A method for preparing low-oxygen magnesium fluoride optical coating material

Abstract

The invention discloses a method for preparing a low-oxygen magnesium fluoride optical coating material, comprising the following steps: (1) preparing a magnesium salt solution; putting metal magnesium into pure water, adding a nitric acid solution with a concentration of 3-5 times that of 20% for reaction, and adding hydrogen peroxide twice; (2) preparing an ammonium bicarbonate solution; (3) synthesizing basic magnesium carbonate; (4) cleaning the basic magnesium carbonate; (5) fluoridation; (6) heat preservation; (7) low-temperature drying and high-temperature dehydration to obtain high-purity magnesium fluoride. The invention has the following beneficial effects: step (1) adding hydrogen peroxide twice to remove impurities such as iron, manganese and heavy metals; step (4) cleaning the basic magnesium carbonate to determine the amount of impurities wrapped in the basic magnesium carbonate, determine the oxygen content of the magnesium fluoride, and prevent the generation of a pop point; step (6) heat preservation by layering to reduce the volatilization of hydrofluoric acid; all steps adopt commonly used industrial raw materials, and can prepare high-purity magnesium fluoride with a purity of more than 99.95%, meeting the requirements of purity, oxygen-free absorption and no pop point.

Description

Technical Field

[0001] The invention relates to the field of magnesium fluoride preparation, and in particular to a method for preparing a low-oxygen magnesium fluoride optical coating material. Background Art

[0002] Magnesium fluoride is a compound of halogen element fluorine and metallic element magnesium. It is a colorless crystal or powder. Magnesium fluoride crystal has excellent optical properties, mechanical properties and chemical stability. It is widely used in ceramic and electronic industries, manufacturing ceramics and glass, metallurgical magnesium metal flux, fluorescent materials for cathode ray screens, flux, etc. At the same time, it is also a very important optical functional crystal material. It is often used to make magnesium fluoride film, which can be used for optical lens coating. Optical equipment is coated with a layer of magnesium fluoride film, which can reduce the reflection of incident light on the lens interface, reduce halo, and improve image quality. Therefore, when it is used as an optical coating material, the purity requirement is extremely high, at least above 99.95%. The purity of industrial magnesium fluoride is generally 95.0% to 99.0%, and it usually contains heavy metal impurities such as iron and manganese. There are problems of oxygen absorption and bounce point, which cannot meet the high purity requirements of optical coating materials for magnesium fluoride. Therefore, a preparation method of high-purity magnesium fluoride polycrystalline raw materials is needed. Summary of the invention

[0003] In view of the deficiencies in the above-mentioned prior art, the present invention provides a method for preparing a low-oxygen magnesium fluoride optical coating material to avoid excessive impurities that result in low purity of magnesium fluoride, oxygen absorption, and bounce points.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is a method for preparing a low-oxygen magnesium fluoride optical coating material, comprising the following steps:

[0005] (1) preparing a magnesium salt solution; placing magnesium metal in pure water, adding 3-5 times the concentration of 20% nitric acid solution, reacting until the specific gravity d=1.05-1.26 g / ml, introducing into a 5T enamel reactor, adjusting the pH of the magnesium salt solution to pH=2-5 and specific gravity d=1.05-1.26 g / ml, adding hydrogen peroxide for the first time under continuous stirring, heating to 80-100° C., adding magnesium hydroxide paste, adjusting the pH to between 7-10, leaving it to precipitate for more than 12 hours, filtering, detecting that there is no iron ion reaction, introducing the filtrate into another enamel reactor, stirring the filtrate continuously, adding hydrogen peroxide for the second time, continuing stirring for 20-40 minutes, heating to boiling, continuing stirring while adding magnesium hydroxide, adjusting the pH to ≥10, leaving it to completely precipitate and filtering to obtain a high-purity magnesium salt solution;

[0006] (2) preparing an ammonium bicarbonate solution; adding food-grade ammonium bicarbonate to pure water, stirring and heating until dissolved, the temperature is always controlled between 25-30° C. during the dissolution process, and the solution is allowed to stand after saturation;

