JPH11189412A - Yttrium hydroxide agglomerate and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce yttrium oxide particles comprising individually separated particles and having a narrow particle size distribution. SOLUTION: The yttrium hydroxide agglomerates are obtained by adding a basic agent to a solution containing a yttrium salt in a concentration of 0.02-2 mole/liter at a temperature of <30 deg.C, comprise agglomerates wherein many <=20 nm-thick flaky particles are agglomerated in states that table surfaces and edge surfaces are joined to each other in card-house structures, are stable, even after the agglomerates are subjected to treatments such as a washing treatment in the agglomerate state and subsequently dried, and have diameters of >=0.5 μm. The yttrium hydroxide agglomerates are calcined to produce yttrium oxide powder which can easily be sintered, when the primary particles have an average particle diameter of 30-500 nm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to yttrium hydroxide, a method for producing the same, and a method for producing fine yttrium oxide powder produced from the yttrium hydroxide. More specifically, the present invention can produce yttrium oxide fine powder in which raw material powder for a transparent sintered body, primary particles suitable for a catalyst or a catalyst carrier, etc. are present in a state of being individually separated, and have a narrow particle size distribution. The present invention relates to yttrium hydroxide aggregated particles and a method for wet-producing the same. In particular, using the easily sinterable yttrium oxide powder obtained by the present invention,
A transparent sintered body that can be used for various arc tubes, laser materials, high-temperature windows, and the like can be manufactured.

[0002]

2. Description of the Related Art Yttrium oxide is currently mainly used as a stabilizer for zirconium oxide or as a densification accelerator for silicon nitride, silicon carbide, aluminum nitride and the like. However, yttrium oxide has a high melting point, and is a material containing yttrium oxide as a main component, which is suitable for a corrosion-resistant and heat-resistant material, a laser host material, a high-pressure Na luminous tube, etc., taking advantage of its advantages such as being transparent and having excellent corrosion resistance. The development of is expected. The main methods for producing high-purity yttrium oxide include oxalate pyrolysis, carbonate pyrolysis, and hydroxide pyrolysis.
The yttrium oxide powder obtained by these methods is used, for example, as a raw material for sintering.

[0003]

Each of these methods has advantages and disadvantages. At present, this method is widely used because, firstly, yttrium ion quantitatively reacts with oxalate ion in an aqueous solution to precipitate yttrium oxalate, which is a precipitation-forming agent. Secondly, it is possible to completely recover yttrium without excessive use of acid. Secondly, since the precipitated yttrium oxalate is fine particles having a good crystallinity and a size suitable for filtration, the washing operation is easy. It is because it is suitable for the production of purity samples. However, when the mother salt of yttrium oxalate is calcined, innumerable primary particles tend to be aggregated to form shaped particles having the outer shape of the mother salt, and the sinterability is generally poor.

[0004] The method of the above also has the disadvantage that if a large amount of a precipitation-producing agent is used in order to increase the yield of yttrium, the sinterability of the yttrium oxide powder obtained by calcining is poor, as in the case of the method. is there. In order to produce an easily sinterable powder by the method described above, the amount of a precipitation-forming agent such as ammonium carbonate or ammonium bicarbonate is limited, and about 1/3
Yttrium ion remains in the filtrate, resulting in a poor yield. The yttrium carbonate immediately after formation is amorphous and changes to crystalline granular particles upon aging.
The reason that the easily sinterable powder was produced by the method described in the above was that this change was properly used to successfully produce a precipitate with less agglomeration. However, since the particle morphology of yttrium carbonate changes greatly during ripening, it is difficult to produce a precipitate having the desired morphology with good reproducibility. In particular, there is a disadvantage that it is necessary to find out appropriate manufacturing conditions with much effort and time every time the production scale is changed. Furthermore, since the precipitated particles of yttrium carbonate from which yttrium oxide which is easy to sinter are obtained are fine, there is also a disadvantage that the filterability is poor.

According to the method described above, it is reported that a sintered body having a theoretical density of 99.4% can be produced by appropriately forming a yttrium hydroxide precipitate (Ceramics International, vo1.9, p59 (1983)). However, the precipitate of yttrium hydroxide formed by the conventional method has a jelly-like shape, and when washing of the precipitate is repeated, the filterability is deteriorated, and the washing becomes rapidly difficult. Also, it was necessary to find a special drying method to obtain a fragile dried body.

