JPH09110420A - Method for producing easily sinterable aluminum oxide powder and yttrium aluminum garnet powder - Google Patents

Abstract

(57) Abstract: To obtain powder which is not only highly pure but also easily sinterable. SOLUTION: For the precipitation of aluminum hydroxide or yttrium-aluminum hydroxide produced by a chemical method much simpler than that of the alkoxide method, the growth of agglomerated particles with uniform crystal axes that progress during calcination is performed. For the purpose of prevention, an organic solvent covering the surface of the primary particles of precipitation is made to act, and then calcination is performed.

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 easily sinterable aluminum oxide powder and yttrium aluminum garnet powder by a pseudo alkoxide method. More specifically, the present invention relates to a Na arc tube,
Easily sinterable aluminum oxide powder and yttrium aluminum garnet powder, useful as raw material powders for laser host materials, transparent sintered bodies such as optical materials for oscillation or light emission such as scintillators, and high-grade ceramics such as corrosion resistant materials. The present invention relates to a manufacturing method of.

[0002]

2. Description of the Related Art Conventionally, a method of calcination of ammonium alum has been known as a method of producing easily sinterable aluminum oxide powder. Furthermore, a method of calcination of aluminum hydroxide obtained by hydrolyzing a compound of aluminum with an organic substance such as alcohol, and a method of calcination of ammonium dawsonite in which the sulfate ion of alum is replaced with a carbonate ion have been developed. There is.

However, in the conventional ammonium alum method, which is not only harmful to the environment, but also produces a large amount of chemically active sulfurous acid gas during calcination, a large-scale desulfurization apparatus is installed and such a method is required. I needed a calcination furnace that could withstand various gas atmospheres. Further, since ammonium alum has a large amount of crystal water as much as 24 mol with respect to 1 mol of aluminum oxide, a large amount of water desorbed in the calcination process dissolves ammonium alum to form a viscous liquid. By further dehydration, bubbles are generated in the liquid and the viscosity of the liquid is further increased,
It becomes difficult to separate the bubbles from the liquid. The liquid eventually changes to a solid containing almost no water, but a large amount of air bubbles remain in the solid, and the apparent volume of the powder obtained by calcination becomes extremely large. A calciner was needed.

In the method of hydrolyzing a compound of aluminum and an organic substance, it is necessary to previously synthesize a compound of aluminum and an organic substance. Aluminum easily reacts with commonly used inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid, and the inorganic compound of aluminum can be generated relatively easily, but it is special to generate the organic compound of aluminum. Since the equipment is required, the manufacturing cost is correspondingly high.

Furthermore, in the production of the easily sinterable powder by the ammonium dawsonite method, there are many factors in the production process that affect the properties of the particles produced. For example, the concentration, reaction temperature, dropping rate, stirring rate, etc. of the reaction solution, such as the reaction solution, until the ammonium dawsonite precipitate is synthesized can be obtained. Affect. Therefore, it is necessary to strictly control those factors, and it is difficult to stably obtain easily sinterable powder.

On the other hand, 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, a polycrystalline yttrium aluminum garnet material using a ceramics manufacturing method which can be produced at a lower cost has been attracting attention. Since the main use of the material is an optical material, it is essential to manufacture a highly transparent sintered body in which pores are completely removed. Therefore, it is necessary to develop a raw material powder having excellent reactivity, easy sinterability, and uniformity.

Conventionally, as a method for producing a yttrium aluminum garnet polycrystal as described above, first, ammonia is added to an acidic solution containing yttrium ions and aluminum ions to coprecipitate yttrium hydroxide and aluminum hydroxide. A method is known in which the material is dried, then calcined, calcined, molded and then sintered.

