JP7104842B2 - Ammonium niobate hydrate and its production method - Google Patents

Description

The present invention relates to a compound containing NH ₄ ⁺ and OH in addition to Nb and O (also referred to as "ammonium niobate hydrate") and a method for producing the same.

Niobium is silvery white in itself, but has the property of shining in beautiful seven colors when a passivation oxide film is formed on the surface. In addition, it is relatively lightweight and has resistance to many chemical substances. It has a high melting point (468 ° C.), low vapor pressure, high elastic modulus, high thermal stability, low coefficient of thermal expansion, and has the highest superconducting transition temperature of all elements. Furthermore, it can be easily molded even at low temperatures and has high biocompatibility. Therefore, niobium has a wide variety of uses, for example, it is used as a coin slot, a corrosion-resistant vapor deposition boat for coating, a crucible for diamond production, an implant material, a material for a superconducting cable and a magnet, and the like.

Niobium hydroxide, niobium oxide and niobium hydrate (collectively referred to as "niobium hydrates") are widely used as raw materials for electronic ceramics such as lithium niobium (LN) crystals or ceramic capacitors. There is.

As a method for producing such niobium hydrates, for example, an ore or scrap containing niobium is prepared as a raw material, the raw material is crushed as necessary, and then liquefied with an alkaline aqueous solution or mineral acid. Perform pretreatment such as cleaning. Then, niobium is dissolved with hydrofluoric acid or the like, and the solution obtained by this dissolution is separated and purified by solvent extraction to obtain a niobium fluoride solution. Then, a method of obtaining niobium hydroxide by mixing the obtained niobium fluoride solution and aqueous ammonia to produce a precipitate, and washing, filtering, and drying the precipitate has been conventionally known. Then, by roasting the niobium hydroxide thus obtained, niobium oxide can be obtained.

As an invention relating to a method for producing niobium hydrates, for example, in Patent Document 1, a solution in which niobium hydroxide is dissolved in hydrofluoric acid or oxalic acid is maintained at pH 1 to 4 and a temperature of 60 ° C. or lower, and an oxide equivalent amount of the above compound ( Disclosed is a method for producing niobium hydroxide, which comprises adding 0.05 wt% or more of ammonium pyrrolidinedithiocarbamate to Nb ₂ O ₅ equivalent) to remove the formed precipitate, and then setting the pH to 6 or more. ing.

Patent Document 2 describes a method for producing niobium oxide, which comprises introducing an ammonia solution containing CO ₂ into an acidic fluoride solution containing niobium until the pH value of this solution becomes 7 or more. Is disclosed.

Patent Document 3 describes a step of mixing a niobium fluoride solution with at least one precipitate selected from ammonia, ammonium carbonate, and ammonium hydrogen carbonate to produce a precipitate, and separating the produced precipitate. -A washing step, a water vapor-containing gas treatment step of holding the obtained precipitate in a water vapor-containing gas atmosphere at 50 ° C. to 300 ° C. for at least 0.5 hours, and a treatment obtained by the water vapor-containing gas treatment. A method for producing niobide hydroxide is disclosed, which comprises a step of drying an object until its intense heat loss is 20% to 90% of the theoretical intense heat loss.

In recent years, the amount of niobate compounds containing alkali metals and the like has been increasing as raw materials for electronic parts such as frequency filters and capacitors, and as target raw materials for sputtering. Recently, as alternative materials for lead zirconate titanate (PZT), which is a typical piezoelectric ceramic, potassium niobate (KNbO ₃ ), sodium niobate (NaNbO ₃ ), lithium niobate (LiNbO ₃ ), and others Niobate compounds such as a solid solution of sodium niobate and barium titanate and a solid solution of sodium niobate and potassium niobate are attracting attention as candidates for lead-free piezoelectric ceramics.

Regarding this type of niobium acid salt compound, Patent Document 4 describes _NaNbO3 particles by a sorbothermal reaction of a suspension composed of a niobium compound and a sodium hydroxide (NaOH) solution for the purpose of improving the performance of piezoelectric ceramics. The method of synthesizing the above is disclosed.
Patent Document 5 describes a method for producing NaNbO ₃ fine particles, in which niobide oxide (Nb ₂ O ₅ ), an aqueous NaOH solution and NaNbO ₃ produced in a separate step are mixed, and high temperature and high pressure are applied to the mixture using an autoclave. A manufacturing method for subjecting to a hydrothermal treatment exposed to the above-mentioned state is disclosed.

In Patent Document 6, a suspension consisting of an alkaline aqueous solution containing sodium hydroxide (NaOH) and potassium hydroxide (KOH), crystalline Nb ₂ O ₅ and a surfactant is prepared, and an autoclave is prepared in this suspension. K ₄ Na ₄ NbO ・ 9H ₂ O particles are synthesized by hydrothermal treatment at 200 ° C., and then the K ₄ Na ₄ NbO ・ 9H ₂ O particles are dehydrated by heat treatment to form an alkali metal niobate. Is disclosed.

Japanese Unexamined Patent Publication No. 1-3133333 Japanese Unexamined Patent Publication No. 8-12333 Japanese Unexamined Patent Publication No. 2005-1920 Japanese Unexamined Patent Publication No. 2010-241658 Japanese Unexamined Patent Publication No. 2013-224228 Japanese Unexamined Patent Publication No. 2011-132118

When producing a niobate compound containing an alkali metal, in order to react ordinary niobium hydrates with an alkali metal salt, as described above, an alkali metal is used under high temperature and high pressure conditions using an autoclave or the like. It was necessary to melt the niobium hydrates in the oxide of the above, or to convert the niobium hydrates into niobide pentoxide and then dissolve it in a solution of hydroxide ions as the pentaoxide.
However, heating using an autoclave as in the former was a burden in terms of equipment and cost. In addition, the fact that the pentaoxide must be passed as in the latter case has poor production efficiency and is a burden for industrial use.

