JPH06199569A - Production of zirconia and zirconia molding stabilized with yttria - Google Patents

Abstract

(57) [Summary] [Purpose] A zirconia sol that can maintain a stable state for a long period of 3 months or more and that can be fired at a lower temperature than conventional methods can be used to form zirconia and yttria-stabilized zirconia molded products. It is intended to provide a manufacturing method. According to a first production method of the present invention, a zirconium alkoxide is dissolved in a solvent, and 1N nitric acid used as a catalyst in the solution is diluted with the solvent to hydrolyze the zirconium alkoxide. Repeatedly pouring water and concentrating until the dispersion medium of the sol obtained by the hydrolysis is replaced with water, gelling the dispersion at room temperature in the air and drying, and the dried formed body Consisting of the steps of baking. The second manufacturing method further includes a step of dissolving yttrium nitrate powder in the dispersion liquid between the water injection and concentration steps and the gelation and drying steps.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing zirconia and yttria-stabilized zirconia (YSZ) molded products by the sol-gel method, and particularly to ZrO ₂ system and Y ₂ system which are applicable to separation membranes, solid electrolyte fuel cells and the like. the O ₃ -ZrO ₂ based molded product of the sol - relates to a process capable of producing at a relatively low temperature firing (densification) temperature by combined use of gel method and liquid phase method.

[0002]

2. Description of the Related Art In recent years, with the rapid growth of demand for ceramics in the industrial field and medical field, high-quality ceramics have been increasingly demanded, and researches on the utilization of ceramics in new fields have been actively conducted.

Zirconia-based ceramics are not only widely used for coating treatment of various materials because of their remarkable corrosion resistance and acid resistance, but especially yttria-stabilized zirconia (hereinafter referred to simply as YS).
It is called Z. ) Has been attracting attention as a material for various separation membranes since it is known that it exhibits permeability only to oxygen.

Conventional methods for obtaining yttria-stabilized zirconia include: 1. A method of mixing fine powders of zirconia and yttria and calcining the mixed powder; Two methods have been considered: a synthetic method by hydrolysis of zirconium alkoxide.

[0005]

SUMMARY OF THE INVENTION In the first method,
There is a limit to the pulverization of the raw material powder and the homogenization of the mixing, it is difficult to obtain a product of uniform quality, and the firing required to densify the crystal structure of the obtained product also requires a high temperature (about 1500 ° C). .

On the other hand, in the second method,
As disclosed in Japanese Patent Application Publication No. 199163, it is said that a product of high purity and high uniformity can be obtained by a low temperature manufacturing process, and further, free shape can be imparted, which is an advantage. There is. However, a solution obtained by hydrolyzing a zirconium alkoxide (hereinafter, simply referred to as a zirconia sol) is unstable and precipitation is likely to occur. In order to prevent this precipitation, it must be treated in a glove box, for example, so as not to come into contact with air, and the operation is complicated and industrialization is difficult.

In order to stabilize the zirconia sol, the above-mentioned publication proposes a method of slowing the hydrolysis by using water of crystallization, but this method has a drawback that it requires a delicate operation. Also, published in 1991, Patent Application No. 2329
In 75, after adjusting the solution, a special device is used for 5 to 6
It has been proposed to stabilize by performing a complicated operation of concentrating more than twice.

Further, in the method for producing a zirconia-based molded article disclosed in any of the above-mentioned publications, although it is lower than the firing temperature in the method before that, it is difficult to densify the crystal structure of the molded article. The temperature for the necessary firing is still high.

The present invention has been made in order to solve the problems in the prior art as described above, and the purpose thereof is to obtain a zirconia sol which maintains a stable state for a long period of time and to have a crystal structure. It is an object of the present invention to provide a method for producing a zirconia- and yttria-stabilized zirconia molded article, which enables firing for densification to be performed at a lower temperature than conventional methods.

[0010]

In order to achieve the above object, according to the first aspect of the present invention, a zirconium alkoxide is dissolved in a solvent, and 0.1 N (used as a catalyst in the solution) is used. 0.1N) to 3N (3N), preferably 1N (1N) nitric acid diluted with a solvent to hydrolyze the zirconium alkoxide, and to disperse the sol obtained by the hydrolysis. Repeated water injection and concentration until the medium was replaced with water, and the thus obtained dispersion containing zirconia particles (hydrosol) was allowed to gel at room temperature in the atmosphere, further dried, and dried. There is provided a method of manufacturing a zirconia molded product, which comprises the steps of firing a molded product.

