JPH04930B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a zirconia-based fine powder and a manufacturing method. In particular, the present invention relates to a method for producing zirconia-based fine powder suitable for high-strength, high-toughness zirconia solid solution ceramics, zirconia-dispersed high-toughness ceramics, and the like.

Zirconia sintered bodies containing square-shaped zirconia solid solution fine particles and zirconia-dispersed sintered bodies containing square-shaped zirconia dispersed therein are attracting attention as high-strength, high-toughness materials, and are in the process of remarkable progress. As a starting material for such strong and tough zirconia ceramics, a fine powder consisting of ultrafine zirconia particles or a zirconia solid solution with a secondary agglomerated particle size of 500 Å or less has been produced.

Currently, most of the manufacturing methods are wet methods to achieve high purity and particle refinement. A method is used in which a colloidal precipitate produced by heating and hydrolyzing an aqueous zirconium salt solution is dried, calcined, and pulverized.

However, such colloidal precipitates
Even if they are sufficiently isolated and dispersed in water, because they are extremely fine, the water remaining between the particles during the drying process creates strong interparticle bonds, causing the colloid particles to gel and lose their fine particle nature. Even if pulverization is applied, in the powder state, the fine particles are
Whether they are secondary particles or secondary agglomerated particles, they do not exist in their generated state. The finer the particles, the more agglomerated they become, forming coarse, higher-order aggregated particles or agglomerated particle agglomerates.

Furthermore, in order to use these dry powders as sintered bodies, they are generally subjected to heat treatment at around 800°C, that is, calcining treatment. This is to densify the powder itself in order to increase the molding density, and to make oxides of different metals such as yttrium and calcium, which are often added to zirconia, as a solid solution in the zirconia. be.

However, at this stage of calcination, the finer the particles, the more easily sintering occurs within and between the aggregated particles, forming a stronger agglomerate, so pulverization is generally always performed after calcination. However, the resulting powder is coarse and has a wide particle size distribution.

The stronger the agglomeration during drying, the stronger the agglomeration of the agglomerates after calcination. Therefore, before drying, replace water with alcohol or use a method such as freeze-drying to solidify the agglomeration. Attempts have also been made to avoid this. However, in addition to being generally expensive, there are drawbacks such as the inability to perform water treatment of the sol on an industrial production scale, for example, drying the sol using a spray dryer or the like.

In addition, for sintered ceramics, generally
It is said that fine powder consisting of well-aligned, isolated particles with a narrow particle size distribution is undesirable for uniformity in mold filling and sintering, but the presence of coarse agglomerates leads to strength deterioration. should be avoided because of
It has hitherto been considered extremely difficult to industrially produce a fine powder consisting of ultrafine particles such as a hydrolysis product, which is a fine powder consisting of well-aligned isolated particles with a narrow particle size distribution.

The present invention basically eliminates these drawbacks, and aims to provide a homogeneous secondary agglomerated particle powder that can relatively easily produce ultrafine particles of 500 Å or less in water treatment on an industrial production scale. This is a method for producing fine zirconia powder. That is, a zirconium salt aqueous solution is heated to 80 to 250°C and hydrolyzed to form a sol in which secondary agglomerated particles of zirconia are dispersed, and the sol is separated by a sedimentation method or a centrifugation method, and the separated zirconia The particles are made of zirconia microcrystals and have a particle size of
This production method is characterized by obtaining a powder of secondary agglomerated particles with a size of 1000 Å to 3000 Å, which is used alone or mixed with other metal compounds, and then calcined at a temperature of 400 to 1000°C.