Therefore, the present invention has high reactivity with alkali metal salts such as sodium carbonate, does not need to be reacted under high temperature and high pressure conditions using an autoclave or the like, and does not need to be reacted via niobide pentoxide. , A novel ammonium niobate hydrate and a method for producing the same, which can be easily obtained by reacting with an alkali metal salt, for example, sodium carbonate.

The present invention is a compound containing NH ₄ ⁺ and OH in addition to Nb and O (also referred to as "ammonium niobate hydrate").
The ammonium niobate hydrate has an integrated volume particle size at an integrated volume of 50% by volume measured by a laser diffraction / scattering method particle size distribution measurement method before ultrasonic dispersion treatment (D50N) and after ultrasonic dispersion treatment at 40 W for 30 seconds. When each of (D50D) was measured, D50N was 1 μm or more and 100 μm or less, and the ratio of D50N to D50D (D50N / D50D) was 10 or less.
In solid ^{1 1} H-NMR measurement, the obtained signal is subjected to Fourier conversion, and the measured spectrum obtained by correcting the phase and chemical shift isotropic values has a baseline whose height is constant with respect to the chemical shift isotropic value. The calculated spectrum created by the sum of the two pseudo-Vault functions is fitted in the range of ¹ H chemical shift isotropic value -2 to 14 ppm, and the measured spectrum is separated into two peaks and a baseline is defined and separated. The peak with the latter peak located in the range of ¹ H chemical shift isotropic value of 7.3 to 7.7 ppm is defined as peak 1, and the peak after separation is in the range of ¹ H chemical shift isotropic value of 5.6 to 7.0 ppm. The peak located at is defined as peak 2.
The value obtained by integrating the pseudo-Vault function of peak 1 in the range of ¹ H chemical shift isotropic value -2 to 14 ppm is defined as the peak integral value 1, and the pseudo-Folk function of peak 2 is defined as the ¹ H chemical shift isotropic value of -2 to 14 ppm. When the value integrated in the range is defined as the peak integral value 2, the ratio of the peak integral value 1 to the total value of the peak integral value 1 and the peak integral value 2 (also referred to as "integral ratio of peak 1") is 40% or more. We propose a certain ammonium niobate hydrate.

The present invention also proposes a method for producing ammonium niobate hydrate, which comprises mixing an aqueous solution of niobium fluoride and an ammonium carbonate salt and heating and reacting them to obtain ammonium niobate hydrate. do.

The ammonium niobate hydrate proposed by the present invention is characterized by having high reactivity with an alkali metal salt such as sodium carbonate. For example, when mixed with sodium carbonate and heated, sodium niobate (NaNbO ₃ ) having less impurities can be obtained. Therefore, the ammonium niobate hydrate proposed by the present invention does not need to be reacted under high temperature and high pressure conditions using an autoclave or the like, and does not need to be reacted via niobium pentoxide, and is an alkali metal salt. Since the niobium pentoxide compound can be easily obtained by reacting with, it can be expected that it can be effectively used industrially.

For the ammonium niobate hydrate (sample) obtained in Example ¹ , the measured spectrum of the 1H spectrum obtained using a 600 MHz NMR spectrometer, the spectrum of each peak calculated by the variables in Table 1, the calculated spectrum, and , It is a figure which showed the residual of the measured spectrum and the calculated spectrum. For the ammonium niobate hydrate (sample) obtained in Example 2, the measured spectrum of the 1H spectrum obtained using ^a 600 MHz NMR spectrometer, the spectrum of each peak calculated by the variables in Table 1, the calculated spectrum, and , It is a figure which showed the residual of the measured spectrum and the calculated spectrum. For the ammonium niobate hydrate (sample) obtained in Comparative Example ¹ , the measured spectrum of the 1H spectrum obtained using a 600 MHz NMR spectrometer, the spectrum of each peak calculated by the variables in Table 1, the calculated spectrum, and , It is a figure which showed the residual of the measured spectrum and the calculated spectrum. It is an X-ray diffraction pattern of the fired product obtained by mixing and heating the ammonium niobium hydrate (sample) obtained in Example 1 and sodium carbonate. It is an X-ray diffraction pattern of the fired product obtained by mixing and heating the ammonium niobium hydrate (sample) obtained in Example 2 and sodium carbonate. It is an X-ray diffraction pattern of the fired product obtained by mixing and heating niobium hydroxide (sample) obtained in Comparative Example 1 and sodium carbonate.

Next, the present invention will be described based on examples of embodiments. However, the present invention is not limited to the embodiments described below.

<Ammonium niobate hydrate>
The ammonium niobate hydrate according to an example of the embodiment of the present invention (also referred to as “ammonium niobate hydrate”) is a compound containing NH ₄₊ and OH in addition to Nb and O, that is, ammonium niobate ^. It is a hydrate.

