JPH0232216B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing ultrafine zirconia powder, which is attracting attention as a raw material for high-strength, high-toughness ceramics.

[Prior art and its problems]

Zirconia has a high melting point and excellent corrosion resistance, so it has been widely used as a refractory material for steel manufacturing.In addition, in recent years, high-strength, high-toughness zirconia with new properties has been developed, and it will continue to be used extensively in the future. It is expected to become one of the evolving engineering ceramics.

As is well known, in order to obtain high-strength, high-toughness zirconia, it is important to accurately control the microstructure of zirconia ceramics. Ultrafine powder is required.

Therefore, much research has been conducted into the production of zirconia-based ultrafine powder, and so far there have been methods for mechanically refining zirconia powder and methods for adding ammonia etc. to a solution containing zirconium salts and metal salts. Methods such as obtaining a precipitate and calcining it are being considered.

However, the former method is limited to fine powder on the micron order, so it is not possible to produce a dense sintered body, and to obtain a sintered body, the particles must be fired at 1700°C to 1800°C. The problem is that it has to be done.

Moreover, the latter method not only requires time to obtain crystal particles, but also has the disadvantage that the obtained crystal particles are amorphous and must be calcined at about 1000° C. for crystallization.

Moreover, these methods have problems such as contamination of impurities, uneven particle size, wide particle size distribution, and failure to prevent agglomeration.

[Means for solving problems]

Therefore, as a result of various experimental studies, the present inventors have discovered that a zirconium salt aqueous solution or a zirconium salt and a desired metal salt, such as magnesium, calcium, yttrium, etc., which exhibit high toughness or stabilize the metal salt, have been developed. Unlike conventional methods, urea, which generates ammonia through a hydrothermal reaction, is added to the aqueous solution containing urea, which is then autoclaved to produce ultrafine zirconia powder with a uniform particle size without agglomeration. This method was successful. Instead of allowing the reaction to proceed slowly as in conventional methods, this method uses a nitrogen compound that generates ammonia through a hydrothermal reaction, and the reaction is rapid through autoclave treatment, resulting in good crystallinity. Zirconia-based fine powder can be synthesized at a relatively low temperature and in a short time, making it possible to reduce manufacturing costs, and its industrial value is extremely large.

[Effect]

The following is an explanation of the effect when an aqueous solution of zirconium oxychloride is used as a starting material and urea, which generates ammonia through a hydrothermal reaction, is used.

CO(NH ₂ ) ₂ +H ₂ O -----→ Heating 2NH ₃ +CO ₂ ↑ 2NH ₃ +2H ₂ O 2NH ⁺ ₄ +2OH ^- ZrOCI ₂ +2NH ⁺ ₄ +2OH --------→ Neutralization reaction ZrO(OH) ₂ ＋2NH ⁺ ＋2Cl ^- ZrO(OH) ₂ ――――――→ Crystallized ZrO ₂ ＋H ₂ O As the temperature increases in the autoclave, urea
Pyrolyzes into ammonia and carbon dioxide. Next, the ammonia neutralizes the zirconium oxychloride to produce hydrous zirconia (zirconium hydroxide), which is further dehydrated and crystallized by continued heating to become crystalline zirconia fine particles. Since this series of reactions occurs continuously through autoclave treatment, the number of steps and treatment time are significantly reduced.

Furthermore, since the autoclave treatment is carried out in a closed container as is well known, the generated ammonia does not scatter, so that the effect as a precipitant is not weakened unlike in conventional methods.

〔Example〕

Example 1 322g of zirconium oxychloride in 1000ml of pure water
Add 70g of urea to the solution containing and dissolve it to make a raw material solution for synthesis, and add 750ml of this raw material solution for synthesis,
Autoclave treatment was carried out under the following conditions using an autoclave treatment apparatus (high temperature and high pressure container) with an internal volume of 1000 ml.

