Ruthenium dioxide nanosheet based on high-temperature molten salt method and preparation method thereof

Abstract

The preparation method comprises the following steps: converting ruthenium nitrosyl nitrate into a reaction product containing the ruthenium dioxide nanosheet through the high-temperature molten salt method, and carrying out ultrasonic washing on the reaction product to remove molten salt, so as to obtain the ruthenium dioxide nanosheet. And centrifugally filtering the ruthenium dioxide nanosheet to obtain the ruthenium dioxide nanosheet based on the high-temperature molten salt method. Compared with the prior art, the method has the advantage that the high-purity ruthenium dioxide nanosheet can be prepared.

Description

Technical Field

[0001] The present invention belongs to the technical field of material preparation, and relates to ruthenium dioxide nanosheets based on a high-temperature molten salt method and a preparation method thereof. Background Art

[0002] Ruthenium dioxide (RuO2) has special chemical properties, such as excellent electrical stability, a wide potential window, a high mass specific capacitance, and excellent electrical conductivity, which make it widely used in the fields of electrocatalysis and supercapacitors. Currently, common methods for preparing ruthenium dioxide include ruthenium oxidation method, hydrolysis method, sol-gel method, electrochemical deposition method, thermochemical decomposition method, etc. Different preparation methods result in great differences in the morphology of the obtained ruthenium dioxide.

[0003] Patent CN107758751A discloses a preparation method of ruthenium dioxide for resistor paste. In this method, a ruthenium chloride solution is first prepared. When the temperature is raised to 60 - 80 °C, a dispersant is added with stirring, and then an alkali solution is added until the pH is 7 - 8 for hydrolysis. When the solution temperature is 80 - 90 °C, it is aged for 1 - 2 h, and then a dispersant and water are added for stirring and washing. Then, it is calcined at 400 - 500 °C for 1 - 2 h to obtain ruthenium dioxide. However, this method has a high preparation cost and is difficult to industrialize. The washing process requires long-term standing, the preparation cycle is too long, and it is impossible to truly achieve this condition during the pH adjustment in the washing process; a large amount of auxiliary materials are added, and it is difficult to guarantee the product purity.

[0004] Patent CN118183882A discloses a ruthenium dioxide and a preparation method and application thereof. The method includes the following steps: hydrolysis and aging, adding an alkali solution to a ruthenium trichloride solution, stopping adding the alkali solution after the pH of the mixed solution reaches 7 - 8, and then aging and solid-liquid separation to obtain a first product; primary washing, alternately washing the first product with an aqueous surfactant solution and an ethanol surfactant solution, followed by solid-liquid separation to obtain a second product, where the temperature of the aqueous surfactant solution is higher than that of the ethanol surfactant solution; calcination, drying the second product and then performing heat treatment, and successively washing the obtained third product with an acidic solution and deionized water, and drying to obtain ruthenium dioxide. However, this method involves operations such as pH adjustment and multiple washings, and the process is relatively cumbersome.

[0005] Patent CN118026299A discloses a preparation method of ruthenium dioxide, a noble metal compound. The preparation method of ruthenium dioxide includes the following steps: Prepare ruthenium sulfide as the basic raw material for standby; crush the standby ruthenium sulfide into powder and filter it through a sieve to obtain fine powder; place the fine powder into a crucible, put it into a sealed tank, heat it to 60 - 70 °C, and keep it warm to obtain preheated powder; introduce oxygen into the sealed tank, adjust the oxygen content to 40 - 45%, continuously heat the crucible, and raise the temperature of the preheated powder to obtain high-temperature powder; burn the high-temperature powder, carry out an oxidation reaction in the sealed tank, and obtain reaction material after cooling; take out the reaction material, place it in a cleaning pool, add dilute ammonia water, soak it for 30 - 50 min to obtain soaked material; filter out the soaked material and rinse it with a weak acid solution to obtain pickled material; put the pickled material into a stirring barrel, add clear water for stirring and cleaning to obtain cleaned material; put the cleaned material into a drying oven, carry out electrothermal drying, and store it in a glass tank in a sealed manner to complete the preparation. However, the preparation process of this method is relatively long and the steps are rather cumbersome.

