JPH0624980B2 - Method for producing porous zirconia spheres - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing fine porous zirconia spheres.

[Conventional technology]

A method for producing fine porous zirconia spheres is disclosed in JP-A-63-123817. In this production method, a solution of zirconium alkoxide in an organic solvent is dispersed in formamide in the form of fine droplets (or ammonia water or oxalic acid added thereto) and heated while maintaining the dispersion state. Spherical particles composed of zirconium hydroxide and zirconium oxide are formed by evaporation of the solvent of the alkoxide solution, hydrolysis and thermal decomposition of zirconium alkoxide, and the particles are separated from the dispersion medium and fired to form zirconia. .

The porous zirconia spheres obtained by such a method are microspheres having a diameter of about 50 to 100 microns and have a large number of radial pores extending from the center toward the surface. And, due to its unique structure, the sensor,
It is expected to be used as a catalyst, a separating material, a medicinal material, a heat insulating material, a refractory material, and the like.

[Problems to be Solved by the Invention]

However, according to the above-mentioned conventional manufacturing method, it is difficult to manufacture porous zirconia spheres having a regular shape in good yield. That is, it is difficult to obtain a true spherical shape (yield 1% or less), and cracks and cracks easily occur.

Therefore, an object of the present invention is to provide a method for producing a spherical spherical zirconia sphere with a high yield.

[Means for Solving the Problems]

The present invention succeeded in achieving the above object, a zirconium alkoxide solution using an organic solvent that is incompatible with formamide as a solvent, is converted into substantially anhydrous formamide cooled to a temperature lower than room temperature and higher than the freezing point. By adding and stirring to disperse it in formamide as fine liquid droplets, water is added to the obtained dispersion liquid with stirring to hydrolyze zirconium alkoxide in the dispersed liquid droplets, and precipitate the resulting zirconium hydroxide. It is characterized in that it is separated, dried, and then fired.

In the production method of the present invention, the zirconium alkoxide solution is added to and dispersed in cooled substantially anhydrous formamide to completely disperse the solution,
Thereafter, water is added to start the hydrolysis of the zirconium alkoxide to prevent the generation of distorted zirconium hydroxide. (When a zirconium alkoxy solution is added to formamide at room temperature or higher as in the conventional method, hydrolysis by water in the formamide starts before the solution is completely dispersed to form spherical droplets. Therefore, isotropic is not expected in the subsequent particle growth.). Further, in the conventional method, zirconium hydroxide and zirconium oxide are produced from the zirconium alkoxide while the solvent is volatilized by heating, but in the present invention, only hydrolysis is caused by addition of water. True spherical shape Since the zirconium alkoxide is decomposed by this single chemical reaction by water molecules diffusing from the surface of the droplet into the spherical shape, and the zirconium hydroxide spheres are not destroyed by the volatilizing solvent, Zirconium hydroxide is produced with a high probability. As described above, it becomes possible to obtain porous zirconia spheres with high yield.

In the production method of the present invention, as the organic solvent for dissolving the zirconium alkoxide, an aromatic hydrocarbon such as benzene, toluene, xylene, or a mixed solvent of an alcohol and an aromatic hydrocarbon (for example, a mixture of dehydrated methanol and toluene) , A mixture of methanol or ethanol with benzene) and the like are suitable. The zirconium alkoxide solution preferably has a concentration of about 0.70-2.
Adjust to 50 mol /. In addition to zirconium alkoxide, a small amount of other metal alkoxides such as yttrium alkoxide and calcium alkoxide can be added to this solution (when yttrium alkoxide and calcium alkoxide are added, they are finally produced from these alkoxides). Yttria and calcia are stabilizers that prevent the phase transition of zirconia at high temperatures). This solution is added to sufficiently cooled formamide and stirred. The temperature is set as low as possible within the range where formamide does not solidify, preferably 10 ° C. or lower.
As the formamide, a substantially anhydrous formamide whose water content is negligible compared to the amount of zirconium alkoxide added is used. As a result, the solution is dispersed in the dispersion medium as fine droplets without causing decomposition of the zirconium alkoxide. The droplets naturally become spherical due to the interfacial tension.

Once the zirconium alkoxide solution is dispersed in sufficiently fine droplets, the amount of water required to hydrolyze the zirconium alkoxide is added in small portions with continued stirring and at low temperature. The added water molecules, after being dissolved in formamide, reach the droplet surface of the zirconium alkoxide solution and react with the zirconium alkoxide to hydrolyze it. The hydrolysis starts from the entire surface of the spherical droplet, and the resulting zirconium hydroxide mass is
Since the alkoxide solvent grows while being squeezed out, innumerable minute gaps from which the solvent has escaped remain, and in a typical case, an aggregate of columnar bodies extending radially from the core is formed. When the hydrolysis is complete, the resulting zirconium hydroxide mass is heavy and thus precipitates in formamide.

Then, the lump of zirconium hydroxide that has settled is separated from formamide so as not to be crushed, washed, and dried.
Further, about 1200 ° C. or higher, preferably 1300 to 15
When heated to 00 ° C. to cause dehydration, crystallization and sintering, zirconia is produced while maintaining the structure of the zirconium hydroxide lumps having gaps (when yttrium alkoxide or the like is added, those oxides are not formed). Also produced), and porous zirconia spheres are obtained.

〔Example〕

Example 1 8.02 mmol of zirconium butoxide 1.52
It was dissolved in 5 ml of benzene together with mmol of calcium ethoxide and the resulting solution was added to formamide 150 at 4 ° C.
poured into g with stirring. After stirring for 3 minutes,
The alkoxide was completely hydrolyzed by adding 45 g of formamide containing 1.26 ml of water and further adding 40 g of formamide containing 2.53 ml of water. The stirring was stopped, and the precipitated zirconium hydroxide was collected by filtration, washed with acetone, dried, and then calcined at 1450 ° C. for 30 minutes.

The produced zirconia contained some non-spherical ones, and the yield of the spherical zirconia obtained by removing this was 40% of the theoretical value.

The result of the powder X-ray analysis shows that this zirconia is tetragonal zirconia, and the result of the composition analysis is ZzO ₂ 92.
It was 05% by weight and CaO was 7.95%.

As is clear from the scanning electron micrographs shown in FIGS. 1 to 3, most of the zirconia particles are spherical, and the inside thereof has zirconia crystals from the core toward the surface. It was growing in a columnar shape, with pores existing radially between them.

〔The invention's effect〕

As described above, according to the present invention, fine spherical fine porous zirconia spheres can be produced in high yield.

[Brief description of drawings]

1 to 3 are electron micrographs of porous zirconia spheres according to an example. Figure 1: Appearance of many spheres (40x magnification) Figure 2: Partial view of sphere surface (2500x magnification) Figure 3: Broken cross-section of sphere (320x magnification)

Claims (2)

[Claims] 1. A zirconium alkoxide solution containing an organic solvent that is incompatible with formamide as a solvent is added to substantially anhydrous formamide cooled to a temperature lower than room temperature and higher than the freezing point, and the mixture is stirred in formamide. As fine droplets, and water is added to the resulting dispersion with stirring to hydrolyze the zirconium alkoxide in the dispersed droplets, and the resulting zirconium hydroxide precipitate is separated and dried and then calcined. A method for producing a porous zirconia sphere, which comprises: 2. The method according to claim 1, wherein the dispersion of the zirconium alkoxide solution and the addition of water are performed at 10 ° C. or lower.