Tantalum pentoxide powder, and preparation method therefor and use thereof

Abstract

The present invention relates to a high-purity tantalum pentoxide powder, and a preparation method therefor and the use thereof. The powder is characterized by the numerical value ratio of a Fisher particle size to an apparent density being greater than 1.5, preferably greater than 2.0, more preferably greater than 2.5, more preferably greater than 3.0, more preferably greater than 3.5, and more preferably greater than 4.5; and same is more preferably 2.0-15.0, and more preferably 2.0-5.0; and the powder is more preferably a high-purity tantalum oxide having a purity of 99.995% or more. The preparation method comprises: (1) adding a fluorotantalic acid (H2TaF7) solution into a reaction kettle, and adding sulfuric acid into the fluorotantalic acid solution, such that the acidity of the fluorotantalic acid solution exceeds 2 mol / L, controlling the temperature of the reaction kettle to exceed 80ºC, adding a precipitant thereto until the pH of the reaction solution is 8-10, then stopping introducing ammonia, and carrying out aging to obtain a tantalum hydroxide slurry; (2) filtering and washing the tantalum hydroxide slurry obtained in step (1), and then subjecting same to solid-liquid separation to obtain a tantalum hydroxide filter cake; (3) drying the filter cake obtained in step (2) to obtain a tantalum hydroxide powder; (4) calcining the tantalum hydroxide powder obtained in step (3), and crushing and screening the calcined sample to obtain a tantalum pentoxide powder; and (5) subjecting the tantalum pentoxide powder obtained in step (4) to a heat treatment at a temperature of 1000-1500ºC to obtain a high-purity tantalum pentoxide powder.

Description

Tantalum pentoxide powder and its preparation method and use Technical Field

[0001] The present invention relates to the field of powder manufacturing, and more particularly to a high-purity tantalum pentoxide powder, a preparation method thereof, and applications thereof. Background Art

[0002] Tantalum pentoxide, commonly known as tantalum oxide (the two can be used interchangeably in this article), is the raw material for the production of metallic tantalum and also has important applications in other industrial fields.

[0003] Chinese invention CN114057227B discloses a low-carbon, high-purity tantalum pentoxide powder and its production method. This invention successfully reduces the carbon content in tantalum oxide to below 15 ppm. However, while the resulting carbon impurity content is low, the overall purity is still unsatisfactory, and the process stability also needs to be improved. Furthermore, the invention does not address the relationship between Fisher's particle size and bulk density.

[0004] Summary of the Invention

[0005] According to a first aspect, the present invention provides a tantalum oxide powder suitable for use as a raw material for preparing tantalum powder by a magnesium reduction method. The tantalum oxide powder has a Fisher particle size (in μm) and an apparent density (in g / cm 3 The ratio of the particle size is greater than 1.5 (for example, the particle size of the fiber is 6.78 μm, the apparent density is 2.3 g / cm 3 , the ratio of the two is 6.78÷2.3=2.95).

[0006] The ratio of the Fisher particle size to the apparent density of the tantalum oxide powder of the present invention is greater than 1.5, preferably greater than 2.0, more preferably greater than 2.5, more preferably greater than 3.0, more preferably greater than 3.5, more preferably greater than 4.5; more preferably 2.0-15.0, most preferably 3.0-5.0.

[0007] Preferably, the tantalum oxide powder is a high-purity tantalum oxide powder with a purity of 99.995% or more, and more preferably, the tantalum oxide powder is a high-purity tantalum oxide powder with a purity of 99.999% or more. The inventors have found that the higher the purity of tantalum oxide, the more conducive it is to improving the electrical properties of tantalum powder.

[0008] The second aspect of the present invention provides a method for preparing tantalum oxide powder, characterized in that before adding a precipitant to a fluorotantalic acid (H2TaF7) solution, sulfuric acid is added to the fluorotantalic acid solution to make the acidity of the fluorotantalic acid solution exceed 2 mol / L, preferably the acidity of the fluorotantalic acid solution exceeds 2.2 mol / L, and more preferably 2.5-3.5 mol / L.

