JP3012925B2 - Method for producing easily sinterable yttrium aluminum garnet powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an easily sinterable yttrium aluminum garnet powder by a pseudo alkoxide method. More specifically, the invention of this application is a translucent sintered body or a transparent sintered body such as a Na arc tube, a laser host material, and an optical material for oscillation or light emission such as a scintillator,
The present invention relates to a method for producing an easily sinterable yttrium aluminum garnet powder which is also useful as a high-grade ceramic raw material powder such as a corrosion-resistant material.

[0002]

2. Description of the Related Art Yttrium aluminum garnet is expected to be applied as an optical material for oscillation or light emission such as a laser host material or a scintillator, and a single crystal material has been mainly used. In recent years, attention has been paid to polycrystalline yttrium aluminum garnet manufactured by a ceramic manufacturing method that can be made more inexpensive. As described above, this yttrium aluminum garnet has to be manufactured as a highly transparent sintered body in which pores have been completely removed because the main use is an optical material. There is a need to develop raw material powders that are excellent in sinterability and uniformity.

[0003] As a method for producing yttrium aluminum garnet polycrystal, conventionally, ammonia was added to an acidic solution containing yttrium ion and aluminum ion to coprecipitate yttrium hydroxide and aluminum hydroxide, followed by drying and calcining. There is known a method of manufacturing by molding and sintering later. However, according to the above-mentioned conventional method, when the coprecipitated precipitate is washed to remove impurity ions mixed in from the mother liquor, the precipitate becomes jelly-like, and filtration becomes difficult.At the same time, when the filtered precipitate is calcined, fine primary particles are strongly solidified. To form large agglomerated particles.

Therefore, a method of improving the conventional uniform precipitation method in which sulfate ions are present in the mother liquor and neutralized with ammonia generated by thermal decomposition of urea (JP-A-2-92817).
Bulletin) was developed. The precipitate obtained by this method is bulky granular, has excellent filterability, and contains little impurity ions from the mother liquor. Therefore, the growth of aggregated particles during calcination is suppressed, and the sinterability is improved. I have.

[0005] In addition, a solid phase method has been developed in which a yttrium aluminum garnet transparent sintered body is produced by preparing a yttrium oxide powder and an aluminum oxide powder, mixing and then performing sintering and a solid phase reaction at the same time to produce a sintered body of yttrium aluminum garnet.

[0006]

However, the method for producing yttrium aluminum garnet powder by the above-mentioned improved uniform precipitation method requires a large amount of urea, and urea is thermally decomposed gradually, so that precipitation occurs. It takes a long time, and the shape of the powder precipitated as granules remains after calcination, and although not as large as in the case of jelly-like precipitation, there are disadvantages such as the generation of large agglomerated particles. It was not enough.

In the solid phase method of mixing and sintering oxide powders, it is necessary to prepare yttrium oxide or aluminum oxide powder having excellent reactivity and sinterability in advance by an alkoxide method or the like. However, in order to obtain yttrium aluminum garnet having no variation in composition, it is necessary to perform firing at a high temperature for a long time.

In general, when aluminum hydroxide is calcined, many fine aluminum oxide crystallites are formed.
It forms giant aggregated particles that are tightly bound together with their crystal axes aligned. Aggregates in which crystallites have the same crystallographic axis are resembled to shaped particles, which are groups of crystallites that retain the outer shape of the mother salt as a result of being thermally decomposed by the crystal structure of the mother salt. However, the primary particles of aluminum hydroxide precipitated from the aqueous solution are extremely fine and smaller than the aluminum oxide crystallites obtained after calcination. It is not possible. In this case, in the process of drying and calcining the aluminum hydroxide, the primary particles of the aluminum hydroxide or the crystallites of the aluminum oxide are rearranged to resemble the skeleton particles, and the directions of the crystal axes are aligned. It should be considered that it has grown into agglomerated particles. In any case, the ultimate density by sintering is governed by the size of the agglomerated particles, so aluminum hydroxide is considered to be one of the representative mother salts that become hardly sinterable powders (ceramics, vo
l.11, No.12, pp.1101-1108). Similarly, when the precipitate obtained by co-precipitating yttrium hydroxide and aluminum hydroxide is calcined, aggregated particles of yttrium aluminum garnet similar to such shaped particles grow.

