JPS6096528A - Preparation of fine powder of zirconia - Google Patents

Abstract

PURPOSE:To obtain fine powder of zirconia with uniform particle size, by adding an aqueous solution of water-soluble zirconium to an alkali solution adjusted to a proper pH with carrying out pH adjustment, followed by separating, drying, and calcining precipitate. CONSTITUTION:>=40g/l calculated as ZrO2 of an aqueous solution of soluble zirconium salt such as ZrOCl2, etc. is added to an alkali solution adjusted to 9.5-13pH. In the operation, pH adjustment is carried out in such a way that pH during the reaction is kept in 9.5-13. If necessary, in order to maintain the pH range, a soluble sulfate in an amount to make a molar ratio of SO4<-2>/calculated ZrO2 of >=0.3 is added to the reaction system. The prepared precipitate is separated, dried, and calcined at >=600 deg.C. By this method, fine powder of zirconia having uniformity, preferably <= about 1mu average particle diameter, partially stabilized zirconia powder, or stabilized zirconia powder is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing fine zirconia powder and a method for producing stabilized or partially stabilized fine zirconia powder.

In the recent field of fine ceramics.

Zirconia 1fJ1 Partially stabilized zirconia powder or stabilized zirconia powder is particularly important in terms of its heat resistance properties. Zirconia powder is zirconium oxide (ZrO2
) and is an excellent heat-resistant material. In addition, partially stabilized and stabilized zirconia powder is not composed of a single component of ZrO2, but also contains Cab, Cab, etc. as stabilizers.
MgO, Y203, rare earth element oxides, etc.
It is a powder containing a few percent to more than ten percent of zirconia powder, and those containing less stabilizer are generally called partially stabilized, and those containing more stabilizer are generally called stabilized zirconia powder.

Partially stabilized zirconia powder is shaped and fired to become a sintered body mainly composed of tetragonal crystals, but if the powder particle size is large and the concentration of the stabilizing agent is not appropriate, a phase transition will occur during the cooling process to room temperature. Cracking occurs at a volumetric expansion of 4-5%. However, in a sufficiently fine powder containing an appropriate amount of stabilizer, the transition energy from tetragonal to monoclinic is stored internally.
A sintered body with high strength and high toughness can be obtained. Application of this to superhard materials is currently being considered.

The stabilized zirconia powder can be made into a cubic crystal sintered body without phase transition by blending a large amount of stabilizer. Since it has oxygen ion conductivity, it is used as an oxygen sensor.

This zirconia powder is a partially stabilized zirconia powder.

All stabilized zirconia powders have uniform fine powder,
Preferably, it is a fine powder with an average particle size of 1 μm or less as measured by an air permeation method. One of the objectives of the present invention is to achieve this.

Partially stabilized zirconia powder and stabilized zirconia powder are in the form of a uniform fine powder as described above.
It is desirable that the degree of mixing of the stabilizer and ZrO2 be uniform. That is, the degree of uniform mixing of the stabilizer and zirconia powder greatly influences the success or failure of subsequent sintering. If the degree of uniformity is insufficient, the treatment time at high temperatures and the temperature will increase, resulting in increased two-grain growth and a decrease in strength compared to a homogeneous mixture. Therefore.

It is desirable that the stabilizer and zirconia are uniformly mixed in a fine powder state. One of the aims of the invention is to achieve this.

The inventors of the present invention have repeatedly conducted various tests and researches, and as a result, have developed a zirconia fine powder that effectively achieves the above objectives.

We were able to establish a method for producing partially stabilized or stabilized zirconia fine powder. That is, the present invention is as follows.

As a method for producing zirconia fine powder (Zr02 single component).

The pII value in one reaction of an aqueous solution in which a soluble zirconium salt is dissolved in an alkaline solution of pn 9.5 to 13 at a concentration of 40 g/j1 or more in terms of ZrO2 is 9.5 to 13.
A method for producing fine zirconia powder (first invention), which comprises adding the zirconia fine powder while adjusting the pH to maintain it in the range of 13, separating and drying the obtained precipitate, and then roasting it at a temperature exceeding 600 ° C. and.

An aqueous solution in which a soluble zirconium salt is dissolved in an acid or alkaline solution with a pH of 2 to 13 at a concentration of 40 g/β or more in terms of ZrO2 + soluble sulfuric acid in an amount such that the molar ratio of 502/converted ZrO2 is 0.3 or more. In the presence of salt, it is added while adjusting the pH so that the pH value during one reaction is maintained in the range of 9.5 to 13, and the resulting precipitate is separated and dried, and then roasted at a temperature exceeding 600 ° C. A method for producing fine zirconia powder (second invention) is provided.