In order to achieve the above object, the second aspect of the present invention
According to an embodiment, the zirconium alkoxide is dissolved in a solvent, and the zirconium alkoxide is used as a catalyst in the solution.
1N (0.1 rule) to 3N (3 rule), preferably 1N
Hydrolyzing the zirconium alkoxide by adding a solution prepared by diluting (1 N) nitric acid with a solvent, and repeatedly performing water injection and concentration until the dispersion medium of the sol obtained by the hydrolysis is replaced with water. Dissolving a powder of yttrium nitrate in a dispersion liquid (hydrosol) containing the zirconia particles thus obtained to cause a complex between the zirconia particles, and a dispersion containing the zirconia particles surface-modified with yttrium. Provided is a method for producing a yttria-stabilized zirconia molded article, which comprises the steps of gelling a liquid in the atmosphere at room temperature, further drying, and baking the dried molded body.

According to one embodiment of the present invention, in the manufacturing method according to any one of the first and second aspects, the zirconium alkoxide contains zirconium in an amount of 0.1 mol / mol. In the solution containing nitric acid, the zirconium content is 0.05 mol / mol. In the production method according to any one of the two aspects, the solvent is 2-propanol. According to still another embodiment of the present invention, in the manufacturing method according to any one of the first and second aspects, the firing is performed at a temperature of 300 to 1000 ° C.

According to still another embodiment of the present invention, in the manufacturing method according to the second aspect, the yttrium powder has a molar ratio (2Y / (2Y + Zr) of yttrium (Y) and zirconium (Zr). ) 0-18
Amounts in the range of% are added.

[0014]

In the present invention, zirconium alkoxide (zirconium-tetra-n-butoxide) is dissolved and hydrolyzed in a 2-propanol solvent in a short time by using a strong acid such as nitric acid as a catalyst. Polycondensation of the zirconia particles dispersed in is suppressed, and the particle size is extremely small (average of about 5 nm). Therefore, the zirconia particle dispersion liquid (sol) after the dispersion medium is replaced with water
For a long time (3 months or more) without agglomeration (gelation)
Keep a stable colloidal dispersion throughout.

Furthermore, when yttrium nitrate powder is added to the sol, complexation (surface modification) occurs between the zirconia fine particles, and even in this state, a stable sol in which the zirconia fine particles are dispersed can be obtained.

After gelling and drying any of the above-mentioned sols, a relatively low temperature (300 to 1000) is obtained in order to obtain a thin film or a bulk shaped product having a densified crystal structure.
℃) is fired.

[0017]

DETAILED DESCRIPTION OF THE INVENTION The present invention will now be described in more detail with reference to the accompanying drawings.

Zirconium alkoxide (zirconium-tetra-n-butoxide) is dissolved in 2-propanol and then reacted with water diluted with 2-propanol at room temperature. Water (H ₂ O) and zirconium (Z
The molar ratio with r) is H ₂ O / Zr = 3. At this time,
The pH of the water is adjusted with nitric acid in order to obtain a stable sol. Subsequently, the dispersion medium is replaced with water from 2-propanol. This replacement is achieved by repeatedly pouring and concentrating excess water.

After the sol dispersion medium was replaced with water, the zirconia dispersed particle size distribution in the sol obtained by dynamic light scattering showed a sharp single peak at 4 nm as shown in FIG. showed that. Then, it was observed with a field emission scanning electron microscope (FE-SEM) that the average primary particle size of the nanostructure of the gelled sample was about 5 nm (see (a) of FIG. 6). From this, it can be understood that the primary particles are dispersed in the sol without being aggregated. Although the details of the reason have not been clarified, zirconium alkoxide is hydrolyzed in a solvent in a short time by a strong acid catalyst, while suppressing polycondensation of zirconia particles dispersed in a solution by the action of a strong acid. This is considered to be the reason. Therefore, the primary particles in the sol are dispersed while maintaining the fine particle state as described above, and this stable state (colloidal dispersion system) can be maintained for a long period of 3 months or more.