[0009] For this reason, it has heretofore hardly been considered to produce an easily sinterable yttrium aluminum garnet powder from the precipitation of a hydroxide. The invention of this application has been made in view of the circumstances described above, and solves the drawbacks of the conventional method for producing yttrium aluminum garnet powder, and yttrium produced by a much simpler chemical method than the alkoxide method. It is an object of the present invention to provide a method for producing an easily sinterable yttrium aluminum garnet powder capable of producing an yttrium aluminum garnet powder having excellent sinterability from the precipitation of aluminum hydroxide with aluminum.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is directed to an invention according to claim 1, wherein an acidic solution containing yttrium ions and yttrium aluminum garnet at a ratio of yttrium aluminum garnet which forms aluminum ions is used. Is added to the mixture, a precipitate of yttrium hydroxide and aluminum hydroxide is formed while maintaining the pH at 6.5 to 10, most of the mother liquor is separated and removed, and the remaining precipitate or this precipitate is further subjected to one or more times. After washing with water and removing most of the washing solution, the remaining precipitate is dispersed in an organic solvent at least 0.1 times the volume of the precipitate without drying,
Next, the present invention provides a method for producing yttrium aluminum garnet powder which is easy to sinter and is calcined at 500 to 1400 ° C. after drying.

The invention according to claim 2 of the present application is
In the invention according to claim 1, when dispersing the precipitate of yttrium hydroxide and aluminum hydroxide in an organic solvent, first disperse in an organic solvent that dissolves water, and after separating and removing most of the liquid, the water is removed. Disclosed is a method for producing an easily sinterable yttrium aluminum garnet powder that is dispersed in an organic solvent that hardly dissolves and then dried.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for producing yttrium aluminum garnet powder having easy sinterability according to the present invention will be described in more detail. According to the invention of this application, it is possible to produce yttrium aluminum garnet powder having high sinterability and high purity from the precipitation of yttrium and aluminum hydroxide produced by a much simpler chemical method than the conventional alkoxide method. It becomes possible. <A> Formation of Precipitate The acidic solution containing yttrium ion and aluminum ion used in the method for producing yttrium aluminum garnet powder which is easy to sinter in the present invention is an acidic aqueous solution containing aluminum ion, for example, aluminum sulfate,
An aqueous acid solution obtained by dissolving a water-soluble aluminum compound such as ammonium alum, aluminum chloride, or aluminum nitrate in water, or dissolving aluminum in sulfuric acid, hydrochloric acid, nitric acid, or the like at an appropriate concentration is added to yttrium sulfate, yttrium chloride. , And yttrium nitrate. An acidic solution containing yttrium ions and aluminum ions can be obtained by dissolving yttrium and aluminum in sulfuric acid, hydrochloric acid, nitric acid, or the like at an appropriate concentration. The concentration may be a concentration having a saturated solution concentration as an upper limit, and is preferably about 0.05 to 0.5 mol per liter of water in terms of Y ₃ Al ₅ O ₁₂ .

The aqueous solution exhibiting basicity used in the invention of the present application is not particularly limited as long as the pH of the aqueous solution containing yttrium ion and aluminum ion can be controlled in the range of 6.5 to 10. The limitation of pH 6.5 to 10 is based on the fact that yttrium hydroxide precipitates at pH 6 and above and aluminum hydroxide dissolves at pH 12 and above. this
Both hydroxides are virtually completely precipitated as long as they are in the pH range.
Aqueous solutions expressing basicity include ammonia, urea,
Aqueous solutions such as ammonium carbonate and ammonium hydrogen carbonate are exemplified. The concentration of these aqueous solutions may be any concentration up to the saturated solution concentration, and is preferably about 0.05 to 3 mol per liter of water.

Ammonium carbonate and ammonium bicarbonate are preferred for generating a uniform precipitate because they generate carbon dioxide when added to an acidic solution and have the ability to stir the reaction solution. Compounds that gradually decompose in the reaction solution to exhibit basicity, such as urea, are particularly preferable because they produce stable bulky granular precipitates. On the other hand, this type of compound has drawbacks such as a long reaction time and a high cost of the reagent. It is suitable for manufacturing special materials with added value such as ultra-high purity materials, which want to avoid grinding after calcination as much as possible.