And as a method for producing nine-part stabilized zirconia fine powder or stabilized zirconia fine powder.

Add 40 g/j of soluble zirconium salt in terms of ZrO2 to an alkaline solution with pi 9.5 to 13! An aqueous solution containing an appropriate amount of a soluble salt of a zirconia stabilizing substance commonly used as a zirconia stabilizing agent dissolved in the above solution was adjusted to pH so that the pfl value was maintained in the range of 9.5 to 13 during the 2 reactions. A method for producing fine zirconia powder (third invention), which comprises adding the precipitate while separating and drying the resulting precipitate, and then roasting it at a temperature exceeding 600°C.

502/ The pH value in one reaction is 7 to 13 in the presence of an amount of soluble sulfate such that the molar ratio of converted ZrO2 is 0.3 or more.
The precipitate was separated and dried.

The present invention provides a method for producing fine zirconia powder (fourth invention), which comprises roasting at a temperature exceeding 600°C.

The present invention will be explained in detail below.

In the present invention, first, an aqueous solution in which a soluble zirconium salt such as zirconium oxychloride or zirconium oxynitrate is dissolved, or an aqueous solution in which an appropriate amount of a soluble salt of a stabilizer such as a chloride of calcium, magnesium, yttrium, F4FF earth metal, etc. is added is added. Therefore, a precipitate is generated through a neutralization operation.

First, the zirconium concentration in this aqueous solution.

40g/7 in terms of ZrO2! Must be above.

Second, the neutralization operation involves preparing an alkaline solution maintained at the pH value specified in each invention (an acidic solution may be used in the fourth invention), and adding the zirconium-containing solution to this pH 1N solution. and do it.

Thirdly, when the zirconium-containing liquid is added to this pH adjustment liquid, the pi of the mixed liquid reaches the pH specified in each invention.
It is fundamentally important to adjust the pH and H of the mixture so that the values are maintained strictly.

Only when these three requirements are complied with, it is possible to prevent adhesion or agglomeration of particles to each other during the subsequent roasting process and obtain a uniform fine powder with a desired particle size or less. In other words, this is thought to be because this neutralization operation generates hydroxides that are virtually resistant to adhesion of H2° and 0', which are factors that cause particles to adhere to each other during roasting. The powdered product after baking becomes an extremely fine powder.

FIG. 1 is a diagram for explaining this neutralization operation. 1 is a neutralization tank, and pH adjustment liquid 2 is prepared in this neutralization tank 1. Then, for this pH adjustment liquid 2, 7. Zr021
! 40g/j in 1! Zirconium-containing liquid 3 having the above concentration is added. Even with this addition, the PL of the mixed solution is maintained strictly at a predetermined pH value.
pH adjustment is carried out by addition of an alkaline solution 4 (eg NH40H solution). This is because the f79 from the p11 electrode is sent to the DH controller 6, and a.

This can be easily done by outputting an on/off control signal to the supply pump 7 for the lukewarm solution.

It is preferable that the neutralization tank 1 is set in a constant temperature tank 8 through which external heat is input and output to keep the reaction temperature constant, and the liquid is stirred by a stirring impeller 9.

In this way, pH! It is important to add the zirconium-containing liquid 3 of both liquids 2 to the II liquid adjustment 2 and adjust the pi.On the contrary, in a neutralization operation in which an alkali is added to the zirconium-containing liquid to adjust the pHm. The purpose of the invention cannot be achieved.

In particular, said neutralization operation according to this invention.

In the method for producing partially stabilized or stabilized zirconia fine powder of the third and fourth inventions, there are two important meanings in coprecipitating the stabilizing substance. In other words, zirconium and stabilizing elements.

Since the precipitate-forming pH range is significantly different, it is difficult to simultaneously obtain a precipitate from the mixed solution when a conventional neutralization method is followed. The conventional coprecipitation method is carried out by adding an alkali to an acidic solution, and in the process of changing pi due to the addition of the alkali, the precipitate formation pH changes.
Hydroxides are produced one after another, and some of the elements are also co-precipitated, but the result is fractional precipitation. However.

According to the neutralization operation according to the present invention, which complies with the above three requirements, a complete coprecipitate can be obtained.

