JP3298164B2 - Zirconia powder and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zirconia powder which is suitable for various molding methods, especially for press molding, and which has excellent rolling granulation characteristics.

[0002]

2. Description of the Related Art Hitherto, as a method for producing zirconia powder, there has been known a hydrolysis method of hydrolyzing a zirconium salt aqueous solution, separating a hydrated zirconia sol by a sedimentation method or the like, and calcining to obtain a zirconia powder (Japanese Patent Laid-Open Publication Aqueous ammonia is added to a suspension of hydrated zirconia fine particles in which a stabilizer is dissolved, and the mixture is filtered, washed with water, and calcined to obtain a zirconia powder. Kaisho 63-
129017), a method of adding a stabilizer made of chloride to zirconium hydroxide and calcining to obtain zirconia powder (Japanese Patent Application Laid-Open No. 61-266307).

[0003]

However, the zirconia powder produced by the above method or the like does not have a sufficient density of the compact by press molding or the like, and the density of the compact does not stabilize. Tend to cause sexuality. In the case of using a sintered body, cracks or lamination are liable to occur in the sintered body, and the sintered density is lowered.

Further, hitherto, the powder obtained by the above-mentioned method or the like cannot be subjected to rolling granulation molding, or even if it can be molded, it cannot form a firm core and has good sphericity. There was no molded body.

In any case, the powder obtained has a low density of the compact and is difficult to compact.

[0006]

Means for Solving the Problems The present inventors have determined that the molding characteristics such as the moldability and the molding density of zirconia powder are largely affected not only by the powder characteristics and the particle shape but also by the characterization of the particle surface. By analyzing the surface of various powders and controlling the charge on the surface of the powder to almost zero, characteristics that could not be obtained with the conventional powder characteristics are newly added, and the moldability is improved. It was found to increase remarkably, leading to the present invention.

That is, according to the present invention, the zeta potential at the time of slurrying (the potential at the slip surface generated near the interface when relative movement is caused between the particle and the liquid interface) is -10 to +
A zirconia powder having a 10 mV and an isoelectric point pH of 5 to 9 is a gist of the present invention. It can be produced by adding an acid or an alkali until the negative electrode potential becomes -10 to +10 mV and the isoelectric point pH becomes 5 to 9.

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

Normally, when powder particles are dispersed in an electrolyte, the particle surface is dissolved or the electrolyte is adsorbed and charged positively or negatively. When the particles are in a charged state, that is, when the zeta potential indicates a positive or negative value, repulsion between the particles is likely to occur, and the particles have dispersibility. When the zeta potential is zero, that is, when the zeta potential is located at the isoelectric point, the particles are easily bonded to each other and form an aggregated state.

The charged state is measured by an electrophoresis method, a streaming potential method, an oscillating potential method, a sedimentation potential method, an electroosmosis method, or the like.

The electrolyte used for measuring the zeta potential is generally water or an aqueous solution of a monovalent monovalent electrolyte such as KCl or NaCl. As the acid group or base supplied for pH adjustment at the time of zeta potential measurement, a general acid or alkali aqueous solution is used.
KOH is mainly used.

The zirconia powder of the present invention needs to have a zeta potential in slurry of -10 to +10 mV and an isoelectric point pH of 5 to 9.

By controlling the absolute value of the zeta potential to 10 mV or less, the molding characteristics of the zirconia powder are significantly increased. By controlling the zeta potential in this way, the particles tend to agglomerate, but their cohesion is very weak and does not impair press formability at all. Further, by controlling the zeta potential as described above, the adhesion of water acting as a binder is increased, so that the rolling formability of the zirconia powder is improved.

On the other hand, when the absolute value of the zeta potential is 10
If it exceeds mV, the molding density will decrease. Also, when the absolute value of the zeta potential increases, the powder becomes hard when an external force is applied, and when the external force is removed, the powder exhibits fluidity, that is, a so-called dilatancy property, making molding impossible at all.

Next, the isoelectric point pH needs to be in the range of 5 to 9, preferably 6.5 to 9.0.

When the isoelectric point pH is less than 5, the reason is not clear, but the moldability is insufficient and the molding density is low. On the other hand, when the isoelectric point pH range exceeds 9,
In some cases, the zirconia powder may become non-uniform, and as a result, the sintered density and the sintering strength of the compact may be reduced.