[0009] Preferably, the method comprises:

[0010] (1) adding a fluorotantalate (H2TaF7) solution into a reaction kettle, adding sulfuric acid to make the acidity of the fluorotantalate solution at least 2 mol / L, adding a precipitant (e.g., passing ammonia gas) until the pH of the reaction solution is 8 to 10 (preferably 8 to 9.5), then stopping the addition of the precipitant and aging the reaction solution (e.g., aging for 2 to 5 hours, preferably 3 to 4 hours) to obtain a tantalum hydroxide slurry;

[0011] (2) filtering and washing the tantalum hydroxide slurry obtained in step (1), and then performing solid-liquid separation to obtain a tantalum hydroxide filter cake;

[0012] (3) drying the filter cake obtained in step (2) to obtain tantalum hydroxide powder;

[0013] (4) calcining the tantalum hydroxide powder obtained in step (3), crushing and sieving the calcined sample to obtain tantalum pentoxide powder; and

[0014] (5) The tantalum pentoxide powder obtained in step (4) is heat-treated at a temperature of 1000° C. to 1500° C. to obtain high-purity tantalum pentoxide powder.

[0015] In step (1), the preferred acidity range is 2 mol / L-5 mol / L. More preferably, when the pH of the reaction solution in step (1) is 8-9, the addition of the precipitant is stopped.

[0016] In step (1), the fluorotantalate solution may be heated, and the temperature of the reactor may be controlled to be above 60°C, preferably above 80°C, and more preferably 85-95°C.

[0017] In step (1), the oxide content of the fluorotantalate (H2TaF7) solution is preferably 20-120 g / L, more preferably 30-110 g / L, for example 40-100 g / L, calculated as Ta2O5. Advantageously, this wider range provides greater process flexibility. "Calculated as Ta2O5" is clear to those skilled in the art. However, to make it easier for those skilled in the art to understand, the inventors explain "calculated as Ta2O5" as follows: This is a commonly used method for expressing the concentration of a fluorotantalate solution (sometimes referred to herein as "tantalate solution"). Tantalum in the fluorotantalate solution mainly exists in the form of a complex. During the measurement process, the tantalum content in the fluorotantalate is detected and then converted into the Ta2O5 content to express the concentration of the tantalate solution. For details, refer to the national standard GB / T15076.1.

[0018] In step (1), the precipitant includes, but is not limited to, one or more of sodium bicarbonate, ammonium carbonate, urea, ammonia water, ammonia gas, and sodium hydroxide. Preferably, ammonia gas is used as the precipitant; in this case, adding the precipitant can also be referred to as introducing ammonia gas. There is no limit on the rate of introducing ammonia gas, but it is preferably introduced slowly. In step (1), stirring is preferably performed in the reactor.

[0019] Preferably, the aging time (also referred to as the resting time) in step (2) is 2 to 5 hours. More preferably, the aging time is 3 to 4 hours. Preferably, the filtration and washing in step (2) is repeated multiple times. For example, the filtration and washing can be performed as follows: the tantalum hydroxide slurry obtained in step (1) is added to a filtration and washing tank, and then filtered and washed with hot pure water (e.g., hot pure water at 90 to 100° C.). Preferably, the solid-liquid separation is performed by negative pressure filtration.

[0020] Preferably, in step (3), drying is performed by placing the filter cake in a hot air oven and drying it at 80-180° C. (preferably 100-160° C., more preferably 120-140° C.), for example, for 8-12 hours (preferably 10-11.5 hours). The tantalum hydroxide powder obtained in this step is generally white.

[0021] Preferably, the calcination in step (4) is preferably carried out by charging the tantalum pentoxide powder obtained in step (3) into a crucible and placing it in a furnace. The furnace used here is preferably a muffle furnace. Preferably, the calcination temperature is 900°C to 1000°C (preferably 800°C to 900°C) and the calcination time is 8h to 12h (preferably 9-11h).

[0022] The high-temperature calcination heat treatment temperature in step (5) is preferably 1200°C to 1500°C (e.g., 1400°C), and the time is preferably 1 to 3 hours. In step (5), the sintering heat treatment atmosphere includes, but is not limited to, vacuum, inert atmosphere (e.g., helium, argon, neon, etc.), and air atmosphere. More preferably, it is carried out under vacuum.

[0023] Preferably, the high-temperature vacuum heat treatment temperature in step (5) is 1200° C. to 1400° C., more preferably 1200° C. to 1300° C. Preferably, the heat treatment time is 1 hour to 5 hours, such as 3 hours.

