JPH11189413A - Production of transparent yttria sintered body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an yttrium oxide sintered body having a high sintered density and high transparency. SOLUTION: This method for producing a transparent yttrium sintered body comprises adding a basic agent to a solution containing an yttrium salt in a concentration of 0.02-2 mole/liter at a temperature of <30 deg.C to produce yttrium hydroxide comprising agglomerates which each comprises many <=20 nm thick flaky particles agglomerated in a state wherein the table surfaces and the end surfaces are jointed to each other in a card-house structure and which each has a diameter of >=0.5 μm, adding a sulfate ion-containing compound in an amount corresponding to 10<-3> to 1 fold mole of the sulfate ion that of the yttrium ion to the yttrium hydroxide so that the pH of the mixture is >=5 at the finish point of the addition, calcining the mixture at >=900 deg.C to form yttrium oxide powder having an average primary particle diameter of 30-500 nm, molding the obtained yttrium oxide particles, and sintering the molded product at a temperature of 1,500-2,000 deg.C in an atmosphere in which the total partial pressure of one or more kinds of atoms substantially not diffused in the yttrium oxide, such as nitrogen atom or argon atom is <=1/3 atm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a fine yttrium oxide powder which is easy to sinter and a method for producing a transparent sintered body using the powder. More specifically, the present invention relates to a method for calcining yttrium hydroxide. Primary particles are present in a state of being separated individually, and can be used for a method for producing easily sinterable yttrium oxide fine powder having a narrow particle size distribution and various arc tubes, laser materials, windows for high temperature, etc. using the powder. The present invention relates to a method for manufacturing a transparent sintered body.

[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 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 the organic solvent is evaporated 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 that occur during washing and drying than yttrium hydroxide, and relatively 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, according to the present invention, a base agent is added to a solution containing a yttrium salt having a concentration of 0.02 mol / L or more and 2 mol / L or less at a temperature lower than 30 ° C. A large number of flaky particles are aggregated in a state where the table surface and the end surface are joined to each other in a card house shape to produce yttrium hydroxide, which is an aggregated particle having a diameter of 0.5 μm or more, and the amount of yttrium ion is added to the yttrium hydroxide. A compound containing a sulfate ion corresponding to 10 ^-3 to 1 times the sulfate ion is added to the mixture, and the pH is 5 or more at the time of the completion of the addition. Average particle size of 30 nm or more and 500 nm
A method for producing an easily sinterable yttrium oxide powder, which comprises forming a powder in the following range. By this method, the bulky floc morphology produced by the precipitation reaction is left in the dried yttrium hydroxide powder, and abnormal grain growth that proceeds during calcination is suppressed by sulfate ions, and the particles are individually formed. A fine yttrium oxide powder that is separated and has a narrow particle size distribution can be produced. In addition, the present invention provides a method for forming a fine powder of yttrium oxide produced by the above-described production method, and then forming a partial pressure of one or more kinds of atoms such as nitrogen atoms and argon atoms which cannot substantially diffuse in yttrium oxide. Is less than 1/3 atm.
The present invention relates to a method for producing a transparent sintered body of yttrium oxide, wherein the sintered body is fired at a temperature of from 00 ° C to 2000 ° C.

[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 dried, hard aggregated particles are formed. The flaky yttrium hydroxide particles in the present invention have a thickness of 2
It is a petal-shaped flake of 0 nm or less. With the tabletop of the flake,
It refers to two opposing 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, the filterability is poor, and at the same time, the powder of yttrium oxide obtained after calcination is an aggregate of hard agglomerated particles, and the sinterability is poor.

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 N
Since it is cubic like aCl and MgO, the surface energy is the smallest on the (100) plane. The particle surface is (00
1) If only the surface is present, the particles become dice. 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 that can be produced by the method of the present invention, compared to the conventional wet method, has a larger raw bulk density of the obtained yttrium oxide powder and has a better sinterability. .

<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 the 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. <H> Molding In the present invention, molding is preferably performed by pressure molding using a mold generally used in the field of ceramics or molding by a slip casting method, and the effects of the present invention are not limited by the molding method.