Autoclave treatment conditions Filling rate: 75% Temperature: 250℃ Treatment time: 12 hours The precipitate formed by the above treatment was repeatedly dehydrated and washed with water using a centrifuge and ultrasonic dispersion machine, and then the water was replaced with ethanol. The mixture was dried at 120° C. for 12 hours to obtain 75 g of zirconia fine powder.

According to X-ray diffraction, the powder thus obtained is monoclinic zirconia with very good crystallinity, as shown in Figure 1, and the average crystallite diameter measured by the Schierer method is extremely fine, 8 nm. It was hot.

Furthermore, observation using a transmission electron microscope confirmed that the particle size was uniform and there was little aggregation.

Example 2 307g of zirconium oxychloride in 1000ml of pure water
and 70 g of urea in an aqueous solution containing 18 g of yttrium chloride.
was added and dissolved to prepare a raw material solution for synthesis, which was autoclaved in an autoclave processing apparatus under the following conditions.

Autoclave treatment conditions Filling rate: 80% Temperature: 200°C Treatment time: 24 hours The precipitate formed by the above treatment was collected in the same manner as in Example 1 to obtain 73 g of zirconia fine powder containing 3 mol% of ittria as a solid solution. . The obtained powder was cubic zirconia with good crystallinity, had an extremely fine average crystallite size of 10 nm, had a uniform particle size, and had little agglomeration.

After uniaxially molding this powder at a molding pressure of 1 ton/ ^cm2 ,
When sintered at 1500°C for 2 hours, a dense sintered body was obtained, sintered to 98% of the theoretical density.

In addition, electron microscopic observation of the fractured surface of the sintered body revealed that the average particle size was as fine as 0.3 μm, and the particle sizes were uniform, and the X-ray diffraction results confirmed that it was composed only of a square solid solution.

The powder obtained in Example 1 was mainly composed of monoclinic solid solution, and the powder obtained in Example 2 was composed only of cubic solid solution, but the powder obtained by autoclaving was By calcining the fine powder obtained using a known method, a monoclinic type can be easily obtained from the powder shown in Example 1, and a square type can be easily obtained from the peach shown in Example 2. . This is the second invention.

〔Effect of the invention〕

As is well known, the conventional method of mechanically refining zirconia powder can only yield particles with a particle size on the micron order, so when sintering, the temperature is 1700℃ to 1800℃.
It is necessary to sinter at a temperature of 80 °C and the density of the sintered body is 80 °C.
Only about % was obtained.

However, according to the present invention, n
Since ultrafine powder on the order of m can be obtained, sintering can be performed at lower temperatures than conventional methods (1400℃ to 1500℃), and the density of the sintered body can be lowered to the theoretical density.
Since the improvement can be made up to 98%, there is an effect that a sintered body that is superior to that extent can be provided.

In addition, compared to the method of adding ammonia etc. to a solution containing zirconium salts and metal salts to obtain a coprecipitate and calcining it, this method requires no calcining and requires only one step of autoclaving, which takes much less time. There is an effect that the target product can be obtained.

Furthermore, the zirconia fine powder according to the present invention has good sinterability because it is fine, non-agglomerated, and has a uniform particle size, so it can be used not only as a raw material for high-strength, high-toughness zirconia ceramics, but also for zirconia toughness-enhanced ceramics and oxygen sensors. A product that can be widely applied to raw material powders, etc. can be obtained.

[Brief explanation of drawings]

FIG. 1 is an X-ray diffraction diagram of the crystalline powder obtained in Example 1.

Claims (1)

[Scope of Claims] 1. A method for producing ultrafine zirconia powder, which comprises adding urea to an aqueous zirconium salt solution or an aqueous solution containing a zirconium salt and a desired metal salt, and autoclaving the solution. 2. A method for producing fine zirconia powder, which comprises adding urea to an aqueous zirconium salt solution or an aqueous solution containing a zirconium salt and a desired metal salt, autoclaving the solution, dehydrating and drying it, and calcining it.