JPH01270515A - Production of zirconia fine powder - Google Patents

Abstract

PURPOSE:To obtain the title fine powder, sharp in particle size distribution, good in dispersibility, reduced in impurity content, by neutralizing a specific basic Zr(SO4)2-contg. slurry with ammonia followed by treatment with ammonia water. CONSTITUTION:(NH4)2SO4 is added to a solution prepared by dissolving a 40-70g/l (on a ZrO2 basis) of a water-soluble Zr compound (e.g., oxy ZnCl4) in water so as to be 0.45-0.55mols per mol of Zr on a SO4 basis is to prepare an aqueous solution. Thence, this solution to which, as a seed crystal, basic Zr(SO4)2 fine powder is added is heated to >=75 deg.C to produce a slurry with basic Zr(SO4)2 precipitate suspended. This slurry is then incorporated, in a single spell, with ammonia water, stirred and adjusted to pH>=8.5 followed by neutralization and filtration and washing to obtain a solid product, which is then treated with ammonia water to eliminate sulfate ion from the basic Zr(SO4)2 into Zr(OH)4, which is then calcined, thus obtaining the objective zirconia fine powder <=0.4 in bulk density and <=5mum in average particle size.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing zirconia fine powder, and in particular to a method for producing zirconia fine powder that has a small particle size and excellent dispersibility, and is widely applicable in the field of fine ceramic production. used.

[Conventional technology]

Zirconia powder is used as a raw material for fine ceramics for electronics, etc. Zirconia powder used for such applications is required to have high purity, small particle size, and sharp particle size distribution, as well as low bulk density, few aggregated particles, and good dispersibility. There is.

However, zirconia powder obtained by the conventional method of heating a solid obtained by precipitation from an aqueous solution of zirconium salts generally contains coarse secondary particles that are strongly coagulated secondary particles.

It cannot be used as is for the above purposes. Therefore, if we try to obtain fine powder by grinding zirconia powder containing such coagulated particles, it will require a long grinding operation, and there is a risk that impurities will be mixed in from the grinding equipment. The resulting powder has a wide distribution width and extremely strong cohesive force, making it difficult to disperse.

As described above, with conventionally known methods, it has been difficult to obtain zirconia powder with few impurities, small particle size, sharp particle size distribution, low bulk density, and good dispersibility.

[Problems to be Solved by the Invention] The purpose of the present invention is to eliminate the drawbacks of the above-mentioned conventional methods, and to improve the effectiveness of zirconia fine powder that has a small particle size, a sharp particle size distribution, good dispersibility, and a low impurity content. The aim is to provide a manufacturing method that is

[Means and operations for solving the problems] The gist of the present invention is as follows.

That is, a step of preparing an aqueous solution by dissolving a water-soluble zirconium compound in water and adding ammonium sulfate to the solution, a step of heating the aqueous solution to obtain a slurry in which precipitates of basic zirconium sulfate are suspended, and a step of preparing the slurry. separating the zirconium hydroxide after treatment with an alkaline substance; and calcining the zirconium hydroxide;
In the method for producing zirconia powder, the concentration of zirconium in the aqueous solution is 40~' as ZrO7.
A step of adjusting the ammonium sulfate concentration to 0.45 to 0.55 mole per mole of zirconia as SO4, and rapidly neutralizing the slurry obtained by heating the aqueous solution with ammonia and filtering and washing. This is a method for producing zirconia fine powder, which comprises the steps of: [during the basic zirconium sulfate] and then treating it with aqueous ammonia to completely remove the sulfate radicals from the basic zirconium sulfate and convert it into silconium hydroxide 11.

The present invention will be explained in detail below.

The "bulk density" of zirconia powder is one of the important items expressing its quality level, and in the market, a product with the lowest possible value is desired.

Therefore, first, a method for reducing this "bulk density" will be described. In the present invention, the term "bulk density" refers to the reciprocal (unit: g/mQ) of the value E (m Q / g) determined by the bulk measurement method specified in JIS K5101 Pigment Test Method.

(A,) First, a water-soluble zirconium compound, such as zirconium oxychloride and ammonium sulfate, are dissolved in water, and the concentration in the solution is 40 to 70 g/ZrO2.
Q, 0.45 to 0 per mole of zirconia as SO4
．． Adjust to 55 mol. The reason for this limitation is as follows. That is, when the ammonium sulfate addition rate is out of the range indicated by -, the bulk density increases by 1. Regarding the zrO2 concentration, if the concentration is too low, the productivity will be poor, while if it is too high, the temperature distribution during basic zirconium sulfate precipitation will become uneven, so it is not practical to limit it to 40 to 70 gIQ. be. In particular, around 50 g/f1 is suitable.

(B) Next, add and mix basic zirconium sulfate fine powder as seed crystals to this aqueous solution! ! Vi? After heating, raise the temperature to 75°C or higher.

