JP4381911B2 - Tantalum oxide powder and method for producing tantalum oxide powder - Google Patents

Description

  The present invention relates to a tantalum oxide powder and a method for producing a tantalum oxide powder. In particular, the present invention relates to a tantalum oxide powder capable of obtaining a uniform mixed state when mixed with other powders, such as when mixed with glass raw material powder during glass production or when mixed with lithium carbonate powder during lithium tantalate production.

Tantalum oxide is used as a raw material for metal tantalum, which is an electronic component material such as a capacitor, and as disclosed in Patent Document 1, recently, as an additive for adjusting optical properties such as refractive index of glass. Useful.
JP 2003-252631 A

  In glass production in which tantalum oxide is added, first, a step of sufficiently mixing powdery glass raw material and tantalum oxide powder and sequentially melting them is employed. This is because tantalum oxide has a higher density than the glass raw material, so it is difficult to obtain a uniform mixed state by mixing in the molten state. Therefore, it is more uniform if the powder (solid) is mixed in advance. It is because it is easy to mix.

  However, even if the above-mentioned consideration is paid, the mixed state of the glass raw material powder and the tantalum oxide powder may become non-uniform. Regarding this problem, the present inventors have stated that the cause is that, in the case of the conventional tantalum oxide powder, a powder solidified by compression exists in the powder. This is because the tantalum oxide powder manufactured by the manufacturer is packed in containers such as cans and bags and shipped via various means of transportation such as car transportation and ship transportation. Due to the external force, a part of the powder is pressed and solidified. And the tantalum oxide powder solidified in this way may become a hard particle | grain depending on the case, will be scattered in a mixed powder, without loosening at the time of mixing with glass raw material powder, and will worsen the mixed state.

  On the other hand, it is conceivable to reduce the particle diameter of the powder as a means for making the powder difficult to compress and solidify. However, simply reducing the particle size is not without problems. This is because, when the particle size of the powder is reduced, the powder tends to adhere to the wall surface of the glass manufacturing facility, and the tantalum oxide powder is supplied with piping, which makes it impossible to supply the raw material smoothly. This is because the glass raw material powder and the tantalum oxide powder cannot be mixed uniformly.

  As described above, when the tantalum oxide powder and other powders are mixed, there is a problem of uniformity of the mixed state. This problem similarly exists in the field of glass production as well as in the production of lithium tantalate single crystals. Accordingly, there has been a demand for a tantalum oxide powder to be used for such applications that is difficult to be compressed and hardly adheres to the wall surface of the apparatus (good fluidity).

Here, when the prior art regarding the conventional tantalum oxide is seen, the following are disclosed as the properties of the tantalum oxide powder as a powder. In these prior arts, a tantalum oxide powder having a BET surface area and a tap filling density (compressed bulk density (TD)) within a predetermined range is described (Patent Document 2). Further, the loose bulk density (stationary apparent density (AD)), the tantalum oxide powder having an average particle diameter measured by the brane air permeation method within a predetermined range, and the ratio TD / d of the true density (d) and TD are within the predetermined range An internal tantalum oxide powder is disclosed (Patent Document 3).
Japanese National Patent Publication No. 11-51352 JP 2004-51383 A

  However, these prior arts do not improve both the compression problem and the adhesion problem. That is, the tantalum oxide described in Patent Document 2 discloses that the average particle diameter of the tantalum oxide particles is adjusted and the particle diameter distribution is narrowed, but it does not improve the problems of compressibility and adhesion. The tantalum oxide described in Patent Document 3 is also intended to improve compressibility, but this tantalum oxide powder does not solve the problem of adhesion.

  The present invention has been made in view of the background as described above, and provides a tantalum oxide powder that is unlikely to be solidified by compression so that a uniform mixed state can be obtained upon mixing with other powders. With the goal. Also disclosed are methods by which such tantalum oxide powders can be produced.

  As described above, the compression and solidification of the tantalum oxide powder is caused by vibrations such as transportation. Therefore, the present inventors considered that the compressibility of the tantalum oxide powder is affected by the fluidity of the powder. That is, the powder having poor fluidity does not flow even when subjected to vibration, and the position of each particle hardly changes. Since it can be said that the compression of the powder is caused by the impact during vibration and the weight of the particles, it is considered that the powder having poor fluidity is likely to be solidified by the compression. In particular, since tantalum oxide has a high specific gravity, it has a high possibility of compression due to the influence of its own weight, and is considered to be easily influenced by fluidity.

