JPH07118016A - Uniform-composition zirconia solid solution monodisperse fine globular powder and its production - Google Patents

Abstract

PURPOSE:To obtain the powder excellent in dispersibility by hydrothermally treating an aq. soln. contg. specified amts. of Zr compd. and hydrochloric acid at >=100 deg.C, immobilizing the compd. into a monoclinic globular zirconia superfine particle and coating the surface with a hydroxide, etc. CONSTITUTION:A soln. consisting of one mol of Zr compd. (as ZrO2), 0.8-2mols of HCI and 6-10mols of H2O is hydrothermally treated at 100-220 deg.C in a closed vessel to obtain monodisperse monoclinic globular zirconia fine particles having 0.2-0.8mum diameter. The particle is vacuum-dried, then heat-treated at >=100 deg.C and immobilized into the globular fine particle stable to water. The fine particle is dispersed in the soln. of the soluble salts of rare-earth elements (Se, Y, Yb) and urea to obtain a uniform mixed suspension. A hydroxide, etc., are then deposited on the fine particle surface by the homogeneous precipitation due to the theraml decomposition of the urea in the soln. The coated particle is calcined at >=700 deg.C to cause it to enter into solid soln.

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 a large amount of submicron homogeneous zirconia solid solution monodispersed spherical fine particle powder useful as a raw material powder for high strength zirconia ceramics and oxygen ion conductive zirconia ceramics. is there.

[0002]

[Background Art] For fine powders of fine ceramics, especially for sintered bodies, densification proceeds at a relatively low temperature,
Usually, fine particle powder is used, but in order to further increase the molding packing density, and to obtain a homogeneous sintered body microstructure with good dimensional accuracy and even progress of sintering, generally high purity, It is said that fine particles having a uniform shape, a spherical shape and excellent isolation are desirable.

However, at present, zirconia fine powder used as a raw material for sintering zirconia-based fine ceramics is generally composed of ultrafine particles having a particle size of 0.2 to 0.8 μm.
Mostly, amorphous zirconium hydroxide or a calcined product such as a colloidal product having a particle size of 0.1 μm or less is finely pulverized by a ball mill or the like, and is manufactured industrially. At present, it is not monodisperse.

In addition to this problem, in zirconia ceramics, ZrO ₂ alone is not used as a sintered body, but an alkaline earth or rare earth metal oxide is always added as a stabilizer, and it is generally used as a solid solution ceramic. Therefore, the uniformity of the chemical composition is also a very important issue. Usually, in zirconia ceramics, a solid solution containing about 3 mol% Y ₂ O ₃ as a high-strength structural material and about 8 to 10 mol% Sc, Y, or Yb oxide of a rare earth metal as an ionic conductor is used. In general, in order to obtain a uniform distribution, a relatively uniform mixture is obtained by coprecipitation with an alkali from a mixed solution of these salts and a Zr salt, and calcined. A solid solution powder is obtained by pulverizing.

However, these rare earth elements are
In comparison with the above, the distribution of rare earth elements in the precipitate is difficult to be uniform, no matter how rapid co-precipitation is attempted, because the basicity is extremely strong and the precipitation rate is slow. Remaining, and in terms of individual fine particles, only those having extremely different solid solution compositions have been obtained so far. For example, for a commercial powder containing 3 mol% Y ₂ O ₃ in bulk, individual particle analysis of 1% to 1
It was said that there was a variation of 8% (Zirconia Ceramics, 9 , 115 (1987)).

The variation in the chemical composition of each fine particle influences the grain growth behavior in the sintering process similarly to the variation in the grain size, and the grain size distribution of the resulting sintered ceramics becomes non-uniform. Partially stabilized zirconia ceramics utilizes the application of volume change due to transition, so-called transition strengthening.Since the transition affects the particle size and the concentration of the stabilizer, the particle size distribution and the concentration distribution of the stabilizer are special. The mechanical strength and deterioration characteristics should be greatly improved by making them uniform. Further, in the stabilized zirconia ceramics used as the oxygen ion conductor, since the conductive property is determined by the concentration of the stabilizer, the uniformity of the concentration distribution is an essential condition for exhibiting excellent conductive performance. In particular, for thin plate ceramics used as a solid electrolyte for fuel cells, all important performances such as conductivity, strength and thermal shock resistance are considered to be determined by the particle size distribution and the concentration distribution of additive component elements. This problem is even more important as it is addressed.

