JP4646055B2 - Tantalum oxide sol and method for producing the same - Google Patents

Description

  The present invention relates to a tantalum oxide sol and a method for producing the same. More specifically, the present invention relates to a novel tantalum oxide sol stabilized by one or more oxycarboxylic acids selected from citric acid, tartaric acid and malic acid, and a method for producing the same.

In recent years, there has been a demand for using tantalum oxide in various applications such as optoelectronic materials, semiconductor materials, antireflection materials, refractive index adjusting materials, high refractive index lenses, rust prevention materials, electrode materials, catalysts, functional paints, etc. In particular, there is a demand for a tantalum oxide raw material having a small particle size and a uniform particle size distribution because of demands for finer and higher performance of these materials.
In order to meet such a demand, a technique for providing a tantalum oxide sol having a particle diameter of several tens of nanometers or less has been developed. For example, the applicant of the present application has developed a technology related to an oxalic acid-stable tantalum oxide sol that can be used for various applications, and filed an application first (see, for example, Patent Document 1).

In the invention described in Patent Document 1, oxalic acid is added to an active tantalum hydroxide compound so that the oxalic acid / Ta ₂ O ₅ molar ratio is in the range of 5 to 30 and a heating reaction is performed. A tantalum oxide sol having a particle diameter of 50 nm or less, in which the tantalum oxide is in the range of oxalic acid / Ta ₂ O ₅ molar ratio 0.5 to 5.0, is obtained. However, since the sol is stabilized with oxalic acid, its use is limited because it is a deleterious substance. On the other hand, from the viewpoint of production, a large amount of oxalic acid is required for peptization of tantalum hydroxide, and after the reaction, a large amount of oxalic acid is discharged out of the system. At present, there is a strong demand for the appearance of tantalum oxide sols.

JP-A-8-143315

  In view of the above situation, the present inventors have conducted extensive studies on a tantalum oxide sol that does not use oxalic acid. As a result, a hydrofluoric acid solution and an alkali solution of tantalum in the presence of a specific oxycarboxylic acid are obtained. As a result of the reaction, it has been found that a novel tantalum oxide sol having a small particle size and a uniform particle size distribution can be obtained, and the present invention has been completed based on such knowledge.

That is, the present invention is click-enoic acid, in the presence of at least one hydroxycarboxylic acid selected from tartaric acid and malic acid, and hydrofluoric acid solution of 0.05 to 5 wt% of tantalum Ta ₂ O ₅ concentration The present invention relates to a method for producing a tantalum oxide sol, wherein an alkaline solution is reacted and the pH after the reaction is 7 or more. However, the abundance of oxycarboxylic acid is in the range of 0.05 to 10 as oxycarboxylic acid / Ta ₂ O ₅ (molar ratio) with respect to the tantalum hydrofluoric acid solution.

  The tantalum oxide sol stabilized with at least one oxycarboxylic acid selected from citric acid, tartaric acid and malic acid of the present invention does not contain oxalic acid, which is a deleterious substance, and thus is easily industrially produced. There is an advantage that it can be used without being particularly limited as a raw material of the material. Further, the particle diameter can be adjusted by adjusting the amount of oxycarboxylic acid used in the reaction, and a tantalum oxide sol having a small particle diameter and a uniform particle size distribution can be obtained.

First, a tantalum oxide sol containing at least one oxycarboxylic acid selected from citric acid, tartaric acid and malic acid of the present invention in the range of oxycarboxylic acid / Ta ₂ O ₅ (molar ratio) 0.05-10. Detailed description. The tantalum oxide sol of the present invention is a novel sol that is stabilized by firmly bonding tantalum oxide particles with at least one oxycarboxylic acid selected from citric acid, tartaric acid and malic acid. By the way, the tantalum oxide sol of the present invention is not limited to Ta ₂ O ₅ but means tantalum hydroxide or a partially hydrated sol. Hereinafter, in order to further explain the sol of the present invention, a specific example will be used.

"Example 1"
After dissolving 50 g of tantalum oxide (purity Ta ₂ O ₅ 99.995 mass%) (manufactured by Taki Chemical Co., Ltd.) in 525 g of hydrofluoric acid (HF 10 mass%), 9,425 g of pure water was added and Ta ₂ was added. A hydrofluoric acid solution of 0.5 mass% O ₅ tantalum was obtained. To this solution, 95 g of citric acid / monohydrate (manufactured by Wako Pure Chemical Industries, Ltd.) was added so as to give a citric acid / Ta ₂ O ₅ molar ratio of 4.0 and completely dissolved. This solution was added to ammonia water (1.0 mass% of NH ₃ ) 7,216 g with stirring for 60 minutes. After completion of the addition, an ultrafiltration module (SLP-1053 manufactured by Asahi Kasei Kogyo Co., Ltd.) was used, and the filtrate was washed until the electrical conductivity reached 20 mS / m to remove impurities, thereby obtaining the sol of the present invention. The composition analysis of the obtained sol was performed, and the results are shown in Table 1.