[0024] Preferably, the tantalum oxide powder obtained in step (5) has a ratio of Fisher's diameter to bulk density greater than 1.5, preferably greater than 2.0, more preferably greater than 2.5, more preferably greater than 3.0, more preferably greater than 3.5, more preferably greater than 4.5; more preferably between 2.0 and 15.0, more preferably between 3.0 and 5.0. More preferably, the tantalum oxide powder has a purity of 99.995%, more preferably 99.999% or greater.

[0025] After extensive experiments, the inventors discovered that by using a higher acidity as described in step (1), the temperature in the reactor can be increased while consuming less external energy due to the heat released by the neutralization reaction. Moreover, the inventors unexpectedly discovered that by using such an acidity, the tantalum oxide powder according to the first aspect of the present invention can be stably produced. The so-called "stable" means that the tantalum powder produced each time can meet the requirements of the ratio of particle size to bulk density and purity specified by the present invention, and there will be no situation where the process meets the requirements one time but not the next, or only one of the two is met at a time. In terms of process stability, the selection of acidity in step (1) (especially with the aid of sulfuric acid) has achieved outstanding and unexpected beneficial effects.

[0026] The overall purity mentioned in this article focuses more on the sum of all impurity contents, rather than being limited to the content of one or more common impurities.

[0027] The third aspect of the present invention also relates to the use of the above-mentioned tantalum oxide powder, such as use in the electronics industry, use in the production of lithium tantalate single crystals and optical glass (especially high-refractive and low-dispersion special optical glass), and use as a catalyst in chemical industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The following drawings are provided to aid understanding of the present invention. The drawings are not intended to limit the scope of the present invention.

[0029] Figure 1 is an electron microscope photograph of the tantalum oxide powder according to the first aspect of the present invention or the tantalum oxide powder obtained by the method according to the second aspect. This figure shows that the microstructure is improved. DETAILED DESCRIPTION

[0030] In order to better illustrate the present invention, the following examples are provided. These examples are only for better enabling those skilled in the art to more easily understand the present invention, and are not intended to limit the present invention.

[0031] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions. If the manufacturers of the reagents or instruments are not specified, they are all commercially available conventional products.

[0032] For the purposes of this specification, all numbers representing the amounts of ingredients, reaction conditions, etc. in the specification and claims are to be understood as being modified by the term "about" in all cases, unless otherwise specified. Accordingly, the numerical parameters given in the following specification and the appended claims are approximate values, which may vary depending on the desired properties sought to be obtained by the present invention, unless otherwise indicated. At a minimum, and without intending to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be interpreted according to the number of reported significant figures and according to conventional rounding techniques.

[0033] The impurity content of tantalum pentoxide powder is analyzed according to the national standard GB / T15076.8, the Fisher particle size is analyzed according to the national standard GB / T3249, and the bulk density is analyzed according to the national standard GB / T1479.1.

[0034] Example 1:

[0035] 1. Measure 100L of fluorotantalate solution, with an oxide content of 90g / L calculated as Ta2O5, and add it to a reactor. Then add sulfuric acid to adjust the acidity of the fluorotantalate solution to 2.8mol / L. Heat the fluorotantalate solution and control the reactor temperature to 95°C. Slowly add ammonia water to the tantalate solution until the pH of the reaction solution reaches 9 to obtain tantalum hydroxide slurry, which is then aged for 3h.

[0036] 2. The tantalum hydroxide slurry was transferred to a filter washing tank, and the reaction precipitate was repeatedly filtered and washed with hot pure water at a temperature of 95°C. Finally, negative pressure filtration was used for solid-liquid separation to obtain a white filter cake.

[0037] 3. Place the white filter cake into a tray, place it in a hot air oven, and dry it at 100°C for 10 hours to obtain tantalum hydroxide white powder.

[0038] 4. The white powder of tantalum hydroxide was placed in a crucible and calcined in a muffle furnace at a temperature of 900°C for 10 h. The sintered sample was crushed and sieved to obtain tantalum pentoxide powder.

[0039] 5. The tantalum pentoxide powder is placed in a crucible, placed in a high-temperature vacuum furnace, and heated at a temperature of 1300° C. for 2 hours to perform heat treatment to obtain high-purity tantalum pentoxide powder.

