Preparation method of ammonium tetrafluoroaluminate for fluoride glass

Abstract

The invention provides a synthesis method of ammonium tetrafluoroaluminate, which comprises the following steps: heating high-purity aluminum in a dilute hydrogen fluoride solution in a water bath, titrating and precipitating the reaction product by using an ammonium fluoride solution, and finally filtering and drying to obtain high-purity ammonium tetrafluoroaluminate for fluoride glass. The preparation process is simple and convenient through a chemical synthesis method of aluminum fluoride and ammonium fluoride.

Description

Technical Field

[0001] This invention relates to the technical field of fluoride raw material synthesis methods, and in particular to a method for preparing ammonium tetrafluoroaluminate raw material for fluoride glass. Background Technology

[0002] Fluoride glass is mainly used for drawing mid-infrared fluoride optical fibers and is one of the important defense materials. Currently, many high-purity fluoride materials are listed in the key control list, and there is an urgent need to develop domestic alternatives. However, the deliquescence and instability of fluoride glass pose challenges to its preparation process. Adding aluminum fluoride to the fluoride glass composition can effectively improve the stability and mechanical properties of the glass. At the same time, oxide impurities are introduced during the melting of fluoride glass. Therefore, adding ammonium tetrafluoroaluminate to the fluoride glass composition is a better solution.

[0003] Currently, ammonium tetrafluoroaluminate is often prepared by mixing a high-concentration aluminum nitrate nonahydrate solution (Al(NO3)3·9H2O) with an ammonium fluoride solution, stirring at 80°C, and then filtering and drying for 24 hours. Alternatively, it can be prepared using 1-ethyl-3-methylimidazole hexafluorophosphate, aluminum isopropoxide, and phosphoric acid. This requires first preparing the precursor 1-ethyl-3-methylimidazole bromide to prepare 1-ethyl-3-methylimidazole hexafluorophosphate, which is then mixed with aluminum isopropoxide and phosphoric acid at 190°C and kept at that temperature for 96 hours. Another method involves using ammonium bifluoride and aluminum chloride (molar ratio of ammonium bifluoride to aluminum chloride is 3:1) as raw materials, mixing and ball milling them at a ball-to-material ratio of 60–120:1, a ball milling speed of 400–500 rpm, a ball milling time of 1–2 hours, and then heat-treating at 200–300°C for 4–6 hours to obtain ammonium tetrafluoroaluminate. For the first and third methods, the reaction will leave a small amount of impurities, and the purity cannot meet the requirements for raw materials used in fluoride glass; for the second method, the reaction temperature is high, and the preparation process is complicated and takes a long time. Summary of the Invention

[0004] Therefore, the present invention provides a wet method for synthesizing ammonium tetrafluoroaluminate for fluorinated optical fiber glass, which is simple to operate, produces uniform and complete reactions, and yields reliable products.

[0005] The technical solution of the present invention includes the following steps:

[0006] S1. Preparation steps of aluminum fluoride solution: Place high-purity aluminum with a molar ratio of aluminum to hydrogen fluoride of 1 to 6:3 and dilute hydrofluoric acid solution in a Teflon water bath heating tank and record the weight of the high-purity aluminum W1. Adjust the water bath temperature and duration of the Teflon water bath heating tank to allow the high-purity aluminum to react fully with the dilute hydrofluoric acid solution in the tank to obtain aluminum fluoride solution.

[0007] S2, Titration Step: After the aluminum block reacted in step S1, weigh it W2. Subtract the weight of the reacted aluminum block W2 from the weight of the high-purity aluminum W1 recorded in step S1 to obtain the weight of the reacted aluminum block W. Al Then, calculate the required weight W of ammonium fluoride based on a mass ratio of ammonium fluoride to aluminum in the reaction of 1.6–1.7:1. NH4F Dissolve the required ammonium fluoride in deionized water to prepare an ammonium fluoride solution. Use a peristaltic pump to drop the prepared ammonium fluoride solution into the aluminum fluoride solution obtained after removing the aluminum block in step S1, and stir. Step S3: Precipitation, filtration and drying: Cool the stirred reaction solution obtained in step S2 to room temperature to precipitate, filter out the precipitate, and dry it completely in a vacuum drying oven to obtain ammonium tetrafluoroaluminate raw material.

[0008] In step S2, the mass ratio of ammonium fluoride to reacting aluminum is set at 1.6 to 1.7:1. If the ratio is lower than this, the reaction will not be complete. If the ratio is higher than this, ammonium fluoride and aluminum fluoride will form ammonium hexafluoroaluminate.

[0009] Furthermore, in step S1, the dilute hydrofluoric acid solution is prepared by adding concentrated hydrofluoric acid solution to deionized water. The molar concentration of the dilute hydrofluoric acid solution is 1-4 mol / L. If the concentration is higher than this, the aluminum fluoride after the reaction cannot be fully dissolved in the solution, which leads to the presence of aluminum fluoride in the generated ammonium tetrafluoroaluminate. If the concentration is lower than this, the content of hydrogen fluoride is lower and the reaction time is longer.