"Specific examples 2 and 3"
Instead of the citric acid monohydrate of Example 1, 67.9 g of tartaric acid (manufactured by Wako Pure Chemical Industries, Ltd.) (specific example 2), 60.6 g of malic acid (manufactured by Wako Pure Chemical Industries, Ltd.) ( Using Example 3), it was added to 6,447 g of ammonia water (NH ₃ 1.0% by mass) to obtain a sol of the present invention in the same manner. The composition analysis of the obtained sol was performed, and the results are shown in Table 1.

"Comparative Example 1"
In place of the citric acid in Example 1, 40.7 g of lactic acid (manufactured by Wako Pure Chemical Industries, Ltd.) was used and added to 5,678 g of ammonia water (NH ₃ 1.0% by mass) in the same manner. Produced and became cloudy, and a sol could not be obtained. The results are shown in Table 1.

"Comparative Example 2"
In place of the citric acid of Example 1, oxalic acid dihydrate (manufactured by Wako Pure Chemical Industries, Ltd.) 57.0 g was similarly added to ammonia solution (NH ₃ 1.0 mass%) 6,447 g. However, immediately after the addition, an aggregated precipitate was formed and became cloudy and a sol could not be obtained. The results are shown in Table 1.

  As a result of observing the state of the sol after leaving the sol obtained in Examples 1 to 3 at 30 ° C. for 30 days, these sols of the present invention showed no formation of precipitates even after 30 days and were stable. The solution was present.

The characteristics of the tantalum oxide sol of the present invention will be described as follows. In the sol of the present invention, among oxycarboxylic acids which are organic acid species, only those stabilized with citric acid, tartaric acid and malic acid can obtain a uniform and highly stable sol. So you can't get a sol. Also, oxalic acid that was effective in the conventional tantalum oxide sol manufacturing method is not clear about its mechanism, but it cannot be used in the present invention, and contains oxalic acid, which is a deleterious substance that has been a problem until now. Therefore, it is a very significant sol in terms of production and use. More specifically, the conventional tantalum oxide sol using oxalic acid required oxalic acid with an oxalic acid / Ta ₂ O ₅ molar ratio of 0.5 or more for stabilization, but the sol of the present invention is limited. By using an external filtration device or the like, the content of the oxycarboxylic acid can be reduced to oxycarboxylic acid / Ta ₂ O ₅ (molar ratio) of 0.5 or less. The sol with reduced oxycarboxylic acid as in the present invention is particularly useful for water-resistant coating agents and applications where it is desired to reduce residual carbon.

As for the particle size of the tantalum oxide sol of the present invention, the amount of at least one oxycarboxylic acid selected from citric acid, tartaric acid and malic acid, as well as the concentration of the tantalum hydrofluoric acid solution and alkali solution used. The tantalum oxide sol having an arbitrary particle size within a range of several nm to 800 nm can be provided. For example, when it is desired to obtain a tantalum sol having a small particle size, it can be specifically reduced to 10 nm or less by increasing the amount of oxycarboxylic acid relative to Ta ₂ O ₅ . It is transparent in appearance, and when used as a thin film, a film without turbidity can be provided.

  Next, the method for producing the tantalum oxide sol of the present invention will be described in detail. The sol production method of the present invention is characterized by reacting a hydrofluoric acid solution of tantalum with an alkaline solution in the presence of at least one oxycarboxylic acid selected from citric acid, tartaric acid and malic acid. What is noteworthy is that the tantalum oxide sol can be produced in a surprisingly simple manner that could not have been anticipated from the prior art.

The hydrofluoric acid solution of tantalum used in the present invention is a hydrofluoric acid of tantalum or a mixed acid solution of hydrofluoric acid and mineral acid, such as a tantalum salt such as tantalum hydroxide, tantalum oxide, tantalum chloride, etc. Can be used as a raw material, and a solution obtained by decomposing and dissolving this with hydrofluoric acid or a mixed acid solution of hydrofluoric acid and mineral acid can be used. Moreover, a hydrofluoric acid solution of tantalum ore extracted by dissolving tantalum ore with a mixed acid can also be used. Regarding the concentration of the tantalum hydrofluoric acid solution, the Ta ₂ O ₅ concentration may be used in the range of 0.05 to 5% by mass. Below the lower limit, the reaction volume becomes excessive, the production efficiency decreases, and the amount of waste water during production increases, which is not economical in industrial production. On the other hand, when the upper limit is exceeded, aggregation of the tantalum hydrate produced during neutralization becomes strong, and aggregation precipitation is likely to occur, and a stable sol cannot be produced. Regarding the concentration of hydrofluoric acid used for dissolving tantalum, 1 to 70% by mass as HF is preferable in the case of hydrofluoric acid alone. In the case of a mixed acid of hydrofluoric acid and mineral acid, 5 mol or more of hydrofluoric acid is used per 1 mol of mineral acid, and the hydrofluoric acid concentration in the mixed acid is 1 to 60% by mass as HF. good.

