JP7591001B2 - Niobium oxide powder - Google Patents

Description

The present invention relates to niobium oxide powder.

Niobium oxide powder is widely used as a raw material for thin film forming materials such as lithium niobate (LN) single crystals, deposition pellets, and sputtering targets, optical products, and fine ceramics. Niobium oxide powder is required to have good fluidity and uniform mixability. In addition, with the exception of some applications, it is required to be easy to sinter at low temperatures and to react with powders other than niobium oxide powder at low temperatures.

Conventionally, niobium oxide powders used for the above-mentioned applications have been those having a relatively small particle size and large specific surface area, for example, an average particle size of 2.0 μm or less and a BET specific surface area of 5.0 m ² /g or more (see Patent Document 1).

Japanese Unexamined Patent Publication No. 6-103814

However, the niobium oxide powder disclosed in Patent Document 1 had a bulk density (TD) of 0.5 g/mL or less, and was therefore very bulky (low bulk density), prone to aggregation, and did not have a satisfactory level of flowability.

In view of the above problems, the present invention aims to provide a niobium oxide powder with excellent fluidity.

The niobium oxide powder of the present invention, which has been made to solve the above problems, is characterized in that the ratio D50(N)/D50(U) of the median diameter D50(N) of niobium oxide particles to the median diameter D50(U) obtained by irradiating the niobium oxide particles with ultrasound is 5 or less.
First, niobium oxide in the present invention is represented by the general formula Nb ₂ O ₅ (niobium pentoxide), but also includes various oxides having different oxidation numbers, and may include the compound alone, its hydrate, or its ammonium salt.
When the ratio D50(N)/D50(U) (also referred to as the D50 ratio) of the median diameter D50(N) of the niobium oxide particles to the median diameter D50(U) obtained by irradiating the niobium oxide particles with ultrasonic waves is 5 or less, the change in average particle size due to the presence or absence of ultrasonic treatment is small, and the niobium oxide particles have a structure in which they are fused to each other. When the primary particles have a fused structure (see FIG. 1) in which they are fused to each other, aggregation is suppressed, and as a result, the D50 ratio approaches the lower limit of 1, that is, a state in which there is no dispersion of aggregates by ultrasonic dispersion. By having such a fused structure, the formation of aggregates is suppressed and the fluidity is excellent, making it suitable as a raw material for thin film formation materials such as sputtering targets, optical products, or fine ceramics. Therefore, the D50 ratio is preferably 1 or more and 5 or less. Here, a D50 ratio of 1 indicates an ideal state in which there is no dispersion of aggregates by ultrasonic dispersion, so the closer the D50 ratio is to 1, the better, and it may be, for example, 1.1 or more or 1.2 or more. Also, the D50 ratio is more preferably 3 or less, even more preferably 2 or less, and particularly preferably 1.5 or less. On the other hand, if the D50 ratio exceeds 5, the above-mentioned fused structure cannot be sufficiently formed, and excessive aggregates that are largely dispersed by ultrasonic irradiation are formed, resulting in a decrease in fluidity.

Here, D50 indicates the particle size that reaches 50% by volume fraction. In the present invention, the particle size distribution is evaluated by a dynamic light scattering method conforming to JIS Z 8828:2019 using a laser diffraction/scattering particle size distribution measuring device (Microtrack Bell Co., Ltd.: MT3300EXII). In addition, filtering is not performed, and a dispersion process using ultrasonic waves as follows is performed.

Specifically, the median diameter D50 (N) of the niobium oxide particles is the median diameter of the niobium oxide powder that has been subjected to particle size evaluation without undergoing ultrasonic dispersion treatment. The median diameter D50 (N) of the niobium oxide particles also includes the median diameter D50 of the niobium oxide particles that have been subjected to ultrasonic dispersion treatment at a frequency and ultrasonic irradiation time that is less than the frequency and ultrasonic irradiation time described below. On the other hand, the median diameter D50 (U) obtained by irradiating the niobium oxide particles with ultrasonic waves is the median diameter of the niobium oxide powder that has been subjected to particle size evaluation immediately after the niobium oxide powder has been subjected to ultrasonic dispersion treatment. Specifically, the procedure for ultrasonic dispersion treatment is as follows. First, as a pretreatment for ultrasonic dispersion treatment, 1 mg of sample powder and 20 mL of pure water are placed in a 50 mL wide-mouthed PP bottle, and the PP wide-mouthed bottle is set in an ultrasonic cleaner (VS-100III, manufactured by AS ONE Corporation). Next, in a state where the inside of the tank of the cleaning machine is filled with pure water up to 5 cm above the floor surface, a dispersion treatment is carried out using ultrasonic waves at a frequency of 28 kHz and an output of 100 W for 60 minutes.