[0006] At present, although there are many preparation methods of ruthenium dioxide, the preparation process generally has problems such as low preparation efficiency, difficult solid-liquid separation, uneven particle size, and high impurity content. There are very few methods that can prepare high-purity ruthenium dioxide.

[0007] Patent CN118704034A discloses a preparation method of a corrosion-resistant alkali-metal atomically doped ruthenium dioxide nanocluster electrolytic water anode catalyst. The steps are as follows: First, add a certain amount of alkali-metal nitrate into a crucible, then put it into a muffle furnace for heating. After it is in a molten state, add ruthenium trichloride for a molten reaction. Take out the crucible and let it cool naturally. Finally, add deionized water for ultrasonic and centrifugal washing, and freeze-dry to obtain the alkali-metal atomically doped ruthenium dioxide nanocluster electrolytic water anode catalyst. However, this patent only targets ruthenium trichloride. Ruthenium in high-level radioactive waste exists in the form of ruthenium nitrosyl nitrate, and it is difficult to directly apply this patent to obtain ruthenium dioxide. Moreover, this patent uses a one-step heating method, and the prepared ruthenium dioxide does not have a characteristic morphology.

[0008] Patent CN113860350A discloses a method for preparing thorium dioxide nanomaterials by a molten salt method and the resulting thorium dioxide nanomaterials. The method comprises the following steps: forming a molten salt composed of lithium chloride and potassium chloride, with the molar ratio of thorium nitrate hexahydrate to the molten salt being 1:5 - 1:80, to form the raw materials; stirring and mixing the raw materials evenly to obtain a mixture; heating the mixture to 400 - 800 °C, calcining for 1 - 8 h, and obtaining a reaction product after complete cooling; adding water to the reaction product and performing ultrasonic treatment to obtain a milky white suspension; subjecting the milky white suspension to suction filtration using a suction filtration device, then repeatedly performing suction filtration and washing with pure water to remove unreacted raw materials, and then drying to obtain thorium dioxide nanomaterials. However, this patent only targets thorium dioxide materials and is difficult to be directly transferred for the preparation of ruthenium dioxide, and also uses a one-step heating method. Summary of the Invention

[0009] The object of the present invention is to overcome at least one defect of the above-mentioned existing technologies, and to provide a ruthenium dioxide nanosheet based on a high-temperature molten salt method and a preparation method thereof. The present invention can prepare high-purity ruthenium dioxide nanosheets.

[0010] The object of the present invention can be achieved by the following technical solutions:

[0011] One technical solution of the present invention lies in providing a ruthenium dioxide nanosheet based on a high-temperature molten salt method. Ruthenium nitrosyl nitrate is converted into a reaction product containing ruthenium dioxide nanosheets by a high-temperature molten salt method. The reaction product is subjected to ultrasonic washing to remove the molten salt, and the ruthenium dioxide nanosheets are obtained by centrifugal filtration to obtain a ruthenium dioxide nanosheet based on a high-temperature molten salt method.

[0012] One technical solution of the present invention lies in providing a preparation method of the ruthenium dioxide nanosheet based on a high-temperature molten salt method, and the method comprises the following steps:

[0013] S1. Mixing a ruthenium nitrosyl nitrate solution and a molten salt to obtain a mixture;

[0014] S2. Subjecting the mixture to two-stage heating and calcination, and cooling to room temperature to obtain a reaction product;

[0015] S3. Adding a dispersant to the reaction product, performing ultrasonic treatment, fully dissolving the molten salt in water, and completely separating it from the ruthenium dioxide nanosheets to obtain a suspension;

[0016] S4. Centrifugally filtering the suspension, and drying the obtained centrifuged solid to obtain a ruthenium dioxide nanosheet based on a high-temperature molten salt method.

[0017] Further, in step S1, the ruthenium concentration of the ruthenium nitrosyl nitrate solution is 0.01 - 100 g / L.

[0018] As a preferred technical solution, the concentration of ruthenium in the ruthenium nitrosyl nitrate solution in step S1 is 1-10 g / L.

[0019] Furthermore, in step S1, the molten salt is selected from one or more of lithium chloride, potassium chloride, lithium nitrate, potassium nitrate, and sodium nitrate.