However, in such a conventional method, in order to remove the impurity ions mixed in from the mother liquor, the coprecipitated precipitate is washed to form a jelly, which makes it difficult to filter. At the same time, if the filtered sample is calcined, it becomes fine. However, there is a drawback that large primary particles are firmly bonded to form large aggregated particles. Therefore, a method improved on the conventional homogeneous precipitation method in which sulfate ions are present in the mother liquor and neutralized with ammonia generated by thermal decomposition of urea (Japanese Patent Publication No. 2-9).
2817) was developed. In the case of precipitation by this method, the particles are bulky, have excellent filterability, and contain little impurity ions from the mother liquor, so that the growth of agglomerated particles during calcination is suppressed and the sinterability is improved. In addition, a solid phase method has also been developed in which yttrium oxide powder and aluminum oxide powder are prepared in advance, and then mixed and simultaneously subjected to sintering and solid phase reaction to produce a yttrium aluminum garnet transparent sintered body.

However, in the above-described improved method for producing yttrium aluminum garnet by the uniform precipitation method, a large amount of urea is required and urea is gradually pyrolyzed, so that it takes a long time to form the precipitate. In addition, since the shape of the powder precipitated as granules remains after calcination, it is not as strong as the agglomerated particles produced by drying the jelly-like precipitate, but there are drawbacks such as the formation of large agglomerated particles. The improvement of sinterability was insufficient. On the other hand, in the solid-phase method in which oxide powders are mixed and sintered, it is necessary to prepare yttrium oxide and aluminum oxide powders having excellent reactivity and sinterability in advance by a method such as an alkoxide method, and thus cost reduction. There are drawbacks such as high temperature and long-term firing at high temperature for obtaining yttrium aluminum garnet without composition fluctuation.

In general, when aluminum hydroxide is calcined, a large number of fine aluminum oxide crystallites form giant agglomerated particles in which crystal axes are aligned and firmly bonded to each other. The aggregate in which the crystal axes of the crystallites are aligned resembles a skeleton particle, which is a group of crystallites that retains the outer shape of the mother salt as a result of thermal decomposition dominated by the crystal structure of the mother salt. However, since the primary particles of aluminum hydroxide precipitated from the aqueous solution are extremely fine and smaller than the crystallites of aluminum oxide obtained after calcination, it is impossible to explain the structure of this aggregated particle by the conventional model of generation of skeletal particles. Can not. That is, in the process of drying and calcination of aluminum hydroxide, the primary particles of aluminum hydroxide or the crystallites of aluminum oxide are rearranged to resemble skeletal particles and aggregated particles whose crystal axes are aligned. It is thought to have grown to. According to the conventional knowledge, since the density achieved by sintering is governed by the size of the agglomerated particles, aluminum hydroxide was considered to be one of the representative mother salts that become hardly sinterable powder (ceramics, Vol. 11, No. 12, p
p. 1101-1108). Similar to the case of aluminum oxide, when the precipitate obtained by coprecipitating yttrium hydroxide and aluminum hydroxide is calcined, agglomerated particles of yttrium aluminum garnet similar to skeletal particles grow.

From such conventional knowledge, it has hardly been considered to produce easily sinterable aluminum oxide powder or yttrium aluminum garnet powder from hydroxide precipitation. The present invention has been made in view of the above circumstances, and is excellent in burning even from the precipitation of aluminum hydroxide or yttrium-aluminum hydroxide produced by a chemical method much simpler than the alkoxide method. An object of the present invention is to provide a method for producing a powder having a binding property.

[0012]

In order to solve the above problems, the present invention adds an aqueous solution expressing basicity to an acidic aqueous solution containing aluminum ions to precipitate aluminum hydroxide and to remove most of the mother liquor. It is separated and removed, and the remaining precipitate is washed with water once or several times to remove most of the washing solution, and the remaining precipitate is not dried and the amount is 0.1 times the volume of the precipitate or more. In an organic solvent, dried, and then 1000 to 1400 ° C
A method for producing an easily sinterable aluminum oxide powder (claim 1), characterized by calcining at.