[0010] Furthermore, in step S1, the water bath temperature of the Teflon water bath heating tank is 70-80°C, and the water bath duration is 5-6 hours.

[0011] Furthermore, in step S2, the molar concentration of the ammonium fluoride solution is 4–5 mol / L. During the titration process, the reaction solution should be stirred with a Teflon stirrer to prevent the generated ammonium tetrafluoroaluminate from clumping.

[0012] Furthermore, in step S3, the temperature of the vacuum drying oven should not be too high, and should be set to 70-80℃ to prevent the decomposition of ammonium tetrafluoroaluminate.

[0013] Compared with existing technologies, the technical effects of the invention are as follows:

[0014] This invention utilizes ammonium fluoride titrating aluminum fluoride, and by adjusting the raw material ratio and temperature, obtains a high-purity ammonium tetrafluoroaluminate raw material for fluoride glass through a wet process. Compared to traditional aluminum fluoride raw materials, ammonium tetrafluoroaluminate, because its coordination sites are occupied by ammonium ions, is difficult to combine with water, and therefore does not pyrolyze to form oxides. During the melting of fluoride glass, it does not introduce water or oxide impurities, and can react with oxide impurities in other raw materials to remove oxygen ions from the glass melt, thus producing high-quality fluoride glass. Furthermore, this invention uses a vacuum drying oven at no more than 80°C, far below the pyrolysis temperature of ammonium tetrafluoroaluminate, preventing the generation of aluminum fluoride impurities during drying and avoiding corrosion by water and oxygen in the external environment. It also avoids the generation of hydrogen fluoride, a highly volatile and corrosive hazardous chemical, making the experimental process safer and more reliable. XRD diffraction verification shows that the diffraction peaks of the product obtained in this invention are consistent with the characteristic diffraction peaks of ammonium tetrafluoroaluminate, with no other impurity diffraction peaks, indicating that a high-purity ammonium tetrafluoroaluminate raw material has been obtained. In addition, the preparation steps of this invention are simple and easy to operate. Attached Figure Description

[0015] Figure 1 This is an XRD diffraction diagram of the ammonium tetrafluoroaluminate raw material for fluoride glass produced in Example 1.

[0016] Figure 2 This is an XRD diffraction diagram of the ammonium tetrafluoroaluminate raw material for fluoride glass produced in Example 2;

[0017] Figure 3 This is an XRD diffraction diagram of the ammonium tetrafluoroaluminate raw material for fluoride glass produced in Example 3;

[0018] Figure 4 This is an XRD diffraction diagram of the ammonium tetrafluoroaluminate raw material for fluoride glass produced in Example 4.

[0019] Figure 5 This is an XRD diffraction diagram of the ammonium tetrafluoroaluminate raw material for fluoride glass produced in Example 5. Detailed Implementation

[0020] The present invention will be further described below with reference to embodiments and accompanying drawings, but this should not be construed as limiting the scope of protection of the present invention.

[0021] Example 1

[0022] Operating steps:

[0023] 1. Weigh 526.5g of high-purity aluminum block and place it in a Teflon container containing 10.0L of dilute hydrofluoric acid solution (concentration of 2.5mol / L). Heat the solution in a water bath at 75℃ for 6.0h.

[0024] 2. Weigh the aluminum block after the reaction, which is 337.4g. Calculate the required ammonium fluoride weight, which is 310.1g. Dissolve the ammonium fluoride in 2.5L of deionized water. Use a peristaltic pump to dropwise add the prepared ammonium fluoride solution into the aluminum fluoride solution while stirring.

[0025] 3. The reaction solution was cooled to room temperature to precipitate, the precipitate was filtered out, and then completely dried in a vacuum drying oven at 80°C to obtain 912.8g of ammonium tetrafluoroaluminate.

[0026] Example 2

[0027] Operating steps:

[0028] 1. Weigh 485.3g of high-purity aluminum block and place it in a Teflon container containing 10.0L of dilute hydrofluoric acid solution (concentration of 2.0mol / L). Heat the solution in a water bath at 75℃ for 5.7h.

[0029] 2. Weigh the aluminum block after the reaction, which is 347.6g. Calculate the required ammonium fluoride weight, which is 227.2g. Dissolve the ammonium fluoride in 1.5L of deionized water. Use a peristaltic pump to drop the prepared ammonium fluoride solution into the aluminum fluoride solution while stirring.

[0030] 3. The reaction solution was cooled to room temperature to precipitate, the precipitate was filtered out and completely dried in a vacuum drying oven at 75°C to obtain 631.5g of ammonium tetrafluoroaluminate.

[0031] Example 3

[0032] Operating steps:

[0033] 1. Weigh 376.4g of high-purity aluminum block and place it in a Teflon container containing 6.0L of dilute hydrofluoric acid solution (concentration of 4.0mol / L). Heat the solution in a water bath at 80℃ for 5.5 hours.

[0034] 2. Weigh the aluminum block after the reaction, which is 212.5g. Calculate the required ammonium fluoride weight, which is 270.4g. Dissolve the ammonium fluoride in 1.5L of deionized water. Use a peristaltic pump to drop the prepared ammonium fluoride solution into the aluminum fluoride solution while stirring.

