JPH10139436A - Zirconia particle for solid electrolyte and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain zirconia particles used for solid electrolytes, eliminated in the defects of products produced by conventional methods, good in moldability, excellent in low temperature sintering ability, and further excellent in ion conductivity, and to provide a method for producing the zirconia powder for the solid electrolytes, enabling to produce the zirconia powder in simple processes. SOLUTION: This zirconia particles for solid electrolytes comprise secondary agglomerates containing solid dissolved yttrium in an amount of 4-10mol.% as a stabilizer and having a BET specific surface area of 8-20m<2> /g and an average particle diameter of 0.1-1.0μm. This method for producing the zirconia particles for the solid electrolytes comprises calcining a mixture comprising a yttrium compound and a zirconia sol hydrate obtained by the hydrolysis of a zirconium salt aqueous solution and having a yttrium content of 4-10mol.% at a temperature of 800-1200 deg.C and subsequently grinding the calcination product into an average particle diameter of 0.1-1.0μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is used in a solid electrolyte used electrically conductive solid membrane for a solid electrolyte type fuel cell, a gas sensor for detecting the oxygen concentration and NO _x gas concentration in the exhaust gas of an engine The present invention relates to a zirconia powder and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, a zirconia powder for a solid electrolyte has a specific surface area obtained by coprecipitation of 2.5 to 7 m.
^A method of firing a solid solution of zirconia powder of Y ₂ O _{3 having a} ² / g average particle diameter of 1 μm or less at 1500 ° C. or less to obtain a solid electrolyte (Japanese Patent Laid-Open No. 1-275467) is known.

[0003]

The zirconia powder for a solid electrolyte obtained by the coprecipitation method is a powder having a small BET specific surface area and having hard coarse particles,
When the specific surface area is reduced as described above, the sintering temperature at the time of molding and sintering increases, the density of the obtained sintered body is low, and the crystal grain size is large. Such a sintered body has a low mechanical and thermal shock strength, has poor ionic conductivity, and is unsuitable for a solid electrolyte.

According to the present invention, a zirconia powder for a solid electrolyte which solves the drawbacks of the conventional method, has good moldability, is excellent in low-temperature sinterability, and is excellent in ion conductivity in addition to these. And a method for producing the zirconia powder for a solid electrolyte by a simple process.

[0005]

Means for Solving the Problems The present inventors have studied in detail the molding characteristics, sintering characteristics and ionic conductivity by paying attention to the BET specific surface area and the average particle size of zirconia powder in which yttria is dissolved. Reached the present invention. That is, the present invention has a yttria content of 4 to 10 as a solid solution as a stabilizer.
mol%, and a BET specific surface area of 8 to ²⁰ m ² / g,
And an average particle size of secondary aggregated particles of 1 μm or less,
As a zirconia fine powder for a solid electrolyte and a method for producing the same, a mixture of a hydrated zirconia sol obtained by hydrolysis of an aqueous solution of a zirconium salt and a yttrium compound and having a yttria content of 4 to 10 mol% is 800 to 1.
A gist of the present invention is a method for producing zirconia fine powder for a solid electrolyte, which is calcined at a temperature of 200 ° C. and pulverized until the average particle diameter becomes 1 μm or less.

In the present specification, the “yttria content” related to zirconia fine powder for a solid electrolyte refers to Y ₂ O ₃
/ (ZrO ₂ + Y ₂ O ₃ ) means a value expressed as mol%.

The “average particle size” refers to the diameter of a sphere having the same volume as the secondary aggregated particles whose volume-based distribution is the median (median), and is measured by a particle size distribution measuring device such as a laser diffraction method or a centrifugal sedimentation method. Can be measured. "Average particle size measured by electron microscope" means the size of each secondary particle observed in an electron micrograph as an area, converts it to a circle, and calculates the average particle size. Say.

[0008] "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 theoretical density of the particles and the BET specific surface area, assuming that the shape of the secondary particles is a sphere.

The "average particle size" of the hydrated zirconia sol is measured by a photon correlation method, and shows substantially the same value as that measured by an electron microscope in the same manner as the above zirconia powder.