Further, according to the present invention, an aqueous solution expressing basicity is added to an acidic solution containing yttrium ions and aluminum ions in a proportion of yttrium aluminum garnet to be produced, and a precipitate is produced while maintaining pH at 6.5 to 10. Then, most of the mother liquor was separated and removed, and the remaining precipitate, or this precipitate was washed once or more times with water, and most of the washing liquid was separated and removed, and the remaining precipitate was reduced to the volume of the precipitate without drying. Also provided is a method for producing yttrium aluminum garnet powder (claim 2), which comprises dispersing in 0.1-fold amount or more of an organic solvent, drying, and then calcining at 500 to 1400 ° C.

In addition, according to the present invention, in any of the above methods, when the precipitate is dispersed in an organic solvent, it is first dispersed in an organic solvent capable of dissolving water, and most of the liquid is removed. One of the preferred methods is to disperse water in an organic solvent that does not dissolve it and then dry it (claim 3).

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, high purity is obtained from the precipitation of aluminum hydroxide or yttrium-aluminum hydroxide produced by the above-mentioned method by a chemical method much simpler than the conventional alkoxide method. It is possible to produce aluminum oxide powder and yttrium aluminum garnet powder which are easily sintered. <A> Generation of Precipitate a) Production of Aluminum Oxide Powder The acidic aqueous solution containing aluminum used in the method for producing the easily sinterable aluminum oxide powder of the present invention is aluminum sulfate, ammonium alum, aluminum chloride,
It can be obtained by dissolving a water-soluble aluminum compound such as aluminum nitrate in water or by dissolving aluminum in sulfuric acid, hydrochloric acid, nitric acid or the like having an appropriate concentration. The concentration is
The concentration may be any concentration up to the saturated solution concentration, but is preferably 0.05 to 1 liter of water in terms of Al ₂ O _3.
It is about 0.5 molar concentration.

Since aluminum is amphoteric, aluminum hydroxide precipitates in the pH range of 4-12. Therefore, the type of the compound expressing basicity used in the present invention is not particularly limited as long as it is a compound capable of realizing this pH range when added to an acidic solution containing aluminum ions. When the pH is in the range of 5 to 10, substantially all the aluminum ions in the aqueous solution are precipitated, so compounds that can realize this range are particularly preferable. Examples of preferable compounds include ammonia, urea, ammonium carbonate, ammonium hydrogen carbonate and the like.
The concentration of these compounds may be any concentration up to the saturated solution concentration, but is preferably 0.05 / liter of water.
It is about 3 mol.

Regarding the acidic aqueous solution containing aluminum, when the concentration of nitrate ion or chlorine ion is high, such as an aqueous solution of aluminum nitrate or aluminum chloride or an aqueous solution of aluminum dissolved in nitric acid or hydrochloric acid,
The precipitated primary particles are coarsely aggregated and relatively easy to filter. However, except for the precipitation containing sulfate ions, the coagulation is easily released by washing with water to form a jelly-like precipitate. When such a precipitate is dried, it becomes a strong lump, and even if it is crushed and calcined in an alumina mortar or the like, dense and strong agglomerated particles grow and it becomes difficult to sinter. However, even in the case of a jelly-like precipitate, a lump of powder that has been dried after being dispersed in an organic solvent becomes fragile and can be easily crushed in an alumina mortar or the like. Therefore, the sinterability can be significantly improved by dispersing it in an organic solvent. However, in any case, the degree of pulverization is insufficient, and strong agglomerated particles tend to be mixed in the aluminum oxide powder after calcination. Therefore, in order to completely destroy the agglomeration of the calcined powder, it is necessary to grind it with a grinder such as a ball mill.