[0020] As a preferred technical solution, in step S1, the molten salt is selected from the combination of lithium chloride and potassium chloride, the combination of lithium nitrate and potassium nitrate, or the combination of potassium nitrate and sodium nitrate. The mole fraction of lithium chloride in the combination of lithium chloride and potassium chloride is 40-70%, the mole fraction of lithium nitrate in the combination of lithium nitrate and potassium nitrate is 40-70%, and the mole fraction of potassium nitrate in the combination of potassium nitrate and sodium nitrate is 40-70%.

[0021] As a preferred technical solution, the mole fraction of lithium chloride in the combination of lithium chloride and potassium chloride is 50-60%, the mole fraction of lithium nitrate in the combination of lithium nitrate and potassium nitrate is 50-60%, and the mole fraction of potassium nitrate in the combination of potassium nitrate and sodium nitrate is 50-60%.

[0022] As a preferred technical solution, the mole fraction of lithium chloride in the combination of lithium chloride and potassium chloride is 50%, 55%, or 60%, the mole fraction of lithium nitrate in the combination of lithium nitrate and potassium nitrate is 50%, 55%, or 60%, and the mole fraction of potassium nitrate in the combination of potassium nitrate and sodium nitrate is 50%, 55%, or 60%.

[0023] Furthermore, in step S1, the molar ratio of ruthenium nitrosyl nitrate to the molten salt is 1:(5-100).

[0024] As a preferred technical solution, in step S1, the molar ratio of ruthenium nitrosyl nitrate to the molten salt is 1:(20-100).

[0025] As a preferred technical solution, the mixing time in step S1 is 1-10 min.

[0026] As a preferred technical solution, the mixing time in step S1 is 8-10 min.

[0027] Furthermore, in step S2, the temperature of the first-stage heating and calcination is 50-150 °C, and the temperature of the second-stage heating and calcination is 300-900 °C.

[0028] As a preferred technical solution, the temperature of the second-stage heating and calcination in step S2 is 450-750 °C.

[0029] Furthermore, in step S2, the heating rate of the first-stage heating and calcination is 1-15 °C / min, and the heating rate of the second-stage heating and calcination is 5-25 °C / min.

[0030] As a preferred technical solution, in step S2, the heating rate of the first-stage heating calcination is 5-10 °C / min, and the heating rate of the second-stage heating calcination is 10-20 °C / min.

[0031] Furthermore, in step S2, the heat preservation time of the first-stage heating calcination is 30-600 min, and the heat preservation time of the second-stage heating calcination is 10-300 min.

[0032] As a preferred technical solution, in step S2, the heat preservation time of the first-stage heating calcination is 30-300 min, and the heat preservation time of the second-stage heating calcination is 30-300 min.

[0033] Furthermore, in step S3, the dispersant is selected from one or more of water, ethanol, acetone, and acetonitrile. The frequency of ultrasonic treatment is 40-100 kHz, and the time is 1-10 min.

[0034] As a preferred technical solution, in step S3, the frequency of ultrasonic treatment is 50-100 kHz, and the time is 3-6 min.

[0035] Furthermore, in step S4, the rotation speed of centrifugal filtration is 200-2000 rpm, and the time is 1-10 min.

[0036] The drying temperature is 50-150 °C, and the time is 2-10 h.

[0037] As a preferred technical solution, in step S4, the rotation speed of centrifugal filtration is 500-2000 rpm, and the time is 2-10 min.

[0038] The drying time is 4-10 h.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) The present invention first directly converts ruthenium nitrosyl nitrate into ruthenium dioxide solid by using the high-temperature molten salt method, then removes the molten salt through ultrasonic washing and further separates it from the product. Finally, pure ruthenium dioxide solid is obtained after centrifugal filtration and drying. Ruthenium in high-level radioactive waste exists in the form of ruthenium nitrosyl nitrate. Through the present invention, ruthenium nitrosyl nitrate extracted from high-level radioactive waste can be used as a source of ruthenium to prepare ruthenium dioxide by solid conversion, and ruthenium dioxide nanosheets can be obtained by the two-stage heating method.

