Synthesis process of tungsten hexafluoride

Abstract

The invention discloses a synthesis process of tungsten hexafluoride, and relates to the technical field of special gas synthesis. The process comprises the following steps: mixing ammonium fluoride and hydrofluoric acid to prepare an activation solution, carrying out ultrasonic activation treatment on tungsten powder to obtain pretreated tungsten powder, and reacting the pretreated tungsten powder with fluorine gas at a certain temperature and pressure to prepare a liquefied crude product tungsten hexafluoride; the preparation method comprises the following steps: by taking aluminum sec-butoxide and the like as raw materials, carrying out sol-gel and ethanol supercritical drying and calcining to prepare highly porous activated aluminum oxide; gasifying the crude tungsten hexafluoride, adsorbing with activated aluminum oxide, and rectifying to obtain purified tungsten hexafluoride liquid; and finally, dissolving in liquid sulfur dioxide, treating under illumination with the wavelength of 395nm, and carrying out distillation separation to obtain high-purity tungsten hexafluoride. According to the method, the activation pretreatment is combined with multi-stage purification, so that the purity and the synthesis efficiency of tungsten hexafluoride are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of specialty gas synthesis technology, specifically a synthesis process for tungsten hexafluoride. Background Technology

[0002] Tungsten hexafluoride is an indispensable key process gas in semiconductor integrated circuit manufacturing, mainly used in chemical vapor deposition (CVD) and other processes to form metallic tungsten films. Its purity directly affects the performance and yield of the final chip product. Currently, the industrial process commonly uses the direct fluorination of tungsten powder with fluorine gas for preparation. However, the crude product obtained by this method often contains hydrogen fluoride, metal fluoride impurities, and complexes such as fluorine-oxytungsten. Traditional purification methods have limited effectiveness in removing specific impurities, making it difficult to meet the increasingly stringent gas purity requirements of high-end semiconductor manufacturing.

[0003] In recent years, with the rapid development of integrated circuit manufacturing technology and the continuous miniaturization of linewidths, the purity requirements for electronic specialty gases such as tungsten hexafluoride have reached ppb (parts per billion) or even higher. Existing production processes face severe challenges in terms of efficiency and deep purification capabilities; excessive impurities directly affect the uniformity and electrical properties of thin film deposition. Therefore, developing a highly efficient, deeply purified, and integrated tungsten hexafluoride preparation technology is of great significance for ensuring the security of the semiconductor industry chain and enhancing the competitiveness of advanced processes. Summary of the Invention

[0004] The purpose of this invention is to provide a synthesis process for tungsten hexafluoride to solve the problems existing in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A process for synthesizing tungsten hexafluoride includes the following steps: Step 1: After activating and pretreating the tungsten powder, it undergoes a fluorination reaction with fluorine gas to obtain liquefied crude tungsten hexafluoride. Step 2: Prepare highly porous active alumina; Step 3: After the liquefied crude tungsten hexafluoride is vaporized, it is sequentially subjected to adsorption and distillation by the highly porous activated alumina to obtain purified tungsten hexafluoride liquid; Step 4: Dissolve the purified tungsten hexafluoride liquid in liquid sulfur dioxide, treat it under light of a specific wavelength, and then obtain high-purity tungsten hexafluoride through stepwise distillation.

[0006] As an optimization, the tungsten powder in step one has a particle size of 8~10μm, a purity of 99.9%, and is manufactured by Stardust Technology (Guangzhou) Co., Ltd.

[0007] As an optimization, the specific process of the activation pretreatment in step one is as follows: ammonium fluoride and hydrofluoric acid are mixed at a mass ratio of 1:(25~29) to prepare an activation solution; tungsten powder is placed in the activation solution at a concentration of 8g / L~12g / L, and ultrasonically treated at 25~30℃ and 300~500W power for 20~30min. After filtration, it is washed 3~5 times with deionized water and vacuum dried to obtain pretreated tungsten powder.

[0008] As an optimization, the conditions for the fluorination reaction in step one are as follows: the pretreated tungsten powder is placed in the reaction zone, and fluorine gas is introduced at an apparent gas velocity of 0.02~0.1 m / s at 200~400℃, while the system pressure is controlled at 0.3~0.5 MPa; when the fluorine concentration in the outlet gas drops to 4%~6% of the initial value, the fluorine supply is stopped, and the outlet gas is cooled to -20~-10℃ to condense, thus obtaining liquefied crude tungsten hexafluoride.