Further, in recent studies, the strength change due to the addition of Al ₂ O _{3 which} hardly forms a solid solution as the third component has also been studied, but in the case of adding a trace amount, zirconia is a submicron ultrafine particle. Therefore, its uniform distribution is still a big problem. Examples of the additive component element in the present invention include chlorides and nitrates of rare earth elements such as Sc, Y, and Yb, and soluble salts such as chlorides and nitrates that easily precipitate with aqueous ammonia such as Mg, Al, and Ni.

[0008]

As described above, although the conventional zirconia fine particle powder is submicron,
Not only are the particle diameters and shapes not uniform, but the chemical composition ratios of individual fine particles are also extremely uneven, so zirconia ceramics made from them have a uniform microstructure. At present, it cannot be said that it does not possess sufficient properties. The object of the present invention is to solve this problem and to make the particle diameter 0.2 to 0.8 μm.
Within a range of substantially spherical monodisperse submicron ultrafine particles, and each of the spherical fine particles has Sc, Y,
Achieving a nearly idealized zirconia solid solution monodispersed spherical fine particle powder characterized by containing substantially the same amount of one or more necessary additional components such as Yb, and economically An object of the present invention is to provide a method for inexpensively and efficiently mass-producing.

[0009]

In order to solve such a problem, the present inventor has repeated a number of experiments and studies, especially on the ZrOCl ₂ -Zr (OH) ₄ -H ₂ O system,
By conducting extensive research by varying the composition, it was found that the particle size of the spherical agglomerated particles produced can be adjusted to 0.2 to 0.8 μm, and the uniform monodispersity of these particles was increased to completely It was found that the following method is indispensable in order to obtain a zirconia monodisperse spherical fine particle powder which is isolated and has excellent dispersibility.

That is, in the first step of the present invention, the zirconium compound, hydrochloric acid and water are the main components, and the chemical composition ratio is Z.
A homogeneous mixture or solution in which HCl is 0.8 to 2.0 mol and H ₂ O is 6 to 10 mol per 1 mol of rO ₂ is placed in an acid-resistant closed hydrothermal container, and the contents are allowed to stand still. The hydrothermal treatment is performed at a temperature of 100 to 220 ° C. for an optimum time without being placed, whereby the particle diameter is 0.2 to 0.
It is possible to synthesize monoclinic crystalline spherical zirconia fine particles that are aggregated in a substantially monodisperse spherical shape of 8 μm.

The reaction product at this time is a thick mud-like substance which is composed mainly of spherical agglomerated fine particles of monoclinic zirconia and has almost no fluidity. However, if this is directly thrown into water, this spherical agglomeration will easily occur. It collapses and disperses into primary ultrafine crystals of 0.01 μm or less, and becomes a semitransparent sol. Also, if you heat-dry the thick mud without adding water,
The spherical agglomerates are more likely to be fused together to form coarse higher-order agglomerates. Therefore, the product of the hydrothermal reaction is first dried under reduced pressure at a temperature of 50 ° C. or lower to remove most of water and hydrochloric acid before heat drying, and then heat treated at a temperature of 100 ° C. or higher for the first time. By the pretreatment, it is necessary to change to a state of spherical aggregation that is stable against water in advance. With this, for the first time,
Spherical agglomerates are isolated without fusion with each other and become spherical agglomerated fine particles excellent in monodispersity, and do not disintegrate in water, and stable spherical fine particles can be obtained.