  Therefore, the present inventors examined tantalum oxide powder with good fluidity based on the above consideration. And as a result, it discovered that the tantalum oxide powder which comprises the following two requirements was preferable.

  The first requirement is that the particle size distribution is within a predetermined range. According to the present inventors, the fluidity of the tantalum oxide powder is preferably related to the uniformity of the particle diameter of the constituent particles and has a particle size distribution with uniform particle diameter and no variation. The second requirement is the relationship between both the tap bulk density (TD) and the loose bulk density (AD). According to the inventors, the smaller the difference between TD and AD, the better the fluidity. The inventors of the present invention have clarified a suitable range for the above two requirements and have come up with the present invention.

  That is, the present invention is a tantalum oxide powder having both of the following two conditions.

(1) Feret diameters D ₁₀ and D ₉₀ in particle size distribution measurement using a scanning electron microscope have a relationship of 1 ≦ D ₉₀ / D ₁₀ ≦ 3.
(2) The tap bulk density (TD) and the loose bulk density (AD) have a relationship of 0.8 ≦ AD / TD.

The ferret diameter of the tantalum oxide particles of requirement (1) of the present invention indicates the maximum diameter of each particle when the tantalum oxide powders observed are measured in a fixed direction. D ₁₀ indicates a particle size of 10 number% from the small particle size side in the cumulative particle size distribution of the tantalum oxide powder, and D ₉₀ indicates 90 number% from the small particle size side in the cumulative particle size distribution. It shows the particle size which becomes. In the present invention, to reduce the ratio D _{90 /} D ₁₀ 1 to 3 and a particle size distribution width of D ₉₀ and D ₁₀ represent respectively the particle diameters when the particle size distribution is wide, the gap between the aggregated particles with a large particle size This is because fine particles intrude and form stronger aggregated particles, and as a result, even if subjected to vibration or the like, it becomes difficult to loosen and becomes a powder with poor dispersibility. The particle diameter is preferably measured with a scanning electron microscope. In the measurement of the particle diameter, it is preferable to measure the ferret diameter of 300 or more particles based on the SEM image observed at a magnification of about 50 to 500 times, and create a cumulative particle size distribution from the measurement result.

  The tap bulk density (TD) and the loose bulk density (AD) of the requirement (2) of the present invention are powder characteristics strictly defined in JIS K5101 and follow their contents. These bulk densities can be measured with a commercially available measuring device (as a typical measuring device, there is a powder tester manufactured by Hosokawa Micron Corporation). In the present invention, the range of AD / TD, which is the ratio of AD and TD, is set to 0.8 or more because the ratio of the two is such that the tantalum oxide powder is a mass formed by compression even when subjected to compression. It is because it is easy to unravel. A more preferable range of AD / TD is 0.85 ≦ AD / TD ≦ 0.98. The lower limit of 0.85 is that powders of 0.85 or more have particularly good mixing properties with other powders (for example, lithium carbonate powder). For example, a container rotating type mixer (or V-type mixer) This is because mixing can be easily performed even with a mixer having a simple structure as described above (in contrast, when AD / TD is less than 0.8, external force is applied like a mixer having rotating blades. A mixing type mixer must be used, and it is necessary to check the mixing state while adding external energy). Further, because of the significance of AD / TD, the value does not exceed 1.0, and the value of what can be practically manufactured is about 0.98.

The tantalum oxide particles according to the present invention particularly preferably have an average particle size (D ₅₀ ) of 10 to ₅₀ μm. When the thickness is less than 10 μm, the cohesiveness of the powder becomes high, the improvement of compressibility is not observed, and the powder easily adheres to the apparatus and is inferior in handling. Moreover, when it exceeds 50 micrometers, when mixing and melt | dissolving with a glass raw material powder, it takes time for making it melt | dissolve uniformly, and it is not practical.

  The tantalum oxide powder is more preferably one having a fluorine content of 10 ppm by weight or less. As an application of tantalum oxide, there is a raw material of lithium tantalate single crystal, and lithium tantalate is produced by a reaction between tantalum oxide and lithium carbonate. If fluorine exists in tantalum oxide, the reaction with lithium carbonate becomes non-uniform, and the produced single crystal is twisted, resulting in a single crystal with poor quality. Therefore, highly accurate lithium tantalate can be produced by setting the fluorine concentration to 10 ppm by weight or less as in the present invention. The fluorine concentration is more preferably 5 ppm by weight, particularly preferably 2 ppm by weight, and further preferably 1 ppm by weight or less. The lower limit of the fluorine concentration is preferably as low as possible, but it is preferably 0.1 ppm by weight or more as a manufacturable range.