The zirconia powder of the present invention is obtained by a hydrolysis method,
It is obtained by neutralizing a zirconia powder produced by a hydrolysis neutralization method or the like. The hydrolysis method and the hydrolysis neutralization method are not particularly limited, and ordinary methods, for example, zirconium oxychloride, zirconyl nitrate,
A hydrolysis method in which an aqueous solution of zirconium chloride or zirconium sulfate is heated and hydrolyzed to obtain a hydrated zirconia sol, and the sol is dried to form a hydrated zirconia gel, which is calcined to obtain a zirconia powder, in the same manner. The obtained hydrated zirconia sol may be neutralized with an alkali such as ammonia, sodium hydroxide, potassium hydroxide, urea, etc., and then treated in the same manner as described above to obtain a hydrolytic neutralization method for obtaining zirconia powder.

In this neutralization treatment, the zeta potential when the target zirconia powder is slurried is -10 to +10 mV.
And the isoelectric point pH must be 5-9. One of the factors that causes the absolute value of the zeta potential to exceed 10 mV is considered to be impurities in the zirconia powder. The presence of an anionic species, such as Cl ⁻ ions, in the powder causes the zeta potential to become positively charged and a cationic species,
For example, the presence of Na ⁺ ions tends to be negatively charged. By measuring the content of these anions and cations, the amount of acid or alkali required for neutralization may be determined in advance, but usually it is necessary to go through trial and error.

The agent used for neutralization is not particularly limited, but when neutralizing with alkali, NaO is usually used.
Although alkali hydroxides such as H, KOH and NH ₄ OH are used, it is preferable to use aqueous ammonia from the viewpoint of suppressing the entry of alkali metals. When the neutralization treatment is performed using an acid, usually, an inorganic acid such as HCl, H ₂ SO ₄ , and HNO ₃ is applied. Moreover, it is also possible to use an organic acid instead of an inorganic acid. These are added in the form of an aqueous solution, and the concentration thereof is not particularly limited. However, it is preferable that the concentration of the zirconia powder is low so as to suppress the dissolution and deterioration of the zirconia powder. The processing temperature, the processing time, and the like are not particularly limited, and can be arbitrarily set. However, it is preferable that the processing be performed at a low temperature and in a short time in consideration of adverse effects on zirconia powder and workability.

The time of the neutralization treatment is not particularly limited. For example, the water may be washed after calcination or after crushing and drying.
This can be done by slurrying again. The rolling granulation can be performed by using an aqueous alkali solution as a binder during the granulation.

The zirconia powder of the present invention requires a stabilizer, such as a compound such as Y, Ca, Mg, or Ce, or a metal compound other than the stabilizer, such as a compound such as Al, a transition metal, or a rare earth metal. May be added accordingly.

[0022]

If the absolute value of the zeta potential when the zirconia powder is slurried is 10 mV or less, the formability is good because the frictional resistance between the particles is small due to the low value, and the slip characteristic is improved. It is considered something.

When the isoelectric point pH is less than 5,
As the content of impurities, especially the content of anions increases,
As a result, the composition of the zirconia powder becomes non-uniform, resulting in insufficient compactibility and low compaction density. On the other hand, when the isoelectric point pH exceeds 9, the sorption rate of Na ⁺ ions increases. However, similarly, it is considered that the composition of the zirconia powder becomes non-uniform, and the sintering density, sintering strength, and the like of the molded body are reduced.

[0024]

The zirconia powder of the present invention can be formed into a uniform and high-density compact, and a compact having good sphericity can be obtained by rolling granulation. further,
Sintered bodies obtained by firing these compacts are less prone to cracking and lamination.

[0025]

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

Example 1 A 0.5 mol / l aqueous solution of zirconium oxychloride with Y
Yttrium oxide was added so that the molar ratio in terms of ₂ O ₃ / ZrO _{2 was} 3/97, and hydrolysis was performed at the boiling temperature for 120 hours to synthesize a hydrated zirconia sol.
It was calcined at 00 ° C, washed with water and dried. Thereafter, the viscosity was adjusted using ammonia water and spray-dried,
The powder has a BET specific surface area of 6.5 m ² / g and an average particle size of 0.72 μm, and has a composition of Y ₂ O ₃ 5.1 wt% Na ₂ O 0.001 wt% Al ₂ O ₃ 0.005 wt% or less SiO A zirconia powder of ₂ 0.005 wt% Cl ^- 0.03 wt% was obtained.

