JP3896614B2 - Zirconia powder and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is used for functional ceramics such as solid electrolytes for fuel cells, oxygen pumps, oxygen sensors, NOx sensors, and thermal barrier coating materials, and structural ceramics such as pulverizer members, precision mechanical parts, and optical connector parts. In particular, the present invention relates to a zirconia powder excellent in moldability and a method for producing the same.
[0002]
[Prior art]
Conventionally, as a zirconia powder and its manufacturing method,
(1) A method of obtaining a zirconia powder by calcining a hydrated zirconia sol having a particle size of 0.3 μm or more obtained by heat hydrolysis of a zirconium salt aqueous solution at a temperature of 1000 ° C. or less (Japanese Patent Publication No. 4-72772), etc. It has been known.
[0003]
[Problems to be solved by the invention]
However, the zirconia powder obtained by the method (1) is obtained by calcining a hydrated zirconia sol having a particle size of 0.3 μm or more obtained by heat hydrolysis at a temperature of 1000 ° C. or less. Since the obtained powder has many pores inside the primary particles, the pores cause the friction between the particles and the mold wall surface and between the particles at the time of molding. It becomes low, and many laminations, cracks, and chipped edges are generated, making it difficult to mold.
[0004]
The present invention provides a zirconia powder having good moldability, that is, good dispersibility and high density of the molded body, which eliminates the disadvantages in the conventional method; and manufacturing the zirconia powder by a simple process. It is intended to provide a method that can be used.
[0005]
[Means for Solving the Problems]
The inventors of the present invention have prepared a zirconia powder obtained by calcining a hydrated zirconia sol or a mixture of the sol and a stabilizer such as yttria, calcia, magnesia, ceria commonly used in the production of zirconia ceramics. consider in detail the dispersibility and microstructural changes in the sum zirconia, BET specific surface area of the zirconia powder obtained by calcining a hydrated zirconia sol having an average particle diameter 0.4~2.0μm is 1 to 5 m ² It was found that a highly dispersible zirconia powder having no strong agglomeration between primary particles, which has not been obtained in the past, can be obtained simply by controlling to / g.
[0006]
That is, in the present invention, the BET specific surface area is 1 to 5 m ² / g, and the ratio of (average particle diameter measured with an electron microscope) / (average particle diameter determined from the BET specific surface area) is 0.9. To zirconia powder composed of primary particles having a particle size of about 2.0, and a zirconia powder is obtained by calcining a hydrated zirconia sol or a mixture of the sol and at least one compound of Y, Ca, Mg and Ce. In the manufacturing method, the average particle diameter φ (μm) of the hydrated zirconia sol is 0.4 to 2.0 μm, the sol is in the range of 1000 to 1500 ° C., and
200 × φ + 900 ≦ T ≦ 200 × φ + 1100
The gist of the method for producing zirconia powder by calcining at a temperature T (° C.) satisfying the above is also included. Hereinafter, the present invention will be described in more detail.
[0007]
In this specification, the “average particle diameter measured with an electron microscope” relating to zirconia powder is the size of each primary particle observed by an electron micrograph taken as an area and converted into a circle. The average value of the calculated particle sizes.
[0008]
“BET specific surface area” refers to a value measured using nitrogen as an adsorbed molecule. The “average particle diameter obtained from the BET specific surface area” refers to a diameter calculated from the BET specific surface area and the theoretical density by converting the shape of the particles into a sphere. The formula used for this calculation is as follows.
[0009]
Average particle size = 6 / (BET specific surface area × theoretical density) (1)
Further, the “average particle diameter” related to the hydrated zirconia sol is almost the same value as that measured by an electron microscope in the same manner as the above zirconia powder, although it is based on the photon correlation method.
[0010]
The zirconia powder of the present invention must have a BET specific surface area of 1 to 5 m ² / g. If the zirconia powder has a BET specific surface area of less than 1 m ² / g, it will be difficult to sinter, and if it exceeds 5 m ² / g, it will become a highly cohesive powder with high adhesion between particles. It becomes difficult to be suitable for ceramic raw material powder. Preferably has a BET specific surface area is 1 to 4 m ² / g, more preferably from 2 to 4 m ² / g.
