JPH07121806B2 - Porous zirconia sphere or method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is expected to have many application fields as highly functional materials such as sensors, catalysts, separation materials, medical materials, heat insulating materials, and fire resistant materials. To finely divided porous zirconia spheres, and to a method for producing such zirconia spheres from zirconium alkoxides.

[Conventional technology]

Heretofore, a method known as a method for producing ceramic spheres has aluminum, magnesium, and silica as a ceramic raw material, makes a sol of the ceramic raw material, and prepares a sol of one kind or a mixed sol of two or more kinds of sol. A high boiling point liquid having a smaller specific gravity and not miscible with water,
A method for producing fine ceramic spheres, which comprises dropping into a liquid bath consisting of two layers with a liquid having a larger specific gravity than sol to form spherical particles, separating the spherical particles from the liquid, and further drying and firing (Japanese Patent Publication No. 58-46342).
However, the technique disclosed in the above publication relates to alumina or magnesium spheres, and does not describe zirconia spheres at all. Further, this publication does not describe a method for producing porous ceramic spheres at all.

[Problems to be solved by the invention]

In the prior art, some attempts have been made on a method for producing a ceramic true sphere, but a method for producing a porous ceramic sphere has not been known. The present invention is
It is an object of the present invention to provide a new method for producing fine and porous zirconia spheres using zirconium alkoxide. Further, such fine and porous zirconia spheres are novel and useful articles, and the present invention aims to provide such novel articles.

[Means for solving problems]

The present inventors diligently studied a method for producing a porous zirconia sphere (hereinafter sometimes simply referred to as "zirconia sphere"). As a result, calcium alkoxide or yttrium alkoxide was added and dissolved in an organic solvent solution of zirconium alkoxide as a dispersoid, and formamide was added to formamide as a dispersion medium or at least one of aqueous ammonia and oxalic acid was added. The alkoxide solution is dispersed in the form of fine droplets therein, and while maintaining the dispersed state, the alkoxide solution is heated to a temperature lower than the boiling point of the solvent used to form solidified spherical particles. We have found that a method for producing porous zirconia spheres, which is characterized in that it is separated from the dispersion medium and then calcined at 1200 to 1500 ℃, is effective, and we succeeded in developing this method.

Therefore, according to the first aspect of the present invention, the above manufacturing method is provided. As a product of this process, according to the second aspect of the present invention, finely divided yttria- or calcia-stabilized zirconia characterized by having a diameter in the range of 50 to 100 microns and having a porous internal structure. A sphere is provided.

The present inventors have found that a zirconium alkoxide represented by the formula Zr (OR) ₄ (where R is an alkyl group) is a useful starting material for producing porous zirconia spheres. It was also found that yttrium alkoxide or calcium alkoxide as a precursor of yttria (Y ₂ O ₃ ) or calcia (CaO) as a stabilizer for preventing phase transition of zirconia can be added to the raw material solution. The formamide used as the dispersion medium in the method of the present invention acts as a dispersion medium for dispersing the raw material zirconium alkoxide solution as fine droplets, and the solvent used in the alkoxide solution (such as benzene) is heated. Zirconia plays an important role in becoming spherical or substantially spherical in the process of vaporizing and evaporating and solidifying spherical particles individually. Ammonia water, which can be added in a small amount, also has the function of rapidly hydrolyzing the metal alkoxide at the interface with the formamide liquid phase, and as a result, calciur alkoxide flows out into the formamide during the process of forming solidified spherical particles. It has the effect of suppressing this and retaining it in the solidified spherical particles. When using oxalic acid, it serves to promote the action of aqueous ammonia.

It is well known that when a zirconia sintered body is manufactured, a certain amount of a stabilizer such as yttria, calcia, magnesia is usually added in order to suppress the phase transition of monoclinic tetragonal crystal accompanied by a remarkable volume change. . Also in the method for producing the porous zirconia spheres according to the present invention, a certain proportion of yttrium alkoxide or calcium alkoxide is added as a precursor of the stabilizing agent for the same purpose when producing the porous zirconia spheres.

The method of the invention will now be generally described.

