JP3680338B2 - Method for producing zirconia granules - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for producing zirconia granules, and more particularly to a method for producing zirconia granules having excellent crushability during molding.
[0002]
[Prior art]
As a forming means in the method for producing a zirconia sintered body, a dry pressure forming method having excellent dimensional accuracy in the case of a simple shape is generally employed.
[0003]
In this dry press molding, uniform filling of the powder into the mold is an essential condition so that the pressure distribution inside the mold does not occur during pressurization.
[0004]
For this reason, conventionally, a method of using fine pulverized zirconia powder having poor fluidity as spherical granules having good fluidity by spray drying granulation has been widely used.
[0005]
It is easy to obtain spherical granules having good fluidity by the spray drying granulation method.
[0006]
However, since the fine ceramic powder is required to have uniform sinterability and easy sinterability, the powder is generally finely pulverized to an average particle size of 1 μm or less.
[0007]
When such a fine powder is granulated by a spray drying method, a granule having a strong crushing strength is generated due to a strong cohesive force between the fine powders.
[0008]
When granules with strong crushing strength with poor crushing properties are used for dry compression molding, uncrushed granules remain in the compact, and the uncrushed granule part becomes a sintering defect, resulting in low density and low strength of the sintered compact. There is a problem that causes
[0009]
For this reason, for the purpose of reducing granule strength, a method of adding a thickener to the zirconia slurry and agglomerating the fine powder in the slurry weakly in advance, or a method of reducing the slurry concentration and reducing the dry agglomeration force However, the granule obtained by such a method does not sufficiently improve the crushing strength, and the bulk density of the granule is also lowered, so that the filling rate into the mold is lowered. Occurs.
[0010]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for producing zirconia granules which improves the above-mentioned problems of the granules and is excellent in filling ability into a mold and crushability during pressing.
[0011]
[Means for Solving the Problems]
In the present invention, when producing zirconia granules by spray drying a zirconia slurry in which zirconia powder is suspended in water, bubbles are included in the high-concentration zirconia slurry, and the specific gravity of the slurry is 0.80 to 1.2 g. The gist of the present invention is a method for producing zirconia granules that are adjusted to / cm ³ and spray-dried.
[0012]
[Action]
Hereinafter, the present invention will be described in more detail.
[0013]
Easily obtain spherical granules of zirconia powder by drying a zirconia slurry in which zirconia powder containing a stabilizer such as yttria is suspended in water with a normal spray dryer of disk type or nozzle type. Can do.
[0014]
The obtained granule has a distribution of usually about 0.01 to 0.2 mm, and the average granule size is about 0.06 mm.
[0015]
Further, the strength of the granules obtained varies depending on the particle diameter and specific surface area of the raw zirconia powder. For example, when the average particle diameter of the powder is 1 μm or less and the BET specific surface area is 10 m ² / g or more, it is obtained. The crushing strength of the granules is about 0.06 kgf / mm ² (measured with a micro compression tester manufactured by Shimadzu Corporation).
[0016]
When the crushing strength of the granules is 0.06 kgf / mm ² or more, uncrushed granules remain even when the molding pressure of the dry pressure molding is 1000 kg / cm ² , and such a compact is sintered at 1500 ° C. The strength of the sintered body is about 90 kgf / mm ² according to the three-point bending strength test method defined in JIS R 1601.
[0017]
The following description is directed to zirconia powder having an average particle diameter of 1 μm or less and a BET specific surface area of 10 m ² / g or more.
[0018]
For this reason, as described above, for the purpose of reducing the granule strength, there are a method of adding a thickener to the zirconia slurry, a method of reducing the slurry concentration, etc., but the bulk density of the granules is reduced, There is a problem that productivity decreases due to a decrease in concentration.
[0019]
The present invention provides a method for producing a granule having excellent crushability without reducing the bulk density of the granule with high productivity.
[0020]
The zirconia concentration of the zirconia slurry of the present invention is preferably 35 to 60 wt%.
[0021]
The reason is that when it is less than 35 wt%, the productivity is lowered, and when it exceeds 60 wt%, the slurry viscosity becomes high and the spray state at the time of spray drying is deteriorated, and the shape of the resulting granule is poor and fluidized. This is because it becomes a bad thing.
[0022]
Further, in the present invention, it is necessary to include bubbles in the slurry and to make the slurry specific gravity 0.80 to 1.2 g / cm ³ .
[0023]
The specific gravity of a slurry in which zirconia powder is usually suspended in water is, for example, about 1.6 g / cm ³ when the zirconia is 50 wt%.
[0024]
The slurry specific gravity of this degree, but in the slurry by the inclusion of gas bubbles to prepare a slurry specific gravity 0.80~1.2g / cm ^3, the slurry specific gravity is less than 0.80 g / cm ^3, the structure of the pump Therefore, it may be difficult to supply the slurry to the spray dryer, which is not preferable.
[0025]
On the other hand, when the slurry specific gravity exceeds 1.2 g / cm ³ , the crushing strength of the granules obtained by spray drying is not sufficiently improved, which is not preferable.