[0006] In addition to the above method, in order to produce yttrium oxide powder which is easy to sinter, it is necessary to strictly control the conditions for forming the precipitate. If improperly controlled, the dried precipitate becomes a hard lump and has poor sinterability. A method for producing ultrafine yttrium oxide powder using an organic solvent has been developed for the purpose of loosening hard lump of yttrium hydroxide (Japanese Patent Application Laid-Open No. 58-223619). This organic solvent dispersion method is also effective for yttrium carbonate (Japanese Patent Application No. 3-100541, Japanese Patent Application Laid-Open No. 4-310516). By the organic solvent dispersion method, a powder dispersed in individual primary particles can be synthesized without strictly controlling production conditions. However, in the case of the precipitation of yttrium hydroxide, depending on the state of the precipitation, the lump of the powder after evaporating the organic solvent may be considerably hard even when the dispersion treatment is performed with the organic solvent.

The present inventors have found that sulfate ions stabilize the bulky floc structure of the precipitate, and suppress the formation of dense and hard agglomerated particles due to the rearrangement of particles that occur when moisture escapes during drying. Was found. A method for producing a powder having extremely weak agglomeration utilizing this effect and the effect of an organic solvent in a synergistic manner has been developed (Japanese Patent Application No. Hei.
No. 4203). Organic solvents have an effective function of suppressing the aggregation of particles, but have many drawbacks such as the need to handle them with care because they are many compounds that are not environmentally friendly and are flammable. Yttrium carbonate is less remarkable in the rearrangement of particles during washing and drying than yttrium hydroxide, and hardly generates hard aggregated particles without the organic solvent dispersion treatment. However, when it is necessary to completely remove pores by sintering as in the case of a transparent sintered body, relatively brittle aggregation is not preferable.

The present inventors have found that the use of the effect of sulfate ions to stabilize the bulky floc structure of yttrium carbonate precipitates can further improve the cleaning effect, and can prevent aggregation by completely removing nitrate ions. discovered. Utilizing this effect, the transparency of the yttrium oxide sintered body derived from yttrium carbonate is further improved (Japanese Patent Application No. 9-2).
02117). However, the effect of sulfate ions is not so large, and in order to stably produce a transparent sintered body, the disadvantage already pointed out as a problem of the production method, that is, at a pH of 4 to 5 at the expense of yield. After a precipitate had formed, further aging was required.

[0009]

Means for Solving the Problems In view of the problems of the prior art as described above, the present inventor has conducted intensive studies, and as a result, it has been found that flake-like particles are bonded to each other while the table surface and end surface of the particles are joined to each other. When particles aggregated in a “card house” structure (FIG. 1 shows a scanning electron microscope (SEM) photograph of the particles; these aggregated particles are hereinafter referred to as card house-like aggregated particles), washing is easy. It has been found that an easily sinterable yttrium oxide powder can be produced in good yield, and that a sintered body having excellent transparency can be produced by using a powder calcined by adding sulfate ions to the yttrium hydroxide. The term “card house” is, for example, a term indicating the state of aggregation of clay particles, and a bulky aggregate formed when the positive end surface and the negative layer surface are combined is called a card house structure. Yes (Masano Maehiro, The Science of Clay, 55-
56 pages, Nikkan Kogyo Shimbun). Further, it is also used as a term indicating a structure in which hexagonal plate-like hydrates of ceramics sintered bodies as seen in a scanning electron micrograph are assembled in the shape of a rose ("Ceramics", July, 1976, Published by The Ceramic Society of Japan). In the present invention, the term “card house” is used in the same meaning.

