JPH11278934A - Production of sintered compact of yttrium oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce dispersion in rectilinear transmissivity by controlling atmosphere in a reaction tank so that a definite equilibrium state is kept between carbon dioxide partial pressure in atmosphere in the reaction tank and carbon dioxide partial pressure in reaction solution while keeping a reaction solution constant within a specific temperature range and carrying out aging of yttrium carbonate. SOLUTION: The temperature of reaction solution of yttrium carbonate during aging is controlled within the range of 25-40 deg.C. Preferable temperature is 30 deg.C and the temperature is controlled within the range of ±3.0 deg.C. Although a method for controlling atmosphere in a reaction tank can be carried out by providing a vent hole having a prescribed size in the upper lid of the reaction tank, forced ventilation is not usually required therefor. It is preferable so as to uniformly produce nucleus of yttrium carbonate in a definite value or above in the reaction tank. A rate enough to uniformly produce nucleus of yttrium carbonate in a definite value or above in the reaction tank and control crystal growth of yttrium carbonate is preferably selected as a stirring rate of yttrium carbonate during aging.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a transparent sintered body of yttrium oxide having a high linear transmittance, which is used for a laser host material, an observation window of various devices for high temperature, an arc tube for a discharge lamp, and the like. And a yttrium oxide sintered body having a high linear transmittance manufactured by the same method.

[0002]

2. Description of the Related Art Yttrium oxide has a cubic crystal structure and no birefringence.
By using yttrium oxide powder having a fine particle size, a powder having high transparency and high linear transmittance of light can be obtained. However, it is difficult to stably obtain yttrium oxide powder having a uniform fine particle size, and thus it is impossible to obtain a yttrium oxide sintered body having a high linear transmittance. . Of course, a method for producing yttrium oxide having a more uniform fine particle size has been proposed, but at present, it has not yet been possible to stably produce an yttrium sintered body having a high linear transmittance. For example, Japanese Unexamined Patent Publication No. 9-315865 discloses that after adding an aqueous solution of a basic carbonate to an aqueous solution of an acidic yttrium salt to precipitate yttrium carbonate in a specific pH range, a reaction containing the precipitated yttrium carbonate is performed. The liquid is kept in a specific temperature range for 10 hours or more while being stirred and aged, and the mixture is calcined to obtain yttrium oxide powder. The obtained yttrium oxide powder is formed into a desired shape and then sintered. A method for producing a desired yttrium oxide has been proposed. However, even if the raw materials and the like are carefully selected and manufactured under as uniform conditions as possible, a sintered body of yttrium oxide obtained can have a high linear transmittance of about 50%, which is very high. In some cases, the linear transmittance of the sintered body of yttrium oxide obtained for each production lot or each production batch varies widely, and the linear transmittance varies within a certain range. At present, it is impossible to manufacture a sintered body of yttrium oxide having a linear transmittance of.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a sintered body of yttrium oxide having little variation in linear transmittance.

[0004]

