JP3339076B2 - Zirconia fine powder - 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 fine powder having good moldability and excellent sinterability.

[0002]

2. Description of the Related Art Conventionally, as a zirconia fine powder and a method for producing the zirconia, ammonia water is added to a suspension of hydrated zirconia fine particles in which a stabilizer is dissolved, followed by filtration, washing with water, and calcination. Method for obtaining powder (JP-A-63-129017) After hydrolyzing a zirconium salt aqueous solution, a hydrated zirconia sol having a particle size in the range of 0.1 to 0.3 μm is separated by sedimentation or centrifugation. And a method of calcining to obtain a zirconia powder (JP-A-58-217430).

[0003]

In the above method, hydrated zirconia sol having an average particle diameter of 1 μm is used as a raw material and calcined at a temperature of 800 ° C. to obtain zirconia powder.
Since the zirconia powder thus obtained has many pores inside the primary particles, the pores cause a large friction between the particles and the mold wall and between the particles due to the pores during molding, The density of the obtained molded body is low, and a large number of laminations, cracks, and chipped edge portions occur, making it difficult to mold. Further, at the time of sintering, many internal defects due to the pores remain, deteriorating the characteristics of the sintered body. Is obtained by separating only a hydrated zirconia sol having a relatively large particle size and calcining the sol at a temperature of 1000 ° C. or less. As in the case of (1), pores are apt to remain inside the primary particles, and as described above, it is difficult to mold, and the characteristics of the sintered body are low.

According to the present invention, there is provided a zirconia fine powder having good moldability, that is, good dispersibility, high compact density, and excellent sinterability, which has solved the disadvantages of the conventional method. It is the purpose.

[0005]

Means for Solving the Problems The present inventors have developed a hydrated zirconia sol or yttria, calcia, magnesia, and a zirconia-based ceramic which are commonly used in the production of zirconia ceramics.
The change in the microstructure of the hydrated zirconia sol when calcining a mixture with a stabilizer such as ceria to obtain a zirconia powder was examined in detail, and the average particle size of the hydrated zirconia sol and the BET during calcination were determined. By controlling the specific surface area, it has been found that a zirconia fine powder having good dispersibility and substantially no strong aggregation between the primary particles can be obtained, and the present invention has been achieved.
That is, according to the present invention, the BET specific surface area is 6 to 28 m ² / g, and the average particle size measured by an electron microscope / BET
It is a zirconia fine powder composed of primary particles having a ratio of the average particle size determined from the specific surface area (hereinafter, referred to as an average particle size ratio) of 0.9 to 2.1. The compact obtained by using the fine powder has a high density and can be sintered at a relatively low temperature. Hereinafter, the present invention will be described in more detail.

In the present specification, the “average particle diameter measured by an electron microscope” relating to zirconia fine powder means that the size of each primary particle observed by an electron micrograph is read in terms of area and is read out in a circular shape. The average value of the particle diameters calculated by converting to "BET specific surface area" refers to a value measured using nitrogen as an adsorbed molecule. The “average particle diameter determined from the BET specific surface area” refers to a diameter calculated from the BET specific surface area and the theoretical density by converting the particle diameter shape into a sphere. The "average particle size" of the hydrated zirconia sol is approximately the same as that measured by an electron microscope as in the case of the above-mentioned zirconia fine powder, though it is determined by the photon correlation method.

The zirconia fine powder of the present invention needs to have a BET specific surface area of 6 to 28 m ² / g. When the BET specific surface area of the zirconia fine powder is smaller than 6 m ² / g, the zirconia fine powder becomes a fine powder that is difficult to be sintered on the low temperature side.
If it is larger than 8 m ² / g, the adhesion between particles becomes remarkably strong and agglomerated powder, which is not suitable for ceramic raw material powder. A more preferable range of the BET specific surface area is 8 to 24 m ² / g, and further preferably 13 to 19 m ² / g.
m ² / g.