This ammonium niobate hydrate is a compound containing NH ₄₊ and OH in addition to Nb and O ⁽ also referred to as "ammonium niobate hydrate").
When the integrated volume particle size at the integrated volume 50% by volume measured by the laser diffraction / scattering method particle size distribution measurement method was measured before the ultrasonic dispersion treatment (D50N) and at 40 W and after the ultrasonic dispersion treatment for 30 seconds (D50D), respectively. It is preferable that D50N is 1 μm or more and 100 μm or less, and the ratio of D50N to D50D (D50N / D50D) is 10 or less.

If the integrated volume particle size (D50N) at 50% by volume of the integrated volume before the ultrasonic dispersion measurement by the laser diffraction / scattering method particle size distribution measurement method is 1 μm or more, the fluidity is often good, and if it is 100 μm or less. , It is preferable because it has a high reactivity with an alkali metal salt.
From this viewpoint, the lower limit of D50N is more preferably 5 μm or more, and further preferably 10 μm or more. On the other hand, the upper limit of D50N is more preferably 80 μm or less, and further preferably 50 μm or less.

When the D50N is 1 μm or more and the D50N / D50D is 10 or less, the effect of good fluidity can be obtained.
From this viewpoint, the D50N / D50D is more preferably 8 or less, further preferably 5 or less, particularly preferably 3 or less, and even more preferably 2 or less. On the other hand, the lower limit of the D50N / D50D is usually 1, but may be less than 1, and is preferably 0.95 or more, preferably 1.00 or more, from the viewpoint of ease of manufacture. More preferably, it is more preferably 1.05 or more.
For the measurement of D50N and D50D, for example, MT3300EXII or MT3300II (both manufactured by Microtrack Bell) can be used as a laser diffraction / scattering method particle size distribution measuring device. Details of the measurement conditions will be described in Examples described later.

It should be noted that the conventionally available ammonium niobate hydrate has low fluidity, so that the mixability when mixed with the alkali metal salt is poor, which is one of the reasons why the reactivity with the alkali metal salt cannot be enhanced. It was. In addition, since the fluidity is low, there is a problem that the input hopper and the transfer pipe are likely to be clogged. On the other hand, in the present ammonium niobate hydrate, such a problem, that is, fluidity can be improved by adjusting the D50N and D50N / D50D ratios.

This ammonium niobate hydrate is further converted to a chemical shift isotropic value in the measured spectrum obtained by correcting the phase and chemical shift isotropic values after Fourier conversion of the obtained signal in the solid ¹ H-NMR measurement. On the other hand, the calculated spectrum created by the baseline with a constant height and the sum of the two pseudo-Vault functions is fitted in the range of ¹ H chemical shift isotropic value -2 to 14 ppm, and the measured spectrum is divided into two peaks. The peak after separation is defined as peak 1 and the peak after separation is ¹ H chemical shift isotropic. The peak located in the range of 7.3 to 7.7 ppm is defined as peak ¹ . A peak located in the range of 5.6 to 7.0 ppm is defined as peak 2.
The value obtained by integrating the pseudo-Vault function of peak 1 in the range of ¹ H chemical shift isotropic value -2 to 14 ppm is defined as the peak integral value 1, and the pseudo-Folk function of peak 2 is defined as the ¹ H chemical shift isotropic value of -2 to 14 ppm. When the value integrated in the range is defined as the peak integral value 2, the ratio of the peak integral value 1 to the total value of the peak integral value 1 and the peak integral value 2 (integral ratio of the peak 1) is preferably 40% or more. ..
At this time, peak 1 is presumed to be the peak of H derived from NH ₄₊ , and peak ² is presumed to be the peak of H derived from OH.
Further, the integration ratio of the peak 1 is the abundance ratio of ¹ H specified by peak 1 to the sum of ^{1 H specified by peak 1 and 1 H} specified by peak 2, that is, the presence of the proton. It means a ratio.

In the present ammonium niobate hydrate, if the integral ratio of peak 1 is 40% or more, the reactivity of the present ammonium niobate hydrate can be enhanced as described later. In particular, the reactivity with alkali metal salts such as sodium carbonate can be enhanced.
Therefore, from this point of view, in this ammonium niobate hydrate, the ratio of the peak integral value 1 to the total value of the peak integral value 1 and the peak integral value 2 (integral ratio of the peak 1) is preferably 40% or more. Among them, 50% or more, 60% or more among them, and 70% or more among them are more preferable.

The ammonium niobate hydrate may be a compound composed of components other than Nb, O, NH ₄₊ and OH, or may contain components other than these (referred to as "other components") ^. good.
It may also contain unavoidable impurities. However, the content of unavoidable impurities is preferably 0.2% by mass or less, each of which is 0.1% by mass or less, of which 0.05% by mass or less, particularly 0.02% by mass or less of each. It is preferable to have it. Examples of unavoidable impurities include Ta, Si, P, B, Sb, Mn, Fe, Ni, Cr, Co, and Cu.

(Reactivity)
As described above, this ammonium niobate hydrate is characterized by having high reactivity with alkali metal salts such as sodium carbonate.
For example, this ammonium niobium hydrate and sodium carbonate are mixed so that Nb: Na = 1.0: 1.1 (mol ratio), and the temperature is maintained at 850 ° C. (product temperature) for 1 hour in the air. A fired product can be obtained by heating in such a manner. At this time, the obtained fired product is composed of NaNbO ₃ and can be made to have few impurities such as Na ₂ Nb ₄ O ₁₁ . Specifically, the calcined product belongs to sodium niobium (NaNbO ₃ ) with respect to the peak intensity (a) of 2θ = 29 ° ± 0.5 ° attributable to Na ₂ Nb ₄ O ₁₁ in X-ray diffraction. The X-ray intensity ratio (32 ° ± 0.5 ° / 29 ° ± 0.5 °) of the peak intensity (b) of 2θ = 32 ° ± 0.5 ° is 10 or more. Among them, it can be 20 or more, and among them, 30 or more.
As described above, since this ammonium niobate hydrate has high reactivity with alkali metal salts such as sodium carbonate, it is not necessary to react under high temperature and high pressure conditions using an autoclave or the like, and niobium pentoxide It is not necessary to react via the above, and the niobate compound can be easily obtained by reacting with an alkali metal salt such as sodium carbonate.