Next, the zirconia powder of Cl ^- After 3 hours stirring was added aqueous ammonia equivalent to 1.2 times the molar amount of ions, washed with water, dried, to obtain a neutralized zirconia powder subjected to subsequent grinding.

This powder was treated as an electrolyte with a 0.01N-KCl solution, the powder slurry concentration was 2 vol%, and the mixture was treated with a shaking machine all day and night.
Was used to measure the zeta potential. As a procedure for measuring the zeta potential, N-HCl was first added to adjust to the acid side, and then N-HCl was added.
-KOH was added to reverse the alkali side. Zee
FIG. 1 shows the measurement results of the ta potential.

The zeta potential of the obtained zirconia powder is about +2 mV at the start point in the figure, and the isoelectric point pH is 7.0. In addition, this powder was
After weighing 15 and 20 g each and performing uniaxial press molding with a molding pressure of 1 Ton / cm ² using a mold having an inner diameter of 15 mm, sintering was performed at 1500 ° C. for 2 hours. No lamination or the like was observed at all, and the density of each sintered body was 6.07, and the bending strength of the sintered body was in the range of 120 to 150 kgf / mm ² .

Next, in order to examine the rolling granulation formability of the zirconia powder, the zirconia powder was made to have a diameter of 0.5 mm.
500 g of this was prepared, and using this as a core, using a normal dish-type tumbling granulator, pure water and zirconia powder were alternately added, granulated to a diameter of 3 mm, dried at 120 ° C. A molded sphere was obtained. .

When the particle size distribution and sphericity of the obtained molded sphere were observed by a stereoscopic microscope, there were no irregularities on the sphere surface, the particle size distribution was uniform, and the ratio of the maximum diameter / minimum diameter of the molded sphere was 1. 02. The density of the molded sphere is 3.
It was 35 g / cm ³ .

EXAMPLE _{2 A} 0.6 mol / l aqueous solution of zirconium oxychloride was added with a molar ratio of Y ₂ O ₃ / ZrO _{2 of} 3 /
Add yttrium oxide so as to obtain 97, hydrolyze at the boiling temperature for 130 hours, synthesize a hydrated zirconia sol, dry, calcine at 1000 ° C., wash with water, dry,
After pulverization, the powder had a specific surface area (BET) of 10.5 m ² / g, an average particle size of 0.85 μm, and a composition of Y ₂ O ₃ 4.8 wt% Na ₂ O 0.007 wt% Al ₂ O ₃ 0.005 wt% or less SiO ₂ 0.005wt% ^Cl - 0.02 was obtained wt% or less of the zirconia powder.

Next, an aqueous hydrochloric acid solution equivalent to 1.2 times the molar amount of Na ⁺ ions of the zirconia powder was added, and the mixture was stirred for 2 hours, washed with water, dried, and then pulverized to obtain a neutralized zirconia powder. Was.

When the zeta potential of this powder was measured in the same manner as in Example 1, the zeta potential upon slurrying was -5 mV, and the isoelectric point pH was 8.0. there were.

Using 20 g of this powder, uniaxial press molding was performed at a molding pressure of 0.75 kg / cm ² using a mold having an inner diameter of 15 mm, and sintering was performed at 1450 ° C. for 2 hours. No cracks, lamination, etc. were observed at all, the sintered body density was 6.05, and the bending strength of the sintered body was 117 kgf / mm ² .

Next, in order to examine the rolling granulation moldability of this zirconia powder, granulation was carried out in the same manner as in Example 1, and drying was performed at 120 ° C. to obtain a compact. .

When the particle size distribution and sphericity of the obtained molded sphere were observed by a stereoscopic microscope, there were no irregularities on the sphere surface, the particle size distribution was uniform, and the ratio of the maximum diameter / minimum diameter of the molded sphere was 1. 04. The density of the molded sphere is 3.
38.

Example 3 Y was added to a 0.4 mol / l aqueous solution of zirconium oxychloride.
Yttrium oxide was added so that the molar ratio in terms of ₂ O ₃ / ZrO _{2 was} 3/97, and hydrolysis was performed at the boiling temperature for 100 hours to synthesize a hydrated zirconia sol. afterwards,
Neutralization treatment is performed by adding sodium hydroxide, and 100
The zirconia powder was obtained by calcining at 0 ° C, washing with water and spray drying.