There is no particular restriction on the quality of the basic zirconium sulfate used as a seed crystal; for example, ammonium sulfate is added to 7 volumes of Zr○, zirconium oxychloride solution with a converted concentration of 50 gIQ at a ratio of 0.46 mol per 1 mol of zirconium. However, it is best to use this aqueous solution kept at 80 to 85°C for 1 hour. Regarding the amount of addition, the slurry is mixed with 1-1 zirconium oxychloride aqueous solution/l.
If mQ or more is added, the time is 1.min.

(C) Next, the slurry in which the basic zirconia sulfate powder is suspended is poured into aqueous ammonia and stirred to neutralize it. The amount of ammonia water is the slurry po after neutralization.
[8.5 or higher]] It is necessary to prepare as follows.

The amount of ammonia water required for neutralization can be reduced by separating the mother liquor from the slurry in which basic zirconium sulfate has precipitated prior to neutralization with ammonia water. However, if the neutralization operation is carried out in this way, the bulk density will become extremely high, making it impossible to achieve the purpose of the present invention.In other words, in order to reduce the bulk density, The first important point is to rapidly increase p I-1 in coexistence.

By the way, as for the neutralization method, since it is sufficient to rapidly increase p I, it is not necessarily limited to the method of adding the slurry to aqueous ammonia as described above. Therefore, adding aqueous ammonia to the slurry The most suitable method may be selected in terms of equipment and operability, such as the method of blowing in ammonia scum.

(D) Next, the slurry is separated from the mother liquor by centrifugation, filtration, etc. to obtain a solid, and then the solid is treated again with aqueous ammonia to substantially completely remove the basic ziraconium sulfate. The sulfate group is removed and converted to zirconium hydroxide. This operation for removing sulfate radicals can be effectively carried out by carrying out an appropriate combination of repulp washing and filtration washing according to a conventional method. Note that it is also possible to replace a part of the ammonia water used in this step with alkali hydroxide. This makes it possible to more efficiently eliminate sulfate radicals and to reduce the amount of expensive ammonia water used. However, care must be taken as alkali metal ions tend to be adsorbed and remain on zirconium hydroxide.

Finally, fine powder zirconia with a low "bulk density" can be obtained by washing until the washing liquid becomes almost neutral, separating the liquid, and calcining it by a conventional method.

The physical properties of the zirconia powder obtained by the above method are as follows:
A bulk density of 0.4 or less, an average particle size of 5 μm or less, and 2
Since the secondary particles are not strongly bonded to each other, pulverization is easy, and a weakly agglomerated fine powder with a particle size of 1 μm or less can be obtained by light pulverization.

Next, a method for further reducing the particle size will be described. In addition, unless otherwise specified, the particle size referred to here is micro I.
- means the average particle diameter (D5o) measured by rack particle size analysis.

(E) The present inventors discovered that the fluidity of the liquid when heating a solution containing a water-soluble zirconium compound and a sulfuric acid group to precipitate basic zirconium sulfate greatly affects the particle size of the final product, zirconia. I found out what to do. In other words, when crystals are precipitated from a solution, stronger stirring generally reduces the particle size, but contrary to this common sense, when using the method of the present invention, weakening the stirring results in smaller particle sizes. They found that the particle size becomes the smallest when heated in a non-flowing state without stirring at all. Therefore, by utilizing this phenomenon, calcined materials can be easily crushed into 1-15 μm particles by very light crushing.
The following zirconia fine powder can be obtained. In this case, even if the particle size changes, the bulk density hardly increases by 1, so if you want a relatively large particle size, you can use the phenomenon described below to increase the bulk density almost by 1. The particle size can be controlled to any value within the range of 1 to 5 μm without changing it. By the way, the fluidity of the liquid due to stirring varies depending on the rotational speed of the stirrer, the shape of the stirring blades, and the shape and size of the container.
By determining the relationship between stirring speed and particle size in advance for a given device through experiments, it becomes possible to control the particle size to an arbitrary value only by changing the stirring speed.

(F) Next, a method for further improving the dispersibility will be explained.

The zirconia powder obtained by the above method has an average particle size of around 0.8 μm, a maximum particle size of 5 μm, and a bulk density of 0.4 or less, and has a small particle size and excellent dispersibility, so it is practically sufficient. It has certain characteristics. By the way, even if the powder has such excellent dispersibility, when the powder is examined under a microscope using the "sprinkle method", the presence of tertiary particles that are extremely weakly aggregated secondary particles may be observed. There is virtually no problem with this degree of agglomeration, but if you wish to prevent the formation of this degree of agglomerated particles, you can heat an aqueous solution of zirconium oxychloride containing ammonium sulfate to form basic zirconium sulfate. This objective can be achieved by adding hydrochloric acid to the aqueous solution prior to precipitating it. The appropriate amount of hydrochloric acid to be added is 0.3 to 0.6 mol per 1 mol of zirconia. 0.3
If it is less than 0.6 mol, the effect will be small, and if it exceeds 0.6 mol, the particle size will become too large.