[0040] The impurity content of the tantalum pentoxide powder was analyzed and the purity of tantalum oxide was calculated. The Fisher particle size and apparent density were analyzed and the ratio of the Fisher particle size to the apparent density test value was calculated. The measured results are listed in Table 1.

[0041] Example 2:

[0042] 1. Measure 100L of fluorotantalate solution, with an oxide content of 90g / L calculated as Ta2O5, and add it to a reactor. Then add sulfuric acid to adjust the acidity of the fluorotantalate solution to 2.2mol / L. Heat the fluorotantalate solution and control the reactor temperature to 85°C. Slowly add ammonia water to the tantalate solution until the pH of the reaction solution reaches 9 to obtain tantalum hydroxide slurry. Aging time: 3h.

[0043] 2. The tantalum hydroxide slurry was transferred to a filter washing tank, and the reaction precipitate was repeatedly filtered and washed with hot pure water at a temperature of 95°C. Finally, negative pressure filtration was used for solid-liquid separation to obtain a white filter cake.

[0044] 3. Place the white filter cake into a tray, place it in a hot air oven, and dry it at 100°C for 10 hours to obtain tantalum hydroxide white powder.

[0045] 4. The white powder of tantalum hydroxide was placed in a crucible and calcined in a muffle furnace at a temperature of 900°C for 10 h. The sintered sample was crushed and sieved to obtain tantalum pentoxide powder.

[0046] 5. The tantalum pentoxide powder is placed in a crucible, placed in a high-temperature vacuum furnace, and heated at 1350° C. for 2 hours to obtain high-purity tantalum pentoxide powder.

[0047] The impurity content of the tantalum pentoxide powder was analyzed and the purity of tantalum oxide was calculated. The Fisher particle size and apparent density were analyzed and the ratio of the Fisher particle size to the apparent density test value was calculated. The measured results are listed in Table 1.

[0048] Example 3:

[0049] 1. Measure 100L of fluorotantalate solution, with an oxide content of 60g / L calculated as Ta2O5, and add it to a reactor. Then add sulfuric acid to adjust the acidity of the fluorotantalate solution to 2.5mol / L. Heat the fluorotantalate solution and control the reactor temperature to 82°C. Slowly add ammonia water to the tantalate solution until the pH of the reaction solution reaches 10 to obtain tantalum hydroxide slurry. Aging time: 3h.

[0050] 2. The tantalum hydroxide slurry was transferred to a filter washing tank, and the reaction precipitate was repeatedly filtered and washed with hot pure water at a temperature of 95°C. Finally, negative pressure filtration was used for solid-liquid separation to obtain a white filter cake.

[0051] 3. Place the white filter cake into a tray, place it in a hot air oven, and dry it at 100°C for 10 hours to obtain tantalum hydroxide white powder.

[0052] 4. The white powder of tantalum hydroxide was placed in a crucible and calcined in a muffle furnace at a temperature of 800°C for 10 hours. The sintered sample was crushed and sieved to obtain tantalum pentoxide powder.

[0053] 5. The tantalum pentoxide powder is placed in a crucible, placed in a high-temperature vacuum furnace, and heated at a temperature of 1200° C. for 2 hours to perform heat treatment to obtain high-purity tantalum pentoxide powder.

[0054] The impurity content of the tantalum pentoxide powder was analyzed and the purity of tantalum oxide was calculated. The Fisher particle size and apparent density were analyzed and the ratio of the Fisher particle size to the apparent density test value was calculated. The measured results are listed in Table 1.

[0055] Example 4:

[0056] 1. Measure 100L of fluorotantalate solution, with an oxide content of 50g / L calculated as Ta2O5, and add it to a reactor. Then add sulfuric acid to adjust the acidity of the fluorotantalate solution to 2.5mol / L. Heat the fluorotantalate solution and control the reactor temperature to 85°C. Slowly add ammonia water to the tantalate solution until the pH of the reaction solution reaches 10 to obtain tantalum hydroxide slurry. Aging time: 3h.

[0057] 2. The tantalum hydroxide slurry was transferred to a filter washing tank, and the reaction precipitate was repeatedly filtered and washed with hot pure water at a temperature of 95°C. Finally, negative pressure filtration was used for solid-liquid separation to obtain a white filter cake.

[0058] 3. Place the white filter cake into a tray, place it in a hot air oven, and dry it at 100°C for 10 hours to obtain tantalum hydroxide white powder.