[0009] As an optimization, the preparation method of highly porous active alumina in step two includes: (1) Aluminum sec-butoxide, ethanol and deionized water are mixed in a mass ratio of 1:(2.8~3.2):(0.02~0.06) and stirred at 65~70℃ until they form a sol to obtain alumina sol; (2) Dissolve aluminum chloride hexahydrate, which is 0.8 to 0.9 times the mass of aluminum sec-butoxide, in anhydrous ethanol at a concentration of 70 wt% to 75 wt% to prepare an aluminum chloride solution; (3) The aluminum chloride solution was poured into the alumina sol under stirring at 25~30℃. After reacting for 8~10 min, the solution was aged at 25~30℃ for 2~3 days. During the period, the solution was washed with ethanol every 12 h to obtain alumina wet gel. (4) The alumina wet gel was placed in a high-pressure reactor, and anhydrous ethanol was injected to immerse it. The mixture was then subjected to supercritical drying at 240-250°C and 60-70 bar for 2-3 hours. After depressurization, the temperature was lowered to 25-30°C to obtain the alumina aerogel precursor. (5) The alumina aerogel precursor is calcined at 490~510℃ for 1.5~2.5h to obtain the highly porous active alumina.

[0010] As an optimization, the specific process of step three is as follows: the liquefied crude tungsten hexafluoride is vaporized by a preheater at 40~50℃, and then introduced from the bottom into an adsorption tower filled with highly porous active alumina, and then liquefied in a distillation tower; high-purity helium is introduced into the distillation tower at 10~20℃ to keep the liquid boiling, and the evaporated gas rises in the distillation column and condenses and refluxes to obtain purified tungsten hexafluoride liquid.

[0011] As an optimization, the specific process of step four is as follows: the purified tungsten hexafluoride liquid is dissolved in liquid sulfur dioxide, and treated with light of 395 nm wavelength at -10~-5℃ for 1~2 hours. The liquid is filtered and collected, and distilled at -5~0℃ to collect the distilled sulfur dioxide. The temperature is raised to 25~30℃ to collect the distilled high-purity tungsten hexafluoride.

[0012] As an optimization, the high-purity tungsten hexafluoride obtained in step four has a purity of 99.999%.

[0013] Compared with the prior art, the beneficial effects achieved by the present invention are: In the preparation of tungsten hexafluoride, the present invention first activates and pretreats tungsten powder to improve its reactivity, and then reacts it with fluorine gas to obtain a liquefied crude product; it is then preliminarily purified by adsorption using specially made highly porous active alumina, and further separated by distillation; finally, it uses a photochemical reduction method based on the difference in oxidizing properties for deep and targeted impurity removal to obtain a high-purity product.

[0014] First, by placing tungsten powder in an activation solution prepared with ammonium fluoride and hydrofluoric acid and then subjecting it to ultrasonic treatment, the surface of the tungsten powder can be effectively cleaned and activated, significantly increasing its specific surface area. This makes the subsequent fluorination reaction more efficient and complete, improving the conversion rate of raw materials and the yield of crude product. The highly porous activated alumina prepared using the sol-gel method combined with supercritical drying and calcination at a specific temperature possesses an extremely high specific surface area and a well-developed pore structure. It exhibits excellent adsorption capacity and selectivity for hydrogen fluoride, providing a crucial material guarantee for subsequent purification steps.

[0015] Secondly, the crude tungsten hexafluoride is vaporized and then adsorbed onto an activated alumina bed, effectively removing most polar impurities. Following this, a distillation process utilizes the difference in boiling points between the components to separate low-boiling-point impurities from the tungsten hexafluoride, resulting in a significantly purified tungsten hexafluoride liquid. Finally, the purified tungsten hexafluoride liquid is dissolved in liquid sulfur dioxide, and a reduction photochemical separation step is introduced. The core principle of this step lies in utilizing the difference in oxidizing power between tungsten hexafluoride and molybdenum hexafluoride. Under specific 395nm wavelength illumination, the more oxidizing molybdenum hexafluoride is preferentially reduced and converted into insoluble molybdenum tetrafluorooxide precipitate, while tungsten hexafluoride remains stable under these conditions. The precipitate can be separated by simple filtration, followed by stepwise distillation to recover sulfur dioxide and ultimately obtain high-purity tungsten hexafluoride. This method achieves deep and selective removal of impurities with similar properties, avoiding secondary pollution that may be caused by introducing new chemical reagents, which is key to obtaining ultra-high purity products in this process. Detailed Implementation

[0016] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0017] To more clearly illustrate the method provided by the present invention, the following embodiments will be described in detail.