〔Example〕

Example 1 Zirconium oxychloride crystal (ZrOCR2・8H2
0) was dissolved as pure ZrO, to give 200 gIQ, and used as a stock solution. 25 ml of stock solution in a beaker
0n+Q was taken and pure water was added to obtain ]-Q, and ammonium sulfate in the capacity shown in Table 1 was added as a solid to completely dissolve it. Next, 1 mfl of a seed crystal slurry prepared by the method described later was added and mixed, and then the beaker was immersed in a water bath to raise the liquid temperature to 80° C. to obtain a slurry in which basic zirconium sulfate was suspended.

Next, the slurry was added at once to the ammonia water while stirring to neutralize it. P I-I of the slurry after neutralization is 9.
It was 1 to 9.3. After separating the mother liquor, the product was washed with pure water, then repulped with aqueous ammonia, washed with pure water, and filtered. This procedure was repeated twice to obtain a precipitate of zirconium hydroxide containing almost no sulfate groups. Note that 300 mQ of ammonia water with a concentration of 10% was used in each case.

Next, this zirconium hydroxide was calcined at 750'C, and after cooling, it was crushed lightly in a mortar and its physical properties were measured, and the results shown in Table 1 were obtained.

Table 1 Example 2 The amount of sampled stock solution was set at the ZrOzllll degree shown in Table 2, and the addition rate of ammonium sulfate 11 (SQ, /ZrO2 molar ratio) was fixed at 0.47. The same operation was performed to obtain the results shown in Table 2.

Table 2 Example 3 ZrO, concentration E + Og/l, ammonium sulfate addition rate was fixed at 0.47, and a stirrer was used to flow at the level shown in Table 3 during temperature rise. The results shown in Table 3 were obtained by operating in the same manner as above.

Table 3 Example 4 Hydrochloric acid in the amount shown in Table 4 was added to a zirconium oxychloride solution containing ammonium sulfate, and the addition rate of ammonium sulfate was fixed at 0.46. The results shown in Table 4 were obtained. In addition, the results of observing SEM images using the "furikake method" are as shown in Figures 1 and 2. Figure 1 shows the case without the addition of hydrochloric acid, and Figure 2 shows 0.3% per mole of zirconia. This is the case when mol of hydrochloric acid is added. As is clear from the comparison between FIG. 1 and FIG. 2, it can be seen that the dispersibility is improved by adding hydrochloric acid.

The seed crystal slurry used in the experiments shown in Table 4-I was prepared by the following method. Ammonium sulfate was added as a solid to a solution of zirconium oxychloride 11 having a ZrO2 equivalent concentration of 50 gIQ at a ratio of 0.46 mol per co-mol of zirconia, and completely dissolved. The aqueous solution was then heated in a water bath and maintained at 80-85° C. for a period of 100-200 hrs.

〔Effect of the invention〕

According to the method of the present invention described in detail, it is possible to easily obtain fine zirconia powder for fine ceramics, which has a small particle size, a sharp particle size distribution, a low bulk density, and excellent dispersibility.

[Brief explanation of the drawing]

Figures 1 and 2 are 250x SEM images showing that the dispersibility of the resulting zirconia fine powder varies depending on the amount of hydrochloric acid present when precipitating basic zirconium sulfate. Figure 2 shows the case where 0.3 mol of hydrochloric acid is added per 1 mol of zirconia.

Claims (3)

[Claims] (1) preparing an aqueous solution by dissolving a water-soluble zirconium compound in water and adding ammonium sulfate to the solution;
heating the aqueous solution to obtain a slurry in which precipitates of basic zirconium sulfate are suspended; treating the slurry with an alkaline substance and then separating zirconium hydroxide; and calcining the zirconium hydroxide. In the method for producing zirconia powder, the concentration of zirconium in the aqueous solution is 40 to 70 as ZrO_2.
g/l, the ammonium sulfate concentration is adjusted to 0.45 to 0.55 mole per mole of zirconia as SO_4, and the slurry obtained by heating the aqueous solution is rapidly neutralized with ammonia and filtered. After washing, the basic zirconium sulfate is treated with aqueous ammonia to completely remove the sulfate radicals and convert it into zirconium hydroxide;
A method for producing zirconia fine powder, characterized by having the following. The method for producing zirconia fine powder according to claim 1, further comprising the step of: (2) heating the aqueous solution in a non-flowing state to precipitate basic zirconium sulfate. 3. The method for producing zirconia fine powder according to claim 1, further comprising the step of adding hydrochloric acid to the aqueous solution and then heating it in a non-flowing state to precipitate basic zirconium sulfate.