Large-scale preparation method of low-water-oxygen rare earth fluoride

Abstract

The invention relates to a large-scale preparation method of low-water-oxygen rare earth fluoride, which comprises the following steps: by taking rare earth metal as a raw material, carrying out multiple hydrogenation and dehydrogenation operations to obtain rare earth metal with the specific surface area of more than 10m < 2 > / g, and then carrying out low-temperature pressurized fluorination reaction on anhydrous hydrogen fluoride and the rare earth metal with the high specific surface area to obtain the rare earth fluoride with the O content of less than or equal to 10ppm and the H2O content of less than or equal to 15ppm.

Description

Technical Field

[0001] The invention relates to a large-scale preparation method of low-water-oxygen rare earth fluoride for optical materials. Background Art

[0002] Rare earth fluorides are the preferred low-refractive index materials in long-wave and ultra-long-wave infrared optical thin film devices, requiring extremely low water and oxygen content.

[0003] In industrial production, the commonly used methods for preparing rare earth fluorides include wet fluorination and dry fluorination, among which: 1. The wet fluorination method is a hydrofluoric acid precipitation (or fluoride salt precipitation) - vacuum dehydration method. The wet production process is simple to operate, but the precipitated rare earth fluoride is colloidal, difficult to filter and wash, takes a long time to clarify, has a high content of non-rare earth impurities, and is incompletely fluorinated. Even if vacuum dehydration is used, it is difficult to solve the problem of high residual oxygen and water.

[0004] 2. The dry fluorination method is divided into the ammonium bifluoride fluorination method and the hydrogen fluoride fluorination method. The hydrogen fluoride fluorination method uses rare earth oxides as raw materials and uses fluorination gas at about 600°C for fluorination. It has the characteristics of short steps and high rare earth yield. The rare earth fluoride prepared by this method has water generated during the reaction process, and forms hydrofluoric acid with hydrogen fluoride to corrode the furnace material and the reaction device, resulting in low purity of the output product, containing metal impurities such as nickel, iron, aluminum, and silicon, and high oxygen impurities and water content. The ammonium bifluoride fluorination method uses rare earth oxides as raw materials, uses ammonium bifluoride to stir, and reacts at 500°C-600°C. The water and oxygen content of the output product is generally high, and it is also difficult to directly apply to high-end rare earth optical materials such as infrared coating materials, luminescent materials, and crystal materials.

[0005] How to more effectively reduce the water and oxygen impurity content in rare earth fluorides and seek high-performance rare earth fluoride materials that are more suitable for use in high-end rare earth material fields such as infrared coating materials, luminescent materials and crystal materials are technical problems that need to be urgently solved in the preparation of rare earth fluorides for optical materials. Summary of the invention

[0006] The present invention aims to provide a simple method for preparing low-water oxygen rare earth fluoride.

[0007] In order to achieve the above object, the present invention provides a large-scale preparation method of low-water oxygen rare earth fluoride, comprising the following steps: S1. Hydrogenation and dehydrogenation: Perform 3-8 hydrogenation and dehydrogenation operations on the rare earth metal to obtain a rare earth metal with a high specific surface area; S2. Fluorination: Anhydrous hydrogen fluoride and a rare earth metal with a high specific surface area are used for low-temperature pressure fluorination reaction to obtain rare earth fluorides with an O content of ≤10ppm and H2O ≤15ppm.

[0008] In certain implementations of the present invention, the hydrogenation, dehydrogenation and fluorination are carried out in one reaction device.

[0009] In certain implementations of the present invention, in said S1, the rare earth metal hydrogenation conditions are: hydrogenation temperature of 350-550° C., hydrogen pressure of 500-1000 kPa, and preferably hydrogenation treatment time of 1.0-2.0 h.

[0010] In certain implementations of the present invention, the purity of the hydrogen used in the hydrogenation step in S1 is ≥ 99.999%.

[0011] In certain implementations of the present invention, in S1, the vacuum dehydrogenation conditions of the rare earth metal hydride are: temperature of 500° C.-850° C., and dehydrogenation time of 2.0-4.0 h.

[0012] In certain implementations of the present invention, the high specific surface area rare earth metal reaches a specific surface area of ​​10 m2 / g-30 m2 / g after multiple hydrogenation and dehydrogenation operations.