The niobium oxide powder of the present invention is characterized in that the niobium oxide particles have a specific surface area SSA of 1 m ² /g or less.
When the specific surface area SSA of the niobium oxide particles is 1 m ² /g or less, the niobium oxide particles have a structure in which they are fused together, and therefore the specific surface area SSA tends to be small. In particular, when the specific surface area SSA is 1 m ² /g or less, the adhesive force between the particles is further reduced, and the formation of aggregates can be suppressed, which is preferable in terms of improving fluidity. Here, the specific surface area SSA of the niobium oxide particles is measured in accordance with "6.2 Fluid method (3.5) One-point method" of JIS R 1626-1996 (Method of measuring specific surface area of fine ceramic powder by gas adsorption BET method). At that time, a mixed gas of helium as a carrier gas and nitrogen as an adsorbate gas is used. The lower limit of the specific surface area SSA of the niobium oxide particles is more than 0 m ² /g. The specific surface area SSA of the niobium oxide particles decreases as the niobium oxide particles form more fused structures, and may be, for example, 0.1 m ² /g or 0.2 m ² /g.

The niobium oxide powder of the present invention is characterized in that it has a specific surface area SSA of 0.4 m ² /g or less.
The specific surface area SSA of the niobium oxide particles is preferably more than 0 m ² /g and not more than 0.4 m ² /g in terms of further improving the fluidity as described above, and more preferably not more than 0.3 m ² /g.

The niobium oxide powder of the present invention is characterized in that the degree of compression calculated based on the loose bulk density AD and the compacted bulk density TD is 25% or less. The niobium oxide powder of the present invention is characterized in that the degree of compression is 20% or less.
The smaller the compression degree calculated based on the loose bulk density AD and the compacted bulk density TD, the less likely the niobium oxide powder of the present invention will aggregate when loaded into a hopper even under pressure, and the less likely it will stick to the wall of the hopper, so that high fluidity can be maintained, which is preferable. Specifically, the compression degree is preferably 25% or less, more preferably 20% or less, and even more preferably 18% or less. Here, the compression degree is theoretically ideal to be 0%, but may be 10% or more, or 15% or more.

Here, the method for measuring the compacted bulk density TD is to measure the compacted bulk density in accordance with "Part 12: Apparent density or apparent specific volume - Section 2: Tamp method" of JIS K 5101-12-2:2004 (Methods for measuring pigments). The method for measuring the loose bulk density AD is to measure the loose bulk density in accordance with "Part 12: Apparent density or apparent specific volume - Section 1: Static method" of JIS K 5101-12-1:2004 (Methods for measuring pigments). The degree of compression calculated based on the loose bulk density AD and the compacted bulk density TD is calculated by the formula: degree of compression (%) = ([compacted bulk density] - [loose bulk density] / [compacted bulk density]) x 100.

Furthermore, it is preferable that the compacted bulk density TD is 1.5 g/mL or more. Niobium oxide powder having a compacted bulk density TD of 1.5 g/mL or more is preferable in that it has a small degree of compression. It is more preferable that the compacted bulk density TD is 2.0 g/mL or more, even more preferable that it is 2.1 g/mL or more, particularly preferable that it is 2.3 g/mL or more, and particularly preferable that it is 2.5 g/mL or more. It is preferable that the compacted bulk density TD is 4.0 g/mL or less, and more preferable that it is 3.0 g/mL or less. On the other hand, it is preferable that the loose bulk density AD is 0.7 g/mL or more. Niobium oxide powder having a loose bulk density AD of 0.7 g/mL or more is preferable in that it has a small degree of compression. It is more preferable that the loose bulk density AD is 1.0 g/mL or more, even more preferable that it is 1.5 g/mL or more, and particularly preferable that it is 1.6 g/mL or more. Additionally, the loose bulk density AD is preferably 3.0 g/mL or less, and more preferably 2.0 g/mL or less.

The niobium oxide powder of the present invention is characterized in that the median diameter D50(U) is 5 μm or more and 120 μm or less.
The niobium oxide powder of the present invention is preferred in that if it has a fused structure in the particle size range of the median diameter D50 (U) of 5 μm or more and 120 μm or less, there is a tendency for the particle size reduction by the above-mentioned dispersion treatment to be difficult to progress.