The zirconia fine powder for a solid electrolyte of the present invention has a yttria content of 4 as a solid solution as a stabilizer.
It must be in the range of 〜１０10 mol%. If the yttria content is less than 4 mol%, the ionic conductivity of the solid electrolyte obtained by molding and sintering the zirconia fine powder deteriorates, while if it exceeds 10 mol%, the ionic conductivity of the obtained solid electrolyte becomes poor. Gets worse,
In addition, the mechanical strength and the thermal shock strength are weakened. The preferred yttria content is 4-8 mol%, more preferably 4-6 mol%.

The above zirconia fine powder needs to have a BET specific surface area of 8 to ²⁰ m ² / g. BET specific surface area of the zirconia powder is sintered hard high temperature sintering of the powder at a low temperature side becomes smaller than 8m ² / g, also becomes larger than 20 m ² / g, and significant powder cohesion between particles Therefore, it becomes difficult and unsuitable as a raw material powder for a solid electrolyte. More desirable B
The ET specific surface area is 10 to 18 m ² / g.

Further, the zirconia fine powder must have an average particle size of the secondary aggregated particles in the range of 0.1 to 1.0 μm. When the average particle size is larger than 1 μm, coarse particles containing many hard agglomerated particles increase, and the hard particles remain in the compact in a shape close to that, thereby causing uneven shrinkage during sintering and sintering. Stomata will remain in the body. Such a low-density sintered body having pores has poor ionic conductivity and is unsuitable as a solid electrolyte. Further, when a binder is added to such a powder and then molded and sintered, cracks due to a decrease in degreasing property become remarkable. On the other hand, when the thickness is less than 0.1 μm, the powder has a remarkable agglomeration force between the particles, so that it is difficult to form the powder and is not suitable as a raw material powder for a solid electrolyte. The preferred average particle size is 0.3-1 μm.

In addition to the above-mentioned BET specific surface area and average particle size, the ratio of the average particle size measured by an electron microscope / the average particle size obtained from the BET specific surface area (hereinafter referred to as the average particle size ratio) is 1 If the conditions of the conditions (1) to (3) are satisfied, a zirconia powder for a solid electrolyte which is more excellent in moldability and low-temperature sinterability, and in addition, has excellent oxygen ion conductivity.
That is, if the average particle size ratio is in the range of 1 to 3, observation of an electron microscope shows that 2 to 10 primary particles are sintered to form one secondary particle. Intermediate solid sintering is hardly observed, and dense particles in which closed pores existing inside the secondary particles are not substantially observed. If the particles are isotropic and dense, this ratio will be 1, but since the particle shape of the zirconia powder is distorted, dense particles will be formed at 1-3. A more desirable average particle size ratio is 1.1 to
1.5.

In order to obtain the zirconia powder for a solid electrolyte of the present invention, a hydrated zirconia sol obtained by hydrolysis of an aqueous solution of a zirconium salt must be used. The hydrated zirconia sol obtained by this reaction is crystalline particles having a uniform particle size, and when the hydrated zirconia sol is calcined and pulverized under the following conditions of the present invention, a zirconia fine powder of a solid electrolyte having good dispersibility is obtained. Can be obtained. For example, a powder obtained by a neutralization coprecipitation method in which a mixed aqueous solution of a zirconium salt and a yttrium salt is neutralized with an alkali and calcined, the amorphous gel hydroxide generated during the neutralization is hard coarse particles during the calcining. Is formed, as described above, resulting in poor oxygen ion conductivity and unsuitable as a solid electrolyte.

When the above-mentioned hydrated zirconia sol is controlled to have an average particle size in the range of 0.05 to 0.09 μm, it becomes a zirconia powder for a solid electrolyte which is more excellent in moldability and low-temperature sinterability. The average particle size of the hydrated zirconia sol can be controlled by adjusting the pH of the reaction solution at the end of the reaction. For example, the pH at the end of the reaction is -0.1 to 0.1.
By adjusting to be 4 or 1 to 1.5,
A hydrated zirconia sol having an average particle size of 0.05 to 0.09 μm is obtained. As a method for controlling the pH, that is, the average particle size of the hydrated zirconia sol, an alkali or an acid is added to an aqueous solution of a zirconium salt; an anion exchange resin removes a part of anions constituting the zirconium salt. In this case, the pH is adjusted to effect hydrolysis. A method of adjusting the pH of a mixed slurry of zirconium hydroxide and an acid to effect hydrolysis is provided. In order to accelerate the reaction rate, a hydrolysis reaction may be performed by adding a hydrated zirconia sol to the above-mentioned aqueous solution of zirconium salt. Examples of the zirconium salt used in the production of the hydrated zirconia sol include zirconium oxychloride, zirconyl nitrate, zirconium chloride, zirconium sulfate, and the like. Alternatively, 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, sodium hydroxide, potassium hydroxide and the like can be mentioned, but in addition to these, compounds which decompose and show basicity like 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.

