JP3205681B2 - Method for producing zirconia powder - Google Patents

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 powder. More specifically, the present invention relates to a method for producing a new zirconia powder useful for application to lead zirconate titanate (PZT), stabilized zirconia (SZ), partially stabilized zirconia (PSZ), and other fine ceramic materials. It is about.

[0002]

2. Description of the Related Art Zirconia ceramics have excellent acid resistance and conductivity at high temperatures, a relatively large coefficient of thermal expansion and thermal conductivity, excellent toughness at high temperatures, and transmission of infrared and visible light at high temperatures. It has relatively good properties and a high refractive index.

Further, zirconia ceramics
Since various functions appear by using various stabilizers and additives, they are widely used not only as structural materials but also as functional materials, and their growth is expected to increase in the future. Conventionally, zirconia sintered bodies have been
In particular, it has been used for refractories for melting glass, steel making and the like. Recently, it has begun to be rapidly used as fine ceramics, and has now accounted for about 20% of all applications. These applications include, for example, thermal functions such as heat insulation (insulation materials, diesel engine parts, etc.) and electrical functions such as conductivity (ultra-high temperature furnace resistance heating elements,
Electronic functions such as automotive exhaust gas temperature sensors, magnetic heads and rollers, ion conductivity, etc. (oxygen sensors for oxygen meters, automotive exhaust gas oxygen sensors, oxygen and carbon measuring elements in metals, CO gas sensors, oxygen pumps, Complete combustion sensors, high-temperature solid electrolyte fuel cells, etc., mechanical functions such as non-magnetic, tough, and cutting properties (crushing balls, coil adjustment drivers, golf club head faces, spike pins, scissors, kitchen knives, cutting tools) , Dies, nozzles, pumps, bearings, etc.), optical functions such as photorefractive properties (cubic zirconia, artificial jewelry, etc.)
There are various materials using In addition, zirconia powder, which is not the main component, but uses zirconia powder as the main component, includes piezoelectric materials (ignition elements, handsets, speakers, ultrasonic transducers, There are devices, ultrasonic power oscillators, oscillators, surface wave filters, and the like, and piezoelectric materials using an electro-optical function (image storage display devices, light modulators, optical shutters, flash blocking glasses, etc.).

[0004] As described above, zirconia (ZrO ₂ ) sintered bodies are widely used as high-temperature materials, electronic materials, and structural materials, and with this, stricter requirements are imposed on their material performance. There are. This zirconia has a transition point at about 1200 ° C., and is accompanied by large volume expansion and contraction. As a result, since the zirconia sintered body is destroyed there, it is rarely used alone.

As a practical material, a stabilizer (CaO, MgO, Y ₂ O ₃ , CeO, etc.) is usually added in an amount of several to several tens percent. In addition, electronic materials (for example, P
In ZT), zirconia powder is used as one of the important main components together with lead oxide (PbO) and titania (TiO ₂ ). In any of these applications, the performance as a material is greatly influenced by the microstructure of the sintered body, and the microstructure is governed particularly by the powder characteristics of the zirconia powder. For this reason, particularly recently, there is a need for a fine and uniform sinterable zirconia powder.

Hitherto, zirconia raw material powder has been industrially produced by a neutralization precipitation method, a hydrolysis method, an alkoxide hydrolysis method,
It is manufactured by a wet method such as hydrothermal synthesis. Of these, zirconia powder by the neutralization precipitation method is usually produced by further pyrolyzing and calcining hydrated zirconia obtained through the steps of melting, zirconium salt precipitation by alkali neutralization, filtration, washing and drying. Have been.
This method is the cheapest method for producing zirconia powder, but zirconia hydrate is an amorphous aggregate,
The properties of the zirconia powder obtained by calcining this are 2
Since it is bad due to the presence of secondary particles and high non-uniformity, there is a considerable problem in using it for fine ceramic materials.