  Next, the manufacturing method of the tantalum oxide powder according to the present invention will be described. As a method for producing tantalum oxide powder, a solvent extraction method has been conventionally used. In this method, first, a raw material containing tantalum is dissolved with hydrofluoric acid, an organic solvent such as 4-methyl-2-pentanone is brought into contact with this solution, and solvent extraction is performed to produce an aqueous tantalum solution. Then, by adding a solution containing ammonia to the tantalum aqueous solution and neutralizing it, tantalum in the tantalum aqueous solution is recovered as a hydroxide, and the tantalum hydroxide is roasted to obtain tantalum oxide.

  The method for producing tantalum oxide according to the present invention basically follows a method including the conventional solvent extraction method described above, but in the ammonia solution addition step, the ammonia addition rate (neutralization rate) is extremely low. It is characterized by performing.

  The reason for slowing the neutralization rate is as follows. The particles constituting the tantalum oxide powder are agglomerated particles formed by agglomeration of finer tantalum oxide particles. In order to obtain a powder that is not easily solidified by compression as intended in the present invention, the particles of the agglomerated particles are used. While matching the diameter, it is necessary to increase the bonding force between the particles constituting the aggregated particles and to appropriately increase the strength of the aggregated particles. This is because agglomerated particles having low strength are easily deformed and broken by an external pressure and are fixed to other agglomerated particles to form agglomerates with poor dispersibility. Then, as a means for increasing the strength of the aggregated particles appropriately while adjusting the particle diameters of the aggregated particles, adjusting the deposition rate of tantalum hydroxide can be considered. Therefore, in the present invention, the tantalum hydroxide is precipitated by controlling the neutralization rate at a low speed, thereby forming the precipitated tantalum hydroxide as dense agglomerated particles, making the particle size uniform, and the particle size distribution. It is trying to optimize. In this regard, the conventional method is not particularly conscious of the addition rate of the ammonia solution, and therefore, hydroxide precipitation occurs randomly. Therefore, in this method, a low-density (coarse) hydroxide is formed, and the particle size is uneven.

  In this ammonia addition step, ammonia is added until the neutralization rate is 1 to 5% / hour and the pH of the tantalum aqueous solution becomes 8 or more. The reason why the neutralization rate is 1 to 5% / hour is that the target aggregated particles are formed even if the neutralization rate is less than 1% / hour, but it takes an extremely long time and is inefficient. Further, if it exceeds 5% / hour, the precipitation of hydroxide starts to be non-uniform, and uniform aggregated particles cannot be obtained. The target value of the pH is set to 8 or more in order to precipitate tantalum hydroxide quantitatively. The neutralization rate at this time is calculated by calculating the amount of ammonia necessary to neutralize the tantalum metal ions in the tantalum aqueous solution, and calculating the amount of ammonia added per hour with this ammonia amount as 100%. Can be determined. The pH of the tantalum aqueous solution is preferably 11 or less. This is because a large amount of ammonia is added until the pH exceeds 11, because the cost becomes high.

  However, this low neutralization rate is preferable for forming suitable tantalum oxide particles, but the entire ammonia addition step is performed at this neutralization rate from the viewpoint of efficient and industrial production of tantalum oxide. It is not preferable. Therefore, in the present invention, the ammonia addition process is divided into two stages. In the first stage, ammonia is added at the same neutralization rate as before until precipitation of tantalum hydroxide, and in the second stage, tantalum hydroxide is added. It is preferable to control the particle size and adjust the strength of the particles.

  The ammonia addition process consisting of these two stages will be described. In the first stage, ammonia is added until the pH of the tantalum aqueous solution becomes 1 to 4. If the pH is less than 1, it is not sufficient as a preliminary stage for precipitation of tantalum oxide, and the time required for the subsequent ammonia addition process in the second stage becomes long and is not practical. On the other hand, when the pH exceeds 4, a large number of insufficiently aggregated hydroxides are generated, and uniform aggregated particles cannot be obtained. In addition, there is no restriction | limiting in particular about the addition rate (neutralization rate) of ammonia in this 1st step.