The effects of adopting the three requirements mentioned above will be specifically shown in Examples below, but to give an overview, first, the zirconium concentration of the first zirconium-containing liquid is
Setting the O2 equivalent to 40 g/It or more is particularly important in the first and third inventions in order to make the final roasted product powder a fine powder of 1 μ or less as measured by the air permeation method. This is desirable in the invention and the fourth invention. ZrO
40g/2, if a lower concentration solution is used.

Even if the other conditions of the invention are met, 112
This is thought to be caused by the inclusion of 0 and 011-, but the particle size increases during roasting, making it impossible to form a fine powder of 1 μm or less.

Further, in the first invention and the third invention, it is necessary to strictly adjust the pH value of the p11 adjustment liquid and the reaction liquid to a certain value in the range of 9.5 to 13. Even within this pH range, if the pH value fluctuates, powder tends to have a relatively wide particle size distribution.

When the pH is lower than 9.5, the average particle size increases in the first invention (Example 2), and the bulk density, specific surface area,
This is not preferable since the average particle diameter becomes large in both cases (comparative example of Example 5).

However, when a sulfate is present as in the second invention and the fourth invention, this pH range can be relaxed, with the second invention having a pH value of 2 to 13, and the fourth invention having a pH value of 7 to 13. Good to have. The presence of this soluble sulfate makes it possible to obtain finer powders with lower bulk density (Example 5.6).
and 7). When this sulfate coexists, a fine powder can be obtained regardless of whether the pH value is set to the lower or higher end of the above range, and the bulk density can be low.

However, in the case of the fourth invention, if the pH is low, the sulfuric acid groups will not be easily incorporated into the sediment, and sulfuric acid gas will be generated during roasting, so it is easier to handle if the pH is 6 or higher. When this sulfate is allowed to coexist, the influence of the zirconium concentration of the zirconium-containing liquid on the particle size and bulk density of the final roasted powder is alleviated, so the concentration of the zirconium-containing liquid does not necessarily have to be 40 g/It in terms of ZrO2. Although the purpose of the present invention can be almost achieved without the above,
It can be said that it is more desirable to set it to /it or more. In order to obtain such an effect of sulfate addition, its concentration must be determined by the molar ratio of the sulfate radical concentration to the converted ZrO2, that is, sob/converted ZrO2.
It is desirable that the molar ratio of O2 is 0.3 or more.

Concentrations below this level are not very effective. During the neutralization operation, this sulfate is added to the pHfli solution (solution 2 in Figure 1).
), or may be added to the zirconium-containing solution (liquid 3 in Figure 1).

In any of the first to fourth inventions, the precipitate obtained by carrying out the neutralization treatment described above is separated from the liquid and dried, and then finally roasted at a temperature exceeding 600°C. Bake. However, if roasted at a temperature exceeding 1000°C, grain growth will occur and the characteristics of a fine powder will be lost, so it is preferable to roast at a temperature exceeding 600°C and below 1000°C. By roasting at this temperature, fine zirconia powder with a high percentage of tetragonal crystals can be obtained. Prior to this roasting at a temperature exceeding 600°C, a finer powder can be obtained by pre-roasting at a temperature of 400 to 50°C.

This is probably because crystallization of metastable tetragonal crystals occurs at around 400 to 500°C, producing fine nuclei, and these fine nuclei serve as base points for grain growth.

[
Peak height of tetragonal (111) plane] B; [Monoclinic (1
[Peak height of monoclinic (111) plane] C: [Peak height of monoclinic (111) plane] is an indicator of the uniformity of mixing with the 9th order chemotactic agent. In other words, for the powder in the one-part stabilization region, zirconia exhibits monoclinic crystals in areas where the degree of mixing with the stabilizer is insufficient or in areas where there is no stabilizer, and in areas where it is sufficiently mixed. Well, since it shows a tetragonal crystal, this is close to 100%.

Indicates that the degree of mixing is uniform. In conventional commercially available products, this tetragonal crystal ratio is usually high (about 76%), whereas in the method of the present invention, it is 100% as shown in the following example.
You can get something close to.

Further, the specific surface area is a value measured by the BET method, and the average particle diameter is a value measured by an air permeation method.

Example 1 In the equipment shown in Fig. 1, Ni was used as the pi adjustment liquid 2 in the neutralization tank l.
14011, the pH of which was adjusted to 10.5, and ZrOCl2 as zirconium-containing liquid 3.8. H,0
The pH value of the mixed solution obtained by adding solution 3 to p11 adjustment solution 2 was maintained at 10.5 by using melting solution at each concentration in Table 1 (each ZrO2 equivalent concentration is also shown in Table 1). liquid 4
(NH4011 solution) alli! During the preparation, a precipitate was formed. The obtained precipitate was filtered from the liquid, dried, and then placed in a roasting furnace maintained at 700°C and roasted for 2 hours. The specific surface area and average particle size of the obtained zirconia powder are also listed in Table 1.