Next, in the present invention, it is necessary to obtain a mixture of the hydrated zirconia sol obtained above and a yttrium compound having a yttria content of 4 to 10 mol%. The method of mixing and drying the hydrated zirconia sol and the yttrium compound is not particularly limited, and the yttrium compound is added to the hydrated zirconia-containing liquid obtained by the above-mentioned hydrolysis so that the yttria content becomes 4 to 10 mol%. It may be added and dried, or an yttrium compound may be added in advance during the hydrolysis reaction. As a method of drying a mixed solution containing the yttrium compound and the hydrated zirconia sol, for example, the mixed solution is spray-dried as it is, or an organic solvent is added to the mixed solution and spray-dried; Filtration, washing with water and drying. Examples of the yttrium compound used as a raw material of the stabilizer include yttrium hydroxide, yttrium oxide, yttrium chloride, yttrium nitrate, yttrium sulfate, yttrium carbonate, yttrium acetate, and the like.

Next, the mixture comprising the above-mentioned hydrated zirconia sol and the yttrium compound is mixed with a mixture of 800 to 1200.
It must be calcined at a temperature of ° C. Calcination temperature is 800
C., the BET specific surface area of the zirconia powder obtained under the following pulverization conditions is larger than 20 m ² / g, while if it is higher than 1200 ° C., the BET specific surface area after pulverization is more than 8 m ² / g. This is because it becomes smaller. Further, the average particle diameter φ (μ) of the hydrated zirconia sol
m) is in the range of 0.05 to 0.09 μm, the calcination temperature T (° C.) is in the range of 800 to 1200 ° C., and if T ≧ 3000 · φ + 650 is satisfied, the moldability and the sintering property are further improved. It becomes a zirconia powder for solid electrolytes having excellent binding properties.

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 hour, it is difficult to uniformly calcine, and if the holding time is longer than 10 hours, productivity is undesirably reduced. Further, the heating rate is 0.5 ° C./m
If the value is smaller than "in", the time required to reach the set temperature becomes longer.

Next, the calcined powder is pulverized until the average particle size of the secondary aggregated particles becomes 1 μm or less. As a grinding method, either a dry method or a wet method may be selected. Various types of crushing equipment can be selected,
Ball mills, vibration mills, pearl mills and the like can be mentioned. The grinding conditions differ depending on the model, but when a ball mill is used, the slurry concentration is 30 to 50% by weight, the grinding time is 30 to 80 hours.
６０60 wt%, optimal for 10 to 30 hours. If necessary, for example, alumina may be added as a sintering aid at the time of pulverization.

[0020]

As described above, the zirconia powder for a solid electrolyte of the present invention has good moldability, excellent low-temperature sinterability, and excellent oxygen ion conductivity in addition to these. Further, the zirconia powder for a solid electrolyte can be easily produced by the method of the present invention.

[0021]

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

In the examples, the average particle size of the hydrated zirconia sol was determined by a photon correlation method. The average particle size of the secondary aggregated particles of the zirconia powder was determined by a laser diffraction method. The average particle size of the secondary particles of the zirconia powder measured by an electron microscope was determined by performing image analysis on 300 secondary particles using a transmission electron microscope. The theoretical density of the zirconia powder required to calculate the average particle size 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 of the X-ray diffraction pattern and using the following formula.

Theoretical density = monoclinic phase ratio × 5.6 + (square + cubic) phase ratio × 6.1 The zirconia powder was molded by a molding press with a molding pressure of 7%.
The operation was carried out at a pressure of 00 kgf / cm ² ,
Sintering was performed at 0 ° C. for 2 hours.

Example 1 After ₂ liters of a 0.4 mol / l ZrOCl ₂ aqueous solution were boiled for 160 hours, 3.6 liters of a ₂ mol / l ZrOCl ₂ aqueous solution and 4.4 liters of distilled water were added to this solution. Boil for another 45 hours,
A hydrated zirconia sol having an average particle size of 0.054 μm was obtained.