The niobium oxide powder of the present invention is generally produced as follows. First, raw materials such as ores, alloys, or scraps containing niobium are prepared, and the raw materials are put into a vibrating mill to be pulverized. The pulverized product obtained is treated with an alkaline aqueous solution and washed with a mineral acid, so that the niobium in the raw materials is dissolved by hydrofluoric acid to obtain a solution containing niobium. Then, a niobium extraction solution adjustment solution is obtained by adjusting the concentration of hydrofluoric acid in the solution containing niobium and the concentration of mineral acids other than hydrofluoric acid (e.g., sulfuric acid). This niobium extraction solution adjustment solution is separated and refined by solvent extraction using an organic solvent of 4-methyl-2-pentanone to obtain a niobium fluoride solution (hereinafter referred to as a niobium refined solution). Next, ultrapure water is added to the niobium refined solution to obtain a niobium diluted solution. Furthermore, the niobium diluted solution and the ammonia water are mixed by a reverse neutralization method in which the niobium diluted solution is added to ammonia water to obtain a precipitate slurry containing niobium. The obtained precipitation slurry is subjected to solid-liquid separation, and the separated precipitation slurry is washed with a washing liquid and ultrapure water, and then squeezed to obtain a precipitation cake. The precipitation cake is then roasted, and the roasted product is pulverized to obtain the niobium oxide powder of the present invention.

When the above-mentioned niobium refined liquid is subjected to solvent extraction, the organic solvent used in the solvent extraction is preferably tributyl phosphate in addition to 4-methyl-2-pentanone. Note that 4-methyl-2-pentanone can be used without dilution, but tributyl phosphate is often used after diluting with a diluent such as a petroleum hydrocarbon.

The niobium fluoride solution thus separated and purified by solvent extraction has a niobium concentration in the solution, calculated as niobium oxide (Nb ₂ O ₅ ), of preferably 50 g/L to 500 g/L, more preferably 70 g/L to 400 g/L. When the niobium concentration in the solution is calculated as niobium oxide (Nb ₂ O ₅ ), the amount of wastewater can be kept within an appropriate amount of liquid, and unnecessary costs and labor are not required for wastewater treatment, and the heat generated when the niobium fluoride solution and the precipitant are mixed in the subsequent process can be suppressed, and the temperature during precipitation can be kept below a predetermined temperature. The niobium in the niobium fluoride solution is considered to be H ₂ NbOF ₅ or H ₂ NbOF ₇ . Here, in the case of the niobium fluoride solution obtained by the solvent extraction method, since there is little excess hydrofluoric acid, most of the niobium in the niobium fluoride solution is considered to be H ₂ NbOF ₅ .

The step of obtaining the above-mentioned niobium-containing precipitate slurry, i.e., the mixing and precipitation step, is characterized in that a solution in which niobium is dissolved is subjected to solvent extraction, ultrapure water is added to the obtained niobium purified solution, and the obtained niobium diluted solution is added to an alkaline aqueous solution by a reverse neutralization method to produce a niobium-containing precipitate slurry.
The above-mentioned mixing and precipitation step uses a reverse neutralization method in which a niobium dilution solution is added to an alkaline aqueous solution, for example, ammonia water, and therefore, since an acidic niobium dilution solution is added to an alkaline ammonia water, niobium hydroxide can be produced while maintaining a high pH. Here, an alkaline aqueous solution of ammonia water is used as a precipitant used to produce the precipitation slurry. As ammonia, gaseous, liquid, or aqueous solution can be used, but an aqueous ammonia solution (ammonia water) is more preferable in terms of excellent handling. Specifically, the ammonia water used as the precipitant is preferably 10% by weight or more, more preferably 25% by weight or more. In addition to ammonia water, other neutralizing agents such as caustic soda and ammonium hydrogen carbonate may also be used, and ammonia water may be used in combination with other neutralizing agents such as caustic soda and ammonium hydrogen carbonate.

In the mixing and precipitation process, it is preferable that the pH of the alkaline aqueous solution to which the niobium dilution solution is added is 10 or more. The pH of the alkaline aqueous solution is always 10 or more, that is, niobium hydroxide can be generated while maintaining the alkalinity, and it is advantageous in that niobium oxide with a large average particle size can be easily formed. Here, if the pH of the alkaline aqueous solution is less than 10, it is difficult to form a structure in which the niobium oxide particles are fused to each other, and the amount of niobium remaining in the solution increases, and the yield of the precipitate decreases, that is, the yield of the niobium oxide decreases. On the other hand, if the pH of the alkaline aqueous solution exceeds 11, the particle size of the niobium oxide particles becomes too large, which may hinder the uniformity of the mixture mixed and reacted with other powders. The process of washing and squeezing the generated precipitate slurry becomes difficult. In addition, in the positive neutralization method in which an alkaline aqueous solution is added to an acidic niobium dilution solution, the pH of the mixture of the niobium dilution solution and the alkaline aqueous solution changes from acidic to alkaline while niobium hydroxide is generated, so the average particle size of the niobium oxide formed is unlikely to become large. The pH is measured by placing a tabletop pH meter (Horiba, Ltd.: F-71S: Standard Tou pH electrode) in the precipitation tank, and the mixture of the niobium diluted solution and the alkaline aqueous solution is measured during the addition of the niobium diluted solution and during stirring for 10 minutes after the addition. The pH is measured after confirming that the liquid temperature has stabilized at 25°C. Furthermore, during the mixing and precipitation process, the temperature of the mixture of the niobium diluted solution and the alkaline aqueous solution may be adjusted to 100°C or less. The temperature of the mixture is preferably 80°C or less, more preferably 50°C or less, and even more preferably room temperature. Here, in order to adjust the temperature to the above-mentioned range, heating with steam or a heater, or cooling with a heat exchanger or a cooling unit may be performed.