[0011]
The average particle size ratio of the zirconia powder of the present invention must be 0.9 to 2.0. If it exists in this range, the sintering between primary particles will be hardly seen from observation of an electron microscope, and the dense primary particle which the pore which exists inside a particle | grain will not be observed is formed. This ratio is 1 if it is an isotropic dense primary particle, but since the particle shape of the zirconia powder is distorted, it becomes a dense primary particle at 0.9 to 2.0. When this ratio is less than 0.9, a number of necks between primary particles are observed by an electron microscope; when such a powder containing a large amount of hard aggregated particles is molded, the hard aggregated particles remain as they are in the resulting molded product. Therefore, when the density of the compact is reduced to a value larger than 2.0, the dispersibility of the zirconia powder is apparently good, but a large number of pores are formed inside the primary particles. This is because the density of the molded body is reduced due to the presence of. A more desirable average particle size ratio is 1 to 1.5.
[0012]
When the hydrated zirconia sol is calcined to obtain the zirconia powder of the present invention, the average particle diameter of the hydrated zirconia must be 0.4 to 2.0 μm. When the average particle size of the hydrated zirconia sol becomes smaller than 0.4 μm, the BET specific surface area of the zirconia powder obtained under the calcining conditions of the present invention described below becomes larger than 5 m ² / g, whereas 2.0 μm This is because it becomes smaller than 1 m ² / g. More preferably, the average particle size of the hydrated zirconia sol is 0.5 to 2.0 μm, and more desirably 0.5 to 1 μm. Regardless of the average particle diameter φ (μm) of the hydrated zirconia sol, the calcining temperature T (° C.) is 1000 to 1500 ° C., and 200 × φ + 900 ≦ T ≦ 200 ×. It must satisfy φ + 1100. When the temperature is lower than 1000 ° C. or 200 × φ + 900 ° C., the average particle size ratio of the obtained zirconia powder is larger than 2.0, while when it is higher than 1500 ° C. or 200 × φ + 1100 ° C., This is because the average particle size ratio becomes smaller than 0.9, and the zirconia powder having good dispersibility of the present invention cannot be obtained. A more preferable calcining temperature is 1100 to 1400 ° C.
[0013]
The holding time of the calcining temperature is preferably 0.5 to 10 hours, and the temperature raising rate is preferably 0.5 to 10 ° C./min. If the holding time is shorter than 0.5, uniform calcination is difficult, and if it is longer than 10 hours, the productivity is lowered, which is not preferable. Also, if the rate of temperature rise is less than 0.5 ° C / min, the time until the set temperature is reached is longer, and if it is greater than 10 ° C / min, the powder scatters vigorously during calcination, resulting in poor operability and production. Sex is reduced. The atmosphere gas in this calcination is generally composed of dry air or air containing water vapor, and the above conditions are for this atmosphere.
[0014]
Furthermore, in addition to the above two conditions of the average particle size of the hydrated zirconia sol and the calcination temperature, the BET specific surface area S (m ² / g) of the zirconia powder obtained by calcination and the average particle of the hydrated zirconia sol The relationship with the diameter φ (μm)
1.7 / S ≦ φ ≦ 2.3 / S
If satisfied, the density of the molded body is further increased, and the zirconia powder is further excellent in moldability.