<This manufacturing method>
Next, a suitable method for producing ammonium niobate hydrate (referred to as “the present production method”) will be described.

As an example of this production method, a method of mixing an aqueous solution of niobium fluoride and an ammonium carbonate salt and heating them to react with each other can be mentioned. However, the method is not limited to this method.
In this production method, it is possible to add other steps or other processes as appropriate.

(Niobium fluoride aqueous solution)
When niobium to niobium oxide is reacted with hydrofluoric acid (HF) to form niobium fluoride (H ₂ NbF ₇ ), it can be dissolved in water to form an aqueous solution of niobium fluoride.
The aqueous niobium solution is preferably adjusted to contain 1 to 200 g / L of niobium in terms of Nb ₂ O ₅ by adding water (for example, pure water).

The niobium fluoride aqueous solution preferably has an elemental amount of fluorine (F) of 30% by mass or less, more preferably 25% by mass or less, and more preferably 20% by mass or less.
The amount of niobium (Nb) converted to Nb ₂ O ₅ is preferably 30% by mass or less, and more preferably 25% by mass or less, and more preferably 20% by mass or less.

(Ammonium carbonate)
Examples of the ammonium carbonate salt include (NH ₄ ) ₂ CO ₃ and (NH ₄ ) HCO ₃ . Of these, (NH ₄ ) HCO ₃ is preferable from the viewpoint that ammonium niobate hydrate having a large ratio of peak integral value 1 can be easily obtained.

It is preferable to mix 5 mol or more of ammonium carbonate in terms of _NH3 with 1 mol of Nb of the niobium fluoride aqueous solution.
Neutralization can be performed more reliably by mixing 5 mol or more of ammonium carbonate in terms of _NH3 with 1 mol of Nb of the niobium fluoride aqueous solution. From this point of view, the mixing amount of the ammonium carbonate salt is more preferably 7 mol or more in terms of _NH3 with respect to 1 mol of Nb of the niobium fluoride aqueous solution, particularly 8 mol or more, particularly 9 mol or more, and 10 mol or more among them. Is even more preferable.
On the other hand, the excess ammonium carbonate salt can be reduced by setting the mixing amount of the ammonium carbonate salt to 13 mol or less in terms of _NH3 with respect to 1 mol of Nb of the aqueous niobium fluoride solution. From this point of view, the mixing amount of the ammonium carbonate salt is more preferably 12 mol or less in terms of _NH3 with respect to 1 mol of Nb of the niobium fluoride aqueous solution, and more preferably 11 mol or less.

(Mixing method)
The order of mixing the niobium fluoride aqueous solution and the ammonium carbonate salt is that even if the ammonium carbonate aqueous solution is added to the niobium fluoride aqueous solution (positive neutralization) and mixed, the niobium fluoride aqueous solution is added to the ammonium carbonate salt (reverse neutralization). May be mixed.

It is preferable that the pH of the solution when the aqueous niobium fluoride solution and the ammonium carbonate salt are mixed is 7.0 or more because neutralization can be performed more reliably. On the other hand, if it is too high, the ammonium carbonate salt may be in excess. Therefore, it is preferable to adjust the pH of the solution when the niobium fluoride aqueous solution and the ammonium carbonate salt are mixed to be 7.0 or more, particularly 8.0 or more or 13.0 or less, and 9.0 or more among them. It is more preferable to adjust so as to be more than or less than or less than 12.0.

Further, it is preferable to mix the niobium fluoride aqueous solution and the ammonium carbonate salt and heat the mixed solution so that the liquid temperature becomes a predetermined temperature.
At this time, the mixed liquid may be heated after mixing, but it is preferable to heat the mixed liquid while mixing.
At this time, the heating temperature needs to be such that the temperature of the mixed liquid is 55 ° C. or higher. Since the decomposition temperature of ammonium carbonate is about 48 ° C., heating to 55 ° C. or higher decomposes ammonium carbonate around the niobic acid, probably ammonium carbonate that is complexed with niobium ions, and releases carbonic acid (degassing). ), And it can be inferred that the bond between NbO ⁻ and NH ₄₊ increases as the ammonia neutralization reaction proceeds rapidly ^.
Since the decomposition reaction of ammonium carbonate is an endothermic reaction, the temperature of the heating means itself needs to be higher than that in order to maintain the solution temperature at 55 ° C. or higher.
From this point of view, the heating temperature is more preferably 55 ° C. or higher, and more preferably 65 ° C. or higher, particularly 75 ° C. or higher.

(Washing)
After mixing and heating as described above to obtain an Nb ammonium solution, it is preferable to perform washing to remove impurities such as ammonium fluoride, if necessary.
The cleaning method at this time is arbitrary. For example, in addition to methods by filtration using a membrane such as reverse osmosis filtration, ultrafiltration, and microfiltration, centrifugation and other known methods can be adopted.

