JPH0764563B2 - Fine powder of crystalline zirconia and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In the present invention, most of the zirconium contained is a crystallite size.
The present invention relates to a monoclinic zirconia powder having a particle size of 30 to 100 Å, wherein the average diameter of secondary agglomerated particles does not exceed 500 Å, and to a fine powder of crystalline zirconia and a method for producing the same. Here, zirconia is not only pure ZrO ₂ but also HfO ₂ of 10% or less, which is generally industrially called zirconia, and Y of up to several%.
_It refers to zirconia in a broad sense, including those containing ₂ O ₃ , other stabilizers and impurities.

Conventionally, zirconium salt aqueous solution is 120-300 under hydrothermal pressure.
A method for obtaining a hydrosol of zirconia by heat treatment at ℃ is known (US Pat. No. 2,984,628), and it is also known that a zirconia fine particle suspension can be obtained by boiling an aqueous zirconium salt solution for a long time [A. ． Clearfield; Inorganic Chemistry, Vol. 3, pp. 146, 1964, (A.Clearfield; Inorg.Chem.3,146
(1964)].

However, the former requires a considerably long time under high pressure and high temperature, and the latter requires a longer heat treatment time, both of which are inefficient and not suitable for industrial mass production. The characteristics are not sufficient, and the size of the secondary agglomerated particles usually exceeds 1000Å, and the size of the secondary particles is not uniform especially in the former case, so that it has hardly been industrially applied.

The present inventor established the method for quantitatively determining the extent of the progress of the formation reaction of the zirconia fine particles by the basic research, and as a result of repeating a large number of experiments under various conditions by this method, finally the peroxidation was finally performed. We have discovered the hydrogen reaction acceleration effect and ultrafine particle formation effect.

Zirconium salt, for example 0.2 mol / l zirconyl chloride aqueous solution continued boiling for 100 hours in a flask with a reflux condenser zirconium in the solution almost completely monoclinic zirconia crystals, which after separation and drying, 400 ° C in vacuum
There is almost no change even in the heat treatment of, and only a monoclinic type is shown in X-ray. Ammonia water is added to the aqueous zirconium salt solution to form a hydroxide precipitate, which is dehydrated under reduced pressure and vacuumed at 400 ° C.
The heat-treated product is crystallized into tetragonal zirconia by X-ray. Therefore, ammonia was added to the suspension in the reaction process which was heat-treated for a certain time, the precipitate obtained was carefully dried under reduced pressure, and heat-treated at 400 ° C in vacuum to obtain a mixture of monoclinic zirconia and tetragonal zirconia. , Its quantitative ratio can be easily known by X-ray diffraction, which is an accurate measure of the degree of progress of the zirconia formation reaction in the solution.

Comparison of the experimental results by this method gives significantly different results than comparison of the degree of cloudiness. For example, 300 cc of 0.2 mol / l concentration of zirconyl chloride aqueous solution is continuously boiled for about 20 hours in a flask equipped with a reflux condenser, but the solution becomes completely cloudy, but the amount of zirconia fine particles produced is about 10% of the total zirconium. On the other hand, the same 0.2 mol / l concentration of zirconyl chloride aqueous solution was previously prepared by the method of the present invention using an anion exchange resin to change Cl ⁻ to a part of OH ⁻ and the pH of the solution.
To 2.0, and then add 10cc of hydrogen peroxide solution (30%) to 3
When the solution of 00cc was boiled for 20 hours in the same flask, the solution became a thin and turbid sol, but the amount of zirconia fine particles produced was 100%, indicating that the production reaction was already completed. . This shows that the method of the present invention remarkably promotes the reaction of forming crystalline zirconia by hydrolysis and that the zirconia product is extremely fine ultrafine particles.

As described above, the present invention has an extremely high economic value due to the advantages of industrial production by promoting the zirconia formation reaction and increasing the efficiency, and the advantages of the characteristics of the produced monoclinic zirconia based on the ultrafine particles. This is all due to the addition of hydrogen peroxide to the starting aqueous zirconium salt solution during manufacture.

That is, most of the zirconium contained in the present invention is monoclinic zirconia having a crystallite of 30 to 100Å, the secondary agglomerated particles are strong and do not easily separate, and the average diameter of the agglomerated particles does not exceed 500Å. And a fine powder of crystalline zirconia. Furthermore, as its manufacturing method,
Hydrogen peroxide or a compound that produces hydrogen peroxide is added to a zirconium salt aqueous solution having a concentration of 0.05 to 2.0 mol / l, and this solution is heat-treated at 80 to 300 ° C to form zirconia into a monoclinic type in the aqueous solution. A crystalline zirconia colloidal sol is obtained by crystallization, a base is added to this sol to cause coagulation and sedimentation, and the coagulated sediment is separated, followed by replacing the water with a polar organic solvent and drying to obtain crystalline zirconia fine powder. The zirconium salt aqueous solution with a concentration of 0.05 to 2.0 mol / l has a pH of 1
~ 3 while adding hydrogen peroxide or a compound that produces hydrogen peroxide, the solution is heat treated at 80 ~ 300 ℃ to crystallize zirconia into a monoclinic form in an aqueous solution,
A crystalline zirconia colloidal sol is obtained, a base is added to the sol to cause coagulation and sedimentation, the coagulated sediment is separated, and then water is replaced with a polar organic solvent to be dried to obtain a fine powder of crystalline zirconia. .