The dried product of the precipitate obtained by filtering from a liquid containing a large amount of nitrate ions and chlorine ions is not as strong as the dried product obtained from the jelly-like precipitate obtained by washing with water. However, due to nitrate ion and chloride ion impurities remaining after drying even after the organic solvent treatment, the sinterability of the finally obtained powder was sufficiently washed with washing water to form a jelly-like precipitate. Is slightly worse than when treated with an organic solvent.
On the other hand, the bulky aggregate of the precipitate formed from the solution containing the sulfate ion is relatively stable, does not change into the jelly form even after washing with washing water for 2 to 3 times, and has relatively good filterability. Is. In particular, aggregates of the precipitate formed at a temperature of 50 ° C or higher are stable. Moreover, the aggregates are bulky, and when dispersed in an organic solvent, the water in the aggregate is easily replaced with the organic solvent. Even if the organic solvent is filtered to remove most of the water and then dried, or if the filtering is omitted and the dispersion liquid is evaporated to dryness, the dry powder can be easily crushed into fine particles. These effects of sulfate ions
The same applies whether the sulfate ion is added before the formation of the precipitate, the suspension after the formation of the precipitate, or the presence of nitrate ion or chloride ion. Further, compared with nitrate ions and chloride ions, the effect of promoting the growth of aggregated particles at the calcination stage of sulfate ions can be ignored.

B) Production of Yttrium Aluminum Garnet Powder Further, in the method for producing yttrium aluminum garnet powder of the present invention, the acidic solution containing yttrium and aluminum is a compound defined with respect to the acidic aqueous solution containing aluminum in the above case. At the same time, it can be obtained by dissolving yttrium sulfate, yttrium chloride, yttrium nitrate, or the like, or by dissolving yttrium and aluminum with sulfuric acid, hydrochloric acid, nitric acid, or the like having an appropriate concentration. The concentration may be such that the concentration of the saturated solution is the upper limit, but it is preferably 0. _{3 with} respect to 1 liter of water in terms of Y ₃ Al ₅ O ₁₂ .
It is about 05 to 0.5 mol. 6.5 in this method
The pH limit of -10 is p of yttrium hydroxide of 6 or more.
Precipitation with H, on the other hand, since aluminum hydroxide dissolves at a pH of 12 or above, it is defined as a condition that both ions in an aqueous solution are substantially completely precipitated.

The compound expressing basicity is 6.5 to 12 in an aqueous solution containing yttrium ion and aluminum ion.
There is no particular limitation as long as the pH can be adjusted. Due to the relatively similar chemistries of aluminum and yttrium, virtually all compounds exhibiting basicity that can be used in the above-described method of making alumina powders can be used as well. Ammonium hydrogen carbonate and ammonium carbonate are preferable for forming a uniform precipitate because they have the ability to generate carbon dioxide gas and stir the reaction solution when added to an acidic solution. In addition, a compound such as urea that gradually decomposes in the reaction solution and exhibits basicity is particularly preferable because it forms a stable and bulky granular precipitate. However,
There are also drawbacks such as a long reaction time and expensive reagents. Therefore, this compound can be expected as a raw material for producing a special material having an increased added value such as an ultra-high purity material which is desired to avoid crushing after calcination. The behavior of coprecipitation of yttrium hydroxide and aluminum hydroxide is the same as in the case of only aluminum hydroxide, and the bulky agglomerated particles generated by the presence of nitrate ions and chloride ions change into jelly upon washing. Further, in the presence of sulfate ion, a bulky precipitate which is stable to washing can be obtained.

As described above, when sulfate ions are present in the aqueous solution, precipitation of aluminum hydroxide or yttrium hydroxide in bulky granular particles can be generated. Therefore, it is preferable to use sulfate or ammonium sulfate as a raw material. However, there is no guarantee that the by-product generated in industrial production is a compound containing sulfate ion or an aqueous solution.

C) Addition of sulfate ion As described above, the effect of sulfate ion is clear in the present invention, but it has a critical point on the low concentration side. In the aqueous solution containing only aluminum ions, bulky granular precipitates are produced when aluminum ions are present, and in the aqueous solution in which yttrium ions and aluminum ions coexist, when 0.05 times or more of the total amount of these ions are present. . The stability of the granular particles increases as the concentration of sulfate ions increases. However, when the number of sulfate ions is four times or more, a particularly remarkable improvement in the effect cannot be recognized. In the case of the above-described method for producing alumina powder, the sinterability of aluminum oxide obtained by calcining aluminum hydroxide is good regardless of the amount of sulfate ions.

