in water. Since it becomes an oxide and is stabilized, elution is prevented, and the anion component of impurities is washed and reduced.

The slurry concentration at the time of washing can be any concentration.

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

The concentration of the alkaline aqueous solution at the time of washing is such that the pH of the zirconia slurry is 8.0 to 13.0, especially 9.0.
It is better to adjust it to 12.0.

If the pH is less than 8.0, the reduction of the anion component of impurities will be insufficient. Moreover, it is difficult to completely suppress the elution of the metal element. On the other hand, the pH is 1
If it exceeds 3.0, zirconium may be eluted as an anion.

The temperature for washing is not particularly limited, but when the temperature is increased, the dissolution concentration of the hydroxide tends to be higher than the equilibrium constant of solubility, and elution is suppressed at lower temperatures. Usually, it is desirable to perform at room temperature in consideration of operability. In addition, the time and number of washings should be set so that the anion component in the zirconia powder reaches a steady value, but if stirring is performed, the time is relatively short, and if not stirring, the time is extended somewhat. The above steady value is obtained by setting the number of times to 1 to 3 in the case of the batch type and 1 to 3 steps in the case of the continuous type.

The zirconia powder thus obtained is washed with water, then pulverized to a desired particle size distribution by using a general pulverizer such as a ball mill and a pal mill, and then generally dried. 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 metal elements of the unreacted residual zirconium salt as a raw material and the stabilizer precursor during hydrolysis and calcination are converted to hydroxides. It is considered that the solution is stabilized and is no longer eluted.

[0022]

According to the present invention, when zirconia powder obtained by the hydrolysis method contains zirconium and a stabilizer, anionic impurities are removed without elution of the metal element and the sintered body has excellent characteristics. Zirconia powder can be produced.

[0023]

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

Example 1 Y was added to a 0.4 mol / l zirconium oxychloride aqueous solution.
Yttrium oxide was added so that the molar ratio converted to 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 this hydrated zirconia sol slurry, the mixture was heated and concentrated by a steam, spray-dried by a spray dryer, and then calcined at 950 ° C. for 2 hours.

This calcined powder was made into a 60 wt% slurry with pure water, and 1 mol / l of ammonia water was added at room temperature with stirring to adjust the slurry pH to about 10 and to about 1
After the lapse of time, the slurry was filtered, followed by washing with water.

When the powder after calcination and the powder after washing with ammonia were analyzed, Cl ⁻ (ppm) Y ₂ O ₃ (wt%) calcined powder 2000 5.30 ammonia washed powder 150 5.30 (analytical method) Cl ⁻ : atomic absorption method, Y: fluorescent X-ray), and Cl ⁻ was reduced, and elution of the metal component of the stabilizer was not observed.

Next, the filtered powder was pulverized by using a general pearl 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. 35 mm x with this powder
After performing uniaxial press molding at a pressure of 1 Ton / cm ^{2 with} a 45 mm square die, sintering was performed at 1400 ° C. for 2 hours, and the sintered body density was 6.07. The bending strength was in the range of 110 to 130 kgf / mm ² .

Example 2 Y was added to a 0.6 mol / l zirconium oxychloride aqueous solution.
Yttrium oxide was added so that the molar ratio converted to 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, which was concentrated and dried, and then at 840 ° C. It was calcined for 2 hours.

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

When the powder after calcination and the powder after washing with ammonia were analyzed, Cl ⁻ (ppm) Y ₂ O ₃ (wt%) calcined powder 7000 5.19 ammonia washed powder 190 5.19 (analytical method) Cl ⁻ : atomic absorption method, Y: fluorescent X-ray), and Cl was reduced, and elution of the metal component of the stabilizer was not observed.

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. 35 mm x with this powder
After performing uniaxial press molding with a pressure of 1 Ton / cm ^{2 using} a 45 mm square die, sintering was performed at 1500 ° C. for 2 hours, and the density of the sintered body 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 used, and the zirconia powder was washed 5 times with 4 times the weight of the pure water. The slurry pH at the last washing with water at this time was 6.5.

The slurry after each washing with water was filtered using an ultrafiltration membrane and the filtrate was analyzed. Cl ⁻ (ppm) Y ₂ O ₃ (wt%) First washing with water 254 179 Second washing with water 86 59 Washing with water As in the case of the 3rd washing with 48 30 water, the 4th washing with 27 19 the 5th washing with water 23 15, the Cl ⁻ decreased, but Y ³⁺ was eluted at the same time. 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 decreased by elution.

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

Using this powder, uniaxial press molding was performed at a pressure of 1 Ton / cm ^{2 in} a square die of 35 mm × 45 mm, and then sintering was performed at 1400 ° C. for 2 hours. The bending strength of the sintered body was 6.01.
It was 90 kgf / mm ² .

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

When this calcinated powder was pulverized, molded and sintered under the same conditions as in Example 1, the density of the sintered body was 6.03 and the bending strength of the sintered body was 95 to 100 kg.
It was f / mm ² .

Claims (1)

[Claims] 1. A method for producing a 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 alkaline aqueous solution. Method.