The precipitated slurry after solid-liquid separation can be washed with a cleaning solution and ultrapure water to reduce the amount of remaining fluorine. For example, when filtering using a filter, the precipitated slurry can be washed by passing a cleaning solution through the filter, or by putting the filter cake and cleaning solution into a washing tank equipped with a stirring means, stirring, and filtering again. When a filter is not used and the supernatant liquid is extracted after settling of the precipitate, the washing is performed by adding a cleaning solution after the supernatant liquid is extracted and thoroughly stirring, stopping the stirring to allow the precipitate to settle, and then extracting the supernatant liquid. This series of washing operations is performed multiple times.

The cleaning solution is preferably an ammoniacal aqueous solution, which is an aqueous solution containing ammonia or ammonium ions and is the same type of aqueous solution as the precipitant. Specifically, ammonia water of 5.0% by weight or less is preferable, ammonia water of 4.0% by weight or less is more preferable, ammonia water of 3.0% by weight or less is even more preferable, and ammonia water of 2.5% by weight is particularly preferable. With ammonia water of 5.0% by weight or less, the ammonia and ammonium ions are suitable for fluorine, and unnecessary increases in costs can be avoided. Furthermore, as the water to be used for cleaning after cleaning with ammonia water, the fewer impurities the better, so ultrapure water is suitable.

The precipitated slurry that has been washed with the above-mentioned washing liquid is fed into a press and squeezed to obtain a precipitated cake.

The precipitate cake obtained by squeezing is placed in a static furnace and fired at a predetermined heating temperature. The heating temperature is preferably 500°C or more and 2,000°C or less. If the heating temperature is 500°C or more and 2,000°C or less, it is a temperature sufficient for the growth of niobium oxide particles, and the firing cost can be suppressed. In addition, since the fired product obtained by firing does not become a hard lump, the labor and cost increase of crushing can be avoided. Furthermore, the heating temperature is more preferably 700°C or more and 1,500°C or less, and even more preferably 900°C or more and 1,500°C or less. Furthermore, the firing time is preferably 0.5 hours to 72 hours. If the firing time is 0.5 hours to 72 hours, it is a time sufficient for the growth of niobium oxide particles, and unnecessary costs can be suppressed. Furthermore, the firing time is more preferably 0.5 hours to 50 hours, and even more preferably 0.5 hours to 30 hours.

The calcined niobium oxide is used as it is as niobium oxide powder. The calcined product may be pulverized and used as niobium oxide powder. Regardless of whether it is pulverized or not, the calcined product may be classified using a sieve, and the undersieve (fine particle side) obtained may be used as niobium oxide powder. The oversieve (coarse particle side) may be pulverized again and classified for use. It is also possible to combine pulverization and classification using a vibrating sieve into which nylon or fluororesin-coated iron balls or the like are charged as pulverization media. By combining classification and pulverization in this way, even if there are niobium oxide particles that are too large after roasting, they can be removed. Specifically, when classifying using a sieve, it is preferable to use one with an opening of 150 μm to 1,000 μm. If the size is between 150 μm and 1,000 μm, the proportion of oversized particles will not be too high, so there will be no need to repeatedly grind the particles again, and the niobium oxide powder that needs to be ground again will not be classified as undersized.

The niobium oxide powder produced by the above-mentioned method for producing niobium oxide powder according to the present invention has a structure in which primary particles of niobium oxide are fused to each other. In this way, the average particle size becomes large due to the structure in which primary particles of niobium oxide are fused to each other, and therefore the gravity acting on the primary particles of niobium oxide becomes large and the degree of compression becomes small. In other words, this shows that the niobium oxide powder of the present invention is a powder that is difficult to crush, and a powder with high flowability that is difficult to form aggregates even under pressure conditions can be obtained. Specifically, preferred are niobium oxide powders having a ratio D50(N)/D50(U) of the median diameter D50(N) of niobium oxide particles to the median diameter D50(U) obtained by irradiating the niobium oxide particles with ultrasound of 5 or less, niobium oxide powders having a specific surface area SSA of 1 ^m2 /g or less, and even 0.4 ^m2 /g or less, niobium oxide powders having a compressibility calculated based on the loose bulk density AD and the compacted bulk density TD of 25% or less, and even 20% or less, and niobium oxide powders having the median diameter D50(U) of 5 μm or more and 120 μm or less.