As a matter of course, as the number of sulfate ions increases, the amount of the basic agent that neutralizes the sulfate ions also increases, which is not preferable. The practical sulfate ion concentration is 0.0 with respect to the aluminum ion concentration in the production method of alumina powder.
It is in the range of 5 to 4.0 times. On the other hand, in the case of the yttrium aluminum garnet powder manufacturing method,
When the sulfate ion becomes 1.2 times or more of the total amount of yttrium ion and aluminum ion, large agglomerated particles appear due to calcination due to the effect of the sulfate ion taken into the coprecipitation of yttrium hydroxide and aluminum hydroxide. Therefore, a dense sintered body cannot be obtained. Therefore, the concentration ratio of the sulfate ion to the total of the yttrium ion and the aluminum ion is preferably 0.05 to 1.2, more preferably 0.2 to 1.1.

In any of the methods for producing the alumina powder or the yttrium aluminum garnet powder of the present invention, a decantation method or a filtration method is appropriately adopted as a method for separating the precipitate dispersed in the mother liquor or the washing solution from the dispersion. It <B> Dispersion in organic solvent and drying When the precipitate produced and separated as described above is dried, primary particles of the precipitate are rearranged to form strong aggregated particles, and even if the precipitate is dispersed in an organic solvent. , It is difficult to completely destroy the aggregate structure. Therefore, in the present invention, the precipitate is dispersed in the organic solvent without being dried. It is preferable to wash the precipitate with water prior to this dispersion. Nitrate ions and chloride ions in the precipitate promote the growth of aggregated particles during calcination,
Furthermore, if this precipitate or powder containing sulfate ions is calcined, harmful gases such as nitric acid gas, chlorine gas, and sulfurous acid gas are generated. It is preferable to wash the precipitate with water in order to remove nitrate ions, sulfate ions, chlorine ions, etc., which are gas generation sources. Washing with water may be performed by a commonly used method. The purity is not particularly limited as long as it is generally as pure as washing water. Usually, ion-exchanged water or distilled water is used.

The organic solvent used in the present invention is replaced with water in the precipitate remaining after removing most of the water to weaken the binding force between the particles of the precipitate and to dry the precipitate containing water. It plays a role of preventing the formation of strong agglomerated particles that occur in the above. Examples of such an organic solvent include those selected from hydrophilic alcohols such as ethyl alcohol, methyl alcohol, propyl alcohol, butyl alcohol, hexanol, octanol, isoamyl acetate, and polyethylene glycol, or polar organic solvents. The type of organic solvent is not particularly limited as long as it satisfies the purpose of use. They can use 1 type (s) or 2 or more types.

Among these organic solvents, an organic solvent capable of dissolving water, for example, an alcohol having a carbon number of 3 or less, easily disperses the precipitate, and at the same time, the water in the precipitate is taken into the organic solvent. Even if it is filtered again after being dispersed, most of the water content is removed, and the surface of the particles is covered with the organic solvent instead, and the effect of the organic solvent is exhibited. However, in this case, since the effect is not so great, it is preferable to form a precipitate of bulky aggregated particles with the aid of sulfate ions.

In the case of an organic solvent which does not substantially dissolve water, it is difficult to disperse the water-containing precipitate.
Therefore, it is necessary to heat the organic solvent containing the precipitate while stirring and to evaporate the organic solvent and at the same time evaporate the water covering the powder surface, and replace the water molecules on the powder surface with the molecules of the organic solvent. is there. The evaporation of the organic solvent may be continued until it is dried, or the organic solvent may be removed by filtration after the molecules of the organic solvent are sufficiently covered on the surface of the precipitated particles. Even if the precipitate treated with the method of the present invention using an organic solvent is jelly-like, the dried lump is fragile and can be easily finely crushed in a mortar or the like.