[0018] Example 1: A process for synthesizing tungsten hexafluoride includes the following preparation steps: Step 1: Mix ammonium fluoride and hydrofluoric acid at a mass ratio of 1:25 to obtain an activation solution; place tungsten powder at a concentration of 8 g / L in the activation solution, sonicate at 25°C and 300W for 20 min, filter, wash three times with deionized water, and vacuum dry to obtain pretreated tungsten powder; place the pretreated tungsten powder in the reaction zone, and introduce fluorine gas at 200°C and an apparent gas velocity of 0.02 m / s, controlling the system pressure at 0.3 MPa. When the fluorine concentration in the outlet gas drops to 4% of the initial value, stop the fluorine supply, and cool the outlet gas to -20°C through a condenser to obtain liquefied crude tungsten hexafluoride; Step 2: Mix aluminum sec-butoxide, ethanol, and deionized water at a mass ratio of 1:2.8:0.02 and stir at 65°C until a sol is formed to obtain alumina sol. Dissolve 0.8 times the mass of aluminum sec-butoxide in aluminum chloride hexahydrate at 70 wt% in anhydrous ethanol to obtain an aluminum chloride solution. Pour the aluminum chloride solution into the alumina sol while stirring at 25°C. After reacting for 8 minutes, age at 25°C for 2 days, washing with ethanol every 12 hours to obtain alumina wet gel. Place the alumina wet gel into a high-pressure reactor and inject anhydrous ethanol to completely immerse it. Maintain at 240°C and 60 bar for 2 hours, then depressurize to allow the supercritical fluid to convert into gas and escape. Cool to 25°C to obtain an alumina aerogel precursor. Place the alumina aerogel precursor in a muffle furnace and calcine at 490°C for 1.5 hours to obtain highly porous active alumina. Step 3: After the crude liquefied tungsten hexafluoride is vaporized by a 40°C preheater, it is introduced into the bottom of an adsorption tower filled with highly porous active alumina. Then, it is introduced into a distillation tower through a pipeline for liquefaction. High-purity helium gas is introduced at 10°C to keep the liquid boiling. The evaporated gas enters the distillation column and rises. During the rising process, it is condensed and refluxed to obtain purified tungsten hexafluoride liquid. Step 4: Dissolve the purified tungsten hexafluoride liquid in liquid sulfur dioxide, irradiate it with 395nm light at -10℃ for 1 hour, filter and collect the liquid, distill it at -5℃, collect the distilled sulfur dioxide, heat it to 25℃, and collect the distilled high-purity tungsten hexafluoride.