(Dry)
Then, if necessary, the obtained Nb ammonium solution is dried to obtain powdered ammonium niobium hydrate.
The drying method at this time is arbitrary.

<Explanation of words>
When expressed as "X to Y" (X and Y are arbitrary numbers) in the present specification, unless otherwise specified, they mean "X or more and Y or less" and "preferably larger than X" or "preferably Y". It also includes the meaning of "smaller".
Further, when expressed as "X or more" (X is an arbitrary number) or "Y or less" (Y is an arbitrary number), it means "preferably larger than X" or "preferably less than Y". Intention is also included.

The present invention will be further described in the following examples. However, the following examples are not intended to limit the invention in any way.

<Example 1>
17.5 g of niobide hydroxide (Nb ₂ O ₅ concentration: 93.5 mass%) was dissolved in 86.7 g of a 22.6 mass% fluoride solution, and an aqueous solution of niobide fluoride (niobic acid concentration: Nb ₂ O ₅ conversion) was dissolved. 151 g / L, Nb ₂ O ₅ concentration: 15.7% by mass, fluorine concentration: 18.9% by mass) was obtained.
To 30 mL (Nb0.0341 mol) of this niobium fluoride aqueous solution, 30 mL of ion-exchanged water was added and diluted. Further, 20 g (0.253 mol in terms of NH ₃ ) of ammonium hydrogen carbonate salt ((NH ₄ ) HCO ₃ , NH ₄ concentration: 22.8% by mass) was added, and the mixture was mixed with stirring at a rotation speed of 200 rpm using a magnetic stirrer. .. Then, the mixture was heated for 75 minutes so that the temperature of the mixed solution was maintained at 75 ° C. to obtain a neutralization reaction solution (pH 7.9).
Next, the neutralization reaction solution was filtered through Nutche using a 5C filter paper, and the recovered niobium-containing precipitate was resurrected with 200 mL of 2.5 mass% ammonia water, and filtered through Nutche in the same manner as described above to remove ammonium fluoride and the like. Washed. This cleaning operation was repeated until the amount of fluorine in the filtrate became 50 ppm or less. Then, it was dried in a dryer set at 110 ° C. to obtain an ammonium niobate hydrate (sample).

<Example 2>
17.5 g of niobide hydroxide (Nb ₂ O ₅ concentration: 93.5 mass%) was dissolved in 86.7 g of a 22.6 mass% fluoride solution, and an aqueous solution of niobide fluoride (niobic acid concentration: Nb ₂ O ₅ conversion) was dissolved. 151 g / L, Nb ₂ O ₅ concentration: 15.7% by mass, fluorine concentration: 18.9% by mass) was obtained.
To 30 mL (Nb0.0341 mol) of this niobium fluoride aqueous solution, 70 mL of ion-exchanged water was added and diluted. Further, 20 g (0.253 mol in terms of NH ₃ ) of ammonium hydrogen carbonate salt ((NH ₄ ) HCO ₃ , NH ₄ concentration: 22.8% by mass) was added, and the mixture was mixed with stirring at a rotation speed of 200 rpm using a magnetic stirrer. .. Then, the mixture was heated for 75 minutes so that the temperature of the mixed solution was maintained at 75 ° C. to obtain a neutralization reaction solution (pH 8.2).
Next, the neutralization reaction solution was filtered through Nutche using a 5C filter paper, and the recovered niobium-containing precipitate was resurrected with 200 mL of 2.5 mass% ammonia water, and filtered through Nutche in the same manner as described above to remove ammonium fluoride and the like. Washed. This cleaning operation was repeated until the amount of fluorine in the filtrate became 50 ppm or less. Then, it was dried in a dryer set at 110 ° C. to obtain an ammonium niobate hydrate (sample).

<Comparative example 1>
17.5 g of niobide hydroxide (Nb ₂ O ₅ concentration: 93.5 mass%) was dissolved in 86.7 g of a 22.6 mass% fluoride solution, and an aqueous solution of niobide fluoride (niobic acid concentration: Nb ₂ O ₅ conversion) was dissolved. 151 g / L, Nb ₂ O ₅ concentration: 15.7% by mass, fluorine concentration: 18.9% by mass) was obtained.
To 30 mL (Nb0.0341 mol) of this niobium fluoride aqueous solution, 30 mL of ion-exchanged water was added and diluted. This diluted aqueous niobium fluoride solution was added to 25 mL of 25% aqueous ammonia (0.334 mol in terms of NH ₃ ) over 30 minutes to obtain a neutralization reaction solution (pH 10.2) without any particular heating.
Next, the neutralization reaction solution was filtered through Nutche using a 5C filter paper, and the recovered niobium-containing precipitate was resurrected with 200 mL of 2.5 mass% ammonia water, and filtered through Nutche in the same manner as described above to remove ammonium fluoride and the like. Washed. This cleaning operation was repeated until the amount of fluorine in the filtrate became 50 ppm or less. Then, it was dried in a dryer set at 110 ° C. to obtain niobium hydroxide (sample).