That is, the production method of the present invention can be carried out at a temperature lower than 30 ° C. at a rate of not less than 0.02 mol / l and not more than 2 mol / l.
A base agent is added to a solution containing a yttrium salt having a concentration of not more than 1 liter, and a large number of flaky particles having a thickness of not more than 20 nm have a diameter of 0. This is a method for producing yttrium hydroxide, which is an aggregated particle of 5 μm or more. The present invention also relates to the agglomerated particles obtained by the above-described method and yttrium oxide powder obtained by calcining yttrium hydroxide as the agglomerated particles. The yttrium hydroxide aggregate of the present invention remains in the form of bulky flocs generated by a precipitation reaction on the dried yttrium hydroxide powder.
Calcination conditions hydroxide yttrium, may be a condition of a normal method, a compound containing sulfate ions corresponding to 10 ^-3 times the amount of yttrium ions to 1 times the sulfate ions to the aqueous yttrium oxide The agglomerated particles are calcined at 900 ° C. or higher, and abnormal grain growth that proceeds during calcination is suppressed by sulfate ions, and the particles are individually separated and the average particle size of the primary particles having a narrow particle size distribution. By forming the yttrium oxide powder having a diameter in the range of 30 nm to 500 nm, an easily sinterable powder can be formed. Using this fine yttrium oxide powder, at least 1500 ° C.
When calcined at a temperature of 000 ° C. or less, a sintered body having a bulk density almost equal to the theoretical density and excellent in transparency can be obtained.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS <A> Yttrium salt as raw material Examples of the yttrium salt used in the present invention include yttrium nitrate, yttrium chloride, yttrium bromide, yttrium iodide, yttrium acetate, yttrium perchlorate and the like. There is no particular limitation as long as it is an yttrium compound soluble in a liquid such as water or an organic solvent, and these may be used alone or as a mixture of a plurality of salts. In the present invention, the concentration of the yttrium salt is preferably from 0.02 mol / L to 2 mol / L, particularly preferably from 0.05 mol / L to 1 mol / L. Even if the concentration of the yttrium salt is 0.02 mol / l or less, or conversely, 2 mol / l or more,
The precipitate becomes jelly-like, and a cardhouse-like bulky precipitate cannot be generated, so that the precipitate is dried to form a relatively hard lump, and even if sufficiently pulverized using a means such as an alumina mortar, the aggregated particles remain after calcination. It is not preferable because it remains.

<B> Basic Agent As a basic agent for forming a hydroxide precipitate used in the present invention, an inorganic base agent such as ammonia, caustic soda, or caustic potash, diethylamine, ethylamine, triethylamine, butylamine, or An organic base agent such as tetramethylguanidine is exemplified, but there is no particular limitation as long as it is a chemical substance which reacts with an yttrium salt to produce a precipitate of yttrium hydroxide. However, when inorganic caustic soda or caustic potash is used, soda or potash etc., which lowers the high-temperature strength and corrosion resistance of the yttrium oxide sintered body, remain in the precipitate, so it is necessary to sufficiently wash the yttrium hydroxide after generating yttrium hydroxide. . On the other hand, since an organic base agent is expensive, the cost of the product increases, which is not preferable. The concentration of these basic agents may be any concentration up to a saturated solution, but may be 0.05 to 3 per liter of solvent.
Molar amounts are preferred. When reacting the above base agent with metal ions, a solution in which those base agents are dissolved may be added to a solution containing yttrium ions, or may be added directly to a solution containing yttrium ions without dissolving in a solvent. .

In the present invention, when producing a precipitate of yttrium hydroxide by an aqueous solution reaction, it is preferable to add a basic agent to the solution containing the yttrium salt. Conversely, if an yttrium salt is added to the basic agent, it becomes a jelly-like precipitate, and a card house-like precipitate, which is a feature of the present invention, cannot be formed. When using an organic solvent as a solvent, even if a solution of a yttrium salt is added to a solution of a base agent,
Or even if it is added in reverse, the precipitate does not become jelly-like,
Good results are obtained.

If the amount of the basic agent used in the present invention is small,
The amount that precipitates as yttrium hydroxide is small. In this case, there is no particular problem in the transparency of the finally obtained yttrium oxide sintered body, but it is not preferable in that the yield is low. On the other hand, even if a large amount of the basic agent is used, the yield does not become 100% or more. Therefore, it is not necessary to add a large amount of the basic agent as the pH exceeds 10 or more after precipitation.