The co-precipitation of yttrium hydroxide and aluminum hydroxide is based on the fact that when the concentration of nitrate ions or chloride ions in the solution produced is high, the primary particles coarsely aggregate,
Filtration is relatively easy. However, except for the precipitate containing sulfate ions, the flocculation is easily dissolved by washing with water, and the precipitate becomes a jelly-like precipitate. When the jelly-like precipitate is dried, a strong lump is formed. Even if the jelly-like precipitate is pulverized in an alumina mortar or the like and calcined, dense and strong agglomerated particles grow and become difficult to be sintered. However, even if it becomes a jelly-like precipitate, the lump of powder dried after being dispersed in an organic solvent is brittle and can be easily pulverized in an alumina mortar or the like. Therefore, in the invention of this application, the precipitate of yttrium hydroxide and aluminum hydroxide is dispersed in an organic solvent to improve sinterability.

However, since the agglomerated yttrium aluminum garnet powder tends to contain strong agglomerated particles, it is necessary to pulverize the powder with a pulverizer such as a ball mill in order to completely destroy the agglomeration. In addition, the dried product of the precipitate of yttrium hydroxide and aluminum hydroxide filtered and separated from an aqueous solution containing a large amount of nitrate ions and hydrochloric acid ions,
It is not as strong as a dried product obtained from a jelly-like precipitate by washing with water. However, in this case, the sinterability of the finally obtained powder is reduced by the organic solvent treatment due to impurities such as nitrate ions and chlorine ions remaining after drying even after the organic solvent treatment. Deterioration is slightly worse than when

On the other hand, the precipitation of yttrium hydroxide and aluminum hydroxide formed from the aqueous solution containing sulfate ions forms bulky aggregates. This aggregate is relatively stable, does not change to a jelly state even after being washed with water two or three times, and has relatively good filterability. Agglomerates of the precipitate formed at temperatures above 50 ° C. are particularly stable. When such a bulky and stable aggregate is dispersed in an organic solvent, the water in the aggregate is easily replaced with the organic solvent, and even if dried after filtration, the dispersion is evaporated without filtration and dried. Even so, the dry powder can be easily crushed into fine particles. This effect of sulphate is realized as long as sulphate is present in the solution, whether sulphate is added before the precipitate forms or to the suspension after the precipitate forms. Alternatively, even if nitrate ions or chloride ions are present, the same effect can be realized.

Further, in the case of sulfate ions, the effect of promoting the growth of aggregated particles in the calcination stage can be neglected as compared with nitrate ions and chloride ions. In this sense, it can be said that the raw material is preferably a sulfate or an ammonium sulfate. As described above, sulfate ions are effective in the invention of this application, but the effect has a critical point on the low concentration side. That is, when the sulfate ion is present at 0.05 times or more of the total amount of the yttrium ion and the aluminum ion, a bulky granular precipitate is formed, and the stability of the granular particles increases as the sulfate ion concentration increases. However, when the sulfate ion becomes 1.2 times or more, large aggregated particles are generated during calcination due to the effect of the sulfate ion incorporated in the coprecipitation of yttrium hydroxide and aluminum hydroxide, and a dense sintered body is produced. Can not be done. For this reason, practical sulfate ions are in a concentration ratio of 0.05 to 1.2 with respect to the total amount of yttrium ions and aluminum ions. Preferably, it is in the range of 0.2 to 1.1.

In the invention of the present application, the precipitates of yttrium hydroxide and aluminum hydroxide formed are separated from the dispersion. At this time, most of the mother liquor is separated and removed, and the remaining mother liquor remains. The precipitate is washed one or more times with water to remove most of the washing solution. As a method for separating the precipitate from the dispersion, a decantation method or a filtration method is appropriately employed. <B> Dispersion in Organic Solvent When the precipitate formed and separated as described above is dried, primary particles of the precipitate are rearranged to form strong aggregated particles,
Even when dispersed in an organic solvent, it is difficult to completely eliminate the aggregated structure. Therefore, in the invention of this application, the precipitate is dispersed in an organic solvent without drying. Prior to dispersion, the precipitate is preferably washed with water as described above. This is because nitrate and chlorine ions in the precipitate promote the growth of aggregated particles during calcination, and at the same time, calcination of the precipitate generates harmful gases such as nitric acid gas, chlorine gas, and sulfurous acid gas. is there. The washing method is
The washing method may be a commonly used method, and the washing water may have a purity that is expected in general washing. Usually, ion exchange water or distilled water is used.