In addition, when the niobium oxide powder according to the present invention is mixed with lithium carbonate powder to produce lithium niobate powder, it is well mixed, a uniform reaction product is obtained, and it has excellent reactivity. The specific method for evaluating this reactivity is as follows. First, niobium oxide powder and lithium carbonate powder are weighed so that the molar ratio of the two is 1:1, and the mixture (total weight 30 g) is mixed and crushed in a ball mill, and the resulting mixed powder is fired in an air atmosphere at a firing temperature of 1,000°C to 1,800°C for a firing time of 1 hour to 8 hours to produce lithium niobate powder. Next, this lithium niobate powder is crushed in an agate mortar, and powder X-ray diffraction measurement using CuKα rays is performed according to the powder X-ray diffraction measurement conditions described later to obtain an X-ray diffraction pattern. Then, if the obtained X-ray diffraction pattern is only a Bragg peak derived from lithium niobate, it is evaluated that the reactivity for the production of lithium niobate powder is good.

The niobium oxide powder of the present invention has excellent fluidity and is suitable as a raw material for thin film forming materials such as sputtering targets, optical products, and fine ceramics.

1 is a scanning electron microscope (SEM) photograph of Example 1 of a niobium oxide powder according to an embodiment of the present invention. 1 is a scanning electron microscope (SEM) photograph of Comparative Example 1 of a niobium oxide powder according to an embodiment of the present invention.

Hereinafter, the niobium oxide powder according to an embodiment of the present invention will be described with reference to the manufacturing method. The niobium oxide powder according to an embodiment of the present invention is an ore, alloy, scrap, or the like that contains niobium (hereinafter referred to as raw material).

Preparation of Niobium Fluoride Solution First, the above-mentioned raw material, for example, ore containing niobium, was put into a vibration mill and pulverized, and the obtained pulverized product was treated with an alkaline aqueous solution and washed with a mineral acid, and then the niobium in the raw material was dissolved with hydrofluoric acid to obtain a solution containing niobium. Then, the concentration of hydrofluoric acid in the solution containing niobium and the concentration of mineral acids other than hydrofluoric acid (for example, sulfuric acid) were adjusted to obtain a niobium extraction solution adjustment solution. This niobium extraction solution adjustment solution was separated and refined by a solvent extraction method using an organic solvent of 4-methyl-2-pentanone to obtain a niobium fluoride solution (hereinafter referred to as a niobium refined solution). Here, the niobium concentration in the obtained niobium fluoride solution was 320 g/L (grams/liter) when converted to niobium oxide (Nb ₂ O ₅ ). Hereinafter, the niobium concentration in the niobium fluoride solution is a concentration converted to niobium oxide.

Example 1 : The niobium purified solution obtained as described above was diluted to a niobium concentration of 60 g/L in terms of niobium oxide by adding ultrapure water to obtain a niobium diluted solution. Next, the niobium diluted solution was mixed with the ammonia water by a reverse neutralization method in which 25 L of 25 wt % ammonia water (13.2 mol/L) in the precipitation tank was stirred while 47 L of the obtained niobium diluted solution was added over 30 minutes to obtain a precipitated slurry containing niobium (hereinafter referred to as the mixing/precipitation step). Here, the ammonia water in the precipitation tank was at room temperature (20°C).

Here, the pH of the ammonia water in the precipitation tank during the addition of the niobium diluted solution was always 10 or more. The pH of the resulting precipitation slurry containing niobium was also 10 or more. The niobium diluted solution to be added to the ammonia water in the precipitation tank was cooled to about 5°C by passing it through a heat exchanger, and then added to the ammonia water. A cooling tube made of fluororesin was installed in the precipitation tank, and cooling water with a tube inlet temperature of about 5°C was circulated to cool the precipitation tank. As a result of cooling in this way, the maximum temperature of the mixture of the niobium diluted solution and the ammonia water was 29°C from the start of the addition of the niobium diluted solution to the end of the precipitation of the precipitation slurry. The pH was measured using a tabletop pH meter (Horiba, Ltd.: F-71S: Standard Tou pH electrode) installed in the precipitation tank, and the mixture of the niobium diluted solution and the alkaline aqueous solution in the precipitation tank during the addition of the niobium diluted solution and during stirring for 10 minutes after the addition. The pH was measured after confirming that the liquid temperature was stable at 25°C. After the addition of the diluted niobium solution was completed, stirring was continued for an additional 30 minutes, and after stirring was completed, the mixture was left to stand for 3 hours to allow the precipitate to settle, yielding a precipitate slurry containing niobium.

After removing the supernatant liquid from the precipitation tank, the precipitated slurry was removed from the precipitation tank and separated into solid and liquid using a filter press. The precipitated slurry was then transferred to a washing tank, where washing water was added and stirred for 30 minutes, and the tank was left to stand for 3 hours. The washing liquid (2.5% by weight ammonia water) was then removed. This series of steps was repeated multiple times until the fluoride ion concentration in the washing liquid after washing was 100 mg/L or less.