The effect of the organic solvent in the present invention is recognized when the amount of the organic solvent is 0.1 times or more the volume of the precipitate. The effect is improved as the amount of the organic solvent increases.
However, even if the amount of the organic solvent exceeds 20 times, no remarkable improvement in the effect is observed. Thus, in the drying of the precipitate dispersed in the organic solvent in the present invention, when the organic solvent dissolves water, the organic solvent containing water may be filtered and then dried to disperse the precipitate. The organic solvent may be evaporated as it is together with water. In the case of an organic solvent that does not substantially dissolve water, it is necessary to desorb water from the surface of the primary particles during precipitation and cover the surface with the molecules of the organic solvent instead. It is necessary to evaporate the water. It is preferable to boil the organic solvent because the water molecules on the surface of the primary particles of the precipitate are rapidly exchanged with the molecules of the organic solvent. Therefore, according to the present invention, the precipitate is first dispersed in an organic solvent that dissolves water, filtered to remove most of the water content, and then dispersed in an organic solvent that hardly dissolves water. The solvent is separated by filtration, and the amount of the organic solvent to be evaporated can be greatly reduced, which is preferable because the working time is shortened. <C> Calcining When aluminum hydroxide is calcined, α-phase aluminum oxide is produced at 1000 ° C. or higher through many intermediate phases such as γ phase and κ phase. The density greatly increases due to the phase transition from the intermediate layer to the α phase. Usually, as a ceramic raw material, α is generally the most stable in order to avoid a change in true density during firing.
Since the powder of the phase is used, the calcination temperature is preferably 1000 ° C. or higher also in the present invention in order to obtain the aluminum oxide powder of the α phase. On the other hand, the calcination temperature is 140
When the temperature is higher than 0 ° C., grain growth is severe and the sinterability is deteriorated, which is not preferable. More preferably 1100 to 1350 ° C
Range. On the other hand, since the coprecipitated yttrium oxide and aluminum hydroxide are fine, even if the temperature is relatively low at 500 ° C., they react quickly to produce yttrium aluminum garnet stable up to the melting point. In the production of, the calcination temperature is 500 ~
The temperature is set to 1400 ° C, more preferably 700 to 1350 ° C.

Hereinafter, the method for producing easily sinterable alumina powder and yttrium aluminum garnet powder by the pseudo-alkoxide method of the present invention will be described in more detail with reference to examples.

[0030]

Example 1 37 g of aluminum nitrate was dissolved in 500 ml of distilled water, and then ammonia water was added to adjust the pH to 7.5. Keep the solution at 90% for 2 hours while maintaining the pH at 7.5.
C. After filtering the precipitate, it was washed twice with distilled water,
Filtered. Divide the precipitate into two equal parts, and immediately halve 200 m
dispersed in 1 liter of isobutyl alcohol. The dispersion was gently boiled in a nitrogen gas stream to evaporate water and organic solvent and dried. After drying, the powder was lightly disintegrated with an alumina mortar and an alumina pestle and calcined at 1250 ° C. for 2 hours in an oxygen stream. The calcined powder was crushed with an alumina mortar and alumina pestle for 3 minutes, and the obtained powder was pressed with a mold to a pressure of 3
It was molded at 0 MPa, further isostatically pressed at 200 MPa, and then sintered at 1500 ° C. for 2 hours in the atmosphere. The remaining precipitate divided into two was air-dried in a nitrogen gas stream without being dispersed in isobutyl alcohol. The subsequent treatment was carried out under the same conditions as the powder obtained by dispersing the organic solvent and then drying.

When the sintered density of the obtained sintered body was examined, the sintered density treated with an organic solvent was 92% of the theoretical density,
That of untreated aluminum oxide was 60%. Further, aluminum oxide treated with an organic solvent and aluminum oxide not treated with an organic solvent were formed into tablets each having a diameter of about 5 mm and a length of about 6 mm, which were baked at a temperature of 10 ° C / min to 1570 ° C. Check the shrinkage rate due to knotting,
The result is shown in FIG.