<I> Sintering In the present invention, a transparent sintered body is produced at 1500 ° C.
It is necessary to bake. When the temperature is 1500 ° C. or less,
The pores cannot be completely removed. Generally, the higher the crystal grain size, the better the transparency and corrosion resistance of the sintered body. Therefore, the higher the sintering temperature, the more preferable. However, if the sintering temperature is 2000 ° C. or higher, a special sintering furnace is required, the energy for heating is rapidly increased, and the cost is increased. Even if the sintering time is shorter as the sintering temperature is higher, preferable results can be obtained. Fifteen
At 00 ° C., it is necessary to maintain the temperature for at least 3 hours. On the other hand, when the sintering temperature exceeds 1500 ° C,
Even if the sintering time is shortened, a transparent sintered body can be manufactured.

If the firing temperature is high, grain growth proceeds and mechanical properties such as mechanical strength are deteriorated. Therefore, when transparency and mechanical strength are required simultaneously, firing at a temperature of 1850 ° C. or less is required. preferable. Sintering with a one-step trapezoidal temperature program often produces white spots in the transparent sintered body. In this case, the temperature is raised at least between 1100 ° C. and 1400 ° C. over 1 hour and then raised to 1500 ° C. or higher, or the temperature is maintained at a certain temperature in the temperature range for 30 minutes or more and then raised again to 1500 ° C. or higher. When a two-stage trapezoidal heating program is used, the generation of white spots can be suppressed.

<J> Firing Atmosphere In the present invention, "a gas that cannot diffuse in yttrium oxide" refers to a gas of atoms, such as nitrogen gas or argon gas, which is more difficult to diffuse in yttrium oxide than oxygen ions. Densification of yttrium oxide by sintering progresses,
When isolated pores appear, it is difficult for gas that is difficult to diffuse in yttrium oxide to escape from the isolated pores.
However, if the sum of the partial pressures of the atomic gas is not more than 1/3 atm, the transparency by sintering is not significantly affected.

[0032]

EXAMPLES Examples of the present invention and comparative examples are shown below, but the present invention is not limited to these examples. Comparative Example 1 A comparative example in which a compound containing a sulfate ion was not added to the agglomerated powder is shown. 200 ml of 20 g of yttrium nitrate
Was dissolved in distilled water, kept at 10 ° C. with a cooler, and stirred with a magnetic stirrer. 150 ml of 2N ammonia water cooled to about 10 ° C. while stirring this solution
Was added dropwise over 30 minutes and 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.

2 g of the loosened powder was added to the agglomerated powder without adding a compound containing a sulfate ion, placed in an alumina boat, and calcined in an oxygen stream at 1100 ° C. for 4 hours in a tubular electric furnace. The calcined powder was observed by SEM, and the results are shown in FIG. Relatively small dice-like particles and very large particles are mixed. Next, the calcined powder was lightly loosened in an alumina mortar, and then primarily molded at 30 MPa using a mold, and then subjected to isostatic pressing at 200 MPa to produce a molded body. The molded body was placed in a vacuum electric furnace to attain a high vacuum of 10 ⁻⁵ Torr or more, and then heated to 1700 ° C. at a rate of 10 ° C./min and kept at that temperature for 1 hour. Then 15
The sample was cooled at a rate of ° C./min, and the sample was taken out after the inside of the furnace was near room temperature. 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.

Comparative Example 2 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 Comparative Example 1 except that aqueous ammonia at room temperature was added dropwise to an aqueous solution of yttrium nitrate kept at 35 ° C. After washing the precipitate, it was divided into two equal parts. 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 Comparative Example 1. This calcined powder was molded and sintered. The density of the obtained sintered body was 84% of the theoretical density.
% And 95%, the sintered density was lower than in Comparative Example 1.

Example 1 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 was generated by the method of Comparative Example 1, the above-mentioned aqueous solution of ammonium sulfate was 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 Comparative Example 1. 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 3 A yttrium oxide sintered body was produced in the same manner as in Example 1 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 the theoretical density of 99.
At 5%, the transparency was much worse than the sintered body obtained in Example 1.

Example 2 Yttrium hydroxide to which sulfate ions were added was produced and calcined according to Example 1 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 4 A comparative example in which the calcination temperature was set to a temperature 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 2 was 9% of the theoretical density.
At 9.3%, it was milky white and had no transparency.