[0007] (3) synthesizing basic magnesium carbonate; adjusting the temperature of the high-purity magnesium salt solution obtained in step (1) to 50-70° C., and then filtering and synthesizing with the ammonium bicarbonate solution obtained in step (2), the volume ratio of the synthesis being not less than 5:4, to obtain a basic magnesium carbonate precipitate;

[0008] (4) Cleaning of basic magnesium carbonate: placing the basic magnesium carbonate precipitate into a filter bag and washing with pure water;

[0009] (5) fluorination; adding hydrofluoric acid into a tetrafluoroethylene reaction kettle, slowly adding the basic magnesium carbonate obtained in step (4), and stirring evenly. After the reaction is terminated, adjusting the pH of the solution to between 2 and 5 to obtain a magnesium fluoride solution;

[0010] (6) keeping warm; heating the magnesium fluoride solution for 18-20 hours to obtain a solution with upper and lower layers;

[0011] (7) low temperature drying and high temperature dehydration; after the upper liquid surface of the upper and lower layered solution obtained in step (6) is sucked out, the magnesium fluoride precipitate is obtained, which is placed in a PTFE dish and dried at a temperature of 130-150° C. for more than 18 hours, and the drying loss after drying is ≤8%. The magnesium fluoride after low temperature drying is placed in an atmospheric condition of 450-550° C. and kept warm for more than 3 hours.

[0012] The mixture was taken out and cooled to room temperature to obtain high-purity magnesium fluoride.

[0013] Furthermore, the metallic magnesium in step (1) is industrial 99.95% metallic magnesium.

[0014] Furthermore, in the step (1), the first addition of 30% hydrogen peroxide is 0.5‰ of the amount of the magnesium nitrate solution, and the second addition of 30% hydrogen peroxide is 1-3‰ of the amount of the magnesium nitrate solution.

[0015] Furthermore, in step (2), the temperature of pure water is between 25° C. and 30° C., and the resulting solution is allowed to stand for about 2.5 hours.

[0016] Furthermore, in step (4), pure water is used for washing until the nitrate content in the washing liquid is ≤0.005%.

[0017] Furthermore, in the step (6), the upper liquid level of the heated magnesium fluoride solution is maintained between 60-80° C., and the lower liquid level is maintained between 90-120° C.

[0018] The preparation method of the low-oxygen magnesium fluoride optical coating material of the present invention has the following beneficial effects: step (1) adding hydrogen peroxide twice, the first step mainly removing iron and heavy metals, and the second step mainly removing most of manganese, so that the manganese ion content of the magnesium nitrate solution is reduced from 150-300ppm to below 30ppm; step (4) cleaning with basic magnesium carbonate, according to the solubility of nitrate, sulfate and chlorate, the amount of impurities wrapped in the basic magnesium carbonate is determined, thereby determining the oxygen content of the magnesium fluoride and preventing the occurrence of popping points; step (6) layered heat preservation, reducing the volatilization of hydrofluoric acid, which is beneficial to the growth of the magnesium fluoride lattice, and obtaining Large-particle and high-purity magnesium fluoride products are produced by removing a small amount of impurities; magnesium metal is reacted with nitric acid to generate magnesium nitrate, which is reacted with ammonium bicarbonate to generate basic magnesium carbonate. Basic magnesium carbonate will wrap a large amount of magnesium nitrate ions, and magnesium nitrate has a large solubility and is easier to clean; the same cleaning times are more complete, basic magnesium carbonate contains a lower content of magnesium nitrate ions, and the generated magnesium fluoride contains less magnesium nitrate ions, so that the magnesium fluoride has a high purity and a lower oxygen content. Commonly used industrial raw materials are used in each step, and the reaction is controllable. Each step is carried out in sequence to obtain high-purity magnesium fluoride with a purity of more than 99.95% and no oxygen absorption and no bounce point requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the powder XRD pattern of magnesium fluoride. DETAILED DESCRIPTION

[0020] Embodiment 1

[0021] A method for preparing a low-oxygen magnesium fluoride optical coating material comprises the following steps:

[0022] (1) preparing a magnesium salt solution; placing 6.5 kg of industrial 99.95% metallic magnesium in pure water, adding 38.5 kg of 20% nitric acid, and reacting until the specific gravity d=1.05 g / ml, first placing magnesium in pure water to facilitate cooling of the large amount of heat generated by the reaction of magnesium and nitric acid, introducing the solution into a 5T enamel reactor, adjusting the pH of the nitrate solution to pH=2 and the specific gravity d=1.05 g / ml, and adding 30% hydrogen peroxide for the first time at 0.5‰ of the amount of the magnesium nitrate solution under constant stirring, heating to 80-100°C, then adding magnesium hydroxide paste, adjusting the pH to 7, leaving the solution to settle for more than 12 hours, filtering, and detecting that there is no iron ion reaction, introducing the filtrate into another enamel reactor, and then heating the solution to 80-100°C, and finally heating the solution to 100-100°C. In a porcelain reactor, the filtrate is continuously stirred, and 30% hydrogen peroxide is added for the second time at 1-3‰ of the amount of the magnesium nitrate solution, and the stirring is continued for 20-40 minutes, and the mixture is heated to boiling. Magnesium hydroxide is added while the stirring is continued, and the pH value is adjusted to ≥ 10. After being allowed to stand for complete precipitation, the mixture is filtered to obtain a high-purity magnesium salt solution, the chemical formula of which is 3Mg+8HNO3→3Mg(NO3)2+2NO↑+4H2O. The chemical formula of adding hydrogen peroxide twice for impurity removal is 2OH-+Mn2+→Mn(OH)2, Fe(NO3)3+3NH3H2O→Fe(OH)3↓+3NH4NO3, so that the manganese ion content of the magnesium nitrate solution is reduced from 280ppm to 23ppm;

[0023] (2) preparing an ammonium bicarbonate solution; adding 41.5 kg of 98% food grade ammonium bicarbonate to pure water, stirring and heating at 25° C. until dissolved, the temperature was always controlled at 25° C. during the dissolution process, and the solution was allowed to stand for 2.5 hours after saturation;

[0024] (3) synthesizing basic magnesium carbonate; adjusting the temperature of the high-purity magnesium salt solution obtained in step (1) to 50° C., and then filtering and synthesizing with the ammonium bicarbonate solution obtained in step (2), the volume ratio of the synthesis being not less than 5:4, to obtain a basic magnesium carbonate precipitate having a chemical formula of Mg(NO3)2+NH4HCO3→MgCO3·Mg(OH)2·H2O3↓+2NH4NO3+H2O+CO2↑;

[0025] (4) Cleaning of basic magnesium carbonate: placing the basic magnesium carbonate precipitate into a filter bag and washing with pure water until the acid radical in the washing liquid is ≤0.005%;

[0026] (5) Fluorination: 14 kg of 50% electronic grade hydrofluoric acid was added to a tetrafluoroethylene reaction kettle, and the basic magnesium carbonate obtained in step (4) was slowly added and stirred evenly. After the reaction was terminated, the pH of the solution was adjusted to 2 to obtain a magnesium fluoride solution having the chemical formula of MgCO3·Mg(OH)2+HF→MgF2+H2O+CO2↑;

[0027] (6) heat preservation; heating the magnesium fluoride solution, maintaining the upper liquid level at 60° C. and the lower liquid level at 90° C., and heat preservation for 18-20 hours to obtain a solution with upper and lower layers;

[0028] (7) low temperature drying and high temperature dehydration; after the upper liquid surface of the upper and lower layered solution obtained in step (6) is sucked out, a magnesium fluoride precipitate is obtained, which is placed in a polytetrafluoroethylene dish and dried at a temperature of 130° C. for more than 18 hours, and the drying loss after drying is ≤8%. The low temperature dried magnesium fluoride is placed under an atmospheric condition of 450-550° C., kept warm for more than 3 hours, taken out and cooled to room temperature, and 9.2 kg of 99.95% high purity magnesium fluoride is obtained, and the magnesium fluoride content is: MgF2 ≥ 99.95%, Mn ≤ 30 ppm, Fe ≤ 10 ppm, magnesium fluoride polycrystalline has no oxygen absorption, the coating has no splashing, and the finished product is pure white.