When the zeta potential of this powder was measured under the same conditions as in Example 1, it showed a potential of +25 mV and an isoelectric point pH of about 8.5.

When the formability of tumbling granulation was examined by using water and ammonia water as a binder in the obtained powder, when water was used as the binder, dilatancy was exhibited and a problem occurred in the formability. By using 0.1N ammonia water as a binder, dilatancy was eliminated and moldability could be imparted.

The powder using ammonia water as a binder has a zeta potential of +8.5 mV and an isoelectric point pH of about 8.5.
Met.

Comparative Example 1 The zirconia powder obtained by the hydrolysis method of Example 1 was evaluated in the same manner as in Example 1 without neutralizing with ammonia water.

FIG. 2 shows the results of the zeta potential of this zirconia powder.

When this zirconia powder was slurried, the zeta potential was +15 mV, and the isoelectric point pH was 7.

Using this powder, a compact was formed in the same manner as in Example 1, and a sintered compact was obtained. The sintered compact had a density of 6.02. In the part, generation of several cracks and lamination was observed.

Next, the zirconia powder was used to examine the rolling granulation formability according to the operation of Example 1. However, at the stage of forming the core, the dilatancy was reduced. And it was impossible to perform granulation.

Comparative Example 2 The zirconia powder obtained by the hydrolysis method of Example 2 was evaluated in the same manner as in Example 1 without neutralizing with a hydrochloric acid aqueous solution.

When this zirconia powder was slurried, the zeta potential was -18 mV and the isoelectric point pH was 8.

Using this powder, a compact was formed in the same manner as in Example 1, and a sintered compact was obtained. The sintered compact had a density of 6.03. In the part, generation of several cracks and lamination was observed.

Next, in order to examine the rolling granulation formability,
As a preliminary evaluation method, several grams of zirconia powder were
Then, pure water was dropped as a binder, and it was examined whether or not this zirconia powder exhibited dilatancy. As a result, kneading was impossible due to the remarkable dilatancy.

Comparative Example 3 Y was added to a 0.4 mol / l aqueous solution of zirconium oxychloride.
Yttrium chloride was added so that the molar ratio in terms of ₂ O ₃ / ZrO _{2 was} 3/97, and NaOH was further added to produce hydrated zirconia.

The hydrated zirconia was aged, spray-dried, and calcined at 900 ° C. to obtain zirconia powder. This powder had a specific surface area of 6.9 m ² / g, an average particle size of 0.9 μm, and a composition of Y ₂ O ₃ 5.05 w.
t%, 0.025 wt% of Na ₂ O, Al ₂ O ₃ <0.
005 wt%, SiO ₂ 0.01 wt%, Cl ⁻ <
It was 0.02 wt%.

The zeta potential of this powder slurry was measured in Example 1.
When measured by the same method as in the above, the value was −30 mV, and the isoelectric point pH was 4.5.

The powder was neutralized with hydrochloric acid equivalent to 1.2 times the molar amount of Na ⁺ ion, washed with water, dried and pulverized. As a result of the sintering, a sintered body density of 6.02 was obtained, but the bending strength of the sintered body was 70 to 90 kgf / mm ² , which was about 40% lower than that of Example 1.

Further, molding was attempted using a dish-type granulating machine with water as a binder, but the shape of the formed body was not constant and the particle size distribution was very wide.

The zirconia powder slurry after the neutralization treatment
Had a zeta potential of -9 mV, but had an isoelectric point pH of 4.6.
Met.

[Brief description of the drawings]

FIG. 1 shows the zirconia powder of the product obtained in Example 1.
It is a figure showing the result of data potential measurement.

FIG. 2 shows the zirconia powder of the product obtained in Comparative Example 1.
It is a figure showing the result of data potential measurement.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C01G 25/02 C04B 35/48

Claims (2)

(57) [Claims] (1) The slurry has a zeta potential of -10.
A zirconia powder having a pH of 5 to 9 and an isoelectric point of 5 to 9; 2. A zirconium powder produced by a hydrolysis method or a hydrolysis neutralization method has a zeta potential of -10 to +10 mV when slurried, and an isoelectric point pH of 5 to 9. A method for producing zirconia powder, characterized by further adding an acid or an alkali to the zirconia powder.