[0008] The average particle size ratio of the zirconia fine powder of the present invention must be 0.9 to 2.1. Within this range, sintering between the particles is hardly observed from observation with an electron microscope, and dense primary particles are formed in which no pores existing inside the particles are observed. Isotropic dense 1
In the case of the secondary particles, this ratio is 1, but since the particle shape of the zirconia fine powder is distorted, the ratio of 0.9 to 2.1
It becomes the next particle. When this ratio is less than 0.9, a number of necks between primary particles are observed by an electron microscope; when a fine powder containing a large amount of such hard agglomerated particles is formed, hard agglomerated particles are obtained in the obtained molded body. The compact remains in its original shape, which reduces the density of the compact because the pore size distribution is widened. In addition, during sintering, non-uniform shrinkage occurs due to the presence of a large number of agglomerated particles, and there are many pores in the sintered compact. It remains and the properties of the sintered body deteriorate. On the other hand,
When it is larger than 2.1, the dispersibility of the zirconia fine powder is apparently good, but the number of pores is present inside the primary particles, so that the density of the compact is reduced. Since it remains, the properties of the sintered body also deteriorate. A more preferred average particle size ratio is 1 to 1.5.

The ζ potential of the zirconia fine powder is
It is preferably in the range of -20 to 20 mV with respect to the potential at the isoelectric point. When the ζ potential is in this range, the adhesion between the primary particles is weakened, and the aggregates or granules of the obtained primary particles are softened. This is because it becomes easily crushed, and becomes a zirconia fine powder having more excellent moldability. More preferably, it is -10 to 10 mV.

In obtaining the zirconia fine powder of the present invention by calcining the hydrated zirconia sol, the hydrated zirconia has an average particle diameter φ (μm) of 0.07 to 0.3 μm, and The relationship with the desired BET specific surface area S (m ² / g) of the zirconia fine powder obtained by calcining must satisfy 1.7 / S ≦ φ ≦ 2.5 / S. When the average particle size of the hydrated zirconia sol is smaller than 0.07 μm, the BET specific surface area of the obtained zirconia fine powder is 28 m ² / g.
Larger than 0.3 μm, whereas smaller than 6 m ² / g; and (1.7
/ S), the average particle size ratio of the obtained zirconia fine powder is smaller than 0.9, whereas when it is larger than (2.5 / S) μm, the average particle size ratio is 2. This is because the zirconia fine powder having good dispersibility of the present invention cannot be obtained because it is larger than 1. More preferably, the average particle size of the hydrated zirconia sol is 0.08 to 0.2.
5 μm, more preferably 0.1 to 0.15 μm
It is. The more preferable average particle size ratio is 1.9 / S ≦ φ ≦ 2.1 / S. When measuring the BET specific surface area, when the impurity content of the zirconia fine powder is high, it is better to measure after removing the impurities. This is because, as the impurity content increases, the error in the BET specific surface area increases, and the measurement accuracy deteriorates. Impurities contained in the zirconia fine powder can be easily removed by washing with water.

In order to obtain the relationship between the average particle size of the hydrated zirconia sol and the BET specific surface area of the zirconia fine powder, two kinds of calcination temperatures are set depending on the presence or absence of the metal compound contained in the hydrated zirconia sol. Must be set under the following conditions. When the dried powder of the hydrated zirconia sol contains a compound having an action of promoting particle growth during calcination, for example, an alkali metal compound, the average particle size of the hydrated zirconia sol is in any of the above ranges. The calcining temperature T (° C.) is in the range of 600 to 1100 ° C.
In addition, it must satisfy the following condition: 1000 · φ + 550 ≦ T ≦ 1830 · φ + 550. When the temperature is lower than 600 ° C. or (1000 · φ + 550) ° C., the average particle size ratio of the obtained zirconia fine powder becomes larger than 2.1, while 1100 ° C. or (1830 · φ)
If the temperature is higher than (+550) ° C., the average particle size ratio of the obtained zirconia fine powder becomes smaller than 0.9, and the zirconia fine powder having good dispersibility of the present invention cannot be obtained. The dried powder of the hydrated zirconia sol not containing the above compound has a calcining temperature of 740 to 1200 ° C.
And is set so as to satisfy 1830 · φ + 650 ≦ T ≦ 2750 · φ + 650. 740 ° C. or (1830
If the temperature is lower than (φ + 650) ° C. or higher than 1200 ° C. or (2750 · φ + 650) ° C., the zirconia fine powder of the present invention cannot be obtained as described above. However, if the hydrated zirconia sol having the above average particle size is calcined under the above conditions, a zirconia fine powder satisfying the relationship of 1.7 / S ≦ φ ≦ 2.5 / S is usually obtained. The above setting conditions of the calcining temperature are for a calcining atmosphere composed of dry air or air containing water vapor. Of course, gases such as nitrogen, oxygen, carbon dioxide, argon, and helium can also be used. Examples of the alkali metal compound include chlorides such as sodium and potassium, hydroxides, nitrates, and sulfates. The optimum content is 0.005 to 2% by weight in terms of the weight ratio of alkali metal to zirconia.