In the method of the present invention, the concentration of the zirconium salt solution is too low at 0.05 mol / l or less, the operation becomes extremely difficult at 2.0 mol / l or more, and the practical concentration range of 0.05 to 2.0 mol / l is 0.2 to 1.0 mol / l is a more preferable concentration range. By adjusting the pH of the zirconium salt aqueous solution to 1 to 3, the hydrolysis reaction is further promoted as compared with the case where the pH is not adjusted, as described below.

A more detailed progress of the formation of crystalline zirconia by hydrolysis is shown in FIG. 1 in comparison with various conditions.

Figure 1 shows 300cc of 0.2 mol / l zirconyl chloride aqueous solution.
Shows the change over time when boiling was continued in a flask with a reflux condenser, the horizontal axis represents the boiling time, and the vertical axis represents the molar ratio of the amount of monoclinic zirconia fine particles produced to the total amount of zirconium in the solution.

This analysis method was performed by the method described above. The numbers attached to each curve in the figure indicate the conditions of the solution at the time of starting (before boiling). The pH value of the solution prepared with anion exchange resin and the amount of hydrogen peroxide solution (31%) added (cc ).

As is clear from the figure, when the conventional method (black circle in the figure) simply heat-treats the zirconinyl chloride aqueous solution,
A continuous boiling for 60 hours for a long time is required to complete the reaction of forming the zirconia fine particles, but by the method of the present invention (white circles in the figure), hydrogen peroxide addition (0.2 M, H ₂ O ₂ -10) is used. observed remarkable reaction promotion effect, further with a pH of 2.0 with an anion exchange resin, and _{(0.2M, pH2, H 2 O} 2 -10) by the addition of hydrogen peroxide time to produce the reaction completion about You can see that it is shortened to about 1/3.

The following table compares the amount of hydrogen peroxide added in the same experiment as in Fig. 1 and the amount of monoclinic crystal zirconia fine particles produced after boiling for 20 hours. Although an accelerating effect is observed, the maximum accelerating effect appears when hydrogen peroxide is added at an equimolar ratio (1: 1) to the number of moles of zirconium in the solution. Is shown. Further, sodium peroxide, magnesium peroxide, and the like that generate hydrogen peroxide in the solution also have the same promoting effect as hydrogen peroxide.

Further, FIG. 2 shows the effect of the present invention when the concentration of zirconyl chloride is high, and is an example in which aqueous ammonia is added to adjust the pH of the solution. Similar to FIG. 1, a solution (cc) of ammonia water (28%) to 300 cc of the solution is shown in the figure. The effect of the present invention is more remarkable when the concentration of zirconyl chloride in the aqueous solution is high, and it is 0.5 when the solution is simply boiled.
At mol / l, zirconia started to form slightly after 40 hours, and at a concentration of 0.8 mol / l or higher, zirconia did not form at all, but the addition of hydrogen peroxide and ammonia resulted in a relatively short time even from a high-concentration solution. Monoclinic crystal zirconia ultrafine particles are generated in time. The figure shows the molar ratio between the amount of zirconium contained in the solution and the zirconia that is formed and crystallized, so it can be seen how high the concentration of zirconia is.

The heat treatment in the method of the present invention does not necessarily require boiling. The present invention is effective even at a temperature of 100 ° C. or lower, and exhibits similar effects even at high temperature treatment under a pressurized atmosphere. This practical processing temperature range is 80 to 300 ° C depending on the production rate and equipment. FIG. 3 shows the effect of the present invention at 100 ° C. or higher, in which a 0.2 mol / l zirconyl chloride solution was used under steam pressurization.
This is the result of holding at 30 ° C. In this case as well, the transparent liquid which had been boiled for 1 hour after the addition of hydrogen peroxide had a production rate more than double that of the non-added solution.

The monoclinic crystal zirconia ultrafine particles produced according to the present invention have crystallite diameters of all 30 to 100Å obtained from the half width of the peak of powder X-ray diffraction, which is almost the same as when the solution is simply boiled or hydrothermally treated at a low temperature. However, there is a marked difference in the size of the secondary agglomerated particles according to the electron microscope observation. That is, usually 2 at the completion of the zirconia formation reaction.
The diameter of the secondary agglomerated particles is 1000 Å or more, which is a strong bond that is not easily divided, but the secondary agglomerated particles according to the method of the present invention have a diameter of 500 Å or less even when the reaction is completed.