From FIG. 1, it can be seen that the shrinkage rate characteristics of the aluminum oxide sintered by the organic solvent treatment of the present invention are much better than those of the comparative example not treated by the organic solvent. The aggregate structure of aluminum oxide treated with an organic solvent and untreated aluminum oxide was also investigated, and the results are shown in FIG. FIG. 2 is a micrograph showing the aggregate structure of aluminum oxide (a) treated with an organic solvent and untreated aluminum oxide (b). The aggregation of aluminum oxide (a) treated with an organic solvent is shown in FIG. It can be seen that the structure is completely destroyed, whereas the untreated aluminum oxide (b) forms large aggregated particles in which fine primary particles are dense. Example 2 After dissolving 32 g of aluminum sulfate in 500 ml of distilled water, an aqueous solution of ammonium carbonate was added to adjust the pH to 7.5. It was kept at 90 ° C. for 2 hours while keeping the pH at 7.5. After filtering the precipitate, 1/3 of the precipitate was air-dried as it was in a nitrogen gas stream, the rest was dispersed in 300 ml of ethyl alcohol, and the mixture was kept at 70 ° C. for 30 minutes and then filtered. Half of this precipitate was air-dried as it was in a nitrogen gas stream. The remaining precipitate was dispersed in 150 ml of isobutyl alcohol, kept at 95 ° C for 30 minutes, filtered, and dried in a dryer kept at 110 ° C. The treatment after drying the three kinds of powders was performed under the same conditions as in Example 1.

When the sintered density of the obtained sintered body was examined, the sintered density of each aluminum oxide was 6 of the theoretical density.
They were 5% (untreated organic solvent), 92% (treated with ethyl alcohol) and 95% (treated with isobutyl alcohol).
Further, with respect to the one treated with ethyl alcohol, the shrinkage rate due to sintering was examined in the same manner as in Example 1, and the result is shown in FIG. Example 3 To 37 g of an aqueous solution of aluminum nitrate, 1 times the amount of sulfate ion was added to that of aluminum ion to prepare a 500 ml aqueous solution. Aqueous ammonia was added to adjust the pH to 7.5. The mixture was heated at 90 ° C. for 2 hours while keeping the pH at 7.5. The precipitate was filtered, washed twice with distilled water, and filtered. Then disperse in 200 ml of normal propyl alcohol, gently boil the dispersion in a stream of nitrogen gas,
Water and organic solvent were evaporated to dryness. The subsequent treatment of the dried powder was performed under the same conditions as in Example 1.

The sintered density of the obtained sintered body was examined.
The sintered density of aluminum oxide is 93% of the theoretical density.
there were. In addition, as in Example 1, the shrinkage ratio due to sintering was adjusted.
The results are shown in FIG. Example 4 Dissolve 37 g of aluminum nitrate in 500 ml of distilled water
Was. Aqueous ammonia was added to adjust the pH to 8. room temperature
Kept for 2 hours and then filtered. Then 200 ml a
Dispersed in sobutyl alcohol and dispersed in a nitrogen gas stream
The liquid is boiled gently to evaporate the organic solvent and water and dry.
Dried. Subsequent processing is performed under the same conditions as in Example 1.
Was.

The sintered density of the obtained sintered body was examined.
The sintered density of aluminum oxide is 85% of the theoretical density.
there were. In addition, as in Example 1, the shrinkage ratio due to sintering was adjusted.
The results are shown in FIG. Example 5 Yttrium nitrate 22g and ammonium alum 4
After dissolving 5.3 g in 1000 ml of distilled water,
Near water was added to adjust the pH to 8. keep the pH at 8
While keeping the solution at 90 ° C. for 2 hours. The precipitate was filtered
Then, it was washed twice with distilled water and filtered. Divide the precipitate in two,
Immediately add half of it to 200 ml of isobutyl alcohol
Disperse, gently boil the dispersion in a stream of nitrogen gas,
Water and organic solvent were evaporated to dryness. The rest of the precipitate is nitrogen
It was air dried in a stream of elementary gas. After drying, both powders are
Lightly disintegrate with a Lumina mortar and alumina pestle at 1100 ° C
Calcined. The treatment after calcination is performed under the same conditions as in Example 1.
Was.

