A preparation method of ultrafine niobium oxide

Abstract

The present invention belongs to the technical field of powder metallurgy. More specifically, it relates to a preparation method of ultrafine niobium oxide. The specific preparation steps of the present invention are as follows: by weight, take 90 - 100 parts of a gelatin solution with a mass fraction of 3 - 5%, 60 - 80 parts of a fluoniobate solution with a mass fraction of 10 - 15%, and 4 - 10 parts of an aluminum salt solution with a mass fraction of 3 - 6%; after mixing the fluoniobate solution, the aluminum salt solution and the gelatin solution, ultrasonically disperse them evenly to obtain a mixed solution; under the stirring state, add a precipitant to the mixed solution to adjust the pH to 9 - 10, continue stirring and reacting, then under the condition of a temperature of 2 - 6°C, refrigerate and stand for 24 - 56 h, then dry and crush to obtain a crushed material; calcine the crushed material in an air atmosphere, and then cool and disperse to obtain a calcined material; after pickling the obtained calcined material with hydrochloric acid, wash it with water and dry it to obtain ultrafine niobium oxide.

Description

Technical Field

[0001] The present invention belongs to the technical field of powder metallurgy. More specifically, it relates to a method for preparing ultrafine niobium oxide. Background Art

[0002] As an important electronic material, niobium pentoxide has been widely used in fields such as ceramic capacitors, piezoelectric ceramics, thick film capacitors, dielectric materials, magnetic materials, and optical materials. Although the total amount is not large, its growth in quantity and expansion in the industry are very rapid. Among them, niobium pentoxide used in capacitors occupies a large proportion, because adding niobium pentoxide can greatly improve the thermal stability of capacitors and at the same time obtain a stable and relatively high dielectric constant.

[0003] Generally, for high-quality target materials, one is required to have a high density (≥99.5%) and high purity (≥99.99%); the other is required to have a good microscopic phase structure, that is, the particle size of the target material crystals is in the micron range and is evenly distributed microscopically. In addition, the niobium pentoxide target material also needs to have good mechanical properties. One of the keys to preparing high-quality niobium pentoxide target materials lies in the physical parameters such as the particle size, dispersibility, and purity of the niobium pentoxide powder. At present, the preparation of niobium pentoxide powder mostly uses niobium fluoride acid and other raw materials. After precipitation reaction, a large amount of inorganic anions such as fluoride ions, chloride ions, and sulfate ions are entrained in the obtained precursor niobium hydroxide, which requires a large amount of pure water for washing and is not easy to wash clean.

[0004] Based on this, how to develop a method for preparing ultrafine niobium oxide to solve the above technical problems is one of the technical problems still faced by those skilled in the art. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: aiming at the problem that in the existing preparation process of niobium oxide, agglomeration is likely to occur, resulting in too large a particle size of the final product, or a relatively wide particle size distribution range, making it difficult to obtain an ideal particle size and a narrow particle size distribution range, a method for preparing ultrafine niobium oxide is provided.

[0006] The purpose of the present invention is to provide a method for preparing ultrafine niobium oxide.

[0007] The above object of the present invention is achieved by the following technical solutions:

[0008] A method for preparing ultrafine niobium oxide, the specific preparation steps include:

[0009] By weight, take 90 - 100 parts of a gelatin solution with a mass fraction of 3 - 5%, 60 - 80 parts of a fluoniobate solution with a mass fraction of 10 - 15%, and 4 - 10 parts of an aluminum salt solution with a mass fraction of 3 - 6%;

[0010] Mix the fluoroniobate solution, aluminum salt solution and gelatin solution, and disperse them evenly by ultrasonic treatment to obtain a mixed solution;

[0011] While stirring, add a precipitating agent dropwise to the mixed solution to adjust the pH to 9 - 10. After continuing the stirring reaction, refrigerate and let stand at 2 - 6 °C for 24 - 56 h, then dry and pulverize to obtain a pulverized material;

[0012] Calcine the pulverized material in an air atmosphere, and then cool and disperse it to obtain a calcined material;

[0013] Pickle the obtained calcined material with hydrochloric acid, wash it with water, and dry it to obtain ultrafine niobium oxide.