  The alkali solution used in the present invention is not particularly limited as long as it reacts with a tantalum hydrofluoric acid solution to form tantalum oxide, but is not limited to hydroxide of alkali metal such as aqueous ammonia, sodium, potassium, etc. And aqueous solutions of alkaline earth metal hydroxides such as calcium and the like. The concentration of this alkaline solution cannot be specified by the type of tantalum hydrofluoric acid solution used, the acid concentration, the type of alkaline solution used, the type of oxycarboxylic acid that coexists during neutralization, etc. What is necessary is just to use for reaction in the range of 0.05-5 mass%. Regarding the amount of the alkaline solution used, it is necessary that the tantalum hydrofluoric acid solution is sufficiently neutralized, and the pH after the reaction needs to be 7 or more. When the pH is 7 or less, tantalum exists in an ionized state and cannot be in the form of a sol, resulting in a decrease in yield. Specifically, when the tantalum hydrofluoric acid solution and aqueous ammonia are reacted in the presence of citric acid, the number of moles of ammonia / (number of moles of hydrofluoric acid + number of moles of citric acid × 3) 1 or more is required.

  In the present invention, in the presence of at least one oxycarboxylic acid selected from citric acid, tartaric acid and malic acid, the prepared tantalum hydrofluoric acid solution and alkali solution are then subjected to the reaction. As the oxycarboxylic acid used in the present invention, citric acid, tartaric acid, malic acid, and water-soluble salts thereof are desirable, and examples thereof include citric acid, tartaric acid, malic acid, and ammonium salts and sodium salts thereof. . It is particularly important to use at least one selected from citric acid, tartaric acid and malic acid and their water-soluble salts. Other than these, oxycarboxylic acids such as lactic acid and glycolic acid, and salts thereof and proposals so far The sol of the present invention cannot be obtained with carboxylic acids such as oxalic acid and salts thereof.

Regarding the amount of oxycarboxylic acid used, it is important to add oxycarboxylic acid / Ta ₂ O ₅ (molar ratio) in the range of 0.05 to 10 with respect to tantalum in the hydrofluoric acid solution of tantalum. It is. That is, when the oxycarboxylic acid / Ta ₂ O ₅ (molar ratio) is less than 0.05, aggregation between particles becomes remarkable and a sol cannot be obtained. On the contrary, oxycarboxylic acid / Ta ₂ O ₅ (molar ratio) If the ratio exceeds 10, sol production is possible, but there is no effect commensurate with the addition and it is not economical.

  Further, regarding the method of coexisting the oxycarboxylic acid of the present invention during the reaction of the tantalum hydrofluoric acid solution and the alkaline solution, it may be added to the acidic solution of tantalum or added to the alkaline solution for the reaction. Also good. Further, an acidic solution and an alkaline solution of tantalum may be added simultaneously to the oxycarboxylic acid solution of the present invention. What is important in the present invention is that oxycarboxylic acid coexists when tantalum oxide is formed. If the oxycarboxylic acid of the present invention is not present during the formation of tantalum oxide, the resulting tantalum oxide can no longer be peptized with the oxycarboxylic acid of the present invention, except for oxalic acid which is the method described in Patent Document 1. It cannot be made into a sol with any organic acid.

  By the way, the reaction temperature at the time of the reaction between the tantalum hydrofluoric acid solution and the alkali solution of the present invention is not particularly limited, and it is sufficient to control the temperature from the standpoint of quality stability. What is necessary is just to perform at -50 degreeC. Although it does not specifically limit regarding reaction time, What is necessary is just to make it react within the range of 30 minutes-3 hours according to reaction scale.

The tantalum oxide sol obtained by reacting as described above can be used as it is, but by means of ultrafiltration or the like, excess oxycarboxylic acid, or raw material fluorine ions or mineral acid ions used during production, Impurities such as alkali-derived cations can be removed and simultaneously adjusted to a desired concentration. When the impurities are sufficiently removed, more oxycarboxylic acid than necessary may be removed. Therefore, it is important to add the oxycarboxylic acid of the present invention within the above-mentioned range in a later step to obtain a stable tantalum oxide sol. is there. By performing such a reaction, the tantalum oxide sol of the present invention can obtain a tantalum oxide sol containing oxycarboxylic acid in the range of oxycarboxylic acid / Ta ₂ O ₅ (molar ratio) 0.05 to 10. it can. Since the tantalum oxide sol of the present invention is stabilized with oxycarboxylic acid, an organic solvent-dispersed tantalum oxide sol can be obtained based on the prior art.