Yttrium in zirconium alkoxide solution
The raw material solution is prepared by mixing and dissolving alkoxide, calcium alkoxide, or both so as to have a predetermined concentration. An appropriate amount of calcium alkoxide added is about 10 to 30 mol%, preferably 20 mol%, per 1 mol of zirconium alkoxide.
The suitable amount of yttrium alkoxide added is about 4 to 16 mol%, preferably 6 mol% (3 mol% for yttria). The solvent for dissolving these metal alkoxides is required to be an organic solvent that is immiscible with formamide and has a lower boiling point. For example, aromatic hydrocarbons such as benzene, toluene and xylene are suitable, Benzene with a low boiling point is most desirable for producing porous spheres. As such solvent, certain ethers such as ethyl ether can also be used.

The concentration of alkoxide in the zirconium alkoxide solution is suitably in the range of 0.1 to 2.0 mol / l, preferably 1.0 to 1.6 mol / l.

The type of alkyl group in the alkoxide group forming zirconium alkoxide, calcium alkoxide or yttrium alkoxide includes methyl group, ethyl group, linear or branched propyl group, butyl group, pentyl group, hexyl group, Although those having 1 to 10 carbon atoms such as heptyl group and octyl group are suitable, zirconium alkoxide used is preferably solid at room temperature. Zirconium methoxide, zirconium
Ethoxide is preferred, and likewise for yttrium or calcium alkoxides, yttrium ethoxide, yttrium isopropoxide, calcium ethoxide, etc. give good results for porous zirconia sphere formation.

Next, the raw material alkoxide solution (dispersoid) is dispersed in formamide as a dispersion medium. Formamide alone can be used as the dispersion medium. In some cases, in order to suppress the outflow of calcium alkoxide into the dispersion medium,
It is also effective to add a small amount of aqueous ammonia or oxalic acid or both of them. Then, for example, while maintaining the dispersed state by stirring, when heated, the solvent in the dispersed droplets volatilizes and solidifies the droplets to form spherical particles, but the heating temperature is usually A temperature below the boiling point of the solvent is suitable, and a temperature of about 60 to 70 ° C is desirable. Heating time is 5-30
The quantile is good.

Decomposition of the alkoxide occurs during this heating operation. The solidified spherical particles formed here consist of zirconium hydroxide and zirconium oxide formed from zirconium alkoxide, and further calcium oxide, calcium hydroxide, or yttrium.
It also contains yttrium oxide and yttrium hydroxide generated from alkoxide.

The solidified spherical particles thus obtained are separated from the dispersion medium by an operation such as filtration, taken out, washed with acetone, alcohol or the like to remove the dispersion medium attached to the particles,
Dry, then at a temperature of around 1200-1500 ° C, preferably 13
Baking at 00 ° C. to crystallize gives spherical particles of zirconia (ZrO ₂ ) having a porous internal structure of the present invention, that is, spheres.

Next, examples of the present invention will be shown, but the present invention is not limited to the examples shown below.

Example 1 0.40 mmol of calcium ethoxide Ca (OEt) ₂
1.60 mmol zirconium ethoxide Zr (OEt) ₄
Solution of benzene containing [C to Zr (OEt) ₄
a (OEt) ₂ ratio: 20 mol%] 3 ml to formamide 250 ml
It was added to the inside and shaken vigorously to form fine droplets and dispersed. While maintaining the dispersed state of the droplets, heating was performed at 60 ° C. for 10 minutes. Volatilization of benzene (boiling point 80 ° C) occurred. Then, the temperature is returned to room temperature, and the generated porous solid spherical particles are collected by filtration. Then, wash it with acetone and dry it at 1300 ℃.
After firing for 1 hour, the porous zirconia spheres of the present invention were obtained.
A scanning electron microscope (SEM) photograph showing the entire structure and particle surface structure of the porous zirconia spherical particles thus produced is shown in FIG. 1 of the accompanying drawings. From the picture in Figure 1,
It can be seen that the spherical particles of zirconia obtained in this example are truly spherical and have a large number of wedge-shaped and slightly large pores on the entire spherical surface. The zirconia spherical particles had a diameter of about 50 μm. Further, FIG. 2 shows a scanning electron micrograph of the particle surface structure showing a part of the surface of the zirconia spherical particles further enlarged. According to the photograph of FIG. 2, wedge-shaped pores having a pore diameter of 1 μm or less and pore diameters of 2 to 2 are formed on the particle surface.
It is recognized that there are many wedge-shaped pores having a size of about 3 μm, and the above-mentioned large pores are scattered among these smaller pores. The result of powder X-ray analysis is 1300.
The tetragonal zirconia (ZrO ₂ ) and monoclinic zirconia peaks were shown at ℃, indicating that the spheres were not calcia (CaO) stabilized zirconia (CSZ). The results of the compositional analysis showed that most of Ca added with 20 mol% of Zr of 95.66 mol% and Ca of 4.34 mol% flowed out of the sphere.