[0019] Example 2: A process for synthesizing tungsten hexafluoride includes the following preparation steps: Step 1: Mix ammonium fluoride and hydrofluoric acid at a mass ratio of 1:27 to obtain an activation solution; place tungsten powder at a concentration of 10 g / L in the activation solution, sonicate at 27°C and 400 W for 25 min, filter, wash four times with deionized water, and vacuum dry to obtain pretreated tungsten powder; place the pretreated tungsten powder in the reaction zone, and introduce fluorine gas at 300°C and an apparent gas velocity of 0.06 m / s, controlling the system pressure at 0.4 MPa. When the fluorine concentration in the outlet gas drops to 5% of the initial value, stop the fluorine supply, and cool the outlet gas to -15°C through a condenser to obtain liquefied crude tungsten hexafluoride; Step 2: Mix aluminum sec-butoxide, ethanol, and deionized water at a mass ratio of 1:3:0.04 and stir at 67°C until a sol is formed to obtain alumina sol. Dissolve 0.85 times the mass of aluminum sec-butoxide in aluminum chloride hexahydrate at 73 wt% in anhydrous ethanol to obtain an aluminum chloride solution. Pour the aluminum chloride solution into the alumina sol while stirring at 27°C. After reacting for 9 minutes, age at 27°C for 3 days, washing with ethanol every 12 hours during this period to obtain alumina wet gel. Place the alumina wet gel into a high-pressure reactor and inject anhydrous ethanol to completely immerse it. Maintain at 245°C and 65 bar for 2.5 hours, then depressurize to allow the supercritical fluid to convert into gas and escape. Cool to 27°C to obtain an alumina aerogel precursor. Place the alumina aerogel precursor in a muffle furnace and calcine at 500°C for 2 hours to obtain highly porous active alumina. Step 3: After the crude liquefied tungsten hexafluoride is vaporized by a 45°C preheater, it is introduced into the bottom of an adsorption tower filled with highly porous active alumina. Then, it is introduced into a distillation tower through a pipeline for liquefaction. High-purity helium is introduced at 15°C to keep the liquid boiling. The evaporated gas enters the distillation column and rises. During the rising process, it is condensed and refluxed to obtain purified tungsten hexafluoride liquid. Step 4: Dissolve the purified tungsten hexafluoride liquid in liquid sulfur dioxide, irradiate with 395nm light at -7℃ for 1.5h, filter and collect the liquid, distill at -3℃, collect the distilled sulfur dioxide, heat to 27℃, and collect the distilled high-purity tungsten hexafluoride.

[0020] Example 3: A process for synthesizing tungsten hexafluoride includes the following preparation steps: Step 1: Mix ammonium fluoride and hydrofluoric acid at a mass ratio of 1:29 to obtain an activation solution; place tungsten powder at a concentration of 12 g / L in the activation solution, sonicate at 30°C and 500 W for 30 min, filter, wash 5 times with deionized water, and vacuum dry to obtain pretreated tungsten powder; place the pretreated tungsten powder in the reaction zone, introduce fluorine gas at 400°C and an apparent gas velocity of 0.1 m / s, control the system pressure at 0.5 MPa, and stop the fluorine supply when the fluorine concentration in the outlet gas drops to 6% of the initial value. Cool the outlet gas to -20°C through a condenser to obtain liquefied crude tungsten hexafluoride. Step 2: Mix aluminum sec-butoxide, ethanol, and deionized water at a mass ratio of 1:3.2:0.06 and stir at 70°C until a sol is formed to obtain alumina sol. Dissolve aluminum chloride hexahydrate (0.9 times the mass of aluminum sec-butoxide) in anhydrous ethanol at 75 wt% to obtain an aluminum chloride solution. Pour the aluminum chloride solution into the alumina sol while stirring at 30°C. After reacting for 10 min, age at 30°C for 3 days, washing with ethanol every 12 h during this period to obtain alumina wet gel. Place the alumina wet gel into a high-pressure reactor and inject anhydrous ethanol to completely immerse it. Maintain at 250°C and 70 bar for 3 h, then depressurize to allow the supercritical fluid to convert into gas and escape. Cool to 30°C to obtain an alumina aerogel precursor. Place the alumina aerogel precursor in a muffle furnace and calcine at 510°C for 2.5 h to obtain highly porous active alumina. Step 3: After the crude liquefied tungsten hexafluoride is vaporized by a 50°C preheater, it is introduced into the bottom of an adsorption tower filled with highly porous active alumina. Then, it is introduced into a distillation tower through a pipeline for liquefaction. High-purity helium gas is introduced at 20°C to keep the liquid boiling. The evaporated gas enters the distillation column and rises. During the rising process, it is condensed and refluxed to obtain purified tungsten hexafluoride liquid. Step 4: Dissolve the purified tungsten hexafluoride liquid in liquid sulfur dioxide, irradiate with 395nm light at -5℃ for 2 hours, filter and collect the liquid, distill at 0℃, collect the distilled sulfur dioxide, heat to 30℃, and collect the distilled high-purity tungsten hexafluoride.