Means for Solving the Problems The present inventors have made various studies in view of the above-mentioned current situation, and have found that yttrium carbonate as a raw material for obtaining a yttrium oxide sintered body having a high linear transmittance is provided. A sharp particle size distribution, which is an essential requirement to be, finer particles, and
In order to satisfy the requirement that the particles are crystallized, the control of the reaction temperature during the aging of yttrium carbonate has a great effect, and in order to generate fine yttrium carbonate crystals, , in order to produce the crystals in high yield, certain equilibrium is between the carbon dioxide partial pressure P _{CO 2} in the reaction vessel atmosphere with carbon dioxide partial pressure P _CO2 in the reaction solution is maintained The present invention has been completed by finding out that it is necessary to perform the above. That is, while the yttrium carbonate aging, keeping constant the temperature of the reaction solution to a specific temperature in the range of 25 ° C. to 40 ° C., the reaction solution with carbon dioxide partial pressure P _CO2 in the atmosphere in the reaction vessel Carbon dioxide partial pressure P
_In order to ensure that a certain equilibrium is maintained with CO2, yttrium carbonate that satisfies the above prerequisites can be obtained by using a reaction vessel covered with a lid having a vent hole of a specific size. They have found what they can get. Thus, according to the present invention, first, an aqueous solution of a basic carbonate is added to an aqueous solution of an acidic yttrium salt to precipitate and precipitate yttrium carbonate, and the precipitated and precipitated yttrium carbonate is aged with stirring, The obtained yttrium carbonate is calcined to obtain yttrium oxide powder, the obtained yttrium oxide powder is molded into a predetermined shape, and the molded yttrium oxide is sintered to obtain a yttrium oxide sintered body, while the temperature of the reaction liquid was kept constant at a particular temperature in the range of 25 ° C. -40 ° C., carbon dioxide partial pressure P _CO2 in the reaction solution with carbon dioxide partial pressure P _CO2 in the atmosphere in the reaction vessel
The method characterized in that the atmosphere in the reaction tank is controlled so as to maintain a certain equilibrium state between the reaction vessel and the aging of yttrium carbonate, Thirdly, the method in which the specific temperature is 30 ° C. ± 3.0 ° C. is a method in which the aging of the yttrium carbonate is performed by increasing the nucleation density of yttrium carbonate crystals in the first or second method. A method is provided in which stirring is performed at a speed sufficient to suppress crystal growth.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for producing a yttrium oxide sintered body according to the present invention, the temperature of the reaction solution during the aging of the raw material yttrium carbonate is kept at a specific temperature within the range of 25 ° C. to 40 ° C. while maintaining the atmosphere in the reaction vessel such that a constant equilibrium state is maintained in between the carbon dioxide partial pressure P _{CO 2} in the atmosphere in the reaction vessel with carbon dioxide partial pressure P _CO2 in the reaction mixture By controlling the particle size distribution of the particles is sharp, the particle size is fine, and crystallized yttrium carbonate is produced, yttrium oxide powder is produced from this yttrium carbonate, and this yttrium oxide powder is molded, This compact is fired. As various raw materials for producing yttrium carbonate used in the method for producing a sintered body of yttrium oxide according to the present invention, for example, those described in JP-A-9-315816 and JP-A-9-315865 are used. it can. The operation up to the start of the dropping operation of the basic carbonate aqueous solution may be performed according to a known method. Therefore, in the following description, the production method of the present invention after the start of the dropping operation will be mainly described. The temperature control of the reaction solution is usually performed using a thermostat for a small scale or a jacketed reaction vessel for a large scale. It is necessary to control the temperature of the reaction solution to a constant temperature throughout the aging step. The temperature control is within a range of ± 0.5 ° C. to ± 3.0 ° C., preferably ± 0.7 ° C. to ± 1.0 ° C. for a specific temperature selected from the above temperature range. It is desirable to carry out in the range of 5 ° C. Temperature control at less than ± 0.5 ° C. is not always economical when carried out industrially, and
Temperature control exceeding ± 3.0 ° C. is not preferable because inconveniences such as the case where the linear transmittance of the sintered body does not reach a desired level may occur. If the temperature of the reaction solution is lower than 25 ° C., the obtained yttrium carbonate may not be sufficiently matured, and if the temperature of the reaction solution exceeds 40 ° C., the particle size of the obtained yttrium carbonate may be too large. The disadvantage is that a sintered body having a desired high linear transmittance cannot be obtained. A preferred temperature is 30 ° C. and this temperature is in the range of ± 3.0 ° C., preferably ± 30 ° C.
Control within 1.5 ° C.