[0059] 4. The white powder of tantalum hydroxide was placed in a crucible and calcined in a muffle furnace at a temperature of 800°C for 10 hours. The sintered sample was crushed and sieved to obtain tantalum pentoxide powder.

[0060] 5. The tantalum pentoxide powder is placed in a crucible, placed in a high-temperature vacuum furnace, and heated at a temperature of 1250° C. for 2 hours to perform heat treatment to obtain high-purity tantalum pentoxide powder.

[0061] The impurity content of the tantalum pentoxide powder was analyzed and the purity of tantalum oxide was calculated. The Fisher particle size and apparent density were analyzed and the ratio of the Fisher particle size to the apparent density test value was calculated. The measured results are listed in Table 1.

[0062] Example 5:

[0063] 1. Measure 100L of fluorotantalate solution, with an oxide content of 35g / L calculated as Ta2O5, and add it to a reactor. Then add sulfuric acid to adjust the acidity of the fluorotantalate solution to 2.5mol / L. Heat the fluorotantalate solution and control the temperature of the reactor to 85°C. Slowly add ammonia water to the tantalate solution until the pH of the reaction solution reaches 10 to obtain tantalum hydroxide slurry. Aging time: 3h.

[0064] 2. The tantalum hydroxide slurry was transferred to a filter washing tank, and the reaction precipitate was repeatedly filtered and washed with hot pure water at a temperature of 95°C. Finally, negative pressure filtration was used for solid-liquid separation to obtain a white filter cake.

[0065] 3. Place the white filter cake into a tray, place it in a hot air oven, and dry it at 100°C for 10 hours to obtain tantalum hydroxide white powder.

[0066] 4. The white powder of tantalum hydroxide was placed in a crucible and calcined in a muffle furnace at a temperature of 800°C for 10 hours. The sintered sample was crushed and sieved to obtain tantalum pentoxide powder.

[0067] 5. The tantalum pentoxide powder is placed in a crucible, placed in a high-temperature vacuum furnace, and heated at 1150° C. for 2 hours to obtain high-purity tantalum pentoxide powder.

[0068] The impurity content of the tantalum pentoxide powder was analyzed and the purity of tantalum oxide was calculated. The Fisher particle size and apparent density were analyzed and the ratio of the Fisher particle size to the apparent density test value was calculated. The measured results are listed in Table 1.

[0069] Example 6:

[0070] 1. Measure 100L of fluorotantalate solution, with an oxide content of 25g / L calculated as Ta2O5, and add it to a reactor. Then add sulfuric acid to adjust the acidity of the fluorotantalate solution to 2.5mol / L. Heat the fluorotantalate solution and control the reactor temperature to 85°C. Slowly add ammonia water to the tantalate solution until the pH of the reaction solution reaches 10 to obtain tantalum hydroxide slurry. Aging time: 3h.

[0071] 2. The tantalum hydroxide slurry was transferred to a filter washing tank, and the reaction precipitate was repeatedly filtered and washed with hot pure water at a temperature of 95°C. Finally, negative pressure filtration was used for solid-liquid separation to obtain a white filter cake.

[0072] 3. Place the white filter cake into a tray, place it in a hot air oven, and dry it at 100°C for 10 hours to obtain tantalum hydroxide white powder.

[0073] 4. The white powder of tantalum hydroxide was placed in a crucible and calcined in a muffle furnace at a temperature of 800°C for 10 hours. The sintered sample was crushed and sieved to obtain tantalum pentoxide powder.

[0074] 5. The tantalum pentoxide powder is placed in a crucible, placed in a high-temperature vacuum furnace, and heated at 1150° C. for 2 hours to obtain high-purity tantalum pentoxide powder.

[0075] The impurity content of the tantalum pentoxide powder was analyzed and the purity of tantalum oxide was calculated. The Fisher particle size and apparent density were analyzed and the ratio of the Fisher particle size to the apparent density test value was calculated. The measured results are listed in Table 1.

[0076] Table 1 Analysis results of high purity tantalum pentoxide

[0077] As can be seen from Table 1, the ratio of the Fisher grain size to the bulk density of the tantalum pentoxide powder obtained by the method of the present invention is significantly ideal. In particular, its purity reaches 99.999%.