Example 2 3 ml of a benzene solution containing 0.40 mmol of calcium ethoxide and 1.60 mmol of zirconium ethoxide [ratio of calcium ethoxide to zirconium ethoxide is 20 mol%] in 250 ml of formamide containing 1.25 ml of 4N aqueous ammonia. In addition, the mixture was vigorously agitated and dispersed by an agitator. Then, while maintaining the dispersed state,
Heated at 60 ° C for 10 minutes. This was returned to room temperature, and the produced porous solid spherical particles were collected by filtration. Then, this was washed with acetone, dried, and calcined at 1300 ° C. for 1 hour to obtain a porous zirconia sphere of the present invention. A scanning electron microscope (SEM) photograph showing the overall structure and particle surface structure of the porous zirconia spherical particles thus produced is shown in FIG. 3 of the accompanying drawings. From the photograph of FIG. 3, it can be seen that the spherical particles of zirconia obtained in this example are spherical and that a large number of small pores having a small pore size are relatively uniformly distributed over the entire spherical surface. The diameter of the zirconia spherical particles was about 60 μm. Further, FIG. 4 shows a scanning electron micrograph of the particle surface structure showing a part of the surface of the zirconia spherical particles in a further enlarged manner. According to the photograph of FIG. 4, pores having an average pore diameter of about 1 μm are uniformly present on the particle surface.
It is recognized that the zirconia spherical particles have a smoother surface structure than that of the spherical particles. It was found that the surface was porous but smooth, and the pore size of the pores was smaller than in Example 1 and the particle sizes were uniform. It is considered that this is because the addition of aqueous ammonia suppressed the outflow of calcium ethoxide into formamide. Further, the powder X-ray analysis results showed a peak of tetragonal zirconia at 1300 ° C., and it was found that the zirconia spheres were calcia-stabilized zirconia (CSZ). As a result of compositional analysis, it was found that Zr was 92.25 mol% and Ca was 7.75 mol%, and the outflow of calcium ethoxide into formamide was suppressed more than in the case of producing the spheres by the method of Example 1.

FIG. 5 shows a scanning electron micrograph showing the internal structure of the porous zirconia spherical particles obtained in this Example 2 when the porous zirconia spherical particles were bisected from the center and divided. In addition, FIG. 6 shows a scanning electron micrograph showing the internal structure of the grain in the fractured surface in such a state further enlarged. According to the photograph in FIG. 6, it can be seen that the band-shaped pores with a width of 1 μm or less extend from the particle surface toward the center of the particle and are in a porous state.

Example 3 A benzene solution containing 0.40 mmol of calcium ethoxide and 1.60 mmol of zirconium ethoxide [Ca
(Ratio of (OEt) ₂ : 20 mol%] 3 ml was added to 250 ml of formamide containing 1.25 ml of 4N aqueous ammonia and 0.35 g of oxalic acid, and was vigorously stirred to disperse. Then, while maintaining the dispersed state, it was heated at 60 ° C. for 10 minutes. This was returned to room temperature, and the produced porous solid spherical particles were collected by filtration. Then, this was washed with acetone, dried, and calcined at 1300 ° C. for 1 hour to obtain a porous zirconia sphere of the present invention. A scanning electron microscope (SEM) photograph showing the entire structure and particle surface structure of the porous zirconia spherical particles thus produced is shown in FIG. 7 of the accompanying drawings. From the photograph in FIG. 7, it can be seen that the spherical particles of zirconia obtained in this example are spherical and that a large number of small pores are relatively uniformly distributed over the entire spherical surface. The diameter of this zirconia spherical particle is about
It was 70 μm. Further, FIG. 8 shows a scanning electron micrograph of the particle surface structure showing a part of the surface of the zirconia spherical particles further enlarged. According to the photograph of FIG. 8, small pores are uniformly distributed on the particle surface, and V-shaped pores having a width of about 0.2 μm and other pores are scattered between the small pores. Is recognized. The surface was porous but smooth, and the pore size of the pores was smaller than that of Example 2. It is considered that this is because the addition of aqueous ammonia and oxalic acid further suppressed the outflow of calcium ethoxide into formamide. Further, the powder X-ray analysis result showed a peak of tetragonal zirconia at 1300 ° C., and it was found that the sphere was calcia-stabilized zirconia (CSZ). As a result of the compositional analysis, it was found that the flow of calcium ethoxide into formamide at Zr86.99 mol% and Ca13.01 mol% was further suppressed as compared with the case of producing the spheres by the method of Example 2. .