Comparative Example 5 A comparative example in which yttrium carbonate powder was precipitated at pH 5 but the aging time was short was shown. After dissolving 20 g of yttrium nitrate in 200 ml of distilled water, the mixture is stirred with a magnetic stirrer. To the solution is added a 2 mol / l aqueous solution of ammonium bicarbonate at room temperature to adjust the pH to 5 to produce a precipitate. 0.3 dissolved in 150 ml of pure water
6 g of ammonium sulfate are added dropwise to the aqueous solution in which the precipitate is dispersed over 20 minutes, and the mixture is aged for 30 minutes, filtered and washed. The produced yttrium carbonate was amorphous. Subsequent treatment of the yttrium carbonate was performed according to Comparative Example 1 and Example 1. The bulk density of the obtained sintered body was 98.5% of the theoretical density.

Comparative Example 6 A comparative example in which yttrium oxalate was calcined instead of yttrium hydroxide is shown. 2 dissolved in 400 ml
0 g of oxalic acid dihydrate 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. The precipitates to which ammonium sulfate was added and the precipitates to which ammonium sulfate was not added were each stirred for 3 hours, and then filtered, washed and calcined according to Comparative Example 1 and Example 2. 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.

Comparative Example 7 A comparative example in which a compound containing a sulfate ion was added to a commercially available yttrium oxide powder instead of the yttrium hydroxide formed in the step of the present invention is shown. 5 g of a commercially available fine yttrium oxide powder (having a specific surface area of 15 M ² / g) was dispersed in 100 ml of ethyl alcohol. 0.36g
Is dissolved in 50 ml of pure water,
50 ml of ethyl alcohol was added. The mixture was added to 20
The mixture was added dropwise to ethyl alcohol in which the yttrium oxide powder was dispersed over a period of minutes, and dried by heating to about 70 ° C. The dried powder was lightly loosened with an alumina mortar and an alumina pestle, and calcined at 1100 ° C. for 4 hours in an oxygen stream. This calcined powder,
Molding and sintering are performed under the conditions described in Comparative Example 1. The bulk density of the obtained sintered body was opaque at 94% of the theoretical density.

Example 3 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. Were kept at about 10 ° C. respectively. 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. The dried product is loosened lightly in an alumina mortar. Subsequent calcination, molding, sintering, etc. of the powder,
The procedure of Comparative Example 1 was performed. When the bulk density of the sintered body was measured by the Archimedes method using water, the bulk density was almost 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%. .

Example 4 The yttrium oxide compact produced by the method of Example 1 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 5 An experiment was conducted in the same manner as in Example 1 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 1 were obtained.

[0045]

According to the method of the present invention, it is possible to produce a powder having substantially a 100% yield and a narrow particle size distribution in which particles are individually separated. The bulk density of the resulting sintered body was almost close to the theoretical density, and it became possible to produce a sintered body having excellent transparency.

[Brief description of the drawings]

FIG. 1 is a scanning electron micrograph (magnification: 20,000 times) showing the fine structure of the aggregated particles of yttrium hydroxide generated during the method of the present invention.

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 formed during the method of the present invention.

Claims (2)

[Claims] At a temperature lower than 30 ° C., a base agent is added to a solution containing a yttrium salt having a concentration of 0.02 mol / L or more and 2 mol / L or less to form a large number of flakes having a thickness of 20 nm or less. The particles are aggregated in a state where the table surface and the end surface are joined to each other in a card house shape to produce yttrium hydroxide, which is an agglomerated particle having a diameter of 0.5 μm or more, and the yttrium hydroxide has an amount of yttrium ions. 1
0 from ^-3 times 1 times of the compound containing sulfate ions corresponding to the sulfate ions are added, and at pH5 or more added finished point in time, the average particle calcined to primary particles the agglomerated particles at 900 ° C. or higher A method for producing an easily sinterable yttrium oxide powder, wherein a powder having a diameter in a range of 30 nm or more and 500 nm or less is formed. 2. After the yttrium oxide fine powder produced by the production method of claim 1 is molded, a gas of one or more atoms such as nitrogen atoms and argon atoms which cannot substantially diffuse in yttrium oxide. A method for producing a transparent sintered body of yttrium oxide, comprising firing at a temperature of 1500 ° C. or more and 2000 ° C. or less in an atmosphere having a total partial pressure of 1/3 atmosphere or less.