[0035] 3. Cool the reaction solution to room temperature to allow precipitation, filter out the precipitate, and completely dry it in a vacuum drying oven at 70°C to obtain 707.5g of ammonium tetrafluoroaluminate.

[0036] Example 4

[0037] Operating steps:

[0038] 1. Weigh 325.1g of high-purity aluminum block and place it in a Teflon container containing 15.0L of dilute hydrofluoric acid solution (concentration of 1.0mol / L). Heat the solution in a water bath at 70℃ for 6.0h.

[0039] 2. Weigh the aluminum block after the reaction, which is 222.5g. Calculate the required weight of ammonium fluoride, which is 164.2g. Dissolve the ammonium fluoride in 1.0L of deionized water. Use a peristaltic pump to drop the prepared ammonium fluoride solution into the aluminum fluoride solution while stirring.

[0040] 3. The reaction solution was cooled to room temperature to precipitate, the precipitate was filtered out and completely dried in a vacuum drying oven at 75°C to obtain 429.6g of ammonium tetrafluoroaluminate.

[0041] Example 5

[0042] Operating steps:

[0043] 1. Weigh 477.6g of high-purity aluminum block and place it in a Teflon container containing 7.0L of dilute hydrofluoric acid solution (concentration of 3.0mol / L). Heat the solution in a water bath at 80℃ for 5.0h.

[0044] 2. Weigh the aluminum block after the reaction, which is 329.1g. Calculate the required ammonium fluoride weight, which is 237.6g. Dissolve the ammonium fluoride in 1.5L of deionized water. Use a peristaltic pump to drop the prepared ammonium fluoride solution into the aluminum fluoride solution while stirring.

[0045] 3. The reaction solution was cooled to room temperature to precipitate, the precipitate was filtered out, and then completely dried in a vacuum drying oven at 80°C to obtain 621.6g of ammonium tetrafluoroaluminate.

[0046] Figure 1-5 This is an XRD diffraction diagram of the ammonium tetrafluoroaluminate raw material for fluoride glass of the present invention. The characteristic diffraction peaks of ammonium tetrafluoroaluminate are clearly visible in the figure, and there are no other impurity diffraction peaks, indicating that a high purity ammonium tetrafluoroaluminate raw material has been obtained.

Claims

1. A method for preparing ammonium tetrafluoroaluminate for fluoride glass, characterized in that, Using a Teflon water bath heating tank as the reaction apparatus, and high-purity aluminum, hydrogen fluoride, and ammonium fluoride as raw materials, the reaction is carried out under solution conditions. The chemical formula of the reaction product is NH4AlF4. The specific steps are as follows: S1. Preparation of aluminum fluoride solution: High-purity aluminum with a molar ratio of aluminum to hydrogen fluoride of 1 to 6:3 and dilute hydrofluoric acid solution are placed in a Teflon water bath heating tank and the weight of the high-purity aluminum W1 is recorded. The water bath temperature and duration of the Teflon water bath heating tank are adjusted to allow the high-purity aluminum to react fully with the dilute hydrofluoric acid solution in the tank to obtain aluminum fluoride solution. S2, Titration: After the aluminum block reacted in step S1, weigh it W2. Subtract the weight of the reacted aluminum block W2 from the weight of the high-purity aluminum W1 recorded in step S1 to obtain the weight of the reacted aluminum block W. Al Then, calculate the required weight W of ammonium fluoride based on a mass ratio of ammonium fluoride to aluminum in the reaction of 1.6–1.7:

1. NH4F Dissolve the required ammonium fluoride in deionized water to prepare an ammonium fluoride solution. Use a peristaltic pump to drop the prepared ammonium fluoride solution into the aluminum fluoride solution obtained after removing the aluminum block in step S1, and stir. S3. Precipitation, filtration and drying: The stirred reaction solution obtained in step S2 is cooled to room temperature to precipitate, the precipitate is filtered out and completely dried in a vacuum drying oven to obtain ammonium tetrafluoroaluminate raw material.

2. The method for preparing ammonium tetrafluoroaluminate for fluoride glass according to claim 1, characterized in that, In step S1, the dilute hydrofluoric acid solution is prepared by adding concentrated hydrofluoric acid solution to deionized water, and the molar concentration of the dilute hydrofluoric acid solution is 1-4 mol / L.

3. The method for preparing ammonium tetrafluoroaluminate for fluoride glass according to claim 1, characterized in that, In step S1, the water bath temperature of the Teflon water bath heating tank is 70-80℃, and the water bath duration is 5-6 hours.

4. The method for preparing ammonium tetrafluoroaluminate for fluoride glass according to claim 1, characterized in that, In step S2, the molar concentration of the ammonium fluoride solution is 4–5 mol / L.

5. The method for preparing ammonium tetrafluoroaluminate for fluoride glass according to claim 1, characterized in that, In step S2, during the titration process, a Teflon stirrer is used to stir the reaction solution.

6. The method for preparing ammonium tetrafluoroaluminate for fluoride glass according to claim 1, characterized in that, In step S3, the temperature of the vacuum drying oven is 70–80°C.

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