[0026]
As a method of including bubbles in the slurry, it is easy to add bubbles to the slurry by adding a small amount of a foaming agent or adding a ceramic binder to improve moldability, and then stirring the slurry slightly stronger. Can be included.
[0027]
Moreover, about the further fall of the slurry specific gravity during spray drying, specific gravity value can be maintained constant by addition of an antifoamer.
[0028]
As described above, a zirconia slurry having a specific gravity of 0.80 to 1.2 g / cm ³ can be obtained by adding an additive to 35 to 60 wt% zirconia slurry and stirring the mixture.
[0029]
The zirconia granules obtained by spray drying the slurry thus prepared have a spherical shape, a particle diameter of 0.02 to 0.2 mm, and a light bulk density of 1.0 to 1.4 g / cm ³ .
[0030]
Further, the crushing strength of the granules can be improved to about 0.02 to 0.04 kg / mm ² .
The reason why the crushing strength of the granules can be improved by including bubbles in the slurry is not clear, but it seems that the dry agglomeration force of the zirconia fine powder during drying is buffered by the bubbles.
[0031]
Using the zirconia granules having improved crushability in this manner, the three-point bending strength of the sintered body formed at a molding pressure of 1000 kg / cm ² by a die press molding method and then sintered at 1500 ° C. is 110-110. It is improved to about 130 kgf / mm ² .
[0032]
According to the present invention, it is possible to improve the crushing strength of the obtained zirconia granules by including a certain amount of bubbles in the slurry and performing the spray drying method, although the reason is not clear. Since the crushed property of the granules is excellent, the strength of the zirconia sintered body obtained by the pressure molding method can be improved.
[0033]
【Example】
The present invention will be specifically described with reference to the following examples, but the present invention is not limited to these examples.
[0034]
Example 1
A zirconia powder containing ₃ mol% of Y ₂ O ₃ (average particle size 1.0 μm, BET specific surface area 16 m ² / g) was suspended in water to prepare a slurry containing 50 wt% zirconia.
[0035]
Next, 3% of the binder for ceramics (acrylic copolymer resin) manufactured by Chuo Rika Kogyo Co., Ltd. was added and mixed with the solid content of the slurry while stirring.
[0036]
The zirconia concentration of the slurry after the addition was 45 wt%, including some bubbles, but the specific gravity of the slurry was 1.30 g / cm ³ .
[0037]
After adding the binder, when slightly agitation was continued for 24 hours to include bubbles, the slurry specific gravity after 24 hours was 1.10 g / cm ³ .
[0038]
Next, the slurry whose specific gravity was adjusted by inclusion of bubbles was dried under hot air at 150 ° C. using a spray dryer to obtain zirconia granules.
[0039]
The lightly loaded bulk density of the obtained zirconia granules was 1.20 g / cm ³ , and the crushing strength of the granules was 0.03 kg / mm ² .
[0040]
Next, 27 g of the obtained zirconia granule was used to perform die press molding at a molding pressure of 1000 kg / cm ² to form a 57 mm × 34 mm plate, and then sintered at 1500 ° C. for 2 hours to obtain a sintered body. Got. The sintered body had a density of 6.051 g / cm ³ and a three-point bending strength value of 125.3 kgf / mm ² on average. (The three-point bending strength was measured at a span of 30 mm for 10 test pieces of 3 mm × 4 mm × 40 mm by the test method defined in JIS R 1601)
Comparative Example 1
Spray drying was performed in the same manner as in Example 1 for the slurry immediately after the addition of (1) the binder and the slurry in which stirring was continued for 48 hours after the addition of the binder.
[0041]
▲ 1 ▼ slurry specific gravity of at 1.30g / cm ^3, ▲ 2 ▼ slurry specific gravity was 0.78 g / cm ^3.
[0042]
The zirconia granules obtained by spray drying the slurry of (1) had a light bulk density of 1.21 g / cm ³ and a crushing strength of the granules of 0.06 kg / mm ² .
[0043]
The obtained zirconia granules were used in the same manner as in Example 1 to evaluate the sintered body.
[0044]
The sintered body had a density of 6.050 g / cm ³ and an average three-point bending strength value of 90.3 kgf / mm ² .
[0045]
Regarding the slurry (2), it was impossible to supply it to the spray dryer with a diaphragm pump, and granules could not be obtained.
[0046]
【The invention's effect】
According to the present invention, zirconia granules having excellent crushability can be easily produced by a simple operation, and particularly suitable for producing a high-strength zirconia sintered body by a pressure molding method.

Claims (1)

In producing zirconia granules by spray-drying a zirconia slurry in which zirconia powder is suspended in water, the zirconia slurry has a zirconia concentration of 35 to 60 wt%, and bubbles are included in the slurry, and the specific gravity of the slurry Is adjusted to 0.80 to 1.2 g / cm ³ and spray-dried. A method for producing zirconia granules.