[0015] <C> Composition metal ion and the hydroxyl group of yttrium hydroxide (OH ^-) to produce an yttrium hydroxide having a composition of only extremely difficult, also part of the anions such as hydroxyl groups at the same time as yttrium salt It is captured. For example, when ammonia water is added to an yttrium chloride aqueous solution, Cl coexists like YCl (OH) ₂ .
However, the nature of the precipitation is close to that of hydroxides of other metals. The yttrium hydroxide in the present invention is a compound containing a hydroxyl group generated by adding a basic agent to a solution of an yttrium salt, and another chemical species may coexist with the yttrium ion and the hydroxyl group.

<D> Formation temperature of precipitate and particle morphology of precipitate In the present invention, the reaction between the yttrium salt and the basic agent is carried out at 30 ° C.
It must be performed at the following temperatures: The melting point of the solution is preferably 25 ° C. or lower, particularly preferably 5 ° C. to 20 ° C.
Even if the temperature is close to the freezing point of the liquid, card house-like aggregated particles can be obtained, but there is a disadvantage that temperature control becomes difficult. On the other hand, when the precipitation reaction is carried out at 30 ° C. or higher, plate-like particles having a larger thickness than the flaky particles (FIG. 3,
Dispersed in an organic solvent and dried to obtain yttrium hydroxide (see SEM photograph). The bonding between the table surface and the end surface of the plate-like particles is weak. When the precipitate of the plate-like particles is washed with water, the rearrangement of the particles proceeds, and when the particles are dried, hard aggregated particles are formed. The flaky yttrium hydroxide particles in the present invention have a thickness of 20%.
It is a petal-shaped thin section of nm or less. The table surface of the flake refers to two opposite surfaces having a particularly large area among the particle surfaces. The end face refers to a particle face other than the table face, and has a width of 20 nm or less.

In the present invention, "the flaky particles are agglomerated in a state in which the table surface and the end surface of the particles are bonded to each other in a card house shape" means that the table surface and the end surface of the flaky particles are predominantly joined. This refers to the aggregation of a plurality of flaky particles in which the frequency of bonding between table surfaces can be substantially ignored. The card house-like structure of the aggregated particles does not substantially collapse even after repeated washing. For this reason, even if washing is repeated, the aggregated state immediately before filtration is not so much collapsed, so that a large gap is formed between the aggregated particles and filtration is quick. In addition, since the card house-like aggregated particles are bulky and have relatively large gaps in the particles, impurity ions such as nitrate ions and ammonium ions existing in the gaps can be easily moved, and the filtration speed is high. There is a feature that the cleaning effect is large. If the production of yttrium hydroxide is inadequate, the particle size may be reduced to 0.5 μm or less, even for particles aggregated in a card house-like structure. In this case, at the same time as the filterability is poor, the powder of yttrium oxide obtained after the calcination becomes an aggregate of hard aggregated particles and the sinterability is poor, so that it is not preferable as a sintering raw material.

When the yttrium hydroxide agglomerated in a card house shape is thermally decomposed, fine yttrium oxide particles appear two-dimensionally in flaky yttrium hydroxide particles. When the calcination temperature is increased, fine particles of yttrium oxide grow. FIG. 2 shows an SEM image of yttrium oxide powder obtained by calcining yttrium hydroxide prepared by the method of the present invention at 1100 ° C. for 3 hours. From the figure, it can be seen that relatively small dice-like particles and large granular particles are mixed. The crystal structure of yttrium oxide is Na
Since it is cubic like Cl and MgO, the surface energy is the smallest in the (100) plane. Particle surface is (001)
If only planes are present, the particles will be dice-like. The shape of the dice particles in FIG. 2 is appropriate from the viewpoint of surface energy. Also, the relatively large granular particles in the figure are considered to be generated from a group in which a large number of dice-like particles are in surface-to-surface contact.

The agglomerated state of the yttrium hydroxide particles produced by the conventional method changes from the floc state before the washing to a densely laminated state due to the rearrangement of the particles by washing. This rearrangement narrows the spacing between the particles and sharply increases the time required for filtration. At the same time, when the sample after filtration is dried, dense and hard aggregated particles are formed. When this yttrium hydroxide is calcined, dense and strong aggregated particles of yttrium oxide having poor sinterability are obtained, while the size of the aggregated particles is substantially maintained. On the other hand, since the card-house-shaped particles have large voids inside, the agglomerated particles of yttrium hydroxide collapse by calcination. There are also many yttrium oxide particles that form aggregated particles during calcination, but the size of the aggregated particles is much smaller than the size of the aggregated particles of yttrium hydroxide. As a result, calcining the card house-like yttrium hydroxide of the present invention results in a larger fresh bulk density of the obtained yttrium oxide powder and better sinterability than the conventional wet method.