[0013] In certain implementations of the present invention, in S2, the fluorination temperature is 200-350°C, the fluorination pressure is 500-850 kPa, the fluorination time is 3-10 hours, and the gas flow is maintained during the fluorination pressure maintenance process.

[0014] In certain implementations of the present invention, the large-scale preparation method of low-water-oxygen rare earth fluorides further includes a pretreatment step, wherein the rare earth metals are washed with 1-2 mol / L hydrochloric acid and sewage alcohol before entering the reaction device.

[0015] In certain implementations of the present invention, the rare earth metal is a block, and the minimum diameter thereof is 20 mm-50 mm.

[0016] Compared with the prior art, the present invention has the following advantages: Compared with the conventional fluorination method, the present invention uses rare earth metals instead of rare earth oxides as the initial raw materials, and washes the oxide surface of large-sized metal blocks by acid washing and anhydrous alcohol, thereby reducing the introduction of water and oxygen at the source; through repeated and multiple enhanced hydrogenation and dehydrogenation, the specific surface area of ​​the rare earth metal is greatly improved, from less than 1 m2 / g to more than 10 m2 / g, which is beneficial to the direct reaction of rare earth metals and anhydrous hydrogen fluoride, promotes the kinetics of the fluorination reaction, and on the other hand is beneficial to the complete fluorination of rare earth metals, avoiding the reaction of unreacted rare earth metals with water and oxygen in the air, resulting in an increase in water and oxygen content.

[0017] In addition, the present invention uses a closed pressure-bearing reaction device to carry out the reaction to prepare rare earth fluoride, and in a reducing or vacuum atmosphere, hydrogenation and dehydrogenation are achieved by temperature control, and then fluorination is carried out. During the preparation process, the rare earth metal is prevented from contacting with water and oxygen in the air, and rare earth fluoride with extremely low water and oxygen content can be obtained. The same closed reaction device is used for operation, and through variable temperature control, variable pressure control, and the introduction and export of changing gas types, there is no transfer of rare earth-containing materials during the reaction, and it is easy to mass produce.

[0018] The fluorination step is promoted by pressurized fluorination, and the hydrogen produced by the fluorination process is gradually discharged from the reaction device to ensure that the further fluorination process can continue.

[0019] During the fluorination process of this method, the reaction between hydrogen fluoride and metal does not involve the generation of water, which is a dry operation. Compared with the dry fluorination of rare earth oxides, no hydrofluoric acid is generated, the problem of equipment corrosion is solved, and the problem of product contamination by the reaction device or the container is avoided.

[0020] During the fluorination process, pressurized fluorination is performed and a relatively low fluorination temperature is used. This is because the fluorination reaction is an exothermic process and is not conducive to the reaction. Too high a reaction temperature will cause the locally generated rare earth fluoride to form a shell, inhibiting the continued fluorination reaction. Low-temperature operation can avoid the inhibition of further metal fluorination reactions by the produced rare earth fluoride shell. DETAILED DESCRIPTION Example

[0021] The raw material is a block of rare earth metal yttrium with a minimum diameter of 20 mm. After washing with 1.0 mol / L dilute hydrochloric acid and anhydrous ethanol, it is placed in a closed reaction furnace and subjected to 6 hydrogenation and dehydrogenation operations to obtain a specific surface area of ​​25.8 m2 / g of metal yttrium. The hydrogenation temperature is 350°C, the hydrogen pressure is 980 kPa, and the hydrogenation time is 2.0 h. The dehydrogenation operation conditions are a temperature of 800°C, a dehydrogenation time of 2.0 h, and a vacuum of 10 -3 Pa.