[0021] Comparative Example 1: A process for synthesizing tungsten hexafluoride includes the following preparation steps: Step 1: Place tungsten powder in the reaction zone, introduce fluorine gas at 300℃ and an apparent gas velocity of 0.06 m / s, control the system pressure at 0.4 MPa, and stop the fluorine supply when the fluorine concentration in the outlet gas drops to 5% of the initial value. Cool the outlet gas to -15℃ through a condenser to obtain liquefied crude tungsten hexafluoride. Step 2: Mix aluminum sec-butoxide, ethanol, and deionized water at a mass ratio of 1:3:0.04 and stir at 67°C until a sol is formed to obtain alumina sol. Dissolve 0.85 times the mass of aluminum sec-butoxide in aluminum chloride hexahydrate at 73 wt% in anhydrous ethanol to obtain an aluminum chloride solution. Pour the aluminum chloride solution into the alumina sol while stirring at 27°C. After reacting for 9 minutes, age at 27°C for 3 days, washing with ethanol every 12 hours during this period to obtain alumina wet gel. Place the alumina wet gel into a high-pressure reactor and inject anhydrous ethanol to completely immerse it. Maintain at 245°C and 65 bar for 2.5 hours, then depressurize to allow the supercritical fluid to convert into gas and escape. Cool to 27°C to obtain an alumina aerogel precursor. Place the alumina aerogel precursor in a muffle furnace and calcine at 500°C for 2 hours to obtain highly porous active alumina. Step 3: After the crude liquefied tungsten hexafluoride is vaporized by a 45°C preheater, it is introduced into the bottom of an adsorption tower filled with highly porous active alumina. Then, it is introduced into a distillation tower through a pipeline for liquefaction. High-purity helium is introduced at 15°C to keep the liquid boiling. The evaporated gas enters the distillation column and rises. During the rising process, it is condensed and refluxed to obtain purified tungsten hexafluoride liquid. Step 4: Dissolve the purified tungsten hexafluoride liquid in liquid sulfur dioxide, irradiate with 395nm light at -7℃ for 1.5h, filter and collect the liquid, distill at -3℃, collect the distilled sulfur dioxide, heat to 27℃, and collect the distilled high-purity tungsten hexafluoride.

[0022] Comparative Example 2: A process for synthesizing tungsten hexafluoride includes the following preparation steps: Step 1: Mix ammonium fluoride and hydrofluoric acid at a mass ratio of 1:27 to obtain an activation solution; place tungsten powder at a concentration of 10 g / L in the activation solution, sonicate at 27°C and 400 W for 25 min, filter, wash four times with deionized water, and vacuum dry to obtain pretreated tungsten powder; place the pretreated tungsten powder in the reaction zone, and introduce fluorine gas at 300°C and an apparent gas velocity of 0.06 m / s, controlling the system pressure at 0.4 MPa. When the fluorine concentration in the outlet gas drops to 5% of the initial value, stop the fluorine supply, and cool the outlet gas to -15°C through a condenser to obtain liquefied crude tungsten hexafluoride; Step 2: After the liquefied crude tungsten hexafluoride is vaporized by a 45°C preheater, it is introduced into the bottom of an adsorption tower filled with commercially available activated alumina (Nake Chemical). Then, it is piped into a distillation column for liquefaction. High-purity helium is introduced at 15°C to keep the liquid boiling. The evaporated gas enters the distillation column and rises. During the rising process, it is condensed and refluxed to obtain purified tungsten hexafluoride liquid. Step 4: Dissolve the purified tungsten hexafluoride liquid in liquid sulfur dioxide, irradiate with 395nm light at -7℃ for 1.5h, filter and collect the liquid, distill at -3℃, collect the distilled sulfur dioxide, heat to 27℃, and collect the distilled high-purity tungsten hexafluoride.