A required amount of yttrium nitrate powder is added to the sol obtained by the above adjustment. The addition amount is determined so that yttrium (Y) and zirconium (Zr) have a relationship of 2Y / (2Y + Zr) = 0 to 18 (mol%).

FIG. 2 shows the relationship between the amount of yttrium nitrate powder added and the particle size distribution in the sol. As is clear from FIG. 2, as the amount of yttrium added increases, the particle size in the sol also increases to 10 to 55 nm. As a reason for this, it is conceivable that the yttrium fine particles are combined so as to function as a bridge between the fine particles of zirconia (surface modification), and when this is represented by a diagram, as shown in FIG. , Zirconia particles are bound to each other through yttrium.

As described above, it is understood that the method of synthesizing the composite oxide of the present invention is completely different from the conventional method of compounding the inside of particles. Therefore, no remarkable change is observed in the nanostructure after gelation of the sol composited by the surface modification of the particles. Aggregation of yttrium with respect to zirconia particles is weak, and it is considered that the film is easily thinned or destroyed during drying or firing after gelation.

FIG. 4 shows the results of differential thermal analysis (DTA) of two types of unsupported samples obtained by gelling a zirconia sol containing no yttrium and a mixed sol containing both yttrium and zirconium, and further drying them. As is clear from this figure, the former is 427 ° C and the latter is 453 ° C.
Shows a very sharp exothermic peak. On the other hand, at these temperatures, no significant change in weight is observed in either of them, which indicates that the heat is generated due to the change in internal structure (crystallization). From the results of X-ray diffraction, the former also shows that the amorphous phase is changed to the monoclinic phase (Zr
It has been demonstrated that O ₂ ) and cubic crystals (YSZ) are generated in the latter case (see X-ray diffraction patterns shown in (a) and (b) of FIG. 5).

FIGS. 6 and 7 show a field emission scanning electron microscope (FE) for each of the above two types of samples.
-SEM) shows the results of observation (micrograph of the internal structure). In both figures, (a) is before firing, (b) is 50
The results are shown after firing at 0 ° C. and (c) after firing at 1000 ° C., respectively.

From these micrographs, both samples were 50
At 0 ° C, an increase in particle size (crystallization) was observed,
It can be seen that at ℃, most of the densification has already been completed. Further, in both (c) of FIG. 6 and FIG. 7, it can be seen that the crystallite size is about 50 nm, and the densification is finely and uniformly controlled.

FIGS. 8 to 13 show microscopic photographs of the internal structure of the field emission scanning electron microscope, which were carried out on two different types of samples. 8 and 11 show the results before firing, FIGS. 9 and 12 show the results after firing at 500 ° C., and FIGS. 10 and 13 show the results after firing at 900 ° C., respectively.

The results shown in FIGS. 8 to 13 have a better internal structure in the crystalline state than the results shown in FIGS. 6 and 7.

Further, when the above-mentioned two kinds of sols were respectively formed into dip films on an alumina porous tube and then baked at 500 ° C., and their nanostructures were observed, different from the case of the above-mentioned unsupported sample, Both grow into rod-shaped crystals,
It was found that it had already been densified at a low temperature of 500 ° C.

Next, examples of the present invention will be shown. Example 1 2 per 9.59 g of zirconium-tetra-n-butoxide
-Add propanol In 1 to 5.5, the resulting zirconia particle size showed a distribution having a sharp peak at 4 nm. (See FIG. 1) The solution was stable for 3 months or longer. Example 2 Four solutions (sols) prepared in the same manner as in Example 1 were prepared,
Yttrium nitrate as powder is added to these, and the molar ratio of yttrium (Y) and zirconium (Zr) is 2Y / (2Y
+ Zr) = 0.03, 0.05, 0.12, and 0.
18 were added to each to prepare a dissolved solution. The pH of these solutions was 5.1 to 5.5, and the particle size of zirconia bound through yttrium increased with an increase in the amount of yttrium added. (See FIG. 2) These solutions were stable for 3 months or longer. Example 3 The solutions (sols) prepared in Examples 1 and 2 were spread on a petri dish, and gelled and dried at room temperature in the air. On the other hand, a thin film was formed by dip-coating these solutions on an alumina porous tube, and gelling and drying were similarly performed in the atmosphere at room temperature. The bulk and thin film dry gels thus obtained were calcined at 300 to 1000 ° C., X-ray diffraction measurement and surface state observation by SEM were carried out, and both were crystallized at 400 ° C. and 1000 ° C. or less. At that time, densification due to grain growth was observed.