<NMR measurement>
(Measurement condition)
^{1 1} H NMR measurement was performed at room temperature using a 600 MHz NMR spectrometer (AVANCE NEO manufactured by Bruker).
The NMR probe used was a 1.3 mm CP-MAS probe, which was measured by the single pulse method under a magic angle spinning at a rotation frequency of 60 kHz.
A 90-degree pulse of 2.5 μs was used as the pulse of the single pulse method, the interval between the observation points of the signal was 1 microsecond, and the observation points were 20000 points (observation time 20 milliseconds).
The interval from signal observation to pulse application for the next measurement (hereinafter referred to as the repetition time) was 8 seconds and 16 seconds, and 8 seconds when there was no change in intensity. When a change was observed, it was set to 16 seconds after confirming that no change was observed in 16 seconds and 32 seconds.
Specifically, the repetition time of each sample was ref: 8 seconds, condition 1:16 seconds, and condition 2: 8 seconds.
The total number of times for each measurement was 16 times, and the dummy scan before measurement was 4 times.
The measurement was performed three times per sample by exchanging the powder.

In the above-mentioned Examples and Comparative Examples, sufficient accuracy was obtained when the measurement was performed under the above-mentioned measurement conditions, but sufficient accuracy could not be obtained under the above-mentioned measurement conditions due to large variations. Sufficient accuracy can be obtained by increasing the total number of measurements from 16 times, or increasing the number of measurements by exchanging powders from 3 times per sample, or at least one of these. ..

(Analysis conditions)
45536 points with zero intensity were added to the signal obtained by the above measurement, and Fourier transform was performed.
After the Fourier transform, the ^phase correction of the 1H spectrum was performed so that all the peaks looked upward.
Next, the chemical shift isotropic value of the 1H spectrum was translated along the horizontal axis so that the 1H peak of adamantane used as ^an external standard substance was 1.91 ppm (based on ⁰ ppm of tetramethylsilane).
The spectrum obtained as described above is referred to as an actually measured spectrum.
For peak separation and baseline determination, a calculated spectrum created by adding a baseline whose height is constant with respect to the chemical shift isotropic value and the sum of ^two pseudo Voigt functions is added to the measured spectrum, and 1H chemical shift isotropic. The value was performed by fitting in the range of -2 to 14 ppm.
The pseudo Voigt function is the sum of the Lorentz function and the Gaussian function with the same full width at half maximum. The pseudo Voigt function f (x) used for peak separation is shown below.

Here, x is the value on the horizontal axis of the ¹ H-NMR spectrum (chemical shift isotropic value), x ₀ is the chemical shift isotropic value at the peak center, A is the scaling coefficient for adjusting to the actual measurement, and η is -∞ ( The peak integral ratio of the Lorentz function (first term) in the range from minus infinity) to + ∞ (plus infinity), H is the half-value full width of the peak, π is the pi, ln is the natural logarithm, and exp is the natural exponent. Represents a function.
In peak separation, the chemical shift isotropic values of the measured spectrum and the calculated spectrum are minimized in the range of -2 ppm to 14 ppm, with x _0, H, η, and A of each of the two pseudo Voigt functions as variables. Fitting was performed using the solver function of Excel.
In this way, in the measured spectrum, the calculated spectrum created by the sum of the baseline and the ^two pseudo Voigt functions whose height is constant with respect to the chemical shift isotropic value is added to the 1H chemical shift isotropic value -2 to 14 ppm. The measured spectrum was separated into two peaks and the height of the baseline was determined by fitting in the range of.
The peak after separation is defined as peak 1 and the peak located in the range of ¹ H chemical shift isotropic value is 7.3 to 7.7 ppm, and the apex of the peak after separation is ¹ H chemical shift isotropic value. The peak located in the range of 6 to 7.0 ppm was defined as peak 2.
Table 1 shows the variables (x ₀ , H, η, A) of the pseudo Voigt functions of peak 1 and peak 2 obtained by peak separation.
For the scaling coefficient A, a numerical value standardized so that the sum of A of all peaks is 100 is described.
In addition, the height of the baseline is a value standardized by dividing by the sum (100) of A of the two peaks.

The numerical values in Table 1 show the average values of the variables (x ₀ , H, η, A) obtained by the peak separation of the measured spectrum by three measurements.
In addition, FIGS. 1, 2 and 3 show the measured spectrum (indicated as "actual measurement" in the figure) and the spectrum of each peak calculated by the variables in Table 1 (indicated as "peak 1" and "peak 2" in the figure). And the calculated spectrum (indicated as "calculation" in the figure) and the residual of the measured and calculated spectrum (indicated as "residual" in the figure) are shown.
Peaks 1 and 2 calculated by substituting the values in Table 1 into the variables x _0, H, η, and A in equation (1) are integrated in the range of ¹ H chemical shift isotropic value -2 to 14 ppm to reach the peak. The integral value 1 and the peak integral value 2 are calculated, and the ratio of the peak integral value 1 to the total value of the peak integral values (peak integral ratio 1) and the ratio of the peak integral value 2 to the total value of the peak integral values (peak integral ratio 2). ) Is shown in Table 2.
In the examples and comparative examples of the present invention, the ratio of the peak integration ratio 1 to the A value of peak 1 and the ratio of the peak integration ratio 2 to the A value of peak 2 are both in the range of 95% or more and 105% or less. Therefore, there is no problem, but if it is less than 95% or more than 105%, the range of 1H chemical shift isotropic values for integrating the fitting and the pseudo ^- Vault function after fitting can be extended and recalculated. can.

^In the above 1H spectrum, the OH peak usually rarely exceeds 7.0 ppm, and the NH peak appears on the higher side than the OH peak. Therefore, the peak near 6.0 ppm is derived from OH. The peak, the peak near 7.5 ppm, can be estimated to be the peak derived from NH ₄₊ ^.