The spherical zirconia fine particles are produced under the strong acidity of hydrochloric acid, and even if a rare earth element compound such as Sc, Y or Yb having a strong basicity is coexistent in the starting material, it is in solution. In principle, it is impossible to remain and form a solid solution directly when the zirconia spherical fine particles are formed. Therefore, in the method of the present invention, as described above, first, the spherical zirconia fine particles which are stable in water are prepared, and then the solid solution is formed into a solid solution. That is, the obtained zirconia spherical agglomerated fine particles which became stable to water were added to Sc, Y, Y
b, etc. Disperse in a solution containing a soluble salt of one or more necessary additional component elements and an appropriate amount of urea to form a uniform mixed suspension solution, which is heat-treated for a certain period of time to remove urea in the solution. By the uniform precipitation method by thermal decomposition, the hydroxide or basic carbonate of the additive component element is deposited on each surface of the zirconia spherical fine particles. After that, this treated product is calcined at a temperature of 700 ° C. or higher in the same manner as in the case of a normal coprecipitate, to be solid solution for each fine particle, or to be fixed for each fine particle.

[0013]

SPECIFIC STRUCTURE In the present invention, zirconium compound, hydrochloric acid and water are the main components, and the chemical composition ratio is 0.8 to 2.0 mol of HCl and 6 to 10 mol of H ₂ O per mol of ZrO _2.
Homogeneous, homogeneous mixtures or solutions are required as starting materials. As the amount of HCl and H ₂ O required,
The reason for limiting the extremely narrow ranges of 0.8 to 2.0 moles of HCl and 6 to 10 moles of H ₂ O to 1 mole of ZrO ₂ is that the diameters of the agglomerated spherical particles of the product are HCl and H ₂ It decreases with a decrease in the O ratio, and when HCl is 0.8 mol or less, the particle size is about 0.1 μm or less, and the spherical shape and the isolation are deteriorated. When HCl is 2.0 mol or more, the hydrothermal reaction is completed. Requires a high temperature and a long time, and the pressure of the hydrothermal container under strong acidity becomes too high to be practical. On the other hand, when H ₂ O is 6 mol or less, the fluidity of the raw material is poor and the product is not uniform. No, H ₂
When O is 10 mol or more, the fluidity of the product becomes too high,
This is because the water content impairs the isolation of the spherical aggregate particles.

In the case of a composition having an extremely high concentration of Zr component as described above, the amount of solution in the mixture is small, and the product after the reaction becomes a thick mud with almost no fluidity. It is desirable to make the raw material uniform by rotating it. When the reaction product is statically fixed, the isolation of the aggregated particles at the bottom becomes somewhat worse, and the upper surface layer becomes somewhat coarser than at the bottom, impairing the monodispersity.

To carry out the process of the invention, a starting composition,
The three variables of temperature and time must be in proper relationship. Naturally, the higher the temperature, the shorter the required treatment time, but in general, the higher the ratio of HCl / H ₂ O in the raw material composition, the larger the agglomerated particle size generated, and the longer the required hydrothermal treatment time. The temperature of the hydrothermal reaction at this time is 100 to 220 ° C.
The reason for limiting the above is that the reaction hardly progresses at 100 ° C. or lower, and at 220 ° C. or higher, the pressure of hydrochloric acid vapor is high and it becomes difficult to work with an ordinary apparatus. The most practical hydrothermal treatment temperature is 130 ° C to 180 ° C. Further, even if this hydrothermal treatment time was too long, sufficient results were not obtained, and it was found that there is an optimum hydrothermal treatment time for each combination of the raw material composition and the treatment temperature. When the hydrothermal treatment time exceeds this optimum time, the produced spherical agglomerated particles gradually collapse and the isolation becomes worse. The optimum hydrothermal treatment time becomes longer as the amount of HCl in the raw material composition increases, and becomes shorter as the hydrothermal treatment temperature becomes higher. The specific optimum temperature is experimentally determined for each raw material composition and treatment temperature. There must be.