Table 1 From the results in Table 1, it was found that when the method of the present invention was followed, there was a clear correlation between the zirconium concentration of the zirconium-containing liquid and the average particle size of the final powder after roasting. The average particle size becomes finer as the grain size increases. To obtain fine powder of 1μ or less, the ZrO2 equivalent concentration of the zirconium-containing liquid is 40g/j! It is clear that the above is necessary.

Example 2 ZrOClz・8. HaO concentration to 400 g/j!
(153.0 g/β in terms of Zr02) and the pH conditions (pH of pH adjustment solution 2 and reaction mixture) were set as shown in Table 2. was carried out. The specific surface area and average particle size of the final powder obtained are also listed in Table 2.

From the results in Table 2, there is a clear correlation between the set pH value and the average particle size of the final roasted powder when implementing the method of the present invention, and the set pH value is lower than 9.5. It can be seen that if it is too low, fine powder with an average particle size of 1 μm or less cannot be obtained. However, a strong alkali with a set p)I value exceeding 13 is not preferred because it is difficult to carry out industrially and there is a risk of contamination with metal ions.

Example 3 ZrOClz 8.1-LO concentration 400 g/l
(153.0 g/12 in terms of ZrOz) and the set pH value was also kept constant at 10.5, and the same process as in Example 1 was carried out, except that the roasting conditions were changed as shown in Table 3. Then, the specific surface area and average particle size of the obtained powder were determined.

The results are also listed in Table 3. Note that the temperature increase rate during roasting was all under the same conditions.

Table 3 From the results in Table 3, it can be seen that if the temperature is maintained at around 400 to 500°C and then roasted at a high temperature, the average particle size becomes finer. This is probably due to the formation of metastable tetragonal micronuclei. However, as shown in Example 1 above, even if the temperature is raised to 600°C or higher and roasted, sufficient fine powder is obtained. can do.

Example 4 In the equipment shown in Fig. 1, N1 was used as the pH adjustment liquid 2 in the neutralization tank 1.
14011 and adjusted the pH to 10, and as zirconium-containing liquid 3, Zr0CI24 a, lha (400 g/J) equivalent to 97 mol in terms of ZrO2,
Using a mixed solution of indium chloride equivalent to 3 moles in terms of Y2O3, add solution 4 (NI + 4011 solution) so that the set pi value of the reaction solution, which is obtained by adding solution 3 to pHlll solution 2, is maintained at 10. Precipitate was generated while maintaining the liquid temperature at 50° C. while adjusting the chill H. The resulting precipitate was filtered from the liquid, dried, and then placed in a roasting furnace maintained at 800"C and roasted for 2 hours.

Also, for comparison, contrary to this example, a mixed solution of zirconium and yttrium with the same concentration as above was placed in the neutralization tank 1, and Ni14011 solution was gradually added to this mixed solution, until the pi This example was carried out under the same conditions except that the concentration was neutralized to 10 to produce a precipitate.

Table 4 shows the characteristic values of the stabilized zirconia powders obtained.

Table 4 From the results shown in Table 4, it can be seen that according to the method of the present invention, partially stabilized zirconia fine powder having an extremely fine average particle size and a completely uniform composition of the stabilizer and zirconia can be obtained.

As mentioned above, the tetragonal fraction is one indicator of homogeneous mixing, and in comparative examples where this ratio is less than 50%, it indicates that a considerable amount of monoclinic crystal is present. In other words, in the conventional and commonly used formulation in which alkali is added to neutralize a mixed solution in which zirconium and a stabilizing substance are dissolved, complete co-precipitation as in the method of the present invention does not occur, but only one-fraction precipitation occurs, which is caused by the final roasting process. It is thought that this deteriorates the tetragonal crystal ratio of the fired product. On the other hand, according to the method of the present invention, a crystal having a tetragonal crystal content of 100% can be obtained, and the average particle size is also much finer.

Example 5 To the mixed solution of zirconium and iso]-lium used in Example 4, an ammonium sulfate adjustment solution was further added at a sulfate concentration such that the molar ratio of SoI/Zro2 was 0.45, and the setting was made. The formulation of Example 4 was followed except that pi was 9.0.

For comparison, the same treatment as above was carried out except that no ammonium sulfate adjustment solution was added.