<E> Kind of Solvent By pyrolyzing and calcining the card house-like yttrium hydroxide, a powder having relatively uniform particle size and excellent sinterability can be obtained. Even if yttrium hydroxide produced by a method other than aqueous solution reaction has a card house shape,
Good results are obtained. For example, even if an organic solvent or a mixed solution of an organic solvent and an aqueous solution is used in place of the aqueous solution, a preferable bulky yttrium hydroxide characterized by the present invention can be produced. However, since organic solvents are more expensive than water, they are not practical except for special purposes such as producing ultra-high purity yttrium hydroxide.

<F> Effect of sulfate ion The compounds containing sulfate ion in the present invention include not only sulfuric acid and yttrium sulfate (Y ₂ (SO ₄ ) ₃ ) but also ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) and sulfuric acid. Ammonium hydrogen (NH ₄ HSO ₄ ), ammonium sulfite ((N
H ₄ ) ₂ SO ₃ ) or ammonium bisulfite (NH ₄
Ammonium salts containing sulfate ions or sulfite ions such as HSO ₃ ), sodium sulfate (Na ₂ SO ₄ ), sodium hydrogen sulfate (NaHSO ₄ ), sodium sulfite (Na ₂ S)
O ₃ ), sodium bisulfite (NaHSO ₃ ), potassium sulfate (K ₂ SO ₄ ), potassium hydrogen sulfate (KHS
O _4), potassium sulfite (K ₂ SO _3), or potassium bisulfite (KHSO ₃₎ is a compound exemplified by alkali metal salts of sulfate ion and sulfite ion, and the like. Among these compounds, alkali metals reduce the high-temperature strength and corrosion resistance of the yttrium oxide sintered body even in a trace amount. Therefore, when an alkali metal salt is added, it is necessary to sufficiently clean the yttrium oxide sintered body. When adding sulfuric acid or yttrium sulfate,
When these compounds have been added, it is necessary to sufficiently add a basic agent to the solution in advance so that the pH becomes 5 or more.

In the case of plate-like precipitation of yttrium hydroxide (JP-A-9-194203) or granular yttrium carbonate (Japanese Patent Application No. 9-202117), sulfate ions stabilize the floc structure of the precipitate. To prevent rearrangement of precipitated particles during washing. On the other hand, the card house-like structure of the yttrium hydroxide particles, regardless of the presence or absence of sulfate ions, even after repeated washing with water,
It hardly changes even when dried. For this reason, it is not necessary to add sulfate ions to the yttrium hydroxide in order to prevent rearrangement of particles that occur during washing. The relatively small particles of yttrium oxide without sulfate ions are hexahedral (see FIG. 2). On the other hand, when sulfate ions are added, as shown in FIG. 4, the number of faces is larger than that of the hexahedron, and the corners of the particles are more rounded, resulting in a polyhedron relatively close to a sphere. At the same time, relatively unusually large particles as shown in FIG. 2 are hardly recognized.

A sphere can be formed when the surface is isotropic such as liquid or glass. This means that the appearance of the above-mentioned polyhedral particles has reduced the anisotropy of the surface of yttrium oxide by the sulfate ions, so that crystal planes other than the (100) plane can also appear. The sulfate ion in the present invention is added for the purpose of changing the anisotropic property of the surface of yttrium oxide to a more isotropic property and for suppressing the appearance of abnormally large particles.

In general, for dense sintering, the particle distribution is narrowed and the particles are uniformly filled, and the properties of the particle surface are isotropic (J. Am. Ceram. Soc., Vol. 67, vol. p.174-78
(1984)). That is, when the card house-shaped yttrium hydroxide to which sulfate ions are added is calcined, an easily sinterable yttrium oxide powder as taught by the sintering theory can be obtained.