[0014] During the research process, the inventors found that when adding the precipitating agent to the fluoroniobate solution, when the concentration of niobium hydroxide formed exceeds the solubility product under this condition, the examples gradually form crystal nuclei by colliding with each other. After the crystal nuclei are formed, the crystal nucleus ions in the solution diffuse to the surface of the crystal nuclei, thereby causing the gradual growth of the crystal nuclei and forming precipitate particles. Based on this, the inventors selected trivalent aluminum salt and fluoroniobate as a compounding system. After the precipitating agent is added, a large number of crystal nuclei can be formed instantaneously. At this time, under the action of gelatin, once crystal nuclei are generated, they can be adsorbed and fixed by it. Thus, a loose precipitate is gradually formed. Specifically, the niobium ion is pentavalent and the aluminum ion is trivalent. Compared with conventional monovalent or divalent metal ions, when forming hydroxide precipitates, they need to combine with more hydroxide ions. Therefore, during the process of further arranging in a specific direction to form a precipitate on the basis of forming crystal nuclei, limited by the relatively slow rate of directional arrangement, the two can gradually form a loosely piled precipitate under the adsorption of gelatin;

[0015] As the reaction continues, after the temperature is lowered to 2 - 6 °C, the gelatin begins to gradually gel, thereby fixing the loose precipitate generated by the reaction and avoiding excessive agglomeration and sedimentation. During the subsequent calcination process, the hydroxide can be dehydrated to gradually form niobium oxide and aluminum oxide, while the gelatin is converted into carbon dioxide and water during the air calcination and is thus smoothly removed without adversely affecting the product purity; the presence of aluminum oxide can also, to a certain extent, prevent niobium oxide from aggregating with each other during the high-temperature calcination process; although aluminum oxide can agglomerate with niobium oxide to a certain extent, during the final pickling process, the acid can dissolve aluminum oxide but cannot dissolve niobium oxide. Thus, niobium oxide is purified; more importantly, the existence of the aforementioned loose precipitate provides a channel for the acid to smoothly diffuse and penetrate into the interior during the subsequent pickling process. When aluminum oxide is dissolved, the niobium oxide around it dissociates naturally, and the niobium oxide that aggregated with aluminum oxide during the calcination process is redispersed again. Thus, a pure, ultrafine niobium oxide product with a small particle size and a narrow particle size distribution range is obtained.

[0016] Further, the isoelectric point of the gelatin ≤ 7.

[0017] For gelatin, its molecular structure contains both amino groups and carboxyl groups. On the basis of the foregoing technical solution, during the process of adjusting the pH to 9 - 10, the hydroxide ions ionized in the solution can ionize the carboxyl groups in the gelatin molecular structure to carry negative charges. Thus, the gelatin molecules are stretched due to the repulsion of like charges, and the negatively charged carboxyl groups can adsorb niobium ions and aluminum ions in the system. In this way, once crystal nuclei are formed, they can be quickly adsorbed and fixed, avoiding further aggregation and growth of the crystal nuclei.

[0018] Further, the fluoro-niobate is selected from any one of potassium fluoro-niobate and sodium fluoro-niobate;

[0019] The aluminum salt is selected from any one of aluminum nitrate, aluminum chloride, and aluminum sulfate.

[0020] Further, the precipitating agent is compounded by ammonia water and ammonium bicarbonate according to a mass ratio of 1:1; wherein, the mass fraction of the ammonia water is 8 - 10%, and the mass fraction of the ammonium bicarbonate solution is 2 - 6%.

[0021] By further selecting ammonia water and ammonium bicarbonate with weak alkalinity to be compounded as the precipitating agent system, mainly because when they ionize in aqueous solution, the concentration of hydroxide ions will not be too high instantaneously, resulting in instantaneous precipitation and explosion aggregation. In addition, due to the presence of ammonium bicarbonate, carbon dioxide gas can be generated during the reaction process. Under the action of the carbon dioxide gas, the stretching of the gelatin molecular chain can become smoother, thus being more conducive to the formation of precipitates with a loose structure. The looser the structure, the more conducive it will be to the diffusion and penetration of acid into the interior during the subsequent reaction process.

[0022] Further, the calcination of the crushed material in an air atmosphere includes: transferring the crushed material into a muffle furnace, and heating and raising the temperature to 550 - 600 °C at a rate of 2 - 5 °C / min in an air atmosphere, and keeping it calcined for 4 - 6 h.

[0023] Further, the pickling of the calcined material with hydrochloric acid includes:

[0024] Mixing the calcined material and a hydrochloric acid solution with a mass fraction of 10 - 15% according to a mass ratio of 1:10 - 12;

[0025] Under the conditions of an ultrasonic frequency of 200 - 250 kHz and a temperature of 40 - 60 °C, continuously keep warm and carry out ultrasonic pickling for 4 - 6 h, then filter, collect the filter cake to obtain the pickled filter cake.

