JP3242970B2 - Zirconia powder composition for tumbling granulation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a raw zirconia powder composition particularly suitable for producing zirconia spheres by a rolling granulation method.

[0002]

2. Description of the Related Art In recent years, there has been an increasing tendency to pulverize raw material powders in various industrial fields, and ceramic spheres used as a pulverizing medium in pulverizers such as high-speed agitating mills have also been reduced to improve pulverization efficiency. There is a tendency to increase the particle size.

[0003] Ceramic spheres used in high-speed stirring mills and the like are required to have high sphericity, high density, high strength, high wear resistance, etc. Zirconia spheres are ceramic spheres satisfying these characteristics. Attention has been paid.

Conventionally, as a method of forming zirconia powder into small-diameter spheres having a diameter of 20 mm or less, a rolling granulation method capable of forming a large amount at a relatively low cost is generally known. As the granulator used, a dish granulator and a drum granulator are widely used as typical rolling granulators.

The sphere obtained by such a molding method is dried and then fired to obtain a zirconia small-diameter sphere.

Since the zirconia spheres used as the grinding media are required to have the above-mentioned mechanical properties, the zirconia raw material used for the production of the spheres is mainly of high purity and fine powder. ing.

[0007] Such high-purity zirconia fine powder is currently manufactured by various manufacturing methods. For example, a neutralization coprecipitation method, a hydrolysis method, a hydrothermal oxidation method, a thermal decomposition method and the like are generally known. Since zirconia powders produced by these production methods have slightly different powder characteristics and sintering characteristics, powders suitable for the intended use and molding method are generally selected and used.

[0008]

In rolling granulation of zirconia powder, not all zirconia powders produced by the above-mentioned manufacturing method can be used. For example, spheres adhere to each other during rolling molding and molding is difficult. There are cases where various problems occur, such as that a sphere having good sphericity cannot be obtained, and a sintered sphere having high density and high strength cannot be obtained. However, at present, the causes of these problems have not been clarified.

An object of the present invention is to clarify the causes of these problems and obtain a homogeneous and high-density compact having good sphericity easily by tumbling granulation and sintering the compact. To provide a zirconia powder composition from which zirconia spheres having excellent mechanical properties can be obtained.

[0010]

As a result of various studies, the present inventors have found powder characteristics of raw zirconia powder suitable for tumbling granulation, and have reached the present invention.

That is, the present invention comprises a zirconia powder and a stabilizer, and the powder has an average particle size of 0.5 to 2.0.
μm, a BET specific surface area of 3 to 12 m ² / g, and a pH of 6 to 8 when the powder is slurried.
Which is a zirconia powder composition for tumbling granulation.

Hereinafter, the present invention will be described in more detail.

A method for producing zirconia spheres by the rolling granulation method is to first produce fine sphere nuclei by using zirconia powder with water as a binder by the rolling granulation method, and then to subject the nuclei to rolling growth to achieve the object. And then dried at 100 to 200 ° C.
It is fired at 00 to 1600 ° C.

In producing the zirconia spheres in this way, the spheres are easy to form, the sphericity of the obtained spheres is good, uniform and high density, and the sinterability of the spheres is good. It is necessary that the obtained sintered spheres satisfy all conditions such as being dense and having excellent mechanical properties.

[0015] It has been found that in order to satisfy all of the above production conditions, it is necessary to use zirconia powder having powder characteristics limited in the above-mentioned range.

First, it is necessary that the average particle diameter of the raw zirconia powder is in the range of 0.5 to 2.0 μm.

Since the strength of the molded sphere is inversely proportional to the particle diameter of the powder, when the average particle diameter is larger than 2.0 μm, the mechanical strength and the shape retention of the molded sphere are reduced, and the drying operation in the subsequent step is difficult. Since it cannot withstand an external load during the sintering operation and the molded spheres collapse, the production is not preferable. Further, when the particle diameter of the powder increases, the sinterability decreases, and it becomes difficult to obtain a dense sintered body, and the mechanical properties of the sintered body also deteriorate.

When a sintered body is obtained by molding and sintering a zirconia powder, a finer powder can be easily sintered and a dense sintered body can be obtained. However, in the case of the tumbling granulation method, the powder is rolled to form a sphere, so that when the average particle diameter becomes smaller than 0.5 μm, the powder has a small bulk density and a rolling compaction of the sphere. And it becomes difficult to obtain a high-density molded sphere, which is not preferable in production.

In addition, a very smooth interface is formed on the surface of the sphere during molding due to the effect of the ultrafine particles contained in the powder.
As a result, the interface formed during the rolling and growth of the sphere and formed during the growth remains as an annual ring-shaped defect, and this defect is undesirable because it causes a decrease in the mechanical properties of the sintered body. Further, when the content of the ultrafine particles in the raw material zirconia powder is increased, the adhesion of the sphere surface becomes strong, and the spheres easily adhere to each other during rolling granulation, so that it is difficult to obtain a sphere having good sphericity.

From the above, zirconia powder having an average particle size in the range of 0.5 to 2.0 μm can be preferably used, but the average particle size of the zirconia powder is 0.5 to 1.0 μm.
Is more preferred. As the particle size distribution of the powder, those having a small content of fine particles and not containing coarse particles of 5 μm or more are more preferable.

Next, the BET specific surface area of the raw zirconia powder must be in the range of 3 to 12 m ² / g, preferably 5 to 10 m ² / g.

When the BET specific surface area of the powder is larger than 12 m ² / g, the amount of water required for molding naturally increases, and as a result, the adhesion between the spheres is increased due to the effect of the surface tension of water, and the spheres having good sphericity are obtained. Is difficult to obtain. Further, when the amount of molding water is increased, the density of the molded body is also reduced, so that it is difficult to obtain a dense sintered body.