[0023] Comparative Example 3: A process for synthesizing tungsten hexafluoride includes the following preparation steps: Step 1: Mix ammonium fluoride and hydrofluoric acid at a mass ratio of 1:27 to obtain an activation solution; place tungsten powder at a concentration of 10 g / L in the activation solution, sonicate at 27°C and 400 W for 25 min, filter, wash four times with deionized water, and vacuum dry to obtain pretreated tungsten powder; place the pretreated tungsten powder in the reaction zone, and introduce fluorine gas at 300°C and an apparent gas velocity of 0.06 m / s, controlling the system pressure at 0.4 MPa. When the fluorine concentration in the outlet gas drops to 5% of the initial value, stop the fluorine supply, and cool the outlet gas to -15°C through a condenser to obtain liquefied crude tungsten hexafluoride; Step 2: Mix aluminum sec-butoxide, ethanol, and deionized water at a mass ratio of 1:3:0.04 and stir at 67°C until a sol is formed to obtain alumina sol. Dissolve 0.85 times the mass of aluminum sec-butoxide in aluminum chloride hexahydrate at 73 wt% in anhydrous ethanol to obtain an aluminum chloride solution. Pour the aluminum chloride solution into the alumina sol while stirring at 27°C. After reacting for 9 minutes, age at 27°C for 3 days, washing with ethanol every 12 hours during this period to obtain alumina wet gel. Place the alumina wet gel into a high-pressure reactor and inject anhydrous ethanol to completely immerse it. Maintain at 245°C and 65 bar for 2.5 hours, then depressurize to allow the supercritical fluid to convert into gas and escape. Cool to 27°C to obtain an alumina aerogel precursor. Place the alumina aerogel precursor in a muffle furnace and calcine at 500°C for 2 hours to obtain highly porous active alumina. Step 3: After the liquefied crude tungsten hexafluoride is vaporized in a 45°C preheater, it is introduced into the bottom of an adsorption tower filled with highly porous active alumina. Then, it is piped into a distillation tower for liquefaction. High-purity helium gas is introduced at 15°C to keep the liquid boiling. The evaporated gas enters the distillation column and rises. The high-purity tungsten hexafluoride gas emitted from the top of the tower is collected in a refined product storage tank.

[0024] Experimental Example 1: This example analyzes the fluorine reaction efficiency, hydrogen fluoride and molybdenum hexafluoride impurity content when synthesizing tungsten hexafluoride gas using the methods of each embodiment and Comparative Examples 1-3.

[0025] The results are shown in Table 1.

[0026] Table 1

[0027] A comparison of Examples 1-3 and Comparative Example 1 reveals that ultrasonic pretreatment of tungsten powder with an ammonium fluoride-hydrofluoric acid activation solution significantly improves its reaction efficiency with fluorine gas. The activation solution formed by the mixture of ammonium fluoride and hydrofluoric acid effectively dissolves and strips the oxide passivation layer and adsorbed impurities on the surface of the tungsten powder. Simultaneously, the cavitation effect generated by ultrasonic treatment further disperses the tungsten powder particles, reduces agglomeration, and increases its specific surface area and surface energy. The pretreated tungsten powder surface is clean, and the active sites are fully exposed, making it easier for fluorine gas to contact tungsten atoms and undergo uniform and rapid fluorination in the subsequent fluorination reaction.

[0028] A comparison of Examples 1-3 and Comparative Example 2 reveals that adsorption treatment using self-made highly porous activated alumina significantly reduces the content of hydrogen fluoride impurities. The self-made alumina, prepared via a sol-gel method combined with supercritical drying and calcination at a specific temperature, forms a unique microstructure with a large specific surface area, abundant mesoporous structure, and high surface activity, exhibiting extremely strong adsorption capacity for the polar impurity hydrogen fluoride. During purification, the self-made material can more efficiently and thoroughly capture and lock hydrogen fluoride molecules in crude tungsten hexafluoride, while commercially available alumina causes some hydrogen fluoride to permeate and remain in the product.

[0029] A comparison of Examples 1-3 with Comparative Example 3 shows that the reduction photochemical separation in step four can directionally remove molybdenum hexafluoride impurities, thereby significantly reducing the content of molybdenum hexafluoride impurities. The principle is that molybdenum hexafluoride can be selectively reduced to insoluble molybdenum tetrafluoride precipitate by liquid sulfur dioxide under 395nm light irradiation, while tungsten hexafluoride remains stable under these conditions. Efficient separation of the two can be achieved through filtration, avoiding the problem of traditional methods failing to completely remove such similar impurities and ensuring the high purity of the product.

[0030] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended technical solutions rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the technical solutions are intended to be included within the present invention.