[0029] Embodiment 2

[0030] A method for preparing a low-oxygen magnesium fluoride optical coating material comprises the following steps:

[0031] (1) preparing a magnesium salt solution; placing 6.5 kg of 99.95% industrial magnesium in pure water, taking 33.5 kg of 20% nitric acid, reacting until the specific gravity d = 1.15 g / ml, first placing magnesium in pure water to facilitate cooling of the large amount of heat generated by the reaction of magnesium and nitric acid, introducing it into a 5T enamel reactor, adjusting the pH of the nitrate solution to pH = 4 and the specific gravity d = 1.15 g / ml, and adding 30% hydrogen peroxide for the first time with a volume of 0.5‰ of the magnesium nitrate solution under constant stirring, heating to 90°C, then adding magnesium hydroxide paste, adjusting the pH to between 9, leaving it to precipitate for more than 12 hours, filtering, and after detecting that there is no iron ion reaction, introducing the filtrate into another enamel reactor, and finally heating the magnesium hydroxide paste to 9. In a reaction kettle, the filtrate is continuously stirred, and 30% hydrogen peroxide is added for the second time at 1-3‰ of the amount of the magnesium nitrate solution, and the stirring is continued for 20-40 minutes, heated to boiling, and magnesium hydroxide is added while stirring, and the pH is adjusted to ≥10. After being allowed to stand for complete precipitation, the solution is filtered to obtain a high-purity magnesium salt solution, the chemical formula of which is 3Mg+8HNO3→3Mg(NO3)2+2NO↑+4H2O, and the chemical formula of adding hydrogen peroxide twice to remove impurities is 2OH-+Mn2+→Mn(OH)2, Fe(NO3)3+3NH3H2O→Fe(OH)3↓+3NH4NO3, so that the manganese ion content of the magnesium nitrate solution is reduced from 280ppm to 24ppm;

[0032] (2) preparing an ammonium bicarbonate solution; adding 37.5 kg of 98% food grade ammonium bicarbonate to pure water, stirring and heating at a temperature of 28° C. until dissolved, the temperature was always controlled at 28° C. during the dissolution process, and the solution was allowed to stand for 2.5 hours after saturation;

[0033] (3) synthesizing basic magnesium carbonate; adjusting the temperature of the high-purity magnesium salt solution obtained in step (1) to 60° C., and then filtering and synthesizing with the ammonium bicarbonate solution obtained in step (2), wherein the volume ratio of the synthesis is not less than 5:4, and obtaining a basic magnesium carbonate precipitate having a chemical formula of Mg(NO3)2+NH4HCO3→MgCO3·Mg(OH)2·H2O3↓+2NH4NO3+H2O+CO2↑;

[0034] (4) Cleaning of basic magnesium carbonate: placing the basic magnesium carbonate precipitate into a filter bag and washing with pure water until the acid radical in the washing liquid is ≤0.005%;

[0035] (5) Fluorination: 12.6 kg of 50% electronic grade hydrofluoric acid was added to a tetrafluoroethylene reaction kettle, and the basic magnesium carbonate obtained in step (4) was slowly added and stirred evenly. After the reaction was terminated, the pH of the solution was adjusted to 3-4 to obtain a magnesium fluoride solution having a chemical formula of MgCO3·Mg(OH)2+HF→MgF2+H2O+CO2↑;

[0036] (6) heat preservation; heating the magnesium fluoride solution, maintaining the upper liquid level at 70° C. and the lower liquid level at 100° C., and heat preservation for 18-20 hours to obtain a solution with upper and lower layers;

[0037] (7) low temperature drying and high temperature dehydration; after the upper liquid surface of the upper and lower layered solution obtained in step (6) is sucked out, a magnesium fluoride precipitate is obtained, which is placed in a polytetrafluoroethylene dish and dried at a temperature of 140° C. for more than 18 hours, and the drying loss after drying is ≤8%. The low temperature dried magnesium fluoride is placed under an atmospheric condition of 450-550° C. and kept warm for more than 3 hours, taken out and cooled to room temperature to obtain 8.2 kg of 99.95% high purity magnesium fluoride, the magnesium fluoride content is: MgF2 ≥ 99.95%, Mn ≤ 50 ppm, Fe ≤ 15 ppm, the magnesium fluoride polycrystal has local oxygen absorption, the coating has no splashing, and the finished product is white.