  And as for the neutralization speed | rate of the 2nd step of an ammonia addition process, it is preferable to add ammonia until the pH of a tantalum aqueous solution will be 8 or more by making a neutralization speed | rate 1-5% / hour like the above. The pH of the tantalum aqueous solution is preferably 11 or less. The reason is the same as above.

  In the ammonia addition step, it is preferable to perform the liquid temperature in a temperature range of 10 to 50 ° C. This is because, when the temperature is low, acicular precipitate particles are likely to be generated, and when the temperature is high, plate-like crystals are likely to be generated. It is preferable to suppress the temperature change at this time within 10 ° C.

  Further, it is preferable to use an ammonia solution having an ammonia concentration of 10 to 30% by weight. When ammonia water having an ammonia concentration of less than 10% by weight is used, the amount of addition increases and the productivity is remarkably lowered, which is inefficient. If it exceeds 30% by weight, it is difficult to control the precipitation of tantalum hydroxide. Thus, it becomes difficult to produce a hydroxide having a uniform particle size distribution. Moreover, it is preferable that the tantalum concentration in the aqueous tantalum solution when the ammonia solution is added is 40 to 120 g / l.

  The tantalum oxide powder produced as described above preferably has a low fluorine concentration. Therefore, in the method according to the present invention, it is preferable to wash the precipitated tantalum hydroxide and remove fluorine remaining in the hydroxide. As a washing method, it is preferable to use a solution having an ammonia concentration of 0.1% by weight or more as washing water and wash the washing water at a temperature of 30 to 100 ° C, particularly 30 to 70 ° C. The reason for limiting the ammonia concentration in the washing water is that if it is less than 0.1% by weight, the effect of removing fluorine is low, and it is difficult to remove fluorine unless washing is repeated a considerable number of times. On the other hand, there is no limitation on the ammonia concentration of the cleaning water from the viewpoint of the effect of removing fluorine, but there is no difference in the effect even when using a cleaning liquid exceeding 2% by weight, and the cost of the cleaning liquid is increased. The ammonia concentration is preferably 2% by weight or less. Further, it is confirmed that the temperature range of the cleaning liquid is less than 30 ° C., even if the ammonia concentration is appropriate, the effect of efficient fluorine removal does not occur. Furthermore, even if the temperature exceeds 70 ° C., the effect of removing fluorine does not change, and the cost of heating and the apparatus is increased. In particular, it becomes significant when the temperature exceeds 100 ° C.

  The tantalum hydroxide is preferably washed until the fluorine concentration in the hydroxide becomes 1.0% by weight or less. The fluorine concentration in the hydroxide after washing naturally affects the fluorine concentration of tantalum oxide after roasting. Here, fluorine is volatilized and removed by roasting, but for tantalum hydroxide having a fluorine concentration exceeding 1.0% by weight, fluorine exceeding 10 wt ppm remains in the tantalum oxide even after roasting. It will be. The fluorine concentration in the tantalum hydroxide is more preferably washed to 0.5% by weight or less. Further, since fluorine has an action of promoting aggregation of tantalum oxide during roasting, in order not to form a large lump of oxide, the fluorine concentration in tantalum hydroxide is up to 0.1% by weight or less. More preferably, it is washed. The fluorine concentration in the hydroxide here is based on the weight of the hydroxide at the time of drying in order to eliminate the influence of moisture. Therefore, when the hydroxide is not dried, or when drying is insufficient and moisture remains, it is necessary to heat it to about 105 ° C. and dry it sufficiently before measuring the fluorine concentration.

  As a method for washing tantalum hydroxide, the precipitated tantalum hydroxide is collected, added with washing water, stirred and allowed to stand, the solid content is allowed to settle, the supernatant liquid is extracted, and washing water is further added. What is added by so-called repulp washing is preferred.

  In the method according to the present invention, the step of producing the tantalum aqueous solution and the step after tantalum hydroxide precipitation are not particularly limited. The process for producing the tantalum aqueous solution is not particularly limited as long as it is a raw material containing tantalum, and may be ore, scrap, or the like. As a solvent for solvent extraction after mixing the raw material with hydrofluoric acid, 4-methyl-2-pentanone, tributyl phosphate, octanol, etc., an organic solvent having low mutual solubility with water, or these were diluted with kerosene, etc. Organic solvents can be applied. Moreover, a quaternary ammonium salt etc. can also be used as a solvent. Further, a separation and purification method using an anion exchange resin can be applied instead of solvent extraction. The tantalum aqueous solution produced in this way usually contains a small amount of hydrofluoric acid and ammonium fluoride.