After removing the washing liquid whose fluoride ion concentration had fallen to 100 mg/L or less, ultrapure water was added to wash the precipitated slurry, which was then squeezed to obtain a precipitated cake. The precipitated cake was then collected and placed in a static furnace and air-fired at a heating temperature of approximately 1,000°C for 3 hours (hereinafter referred to as the firing process).

After firing, the obtained roasted powder was pulverized in a ball mill to obtain a powder form. Here, the ball mill media used was urethane-coated media with a diameter of about 15 mm. The mixture was then sieved through a mesh with an opening of 200 μm, and the powder that fell through the sieve was collected to obtain the niobium oxide powder according to Example 1.

Example 2 : This example is the same as Example 1, except that the diluted niobium solution was diluted so that the niobium concentration was 40 g/L calculated as niobium oxide, and therefore a description thereof will be omitted.

Example 3 : This example is the same as Example 1, except that in the mixing and precipitation step, the ammonia water in the precipitation tank was set to 10% by weight (5.9 mol/L) and the volume was set to 50 L, and therefore a description thereof will be omitted.

Example 4 : This example is the same as Example 1, except that the diluted niobium solution was diluted so that the niobium concentration was 20 g/L calculated as niobium oxide, and therefore a description thereof will be omitted.

Example 5 : This example is the same as Example 1 except that the time for adding the diluted niobium solution was 90 minutes, so a detailed explanation is omitted.

Example 6 : This example is the same as Example 1 except that the niobium diluted solution was diluted to a niobium concentration of 20 g/L calculated as niobium oxide, and the ammonia water in the precipitation tank was adjusted to 10% by weight (5.9 mol/L) and the volume was adjusted to 50 L. Therefore, a description thereof will be omitted.

Comparative Example 1 : In this comparative example, the niobium diluted solution was diluted so that the niobium concentration was 90 g/L in terms of niobium oxide. In addition, contrary to the reverse neutralization method of Example 1, the niobium diluted solution and the ammonia water were mixed by a normal neutralization method in which 63 L of the niobium diluted solution in the precipitation tank was stirred while 30 L of 25 wt % ammonia water (13.2 mol/L) was added over 10 minutes to obtain a precipitation slurry containing niobium. The pH of the obtained precipitation slurry containing niobium was 9.5. Other conditions were the same as those of Example 1, so the explanation will be omitted.

Comparative Example 2 : In this comparative example, the niobium dilution liquid and the ammonia water were mixed by the positive neutralization method as in Comparative Example 1 to obtain a precipitation slurry containing niobium. Furthermore, as in Example 1, the obtained precipitation slurry was washed and pressed to obtain a precipitation cake. Then, before the firing process, the obtained precipitation cake was placed in a static furnace and fired in the air at a heating temperature of about 100 to 200°C for 12 hours (hereinafter referred to as the preliminary drying process). Before the firing process, the preliminary dried precipitation cake was classified by a turbo screener. The classification conditions of the turbo screener were mesh opening: 32 μm, and rotation frequency: 90 Hz. Other conditions were the same as in Example 1, so the explanation will be omitted.

The manufacturing conditions for the niobium oxide powders of Examples 1 to 6 and Comparative Examples 1 and 2 described above are shown in Table 1 below.

The following physical properties were measured for the niobium oxide powders obtained in Examples 1 to 6 and Comparative Examples 1 and 2. The measured physical properties and the methods for measuring the physical properties are shown below, and the measurement results are shown in Table 2.

Particle size distribution : The particle size distribution was evaluated by a dynamic light scattering method according to JIS Z 8828:2019 using a laser diffraction/scattering particle size distribution measuring device (Microtrack Bell Co., Ltd.: MT3300EXII). In addition, no filtering was performed, and a dispersion process using ultrasonic waves as described below was performed. D50 indicates the particle size that reaches 50% in volume fraction.

Ultrasonic treatment: D50 (N) is the median diameter of the niobium oxide powder evaluated for particle size without performing ultrasonic dispersion treatment. Meanwhile, D50 (U) is the median diameter of the niobium oxide powder evaluated for particle size immediately after performing ultrasonic dispersion treatment. Specifically, the procedure of ultrasonic dispersion treatment is as follows. First, as a pretreatment for ultrasonic dispersion treatment, 1 mg of sample powder and 20 mL of pure water were put into a 50 mL wide-mouthed PP bottle, and the PP wide-mouthed bottle was set in an ultrasonic cleaner (manufactured by AS ONE CORPORATION: VS-100III). Next, in a state where the inside of the cleaning machine was filled with pure water up to 5 cm above the floor surface, ultrasonic dispersion treatment was performed for 60 minutes at a frequency of 28 kHz and an output of 100 W.

Tacked bulk density (TD) : Tacked bulk density was measured in accordance with "Part 12: Apparent density or apparent specific volume - Section 2: Tamp method" of JIS K 5101-12-2:2004 (Methods for measuring pigments).