Then, 0.42 mol of YCl ₃ (Y ₂ O ₃ content of 5 mol) was added to the above-mentioned liquid containing hydrated zirconia sol.
%) And spray dried, hydrated zirconia and YCl ₃
Was obtained, and the mixture was calcined at a temperature of 1050 ° C. for 2 hours. After the obtained calcined powder was washed with water, Al ₂ O ₃ was added to (ZrO ₂ + Y ₂ O ₃ ) for 0.2 w.
Then, the mixture was pulverized at a slurry concentration of 35 wt% for 16 hours using a vibration mill.

The obtained zirconia powder has an average particle size of secondary aggregated particles of 0.7 μm by a laser diffraction method.
BET specific surface area is 11 m ² / g, monoclinic phase 3%,
The (square + cubic) phase is 97% and the theoretical density is 6.1. Therefore, according to the electron microscope, the average particle size of the secondary particles is 0.11 μm (that is, the average particle size ratio = 1.
2) It was confirmed that dense secondary particles were formed.

Next, a compact was produced by press molding using the zirconia powder obtained above, and the compact density was 2.77 g / cm ³ . The density of the sintered body obtained by firing this molded body was 6.02 g / cm ³ , and the bending strength was 68 kgf / mm ² . Oxygen ion conductivity was measured using this sintered body.
At a temperature of 0 ° C., the electrical conductivity was 3 × 10 ⁻³ Ω− ¹ · cm ⁻¹ .

EXAMPLE 2 0.7 mol of YCl ₃ was added to the hydrated zirconia sol-containing solution.
Example 1 (Y ₂ O ₃ content: 8 mol%)
The same conditions were used.

The obtained zirconia powder has an average particle size of secondary aggregated particles of 0.6 μm by a laser diffraction method.
BET specific surface area is 12 m ² / g, monoclinic phase 0%,
The (square + cubic) phase is 100% and the theoretical density is 6.1. Therefore, according to the electron microscope, the average particle size of the secondary particles is 0.10 μm (that is, the average particle size ratio = 1.
2) It was confirmed that dense secondary particles were formed.

Next, a compact was produced by press molding using the zirconia powder obtained above, and the compact density was 2.78 g / cm ³ . The density of the sintered body obtained by firing this molded body was 6.04 g / cm ³ , and the bending strength was 33 kgf / mm ² . Oxygen ion conductivity was measured using this sintered body.
At a temperature of 0 ° C., the electrical conductivity was 9 × 10 ⁻³ Ω ⁻¹ · cm ⁻¹ .

Comparative Example 1 1.1 mol of YCl ₃ was added to the hydrated zirconia sol-containing liquid.
(Y ₂ O ₃ content: 12 mol%), and the calcination temperature was 13
The procedure was performed under the same conditions as in Example 1 except that the temperature was set to 00 ° C. The average particle size of the secondary aggregated particles of the obtained zirconia powder by a laser diffraction method is 1.5 μm,
The BET specific surface area was 2 m ² / g. Next, when a compact was produced by press molding using the zirconia powder obtained above, the compact density was 2.58 g / cm.
^3, and the density of the sintered body obtained by firing the molded body is 5.85 g / cm ^3, the electrical conductivity at a temperature of 600 ° C. is ^{2 × 10 -3 Ω -1 · cm} -1 However, the flexural strength was extremely low and was 10 kgf / mm ² or less.

Claims (2)

[Claims] (1) The content of yttria as a solid solution as a stabilizer is 4 to 10 mol%, and the BET specific surface area is 8 to 10 mol%.
A zirconia fine powder for a solid electrolyte, comprising secondary aggregated particles having a particle size of 20 m ² / g and an average particle size in a range of 0.1 to 1.0 μm. 2. A mixture of a hydrated zirconia sol obtained by hydrolysis of an aqueous solution of a zirconium salt and a yttrium compound having a yttria content of 4 to 10 mol% is prepared by mixing 8
Calcined at a temperature of 00 to 1200 ° C and an average particle size of 0.1 to
The method for producing zirconia fine powder for a solid electrolyte according to claim 1, wherein the zirconia is pulverized to a range of 1.0 μm.