  The conditions for roasting the precipitated tantalum hydroxide are preferably heating at 800 ° C. to 1200 ° C. for 1 hour to 24 hours. The tantalum oxide lump after roasting can be loosened with a reiki machine, a sieve or the like. Note that sand mills, simpson mullers and the like, which are general pulverizers, are not preferred for use in the present invention because they may destroy the tantalum oxide particles and impair the uniformity of the particles.

  The tantalum oxide powder according to the present invention manufactured through the above manufacturing method has the aggregated particles having substantially the same particle size, and further has a high bonding strength between the particles constituting the aggregated particles and a moderately high strength. It is. Here, it is difficult to directly measure the strength (hardness) of the particles. For example, the tantalum oxide powder according to the present invention is a laser after applying 30 W ultrasonic waves in a solvent for 2 minutes. The average particle diameter determined by diffraction particle size distribution measurement is 0.5 to 1 times the average particle diameter of the ferret diameter determined from SEM. This indicates that the particles are difficult to be destroyed by external pressure due to vibration or the like, and it is understood that the present invention is made of tantalum oxide having high strength by such an indirect measurement.

  As described above, the tantalum oxide powder according to the present invention is a powder that has an excellent particle size distribution and does not compress or solidify even when subjected to vibration due to transportation or the like. And a favorable mixed state can be obtained also at the time of mixing with other powders, such as glass raw material powder. Further, the tantalum oxide powder according to the present invention is less likely to adhere to the apparatus wall surface. The present invention is a tantalum oxide powder suitable for glass additives and the like. Furthermore, the tantalum oxide powder according to the present invention has a reduced fluorine concentration and is suitable as a raw material for high-quality single crystals without twisting as a raw material for lithium tantalate single crystals.

  Hereinafter, preferred embodiments of the tantalum oxide powder and the production method thereof according to the present invention will be described.

Example 1 : A tantalum-containing raw material (tantalum condenser scrap) was dissolved with hydrofluoric acid, 4-methyl-2-pentanone was added to this solution as an organic phase, and solvent extraction was performed. A small amount of hydrofluoric acid was then added. An aqueous tantalum solution was prepared. The tantalum metal ion concentration in this tantalum aqueous solution was 70 g / l, and the liquid volume was 2500 l.

  Ammonia was added to the aqueous tantalum solution, neutralized to pH 2, and maintained at 35 ° C. with stirring (first stage). At this time, the generation of precipitates in the solution was not observed with the naked eye.

  Next, ammonia (82 kg), which is 5 times the tantalum metal ion concentration, was added to the aqueous tantalum solution so that the neutralization rate per hour was 2% (second stage). This ammonia was added over 50 hours while maintaining the liquid temperature at 35 ± 5 ° C., and ammonia was added at the same rate until the pH reached 9, resulting in a slurry of hydroxide.

  The obtained slurry was filtered, washed with 1 wt% ammonia water (temperature 20 ° C.), and further washed with pure water to obtain a tantalum hydroxide cake containing 1.5 wt% fluorine. And this cake was baked at 1000 degreeC and it was set as the tantalum oxide powder.

Example 2 As in Example 1, the first stage of ammonia addition was performed, and the neutralization rate during the second stage of ammonia addition was 1% / hour. The other operations were the same as in Example 1. The fluorine content of the hydroxide obtained in the process of this example was 3.2% by weight.

Example 3 As in Example 1, the first-stage ammonia addition was performed, and the neutralization rate during the second-stage ammonia addition was 5% / hour. The other operations were the same as in Example 1. The fluorine content of the hydroxide obtained in the process of this example was 1.4% by weight.

Comparative example 1 : As comparison with the said Example , the commercially available tantalum oxide powder (The Stark company make, grade name: Ultrapure) was first used for the evaluation object.

Comparative Example 2 : Here, a tantalum aqueous solution was produced in the same manner as in Example 1, and ammonia (82 kg), which is 5 times the tantalum metal ion concentration, was added in one hour (that is, the neutralization rate per hour was changed). Only one stage of ammonia addition to 100% was performed.) The other operations were the same as in Example 1. In addition, the fluorine content of the hydroxide obtained in the process of this comparative example was 1.3% by weight.