The zirconia powder obtained by the hydrolysis method is obtained by further calcining zirconia hydrate obtained through dissolving, hydrolyzing and drying a zirconium salt. The hydrated zirconia obtained by this method is crystalline, and although various properties of the zirconia powder are considerably improved as compared with the conventional hydration precipitation method, the uniformity thereof is not yet sufficient. Further, in order to obtain a uniform crystalline zirconium hydrate, it is necessary to ripen at a temperature of 100 to 200 ° C. for 1 to 2 days, which is economically problematic.

In the hydrothermal synthesis method, a high-quality crystalline zirconia powder can be obtained by subjecting a dissolved zirconium salt to a hydrothermal reaction, filtration and washing with water. Although there is an advantage that a calcination step is unnecessary, the hydrothermal reaction requires a temperature of 300 ° C. or more, a pressure of 100 MPa or more, and a reaction time of one day or more. Therefore, there is a problem in cost, and it is not yet suitable for mass production.

In the alkoxide method, zirconium chloride is reacted with an alcohol in the presence of ammonia to hydrolyze the obtained zirconium alcoholate, and after drying and pulverization, is calcined. The zirconia hydrate obtained by this method is non-crystalline, and the powder properties of zirconia are much better than those of the neutralization precipitation method and hydrolysis method. However, in this production method, iso-propyl
Due to the use of alcohol, the resulting zirconia powder is much more costly and has considerable problems in applications other than high value-added thick films.

On the other hand, many fine ceramic materials are industrially manufactured by a so-called dry method by mixing high-purity oxide powder. In this case, the largest factor that affects the microstructure and physical properties of the sintered body is the powder characteristics of the oxide powder. For example, in a PZT piezoelectric material that is a functional material,
Zirconia is only one of the constituent components (1/4 mol%), but what significantly governs the microstructure and piezoelectric properties of the sintered body is the powder properties of the zirconia powder. If the powder characteristics of zirconia are poor, the firing temperature of PZT increases, and as a result, PbO evaporates remarkably and the distribution of zirconium and titanium becomes more biased. As a result, not only is the microstructure of the sintered body inhomogeneous,
The piezoelectric characteristics are significantly reduced. On the other hand, in the case of PZT, which is a structural material, if the powder characteristics of the zirconia powder are poor, a high-density sintered body cannot be obtained, and the dispersion of the stabilizer becomes uneven. Unless a highly dense sintered body is obtained, it cannot be used as a structural material. Also, non-uniform distribution of the stabilizer results in the appearance of multiple crystalline phases and non-uniform microstructure. As a result, mechanical properties such as fracture strength and fracture toughness are greatly reduced. Therefore, obtaining a zirconia powder having excellent powder properties is one of the important issues for functional materials and structural materials.

In such a situation, no matter how fine,
Whether to produce uniform and easily sinterable high-quality zirconia powder at lower cost is an issue that must be resolved promptly, and as a means of solving this issue, the most practical low-cost method As described above, there is a need for a drastic improvement in the neutralization precipitation method. Therefore, when examined in more detail, the zirconium hydrate obtained by the neutralization precipitation method is usually a sol-like precipitate, and therefore, washing and filtration are almost impossible. When ammonium water is titrated to the zirconium solution, for example, as shown in FIG. 1, zirconium hydrate precipitates in two stages (exactly three stages). The first stage is a precipitate of perzirconic acid [H ₂ ZrO ₅ ] formed in a strongly acidic region (around pH = 2), and the second stage is a zirconia formed in a slightly neutral region (around pH = 6.5). This is a precipitate of tetrahydrate [Zr (OH) ₄ ]. The zirconia powder obtained by calcining such a hydrate acts as two types of mixtures (exactly three types) having different powder characteristics, despite having exactly the same chemical composition. Since this is the nature of the zirconia solution itself, it is impossible in principle to obtain a uniform precipitate and a uniform calcined powder even if the conditions of the neutralization precipitation method are controlled.

It is a well-known fact that the use of aqueous ammonia [NH ₄ OH] as a precipitation-forming agent deteriorates the precipitation properties of zirconium hydrate. When the precipitation properties deteriorate, not only washing and filtration become difficult, but also
Occlusion of anions and adsorption of cations increase. The anions occluded on the surface of the precipitate promote the growth of primary particles and the formation of secondary particles of zirconia during the calcination process.