Through detailed research, the inventor found that the suspended particles produced by heating and hydrolyzing a zirconium salt solution at 80 to 250°C are secondary agglomerated particles consisting of monoclinic zirconia microcrystals with a crystallite diameter of 100 Å or less. It was discovered that the size of the secondary agglomerated particles had a distribution of 30 to 3000 Å. (See Yoshio Murase, Etsuro Kato, Ceramics Association Journal Vol. 84, p. 478 (1976). Further research revealed that these secondary agglomerated particles
1.5 to 0. Particles of about 1000 Å or less remain in the liquid as suspended particles when left standing in an acidic solution for several days or are centrifuged, while particles of about 1000 Å or more Only the secondary agglomerated particles can be separated by sedimentation, and even though these crystalline secondary agglomerated particles, from which suspended particles of about 1000 Å or less are removed, are composed of microcrystals of 100 Å or less, they do not form strong agglomerates after drying. It has been found that it gives a powder of excellent properties. According to experimental results, when these secondary agglomerated particles, excluding fine particles, are calcined at temperatures below 900°C, the agglomerated particles themselves become stronger secondary particles, but the bonds between the secondary particles are extremely weak and light. Easily loosened by grinding, primary particles reach 500A
or less, and the size of the secondary agglomerated particles is 1000Å~
Gives a uniform fine powder of about 3000Å. Surprisingly, this secondary powder, which is inert to agglomeration, is still sinterable and reactive. For example, if yttrium nitrate or the like is mixed and calcined with the dry powder before calcination, a square or cubic solid solution powder can be easily obtained at a low temperature of 600°C or less. In addition, the powder after calcination is
Consists of microcrystals of less than 500 Å, but approximately 1000 to 3000 Å
Since the bonds between the aggregated particles are relatively weak, they are easily loosened and powdered, and furthermore, they do not form strong, coarse aggregates during subsequent water treatment. Therefore, water treatment using an industrial spray dryer or the like is possible, and the molded article has a high and uniform packing density. At this time, not only does the activity of the primary fine particles remain, but the secondary particles themselves with a diameter of 3000 Å or less are still extremely sintering active, and a sintered body having almost the theoretical density is formed at a firing temperature of usually about 1400° C. or less.

As mentioned above, the effect of powder from which fine particles of about 1000 Å or less have been removed on the workability, molding properties, and sintering properties is extremely remarkable, but on the other hand, if the secondary agglomerated particles contain particles of 3000 Å or more, The structure of the sintered body tends to become coarse, and the most suitable particle size range for the sintered body is approximately 1000 Å to 3000 Å. However, since secondary agglomerated particles with a size of 3000 Å or more are hardly produced in the ordinary hydrolysis method, there is no need to particularly consider their removal.

The conditions for hydrolysis are that it takes too long to proceed with hydrolysis at temperatures below 80℃, and at temperatures below 250℃.
Above this, the hydrolysis becomes faster, but the growth of the primary particles becomes too large and the reaction activity is lost. The most preferred range is 90-120°C. In addition, as mentioned above, calcination treatment is generally performed to agglomerate and densify the ultrafine particles produced and to form a solid solution of the added foreign oxide into zirconia. A dried sol containing ultrafine particles, which are secondary agglomerated particles, tends to solidify into agglomerates after drying due to the presence of the ultrafine particles, and becomes even more solidly agglomerated by calcination treatment.

In the method of the present invention, by performing hydrolysis at a temperature of 80 to 250°C, the primary particles are microcrystals with a diameter of 100 Å or less, but they aggregate and become isolated.
First, a sol containing many secondary agglomerated particles of 1000 to 3000 Å is produced. Then from this sol 1000
This is a method that removes secondary agglomerated particles of Å or less in advance.
Fine particles of 1000 to 3000 Å (0.1 to 0.3 μm) alone cannot
It was discovered that it does not easily form into strong agglomerates.

In other words, the aggregates in the dry fine powder are 2
Since there are no secondary agglomerated particles, it is relatively sparse.
It easily loosens and is difficult to form strong aggregates during calcination treatment. If the calcination temperature is 400° C. or lower, the desired densification of the fine particles and change to solid solution formation are insufficient. Furthermore, when the calcination temperature exceeds 1000°C, sintering occurs between secondary agglomerated particles, coarse agglomerates are generated, and sintering activity is lost.

The greatest feature of the present invention is that it uses a simple method to remove the fine particles with a diameter of about 1000 Å or less and uses only those with a diameter of about 1000 Å or more. No loss of zirconium occurs as it can be processed and grown. As described above, the present invention has a remarkable effect with extremely simple improvements in the manufacturing process, and provides great benefits particularly in industrial production in terms of powder properties. Typical examples will be described below.