  With respect to the above tantalum oxide powder, the form of the powder was observed 500 times with a scanning electron microscope, and the particle diameter was measured in a fixed direction for 300 particles to obtain a ferret diameter. Further, the tap bulk density (TD) and the loose bulk density (AD) were measured with a powder tester PT-R manufactured by Hosokawa Micron Corporation. In addition, the powder after the tap bulk density measurement was evaluated for ease of mixing with other powders (hereinafter referred to as dry blend) and adhesion. In this evaluation, the powder after measuring the tapped bulk density was put together with lithium carbonate of the same weight into a wide-mouthed polybin, shaken for 3 minutes with a shaker (amplitude 50 mm, 60 times / min), and the state of the powder in the polybin was observed. Was not visually observed as a dry blend ○, and what was seen as x. Moreover, the adhesion state of the powder to a polybin wall surface was observed, and what was not attached was made into adhesiveness (circle), and what was seen was set as x. Table 1 shows a summary of these evaluation results.

As can be seen from Table 1, it was confirmed that the tantalum oxide powders according to Examples 1 to 3 in which D ₉₀ / D ₁₀ and AD / TD were in appropriate ranges had good dry blend and adhesion. On the other hand, Comparative Example 1, which is a commercial product, was confirmed to be inferior to dry blending, although there was no problem with the adhesion. Moreover, it turned out that the dry blend and adhesiveness are inferior in the comparative example 2 which performed ammonia addition to the tantalum aqueous solution at once like the past.

  Next, in order to examine the hardness (strength) of each tantalum oxide powder, the particle size distribution was measured using LA-920 manufactured by Horiba, Ltd. as a laser diffraction measuring device, and the average particle size was determined. . Here, a sample of tantalum oxide powder dispersed in water was placed in an apparatus, 30 W ultrasonic waves were applied for 2 minutes with an ultrasonic apparatus attached to the apparatus, and the particle size distribution was immediately measured. And the value of the average particle diameter obtained here was compared with the average particle diameter obtained from the ferret diameter measured by SEM observation in the powder state. The results are shown in Table 2.

  From Table 2, in the tantalum oxide powders according to Comparative Examples 1 and 2, the ratio (B / A) between the average particle diameter after application of ultrasonic waves and the average particle diameter determined from the ferret diameter measured by SEM observation is Is also below 0.5. This is considered to be due to the fact that the tantalum oxide powder of the comparative example collapses into fine particles by breaking up the aggregated particles by application of ultrasonic waves. On the other hand, in the tantalum oxide powder according to Examples 1 to 3, B / A is 0.69 to 0.89 and a value exceeding 0.5, and the aggregated particles do not collapse even after application of ultrasonic waves. The particle size is maintained. From this test result, it was confirmed that the tantalum oxide powder according to the example had higher strength (hardness) of the aggregated particles than the conventional product.

  1 to 3 are SEM images of the tantalum oxide powder produced in Example 1 (the magnifications are 200 times, 500 times, and 5000 times, respectively). The tantalum oxide powder produced in Example 1 was found to have almost spherical particles. Moreover, it can be confirmed from the photograph that the particle diameters are almost uniform. Further, when this tantalum oxide powder was observed at a high magnification of 5000 times, it was found that the surface was covered with needle-like crystals as a form of aggregated particles. 4 to 6 are SEM images of the tantalum oxide powder of Comparative Example 2. Comparing the two clearly shows that there is a big difference in the form.

Example 4 : A tantalum aqueous solution containing hydrofluoric acid was prepared by dissolving a tantalum-containing raw material with hydrofluoric acid and performing solvent extraction. The tantalum metal ion concentration in the tantalum aqueous solution at this time was 85 g / l, and the liquid volume was 2700 l. Then, similarly to Example 1, ammonia was added to the tantalum aqueous solution, neutralized to pH 2, and maintained at 35 ° C. with stirring (first stage).

  Next, 25% by weight of aqueous ammonia was added until the pH reached 9 so that the neutralization rate was 1% / hour, and the temperature was maintained at 38 ° C. with stirring. At this time, 475 l of aqueous ammonia was added.