This comparative example has the same processing conditions as Example 4, except that the pH value set in Example 4 was set at 9.0, whereas it was set at 9.0.

The following is clear from the results in Table 5.

The presence of sulfate results in a significantly smaller average particle size, lower bulk density and higher specific surface area than in its absence. The set pi value is 9 in the presence of this sulfate.
．． Even if it is less than 5, the object of the present invention can be achieved. but,
In the absence of sulfate, as seen in the comparative example, a fine powder with a fine average particle size as aimed at in the present invention cannot be obtained at a set pH value of 9.0.

Example 6 Melt zirconium and yttrium at the same concentrations used in Example 5 and add ammonium sulfate + SO2
/ Zr O2 The same recipe as in Example 5 was carried out, except that the mixed solution was added at a concentration of sulfate groups such that the molar ratio was 0.6, and the set pH value was changed as shown in Table 6. did. Table 6 shows the characteristic values of the final powder obtained.

Table 6 From the results in Table 6, it can be seen that in the case of sulfate addition, the specific surface area shows a maximum at a set pH value of about 9.

Overall, the specific surface area is larger, the average particle size is smaller, and the bulk density is maintained lower than that of the above-mentioned sulfate-free system.

Example 7 Ammonium sulfate was added to the pH adjusting solution 2 side in Figure 1 in an amount such that the molar ratio of so2 /ZrO2 was 1.0, and zirconium oxychloride (zrOC12. 81 (20) at 300 g/1,
A mixed solution (corresponding to the solution 3 in FIG. 1) in which iso-lium chloride was dissolved in Y2O3 in an amount equivalent to 3 moles was added, and the set ρ11 value was set to 10 to form a precipitate.

After dehydration and drying, this was roasted at 800°C for 5 hours.

The obtained powder is.

The bulk density (g/aa) was 0.63, the specific surface area (I/g) was 37.1, the average particle size (μ) was 0.60, and the tetragonal crystal ratio (%) was 89.7. In this way, fine powder can be obtained even if the sulfate is added to the side of the pn adjustment solution. However, in this case, the square product rate seems to decrease slightly.

[Brief explanation of drawings]

FIG. 1 is an equipment layout diagram for explaining the operating procedure for carrying out the method of the present invention. 1. Neutralization tank, 2. pH adjustment liquid 2, 3. Zirconium-containing liquid, 4. Alkaline solution. 5...pH electrode, 6...p■controller. 9. Constant temperature bath.

Claims (1)

[Claims] +11. An aqueous solution prepared by dissolving a soluble zirconium salt in an alkaline solution having a pH of 9.5 to 13 at a concentration of 40 g/N or more in terms of Zr0z was added to an alkaline solution having a pH value of 9.5 to 13 during one reaction.
pH1i regulating force (
A method for producing fine zirconia powder, which comprises adding the precipitate obtained from the above, separating and drying the resulting precipitate, and then roasting it at a temperature exceeding 600°C. (21, an aqueous solution in which a soluble zirconium salt is dissolved in an acid or alkaline solution with a pH of 2 to 13 at a concentration of 40 g/n or more in terms of ZrO2 + 502 / converted Zr0z
In the presence of an amount of soluble sulfate such that the molar ratio of A method for producing fine zirconia powder, which comprises separating and drying the precipitate and then roasting it at a temperature exceeding 600°C. (3) In an alkaline solution with a pH of 9.5 to 13, a soluble zirconium salt was dissolved in an amount of 40 g/J or more in terms of ZrO2, and an appropriate amount of a soluble salt of a zirconia stabilizing substance commonly used as a zirconia stabilizer was dissolved. 1 aqueous solution
Zirconia fines are added while adjusting pn so that the pH value during the reaction is maintained in the range of 9.5 to 13, the resulting precipitate is separated and dried, and then roasted at a temperature exceeding 600°C. Method of manufacturing powder. (41, an aqueous solution in which a soluble zirconium salt is dissolved in an alkaline solution with a pH of 7 to 13 to a concentration of 40 g/J or more in terms of ZrO2, and an appropriate amount of a soluble salt of a zirconia stabilizing substance commonly used as a zirconia stabilizer is dissolved, SO2
In the presence of an amount of soluble sulfate such that the molar ratio of ZrO2/converted ZrO2 is 0.3 or more, the pH value in one reaction is 7 to 7.
Addition was made while adjusting the pi to maintain it within the range of 13, and the resulting precipitate was separated and dried. A method for producing fine zirconia powder, which comprises roasting at a temperature exceeding 600°C.