Example 1 Approximately 40 g of reagent zirconyl chloride (ZrOCl _{2.8H 2} O)
was dissolved in about 600 ml of distilled water to make a solution of about 0.2 mol/ml, and this solution was heated to 80 ml in a flask with a reflux condenser.
The mixture was boiled for a period of time to obtain a sol in which secondary agglomerated particles of zirconia were dispersed. This suspension was treated with a centrifuge at a rotation speed of 12,000 rpm for about 5 minutes to remove the thinly milky part at the top, and the remaining part was resuspended in 0.3N hydrochloric acid and sedimented with the same centrifuge. This precipitated portion was washed with alcohol and dried. The obtained powder is a monoclinic zirconia crystal according to X-rays, and its apparent average crystallite diameter is 43 Å, but according to an electron microscope, it has a thickness of 700 Å to 700 Å, as shown in Figure 1.
They were disc-shaped aggregated particles with extremely uniform particle diameters of 1,200 Å and diameters of 1,200 to 2,600 Å. This dry powder is heated at 500℃.
1 at 600℃, 700℃, 800℃ and 1000℃ respectively
When calcined for an hour, the average crystallite diameter is approximately 95
Å, 120 Å, 160 Å, 210 Å, and 350 Å, but according to electron microscopy, these growths mainly occur inside the secondary particles, and the calcined material is easily divided into individual secondary particles, and the secondary particles The particle size is
It was 1000 Å to 1500 Å. 1 t/cm ² of the obtained powder
When molded into a disk shape under a molding pressure of
A sintered body consisting only of monoclinic zirconia with a bulk density corresponding to % was obtained. At this time, the firing shrinkage rate is 800
The temperature calcined product was the smallest and suitable. The 1000℃ calcined product has a smaller firing shrinkage rate, but the final sintered density is 92
%.

Example 2 Yttrium nitrate in an amount equivalent to 3 mol% of zirconia was added to a powder consisting of secondary agglomerated particles of zirconia of approximately 1500 Å to 2200 Å obtained by thermal hydrolysis and centrifugation in the same manner as in Example 1. , and calcined at 800℃ for 1 hour. The obtained powder is
It was a linearly tetragonal crystal, and no free Y ₂ O ₃ was observed. This powder is easily dispersed by gentle grinding in water, but does not form strong agglomerates upon drying. Using experimental simple granules
When it was press-molded to 1 t/cm ² and fired at 1320°C for 1 hour, a sintered body having approximately 96% of the theoretical density was obtained. According to X-ray diffraction, this sintered body consisted of only square crystals, and scanning electron microscopy of the fractured surface showed a uniform fine grain structure of about 0.3μ. When a similar experiment was performed on hydrolyzed zirconia containing a mixture of fine and coarse particles without centrifugation, a rather strong agglomerate was formed during calcination, and the structure of the sintered body was non-uniform, resulting in a relative The density also reached only 92%.

Example 3 A suspension obtained by heating and hydrolysis in the same manner as in Example 1 was allowed to stand in a dark place for 1 hour, and a precipitate was obtained at the bottom. This sedimented part was washed with water, and basic magnesium carbonate powder was added in an amount equivalent to 10 mol% of MgO to _ZrO2 , mixed well, and
It was calcined at ℃. The calcined product had square and cubic solid solution crystals and was easily loosened into fine powder.
As in Example 2, it exhibited high sinterability and reached 96% of the theoretical density at 1350°C.

[Brief explanation of drawings]

FIG. 1 is a transmission electron micrograph of a zirconia fine powder made of secondary agglomerated particles of zirconia according to the present invention, after drying and before calcining.

Claims (1)

[Claims] 1. Heat the zirconium salt aqueous solution to 80-250℃,
Hydrolysis is performed to form a sol in which secondary agglomerated particles of zirconia are dispersed, the sol is separated by a sedimentation method or a centrifugation method, and the separated zirconia particles are dried to produce a sol consisting of zirconia microcrystals, and A zirconium-based product characterized by obtaining a powder of secondary agglomerated particles with a particle size of 1000 Å to 3000 Å, and calcining the powder alone or with other metal compounds at a temperature of 400 to 1000°C. Method for producing fine powder.