The holding time of the calcination temperature is preferably 0.5 to 10 hours, and the heating rate is preferably 0.5 to 10 ° C./min.
If the holding time is shorter than 0.5, it is difficult to uniformly calcine, and if the holding time is longer than 10 hours, the productivity is lowered, which is not preferable. Further, when the heating rate is lower than 0.5 ° C./min, the time required to reach the set temperature becomes longer,
If it is higher than 10 ° C./min, the powder will be scattered violently during calcination, resulting in poor operability and reduced productivity.

The above-mentioned hydrated zirconia sol may be obtained under any reaction conditions as long as it has an average particle size within the above range. In the case of the hydrolysis reaction of the zirconium salt, the average particle size of the obtained hydrated zirconia sol is such that the pH of the reaction solution at the end of the reaction is 0.2 to
By adjusting the average particle diameter to be 1.3, the average particle diameter becomes 0.3.
A hydrated zirconia sol of 07-0.3 μm is obtained. As a method for controlling the pH, that is, the average particle size of the hydrated zirconia sol, for example, an alkali or an acid is added to an aqueous solution of a zirconium salt; a part of the anion constituting the zirconium salt by an anion exchange resin is removed. The removal is performed to adjust the pH for hydrolysis, and a method of adjusting the pH of a mixed slurry of zirconium hydroxide and an acid for hydrolysis may be used. Further, in order to accelerate the hydrolysis reaction, hydrolysis may be performed by adding a hydrated zirconia sol to the reaction solution. At this time, the added amount of the hydrated zirconia sol depends on ZrO ₂
When expressed as a ratio of the amount of ZrO _{2 in the} hydrated zirconia sol to the amount, 0.5 to 20% by weight is the optimum addition amount.
Examples of the zirconium salt used for producing the hydrated zirconia sol include zirconium oxychloride, zirconyl nitrate,
Zirconium chloride, zirconium sulfate and the like can be mentioned, but a mixture of zirconium hydroxide and an acid may be used. As the alkali added to control the average particle size of the hydrated zirconia sol, ammonia,
Examples thereof include sodium hydroxide and potassium hydroxide. In addition to these, compounds which decompose and show basicity such as urea may be used. Examples of the acid include hydrochloric acid, nitric acid, and sulfuric acid. In addition, organic acids such as acetic acid and citric acid may be used. When zirconium hydroxide is used as a raw material for the hydrated zirconia sol, various methods can be selected for its production, and zirconium hydroxide can be obtained by neutralizing a zirconium salt aqueous solution with an alkali.

The method for drying the hydrated zirconia sol-containing liquid obtained by this reaction is not limited. For example, a suspension containing the hydrated zirconia sol may be sprayed as it is or by adding an organic solvent to the suspension. Examples of the method include a method of drying, a method of adding an alkali or the like to the suspension, filtration, washing with water, and drying. When obtaining a zirconia fine powder in which a stabilizer is dissolved, a suspension of a hydrated zirconia sol, for example, Y, Ca, Mg, C
Compounds such as e may be added and dried, or may be added in advance during hydrolysis. If necessary, a metal compound other than the stabilizing compound, for example, a compound of Al, transition metal, rare earth metal, alkali metal, alkaline earth metal or the like may be added in the same manner as described above. In particular, when an alkali metal compound is added, dense primary particles can be obtained at a relatively low calcination temperature by the action of promoting the grain growth of the metal, as described above. It is effective in improving the hydrated zirconia sol. Therefore, when the average particle size of the hydrated zirconia sol is 0.16 to 0.3 μm, it is better to add an alkali metal compound and calcine.