Claims

1. A tantalum pentoxide powder, characterized in that: The ratio of Fisher particle size to bulk density is greater than 1.5, preferably greater than 2.0, more preferably greater than 2.5, more preferably greater than 3.0, more preferably greater than 3.5, more preferably greater than 4.5; more preferably 2.0-15.0, more preferably 3.0-5.0; more preferably 99.995%, most preferably 99.999% or more purity of tantalum oxide.

2. A method for preparing tantalum pentoxide powder, characterized in that: Sulfuric acid is added to the fluorotantalate solution to make the acidity of the fluorotantalate solution exceed 2 mol / L, preferably the acidity of the fluorotantalate solution exceeds 2.2 mol / L, more preferably 2.5-3.5 mol / L.

3. A method for preparing tantalum pentoxide powder, the method comprising: (1) adding a fluorotantalate (H2TaF7) solution into a reaction kettle, adding sulfuric acid into the fluorotantalate solution to make the acidity of the fluorotantalate solution exceed 2 mol / L, controlling the temperature of the reaction kettle to be above 80°C (preferably above 85°C, more preferably 85-95°C), adding a precipitant until the pH of the reaction solution is 8-10 (preferably 8-9.5), then stopping the flow of ammonia, and performing aging (for example, aging for 2-5 hours, preferably 3-4 hours) to obtain tantalum hydroxide slurry; (2) filtering and washing the tantalum hydroxide slurry obtained in step (1), and then performing solid-liquid separation to obtain a tantalum hydroxide filter cake; (3) drying the filter cake obtained in step (2) to obtain tantalum hydroxide powder; (4) calcining the tantalum hydroxide powder obtained in step (3), crushing and sieving the calcined sample to obtain tantalum pentoxide powder; and (5) The tantalum pentoxide powder obtained in step (4) is heat treated at a temperature of 1000° C. to 1500° C. to obtain high-purity tantalum pentoxide powder. More preferably, in step (1), when the pH of the reaction solution is between 8 and 9, the addition of the precipitant is stopped.

4. The method according to claim 3, wherein in step (1), the precipitant is selected from one or more of sodium bicarbonate, ammonium carbonate, urea, ammonia water, ammonia gas, and sodium hydroxide, preferably, ammonia water is used as the precipitant; and / or preferably, stirring is performed in the reactor, more preferably, the stirring time is 5 to 10 minutes.

5. The method according to any one of claims 3-4, wherein the aging time in step (2) is 2 to 5 hours, more preferably 3 to 4 hours; and / or wherein preferably, the filtration and washing in step (2) are repeated multiple times; and / or wherein in step (2), solid-liquid separation is performed by negative pressure filtration.

6. The method according to any one of claims 3 to 5, wherein in step (3), drying is carried out by placing the filter cake in a hot air oven and drying it at 80 to 180° C. (preferably 100 to 160° C., more preferably 120 to 140° C.), for example, drying for 8 h to 12 h (preferably 10 to 11.5 h).

7. The method according to any one of claims 3 to 6, wherein the calcination in step (4) is carried out by: charging the tantalum hydroxide powder obtained in step (3) into a crucible and placing it in a furnace, wherein the furnace used is preferably a muffle furnace; preferably, the calcination temperature is 900° C. to 1000° C., and the calcination time is preferably 8 h to 12 h (preferably 9-11 h).

8. The method according to any one of claims 3 to 7, wherein in the step (5), the high temperature heat treatment temperature is preferably 1200°C to 1500°C (preferably 1200°C to 1400°C, for example 1400°C, more preferably 1200-1300°C), and the time is preferably 1 to 5 hours; and / or wherein preferably, the sintering heat treatment atmosphere includes but is not limited to vacuum, inert atmosphere (for example helium, argon, neon, etc.) and atmospheric atmosphere, and is more preferably carried out under vacuum.

9. Tantalum pentoxide powder obtained according to the method of any one of claims 3 to 8, preferably the powder has a ratio of Fisher particle size to bulk density test value greater than 1.5, preferably greater than 2.0, more preferably greater than 2.5, more preferably greater than 3.0, more preferably greater than 3.5, more preferably greater than 4.5; more preferably 2.0-15.0, more preferably 3.0-5.0; more preferably 99.995% or more high purity tantalum oxide.

10. Use of the tantalum pentoxide powder according to claim 1 or 9 in the production of lithium tantalate single crystals and catalysts and in the production of optical glass.

Images