On the other hand, the cations adsorbed inside the precipitate remain in the calcined product. The cationic impurities remaining in the zirconia powder not only suppress sintering but also adversely affect the microstructure of the sintered body and its physical properties. Further, when the properties of the zirconium solution are changed (for example, formation of a complex), the precipitation property of the zirconium hydrate tends to be further deteriorated. When an alkali such as caustic soda [NaOH] or caustic potash [KOH] is used as a precipitate-forming agent, a small amount of alkali metal remains not only in the hydrate but also in the calcined powder,
This has a very bad effect on the sinterability, microstructure, piezoelectric properties, fracture toughness, etc. of the sintered body.

As described above, basic problems have been clarified in the conventional neutralization precipitation method. However, at present, there has not been found any means for solving these problems and producing a fine and uniform zirconia powder that is easy to sinter.
The present invention has been made in view of the above circumstances, and overcomes the disadvantages of the prior art to achieve high purity, easy sinterability,
It is an object of the present invention to provide a new method capable of producing a highly uniform zirconia powder without secondary particles by a more economical method.

[0015]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method for producing zirconia powder by thermally decomposing and calcining a zirconium hydrate obtained by a neutralization reaction of a zirconium solution and aqueous ammonia. The present invention provides a method for producing zirconia powder, which comprises adding hydrogen peroxide to a zirconium solution.

Further, according to the present invention, in the above method, ammonium sulfate is added to the aqueous ammonia,
In some embodiments, the amounts of hydrogen peroxide and ammonium sulfate are controlled.

[0017]

The present invention has the features as described above. The background and technical basis will be described first as follows. That is, in order to obtain a uniform zirconia powder, it is necessary to firstly precipitate zirconia hydrate in one stage. As the method, a method of obtaining a precipitate (for example, oxalate) other than the hydroxide or a method of changing the properties of the zirconium solution and then precipitating the hydroxide can be considered.

The former is an easier method in terms of chemical reaction, but oxalate, for example, is somewhat toxic and somewhat disadvantageous in cost. In contrast, the latter is much more economically advantageous as long as it utilizes existing equipment. As a method of changing the properties of the solution, a method of changing the type of the solvent or forming a complex can be considered. A method of changing the solvent to a solvent other than water (eg, an alkoxide method) has already been tried, but has a problem in cost. On the other hand, if the formation of the complex can be utilized, existing facilities may be used as they are. In order for the complex to be usable, the following conditions must be satisfied. That is, there is only one kind of hydrate to be precipitated, cheap ammonia water can be used to form the precipitate, good-quality precipitate can be obtained, and impurities such as metal oxides do not remain after calcination. is there. The inventor of the present invention diligently studied from the above viewpoints, and found hydrogen peroxide as a material satisfying these conditions from the results of enormous experimental verification.

It has been confirmed that hydrogen peroxide forms a complex with zirconium ions when added to a zirconium solution, and satisfies the above conditions, thereby producing a hydrate precipitate having excellent properties. . The present invention has been completed in view of such extremely important and new technical knowledge.

Furthermore, the inventor of the present invention has reported that zirconium hydrate inherently yields only precipitates having poor properties, which is due to the fact that the rate of precipitate formation is extremely slow relative to the rate of neutralization reaction. It was also noted that if the growth rate could be increased relative to the nucleation rate of the precipitate, a hydrate precipitate with good properties could be obtained. For this purpose, there are methods such as adding a solution stabilizer to suppress the nucleation rate and adding a precipitation flocculant. For this method to be usable, the following conditions must be met: That is, the properties of the precipitation are improved, the neutralization reaction is not adversely affected, the process is simple, and no impurities such as metal oxides remain after calcination. And, specifically, the inventor of the present invention has found that a sulfate, particularly ammonia sulfate, satisfies these conditions.