  Then, the obtained slurry is allowed to stand to precipitate hydroxide, the supernatant is taken out, the precipitate is taken out, and repulp washing is performed using ammonia water having a liquid temperature of 50 ° C. and a concentration of 1.1% by weight as a washing liquid (the number of washings). : 6 times, amount of washing liquid: 3000 l / time, washing (stirring) time: 1 hour / time). After washing, the tantalum hydroxide cake obtained by filtering with a filter press is heated and dried at 130 ° C. for 15 hours, further baked at 1100 ° C. for 4 hours, and oxidized by vibration sieve classification (aperture 500 μm). Tantalum powder was used.

Examples 5 and 6 : Here, neutralization was performed in Example 4 so that the neutralization rate was 1.5% / hour and 5% / hour. Other conditions are the same as in the fourth embodiment.

Comparative Example 3 Tantalum oxide powder was manufactured at a neutralization rate of 10% / hour with respect to Examples 4 to 6. Other conditions are the same as in the fourth embodiment.

Examples 4 to 6 : For the tantalum oxide powder produced in Comparative Example 3, the ferret diameter, tap bulk density (TD), and loose bulk density (AD) were measured in the same manner as in Examples 1 to 3. Furthermore, dry blend and adhesion were evaluated. The results are shown in Table 3.

From Table 3, it was confirmed that a tantalum oxide powder having suitable particle characteristics can be produced by maintaining the neutralization rate at a low rate of 5% or less as in Examples 4 to 6. And it has confirmed that the tantalum oxide powder which concerns on these Examples was also good in dry blend and adhesiveness. On the other hand, when the neutralization rate exceeds 10% / hour and exceeds 5% / hour as in Comparative Example 3, the resulting tantalum oxide powder has a D ₉₀ / D ₁₀ of more than 3 and an AD / TD of 0.8. The dry blend and adhesion were poor. 7 to 9 are SEM images showing the appearance of the tantalum oxide powder produced in Example 6. FIG. From these, it was confirmed that the tantalum oxide powder according to Example 6 had a substantially spherical shape similar to that of the tantalum oxide powder according to Example 1.

  Moreover, the fluorine concentration was measured about the tantalum hydroxide after washing | cleaning and the manufactured tantalum oxide by the manufacturing process of Example 4-6. In this fluorine concentration measurement, the hydroxide was alkali-melted and then extracted with hot water, and measured by the fluoride ion electrode method. The fluorine concentration of the oxide was measured by thermal hydrolysis separation lanthanum / alizarin complexone spectrophotometry. The results are shown in Table 4.

  As can be seen from Table 4, it was confirmed that the tantalum oxide powders of Examples 4 to 6 that had been subjected to an appropriate cleaning operation had a fluorine concentration of 3 ppm by weight or less.

Example 7 : Here, in the process of Example 4, the neutralization rate was fixed at 2% / hour, and among the conditions of the cleaning process, the temperature of cleaning water (1.1 wt% ammonia water) and the number of times of cleaning were set. Various changes were made to produce tantalum oxide powder. And the fluorine concentration in the hydroxide and tantalum oxide after washing was measured and examined. The conditions other than the neutralization rate and cleaning solution temperature / number of times were the same as in Example 4. The results are shown in Table 5.

  From Table 5, when the cleaning water temperature is less than 30 ° C., no matter how many times the cleaning is performed, fluorine cannot be sufficiently removed from the hydroxide. As a result, high concentration of fluorine is also present in the tantalum oxide powder. Remains. In this regard, although ammonia water cleaning was performed in the first embodiment, the liquid temperature was 20 ° C., so it can be said that the residual fluorine concentration was high. In addition, even if the liquid temperature is appropriate (30 ° C.), fluorine may remain in the tantalum oxide powder unless it is washed repeatedly until the fluorine concentration in the tantalum hydroxide is sufficiently reduced to 1% by weight or less. It could be confirmed. From Table 5, it can be considered that the fluorine concentration in the tantalum oxide needs to be cleaned up to a fluorine concentration of about 1% by weight in order to make it 10 ppm or less.

Example 8 : Here, in Example 4, the neutralization rate was fixed at 2% / hour, and cleaning was performed using cleaning water having various ammonia concentrations to produce tantalum oxide powder. And the fluorine concentration in the hydroxide and tantalum oxide after washing was measured and examined. The conditions other than the neutralization rate and cleaning solution concentration were the same as in Example 4. The results are shown in Table 6.