(Discussion)
From the above results, the ammonium niobate hydrates (samples) of Examples 1 and 2 have a peak of ¹ H chemical shift isotropic value 7.3 to 7 using a pseudo Vogt function in solid ¹ H-NMR measurement. Separated into two peaks, a peak located in the range of .7 ppm (hereinafter, peak 1) and a peak located in the range of ¹ H chemical shift isotropic value of 5.6 to 6.0 ppm (hereinafter, peak 2). The value obtained by integrating the pseudo Voigt function of peak 1 in the range of ¹ H chemical shift isotropic value -2 to 14 ppm is defined as the peak integral value 1, and the pseudo Voigt function of peak 2 is defined as the ¹ H chemical shift equilateral value -2 to 14 ppm. When the value integrated in the range was set to the peak integral value 2, it was found that the ratio of the peak integral value 1 to the total value of the peak integral value 1 and the peak integral value 2 was 40% or more.

<Reactivity>
The ammonium niobium hydrate (sample) obtained in Examples 1 and 2 or the niobium hydroxide (sample) obtained in Comparative Example 1 and sodium carbonate were added to Nb: Na = 1.0: 1.1 (mol). The mixture was mixed so as to have a ratio of), and heated in the air so as to maintain 850 ° C. (product temperature) for 1 hour to obtain a baked product.
The obtained fired product was subjected to XRD measurement under the following conditions using the device name "MiniFlexII manufactured by Rigaku Co., Ltd." to obtain a diffraction pattern (Figs. 4, 5 and 6), and the peak intensity and peak intensity ratio were obtained based on this. Asked.

= XRD measurement conditions =
X-ray source: CuKα, operating axis: 2θ / θ, measuring method: continuous, counting unit: cps
Start angle: 37 °, end angle: 41 °,
Sampling width: 0.01 °, scan speed: 0.1 ° / min,
Voltage: 50kV, Current: 300mA
Divergence slit: 2/3 °, divergence length: 10 mm
Scattering slit: 2/3 °, light receiving slit: 0.15 mm

The evaluation was made according to the following criteria.
〇 (good): The XRD peak intensity ratio (32 ° ± 0.5 ° / 29 ° ± 0.5 °) was 10 or more.
X (poor): The XRD peak intensity ratio (32 ° ± 0.5 ° / 29 ° ± 0.5 °) was less than 10.

As a result of the above X-ray diffraction, 2θ = 32 ° ± 0.5 ° attributable to sodium niobium (NaNbO ₃ ) with respect to the peak intensity of 2θ = 29 ° ± 0.5 ° attributable to Na ₂ Nb ₄ O ₁₁ . The peak intensity ratio, that is, the X-ray intensity ratio (32 ° ± 0.5 ° / 29 ° ± 0.5 °) is significantly higher in Examples 1 and 2 than in Comparative Example 1, and is 10 or more, especially 20 or more, among them. It was 30 or more. That is, most of the fired product was composed of Na Nb O ₃ , and impurities such as Na ₂ Nb ₄ O ₁₁ were few. The identification of NaNbO ₃ and Na ₂ Nb ₄ O ₁₁ was performed based on the respective card numbers (NaNbO _3: 01-074-2440, Na ₂ Nb ₄ O ₁₁ : 01-072-1694).
From this, the ammonium niobate hydrates (samples) of Examples 1 and 2 have high reactivity with alkali metal salts such as sodium carbonate, and when they are mixed with sodium carbonate and fired, they are heated to a high temperature using an autoclave or the like. It was found that sodium niobate (NaNbO ₃ ) with less impurities can be obtained without reacting under high pressure conditions or via niobide pentoxide.

<Nb yield>
A part (Bg) was collected from the mass (Ag) of the ammonium niobate hydrate (sample) obtained in the examples, and the collected product was fired in the air at 800 ° C. for 1 hour, and then the obtained Nb ₂ was obtained. The mass (Cg) of O ₅ was measured, and the Nb yield was calculated from the following formula.
Nb yield (%) = C x A ÷ B ÷ 4.53 x 100
In addition, 30 mL of an aqueous niobium fluoride solution containing Nb at 151 g / L in terms of Nb ₂ O ₅ contains 4.53 g in terms of Nb ₂ O ₅ .

<Measurement of D50N>
Laser diffraction / scattering method Particle size distribution measuring device MT3300EXII (Microtrac Bell) is filled with a dispersion medium (0.1 mass% sodium hexametaphosphate aqueous solution) in the circulation device and measurement cell, and the sample is circulated while the dispersion medium is circulated. Was charged to the circulation device until it was displayed that the device was within the measurable range. After confirming that the display was stable, the measurement was performed.

<Measurement of D50D>
Place 2 mg of the sample in a 100 mL glass beaker, fill the 0.1 mass% hexametaphosphate aqueous solution up to the 50 mL mark line of the glass beaker, and use an ultrasonic cleaner VS-100III (manufactured by AS ONE) at an output of 40 W for 3 minutes. D50D was measured by operating in the same manner as in the case of D50N, except that the slurry obtained by performing ultrasonic treatment was charged into the sample circulation device.
For D50N / D50D, the values obtained by the above two types of measurements were used for calculation.

<Liquidity evaluation>
The samples to be used for the fluidity evaluation were prepared by scaling up each Example and each Comparative Example.
The fluidity evaluation was performed by putting 500 g of powder (Nb ₂ O ₅ equivalent) into a PP (polypropylene) powder funnel (manufactured by AS ONE, diameter 60 mm, foot length 18 mm, foot outer diameter 15 mm) over 10 seconds. rice field.
For the evaluation, the state after charging was observed, and those with clogging were marked with "x" and those without clogging were marked with "○".