[0026] Further, the specific preparation steps further include:

[0027] By weight, take 90 - 100 parts of a gelatin solution with a mass fraction of 3 - 5%, 60 - 80 parts of a fluoniobate solution with a mass fraction of 10 - 15%, 4 - 10 parts of an aluminum salt solution with a mass fraction of 3 - 6%, and 0.6 - 0.8 parts of nano-graphene oxide;

[0028] After mixing the fluoniobate solution, the aluminum salt solution, the gelatin solution and the nano-graphene oxide, under the condition of an ultrasonic frequency of 250 - 300 kHz, ultrasonically disperse for 20 - 40 min to obtain a mixed solution;

[0029] Under stirring, add a precipitant to the mixed solution to adjust the pH to 9 - 10. After continuing the stirring reaction, under the condition of a temperature of 2 - 6 °C, refrigerate and stand for 24 - 56 h, then dry and pulverize to obtain a pulverized material;

[0030] Calcine the pulverized material in an air atmosphere, and then cool and disperse to obtain a calcined material;

[0031] Wash the obtained calcined material with hydrochloric acid, then wash with water and dry to obtain ultrafine niobium oxide.

[0032] Further, the D50 of the nano-graphene oxide is 60 - 80 nm.

[0033] The inventor further found that if a certain amount of nano-sized graphene oxide is added to the system, under the ultrasonic treatment condition of 250 - 300 kHz, the lamellar structure can be gradually peeled off to form a single-layer structure, thus fully exposing polar functional groups such as carboxyl, hydroxyl and epoxy groups in the graphene oxide structure. These functional groups can form hydrogen bond forces with gelatin. In this way, during the formation of the loose precipitate, the single-layer graphene oxide can be embedded in its loose structure. During the calcination process, graphene oxide is essentially carbon, and it can also be removed during the calcination in the air atmosphere. During this process, heat can be rapidly transferred, accelerating the calcination efficiency. At the same time, and more importantly, after it is removed, the precipitate adsorbed on its surface can also dissociate, thus forming ultrafine-sized niobium oxide. Specific Embodiments

[0034] The following specific examples are used to further illustrate the present invention, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the technical field.

[0035] Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0036] Example 1

[0037] By weight, take 90 parts of a gelatin solution with a mass fraction of 3%, 60 parts of a fluoniobate solution with a mass fraction of 10%, 4 parts of an aluminum salt solution with a mass fraction of 3%, and 0.6 parts of nano-graphene oxide;

[0038] The D50 of the nano-graphene oxide is 60 nm;

[0039] The isoelectric point of the gelatin is 6.8;

[0040] The fluoniobate is selected from potassium fluoniobate;

[0041] The aluminum salt is selected from aluminum nitrate;

[0042] The precipitant is prepared by compounding ammonia water and ammonium bicarbonate according to a mass ratio of 1:1; among them, the mass fraction of the ammonia water is 8%, and the mass fraction of the ammonium bicarbonate solution is 2%;

[0043] After mixing the fluoniobate solution, the aluminum salt solution, the gelatin solution and the nano-graphene oxide, under room temperature conditions, under an ultrasonic frequency of 250 kHz, ultrasonically disperse for 20 min to obtain a mixed solution;

[0044] Under a stirring state with a rotation speed of 300 r / min, add the precipitant to the mixed solution at a rate of 8 mL / min to adjust the pH to 9. After the addition is completed, continue to stir and react for 40 min with a stirrer at a rotation speed of 200 r / min. Subsequently, under the condition of a temperature of 2 °C, refrigerate and stand for 24 h, then vacuum freeze-dry to obtain a dry material. Then, after crushing the dry material, pass through a 400-mesh sieve to obtain a crushed material;

[0045] Transfer the crushed material into a muffle furnace, in an air atmosphere, heat and rise the temperature to 550 °C at a rate of 2 °C / min, keep the temperature and calcine for 6 h, cool to room temperature with the furnace, and disperse to obtain a calcined material;

[0046] After mixing the calcined material and a hydrochloric acid solution with a mass fraction of 10% according to a mass ratio of 1:10;

[0047] Under an ultrasonic frequency of 200 kHz and a temperature of 40 °C, continuously keep the temperature and ultrasonically pickle for 4 h, then filter, collect the filter cake to obtain a pickled filter cake, and then wash the pickled filter cake with water until the washing liquid is neutral, and dry to obtain ultrafine niobium oxide.