  From Table 6, it can be seen that when the ammonia concentration of the washing water is less than 0.1% by weight, the fluorine concentration in the produced tantalum oxide powder cannot be made 10 ppm by weight or less. On the other hand, even when the ammonia concentration was 5% by weight, the effect of removing fluorine was not changed from the case of 2% by weight, and it was confirmed that excessive ammonia concentration was not effective for removing fluorine.

  And the lithium tantalate single crystal was manufactured using the tantalum oxide powder manufactured in Example 8, and the property was examined. Each tantalum oxide powder and 99.99% by weight of lithium carbonate powder were mixed at a ratio of 227.133 g: 35.91 g (51.40: 48.60 in molar ratio) and put into a platinum crucible. This was melted by high-frequency heating, and a lithium tantalate single crystal was produced from this melt by the Czochralski method (growth speed 0.5 mm / h, rotation speed 30 rpm). And the external appearance of the manufactured single crystal was inspected and the presence or absence of twist was investigated. The results are shown in Table 7.

  As can be seen from Table 7, when the fluorine concentration in the tantalum oxide powder exceeds 10 ppm by weight, a lithium tantalate single crystal with many twists is produced. Therefore, when producing a high-quality lithium tantalate single crystal, it is necessary to reduce the amount of residual fluorine in addition to improving the mixability (dry blend) of the tantalum oxide powder. In addition to controlling the neutralization rate, it was confirmed that it is preferable to perform an appropriate washing step.

2 is an SEM image (× 200) of the tantalum oxide powder produced in Example 1. FIG. 3 is an SEM image (× 500) of the tantalum oxide powder produced in Example 1. FIG. 2 is an SEM image (x5000) of the tantalum oxide powder produced in Example 1. FIG. 4 is an SEM image (× 100) of the tantalum oxide powder produced in Comparative Example 2. FIG. 4 is an SEM image (× 1000) of the tantalum oxide powder produced in Comparative Example 2. FIG. 3 is an SEM image (x5000) of the tantalum oxide powder produced in Comparative Example 2. FIG. 4 is an SEM image (× 200) of the tantalum oxide powder produced in Example 6. FIG. 4 is an SEM image (× 500) of the tantalum oxide powder produced in Example 6. FIG. 4 is an SEM image (× 5000) of the tantalum oxide powder produced in Example 6. FIG.

Claims (7)

Tantalum oxide powder having both of the following three conditions.
(1) Feret diameters D ₁₀ and D ₉₀ in particle size distribution measurement using a scanning electron microscope have a relationship of 1 ≦ D ₉₀ / D ₁₀ ≦ 3.
(2) The tap bulk density (TD) and the loose bulk density (AD) have a relationship of 0.8 ≦ AD / TD.
(3) The average particle diameter D50 in the particle size distribution measurement using a scanning electron microscope is _10-50 micrometers. The tantalum oxide powder according to claim 1 , wherein the fluorine content is 10 ppm by weight or less. In the method for producing tantalum oxide powder, including a step of depositing a tantalum hydroxide by adding a solution containing ammonia to an aqueous solution containing tantalum, a step of roasting the tantalum hydroxide,
The step of adding the solution containing ammonia comprises adding a solution containing ammonia until the neutralization rate is 1 to 5% / hour and the pH of the aqueous solution containing tantalum is 8 or more. Manufacturing method. The step of adding the solution containing ammonia includes
Adding a solution containing ammonia until the pH of the aqueous solution containing tantalum is 1-4;
A method for producing a tantalum oxide powder according to claim 3 , comprising a second step of adding a solution containing ammonia until the pH of the aqueous tantalum solution becomes 8 or more at a neutralization rate of 1 to 5% / hour. The manufacturing method of the tantalum oxide powder of Claim 3 or Claim 4 which adds ammonia solution, maintaining the liquid temperature of tantalum aqueous solution at 10-50 degreeC. The precipitated tantalum hydroxide is washed with washing water having a liquid temperature of 30 to 70 ° C. and an ammonia concentration of 0.1% by weight or more to remove fluorine in the tantalum hydroxide, and then the tantalum hydroxide is roasted. The method for producing a tantalum oxide powder according to any one of claims 3 to 5 , wherein the tantalum oxide powder is fired. The method for producing a tantalum oxide powder according to claim 6 , wherein the tantalum hydroxide powder is washed until the fluorine concentration in the tantalum hydroxide is 1.0 wt% or less.

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