JPH0458413B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing zirconia fine powder,
In particular, the present invention relates to a method for producing fine zirconia powder that has a small particle size and excellent dispersibility, and is widely used in the field of fine ceramics production. [Prior Art] Zirconia powder is used as a raw material for fine ceramics for electronics and the like. 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 precipitating and precipitating from an aqueous solution of zirconium salts generally contains coarse secondary particles that are strongly coagulated primary particles. It cannot be used for the above purposes.
Therefore, if one attempts to obtain a fine powder by grinding zirconia powder containing such coagulated particles, a long grinding operation is required, and there is a risk that impurities may be mixed in from the grinding equipment. The result is a powder with a wide particle size distribution 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, which has a fine 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 effects 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 a precipitate of basic zirconium sulfate is suspended, and a step of preparing the starry. A method for producing zirconia powder comprising the steps of separating zirconium hydroxide after treatment with an alkaline substance, and calcining the zirconium hydroxide, wherein the concentration of zirconium in the aqueous solution is 40% as ZrO ₂ ~70
g/, adjusting the ammonium sulfate concentration to 0.4 to 0.55 mol as SO ₄ per 1 mol of zirconia, and rapidly neutralizing the slurry obtained by heating the aqueous solution with ammonia, filtering and washing it, and then adding ammonia. This is a method for producing fine zirconia powder, comprising the step of treating with water to completely remove sulfate groups from basic zirconium sulfate and converting it into zirconium hydroxide. The present invention will be explained in detail below. The "bulk density" of zirconia powder is one of the important items that expresses its quality level, and in the market it is desired that the value be as low as possible. Therefore, first, a method for reducing this "bulk density" will be described. In the present invention, the term "bulk density" refers to the value E determined by the bulk measurement method specified in JISK5101 Pigment Test Method.
It refers to the reciprocal of (ml/g) (unit: g/ml). (A) First, water-soluble zirconium compounds, such as zirconium oxychloride and ammonium sulfate, are dissolved in water, and the concentration in the solution is 40 to 40% as _ZrO2 .
70g/, per mole of zirconia as SO ₄
Adjust to 0.45 to 0.55 mol. The reason for this limitation is as follows. That is, when the ammonium sulfate addition rate is out of the above range, the bulk density increases. Regarding the ZrO ₂ concentration, if the concentration is too low, productivity will deteriorate, and if it is too high, the temperature distribution during basic zirconium sulfate precipitation will become uneven, so it should be limited to 40 to 70 g/ZrO2 for practical purposes. be. Particularly suitable is around 50g/. (B) Next, fine powder of basic zirconium sulfate is added as a seed crystal to this aqueous solution, mixed and suspended, and then heated to raise the temperature to 75°C or higher. There is no particular restriction on the quality of the basic zirconium sulfate used here as a seed crystal. For example, ammonium sulfate is added to a zirconium oxychloride solution with a ZrO ₂ equivalent concentration of 50 g/1 mole of zirconium. An aqueous solution kept at 80 to 85°C for 1 hour may be used. Regarding the amount to be added, it is sufficient to add 1 ml or more of the slurry per 1 zirconium oxychloride aqueous solution. (C) Next, the slurry in which basic zirconium sulfate is suspended is poured into aqueous ammonia all at once, and neutralized by stirring. The amount of ammonia water needs to be prepared so that the slurry pH after neutralization is 8.5 or higher. Note that 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, when the neutralization operation is performed in this way,
The "bulk density" becomes extremely high, making it impossible to achieve the object of the present invention. In other words, in order to reduce the bulk density, it is necessary to rapidly
The important point is to raise the PH. By the way, the neutralization method does not necessarily have to be limited to the method of introducing the slurry into aqueous ammonia as described above, since it is sufficient to rapidly increase the pH. Therefore, the most suitable method may be selected in terms of equipment and operability, such as adding ammonia water to the slurry or blowing ammonia gas. (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 from the sulfuric acid. The roots are detached and converted into zirconium hydroxide. This operation for removing sulfate radicals can be effectively carried out by carrying out an appropriate combination of repulping 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. By this,
It is possible to more reliably remove sulfate radicals and 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, wash until the washing liquid is almost neutral,
By separating the liquid and calcining it by a conventional method, zirconia in the form of a fine powder with a low "bulk density" can be obtained. The physical properties of the zirconia powder obtained by the above method are that it has a bulk density of 0.4 or less and an average particle size of 5 μm or less, and is easy to grind because the secondary particles are not strongly bonded to each other. Diameter 1μ
It can be made into a fine powder with weak agglomeration of less than m. Next, a method for further reducing the particle size will be described. Note that the particle size herein means the average particle size (D ₅₀ ) measured with a Microtrac particle size analyzer, unless otherwise specified. (E) The present inventors discovered that the fluidity state of the liquid when heating a solution containing a water-soluble zirconium compound and a sulfate group to precipitate basic zirconium sulfate is
It was found that the particle size of the final product, zirconia, is greatly affected. In other words, when crystals are precipitated from a solution, the stronger the stirring the smaller the particle size, but in the case of the method of the present invention, contrary to this common sense, the weaker the stirring the smaller the particle size. 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, fine zirconia powder of 1.5 μm or less can be easily obtained by simply crushing the calcined material very lightly. In this case, the bulk density hardly increases even if the particle size changes, so if you want a relatively large particle size, you can change the bulk density almost by using the above phenomenon. The particle size can be controlled to any value within the range of 1 to 5 μm. By the way, the flow state of 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, but it is necessary to conduct experiments to determine the relationship between stirring speed and particle size for a given device in advance. By determining this in advance, it becomes possible to control the particle size to an arbitrary value by adjusting only the stirring speed. (F) Next, a method for further improving 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. It has 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, which 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 precipitation. The appropriate amount of hydrochloric acid to be added is 0.3 to 0.6 mol per 1 mol of zirconia. If it is less than 0.3 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 (ZrOCl ₂
8H ₂ O) was dissolved as pure ZrO ₂ in an amount of 200 g/dose and used as a stock solution. 250 ml of the stock solution was placed in a beaker, and pure water was added to bring the solution to 1. Ammonium sulfate in the amount shown in Table 1 was added as a solid to completely dissolve it. Next, 1 ml of seed crystal slurry prepared by the method shown below was added and mixed, and the beaker was immersed in a water bath to bring the liquid temperature to 80°C.
A slurry in which basic zirconium sulfate was suspended was obtained. Next, while stirring the ammonia water, the slurry was added all at once to neutralize it. PH of slurry after neutralization
After separating the mother liquor, washing with pure water, followed by repulping with aqueous ammonia, washing with pure water, and filtering were repeated twice to produce zirconium hydroxide containing almost no sulfate radicals. A precipitate was obtained. Note that 300 ml 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 lightly crushed in a mortar and its physical properties were measured, and the results shown in Table 1 were obtained.