[0048] Example 2

[0049] By weight, take 95 parts of a gelatin solution with a mass fraction of 4%, 70 parts of a fluoniobate solution with a mass fraction of 12%, 6 parts of an aluminum salt solution with a mass fraction of 5%, and 0.7 parts of nano-graphene oxide;

[0050] The D50 of the graphene oxide nanosheets is 70 nm;

[0051] The isoelectric point of the gelatin is 6.6;

[0052] The fluoro-niobate is selected from sodium fluoro-niobate;

[0053] The aluminum salt is selected from aluminum chloride;

[0054] The precipitant is prepared by compounding ammonia water and ammonium bicarbonate according to a mass ratio of 1:1; wherein, the mass fraction of the ammonia water is 9%, and the mass fraction of the ammonium bicarbonate solution is 4%;

[0055] After mixing the fluoro-niobate solution, the aluminum salt solution, the gelatin solution and the graphene oxide nanosheets, under room temperature conditions and at an ultrasonic frequency of 280 kHz, ultrasonically disperse for 30 min to obtain a mixed solution;

[0056] Under the stirring state at a rotation speed of 300 r / min, dropwise add the precipitant to the mixed solution at a rate of 9 mL / min to adjust the pH to 9.5. After the dropping is completed, continue to stir and react for 50 min with a stirrer at a rotation speed of 200 r / min. Subsequently, under the condition of a temperature of 4 °C, refrigerate and stand for 48 h, then vacuum freeze-dry to obtain a dried material. Then, crush the dried material and pass through a 400-mesh sieve to obtain a crushed material;

[0057] Transfer the crushed material into a muffle furnace, under an air atmosphere, heat and rise the temperature to 580 °C at a rate of 3 °C / min, keep the temperature for calcination for 5 h, cool to room temperature with the furnace, and break up to obtain a calcined material;

[0058] After mixing the calcined material and a hydrochloric acid solution with a mass fraction of 12% according to a mass ratio of 1:11;

[0059] Under the conditions of an ultrasonic frequency of 220 kHz and a temperature of 50 °C, continuously keep the temperature and ultrasonically pickling for 5 h, then filter, collect the filter cake to obtain a pickled filter cake, and then wash the pickled filter cake with water until the washing liquid is neutral, and dry to obtain ultrafine niobium oxide.

[0060] Example 3

[0061] By weight, take 100 parts of a gelatin solution with a mass fraction of 5%, 80 parts of a fluoro-niobate solution with a mass fraction of 15%, 10 parts of an aluminum salt solution with a mass fraction of 6%, and 0.8 part of graphene oxide nanosheets;

[0062] The D50 of the graphene oxide nanosheets is 80 nm;

[0063] The isoelectric point of the gelatin is 6.5;

[0064] The fluoro-niobate is selected from potassium fluoro-niobate;

[0065] The aluminum salt is selected from aluminum sulfate.

[0066] The precipitating agent is prepared by compounding ammonia water and ammonium bicarbonate according to a mass ratio of 1:1; wherein, the mass fraction of the ammonia water is 10%, and the mass fraction of the ammonium bicarbonate solution is 6%;

[0067] After mixing the fluoniobate solution, the aluminum salt solution, the gelatin solution and the nano-graphene oxide, under room temperature conditions and at an ultrasonic frequency of 300 kHz, ultrasonic dispersion is carried out for 40 min to obtain a mixed solution;

[0068] Under the stirring state with a rotation speed of 300 r / min, the precipitating agent is added dropwise to the mixed solution at a rate of 10 mL / min to adjust the pH to 10. After the addition is completed, the mixture is continuously stirred with a stirrer at a rotation speed of 200 r / min for 60 min. Subsequently, under the condition of a temperature of 6 °C, refrigeration and static settlement are carried out for 56 h, followed by vacuum freeze-drying to obtain a dry material. Then, the dry material is pulverized and sieved through a 400-mesh sieve to obtain a pulverized material;

[0069] The pulverized material is transferred into a muffle furnace. In an air atmosphere, it is heated and raised to 600 °C at a rate of 5 °C / min, kept for calcination for 4 h, cooled to room temperature with the furnace, and dispersed to obtain a calcined material;

[0070] The calcined material and a hydrochloric acid solution with a mass fraction of 15% are mixed according to a mass ratio of 1:12;

[0071] Under the conditions of an ultrasonic frequency of 250 kHz and a temperature of 60 °C, continuous heat preservation and ultrasonic pickling are carried out for 6 h, followed by filtration to collect the filter cake to obtain a pickled filter cake. Then, the pickled filter cake is washed with water until the washing liquid is neutral, and dried to obtain ultrafine niobium oxide.

[0072] Example 4

[0073] Compared with Example 1, the difference in this example is that: nano-graphene oxide is not added, and the rest of the conditions remain unchanged.