In the method for producing a yttrium oxide sintered body according to the present invention, a constant equilibrium state between the carbon dioxide partial pressure P _CO2 in the atmosphere of the reaction vessel and the carbon dioxide partial pressure P _CO2 in the reaction solution is provided. As a method of controlling the atmosphere in the reaction tank so that the pressure is maintained, a method in which a vent hole having a predetermined size is provided in the upper lid of the reaction tank may be used. Usually does not require forced ventilation. The size of the vent holes may be any such size constant equilibrium state is maintained in between the carbon dioxide partial pressure P _CO2 in the reaction solution with carbon dioxide partial pressure P _CO2 in the ambient atmosphere, If it is too small, the partial pressure of carbon dioxide becomes high, and the crystal of yttrium carbonate may become large, which is not preferable.If it is too large, the concentration of carbon dioxide in the reaction solution becomes low, and as a result, the yield of yttrium carbonate decreases. It is not preferable because it lowers. A preferred size is such that the carbon dioxide released from the reaction solution slowly releases the carbon dioxide from the atmosphere in the reaction tank so as not to increase the partial pressure of the carbon dioxide in the reaction tank. If necessary, the size of the vent hole may be adjusted by measuring the concentration of the released carbon dioxide gas. It is preferable that the partial pressure of carbon dioxide in the reaction tank and the partial pressure of carbon dioxide in the reaction solution are maintained in an equilibrium state even during the dropping operation of the basic carbonate aqueous solution. In this case, the dropwise addition of the aqueous solution of the basic carbonate
What is necessary is just to perform through the said ventilation hole. In the method for producing a sintered body of yttrium oxide according to the present invention, the stirring speed during the aging of yttrium carbonate is such that a reaction for generating nuclei of yttrium carbonate having a certain value or more occurs uniformly throughout the reaction vessel. It is preferable that the speed is sufficient to suppress the crystal growth of yttrium carbonate. Usually, such a speed is such that the rotation speed of the stirrer is 100 rpm or more.
A speed within the range of 1,500 rpm is sufficient. However, this speed is determined by the ratio between the size of the reaction tank and the size of the blade of the stirrer. When this ratio is small,
What is necessary is just to reduce a rotation speed. In the case of a small scale, a magnetic stirrer is preferably used. In the case of a large scale, it is necessary to use a stirrer in which the tip of the stirrer reaches the bottom of the reaction tank sufficiently and has a structure sufficient to disperse the fine powder of yttrium carbonate precipitated at the bottom. A stirrer having such a configuration is well known to those skilled in the art.

In the method for producing a yttrium oxide sintered body according to the present invention, the aging time of yttrium carbonate is usually 5 hours to 60 hours, preferably 20 hours or more, depending on the holding temperature of the reaction solution. If the aging time is less than 5 hours, the yttrium carbonate precipitated at the beginning of the lowering step of the aqueous solution of the basic carbonate is amorphous even if the holding temperature of the reaction solution is set to the upper limit of 40 ° C. However, there is a problem that fine yttrium oxide with high uniformity cannot be obtained because the amorphous yttrium carbonate generated in the early stage remains without being completely converted to crystalline yttrium carbonate. The linear transmittance varies from lot to lot, and it is not possible to produce a sintered body of yttrium oxide having a linear transmittance of about 50% or more. Further, even if the aging time exceeds 60 hours, the size, particle size distribution, dispersion state and the like of the fine yttrium carbonate powder are not particularly affected, so that the aging time beyond this is unnecessary. The fine powder of yttrium carbonate is collected by filtration, and the filtered fine powder is added in an amount of 0.005% by weight to 0.5%.
Thoroughly wash with an aqueous solution of ammonium sulfate by weight. The filtered yttrium oxide is sufficiently washed with an aqueous solution of ammonium sulfate to obtain yttrium carbonate powder having a uniform fineness. The treatment method after aging may be in accordance with the method described in JP-A-9-315816. That is, the sufficiently washed fine yttrium carbonate powder is dried at 100 ° C., and the dried yttrium carbonate is dried at 700 ° C. to 1300 ° C., preferably 900 ° C. in an oxygen atmosphere.
Calcinate at 1200C to 1200C. Usually, a calcination time of 3 hours to 5 hours is sufficient. In the method for producing a yttrium oxide sintered body according to the present invention, the yttrium oxide fine powder obtained by calcination is formed into a desired shape, and the resulting powder is formed into a desired shape.
0 ° C to 1800 ° C, preferably 1500 ° C to 1700
What is necessary is just to sinter at 1 degreeC for 1 hour to 5 hours. When sintering,
By pre-sintering at 1000 ° C. to 1300 ° C. for 2 hours to 3 hours and then sintering at 1600 ° C. to 1700 ° C. for 2 hours to 3 hours, a yttrium oxide sintered body having a higher linear transmittance can be manufactured.

[0008]

EXAMPLES Hereinafter, the present invention will be described with reference to Examples and Comparative Examples. However, needless to say, the present invention is not limited to these Examples. The method for measuring the linear transmittance of the light beam used in the following examples will be described. A linear light having a diameter of 2 mm and a wavelength of 600 nm is emitted from the light source, and is accurately irradiated on a detector having a diameter of 2 mm 100 mm away from the light source. The amount of light detected at this time is defined as y. A sample whose both surfaces are mirror-polished and made into a flat plate having a thickness of 1 mm is inserted into the center between the light source and the detector so that the polished surface is perpendicular to the linear light, and the light beam is blocked. The detected amount of light detected at this time is x. The result is applied to the following equation to calculate the linear transmittance of each sample. Linear transmittance (%) = (x ÷ y) × 100