The calcined powder obtained as described above hardly undergoes strong coagulation between particles, so that it becomes a finely dispersed zirconia fine powder only by easy pulverization.
At this time, the pulverization usually changes the BET specific surface area in the range of 0.95 to 1.1 times that of the calcined powder.
Further, for example, alumina or the like may be added as a sintering aid as needed at the time of pulverization. In particular, the zirconia fine powder having a BET specific surface area of 6 to 12 m ² / g is preferably added with a sintering aid to improve sintering characteristics.

The zeta potential of the zirconia fine powder can be controlled by washing it with an aqueous solution of an alkali or an acid. For example, when the ζ potential is higher than 10 mV with respect to the isoelectric point, the zirconia fine powder is washed with an alkali aqueous solution and washed with water; when the ζ potential is lower than −10 mV, the zirconia fine powder is washed with an acid aqueous solution and washed with water. Then, it may be adjusted so as to fall within the range of -10 to 10 mV. The operation is preferably performed before grinding. This is because the filterability at the time of washing and water washing is good. Further, the ζ potential can be controlled in the production process of the zirconia fine powder. For example, when the hydrated zirconia-containing liquid is dried, an alkaline aqueous solution is added thereto, followed by filtration and washing with water, thereby removing impurities and controlling the zeta potential of the obtained zirconia fine powder. Ammonia, sodium hydroxide, potassium hydroxide and the like are used as alkalis for controlling these ζ potentials;
Examples thereof include sulfuric acid, acetic acid, and citric acid. In addition, the ζ potential of the zirconia fine powder may be controlled by adding an organic dispersant, a plasticizer, and the like as necessary.

[0017]

The microstructure of the hydrated zirconia sol obtained by the hydrolysis of the aqueous solution of zirconium salt is composed of particles of ultrafine particles having good crystallinity. When the hydrated zirconia sol is calcined, the microstructure becomes It is observed by an electron microscope that the particles are sintered between the ultrafine particles while maintaining the particle shape and change into dense primary particles. From this, when the average particle size of the zirconia fine powder obtained from the electron microscope and the average particle size obtained from the BET specific surface area satisfy a certain relationship, good dispersibility, that is, strong aggregation between particles occurs It is presumed that fine zirconia fine powder was not formed.

[0018]

As described above, the zirconia fine powder of the present invention has good moldability, that is, good dispersibility, high compact density, and excellent sinterability.

[0019]

The present invention will be described below in detail with reference to examples. In the examples, the average particle size of the zirconia fine powder measured by an electron microscope was determined by performing image analysis processing on 300 particles using a transmission electron microscope. The theoretical density of the zirconia powder required to determine the average particle diameter determined from the BET specific surface area was determined by calculating the composition of each crystal phase from the peak intensity of the diffraction line in the X-ray diffraction pattern, and using the following formula ( In the examples, cubic crystals were not included).

Theoretical density = monoclinic crystal content × 5.6 + tetragonal crystal content × 6.1 The zirconia fine powder was molded by a die press at a molding pressure of 700 kgf / cm ² .

Example 1 To 2 liters of a 2 mol / l zirconium oxychloride aqueous solution, 500 ml of 2N ammonia water was added, and distilled water was further added to prepare 10 liters of a 0.4 mol / l zirconium oxychloride aqueous solution. The hydrolysis reaction was performed at the boiling temperature for 120 hours while stirring the raw material liquid. The average particle size of the obtained hydrated zirconia sol by a photon correlation method was 0.1 μm. Next, 49 g of yttrium chloride was added to the suspension containing the hydrated zirconia sol, concentrated by heating, and spray-dried to prepare a dry powder of hydrated zirconia. The obtained dry powder was calcined at 900 ° C. for 2 hours in air having a partial pressure of steam of 30 mmHg or more. The calcined powder was washed with 1N aqueous ammonia, further washed with distilled water and pulverized.

The obtained zirconia fine powder has a BET specific surface area of 20 m ² / g, a monoclinic structure of 23 wt% and a tetragonal structure of 77 wt%, a theoretical density of 6.0, and an average particle size measured by an electron microscope. The diameter was 0.05 μm (that is, φ · S = 2, average particle size ratio = 1.2), and it was observed that the powder had good dispersibility.