Loose bulk density (AD) : The loose bulk density was measured in accordance with JIS K 5101-12-1:2004 (Methods for measuring pigments) "Part 12: Apparent density or apparent specific volume - Section 1: Static method".

Compressibility : The compressionibility was calculated according to the following formula (1).

Specific surface area (SSA) : Measurement was performed in accordance with "6.2 Flow method (3.5) Single point method" of JIS R 1626-1996 (Method for measuring specific surface area of fine ceramic powder by gas adsorption BET method). A mixed gas of helium as carrier gas and nitrogen as adsorbate gas was used.

PFT slope : The PFT slope represents the slope of the approximate curve obtained by linear fitting the measurement data plotted on the graph using the least squares method when the uniaxial collapse strength (unit: kPa) is the vertical axis and the maximum principal consolidation stress (unit: kPa) is the horizontal axis. The measurement of the uniaxial collapse strength and the maximum principal consolidation stress was performed using a powder flow tester (manufactured by Brookfield, PET) in accordance with the measurement conditions of the Standard Flow Function Test. The maximum principal consolidation stress ranged from 1 kPa to 25 kPa, and the slope was calculated from the plot of five points. Here, the slope of the uniaxial collapse strength/maximum principal consolidation stress of the powder flow tester means how little force is required to break up a powder mass that has solidified at one end due to pressure, and powder with a small slope flows easily even if it solidifies at one end due to pressure, so it has the effect of being less likely to become "clogging" in a hopper, etc. A hopper is a device that temporarily holds powder such as ready-mix concrete or soil and pours it into the desired location, and is a container shaped like an inverted cone or inverted pyramid.

Presence or absence of voids : The presence or absence of voids (air bubbles) formed on the surface of the primary particles of the niobium oxide powder was observed by observing five SEM images (20 μm × 20 μm) at a magnification of 5,000 times under the condition of an acceleration voltage of 1 kV with a scanning electron microscope (SEM), and the presence or absence of voids with a circumscribed circle diameter of 1 μm or less was observed. Under the above observation conditions, the case where no voids were observed on the surface of the primary particles was evaluated as "○", and the case where one or more voids were observed on the surface of the primary particles was evaluated as "×". Here, a scanning electron microscope (SEM) photograph of Example 1 of the niobium oxide powder according to the embodiment of the present invention is shown in FIG. 1, which shows a structure in which the primary particles of the niobium oxide powder according to Example 1 are fused to each other. On the other hand, a scanning electron microscope (SEM) photograph of Comparative Example 1 of the niobium oxide powder according to the embodiment of the present invention is shown in FIG. 2, which shows a structure in which the primary particles of the niobium oxide powder according to Comparative Example 1 are not fused to each other.

Hopper clogging test : A hopper with a capacity of 20 L was attached to a small powder filling machine (RD703-T+SU01, manufactured by Naomi Co., Ltd.), niobium oxide powder was fed into the hopper at 5 kg/min, and the presence or absence of clogging during continuous operation for 60 minutes was evaluated. Specifically, when the discharge rate of the fed niobium oxide powder from the hopper continued to be maintained at a rate exceeding 4 kg/min, it was determined that no clogging occurred in the hopper and the niobium oxide powder continued to flow, and was evaluated as "○". On the other hand, when the discharge rate of the fed niobium oxide powder from the hopper became 4 kg/min or less, it was determined that clogging occurred in the hopper and the niobium oxide powder no longer flowed, and was evaluated as "×".

Reactivity test : A lithium niobate powder produced by mixing niobium oxide powder and lithium carbonate powder was used as a sample, and a powder X-ray diffraction measurement using CuKα radiation was performed according to the following powder X-ray diffraction measurement conditions, and the obtained X-ray diffraction pattern was confirmed to evaluate the reactivity. The lithium niobate powder sample was produced as follows. First, niobium oxide powder and lithium carbonate powder (manufactured by Wako Pure Chemical Industries, Ltd.) were weighed so that the molar ratio of the two was 1:1, and the mixture (total weight 30 g) was mixed and crushed in a ball mill, and the resulting mixed powder was fired in an air atmosphere at a firing temperature of 1,600°C to 1,800°C for a firing time of 8 hours to produce a lithium niobate powder. Next, this lithium niobate powder was crushed in an agate mortar, and a powder X-ray diffraction measurement using CuKα radiation was performed according to the following powder X-ray diffraction measurement conditions to obtain an X-ray diffraction pattern. When the obtained X-ray diffraction pattern only had a Bragg peak derived from lithium niobate, it was judged that the niobium oxide powder and the lithium carbonate powder were mixed well and the reactivity for the production of lithium niobate powder was good, and was evaluated as "○". On the other hand, when the obtained X-ray diffraction pattern contained at least one peak derived from niobium pentoxide (2θ = 22.7 ° ± 0.5 °, 32.7 ° ± 0.5 °, and/or 36.5 ° ± 0.5 °) other than the Bragg peak derived from lithium niobate, it was judged that the niobium oxide powder and the lithium carbonate powder were mixed poorly, unreacted niobium oxide and lithium carbonate remained, and the reactivity for the production of lithium niobate powder was poor, and was evaluated as "×".