(Embodiment) The inner diameter is 170 mm and the height is 26.
0.5 mol / l in a 0 l 5 l glass reaction vessel
1 ml of an aqueous solution of yttrium nitrate 2500 ml
This reaction vessel is placed in a thermostat controlled at 30 ° C. ± 0.5 ° C., and after the liquid temperature is adjusted to the above temperature, a stirrer having a length of 105 mm and a diameter of 30 mm is placed in the reaction vessel. After the reaction vessel is covered with a glass lid having a diameter of 175 mm and a ventilation hole having a diameter of 20 mm in order to control the atmosphere in the reaction vessel under constant conditions, the above stirrer is used. While stirring the reaction solution while rotating at a speed of 600 rpm, a 2.5 mol / l aqueous solution of ammonium bicarbonate was added dropwise through the vent hole, and the pH of the reaction solution was adjusted to 4.5 to remove yttrium carbonate. The precipitate was precipitated. After the dropping of the aqueous solution of ammonium hydrogen carbonate is completed, the mixture is further stirred at the above rotation speed for 48 hours while maintaining the above temperature and the above atmosphere so that the precipitated yttrium carbonate particles are sufficiently dispersed in the reaction mother liquor. Aging continued. After aging, the precipitated yttrium carbonate was collected by filtration, and the filtered yttrium carbonate was sufficiently washed with a 0.05% by weight aqueous solution of ammonium sulfate. Drying the washed yttrium carbonate at 100 ° C.
Acicular crystals of yttrium carbonate were obtained. This yttrium carbonate was calcined in an oxygen atmosphere for 4 hours to obtain yttrium oxide powder. This yttrium oxide powder was subjected to hydrostatic pressure 2t /
cm ² , and vacuum-sintered at 10 ⁻⁵ Torr and 1700 ° C. The same operation was repeated 10 times, and the linear transmittance of the obtained sintered body was measured, and the results are shown in Table 1.

[0010]

[Table 1]

(Comparative Example) Yttrium carbonate precipitation step,
In the aging step, the temperature of the reaction solution was not controlled, and the room temperature (20
C)), and a yttrium oxide sintered body was produced using the same raw materials, reaction vessel, and reaction conditions as those used in the above Examples, except that the reaction vessel was not covered with a lid. The linear transmittance of the ten sintered bodies was measured,
It is shown in Table 2.

[0012]

[Table 2]

As is clear from the results of Tables 1 and 2 above, the linear transmittance of the yttrium oxide sintered body according to the present invention is within a certain range of 52% to 55%, and On the contrary, the linear transmittance of the comparative example is higher than 10%.
It can be said that this method has a little problem in industrially adopting it with a large variation of 54%.

[0014]

[Effects of the Invention] Each of the yttrium oxide sintered bodies manufactured by the method according to the present invention has a high linear transmittance of 52% or more, and therefore, a sintered body having a high linear transmittance can be manufactured. It can be said that this is an industrially excellent method.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroaki Sakai 2-56 Sudacho, Mizuho-ku, Nagoya, Aichi Prefecture Inside Nihon Insulators Co., Ltd. (72) Inventor Shuichi Ichikawa 2-56, Sudacho, Mizuho-ku, Nagoya-shi, Aichi Prefecture No. Nihon Insulator Co., Ltd.

Claims (3)

[Claims] 1. An aqueous solution of a basic carbonate is added to an aqueous solution of an acidic yttrium salt to precipitate and precipitate yttrium carbonate, and the precipitated and precipitated yttrium carbonate is aged with stirring, and the obtained yttrium carbonate is temporarily prepared. Baking to obtain yttrium oxide powder, forming the obtained yttrium oxide powder into a predetermined shape, and sintering the formed yttrium oxide to obtain a yttrium oxide sintered body. While maintaining the temperature constant at a specific temperature in the range of −40 ° C., the carbon dioxide partial pressure P
_The above method, wherein the atmosphere in the reaction tank is controlled to ripen yttrium carbonate so that a certain equilibrium state is maintained between _CO2 and the partial pressure of carbon dioxide in the reaction solution, PCO2. 2. The method according to claim 1, wherein the specific temperature is 30 ° C. ± 3.0 ° C. 3. The method according to claim 1, wherein the yttrium carbonate is aged while stirring at a speed sufficient to increase the nucleation density and suppress crystal growth.