JP2001335370A - Slurry of rare earth element hydroxide, manufacturing method therefor and sintered ceramics - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a slurry of rare earth element hydroxide suitable to an additive or sintering assistant for ceramics. SOLUTION: The slurry of rare earth element hydroxides has the primary particles diameter of <=150 nm in a solid particle and has electric conductivity <=2 mS/cm. The aqueous rare earth element hydroxides and basic compounds are mixed with a surface active agent, and the above hydroxide precipitate becomes is filtered, washed with deionized water till the electric conductivity of the filtrate becomes <= 3 mS/cm and is dispersed in deionized water. The slurry of the hydroxides is added to pulverized ceramics, mixed, dispersed, dried, molded and sintered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth hydroxide slurry suitable for use as a sintering aid or additive for ceramics, a method for producing the same, and a ceramic sintered body using the slurry.

[0002]

2. Description of the Related Art Rare earth element compounds used as sintering aids and additives for ceramics are required to be fine powders since sinterability, reactivity and dispersibility are emphasized.
Usually, fine powder of a rare earth element oxide is used for this purpose, and various methods have been conventionally proposed as a method for producing the same. For example, oxalate from rare earth compound solution,
Typical examples thereof include a method in which fine precursor particles such as carbonates and hydroxides are crystallized and calcined, and a method in which coarse oxide particles are finely pulverized by a pulverizer. However, the rare-earth element oxide produced by these methods has a particle diameter of about 1 μm, though it is fine powder, and a rare-earth element compound having a finer particle diameter is desired in view of matching with the increasingly finer ceramic base material. It has come to be.

[0003]

The present invention satisfies such a demand by providing a primary particle size of 150 nm or less,
An object of the present invention is to provide a stable rare earth element hydroxide slurry which is excellent in dispersibility and hardly settles, a method for producing the same, and a ceramic sintered body using the same.

[0004]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have studied the dispersion conditions of the rare earth element hydroxide slurry and completed the present invention. This is a rare earth hydroxide slurry in which the primary particle diameter is 150 nm or less, and the electric conductivity of the slurry in which the primary particle diameter is dispersed is 2 mS / cm or less. The method of producing the rare earth element hydroxide slurry is to mix the aqueous solution of the rare earth element compound and the aqueous solution of the basic compound, or to further mix a surfactant, and to separate the resulting rare earth element hydroxide precipitate by filtration. After washing with deionized water until the electric conductivity of the sample becomes 3 mS / cm or less, the rare earth element hydroxide is dispersed in deionized water. Also, the rare earth hydroxide slurry is added to the ceramic powder, mixed and dispersed,
A ceramic sintered body characterized by being dried, shaped and fired.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The rare earth element referred to here is Y, La, Ce, Pr, N
d, Sm, Eu, Gd, Tb, Dy, Ho, Er, T
m, Yb, and Lu. The first step of the present invention is to mix a rare earth compound aqueous solution and a basic compound aqueous solution, or even a surfactant, to produce a rare earth element hydroxide precipitate. The rare earth element compound may be any water-soluble compound, such as chloride, sulfate,
Nitrate, aliphatic ammonium salt, sulfate ester salt, phosphate ester salt, sulfonate, carboxylate, ethers and the like can be mentioned. The basic compound is not particularly limited, but preferred examples include sodium hydroxide, potassium hydroxide, and ammonium hydroxide.

[0006] The addition of a surfactant is optional, but if it is classified according to ionicity, a cationic surfactant, an anionic surfactant, a nonionic surfactant, and an amphoteric surfactant can be mentioned. The following are mentioned as each surfactant. Cationic surfactants include alkylamine salts such as alkyltrimethylammonium chloride. Examples of the anionic surfactant include sodium alkylbenzenesulfonate, sodium lauryl sulfate, and ammonium lauryl ether sulfate. Examples of the nonionic surfactant include polyoxyalkylene alkyl ethers such as polyoxyethylene alkyl ether, and polyoxyethylene alkyl phenyl ethers such as polyoxyethylene nonyl phenyl ether.