= Powder X-ray diffraction measurement conditions =
Diffraction device: MiniFlex2 (Rigaku Corporation)
・X-ray tube: Cu
Tube voltage/current: 30 kV, 15 mA
・Slit: DS-SS; 1.25 degrees, RS; 0.3mm
Graphite monochromator Measurement interval: 0.01 degree Counting method: Constant counting method

As shown in Table 2, when the niobium oxide powders according to Examples 1 to 6 have a D50 ratio, i.e., D50(N)/D50(U), of 5 or less, as shown in Figure 1, the primary particles of the niobium oxide powder of Example 1 have a structure in which they are fused together, suppressing the formation of agglomerates, and as shown by the results of the hopper clogging test, a niobium oxide powder with high fluidity was obtained.

In the niobium oxide powders according to Examples 1 to 6, when the specific surface area SSA was 1 m ² /g or less, the adhesive force between the niobium oxide particles was further reduced, the formation of agglomerates was suppressed, and as shown by the results of the hopper clogging test, a niobium oxide powder with high fluidity was obtained.

When the compression ratio of the niobium oxide powder according to Examples 1 to 6 calculated based on the loose bulk density AD and the compacted bulk density TD was 25% or less, this indicated that the niobium oxide powder according to Examples 1 to 6 was a powder that was difficult to crush, and a niobium oxide powder with high fluidity and low agglomeration was obtained even when it was put into a hopper and pressure was applied.

The niobium oxide powders according to Examples 1 to 6 tended to have a larger D50 (U), which is the median particle size evaluated immediately after the ultrasonic dispersion process, when the D50 (U) was 5 μm or more and 120 μm or less, compared to the niobium oxide powders according to Comparative Examples 1 and 2, which were largely dispersed by the ultrasonic dispersion process.

The slope of the uniaxial collapse strength/maximum principal consolidation stress of the powder flow tester for the niobium oxide powders of Examples 1 to 6 is significantly smaller than that of the niobium oxide powders of Comparative Examples 1 and 2, and the powder lumps in the niobium oxide powders of Examples 1 to 6 are easily broken apart with a small force.

The niobium oxide powder of this embodiment is produced through a reverse neutralization method, and has a structure in which the primary particles are fused together, which increases the particle size. The degree of compression is small, and agglomerates are unlikely to form even under pressure, making this a powder with excellent fluidity.

Furthermore, the niobium oxide powders of Examples 1 to 6 are easily mixed with lithium carbonate powder, and a uniform lithium niobate powder is obtained, which also has excellent reactivity.

The inventions disclosed in this specification include, in addition to the configurations of each invention or embodiment, to the extent applicable, those that are specified by changing these partial configurations to other configurations disclosed in this specification, those that are specified by adding other configurations disclosed in this specification to these configurations, or those that are specified as higher-level concepts by deleting these partial configurations to the extent that partial effects are obtained.

The niobium oxide powder of the present invention has excellent fluidity and is therefore suitable as a raw material for thin film forming materials such as sputtering targets, optical products, and fine ceramics.

Claims (5)

a ratio D50(N)/D50(U) of a median diameter D50(N) of the niobium oxide particles to a median diameter D50(U) obtained by irradiating the niobium oxide particles with ultrasonic waves under conditions of a frequency of 28 kHz, an output of 100 W, and a time period of 60 minutes is 5 or less;
The niobium oxide particles have a specific surface area SSA of 0.4 m ² /g or less;
The degree of compression calculated based on the loose bulk density (AD) and the compacted bulk density (TD) is 25% or less;
The niobium oxide powder has a median diameter D50 (U) of 5 μm or more and 120 μm or less . 2. The niobium oxide powder according to claim 1, characterized in that the degree of compression is 20% or less. A method for producing a niobium oxide powder according to claim 1 or 2,
A method for producing niobium oxide powder, comprising the steps of: subjecting a solution in which niobium is dissolved to a solvent extraction; adding ultrapure water to the resulting niobium purified solution; and adding the resulting niobium diluted solution to an alkaline aqueous solution by a reverse neutralization method to produce a precipitate slurry containing niobium. 4. The method for producing niobium oxide powder according to claim 3 , wherein the alkaline aqueous solution to which the diluted niobium solution is added has a pH of 10 or more. 4. The method for producing niobium oxide powder according to claim 3 , wherein the alkaline aqueous solution is ammonia water.

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