Next, a compact was prepared using the zirconia fine powder obtained above.
It was 69 g / cm3. This molded body was fired at a temperature of 1400 ° C. for 2 hours. The density of the obtained sintered body is 6.
07 g / cm ³ and a flexural strength of 120 kgf / mm ²
Met.

Example 2 A zirconia fine powder was obtained under the same conditions as in Example 1 except that pulverization was performed by adding 0.3% by weight of alumina during pulverization. When a compact was produced using this zirconia fine powder, the compact had a density of 2.71 g / cm ³ , and was fired at a temperature of 1250 ° C. for 2 hours to obtain a density of a sintered compact. Was 6.07 g / cm ³ and the flexural strength was 110 kgf / mm ² .

Example 3 One liter of 2N aqueous ammonia was added to 2 liters of a 2 mol / l aqueous zirconium oxychloride solution, and distilled water was further added to prepare 10 liters of a 0.4 mol / l aqueous zirconium oxychloride solution. . The hydrolysis reaction was performed at the boiling temperature for 110 hours while stirring the raw material liquid. The average particle size of the obtained hydrated zirconia sol by a photon correlation method was 0.14 μm. Next, 49 g of yttrium chloride was added to the suspension containing the hydrated zirconia sol, concentrated by heating, and spray-dried to prepare a dry powder of hydrated zirconia. The obtained dry powder was calcined at 970 ° C. for 2 hours in air having a partial pressure of water vapor of 30 mmHg or more. The calcined powder was washed with 1N aqueous ammonia, further washed with distilled water and pulverized.

The obtained zirconia fine powder has a BET specific surface area of 14 m ² / g, a monoclinic crystal of 16 wt% and a tetragonal crystal of 84 wt%, a theoretical density of 6.0, and an average value by an electron microscope. The particle size was 0.07 μm (that is, φ · S = 2, average particle size ratio = 1.0), and it was observed that the powder had good dispersibility.

Next, when a compact was produced using the zirconia fine powder obtained above, the compact density was 2.7.
8 g / cm ³ , and the density of the sintered body obtained under the firing conditions of 1450 ° C. for 2 hours is 6.09 g / cm ³ ,
The bending strength was 125 kgf / mm ² .

Example 4 A zirconia fine powder was obtained under the same conditions as in Example 3 except that pulverization was performed by adding 0.3% by weight of alumina during pulverization. When a compact was produced using this zirconia fine powder, the compact had a density of 2.79 g / cm ³ , and was sintered at a temperature of 1330 ° C. for 2 hours to obtain a sintered compact. Was 6.08 g / cm ³ and the flexural strength was 130 kgf / mm ² .

Example 5 2 liters of a 2 mol / l zirconium oxychloride aqueous solution was added to 1.9 liters of 2N aqueous ammonia and 0.1 liter
0.5 L of a specified aqueous sodium hydroxide solution was added, and distilled water was further added to prepare 10 L of a 0.4 mol / L zirconium oxychloride aqueous solution. The hydrolysis reaction was performed at the boiling temperature for 100 hours while stirring the raw material liquid. The average particle size of the obtained hydrated zirconia sol by a photon correlation method was 0.25 μm. Next, yttrium chloride was added to the suspension containing the hydrated zirconia sol for 49 hours.
g, and concentrated by heating, followed by spray drying to prepare a dried powder of hydrated zirconia. The obtained dry powder was calcined at 920 ° C. for 2 hours in air having a partial pressure of water vapor of 30 mmHg or more. The calcined powder was washed with a 0.1N aqueous ammonia solution and further washed with distilled water. Before pulverization, 0.3% by weight of alumina was added and pulverized.

The obtained zirconia fine powder has a BET specific surface area of 8 m ² / g, a monoclinic crystal of 18 wt% and a tetragonal crystal of 82 wt%, a theoretical density of 6.0, and
The average particle size was 0.16 μm by an electron microscope (that is, φ · S = 2, average particle size ratio = 1.3), and it was observed that the powder had good dispersibility.