The reaction product of hydrothermal treatment in the present invention is
It is a thick mud that has almost no fluidity and consists mainly of spherical agglomerated ultrafine particles of monoclinic zirconia.
When heated and dried at 0 ° C. or higher, they are easily partially fused to each other to easily generate secondary or tertiary aggregated particles, and it is difficult to form isolated monodispersed spherical aggregated fine particles. It is essential that the reaction product is first dried under reduced pressure at a temperature of 50 ° C. or lower to remove most of water and hydrochloric acid before heating and drying. The temperature of this reduced-pressure drying has an upper limit of about 50 ° C., and the lower the temperature, the better the isolated dispersibility of the spherical aggregated particles.

The zirconia monodisperse spherical ultrafine particles thus obtained can be easily disintegrated and dispersed even if they are simply put into water, and the ultrafine particles of ultrafine particles can be obtained.
It changes into a sol in which ultrafine crystals of less than 01 μm are dispersed. Therefore, heat treatment at 100 ° C. or higher is required after the drying under reduced pressure in order to obtain a spherical aggregate ultrafine powder that is stable against water. It is considered that in the heat treatment after drying, the soluble zirconium salt or the like which remains as an unreacted substance slightly changes to ZrO ₂ , and the spherical aggregated particles are fixed and become stable to water. For this purpose, treatment with ammonia gas may be considered.

Since the zirconia spherical agglomerated fine particles which have been stabilized against water are uniformly dispersed as spherical particles in a weakly acidic aqueous solution having a pH of 7 or less, necessary additive element elements, for example, nitrates and chlorides of rare earth elements are required. Can be uniformly dispersed and mixed in the aqueous solution. When urea is dissolved in this aqueous solution and heated to about 90 ° C., urea is decomposed into carbon dioxide and ammonia, and the pH of the solution is gradually and uniformly increased from the inside. For example, YNO _{3 is} produced by a so-called uniform precipitation process. Yttrium hydroxide or basic yttrium carbonate is precipitated in the aqueous solution. The dispersed zirconia spherical fine particles are agglomerated particles composed of ultrafine primary particles, and since they are still porous and surface active,
The precipitation of hydroxides or basic carbonates of these additive component elements occurs exclusively on the surface of the fine particles under appropriate conditions.

When the content of the zirconia spherical fine particles in the suspension increases, the chance of contact between the zirconia fine particles in the liquid increases, and when the concentration of the soluble additive component element salt is high, the metal content increases. Nuclei of hydroxides or basic carbonate precipitates are generated not only on the surface of the fine particles but also in the solution, and in any case, the isolated dispersibility of zirconia and the uniform distribution of the additive component elements are deteriorated. The zirconia content of the suspension which can be appropriately treated is about 1 to 10 g / l, and the concentration of the soluble additive component metal salt is 0.1 mol / l or less. Further, the heat treatment temperature of the suspension also influences the result, and uniform skinning is unlikely to occur even when the temperature is low or too high. According to the result of the experiment, the temperature of about 90 ° C was appropriate. In the case of a rare earth metal salt such as YCl ₃ , hydroxide is mainly precipitated when the suspension is heat-treated in an open container, and basic carbonate is mainly precipitated when the suspension is heat-treated in a closed container. It seems that under the proper treatment, all of them were uniformly skinned, and no particular difference was observed in the powder after calcination.

In the present invention, since the spherical fine particles suspended in the solution are considered to have substantially the same size and the same particle surface area, the amount of the additive component element compound deposited from the solution can be determined by the uniform precipitation method. Therefore, it can be considered that the spherical fine particles have substantially the same amount. Therefore, when such spherical fine particle powder is calcined at a temperature of 700 ° C. or higher, the individual spherical fine particles each become a solid solution under an extremely constant environment, and the distribution of rare earth elements becomes different due to the diffusion phenomenon at high temperature. It becomes extremely uniform with respect to the zirconia spherical fine particles. Further, the zirconia spherical fine particles are spherical agglomerated particles, the individual spherical fine particles are porous, and since solid solution is mainly performed in a form in which Y ₂ O ₃ diffuses in ZrO ₂ , the initial zirconia particles are not calcined. The shape of zirconia spherical agglomerated fine particles is maintained, and each spherical fine particle is densified by sintering inside the agglomerated particles without becoming a strong agglomerate, and is easily disentangled by mild milling, resulting in isolated dispersibility. Spherical fine particle powder with good quality can be obtained. The reason why the calcination temperature is 700 ° C. or higher is that, at a temperature of 700 ° C. or lower, the solid solution of the additive component elements is insufficient and the zirconia spherical agglomerated particles do not become fine particles that are sufficiently densified individually.