When the yttrium hydroxide is plate-like particles, the effect of adding sulfate ions is small. On the other hand, in the case of yttrium oxalate or yttrium oxide, the addition effect is hardly recognized. In the case of yttrium carbonate, the effect of sulfate ions is not recognized on the amorphous particles formed immediately after the formation of the precipitate and on the yttrium carbonate generated at a high pH in order to increase the yield. That is, in order to produce the yttrium oxide transparent sintered body by exerting the effect of the sulfate ion, it was necessary to strictly control the shape of the mother salt.

The sulfuric acid compound is added to yttrium at a concentration of 0.1%.
It is preferable to add an amount corresponding to 001 to 1 times the amount of sulfate ion, but an amount of 0.002 to 0.5 times is particularly preferable. If the amount of sulfate ion is 1 time or more, the yttrium hydroxide precipitate after drying becomes a hard lump, and the yttrium oxide obtained by calcination becomes dense and strong aggregated particles, and the sinterability is reduced. descend. On the other hand, if it is 0.001 or less, the effect of adding sulfate ions is small. Although the characteristics of the present invention are exhibited even when the compound containing sulfate ions is added to the solution in which the yttrium salt is dissolved in advance, it is more preferable to add the compound after the precipitation of yttrium hydroxide. Further, even if the precipitate is washed with washing water in which a compound containing a sulfate ion is dissolved, a favorable result can be obtained because the sulfate ion is strongly adsorbed to the precipitate and remains in the precipitate.

<G> Calcination In the present invention, from the viewpoint of producing an easily sinterable powder,
It is necessary to produce yttrium oxide powder having an average primary particle size of 30 nm or more and 500 nm or less. In order to satisfy this condition, yttrium hydroxide needs to be calcined at 900 ° C. or more, and the range of 1050 ° C. to 1250 ° C. is particularly preferable. If the calcining temperature is low, it is necessary to calcine for a long time to produce a powder having an average particle size of 30 nm or more. For example, when the calcination temperature is 900 ° C., it is necessary to perform calcination for at least 4 hours. On the other hand, 1400 ° C
When the temperature is high as described above, it is necessary to limit the calcination time to one hour or less.

If the average particle size is less than 30 nm, the friction between the particles becomes extremely large, and the filling property of the powder becomes uneven. Therefore, large voids remain between the particles that cannot be removed by ordinary sintering, and the sintering density decreases. On the other hand, when the average particle size is 500 nm or more, the specific surface area of the powder is very small and the driving force for sintering is also small, so that the sinterability is reduced and a transparent sintered body cannot be obtained.

On the other hand, when a powder having a large specific surface area such as a catalyst is generally desired, the calcining temperature is preferably lower. However, unless calcined at a high temperature, the desired catalytic activity may not be exhibited. For this reason, when using the yttrium hydroxide agglomerated in a card house shape of the present invention as a starting material for the catalyst, it is necessary to calcine at a temperature suitable for the purpose of use.

[0030]

EXAMPLES Examples of the present invention and comparative examples are shown below, but the present invention is not limited to these examples. Example 1-1 After dissolving 20 g of yttrium nitrate in 200 ml of distilled water, the mixture was kept at 10 ° C with a cooler and stirred with a magnetic stirrer. While stirring the solution, 150 ml of 2N aqueous ammonia cooled to about 10 ° C. was added dropwise over 30 minutes, and the solution was maintained for 3 hours. After filtration and washing, it was dried at room temperature. FIG. 1 shows an SEM image of the dried powder lightly loosened in an alumina mortar. Agglomerated particles of yttrium hydroxide are mainly joined at the table surface and the end surface, and the frequency of joining between the table surface and the table surface can be ignored. The table surface and the end surface were joined in a card house shape, but the aggregation did not collapse even in the washing treatment or the drying treatment. For this reason, the time required for filtration and drying is one-third to one-third that of the jelly-like precipitate generated by the conventional manufacturing method.
5 and the workability is very good.