Next, when a compact was produced using the zirconia fine powder obtained above, the compact density was 2.7.
It was 2 g / cm ³ . The density of the sintered body obtained by firing this molded body at a temperature of 1370 ° C. for 2 hours is 6.05 g.
/ Cm ³ , and the flexural strength was 115 kgf / mm ² .

Comparative Example 1 The procedure was performed under the same conditions as in Example 1 except that the calcination temperature was set at 500 ° C. The obtained zirconia fine powder is B
ET specific surface area is 78 m ² / g, monoclinic 35 wt%
And a tetragonal crystal of 65 wt%, a theoretical density of 5.9, and an average particle size measured by an electron microscope of 0.1 μm.
m (that is, φ · S = 7.8, average particle size ratio =
7.7). From the electron microscope, many pores inside the particles were confirmed.

Next, when a compact was produced using the zirconia fine powder obtained above, the compact density was 2.4.
It was 8 g / cm ³ . The density of the sintered body obtained by firing this molded body at a temperature of 1400 ° C. for 2 hours is 5.91 g.
/ Cm ³ , and the flexural strength was 57 kgf / mm ² .

COMPARATIVE EXAMPLE 2 270 g of aluminum chloride was added to 1 liter of a 2 mol / l zirconium oxychloride aqueous solution, and distilled water was added thereto to prepare a 0.2 mol / l zirconium oxychloride aqueous solution 1
0 liters were prepared. This raw material liquid is placed in a closed container at 1
The hydrolysis reaction was performed at 50 ° C. for 50 hours. The average particle size of the obtained hydrated zirconia sol according to the photon correlation method is 0.1.
It was 4 μm. Next, the suspension containing the hydrated zirconia sol was filtered through an ultrafiltration membrane having a molecular weight cutoff of 3,000,000, washed with water to remove aluminum chloride, and added with 25 g of yttrium chloride. Further, an excess amount of aqueous ammonia was added, the mixture was filtered, washed with water, and dried by standing to prepare a dry powder of hydrated zirconia. The obtained dry powder is dried at a temperature of 1250 ° C. in air having a partial pressure of water vapor of 30 mmHg or more.
It was calcined for a time, washed with water, and then ground.

The obtained zirconia fine powder has a BET specific surface area of 3 m ² / g, a monoclinic crystal of 30 wt% and a tetragonal crystal of 70 wt% and a theoretical density of 6.0.
The average particle size measured by an electron microscope was 0.27 μm (ie, average particle size ratio = 0.8).

Next, when a compact was prepared using the zirconia fine powder obtained above, the compact density was 2.5%.
1 g / cm ³ , weak strength, and many laminations were observed. The density of the sintered body obtained by firing this molded body at a temperature of 1500 ° C. for 2 hours is 5.80 g / cm.
³ , and the flexural strength was 85 kgf / mm ² .

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

Claims (3)

(57) [Claims] 1. A BET specific surface area of 6 to 28 m ² / g, and a ratio of average particle diameter measured by an electron microscope / average particle diameter determined from BET specific surface area of 0.9 to 2.1. A zirconia fine powder comprising primary particles. 2. A method for obtaining a zirconia fine powder by drying and calcining a hydrated zirconia sol obtained by hydrolyzing an aqueous solution of a zirconia salt, wherein the hydrated zirconia sol has an average particle diameter φ (μm) of 0.07 to 0.07. The zirconia fine powder obtained by calcination and having a BET specific surface area S (m ² / g) of 0.3 μm satisfies the following relational expression.
A method for producing the zirconia fine powder described above. 1.7 / S ≦ φ ≦ 2.5 / S 3. An average particle diameter φ (μm) of a hydrated zirconia sol.
The method for producing zirconia fine powder according to claim 2, wherein the calcination temperature T (° C) satisfies the following relational expression. (I) When the dry powder of hydrated zirconia sol contains a compound that promotes particle growth: 600 ≦ T ≦ 1100 and 1000 · φ + 550 ≦ T ≦ 1830 · φ + 550 (1) (ii) Dry powder of hydrated zirconia sol 740 ≦ T ≦ 1200 and 1830 · φ + 650 ≦ T ≦ 2750 · φ + 650 (2)