[0021]

EXAMPLES The present invention will be described in more detail below by showing Examples of the present invention.

[0022] Example 1 Reagent zirconyl chloride _{(ZrOCl 2 · 8H 2 O)} , semi-dried hydrous zirconium hydroxide _{(ZrOH 4 · xH 2 O)} ,
And distilled water were blended in the proportions shown in Table 1, respectively, and well mixed in a mortar to prepare a mixture of four kinds of samples A, B, C, and D. These chemical compositions are as shown in Table 1, with respect to 1 mole of ZrO _2,
HCl is 1.0 mol to 1.9 mol, and H ₂ O is 7.0 mol.
Corresponding to mol to 8.2 mol, all within the scope of the claims. Each of these mixtures was filled in a hard Teflon container (internal volume: 25 ml) in a pressure resistant container made of stainless steel. The volume of each mixture was about 20 ml, and the volume ratio of the filling material in each container was about 80% of the inner volume of the container. Each pressure-resistant container filled with the raw material mixture is hermetically sealed, set on a rotating shaft in a hot air circulation type dry oven, and while rotating the pressure-resistant container so that the inside rolls, the materials A, B, and C are , 200 ° C., and the sample of D was heated at 150 ° C. for a predetermined time. The required optimum time of hydrothermal treatment is as shown in Table 1, and it becomes longer as the molar ratio of HCl and H ₂ O becomes larger, and becomes longer as the processing temperature becomes lower.

After each sample was heat-treated, it was left at room temperature for 10 hours together with a sealed pressure-resistant container, then opened and taken out. As a result, a white, thick, almost mud-like substance was formed. Each of these was scraped out on an evaporation dish and placed in a vacuum desiccator as it was, and dried under reduced pressure by a vacuum pump. In the dried state under reduced pressure, all of these products are white soft powder aggregates, but if they are put into water as they are, they are easily dispersed in primary ultrafine particles of 0.01 μm or less to form a translucent sol. give. However, by heating at about 250 ° C. for several hours, it no longer disintegrated and dispersed in water. The product was a soft lump and was easily loosened into a powder with only a slight hold. Scanning electron micrographs of this powder consisted of well-isolated spherical monodisperse ultrafine particles. The samples of B, C, and D are almost the same, but their particle sizes are as shown in Table 1, HCl and H
_It becomes smaller as the molar ratio of ₂ O becomes smaller.

[0024]

[Table 1]

2.00 g of each of the above three kinds of spherical fine particles having different sizes A, B, and C was added to YCl ₃ 0.
An aqueous solution 1 containing 203 g (corresponding to 3 mol% of Y ₂ O _{3 with} respect to ZrO ₂ ) and a sufficient amount of about 0.5 g of urea.
Disperse and suspend in 000 ml and stir at about 90 ° C for 5
A heat treatment for uniform precipitation was performed for a period of time. According to a scanning electron microscope, all of these products were spherical fine particles having substantially the same size as the spherical fine particles before precipitation, and no other precipitate than the spherical fine particles was observed. Sample B in Figure 1
2 shows a scanning electron micrograph of the example of FIG.