When the sintered density of the obtained sintered body was examined, the yttrium aluminum garnet treated with the organic solvent had a sintered density of 95% of the theoretical density and the untreated yttrium aluminum garnet was 65%. In addition, yttrium aluminum garnet treated with an organic solvent and untreated yttrium aluminum garnet were made into tablets each having a diameter of about 5 mm and a length of about 6 mm.
The shrinkage rate due to sintering when the temperature was raised to 1570 ° C. at a rate of 0 ° C./min was examined, and the results are shown in FIG. Example 6 (Comparative Example) According to the method disclosed in Japanese Patent Publication No. 2-92817, 7 g of yttrium nitrate and ammonium alum 1
After dissolving 4.4 g and 50 g of urea in 1000 ml of distilled water, the temperature was raised to 95 ° C. and kept at that temperature for 5 hours, then 2 liters of water was added to stop the decomposition of urea, and the mixture was filtered. The precipitate was washed 3 times with water and dried in a nitrogen gas stream. The treatment of the sample after drying was performed under the same conditions as in Example 5.

The sintered density of the obtained sintered body was examined.
B) The density of the sintered body of yttrium aluminum garnet
The degree was 70% of theoretical density. Also, as in Example 5.
The shrinkage rate due to sintering was investigated and the results are shown in FIG. Example 7 Yttrium nitrate 11.02 g and aluminum nitrate 1
Dissolve 8.8 g in 500 ml of distilled water and add ammonia water.
Adjust the pH to 8 with and keep this pH for 2 hours, then filter.
And dispersed in isobutyl alcohol. In a nitrogen gas stream
The dispersion was heated to boil gently and dried. Dry
The subsequent treatment was performed under the same conditions as in Example 5.

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, the shrinkage rate due to sintering was examined in the same manner as in Example 5, and the results are shown in FIG.

[0039]

EFFECT OF THE INVENTION Since the organic solvent used in the present invention can be completely removed from the powder by burning during calcination, the obtained aluminum oxide powder and yttrium aluminum garnet powder have not only high purity but also high purity. Since it is easily sinterable, it is extremely useful as a raw material powder for producing a transparent sintered body such as a Na arc tube or a laser host material, or a high-grade ceramic such as a corrosion resistant material.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a shrinkage rate and a sintering temperature of aluminum oxide of Examples and Comparative Examples of the present invention due to sintering.

FIG. 2 is a micrograph as a substitute for a drawing, which shows an aggregate structure of aluminum oxide (a) treated with an organic solvent and untreated aluminum oxide (b).

FIG. 3 is a diagram showing the relationship between the shrinkage rate and the sintering temperature of the yttrium aluminum garnets of Examples and Comparative Examples of the present invention.

Claims (3)

[Claims] 1. An aqueous solution expressing basicity is added to an acidic aqueous solution containing aluminum ions to precipitate aluminum hydroxide, most of the mother liquor is separated and removed, and the remaining precipitation or further this precipitation is performed once or a plurality of times. The precipitate remaining after separating and removing most of the washing solution by washing with water is dispersed in an organic solvent of not less than 0.1 times the volume of the precipitate without drying, and dried, and then 1000 to 1400 ° C. A method for producing an easily sinterable aluminum oxide powder, which comprises producing an alumina powder by calcining at. 2. An aqueous solution expressing basicity is added to an acidic solution containing yttrium ions and aluminum ions in a proportion of yttrium aluminum garnet produced,
A precipitate was formed while keeping the pH at 6.5 to 10, most of the mother liquor was separated and removed, and the remaining precipitate or this precipitate was washed once or more times with water to separate and remove most of the washing liquid. The yttrium aluminum garnet powder, characterized in that the remaining precipitate is dispersed in an organic solvent in an amount not less than 0.1 times the volume of the precipitate without drying, dried, and then calcined at 500 to 1400 ° C. Manufacturing method. 3. When dispersing a precipitate of aluminum hydroxide or a precipitate of yttrium hydroxide and aluminum hydroxide in an organic solvent, first disperse in an organic solvent that dissolves water, remove most of the liquid, and then remove water. 3. The method according to claim 1 or 2, wherein the compound is dispersed in an organic solvent which hardly dissolves and then dried.