In the examples, 1N nitric acid was preferably used as a catalyst in the zirconium alkoxide propanol solution, but 0.1N to 3N nitric acid may be used if necessary.

The above description is merely illustrative of the preferred embodiments of the present invention and the scope of the present invention is not limited thereto. Many variations and modifications of the invention will be readily apparent to those of ordinary skill in the art without departing from the scope of the invention.

[0032]

As described above, according to the present invention, it is possible to prepare a zirconia sol and a YSZ sol which are stable over a long period of time as compared with the conventional method, and the diameter of zirconia particles dispersed in the obtained sol. Is also extremely small. Therefore, the crystallization temperature and the densification temperature also become extremely low, various related operations are facilitated, and energy can be saved greatly from the economical aspect.

Furthermore, since the zirconia and yttria-stabilized zirconia molded products obtained after firing have a fine and uniform crystal structure, they can be suitably used for various separation membranes, solid electrolyte fuel cells and the like. It is certain that it could be widely applied to undeveloped applications.

[Brief description of drawings]

FIG. 1 is a graph showing a particle size distribution of zirconia zirconia fine particles in a zirconia sol of the present invention.

FIG. 2 is a graph showing the relationship between the particle size of yttrium-bonded zirconia particles in the yttrium-containing zirconia sol of the present invention and the amount of yttrium added.

FIG. 3 is an explanatory view of the surface modification of the present invention in which yttrium is bonded to zirconia particles.

FIG. 4 is a graph showing the differential thermal analysis results for the zirconia and yttria-stabilized zirconia molded products of the present invention.

FIG. 5 is a graph showing the X-ray diffraction results of the zirconia and yttria-stabilized zirconia moldings of the present invention, (a) showing the results of zirconia moldings, and (b) showing the results. It is a result performed on a yttria-stabilized zirconia molded product.

FIG. 6 is a photomicrograph of the internal structure of a zirconia molded article of the present invention, taken by a field emission scanning electron microscope, in which (a) is unbaked and (b) is baked at 500 ° C. (C) is what was baked at 1000 degreeC.

FIG. 7 is a photomicrograph of the internal structure of a yttria-stabilized zirconia molded article according to the present invention, which was observed by a field emission scanning electron microscope.
Is baked at 500 ° C., and (c) is baked at 1000 ° C.

FIG. 8 is a photomicrograph of the internal structure of another unsintered zirconia molded product of the present invention, which is obtained by a field emission scanning electron microscope.

FIG. 9 is a photomicrograph of the internal structure of another zirconia molded product fired at 500 ° C. according to the present invention, taken by a field emission scanning electron microscope.

FIG. 10 is a photomicrograph of the internal structure of a zirconia molded product fired at 900 ° C. according to the present invention, taken by a field emission scanning electron microscope.

FIG. 11 is a photomicrograph of the internal structure of another unfired yttria-stabilized zirconia molding of the present invention, taken by a field emission scanning electron microscope.

FIG. 12 is a photomicrograph of the internal structure of another yttria-stabilized zirconia molded product fired at 500 ° C. according to the present invention, taken by a field emission scanning electron microscope.

FIG. 13 is a photomicrograph of the internal structure of another yttria-stabilized zirconia molded product fired at 900 ° C. according to the present invention, taken by a field emission scanning electron microscope.

[Procedure amendment]

[Submission date] December 22, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is a graph showing a particle size distribution of zirconia zirconia fine particles in a zirconia sol of the present invention.

FIG. 2 is a graph showing the relationship between the particle size of yttrium-bonded zirconia particles in the yttrium-containing zirconia sol of the present invention and the amount of yttrium added.

FIG. 3 is an explanatory view of the surface modification of the present invention in which yttrium is bonded to zirconia particles.

FIG. 4 is a graph showing the differential thermal analysis results for the zirconia and yttria-stabilized zirconia molded products of the present invention.