As described above, the technical idea of the method for producing zirconia powder according to the present invention comprises a first step of forming a zirconium complex and a second step of improving the properties of precipitation. It is. The first stage of the process involves hydrogen peroxide [H ₂ in a zirconium solution.
O ₂ ] to form a zirconium complex. That is, a predetermined amount of hydrogen peroxide is added to the zirconium solution. The amount of added hydrogen peroxide

[0022]

(Equation 3)

It is preferred that If the addition amount is less than that, the effect of forming a zirconium complex is effective, but the effect is not always sufficient. However, when the added amount is 1 × 10 ⁻² or more , the effect reaches a saturated state. Although it may be added above the saturation value, the excess aqueous hydrogen peroxide present in the mother liquor rapidly foams due to impact, heating, or the like, and at that time, the precipitate may be scattered.

Oxygen (O ₃ ) has the same effect as hydrogen peroxide.
However, in this case, there is a problem that it is somewhat difficult to control the addition amount. In the second stage process, aqueous ammonia containing sulfate is more preferably used.
This is a process of titrating ammonia water containing ammonium sulfate into a zirconium solution. In this case, there is sulfate
Or the amount of ammonium sulfate [(NH ₄ ) ₂ SO ₄ ]

[0025]

(Equation 4)

[0026] and so as preferable to the. When the addition amount is less than that, the effect of improving the properties of hydrate precipitation is recognized, but the effect is not necessarily sufficient.
When the added amount is 1.0 or more, the effect of improving the properties of hydrate precipitation is further promoted. However, if it exceeds 5.0, not only the primary particles of the calcined zirconia powder become large, but also the generation of secondary particles tends to be remarkable.
Therefore, depending on the intended use of the zirconia powder, sulfate,
More preferably, it is necessary to adjust the amount of ammonium sulfate added. The effect of improving the properties of the hydrated precipitate is sulfate ion [SO ₄ ²⁻ ] , and if it is a water-soluble sulfate, it exhibits almost the same effect as ammonium sulfate. However, many sulfates contain metal ions and are not preferred in terms of residual impurities.

Examples of the method of adding ammonium sulfate include a method of mixing the zirconium solution with the zirconium solution prior to the titration of the aqueous ammonia, a method of dissolving the same in the aqueous ammonia and titrating the same, and a method of mixing the titrated aqueous ammonia after the titration. However, if a sulfate group (SO ₄ ²⁻ ) is added to the zirconium solution, the complex may be decomposed, which is not a very preferable method. On the other hand, if added after titration of aqueous ammonia, the effect is reduced. Both of these methods involve a one-step process.
Since the number of floors increases, it is more preferable to dissolve ammonium sulfate in ammonia water in advance and add it to the zirconium solution.

For the ammonium sulfate solution, 2 g /
It is also effective to use about 1000 ml for washing the precipitate. The hydrate precipitate of zirconium obtained through the above two processes is converted into a zirconia powder through a normal drying, thermal decomposition and calcination process. Needless to say, various kinds of zirconium salts forming a zirconium solution can be used as in the conventional case.

The zirconia powder obtained according to the present invention has high purity, fineness and good dispersibility. Therefore, it is optimal as a raw material powder used for PZT and a raw material powder used for PSZ. Hereinafter, the present invention will be described in more detail with reference to Examples.

[0030]

EXAMPLE 1 Zirconyl nitrate having a concentration of 0.1 mol [ZrO (NO ₃ )
₂ ] An aqueous solution of hydrogen peroxide [H ₂ O ₂ ] (3
(0% solution) 2 ml are added. Separately, 0.5 g of ammonium sulfate [(NH ₄ ) ₂ SO ₄ ] is dissolved in 30 ml of (1: 9) aqueous ammonia [NH ₄ OH].