[Table] Example 2 The procedure was the same as in Example 1, except that the amount of stock solution collected was set to the ZtO ₂ concentration shown in Table 2, and the ammonium sulfate addition rate (SO ₄ /ZrO ₂ molar ratio) was fixed at 0.47. The results shown in Table 2 were obtained.

[Table] Example 3 ZrO ₂ concentration 50g/, ammonium sulfate addition rate
The procedure was carried out in the same manner as in Example 1, except that the temperature was fixed at 0.47, and a stirrer was used to flow at the level shown in Table 3 while the temperature was rising, and the results are shown in Table 3.

[Table] Example 4 The same procedure as in Example 1 was performed except that hydrochloric acid in the amount shown in Table 4 was added to the zirconium oxychloride solution containing ammonium sulfate, and the addition rate of ammonium sulfate was fixed at 0.46. We obtained the results shown below. Furthermore, as a result of observing SEM images using the "sprinkle method", it was confirmed that the dispersibility was improved by adding hydrochloric acid.

〔Effect of the invention〕

According to the method of the present invention detailed above, 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.

Claims (1)

[Claims] 1. A step of preparing an aqueous solution by dissolving a water-soluble zirconium compound in water and adding ammonium sulfate to the solution, and a step of heating the aqueous solution to obtain a slurry in which a precipitate of basic zirconium sulfate is suspended. A method for producing zirconia powder comprising the steps of: treating the slurry with an alkaline substance and then separating zirconium hydroxide; and calcining the zirconium hydroxide, the concentration of zirconium in the aqueous solution is 40-70g/ as ZrO ₂
, adjusting the ammonium sulfate concentration to 0.45 to 0.55 mol per 1 mol of zirconia as SO ₄ , and rapidly neutralizing the slurry obtained by heating the aqueous solution with ammonia, filtering and washing it, and then using aqueous ammonia. A method for producing fine zirconia powder, comprising the step of treating basic zirconium sulfate to completely remove sulfate groups and converting it into zirconium hydroxide. 2. The method for producing zirconia fine powder according to claim 1, comprising the step of 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 further adding hydrochloric acid to the aqueous solution and then heating it in a non-flowing state to precipitate basic zirconium sulfate.