Although the essence of the action of hydrogen peroxide in the present invention is not always clear, it is indispensable for refining the secondary agglomerated particles of zirconia to be produced, and therefore hydrogen peroxide is effective for crystal nucleation rather than crystal growth. It is believed that there is.

Further, it is considered that the pH adjustment with ammonia or the like does not directly contribute to the miniaturization of the secondary agglomerated fine particles, so that it is effective in promoting crystal growth rather than nucleation. In any case, the method of the present invention makes the production of monoclinic zirconia fine particles highly efficient and makes the product ultrafine. That is, while enabling industrial mass production of monoclinic crystal zirconia ultrafine particles,
By applying ultrafine particles, the quality of the applied products will be improved.

When a base such as ammonia is added to the sol obtained by the method of the present invention, suspended particles are aggregated and precipitated, and after separation, water is replaced with a polar solvent such as alcohol and acetone and dried to form isolated ultrafine particles of crystalline zirconia. A fine powder is obtained, which is more sinterable and unique than any previously obtained zirconia powder. For example, this powder compact gives a high-purity zirconia sintered body consisting of only monoclinic crystals of almost theoretical density at a low temperature of 1100 ° C. This is conventionally obtained only by a hot press or a special method under hydrothermal conditions. In addition, the powder obtained from the sol of the method of the present invention has extremely fine secondary agglomerated particles, and therefore has excellent miscibility with other powders, and when used as a raw material for solid reaction such as the production of lead zirconate, the contact area increases. As a result, it has extremely high reactivity and low-temperature sinterability, has the highest dispersibility as other additives for ceramics, and enables a small amount of uniform addition.

FIGS. 1, 2, 3 and Table are examples showing that the method of the present invention is much superior in production rate and efficiency of crystalline zirconia fine particles to the conventional method. Specific examples of the crystalline zirconia fine powder of the present invention are shown in FIG.

Example 1 97 g of a special grade reagent zirconyl chloride (ZrOCl ₂ 8H ₂ O) was distilled in about 300 parts.
Dissolve it in cc to make a solution of about 1.0 mol / l, add 90 cc of hydrogen peroxide solution (31%) and stir it, then gradually add 30 cc of ammonia water (28%), and add this solution to a reflux condenser. It was boiled for 50 hours in an attached flask to obtain a semitransparent emulsion sol. When ammonia water is added to this sol, suspended particles aggregate and settle, so decant and replace water with acetone.
It was filtered and dried. The crystallite size of the primary particles of this powder is 44 Å as calculated from the half-width of powder X-ray diffraction, and according to the observation with an optical microscope and an electron microscope, a relatively large agglomerated particle is found. The size of the strong secondary agglomerated particles is 50 because it is a fragile material that is close to physical adhesion.
It is recognized that the particle size is 0 Å or less and the particle size is almost uniform. This powder is a dried product as it is in the mold 2t / cm ²
After molding into a disc with a diameter of 16 mm by the molding pressure of 1 at 1100 ℃ in air
Only by firing for a long time, a highly pure and dense polycrystal composed of monoclinic crystals with a bulk density of 96% of the theoretical density was obtained.

[Brief description of drawings]

FIG. 1 shows the boiling time and monoclinicity in the method of the present invention and the conventional method.
The change in the production rate of ZrO ₂ is shown. FIG. 2 shows changes in boiling time and monoclinic ZrO ₂ production rate in the method of the present invention and the conventional method when the zirconium salt concentration was changed. FIG. 3 shows changes in boiling time and monoclinic ZrO ₂ production rate in the method of the present invention and the conventional method under hydrothermal conditions. In both cases, the white circles are the method of the present invention and the black circles are the conventional methods.

Claims (3)

[Claims] 1. Most of the zirconium contained is monoclinic zirconia having a crystallite size of 30 to 100Å, the secondary agglomerated particles are strong and do not easily separate, and the average diameter of the agglomerated particles does not exceed 500Å. A fine powder of crystalline zirconia characterized by the above. 2. Zirconia is added to an aqueous solution of zirconium salt having a concentration of 0.05 to 2.0 mol / l by adding hydrogen peroxide or a compound that produces hydrogen peroxide to the solution and heat-treating the solution at 80 to 300 ° C. Monoclinic crystallization to obtain a crystalline zirconia colloidal sol, a base is added to this sol to cause coagulation and sedimentation, the coagulated sediment is separated, and then water is replaced with a polar organic solvent for drying. Method for producing fine powder of zirconia. 3. The method for producing fine crystalline zirconia powder according to claim 2, wherein the pH of the zirconium salt aqueous solution is 1 to 3.