FIG. 5 is a graph showing the results of X-ray diffraction performed on the zirconia and yttria-stabilized zirconia molded products of the present invention, (a) showing the results performed on the zirconia molded products, and (b). Are the results obtained for yttria-stabilized zirconia moldings.

6A and 6B are micrographs of the internal grain structure of a zirconia molded article of the present invention, which were taken by a field emission scanning electron microscope. FIG.
And (c) are those fired at 1000 ° C.

FIG. 7 is a photomicrograph of the internal grain structure of the yttria-stabilized zirconia molded product of the present invention, which was observed by a field emission scanning electron microscope, and (a) is an unfired product.
(B) is fired at 500 ° C, (c) is 1000 ° C
It was baked in.

FIG. 8 is a micrograph of a grain structure inside by a field emission scanning electron microscope, which was performed on another unfired zirconia molded product of the present invention.

FIG. 9 is a micrograph of a grain structure inside by a field emission scanning electron microscope, which is performed on another zirconia molded product fired at 500 ° C. of the present invention.

FIG. 10 is a photomicrograph of a grain structure inside by a field emission scanning electron microscope, which was performed on another zirconia molded product fired at 900 ° C. of the present invention.

FIG. 11 is a photomicrograph of the internal grain structure by field emission scanning electron microscopy performed on another green yttria-stabilized zirconia molding of the present invention.

FIG. 12 is a photomicrograph of grain evolution inside by a field emission scanning electron microscope performed on another yttria-stabilized zirconia molding fired at 500 ° C. of the present invention.

FIG. 13 is a photomicrograph of the internal grain structure of a yttria-stabilized zirconia molded article of the present invention fired at 900 ° C. by a field emission scanning electron microscope.

Claims (9)

[Claims] 1. A zirconium alkoxide is dissolved in a solvent, and a zirconium alkoxide used as a catalyst in the solution is used.
1N (0.1 rule) to 3N (3 rule), preferably 1N
Hydrolyzing the zirconium alkoxide by adding a solution prepared by diluting (1N) nitric acid with a solvent, and repeatedly performing water injection and concentration until the dispersion medium of the sol obtained by the hydrolysis is replaced with water. And a zirconia molded article comprising the steps of gelling the dispersion (hydrosol) containing the zirconia particles thus obtained at room temperature in the atmosphere and further drying, and calcining the dried molded article. Production method. 2. A zirconium alkoxide is dissolved in a solvent, and a zirconium alkoxide used as a catalyst in the solution is used.
1N (0.1 rule) to 3N (3 rule), preferably 1N
Hydrolyzing the zirconium alkoxide by adding a solution prepared by diluting (1N) nitric acid with a solvent, and repeatedly performing water injection and concentration until the dispersion medium of the sol obtained by the hydrolysis is replaced with water. Dissolving a powder of yttrium nitrate in a dispersion liquid (hydrosol) containing the zirconia particles thus obtained to cause a complex between the zirconia particles, and a dispersion containing the zirconia particles surface-modified with yttrium. A method for producing a yttria-stabilized zirconia molded article, which comprises the steps of gelling a liquid in the air at room temperature, further drying, and calcining the dried molded body. 3. The zirconium alkoxide contains 0.1 mol of zirconium. The solution containing nitric acid with respect to the solution containing coxide,
Zirconium is 0.05 Method for manufacturing near-molded article. 4. The zirconium alkoxide has a zirconium content of 0.1 The solution containing nitric acid with respect to the solution containing coxide,
Zirconium is 0.05 A method for producing a rear-stabilized zirconia molded product. 5. The method for producing a zirconia molded article according to claim 1, wherein the solvent is 2-propanol. 6. The method for producing a yttria-stabilized zirconia molded article according to claim 2, wherein the solvent is 2-propanol. 7. The method for producing a zirconia molded article according to claim 1, wherein the firing is performed at a temperature of 300 to 1000 ° C. 8. The yttrium powder has a molar ratio (2Y / (2Y) of yttrium (Y) and zirconium (Zr).
The method for producing a yttria-stabilized zirconia molded article according to any one of claims 2 and 4 and 6, characterized in that + Zr)) is dissolved in an amount of 0 to 18%. 9. The calcination is carried out at a temperature of 300 to 1000 ° C. 2.
A method for producing the yttria-stabilized zirconia molded article according to any one of 1.