[0022] Anhydrous hydrogen fluoride and the above-mentioned high specific surface metal yttrium are subjected to a pressurized fluorination reaction, wherein: the fluorination temperature is 240°C, the fluorination pressure is 850kPa, the fluorination time is 4h, and during the fluorination pressure maintenance process, P is maintained. 氟化氢 / P 氢气 Greater than 20. Finally, yttrium fluoride with an O content of 8ppm and H2O of 13ppm was obtained. Example

[0023] The raw material is a block of rare earth metal ytterbium with a minimum diameter of 40 mm. After washing with 1.5 mol / L dilute hydrochloric acid and anhydrous ethanol, it is placed in a closed reactor and subjected to four hydrogenation and dehydrogenation operations to obtain a specific surface area of ​​17.8 m2 / g of metal ytterbium. The hydrogenation temperature is 300 °C, the hydrogen pressure is 680 kPa, and the hydrogenation time is 4.0 h. The dehydrogenation operation conditions are a temperature of 700 °C, a dehydrogenation time of 3.0 h, and a vacuum is drawn to a vacuum degree of 1.2×10 -3 Pa.

[0024] Anhydrous hydrogen fluoride and the above-mentioned high specific surface metal ytterbium are subjected to a pressurized fluorination reaction, wherein: the fluorination temperature is 300°C, the fluorination pressure is 650kPa, the fluorination time is 4h, and during the fluorination pressure maintenance process, P is maintained. 氟化氢 / P 氢气 Greater than 30. Finally, ytterbium fluoride with an O content of 7ppm and a H2O content of 10ppm was obtained. Example

[0025] The raw material is a block of rare earth metal lanthanum with a minimum diameter of 35 mm. After washing with 1.9 mol / L dilute hydrochloric acid and anhydrous ethanol, it is placed in a closed reaction furnace and subjected to three hydrogenation and dehydrogenation operations to obtain a metal lanthanum with a specific surface area of ​​12.8 m2 / g. The hydrogenation temperature is 300°C, the hydrogen pressure is 600 kPa, and the hydrogenation time is 4.0 h. The dehydrogenation operation conditions are a temperature of 800°C, a dehydrogenation time of 3.9 h, and a vacuum is performed with a vacuum degree of 2.2×10 -3 Pa.

[0026] Anhydrous hydrogen fluoride and the above-mentioned high specific surface metal lanthanum are subjected to a pressurized fluorination reaction, wherein: the fluorination temperature is 300°C, the fluorination pressure is 650kPa, the fluorination time is 4h, and during the fluorination pressure maintenance process, P is maintained. 氟化氢 / P 氢气 Greater than 15. Finally, lanthanum fluoride with an O content of 9 ppm and a H2O content of 13 ppm was obtained.

Claims

1. A large-scale preparation method of low-water oxygen rare earth fluoride, characterized in that: S1. Hydrogenation and dehydrogenation: The rare earth metal is subjected to 3-8 hydrogenation and dehydrogenation operations to obtain rare earth metals with high specific surface area; S2. Fluorination: Anhydrous hydrogen fluoride is used to carry out low-temperature pressurized fluorination reaction with rare earth metals with high specific surface area to obtain rare earth fluorides with O content ≤10ppm and H2O ≤15ppm.

2. The method according to claim 1, characterized in that: The hydrogenation, dehydrogenation and fluorination are carried out in one reaction device.

3. The method according to claim 1, characterized in that: In the above-mentioned S1, the rare earth metal hydrogenation conditions are: hydrogenation temperature is 350-550°C, hydrogen pressure is 500-1000 kPa, and the preferred hydrogenation treatment time is 1.0-2.0 h.

4. The method according to claim 1, characterized in that: The purity of the hydrogen used in the hydrogenation step in S1 is ≥ 99.999%.

5. The method according to claim 1, characterized in that: In the above-mentioned S1, the vacuum dehydrogenation conditions of the rare earth metal hydride are: temperature of 500°C-850°C, and dehydrogenation time of 2.0-4.0h.

6. The method according to claim 1, characterized in that: After multiple hydrogenation and dehydrogenation operations, the high specific surface rare earth metal has a specific surface area of ​​10 m2 / g-30 m2 / g.

7. The method according to claim 1, characterized in that: In the S2, the fluorination temperature is 200~350°C, the fluorination pressure is 500~850kPa, the fluorination time is 3~10h, and the gas flow is maintained during the fluorination pressure maintenance process.

8. The method according to claim 1, characterized in that: The method also includes a pre-treatment step, in which the rare earth metal is cleaned with 1-2 mol / L hydrochloric acid and sewage alcohol before entering the reaction device.

9. The method according to claim 1, characterized in that: The rare earth metal is a block, and the minimum diameter thereof is 20 mm to 50 mm.