Examples of the amphoteric surfactant include betaine lauryldimethylaminoacetate. Any of cationic, anionic, nonionic and amphoteric surfactants can be used. Among them, cationic surfactants are particularly effective, and Armac C (Lion Akzo Co., Ltd. ) Trade name, alkylamine salt-based cationic surfactant) and the like. The addition amount is preferably 0.01 to 10 g, preferably 0.1 to 10 g, and more preferably 0.5 to 5 g, per mole of the rare earth element. If it is less than 0.01 g, the effect of addition cannot be exhibited, and if it exceeds 10 g, further effects cannot be expected and it is uneconomical.

The method of mixing the aqueous solution of the rare earth element compound and the aqueous solution of the basic compound is basically a method of adding the aqueous solution of the basic compound to the aqueous solution of the rare earth element compound, and a method of adding the aqueous solution of the rare earth element compound to the aqueous solution of the basic compound. There is a method of simultaneously adding a rare earth element compound aqueous solution and a basic compound aqueous solution to water, and further mixing a surfactant, the surfactant is a rare earth element compound aqueous solution, a basic compound aqueous solution, any of water or It is good to add it to all beforehand. The rare earth hydroxides desired in the present invention can be obtained by any of these methods. The concentrations of the aqueous solution of the rare earth element compound and the aqueous solution of the basic compound are adjusted so that the slurry concentration of the generated rare earth element hydroxide is 0.2 mol / liter or less.
When the slurry concentration of the generated rare earth element hydroxide exceeds this, gelation occurs and stirring becomes difficult.

The ratio of the basic compound to the rare earth element compound is 1.0 to 1.5 times the equivalent required for completely converting the rare earth element ions to hydroxide. If the amount of the basic compound is less than this range, the yield of the rare earth element hydroxide decreases, and if it exceeds this range, the yield is not improved, and both are uneconomical. The reaction temperature is not particularly limited, but the reaction is preferably performed at 50 ° C. or lower, more preferably at room temperature or lower. When the temperature is too high, the primary particle size of the generated hydroxide tends to increase. There is. There is no particular limitation on the time required for addition. After completion of the addition, stirring of the slurry may be continued as so-called aging.

[0010] The next step of the present invention is to wash the resulting rare earth hydroxide slurry with deionized water. As a preferred example of the washing method, a method in which a rare earth element hydroxide is separated by filtration using a filter and washed with a large amount of deionized water can be mentioned. At this time,
The electric conductivity of the filtrate is measured, and washing with water is continued until it becomes 3 mS / cm or less. If the electric conductivity exceeds 3 mS / cm, cohesion is strong, and there is a possibility that only those which are difficult to disperse can be obtained. When the electric conductivity becomes 3 mS / cm or less, the washing with water is completed and dried, and the rare earth element hydroxide cake is recovered.

The last step of the present invention is the dispersion of the rare earth hydroxide cake in deionized water. The above-mentioned rare earth element hydroxide cake is put into a stirring tank filled with deionized water, and the rare earth element hydroxide is dispersed by vigorous stirring with a stirrer. If a homogenizer such as a homogenizer is used, a high dispersion state can be obtained in a short time. If the slurry concentration is too high, the viscosity becomes high and it becomes difficult to disperse. If the slurry concentration is too low, the volume is too large to be used. Adjust to less than.

By using the thus obtained rare earth element hydroxide slurry, a uniform mixture can be easily formed, and the mixture is added to ceramic powders such as silicon nitride, aluminum nitride, zirconia, barium titanate and mixed.
By dispersing and molding, it is possible to obtain a ceramic molded body in which the rare earth element is highly dispersed, and the relative density of the ceramic sintered body obtained by sintering it at preferably 600 to 1600 ° C. is very high. , It becomes dense. The ceramic powder referred to herein preferably has an average particle diameter of 1 μm or less in order to make use of the fine-particle and high-dispersion characteristics of the rare earth hydroxide slurry.
The addition amount is 0.1 to 2 with respect to the ceramic powder.
It is advisable to add 0% by weight, more preferably 0.5 to 10% by weight, for molding.