Example 4 0.12 mmol of yttrium ethoxide Y (OC ₂ H ₅ ).
Benzene solution containing ₃ and 1.88 mmol zirconium ethoxide [Y (OC
₂ H ₅ ) ₃ ratio: 6 mol%, Y ₂ O ₃ ratio: 3 mol%] 3
ml was added to 250 ml of formamide and shaken vigorously to form fine droplets to disperse. While keeping the dispersed state,
Heated at 60 ° C for 10 minutes. Then return to room temperature, filter,
The generated porous solid spherical particles were collected by filtration. Then, this was washed with acetone, dried, and calcined at 1300 ° C. for 1 hour to obtain a porous zirconia sphere of the present invention. A photograph of the obtained zirconia spheres by a scanning electron microscope (SEM) is similar to that shown in FIG. 1, and it was found that the spheres were 50-100 μm in diameter and were porous. The result of powder X-ray analysis is 1300.
The peak of tetragonal zirconia was shown at ℃, and the sphere was found to be yttria (Y ₂ O ₃ ) stabilized zirconia (YSZ). As a result of compositional analysis, Zr was 94.08 mol% and Y was 5.92 mol%, and it was found that yttrium ethoxide was hardly released into formamide.

〔The invention's effect〕

According to the present invention, a porous zirconia sphere having the following characteristics can be obtained. That is, it has the characteristics that it is a porous sphere having uniform pores with a pore diameter of about 1 μm, and that the surface is smooth and the particle size of the spheres is 50-100 μm. Moreover, according to the present invention, these porous zirconia spheres can be produced by a relatively simple method and can be easily produced on an industrial scale.

The fine zirconia spheres having a porous structure thus obtained are
Zirconia has excellent properties such as high strength, high toughness, wear resistance, and chemical resistance, as well as the special property of having uniform fine pores of about 1μ, and it is a highly functional material such as industrial and medical materials. For example, it is expected to be used as a sensor, a catalyst, a refractory material in many application fields.

[Brief description of drawings]

FIG. 1 is a scanning electron micrograph showing the entire structure and particle surface structure of the porous zirconia spherical particles obtained in Example 1 of the present invention, and FIG. 2 is a particle obtained by further enlarging a part of the surface of the particles. FIG. 3 is a scanning electron micrograph of the surface structure; FIG. 3 is a scanning electron micrograph showing the entire structure and particle surface structure of the porous zirconia spherical particles obtained in Example 2, FIG.
The figure shows a scanning electron micrograph of the particle surface structure in which a part of the surface of the particle is further enlarged, and FIG. 5 shows the internal structure of the particle when the zirconia spherical particles are divided in half. FIG. 6 is a scanning electron micrograph of the internal structure of the particle shown in a further enlarged scale of the fracture surface of the particle shown in FIG. 5; FIG. 7 is the entire zirconia spherical particle obtained in Example 3. A scanning electron micrograph showing the structure and the particle surface structure, and FIG. 8 is a scanning electron micrograph of the particle surface structure in which a part of the surface of the particle is further enlarged.

Claims (2)

[Claims] 1. Zirconium melted by adding calcium alkoxide or yttrium alkoxide
An organic solvent solution of an alkoxide was used as a dispersoid, and this solution was dispersed in formamide as a dispersion medium or in formamide to which at least one of aqueous ammonia and oxalic acid was added in the form of fine droplets. While maintaining the state, to form solidified spherical particles by heating to a temperature lower than the boiling point of the solvent used for the alkoxide solution, separate these spherical particles from the dispersion medium, and then 1200
A method for producing fine porous zirconia spheres, which comprises firing at -1500 ° C. 2. Yttria- or calcia-stabilized zirconia microspheres having a diameter in the range of 50 to 100 microns and a porous internal structure.