[0041] (2) The operation method of the present invention is simple, fast, convenient, feasible, and inexpensive, and can realize the regulation of morphology, having broad application prospects in the industrial preparation of solid oxide materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1XRD pattern of ruthenium dioxide nanosheets based on the high-temperature molten salt method in Example 1 of the present invention;

[0043] Figure 2 SEM image of ruthenium dioxide nanosheets based on the high-temperature molten salt method in Example 1 of the present invention. Detailed implementation manners

[0044] The present invention will be described in detail below with reference to specific embodiments. These embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation manners and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0045] Unless otherwise specified, the equipment used in the following embodiments is all conventional equipment in the art; unless otherwise specified, the reagents used are all commercially available products or prepared by conventional methods in the art. Those not described in detail in the following embodiments can be achieved by conventional experimental means in the art.

[0046] The ruthenium nitrosyl nitrate solution is purchased from Aladdin, and the solvent of the ruthenium nitrosyl nitrate solution is dilute nitric acid.

[0047] Example 1:

[0048] A ruthenium dioxide nanosheet based on the high-temperature molten salt method and its preparation method are as follows:

[0049] S1. Composition ratio and treatment of raw materials: The concentration of ruthenium in the ruthenium nitrosyl nitrate solution is 1 g / L. A molten salt system of 60% lithium chloride and 40% potassium chloride by mole fraction is used. The molar ratio of ruthenium nitrosyl nitrate to the molten salt is 1:20. The ruthenium nitrosyl nitrate solution and the molten salt raw materials in the above ratio are added to an alumina crucible, and stirred with a glass rod for 10 min to mix the raw materials evenly to obtain a mixture;

[0050] S2. Calcination of raw materials: The alumina crucible containing the mixture is placed in a muffle furnace and heated from room temperature to 100 °C at a rate of 10 °C / min for calcination, held for 30 min, then heated from 100 °C to 450 °C at a rate of 20 °C / min for calcination, held for 30 min. The ruthenium nitrosyl nitrate is converted into ruthenium dioxide nanosheets by the high-temperature molten salt method, and naturally cooled to room temperature to obtain a reaction product;

[0051] S3. Treatment of the reaction product: Deionized water is added to the reaction product, transferred to a beaker and ultrasonicated at 50 kHz for 5 min to wash away the molten salt. The molten salt is fully dissolved in water and completely separated from the ruthenium dioxide nanosheets to obtain a suspension;

[0052] S4. Suspension treatment: Centrifuge and filter the suspension at 1000 rpm for 5 min, and dry the obtained centrifuged solid at 120 °C for 10 h to obtain ruthenium dioxide nanosheets based on the high-temperature molten salt method, with a macroscopic morphology of a black solid.

[0053] Perform the following detections or tests on the above ruthenium dioxide nanosheets, and then analyze the detection or test results.

[0054] Test example:

[0055] Characterize the above ruthenium dioxide nanosheets using X-ray diffraction (XRD) and scanning electron microscopy (SEM).

[0056] As Figure 1 shown, the results show that the ruthenium dioxide nanosheets in Example 1 are consistent with the X-ray diffraction card of standard ruthenium dioxide (RuO2) crystals, proving that pure ruthenium dioxide solid was successfully prepared in Example 1.

[0057] As Figure 2 shown, the results show that the microscopic morphology of the ruthenium dioxide solid in Example 1 is regular flaky.

[0058] Example 2:

[0059] A ruthenium dioxide nanosheet based on the high-temperature molten salt method and its preparation method are as follows:

[0060] S1. Raw material composition ratio and treatment: The concentration of ruthenium in the nitrosyl ruthenium nitrate solution is 10 g / L. Using lithium chloride and potassium chloride with a molar fraction of 50% each as the molten salt system, the molar ratio of nitrosyl ruthenium nitrate to the molten salt is 1:50. Add the nitrosyl ruthenium nitrate solution and the molten salt raw materials with the above ratio to an alumina crucible, and stir with a glass rod for 10 min to make the raw materials mix evenly to obtain a mixture.

[0061] S2. Raw material calcination: Place the alumina crucible containing the mixture in a muffle furnace, heat from room temperature to 100 °C at a rate of 5 °C / min for calcination, hold for 100 min, then heat from 100 °C to 600 °C at a rate of 10 °C / min for calcination, hold for 30 min, convert nitrosyl ruthenium nitrate into ruthenium dioxide nanosheets by the high-temperature molten salt method, and naturally cool to room temperature to obtain a reaction product.