[0013]

EXAMPLES Hereinafter, embodiments of the present invention will be described with reference to examples, but the present invention is not limited thereto. Example 1 A 200-liter reactor was charged with 100 liters of water at a liquid temperature of 19 ° C., and 2.5 liters of a 2.0 mol / l holmium nitrate aqueous solution and a surfactant Amac C (Lion Akzo Co., Ltd.) 5 g of an alkylamine salt-based cationic surfactant (trade name, manufactured by Toshiba Corporation). While stirring with a stirrer, 1.1 liter of 15 mol / l ammonia water was added to this aqueous solution for 1 minute to form a precipitate of holmium hydroxide.

At this time, the electric conductivity of the slurry is 11.9.
mS / cm. The precipitate is filtered off with a centrifuge,
The filtrate was washed with deionized water until the electrical conductivity of the filtrate fell below 3 mS / cm. The electric conductivity of the slurry was measured using a conductivity meter B-173 manufactured by HORIBA. After the water was removed by turning the centrifuge for an additional hour, 3050 g of holmium hydroxide cake (converted to holmium oxide: 931 g)
Was recovered. Next, 6 liters of deionized water was placed in a 10 liter stirring tank, and 3000 g of the recovered holmium hydroxide cake was added thereto. The mixture was stirred for 4 hours with a stirrer to disperse the holmium hydroxide in deionized water. A holmium oxide slurry was obtained. The concentration of this slurry was 10.1% in terms of holmium oxide. The electric conductivity (20 ° C.) of the slurry was 0.62 mS / cm.

The results of observing the primary particle size of holmium hydroxide with a transmission electron microscope (TEM) are shown in FIGS. 1 and 2 are transmission electron micrographs showing the dispersion state and primary particle diameter of holmium hydroxide in the holmium hydroxide slurry dispersed in the above-mentioned deionized water, and FIG. FIG. 2 is a photograph of the same visual field taken at a magnification of 250,000. As shown in FIGS. 1-2,
The primary particle size was at most about 100 nm. In order to evaluate the sedimentation of this slurry, 100 g of the slurry
mm cylindrical glass container, left for 30 days,
The container was turned upside down, the slurry was discarded, the residue in the container was dissolved with nitric acid, and the remaining amount of holmium hydroxide was analyzed.
It was only 0.2% by weight (in terms of holmium oxide) in the slurry used for the test. From this result, it was confirmed that the slurry was extremely stable and hardly settled.

Next, a Si ₃ N ₄ powder (average particle size 0.9 μm)
m): 92 g, the holmium hydroxide slurry: 49.5
g (equivalent to 5 g of holmium oxide) and Al ₂ O ₃ powder (average particle size: 0.9 μm) in a mixing ratio of 3 g, and mixed with water as a mixing medium in a resin ball mill for 24 hours to obtain a slurry. Was dried and passed through a 100-mesh sieve, and the mixed powder was dried using a mold at 29.42 MPa (300 kPa).
g / cm ² ) to obtain a cylindrical body having a diameter of 20 mm and a thickness of about 10 mm. Next, the obtained molded body was wrapped with a rubber sheet, and was subjected to 117.7 MPa
(1200 kgf / cm ² ). The molded body was fired at 1850 ° C. for 8 hours in a nitrogen atmosphere. As a result of measuring the relative density of the sintered body by the Archimedes method,
It was 99.3%, which was extremely dense.

Example 2 A 200-liter reactor was charged with 100 liters of water at a liquid temperature of 20 ° C., and 2.5 liters of a 2.0 mol / l dysprosium nitrate aqueous solution and a surfactant, Armac C (described above). ) 10 g were added.
While stirring with a stirrer, 1.1 liter of 15 mol / l ammonia water was added to this aqueous solution for 1 minute to form a dysprosium hydroxide precipitate. At this time, the electric conductivity of the slurry was 12.8 mS / cm. The precipitate was filtered off with a centrifuge and washed with deionized water until the filtrate had an electrical conductivity of less than 3 mS / cm. After the water was drained by turning the centrifuge for another 1 hour, 3046 g of dysprosium hydroxide cake (calculated as dysprosium oxide: 92%)
0 g) was collected.