[0015]
The hydrated zirconia sol may be obtained under any reaction conditions as long as the average particle diameter is obtained within the above range. For example, in the case of hydrolysis of an aqueous zirconium salt solution, a hydrated zirconia sol produced by hydrolysis of the zirconium salt is added to the aqueous zirconium salt solution, and the H ⁺ concentration at the end of the reaction is 0.1 to 0.6 mol / liter. When the hydrolysis is carried out so that the average particle size of the obtained hydrated zirconia sol becomes larger than that added to the zirconium salt solution, the average particle size is obtained by repeating this series of hydrolysis operations. A hydrated zirconia sol having a diameter of 0.4 to 2.0 μm can be obtained. The optimum addition amount of the hydrated zirconia sol added to the zirconium salt aqueous solution is 20 to 80 mol% when expressed as a molar ratio of the hydrated zirconia sol to (zirconium salt + hydrated zirconia sol). As a method for controlling the H ⁺ concentration at the end of the reaction, for example, an alkali or acid is added to the zirconium salt aqueous solution; a part of the anion constituting the zirconium salt is removed by an anion exchange resin. A method in which the H ⁺ concentration of the mixed slurry of zirconium hydroxide and acid is adjusted to cause hydrolysis. Zirconium salts used for the production of the hydrated zirconia sol include zirconium oxychloride, zirconyl nitrate, zirconium chloride, zirconium sulfate, etc. In addition, a mixture of zirconium hydroxide and acid may be used. . Examples of the alkali added to control the average particle diameter of the hydrated zirconia sol include ammonia, sodium hydroxide, potassium hydroxide, and the like. The compound shown may be sufficient. Examples of the acid include hydrochloric acid, nitric acid, and sulfuric acid, but in addition to these, 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 as its production method, and zirconium hydroxide can be obtained by neutralizing an aqueous zirconium salt solution with an alkali.
[0016]
There is no limitation on the drying method of the hydrated zirconia sol-containing liquid obtained by this reaction. For example, a method of spray drying a suspension containing the hydrated zirconia sol as it is or adding an organic solvent to the suspension. Further, a method of adding an alkali or the like to the suspension, filtering, washing with water and then drying can be mentioned. Further, when obtaining a zirconia powder in which the stabilizer is dissolved, a stabilizer, for example, a compound such as Y, Ca, Mg, or Ce may be added to the hydrated zirconia sol-containing liquid and dried. Alternatively, it may be added in advance at the time of hydrolysis. If necessary, metal compounds other than stabilization, for example, compounds such as Al, transition metals, rare earth metals, alkali metals, alkaline earth metals, etc. may be added in the same manner as described above.
[0017]
Since the calcined powder obtained as described above hardly undergoes strong agglomeration between particles, it becomes a zirconia powder with good dispersibility by simply crushing. Further, before and after crushing, if necessary, a sintering aid such as alumina and silica, an organic binder, and the like may be added to the zirconia powder.
[0018]
【Example】
EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.
[0019]
In the examples, the average particle size of the hydrated zirconia sol was determined by a laser diffraction method. The average particle diameter of the zirconia powder measured with an electron microscope was determined by performing image analysis processing on 100 primary particles using a transmission electron microscope. The theoretical density of the zirconia powder necessary to determine the average particle diameter calculated from the BET specific surface area is determined by calculating the peak intensity of the diffraction line of the X-ray diffraction pattern, and calculating the theoretical density calculated by the following formula = Monoclinic phase ratio × 5.6 + square phase ratio × 6.1
The zirconia powder was molded by a mold press at a molding pressure of 700 kgf / cm ² . The obtained molded body was sintered under the condition of 1500 ° C.-2 h.
[0020]
Example 1
10 liters of a 0.2 mol / liter ZrOCl ₂ aqueous solution was prepared, and the hydrolysis reaction was carried out at the boiling temperature for 100 hours to obtain a hydrated zirconia sol having an average particle size of 0.25 μm. 4 liters of the hydrated zirconia sol-containing liquid and 6 liters of a 0.2 mol / liter ZrOCl ₂ aqueous solution were mixed and subjected to a hydrolysis reaction at the boiling temperature for 60 hours. The hydrolysis reaction was carried out for 60 hours by mixing 1 liter and 6 liter of 0.2 mol / liter ZrOCl ₂ aqueous solution. The average particle diameter of the obtained hydrated zirconia sol was 0.7 μm.