Example 1-2 2 g of the powder obtained by loosening the agglomerated powder obtained in Example 1-1 without adding a compound containing a sulfate ion was put into an alumina boat, and was placed in an oxygen stream at 1100 ° C. in a tubular electric furnace. And calcined for 4 hours. The calcined powder was subjected to SEM observation, and as a result, as shown in FIG. 2, the powder was a mixture of relatively small dice-like particles and very large particles. This calcined powder is lightly loosened in an alumina mortar, and then 3
After primary molding at 0 MPa, it was subjected to isostatic pressing at 200 MPa to produce a molded body. The molded body is placed in a vacuum electric furnace, and a high vacuum of 10 ^-5 Torr or more is applied.
The temperature was raised at a rate of 10 ° C./min until the temperature was maintained for one hour. After that, the sample was cooled at a rate of 15 ° C./min. The sintered body was milky white. When the density of the sintered body was measured by the Archimedes method using water, it was 99% of the theoretical density. This powder is not suitable as a raw material for producing a transparent sintered body, but can be used as a catalyst.

Comparative Example 1 A comparative example in which the temperature of the solution containing yttrium is set to a temperature exceeding 30 ° C. A yttrium hydroxide precipitate was formed under the same conditions as in Example 1-1 except that aqueous ammonia at room temperature was dropped into the aqueous solution of yttrium nitrate kept at 35 ° C. The precipitate was washed. The time required for this cleaning was about five times that of Example 1. The washed precipitate is
Divided equally. Half of it was dried as it was. The other half was dispersed in isobutyl alcohol and heated to 110 ° C. to completely evaporate the alcohol. The former dried body was hard and the latter was fragile. These two types of dried bodies were each loosened and calcined by the method of Example 1-2. This calcined powder was molded and sintered. The densities of the obtained sintered bodies were 84% and 95% of the theoretical density, respectively, and the sintered density was smaller than that of Example 1-2.

Example 2 0.36 g of ammonium sulfate is dissolved in 150 ml of pure water and kept at about 10 ° C. After the precipitation of yttrium hydroxide by the method of Example 1-1, the above-mentioned aqueous solution of ammonium sulfate is added dropwise over 20 minutes while maintaining the temperature at 10 ° C. After stirring with a magnetic stirrer for 3 hours, the mixture was filtered, washed and dried. The dried body was loosened and calcined by the method of Example 1-2. This calcined powder was molded and sintered. As a result, the bulk density of the obtained sintered body was almost close to the theoretical density, and the linear transmittance of the sintered body having a thickness of 1 mm with respect to light having a wavelength of 500 nm was about 40%.

Comparative Example 2 A yttrium oxide sintered body was produced by the method of Example 2 except that the production of yttrium hydroxide and the maintenance of the precipitation were performed at 35 ° C. The bulk density of the obtained sintered body was 99.5 of the theoretical density.
%, The transparency was much worse than that of the sintered body obtained in Example 2.

Example 3 Yttrium hydroxide to which sulfate ions were added was produced and calcined according to Example 2 except that 16 g of yttrium chloride was used instead of yttrium nitrate. This calcined powder was molded and sintered. The bulk density of the obtained sintered body was almost close to the theoretical density, and the linear transmittance of the sintered body having a thickness of 1 mm with respect to light having a wavelength of 500 nm was about 45%.

Comparative Example 3 A comparative example in which the calcining temperature is lower than 900 ° C. is shown. Except for calcination at 800 ° C. for 4 hours, the bulk density of the sintered body manufactured under the conditions of Example 3 was 9% of the theoretical density.
At 9.3%, it was milky white and had no transparency.

Comparative Example 4 A comparative example in which yttrium oxalate was calcined instead of yttrium hydroxide is shown. 2 dissolved in 400 ml
0 g of dihydrated oxalic acid was dissolved in 400 ml of distilled water while stirring with a magnetic stirrer at room temperature.
Was added dropwise over 30 minutes. The liquid in which the precipitate of yttrium oxalate was dispersed was divided into two equal parts. Further, 0.36 g of ammonium sulfate dissolved in 150 ml of pure water was added dropwise over 20 minutes. Both the precipitate with and without ammonium sulfate were stirred for 3 hours, and then stirred according to Example 1-2 and Example 3.
Filtered, washed and calcined. This calcined powder was molded and fired. The bulk density of the obtained sintered body was 85% irrespective of whether or not sulfate ions were added.