Next, 6 liters of deionized water was placed in a 10 liter stirring tank, and 3000 g of the recovered dysprosium hydroxide was added thereto, followed by stirring with a stirrer for 4 hours to disperse dysprosium hydroxide in deionized water. Thus, a dysprosium hydroxide slurry was obtained. The concentration of this slurry was 10.2% in terms of dysprosium oxide. The electric conductivity of the slurry was 1.33 mS / cm. Observation of the primary particle diameter of dysprosium hydroxide with a transmission electron microscope (TEM) revealed that the primary particle diameter was about 100 n at maximum.
m. When the sedimentability of this slurry was evaluated in the same manner as in Example 1, the residue in the container was only 0.1% by weight (in terms of dysprosium oxide).

Example 3 A hydroxide slurry was obtained in the same manner as in Example 1 except that the temperature of the aqueous holmium nitrate solution was set at 40 ° C. The slurry concentration was 10.3% in terms of holmium oxide, the electric conductivity was 1.0 mS / cm, and the maximum diameter of the primary particles was 130 nm. When the sedimentability of the slurry was evaluated in the same manner as in Example 1, the residue in the container was 0.5% by weight (in terms of holmium oxide).

Comparative Example 1 A holmium hydroxide slurry was obtained under exactly the same conditions as in Example 1 except that washing with deionized water was omitted. At this time, the concentration of the slurry was 10.2% in terms of holmium oxide, and the electric conductivity was 3.
It was 2 mS / cm. When the settling property of this slurry was evaluated in the same manner as in Example 1, the residue in the container was 27% by weight.
(In terms of holmium oxide).

Comparative Example 2 Si ₃ N ₄ powder: 92 g, holmium oxide powder (average particle size: 1.1 μm): 5 g, Al ₂
O ₃ powder: blended in a blending ratio of 3 g, mixed in a resin ball mill for 24 hours using water as a mixing medium, dried the obtained slurry, passed through a 100-mesh sieve, and then mixed with a mold. 29.42 MPa (300 kg / cm
² ) Press under the pressure of 20mm, diameter about 20mm, thickness about 10mm
Was obtained. Next, the obtained molded body was wrapped with a rubber sheet, and was subjected to 117.7 MPa (1200
It was pressed at a pressure of kgf / cm ² ). The molded body was fired at 1850 ° C. for 8 hours in a nitrogen atmosphere. As a result of measuring the relative density of the sintered body by the Archimedes method, 97.8%
Met.

[0022]

According to the present invention, the primary particle diameter is 150 n.
When it is less than m, a stable rare earth hydroxide slurry having excellent dispersibility and hardly settling can be obtained, and its industrial value is extremely high.

[Brief description of the drawings]

FIG. 1 is a transmission electron micrograph taken at a magnification of 50,000 times showing the dispersion state and primary particle diameter of a holmium hydroxide slurry obtained in Example 1.

FIG. 2 is a transmission electron micrograph of the same field of view as in FIG. 1 taken at a magnification of 250,000.

Claims (4)

[Claims] The solid particles have a primary particle diameter of 150 nm or less, and a slurry in which the particles are dispersed has an electric conductivity of 2 m.
A rare earth element hydroxide slurry having an S / cm or less. 2. A rare earth element hydroxide precipitate formed by mixing an aqueous solution of a rare earth element compound and an aqueous solution of a basic compound is separated by filtration and washed with deionized water until the filtrate has an electric conductivity of 3 mS / cm or less. Thereafter, dispersing the rare earth element hydroxide in deionized water, a method for producing a rare earth element hydroxide slurry. 3. A rare earth element hydroxide precipitate formed by mixing a rare earth element compound aqueous solution, a surfactant and a basic compound aqueous solution is separated by filtration, and deionized until the filtrate has an electric conductivity of 3 mS / cm or less. A method for producing a rare earth hydroxide slurry, comprising washing the rare earth hydroxide with water and then dispersing the rare earth hydroxide in deionized water. 4. A rare earth element hydroxide slurry in which the primary particle diameter of solid particles is 150 nm or less and the electric conductivity of a slurry in which the solid particles are dispersed is 2 mS / cm or less is added to the ceramic powder. A ceramic sintered body characterized by being dispersed, dried, molded and fired.