[0021]
Next, 0.062 mol of YCl ₃ was added to the hydrated zirconia sol-containing liquid and spray-dried to prepare a dry powder of hydrated zirconia. The obtained dry powder was calcined at a temperature of 1180 ° C. for 2 hours in air in the presence of water vapor. The obtained calcined powder was crushed after adding 0.3% by weight of alumina.
[0022]
The obtained zirconia powder has a BET specific surface area of 2.5 m ² / g, a monoclinic phase of 10 wt% and a tetragonal phase of 90 wt%, a theoretical density of 6.05, and an average particle diameter determined by an electron microscope. 0.4 μm (that is, φ · S = 1.8). From this BET specific surface area and theoretical density, the “average particle diameter obtained from the BET specific surface area” is calculated as 0.4 μm from the above-mentioned equation (1), and (average particle diameter measured with an electron microscope) / ( The ratio of the average particle diameter obtained from the BET specific surface area was changed from 0.4 μm / 0.4 μm to 1.0, and it was observed that the powder had good dispersibility.
[0023]
Next, when a molded body was produced using the zirconia powder obtained above, the molded body density was 2.88 g / cm ³ , the sintered body density was 6.02 g / cm ³ , and bending strength. Was 122 kgf / mm ² .
[0024]
Example 2
4 liters of a hydrated zirconia sol-containing liquid having an average particle diameter of 0.7 μm obtained in Example 1 and 6 liters of a 0.2 mol / liter ZrOCl ₂ aqueous solution were mixed and subjected to hydrolysis for 60 hours. The hydrated zirconia sol-containing liquid, 4 liters, and 6 liters of 0.2 mol / liter ZrOCl ₂ aqueous solution were mixed and hydrolyzed for 60 hours. The average particle diameter of the obtained hydrated zirconia sol was 1.2 μm. Next, 0.062 mol of YCl ₃ was added to the hydrated zirconia sol-containing liquid and spray-dried to prepare a dry powder of hydrated zirconia. The obtained dry powder was calcined in air in the presence of water vapor at a temperature of 1260 ° C. for 2 hours. The obtained calcined powder was crushed after adding 0.3% by weight of alumina.
[0025]
The obtained zirconia powder has a BET specific surface area of 1.8 m ² / g, a monoclinic phase of 12 wt% and a tetragonal phase of 88 wt%, a theoretical density of 6.04, and an average particle diameter determined by an electron microscope. It was 0.6 μm (that is, φ · S = 2.2). From this BET specific surface area and theoretical density, the “average particle diameter determined from the BET specific surface area” is calculated as 0.55 μm from the above-described equation (1), and (average particle diameter measured with an electron microscope) / ( The ratio of the average particle diameter obtained from the BET specific surface area was changed from 0.6 μm / 0.55 μm to 1.1, and it was observed that the powder had good dispersibility.
[0026]
Then, by using the zirconia powder obtained above, were manufactured molded body, the molded body density of 2.89 g / cm ^3, the sintered density was 6.00 g / cm ^3, flexural strength Was 109 kgf / mm ² .
[0027]
Example 3
10 liters of a 0.1 mol / liter ZrOCl ₂ aqueous solution was prepared, and the hydrolysis reaction was carried out at the boiling temperature for 70 hours to obtain a hydrated zirconia sol having an average particle size of 0.13 μm. 5 liters of the hydrated zirconia sol-containing liquid and 5 liters of a 0.1 mol / liter ZrOCl ₂ aqueous solution were mixed and subjected to a hydrolysis reaction at the boiling temperature for 50 hours. The hydrolysis reaction was carried out for 50 hours by mixing 1 liter and 5 liter of 0.1 mol / liter ZrOCl ₂ aqueous solution. The average particle size of the obtained hydrated zirconia sol was 0.5 μm. Next, 0.031 mol of YCl ₃ was added to the hydrated zirconia sol-containing liquid and spray-dried to prepare a dry powder of hydrated zirconia. The obtained dry powder was calcined in air in the presence of water vapor at a temperature of 1090 ° C. for 2 hours. The obtained calcined powder was crushed after adding 0.3% by weight of alumina.