[0062] S3. Reaction product treatment: Add deionized water to the reaction product, transfer it to a beaker, and ultrasonically wash at 100 kHz for 6 min to remove the molten salt. Dissolve the molten salt fully in water and completely separate it from the ruthenium dioxide nanosheets to obtain a suspension.

[0063] S4. Suspension treatment: Centrifuge and filter the suspension at 2000 rpm for 5 min, dry the obtained centrifuged solid at 120 °C for 5 h to obtain ruthenium dioxide nanosheets based on the high-temperature molten salt method, with a macroscopic morphology of a black solid.

[0064] The ruthenium dioxide nanosheets in Example 2 were consistent with the standard ruthenium dioxide crystal X-ray diffraction card, proving that pure ruthenium dioxide solid was successfully prepared in Example 2.

[0065] The microscopic morphology of the ruthenium dioxide solid in Example 2 was regular flakes.

[0066] Example 3:

[0067] A ruthenium dioxide nanosheet based on the high-temperature molten salt method and its preparation method are as follows:

[0068] S1. Raw material composition ratio and treatment: The concentration of ruthenium in the nitrosyl ruthenium nitrate solution is 5 g / L. Using potassium nitrate with a molar fraction of 55% and sodium nitrate with a molar fraction of 45% as the molten salt system, the molar ratio of nitrosyl ruthenium nitrate to the molten salt is 1:100. Add the nitrosyl ruthenium nitrate solution and the molten salt raw materials in the above ratio to an alumina crucible, and stir with a glass rod for 8 min to make the raw materials evenly mixed to obtain a mixture.

[0069] S2. Raw material calcination: Place the alumina crucible containing the mixture in a muffle furnace, heat from room temperature to 100 °C at a rate of 10 °C / min for calcination, keep warm for 300 min, then heat from 100 °C to 750 °C at a rate of 10 °C / min for calcination, keep warm for 100 min, convert nitrosyl ruthenium nitrate into ruthenium dioxide nanosheets by the high-temperature molten salt method, and naturally cool to room temperature to obtain a reaction product.

[0070] S3. Reaction product treatment: Add deionized water to the reaction product, transfer it to a beaker, and ultrasonically wash at 60 kHz for 3 min to remove the molten salt. Dissolve the molten salt completely in water and separate it completely from the ruthenium dioxide nanosheets to obtain a suspension.

[0071] S4. Suspension treatment: Centrifuge and filter the suspension at 500 rpm for 10 min, dry the obtained centrifuged solid at 120 °C for 5 h to obtain ruthenium dioxide nanosheets based on the high-temperature molten salt method, with a macroscopic morphology of a black solid.

[0072] The ruthenium dioxide nanosheets in Example 3 were consistent with the standard ruthenium dioxide crystal X-ray diffraction card, proving that pure ruthenium dioxide solid was successfully prepared in Example 3.

[0073] The microscopic morphology of the ruthenium dioxide solid in Example 3 was regular flakes.

[0074] Example 4:

[0075] A ruthenium dioxide nanosheet based on a high-temperature molten salt method and a preparation method thereof are as follows:

[0076] S1. Composition ratio and treatment of raw materials. The concentration of ruthenium in the nitrosyl ruthenium nitrate solution is 3 g / L. A molten salt system of lithium nitrate and potassium nitrate with a molar fraction of 50% is used. The molar ratio of nitrosyl ruthenium nitrate to the molten salt is 1:20. Add the nitrosyl ruthenium nitrate solution and the molten salt raw materials with the above ratio into an alumina crucible, and stir with a glass rod for 8 min to make the raw materials evenly mixed to obtain a mixture;

[0077] S2. Calcination of raw materials. Put the alumina crucible containing the mixture into a muffle furnace, heat it from room temperature to 100 °C at a rate of 10 °C / min for calcination, keep it warm for 300 min, then heat it from 100 °C to 600 °C at a rate of 20 °C / min for calcination, keep it warm for 300 min, convert the nitrosyl ruthenium nitrate into ruthenium dioxide nanosheets by the high-temperature molten salt method, and naturally cool it to room temperature to obtain a reaction product;

[0078] S3. Treatment of the reaction product. Add deionized water to the reaction product, transfer it to a beaker, and ultrasonically wash it at 50 kHz for 5 min to remove the molten salt. Dissolve the molten salt completely in water and separate it completely from the ruthenium dioxide nanosheets to obtain a suspension;

[0079] S4. Treatment of the suspension. Centrifuge and filter the suspension at 800 rpm for 2 min, and dry the obtained centrifuged solid at 120 °C for 4 h to obtain ruthenium dioxide nanosheets based on the high-temperature molten salt method, and the macroscopic morphology is in the shape of a black solid.