The organic solvent replaces the water in the precipitate remaining after removing most of the water, thereby weakening the bonding force between the particles and preventing the formation of strong agglomerated particles that occur when dried. . Examples of such an organic solvent include hydrophilic or polar organic solvents such as ethyl alcohol, methyl alcohol, propyl alcohol, butyl alcohol, hexanol, octanol, isoamyl acetate, and polyethylene glycol. The type is not particularly limited as long as the above purpose of use is satisfied. Further, the organic solvent may be used alone or in combination of two or more.

An organic solvent capable of dissolving water in an organic solvent, for example, an alcohol having 3 or less carbon atoms can easily disperse the precipitate and take in water during the precipitation. Most of the water is removed by filtering again after the dispersion, and the particle surface can be covered with an organic solvent. However, the effect is not so great,
When selecting an organic solvent capable of dissolving water, it is preferred to produce bulky aggregate precipitates with the aid of sulfate ions.

The drying is performed after removing the organic solvent containing water. Alternatively, the drying may be performed by evaporating the organic solvent together with the moisture while keeping the precipitate dispersed. On the other hand, with an organic solvent that does not dissolve water, it is substantially difficult to disperse a precipitate containing water. Therefore, when selecting an organic solvent that does not dissolve water, the organic solvent including the precipitate is heated while being stirred and mixed to evaporate the organic solvent and, at the same time, evaporate the water covering the particle surface to evaporate the water on the particle surface. Replace the molecule with the organic solvent molecule. Boiling the organic solvent is preferred because water molecules on the surface of the primary particles of the precipitate quickly replace the organic solvent molecules. Evaporation of the organic solvent may be performed until the organic solvent is dried, or the organic solvent may sufficiently cover the surface of the precipitated particles. In that case, the organic solvent may be removed by filtration.

Such an effect of dispersion in an organic solvent is recognized when the amount of the organic solvent is 0.1 times or more the volume of the precipitate. The effect increases as the amount increases, but when the amount exceeds 20 times, no particularly remarkable improvement in the effect is observed.
In the invention of this application, the precipitate is first dispersed in an organic solvent that dissolves water, most of the liquid is separated and removed, and then dispersed in an organic solvent that hardly dissolves water. This is preferable because the amount of the organic solvent to be removed and evaporated can be greatly reduced, and the operation time is shortened. <C> Calcination The coprecipitated yttrium hydroxide and aluminum hydroxide are fine, so that the reaction proceeds rapidly even at a relatively low temperature of 500 ° C., and yttrium aluminum garnet stable to the melting point is formed. Therefore, the calcination temperature is 50
The range of 0 to 1400 ° C is suitable, and preferably 700 to 13 ° C.
50 ° C.

The present invention will be described in more detail with reference to the following examples, which illustrate a method for producing yttrium aluminum garnet powder of the present invention.

[0025]

【Example】

Example 1, Comparative Example 1 After dissolving 22 g of yttrium nitrate and 45.3 g of ammonium alum in 1000 ml of distilled water, the pH was adjusted to 8 by adding aqueous ammonia. And
While maintaining the pH at 8, this solution was kept at 90 ° C. for 2 hours. After the formed precipitate was filtered, the precipitate was washed twice with distilled water and filtered again. The resulting precipitate was divided into two equal parts, one of which (Example 1) was immediately dispersed in 200 ml of isobutyl alcohol, and the dispersion was gently boiled in a stream of nitrogen gas.
The water and organic solvent were evaporated and dried. The other half of the precipitate (Comparative Example 1) was air-dried in a stream of nitrogen gas. After drying,
Lightly pulverize both powders with an alumina mortar and alumina pestle, 1100
It was calcined at ℃.