[0028]
The obtained zirconia powder has a BET specific surface area of 3.9 m ² / g, a monoclinic phase of 11 wt% and a tetragonal phase of 89 wt%, a theoretical density of 6.05 g / cm ³ , and an average by electron microscope The particle size was 0.26 μm (that is, φ · S = 2.0).
[0029]
From this BET specific surface area and theoretical density, the “average particle diameter determined from the BET specific surface area” is calculated as 0.25 μm from the above-mentioned equation (1), and (average particle diameter measured with an electron microscope) / ( The ratio of the average particle diameter obtained from the BET specific surface area was changed from 0.26 μm / 0.25 μm to 1.0, and it was observed that the powder had good dispersibility.
[0030]
Next, when a molded body was produced using the zirconia powder obtained above, the molded body density was 2.86 g / cm ³ , the sintered body density was 6.01 g / cm ³ , and bending strength. Was 118 kgf / mm ² .
[0031]
Comparative Example 1
It carried out on the same conditions except having set the calcination temperature of Example 1 to 800 degreeC. The obtained zirconia powder has a BET specific surface area of 24 m ² / g, a monoclinic phase of 9 wt% and a tetragonal phase of 91 wt%, a theoretical density of 6.06 g / cm ³ , and an average particle diameter measured by an electron microscope. Was 0.6 μm (that is, φ · S = 17).
[0032]
From this BET specific surface area and theoretical density, the “average particle diameter determined from the BET specific surface area” is calculated as 0.041 μm from the above-described equation (1), and (average particle diameter measured with an electron microscope) / ( The ratio of the average particle diameter determined from the BET specific surface area was changed from 0.6 μm / 0.041 μm to 15, and a large number of pores were observed inside the primary particles.
[0033]
Then, by using the zirconia powder obtained above, were manufactured molded body, the molded body density of 2.55 g / cm ^3, the sintered density was 5.95 g / cm ^3, flexural strength Was 90 kgf / mm ² .
[0034]
Comparative Example 2
Except for the calcination temperature set to 1600 ° C. and pulverization, the same conditions as in Example 1 were used. The obtained zirconia powder has a BET specific surface area of 0.5 m ² / g, a monoclinic phase of 45 wt% and a tetragonal phase of 55 wt%, a theoretical density of 5.90 g / cm ³ , and an average by electron microscope The particle size was 0.4 μm (that is, φ · S = 0.35).
[0035]
From this BET specific surface area and theoretical density, the “average particle diameter determined from the BET specific surface area” is calculated as 2.03 μm from the above-described equation (1), and (average particle diameter measured with an electron microscope) / ( The ratio of the average particle diameter obtained from the BET specific surface area was changed from 0.4 μm / 2.03 μm to 0.20, and many aggregations and necks between the primary particles were observed.
[0036]
Next, when a molded body was produced using the zirconia powder obtained above, the molded body density was 2.58 g / cm ³ , the sintered body density was 5.49 g / cm ³ , and the bending strength was Was 52 kgf / mm ² .
[0037]
【The invention's effect】
As described above, the zirconia powder of the present invention is excellent in moldability because of good dispersibility and a high density of the molded body.

Claims (2)

A BET specific surface area of 1 to 5 m ² / g and a ratio of (average particle diameter measured by electron microscope) / (average particle diameter determined from BET specific surface area) of 0.9 to 2.0 Zirconia powder consisting of secondary particles. In a method for producing a zirconia powder by calcining a hydrated zirconia sol having an average particle size of 0.4 to 2.0 μm or a mixture of the sol and at least one compound of Y, Ca, Mg and Ce, The average particle diameter φ (μm) of the sum zirconia sol is 0.4 to 2.0 μm, the temperature T (° C.) satisfying 200 × φ + 900 ≦ T ≦ 200 × φ + 1100 in the range of 1000 to 1500 ° C. The method for producing zirconia powder according to claim 1, wherein the zirconia powder is calcined.