Example 4-1 A solution prepared by dissolving 20 ml of 25% aqueous ammonia in 150 ml of ethyl alcohol and a solution prepared by dissolving 0.36 g of ammonium sulfate in 20 ml of pure water and then dissolving it in 100 ml of ethyl alcohol were prepared. , Each kept at about 10 ° C. 20 g of yttrium nitrate in 15
After dissolving in 0 ml of ethyl alcohol,
The mixture was stirred with a magnetic stirrer while maintaining the temperature at 0 ° C. While stirring this solution, the above-mentioned aqueous ammonia solution was added for 30 minutes.
A drop was formed over a minute to produce a precipitate. Only 5 minutes after the completion of the dropping of the aqueous ammonia, the already prepared solution of ammonium sulfate in ethyl alcohol was dropped over 20 minutes, and then kept for 3 hours. After filtration, washing with ethyl alcohol and drying at room temperature, an aggregate of yttrium hydroxide was obtained.

Example 4-2 The dried aggregate was lightly loosened in an alumina mortar. The subsequent calcination, molding, sintering, and the like of the powder were performed according to the procedure of Example 1-2. The bulk density of the sintered body was measured by the Archimedes method using water.
The linear transmittance of the sintered body having a thickness of 1 mm with respect to light of m was about 40%.

Example 5 The yttrium oxide compact produced by the method of Example 2 was calcined in an oxygen stream at 1600 ° C. for 4 hours. The bulk density of the obtained sintered body is almost equal to the theoretical density and the wavelength is 500 n.
The linear transmittance of a sintered body having a thickness of 1 mm for light of m
It was about 35%.

Example 6 An experiment was conducted in the same manner as in Example 2 except that an aqueous solution of ammonium sulfite containing the same mole number of sulfate ions as the sulfate ion was used instead of the aqueous solution of ammonium sulfate. Almost the same results as in Example 2 were obtained.

[0042]

According to the present invention, the fine yttrium oxide powder obtained by calcining the yttrium hydroxide agglomerate produced by the method of the present invention, in which the yield is substantially 100% and the particles are individually separated, is obtained. Can be manufactured. By using this powder, the bulk density of the sintered body obtained by firing was almost close to the theoretical density, and it became possible to produce a sintered body excellent in transparency. Also, it exhibits excellent properties for other uses of the fine yttrium oxide powder.

[Brief description of the drawings]

FIG. 1 is a scanning electron micrograph (magnification: 2) showing the fine structure of the aggregated particles of yttrium hydroxide produced by the method of the present invention.
10,000 times).

FIG. 2 is a scanning electron micrograph (magnification: 80,000) showing the fine structure of the yttrium oxide powder obtained by calcining the yttrium hydroxide shown in FIG.

FIG. 3 is a scanning electron micrograph (magnification: 80,000) showing the fine structure of the yttrium hydroxide aggregated particles of the comparative example.

FIG. 4 is a scanning electron micrograph (magnification: 60,000 times) showing the fine structure of yttrium oxide powder calcined by adding nitrate ions to yttrium hydroxide produced by the method of the present invention.

Claims (4)

[Claims] 1. A large number of flaky particles having a thickness of 20 nm or less formed by adding a basic agent to a solution containing an yttrium salt aggregate with a table surface and an end surface joined to each other in a card house shape. Even if the coagulation state is subjected to washing or other treatments, the diameter that can exist stably until the precipitate is dried is 0.5 μm.
Yttrium hydroxide characterized by being the above aggregated particles. 2. At a temperature lower than 30 ° C., 0.02 mol /
A base agent is added to a solution containing a yttrium salt at a concentration of 1 mol or more and 2 mol / l or less, and a large number of flaky particles having a thickness of 20 nm or less aggregate in a state where the table surface and the end surface are joined to each other in a card house shape. And producing aggregated particles having a diameter of 0.5 μm or more. 3. An yttrium oxide powder formed by calcining the yttrium hydroxide according to claim 1. 4. The primary particles have an average particle size of 30 nm or more and 50 or more.
The yttrium oxide powder according to claim 3, wherein the yttrium oxide powder is in a range of 0 nm or less and is easily sinterable.