[0038] Embodiment 3

[0039] A method for preparing a low-oxygen magnesium fluoride optical coating material comprises the following steps:

[0040] (1) preparing a magnesium salt solution; placing 6.5 kg of industrial 99.95% metallic magnesium in pure water, adding 43.5 kg of 20% nitric acid, and reacting until the specific gravity d = 1.05 g / ml, first placing magnesium in pure water to facilitate cooling of the large amount of heat generated by the reaction of magnesium and nitric acid, introducing the solution into a 5T enamel reactor, adjusting the pH of the nitrate solution to pH = 2 and the specific gravity d = 1.05 g / ml, and adding 30% hydrogen peroxide for the first time with a volume of 0.5‰ of the magnesium nitrate solution under constant stirring, heating to 80-100° C., then adding magnesium hydroxide paste, adjusting the pH to 7, leaving the solution to settle for more than 12 hours, filtering, and detecting that there is no iron ion reaction, introducing the filtrate into another enamel reactor, stirring the filtrate continuously, and adding the solution for the second time; Add 30% hydrogen peroxide to 1-3‰ of the amount of magnesium nitrate solution, continue stirring for 20-40 minutes, heat to boiling, continue stirring and add magnesium hydroxide, adjust pH ≥ 10, let it stand and completely precipitate, then filter to obtain a high-purity magnesium salt solution with a chemical formula of 3Mg+8HNO3→3Mg(NO3)2+2NO↑+4H2O, add hydrogen peroxide twice to remove impurities with a chemical formula of 2OH-+Mn2+→Mn(OH)2, Fe(NO3)3+3NH3H2O→Fe(OH)3↓+3NH4NO3, so that the manganese ion content of the magnesium nitrate solution is reduced from 300ppm to 25ppm;

[0041] (2) preparing an ammonium bicarbonate solution; adding 45.5 kg of 98% food grade ammonium bicarbonate to pure water, stirring and heating at 30° C. until dissolved, the temperature was always controlled at 30° C. during the dissolution process, and the solution was allowed to stand for 2.5 hours after saturation;

[0042] (3) synthesizing basic magnesium carbonate; adjusting the temperature of the high-purity magnesium salt solution obtained in step (1) to 70° C., and then filtering and synthesizing with the ammonium bicarbonate solution obtained in step (2), wherein the volume ratio of the synthesis is not less than 5:4, and obtaining a basic magnesium carbonate precipitate having a chemical formula of Mg(NO3)2+NH4HCO3→MgCO3·Mg(OH)2·H2O3↓+2NH4NO3+H2O+CO2↑;

[0043] (4) Cleaning of basic magnesium carbonate: placing the basic magnesium carbonate precipitate into a filter bag and washing with pure water until the acid radical in the washing liquid is ≤0.005%;

[0044] (5) Fluorination: 15.5 kg of 50% electronic grade hydrofluoric acid was added to a tetrafluoroethylene reaction kettle, and the basic magnesium carbonate obtained in step (4) was slowly added and stirred evenly. After the reaction was terminated, the pH of the solution was adjusted to 3-4 to obtain a magnesium fluoride solution having a chemical formula of MgCO3·Mg(OH)2+HF→MgF2+H2O+CO2↑;

[0045] (6) heat preservation; heating the magnesium fluoride solution, maintaining the upper liquid level at 70° C. and the lower liquid level at 100° C., and heat preservation for 18-20 hours to obtain a solution with upper and lower layers;

[0046] (7) low temperature drying and high temperature dehydration; after the upper liquid surface of the upper and lower layered solution obtained in step (6) is sucked out, a magnesium fluoride precipitate is obtained, which is placed in a polyfluoroethylene dish and dried at a temperature of 140° C. for more than 18 hours, and the drying loss after drying is ≤8%. The low temperature dried magnesium fluoride is placed under atmospheric conditions of 450-550° C., kept warm for more than 3 hours, taken out and cooled to room temperature to obtain 10.1 kg of 99.95% high purity magnesium fluoride, the magnesium fluoride content is: MgF2 ≥ 99.95%, Mn ≤ 100 ppm, Fe ≤ 20 ppm, magnesium fluoride polycrystalline has oxygen absorption, the coating has splashing and the finished product is dark.