The Nb yield of Example 1 was sufficiently high. From this, it was found that in order to increase the Nb yield, it is preferable to mix and heat the niobium fluoride aqueous solution and the ammonium carbonate salt.
Considering the results of the reactivity test in Table 3, if D50N is 1 μm or more and 100 μm or less, particularly preferably 10 μm or more and 50 μm or less, and D50N / D50D is 10 or less, particularly preferably 2 or less. It was found that it has excellent fluidity and can further enhance the reactivity with alkali metal salts.

Claims (5)

A compound containing NH ₄₊ and OH in addition to Nb and O ⁽ also referred to as "ammonium niobate hydrate").
The ammonium niobate hydrate has an integrated volume particle size at an integrated volume of 50% by volume measured by a laser diffraction / scattering method particle size distribution measurement method before ultrasonic dispersion treatment (D50N) and after ultrasonic dispersion treatment at 40 W for 30 seconds. When each of (D50D) was measured, D50N was 1 μm or more and 100 μm or less, and the ratio of D50N to D50D (D50N / D50D) was 10 or less.
In solid ^{1 1} H-NMR measurement, the obtained signal is subjected to Fourier conversion, and the measured spectrum obtained by correcting the phase and chemical shift isotropic values has a baseline whose height is constant with respect to the chemical shift isotropic value. The calculated spectrum created by the sum of the two pseudo-Vault functions is fitted in the range of ¹ H chemical shift isotropic value -2 to 14 ppm, and the measured spectrum is separated into two peaks and a baseline is defined and separated. The peak with the latter peak located in the range of ¹ H chemical shift isotropic value of 7.3 to 7.7 ppm is defined as peak 1, and the peak after separation is in the range of ¹ H chemical shift isotropic value of 5.6 to 7.0 ppm. The peak located at is defined as peak 2.
The value obtained by integrating the pseudo-Vault function of peak 1 in the range of ¹ H chemical shift isotropic value -2 to 14 ppm is defined as the peak integral value 1, and the pseudo-Folk function of peak 2 is defined as the ¹ H chemical shift isotropic value of -2 to 14 ppm. Ammonium niobate hydrate in which the ratio of the peak integral value 1 to the total value of the peak integral value 1 and the peak integral value 2 is 40% or more, where the value integrated in the range is the peak integral value 2. The ammonium niobate hydrate and sodium carbonate are mixed so as to have Nb: Na = 1.0: 1.1 (mol ratio), and the temperature is maintained at 850 ° C. (product temperature) for 1 hour in the air. When heated, in X-ray diffraction, 2θ = 29 ° ± 0.5 ° peak intensity (a) attributable to Na ₂ Nb ₄ O ₁₁ versus 2θ = 32 ° ± 0 attributable to sodium niobium (NaNbO ₃ ). The ammonium niobium hydrate according to claim 1, wherein a calcined product having a peak intensity (b) of 5 ° and an X-ray intensity ratio (32 ° ± 0.5 ° / 29 ° ± 0.5 °) of 10 or more can be obtained. .. A method for producing ammonium niobate hydrate, which comprises mixing an aqueous solution of niobium fluoride and an ammonium carbonate salt and heating them to 55 ° C. or higher for reaction to obtain ammonium niobate hydrate.
The ammonium niobate hydrate produced is a compound containing ^NH ₄₊ and OH in addition to Nb and O.
When the integrated volume particle size at the integrated volume 50% by volume measured by the laser diffraction / scattering method particle size distribution measurement method was measured before the ultrasonic dispersion treatment (D50N) and at 40 W and after the ultrasonic dispersion treatment for 30 seconds (D50D), respectively. D50N is 1 μm or more and 100 μm or less, and the ratio of D50N to D50D (D50N / D50D) is 10 or less.
In solid ^{1 1} H-NMR measurement, the obtained signal is subjected to Fourier conversion, and the measured spectrum obtained by correcting the phase and chemical shift isotropic values has a baseline whose height is constant with respect to the chemical shift isotropic value. The calculated spectrum created by the sum of the two pseudo-Vault functions is fitted in the range of ¹ H chemical shift isotropic value -2 to 14 ppm, and the measured spectrum is separated into two peaks and a baseline is defined and separated. The peak with the latter peak located in the range of ¹ H chemical shift isotropic value of 7.3 to 7.7 ppm is defined as peak 1, and the peak after separation is in the range of ¹ H chemical shift isotropic value of 5.6 to 7.0 ppm. The peak located at is defined as peak 2.
The value obtained by integrating the pseudo-Vault function of peak 1 in the range of ¹ H chemical shift isotropic value -2 to 14 ppm is defined as the peak integral value 1, and the pseudo-Folk function of peak 2 is defined as the ¹ H chemical shift isotropic value of -2 to 14 ppm. When the value integrated in the range is defined as the peak integral value 2, the ratio of the peak integral value 1 to the total value of the peak integral value 1 and the peak integral value 2 is 40% or more. Production method. The method for producing ammonium niobate hydrate according to claim 3, wherein the pH is adjusted to 7.0 or higher by mixing an aqueous solution of niobium fluoride and an ammonium carbonate salt. A method for producing a niobate compound, wherein the ammonium niobate hydrate according to claim 1 or 2 and an alkali metal salt are mixed and heated in the air.

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