The spherical fine particles are extremely fine, and Y
It is difficult to confirm whether (OH) ₃ or Y (CO ₃ ) _x (OH) _y is uniformly adhered to the surface of each spherical fine particle, but it is almost possible to confirm by the following method. It can be confirmed that the Y component is uniformly distributed. That is, with respect to the sample B, Y ₂ O ₃ was added by various methods such as a coprecipitation method and a uniform precipitation method, and the residual ratio of the monoclinic crystal zirconia after calcination was compared and the result is shown in FIG. Is. That is, a suspension aqueous solution containing the spherical zirconia fine particles and YCl ₃ corresponding to 3 mol% as Y ₂ O ₃ was prepared,
When this suspension was dropped into 14.5 N concentrated ammonia water (a), conversely when concentrated ammonia water was dropped into the suspension (b), and the above uniform precipitation with urea was conducted at 100 ° C.
The X-ray diffraction patterns of the powders obtained by calcination at 800 ° C. for the samples obtained in (c) at 90 ° C. and (d) at 90 ° C. are shown in comparison. In addition to tetragonal crystal zirconia (T phase) showing solid solution in any of a, b, and c, residual or formation of monoclinic crystal zirconia (M phase) was observed, and Y ₂
It shows that O ₃ was locally insufficient in a minute part,
In the case of d, almost only tetragonal zirconia (T phase) was formed, indicating that Y ₂ O ₃ was distributed almost uniformly.

[0027]

As is apparent from the above description, according to the present invention, it is possible to obtain 0.2 to 0.2 which has never been obtained conventionally.
For the first time, it is possible to produce almost idealized zirconia monodisperse spherical fine particle powders having a uniform composition which is completely isolated and has excellent dispersibility in the ultrafine particle region of 0.8 μm.
Since monodispersed spherical ultrafine particles will be put to practical use industrially as a raw material powder for high-quality fine ceramics, it is expected to make a great contribution to the industry of zirconia-based fine ceramics. In particular, since the particles are spherical monodisperse and the chemical composition of each fine particle is almost the same, the microstructure of the sintered body obtained using this becomes extremely uniform, and the mechanical properties and ionic conductivity, etc. It is expected that every performance will be exceptionally excellent.
In addition, since expensive raw materials such as alkoxides are not used, the manufacturing process is relatively simple, and hydrothermal treatment can be performed at a very high concentration of about 5 mol / l with ZrO ₂ concentration, which is highly efficient, and uniform precipitation. The surface skinning by means of 100 ° C. or less has a remarkable advantage in productivity such as easy mass processing.

[Brief description of drawings]

FIG. 1 is a representative sample B in which 3 mol% Y ₂ O ₃ is solid-dissolved.
2 is a scanning electron micrograph of FIG.

FIG. 2 is a comparison of powder X-ray diffraction patterns after calcination of Sample B in which the method of adding Y ₂ O ₃ is different.

Claims (2)

[Reference number] ZR0011 [Claims] 1. A particle diameter in the range of 0.2 to 0.8 μm,
A uniform composition characterized by comprising substantially spherical monodisperse submicron ultrafine particles, and each individual spherical ultrafine particle contains substantially the same amount of one or more rare earth elements such as Sc, Y, and Yb. Zirconia solid solution monodisperse spherical fine particle powder. 2. A zirconium compound, hydrochloric acid and water as main components, and the chemical composition ratio is 0.8 to 2.0 moles of HCl and 6 to 10 moles of H ₂ O with respect to 1 mole of ZrO ₂ .
The homogeneous mixture or solution is subjected to hydrothermal treatment at a temperature of 100 to 220 ° C. for an optimum time required in an acid-resistant closed hydrothermal container, and aggregated into almost monodisperse spherical particles having a particle diameter of 0.2 to 0.8 μm. After synthesizing the monoclinic crystalline spherical zirconia ultrafine particles that have been prepared, and fixing them to water-stable spherical fine particles by drying under reduced pressure and heat treatment at 100 ° C. or more, one or more necessary additional component elements such as rare earth elements Dispersed in a solution containing an appropriate amount of urea and a suitable amount of urea to form a uniform mixed suspension solution, and by a uniform precipitation method by thermal decomposition of urea in this solution, on each surface of spherical zirconia agglomerated fine particles. A uniform composition characterized in that a hydroxide or a basic carbonate of a necessary additional component element is deposited and deposited, and this is calcined at a temperature of 700 ° C. or higher to solidify each zirconia spherical fine particle. Method for producing a zirconia solid solution monodisperse spherical fine particles.