Claims

1. A process for synthesizing tungsten hexafluoride, characterized in that, Includes the following steps: Step 1: After activating and pretreating the tungsten powder, it undergoes a fluorination reaction with fluorine gas to obtain liquefied crude tungsten hexafluoride. Step 2: Prepare highly porous active alumina; Step 3: After the liquefied crude tungsten hexafluoride is vaporized, it is sequentially subjected to adsorption and distillation by the highly porous activated alumina to obtain purified tungsten hexafluoride liquid; Step 4: Dissolve the purified tungsten hexafluoride liquid in liquid sulfur dioxide, treat it under light of a specific wavelength, and then obtain high-purity tungsten hexafluoride through stepwise distillation.

2. The synthesis process of tungsten hexafluoride according to claim 1, characterized in that, The tungsten powder mentioned in step one has a particle size of 8~10μm and a purity of 99.9%.

3. The synthesis process of tungsten hexafluoride according to claim 1, characterized in that, The specific process of the activation pretreatment in step one is as follows: ammonium fluoride and hydrofluoric acid are mixed at a mass ratio of 1:(25~29) to prepare an activation solution; tungsten powder is placed in the activation solution at a concentration of 8g / L~12g / L, and ultrasonically treated at 25~30℃ and 300~500W power for 20~30min. After filtration, it is washed 3~5 times with deionized water and vacuum dried to obtain pretreated tungsten powder.

4. The synthesis process of tungsten hexafluoride according to claim 1, characterized in that, The conditions for the fluorination reaction in step one are as follows: the pretreated tungsten powder is placed in the reaction zone, and fluorine gas is introduced at an apparent gas velocity of 0.02~0.1 m / s at 200~400℃, while the system pressure is controlled at 0.3~0.5 MPa; when the fluorine concentration in the outlet gas drops to 4%~6% of the initial value, the fluorine supply is stopped, and the outlet gas is cooled to -20~-10℃ to condense, thus obtaining liquefied crude tungsten hexafluoride.

5. The synthesis process of tungsten hexafluoride according to claim 1, characterized in that, The preparation method of highly porous active alumina in step two includes: (1) Aluminum sec-butoxide, ethanol and deionized water are mixed in a mass ratio of 1:(2.8~3.2):(0.02~0.06) and stirred at 65~70℃ until they form a sol to obtain alumina sol; (2) Dissolve aluminum chloride hexahydrate, which is 0.8 to 0.9 times the mass of aluminum sec-butoxide, in anhydrous ethanol at a concentration of 70 wt% to 75 wt% to prepare an aluminum chloride solution; (3) The aluminum chloride solution was poured into the alumina sol under stirring at 25~30℃. After reacting for 8~10 min, the solution was aged at 25~30℃ for 2~3 days. During the period, the solution was washed with ethanol every 12 h to obtain alumina wet gel. (4) The alumina wet gel was placed in a high-pressure reactor, and anhydrous ethanol was injected to immerse it. The mixture was then subjected to supercritical drying at 240-250°C and 60-70 bar for 2-3 hours. After depressurization, the temperature was lowered to 25-30°C to obtain the alumina aerogel precursor. (5) The alumina aerogel precursor is calcined at 490~510℃ for 1.5~2.5h to obtain the highly porous active alumina.

6. The synthesis process of tungsten hexafluoride according to claim 1, characterized in that, The specific process of step three is as follows: the liquefied crude tungsten hexafluoride is vaporized by a preheater at 40~50℃, and then introduced from the bottom into an adsorption tower filled with highly porous active alumina, and then liquefied in a distillation tower; high-purity helium is introduced into the distillation tower at 10~20℃ to keep the liquid boiling, and the evaporated gas rises in the distillation column and condenses and refluxes to obtain purified tungsten hexafluoride liquid.

7. The synthesis process of tungsten hexafluoride according to claim 1, characterized in that, The specific process of step four is as follows: the purified tungsten hexafluoride liquid is dissolved in liquid sulfur dioxide, and treated with light of 395nm wavelength at -10~-5℃ for 1~2h. The liquid is filtered and collected, and distilled at -5~0℃ to collect the distilled sulfur dioxide. The temperature is raised to 25~30℃ to collect the distilled high-purity tungsten hexafluoride.

8. The synthesis process of tungsten hexafluoride according to claim 1, characterized in that, The high-purity tungsten hexafluoride obtained in step four has a purity of 99.999%.

Images