[0080] The ruthenium dioxide nanosheet in Example 4 is consistent with the standard ruthenium dioxide crystal X-ray diffraction card, which proves that pure ruthenium dioxide solid is successfully prepared in Example 4.

[0081] The microscopic morphology of the ruthenium dioxide solid in Example 4 is regular sheet-like.

[0082] The above description of the embodiments is for the convenience of those of ordinary skill in the art to understand and use the invention. It is obvious that those who are familiar with the technology in this field can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art according to the disclosure of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A ruthenium dioxide nanosheet based on the high-temperature molten salt method, characterized in that, Convert ruthenium nitrosyl nitrate into a reaction product containing ruthenium dioxide nanosheets by the high-temperature molten salt method. Remove the molten salt from the reaction product by ultrasonic washing, and obtain ruthenium dioxide nanosheets based on the high-temperature molten salt method by centrifugal filtration of the ruthenium dioxide nanosheets.

2. A method for preparing ruthenium dioxide nanosheets based on the high-temperature molten salt method as described in claim 1, characterized in that, This method includes the following steps: S1. Mix a ruthenium nitrosyl nitrate solution and a molten salt to obtain a mixture; S2. Calcinate the mixture by two-stage heating to obtain a reaction product; S3. Add a dispersant to the reaction product and ultrasonicate to obtain a suspension; S4. Centrifugally filter the suspension, and dry the obtained centrifuged solid to obtain ruthenium dioxide nanosheets based on the high-temperature molten salt method.

3. The preparation method of ruthenium dioxide nanosheets based on the high-temperature molten salt method according to claim 2, wherein, In step S1, the concentration of ruthenium in ruthenium nitrosyl nitrate is 0.01 - 100 g / L.

4. The preparation method of ruthenium dioxide nanosheets based on the high-temperature molten salt method according to claim 2, wherein In step S1, the molten salt is selected from one or more of lithium chloride, potassium chloride, lithium nitrate, potassium nitrate, and sodium nitrate.

5. The preparation method of ruthenium dioxide nanosheets based on the high-temperature molten salt method according to claim 2, wherein In step S1, the molar ratio of ruthenium nitrosyl nitrate to the molten salt is 1:(5 - 100).

6. The preparation method of ruthenium dioxide nanosheets based on the high-temperature molten salt method according to claim 2, characterized in that, In step S2, the temperature for the first-stage heating calcination is 50 - 150 °C, and the temperature for the second-stage heating calcination is 300 - 900 °C.

7. The preparation method of ruthenium dioxide nanosheets based on the high-temperature molten salt method according to claim 2, characterized in that, In step S2, the heating rate for the first-stage heating calcination is 1 - 15 °C / min, and the heating rate for the second-stage heating calcination is 5 - 25 °C / min.

8. The preparation method of ruthenium dioxide nanosheets based on the high-temperature molten salt method according to claim 2, characterized in that, In step S2, the heat preservation time for the first-stage heating calcination is 30 - 600 min, and the heat preservation time for the second-stage heating calcination is 10 - 300 min.

9. The preparation method of ruthenium dioxide nanosheets based on the high-temperature molten salt method according to claim 2, characterized in that, In step S3, the dispersant is selected from one or more of water, ethanol, acetone, and acetonitrile. The ultrasonic frequency is 40 - 100 kHz, and the time is 1 - 10 min.

10. The preparation method of ruthenium dioxide nanosheets based on the high-temperature molten salt method according to claim 2, characterized in that, In step S4, the rotation speed for centrifugal filtration is 200 - 2000 rpm, and the time is 1 - 10 min. The drying temperature is 50 - 150 °C, and the time is 2 - 10 h.

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