[0074] Example 5

[0075] Compared with Example 1, the difference in this example is that:

[0076] After mixing the fluoniobate solution, the aluminum salt solution, the gelatin solution and the nano-graphene oxide, under room temperature conditions and at an ultrasonic frequency of 80 kHz, ultrasonic dispersion is carried out for 40 min to obtain a mixed solution;

[0077] The rest of the conditions remain unchanged.

[0078] Example 6

[0079] Compared with Example 1, the difference in this example is that the precipitant is ammonia water, and the ammonium bicarbonate solution is not added, while the other conditions remain unchanged.

[0080] Comparative Example 1

[0081] Compared with Example 1, the difference in this comparative example is that an equal mass of a 3% polyvinyl alcohol solution is used to replace the gelatin solution, while the other conditions remain unchanged.

[0082] Comparative Example 2

[0083] Compared with Example 1, the difference in this comparative example is that an equal mass of deionized water is used to replace the aluminum salt solution, while the other conditions remain unchanged.

[0084] The particle size of the products obtained in the above examples and comparative examples was tested using a laser particle size analyzer to obtain the D50 and particle size distribution range of the products respectively;

[0085] The impurities of the obtained products were analyzed by chemical analysis and atomic spectroscopy to obtain the purity of the products. For details, please refer to Table 1;

[0086] Table 1: Product test results

[0087] D50 / μm Particle size distribution / μm Purity / % Example 1 0.12 0.03-0.26 99.5 Example 2 0.13 0.02-0.24 99.6 Example 3 0.11 0.02-0.22 99.5 Example 4 0.18 0.01-0.35 99.6 Example 5 0.16 0.01-0.32 99.4 Example 6 0.15 0.02-0.30 99.3 Comparative Example 1 0.25 0.01-0.55 99.1 Comparative Example 2 0.20 0.01-0.40 99.4

[0088] It can be seen from the test results in Table 1 that the products obtained by the present invention have a smaller particle size, a narrow particle size distribution range, and moreover, the purity of the products can be guaranteed.

[0089] The above examples are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above examples. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for preparing ultrafine niobium oxide, characterized in that: The specific preparation steps include: By weight, take 90-100 parts of a gelatin solution with a mass fraction of 3-5%, 60-80 parts of a fluoroniobate solution with a mass fraction of 10-15%, 4-10 parts of an aluminum salt solution with a mass fraction of 3-6%, and 0.6-0.8 parts of nano-graphene oxide; After mixing the fluoroniobate solution, the aluminum salt solution, the gelatin solution and the nano-graphene oxide, the mixture is ultrasonically dispersed for 20-40 minutes at an ultrasonic frequency of 250-300 kHz to obtain a mixed solution; Under stirring, a precipitant is added dropwise to the mixed solution to adjust the pH to 9-10, and the mixture is stirred for reaction. After being refrigerated and allowed to stand for 24-56 hours at a temperature of 2-6° C., the mixture is dried and crushed to obtain a crushed material; The crushed material is calcined in an air atmosphere, and then cooled and broken up to obtain a calcined material; The obtained calcined material is pickled with hydrochloric acid, washed with water, and dried to obtain ultrafine niobium oxide; The isoelectric point of the gelatin is ≤7; The precipitant is prepared by mixing ammonia water and ammonium bicarbonate in a mass ratio of 1:1; wherein the mass fraction of the ammonia water is 8-10%, and the mass fraction of the ammonium bicarbonate solution is 2-6%.

2. The method for preparing ultrafine niobium oxide according to claim 1, characterized in that: The fluoroniobate is selected from any one of potassium fluoroniobate and sodium fluoroniobate; The aluminum salt is selected from any one of aluminum nitrate, aluminum chloride and aluminum sulfate.

3. The method for preparing ultrafine niobium oxide according to claim 1, characterized in that: The calcining of the crushed material in an air atmosphere comprises: transferring the crushed material into a muffle furnace, heating the crushed material to 550-600° C. at a rate of 2-5° C. / min in an air atmosphere, and calcining the crushed material for 4-6 hours.

4. The method for preparing ultrafine niobium oxide according to claim 1, characterized in that: The step of pickling the obtained calcined material with hydrochloric acid comprises: The calcined material and a hydrochloric acid solution with a mass fraction of 10-15% are mixed in a mass ratio of 1:10-12; At a temperature of 40-60° C., ultrasonic pickling is performed for 4-6 hours under heat preservation, and then the filter cake is filtered and collected to obtain an acid-washed filter cake.

5. The method for preparing ultrafine niobium oxide according to claim 1, characterized in that: The D50 of the nano graphene oxide is 60-80nm.