Examples of the present invention will be described below and further explained, but the present invention is not limited to these. Moreover, unless otherwise indicated,% shows the mass% altogether.
The physical properties of the tantalum oxide sol of the present invention are measured by the following method.

(1) Measurement of average particle size The average particle size was measured using a dynamic light scattering color particle size distribution analyzer LB-500 (manufactured by Horiba, Ltd.).

(2) Measurement of haze ratio The haze ratio was measured using a color difference meter COH-300A (manufactured by Nippon Denshoku Industries Co., Ltd.). As a measurement condition, a sample having a Ta ₂ O ₅ concentration of 10% was put in a glass cell having an optical path length of 1 cm and measured.

After dissolving 50 g of tantalum oxide (purity Ta ₂ O ₅ 99.995 mass%) (manufactured by Taki Chemical Co., Ltd.) in 525 g of hydrofluoric acid (HF 10%), 9,425 g of pure water was added and Ta ₂ O was added. _{5 A} 0.5% tantalum hydrofluoric acid solution was obtained. To this solution, 35.6 g of citric acid / monohydrate (manufactured by Wako Pure Chemical Industries, Ltd.) was added so that the citric acid / Ta ₂ O ₅ molar ratio was 1.5, and the solution was completely dissolved. This solution was added to 5,774 g of aqueous ammonia (NH ₃ 1.0%) over 60 minutes. After completion of the addition, an ultrafiltration module (SLP-1053 manufactured by Asahi Kasei Kogyo Co., Ltd.) is used, the filtrate is washed until the electric conductivity becomes 20 mS / m, impurities are removed, and the sol (Ta ₂ O of the present invention) ₅ concentration 10%). The obtained sol was a white sol having a haze ratio of 31%, an average particle diameter of 109 nm, citric acid / Ta ₂ O ₅ (molar ratio) of 0.31, and fluorine of 290 ppm. As a result of observing the state at 30 ° C. for 30 days, a stable sol state was exhibited without thickening or precipitation.

50 g of tantalum oxide (purity Ta ₂ O ₅ 99.995% by mass) (manufactured by Taki Chemical Co., Ltd.) was mixed with hydrofluoric acid and sulfuric acid (HF / H ₂ SO ₄ (molar ratio) = 8.0, HF40) %) After being dissolved in 150 g, 9,850 g of pure water was added to obtain a 0.5% Ta ₂ O ₅ tantalum hydrofluoric acid solution. 166.3 g of citric acid monohydrate (manufactured by Wako Pure Chemical Industries, Ltd.) was used so that the citric acid / Ta ₂ O ₅ molar ratio of Example 1 was 7.0, and aqueous ammonia (NH ₃ 1.0%) A sol of the present invention was obtained in the same manner as in Example 1 using 11,456 g. The obtained sol was a fine white sol having a haze ratio of 4.4%, an average particle diameter of 11 nm, citric acid / Ta ₂ O ₅ (molar ratio) 0.61, fluorine 266 ppm, and SO ₄ 197 ppm. As a result of observing the state at 30 ° C. for 30 days, a stable sol state was exhibited without thickening or precipitation.

A sol of the present invention was obtained in the same manner as in Example 1 except that 13,586 g of an aqueous sodium hydroxide solution (1.0% NaOH) was used instead of 5,774 g of aqueous ammonia (NH ₃ 1.0%) in Example 1. The obtained sol was a white sol having a haze ratio of 29%, an average particle diameter of 91 nm, citric acid / Ta ₂ O ₅ (molar ratio) of 0.32, and fluorine of 238 ppm. As a result of observing the state at 30 ° C. for 30 days, a stable sol state was exhibited without thickening or precipitation.
“Comparative Example 3”

0.48 g of citric acid monohydrate (manufactured by Wako Pure Chemical Industries, Ltd.) was used so that the citric acid / Ta ₂ O ₅ molar ratio of Example 1 was 0.02, and ammonia water (NH ₃ 1.0%) Tested in the same manner as in Example 1 except that 4,921 g was used. As a result, a white precipitate was formed, and a sol could not be obtained.

Claims (1)

In the presence of at least one oxycarboxylic acid selected from citric acid, tartaric acid and malic acid, 0.05 to 5% by mass of a hydrofluoric acid solution of tantalum as a Ta ₂ O ₅ concentration and an alkali solution are reacted, A method for producing a tantalum oxide sol, wherein the pH after the reaction is 7 or more.
However, the abundance of oxycarboxylic acid is in the range of 0.05 to 10 as oxycarboxylic acid / Ta ₂ O ₅ (molar ratio) with respect to the tantalum hydrofluoric acid solution.