If the BET specific surface area of the powder is less than 3 m ² / g, the moldability is improved, but in particular, the sinterability is reduced and a high temperature is required to obtain a dense sintered body, which is not preferable in production. .

Further, it is necessary that the zirconia powder has a pH of 6 to 8 when it is slurried.

In the powder having a pH higher than 8, the agglomeration between the powder particles becomes stronger, and the powder supply during rolling granulation tends to be non-uniform, so that the uniform growth of spheres is prevented. as a result,
It is not preferable because the sphericity of the sphere deteriorates, the homogeneity inside the sphere decreases, and the mechanical properties of the sintered body decrease.

In the powder having a pH lower than 6, the dispersibility of the powder particles in water is improved, and the fluidity of the powder greatly changes only by slightly changing the amount of water mixed with the powder during tumbling granulation. It is difficult to adjust moisture. In addition, when the water content at the time of tumbling granulation becomes just before slurrying, a dilatancy phenomenon of solidification or slurrying depending on the presence or absence of external pressure may be exhibited. Adjustment becomes very difficult and in practice granulation becomes impossible.

As described above, when zirconia spheres are manufactured by the rolling granulation method, the powder characteristics of the zirconia powder include the formability, sphericity, compact density, sinterability, and the like.
Since the mechanical properties of the sintered body are greatly affected, the powder properties of the raw zirconia powder are very important.

Next, as a stabilizer in the zirconia powder, Y2O3, CaO, MgO or the like is generally used. For example, in the case of Y2O3, 2.0 to 5.0 mol is used.
%, The production of monoclinic or equiaxed zirconia during sintering is appropriately suppressed, and a sintered body having excellent mechanical properties can be obtained.

The stabilizer may be added during the production process of the zirconia powder, or may be directly mechanically mixed with the zirconia powder, but the method is not particularly limited.

In addition, Al is used as a sintering aid for zirconia.
Powders to which 2O3 or the like has been added have improved sinterability and can be suitably used.

[0031]

The use of zirconia powder within the range of the powder characteristics of the present invention makes it possible to easily perform the rolling granulation operation and obtain a homogeneous and high-density compact having good sphericity. By sintering, zirconia spheres having excellent mechanical properties can be obtained.

[0032]

【Example】

Examples 1 to 7 and Comparative Examples 1 to 6 Starting from an aqueous solution of zirconium oxychloride to which Y ₂ O ₃ was added, various kinds of powders containing ₃ mol% of Y ₂ O ₃ by hydrolysis and having the powder properties shown in Table 1 were used. Zirconia powder was synthesized.

Using these powders, each sphere was formed using a conventional dish-type tumbling granulator using water as a binder. After drying the obtained molded sphere at 150 ° C.,
Sintering was performed at 1500 ° C. for 2 hours to obtain a zirconia sphere having a diameter of 2 mm.

Next, various physical properties of the obtained zirconia sphere were measured. Table 1 shows the results.

The crushing load value in Table 1 is a load value required to crush one sphere in a one-ball system. Examples 1 to 1 shown in Table 1
The powder characteristics of No. 7 are within the range of the present invention, and the average particle diameter, BET specific surface area, and slurry pH are slightly different from each other. The zirconia spheres obtained with good moldability satisfied all the physical properties.

When the powder of Comparative Example 1 using the powder having an average particle diameter of 0.3 μm was used, the adhesion between the spheres at the time of molding was strong, and a sphere with good sphericity was not obtained.

The average particle size of Comparative Example 2 was 2.5 μm
When the powder was used, the compactability was good, but the density of the zirconia sphere was low, and the zirconia sphere was low in strength and low in crushing load.

Comparative Examples 3 and 4 differ in the BET specific surface area of the zirconia powder, and the BET specific surface area of Comparative Example 3 is 2 m ² /
In the case of g, the density of zirconia spheres was low.

The BET specific surface area of Comparative Example 4 was 16 m ² / g
As for Comparative Example 1, as in Comparative Example 1, adhesion between spheres was strong and a sphere with good sphericity could not be obtained.

When water was added during molding, the slurry of Comparative Example 5 having a pH of 5.0 exhibited a dilatancy phenomenon and could not be molded into a sphere.

In Comparative Example 6, when the slurry pH was 9.0, the sphericity was poor and the strength of the sintered body was low.

Table 1 Properties of zirconia powder and physical properties of zirconia spheres Zirconia powder properties Zirconia sphere physical properties Average particle size BET 10 wt% * Sphericity Density Crush load No Specific surface area Slurry μm m ² / g p H g / cm3 Kg Example 1 0.7 7.7 1.03 6.08 290 2 1.2 67 7 1.02 6.07 280 3 1.5 57 7 1.02 6.07 270 4 1.0 11 7 1.03 6.08 280 5 1.2 47 7 1.02 6.07 270 6 1.0 6 6.2 1.03 6.08 290 7 1.0 6 7.5 1.03 6.08 280 Comparative Example 1 0.3 12 7 1.07 6.08 220 2 2.5 47 7.02 5.80 180 3 1.5 27 1.02 5.87 190 4 1.0 16 7 1. 08 6.06 230 5 1.08 5 Unformable 6 1.0 8 9 1.08 6.00 190 * Sphericality = maximum diameter / minimum diameter of the same sphere The target value of the sphericity is 1.05 Less than

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C01G 25/02 CA (STN)

Claims (1)

(57) [Claims] 1. A powder comprising a zirconia powder and a stabilizer, the powder having an average particle size of 0.5 to 2.0 μm, a BET specific surface area of 3 to 12 m ² / g, and a slurry of the powder. A zirconia powder composition for tumbling granulation, which has a pH of 6 to 8 when formed.