[0047] In summary, magnesium fluoride can also be prepared by using 20% ​​sulfuric acid and 20% hydrochloric acid, and the purity is above 99.9%, which can meet the purity, oxygen-free absorption and bounce-point-free requirements of optical coating materials.

[0048] The above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by those skilled in the art within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for preparing a low-oxygen magnesium fluoride optical coating material, characterized in that: The following steps are involved: (1) preparing a magnesium salt solution; placing magnesium metal in pure water, adding 3-5 times the concentration of 20% nitric acid solution, reacting until the specific gravity d=1.05-1.26 g / ml, introducing into a 5T enamel reactor, adjusting the pH of the magnesium salt solution to pH=2-5 and specific gravity d=1.05-1.26 g / ml, adding hydrogen peroxide for the first time under continuous stirring, heating to 80-100° C., adding magnesium hydroxide paste, adjusting the pH to between 7-10, leaving it to precipitate for more than 12 hours, filtering, detecting that there is no iron ion reaction, introducing the filtrate into another enamel reactor, stirring the filtrate continuously, adding hydrogen peroxide for the second time, continuing stirring for 20-40 minutes, heating to boiling, continuing stirring while adding magnesium hydroxide, adjusting the pH to ≥10, leaving it to completely precipitate and filtering to obtain a high-purity magnesium salt solution; (2) preparing an ammonium bicarbonate solution; adding food-grade ammonium bicarbonate to pure water, stirring and heating until dissolved, the temperature is always controlled between 25-30° C. during the dissolution process, and the solution is allowed to stand after saturation; (3) synthesizing basic magnesium carbonate; adjusting the temperature of the high-purity magnesium salt solution obtained in step (1) to 50-70° C., and then filtering and synthesizing with the ammonium bicarbonate solution obtained in step (2), the volume ratio of the synthesis being not less than 5:4, to obtain a basic magnesium carbonate precipitate; (4) Cleaning of basic magnesium carbonate: placing the basic magnesium carbonate precipitate into a filter bag and washing with pure water; (5) fluorination; adding hydrofluoric acid into a tetrafluoroethylene reaction kettle, slowly adding the basic magnesium carbonate obtained in step (4), and stirring evenly. After the reaction is terminated, adjusting the pH of the solution to between 2 and 5 to obtain a magnesium fluoride solution; (6) keeping warm; heating the magnesium fluoride solution for 18-20 hours to obtain a solution with upper and lower layers; (7) low temperature drying and high temperature dehydration; after the upper liquid surface of the upper and lower layered solution obtained in step (6) is sucked out, a magnesium fluoride precipitate is obtained, which is placed in a polytetrafluoroethylene dish and dried at a temperature of 130-150° C. for more than 18 hours, and the drying loss after drying is ≤8%. The low temperature dried magnesium fluoride is placed in an atmospheric condition of 450-550° C., kept warm for more than 3 hours, taken out and cooled to room temperature to obtain high purity magnesium fluoride.

2. The method for preparing a low-oxygen magnesium fluoride optical coating material according to claim 1, characterized in that: The metallic magnesium in the step (1) is industrial 99.95% metallic magnesium.

3. The method for preparing a low-oxygen magnesium fluoride optical coating material according to claim 2, characterized in that: In the step (1), the concentration of the hydrogen peroxide added for the first time is 0.5‰, and the concentration of the hydrogen peroxide added for the second time is 1-3‰.

4. The method for preparing a low-oxygen magnesium fluoride optical coating material according to claim 3, characterized in that: In step (2), the temperature of pure water is between 25° C. and 30° C., and the resulting solution is allowed to stand for about 2.5 hours.

5. The method for preparing a low-oxygen magnesium fluoride optical coating material according to claim 4, characterized in that: In the step (4), pure water is used for washing until the nitrate content in the washing liquid is ≤ 0.005%.

6. The method for preparing a low-oxygen magnesium fluoride optical coating material according to claim 5, characterized in that: In the step (6), the upper liquid level of the heated magnesium fluoride solution is maintained between 60-80° C., and the lower liquid level is maintained between 90-120° C.

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