While stirring the zirconyl nitrate solution,
The aqueous ammonia was titrated to obtain a zirconium hydrate precipitate. Despite the relatively large settling volume, 1
The filtration time per run was within a few minutes. After drying this precipitate, it was pyrolyzed and calcined at 700 ° C. for 2 hours. The crystal phase of the obtained calcined product [ZrO ₂ ] was monoclinic.
The surface area of this powder was 15 m ² / g, the average particle size by the sedimentation method was 0.33 μm, and the geometric standard deviation was 2.5. The particle size distribution was as shown in FIG. Example 2 In Example 1, when 0.2 g of ammonium sulfate was added, almost the same results were obtained, but the surface area of the zirconia powder was 16 m ² / g, and the average particle size was 0.28 μm. Example 3 Zirconium oxychloride having a concentration of 0.1 mol [ZrOC
l ₂ ] aqueous solution of hydrogen peroxide [H ₂ O ₂ ] in 50 ml of aqueous solution
Add 2 ml (30% solution). Separately, 0.5 g of ammonium sulfate [(NH ₄ ) ₂ SO ₄ ] is dissolved in 30 ml of (1: 9) aqueous ammonia [NH ₄ OH].

While stirring the zirconium oxychloride solution, the aqueous ammonia was titrated to obtain a zirconium hydrate precipitate. After drying the precipitate, 700
Thermal decomposition and calcination at 2 ° C. for 2 hours. The obtained calcined product [Z
[rO ₂ ] was monoclinic. The surface area of this powder was 16 m ² / g, and the average particle size by the sedimentation method was 0.32 μm.
m, geometric standard deviation was 2.6. Example 4 In Example 1, when 20 g of ammonium sulfate was added, a precipitate having good filterability was obtained. Crystal phase 100%
It was an orthorhombic phase. The surface area of the zirconia powder is about 5 m ² /
g, the average particle size was 0.67 μm. Comparative Example 1 When ammonium sulfate was not used in Example 1, a sol-like hydrate precipitate having a large sedimentation volume was obtained.
The filtration time of this precipitate was about 8 times that of the precipitate obtained in Example 1.
It took twice as long. When calcined under the same conditions as in Example 1, about 85% of the crystal phase of the obtained powder was tetragonal and about 15% was orthorhombic. The surface area of this powder is 5 m ²
/ G, the average particle size by the sedimentation method was 0.60 μm, and the distribution curve was divided into two. FIG. 3 shows the distribution. Comparative Example 2 When ammonium sulfate was not used in Comparative Example 1, a hydrate precipitate having a considerably large settled volume was obtained. The filtration time of this precipitate required about 30 times as long as the precipitate obtained in Example 1. Comparative Example 3 In Comparative Example 1, a hydrate precipitate having a relatively small sedimentation volume was obtained when no hydrogen peroxide was used. The filtration time of the precipitate was almost the same as the precipitate obtained in Example 1.

[0033]

As described above in detail, according to the present invention, a zirconia powder having not only high purity and fine particles but also high quality characteristics that there is almost no secondary particles, and is extremely advantageous in terms of cost can be obtained. It becomes possible.
Further, the zirconia powder obtained by the present invention is:
Particularly, it is extremely useful as a raw material powder for fine ceramics such as PZT and PSZ. Further, it can be widely used as a raw material powder of zirconia used for various other uses.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the pH value and the formation of a precipitate in a conventional neutralization precipitation method.

FIG. 2 is a particle size distribution diagram of a zirconia powder as an example of the present invention.

FIG. 3 is a particle size distribution diagram of a zirconia powder according to a conventional method as a comparative example.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-59-35029 (JP, A) JP-A-4-104910 (JP, A) JP-A-2-141424 (JP, A) JP-A-3- 257021 (JP, A) JP-A-61-44717 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01G 25/02

Claims (4)

(57) [Claims] 1. A method for producing a zirconia powder by thermally decomposing and calcining a zirconium hydrate obtained by a neutralization reaction of a zirconium solution and aqueous ammonia, wherein hydrogen peroxide is added to the zirconium solution .
One method of producing a zirconia powder, wherein Rukoto adding sulfate to aqueous ammonia. 2. The method according to claim 1, wherein the sulfate is ammonium sulfate. 3. The amount of hydrogen peroxide added is given by 3. The method according to claim 1, wherein: 4. The amount of ammonium sulfate to be added 3. The method according to claim 2, wherein