The calcined powder thus obtained is crushed with an alumina mortar and an alumina pestle for about 3 minutes, molded using a mold at a pressure of 30 MPa, further subjected to isostatic pressing at 200 MPa, and then heated to 1500 ° C. in an air atmosphere. For 2 hours. When the sintered density of the obtained sintered body was examined, it was 95% of the theoretical density with the organic solvent treatment (Example 1) and 65% with the untreated one (Comparative Example 1).

The yttrium aluminum garnet treated with an organic solvent and untreated was formed into tablets each having a diameter of about 5 mm and a length of about 6 mm, and the tablets were heated at a rate of 10 ° C./min to 1570 ° C. to reduce the shrinkage due to sintering. Examined. FIG. 1 shows the result. As is clear from FIG. 1, the yttrium aluminum garnet treated with the organic solvent (Example 1) has much better shrinkage characteristics than those without the organic solvent treatment (Comparative Example 1). (Comparative Example 2) According to the method described in JP-A-2-92817, 7 g of yttrium nitrate, 14.4 g of ammonium alum, and 50 g of urea were dissolved in 1000 ml of distilled water, and the temperature was raised to 95 ° C. For 5 hours. Then, 2 liters of water was added to stop the decomposition of urea and filtered. The resulting precipitate was washed three times with water and air-dried in a stream of nitrogen gas. The same treatment as in Example 1 was performed on the dried powder under the same conditions.

When the sintered density of the obtained sintered body was examined, the sintered density of yttrium aluminum garnet was 70% of the theoretical density. The yttrium aluminum garnet was examined for shrinkage due to sintering in the same manner as in Example 1, and the results are shown in FIG. Example 2 After dissolving 11.02 g of yttrium nitrate and 18.8 g of aluminum nitrate in 500 ml of distilled water, the pH was adjusted to 8 by adding aqueous ammonia, and the resulting precipitate was filtered after keeping at this pH for 2 hours. Dispersed in isobutyl alcohol. Next, the dispersion was gently boiled in a stream of nitrogen gas, and the water and the organic solvent were evaporated to dryness. The same treatment as in Example 1 was performed on the dried powder under the same conditions.

When the sintered density of the obtained sintered body was examined, the sintered density of yttrium aluminum garnet was 85% of the theoretical density. Further, for this yttrium aluminum garnet, the shrinkage due to sintering was examined in the same manner as in Example 1, and the results are shown in FIG. Of course, the invention of this application is not limited by the above embodiments.

[0030]

As described in detail above, the invention of this application makes it possible to produce easily sinterable yttrium aluminum garnet powder without various problems. Further, the organic solvent burns during the calcination and is completely removed from the powder, and the obtained yttrium aluminum garnet powder has high purity. Therefore, the easily sinterable yttrium aluminum garnet powder produced by the invention of this application is used as a raw material powder for producing high-quality ceramics such as transparent sintered bodies such as Na arc tubes and laser host materials and corrosion-resistant materials. It will be extremely useful.

[Brief description of the drawings]

FIG. 1 is a correlation diagram showing, together with a comparative example, a change in shrinkage ratio due to sintering of yttrium aluminum garnet produced by the method for producing yttrium aluminum garnet powder having easy sinterability according to the present invention.

Claims (2)

(57) [Claims] An aqueous solution exhibiting basicity is added to an acidic solution containing yttrium aluminum garnet at a ratio of yttrium aluminum garnet that produces yttrium ions and aluminum ions.
Is maintained at 6.5 to 10, a precipitate of yttrium hydroxide and aluminum hydroxide is formed, most of the mother liquor is separated and removed, and the remaining precipitate or this precipitate is washed one or more times with water, and most of the washing solution is washed. The precipitate remaining after separation and removal is dispersed in an organic solvent in an amount of at least 0.1 times the volume of the precipitate without drying, and then dried to 500 to 1400.
A method for producing an easily sinterable yttrium aluminum garnet powder, wherein the powder is calcined at a temperature of ° C. 2. When dispersing a precipitate of yttrium hydroxide and aluminum hydroxide in an organic solvent, first disperse the precipitate in an organic solvent that dissolves water, and after separating and removing most of the liquid,
The method for producing an easily sinterable yttrium aluminum garnet powder according to claim 1, wherein the powder is dispersed in an organic solvent that hardly dissolves water and then dried.