Anode, device, system and method for producing tungsten hexafluoride through electrolysis

Abstract

The invention provides an anode, a device, a system and a method for producing tungsten hexafluoride through electrolysis. A tungsten-nickel alloy with the nickel content being 5-15 wt% is adopted for the anode, a NiF2-WF2 composite fluorinated layer with the thickness being 10-50 microns is pre-generated, the layer has high fluorine ion conductivity, and anode passivation is fundamentally inhibited. KF.2HF fused salt is used as a basic electrolyte of the electrolysis device, LiF and CsF are innovatively added as composite functional additives, LiF improves the wettability of a melt, CsF inhibits the anode effect, and efficient and stable electrolysis operation is guaranteed through cooperation of LiF and CsF. The production system is integrated with a gradient solidification separator, and condensation recovery of HF and desublimation collection of high-purity WF6 crystals are realized through the design of three temperature zones of 28-32 DEG C, 20-25 DEG C and-25--30 DEG C based on the vapor pressure difference of WF6 and HF. According to the scheme, through multi-level innovation and cooperation of materials, interfaces and systems, the defects that in a traditional method, anode failure is fast, product separation is difficult, and purity is low are overcome, efficient, long-period and high-purity production of tungsten hexafluoride is achieved, and the method is particularly suitable for high-end manufacturing industries such as semiconductors.

Description

Technical Field

[0001] This invention relates to the field of tungsten hexafluoride synthesis technology, and in particular to an anode, apparatus, system and method for electrolytic production of tungsten hexafluoride. Background Technology

[0002] Tungsten fluoride (WF6) is a crucial electronic specialty gas indispensable in semiconductor manufacturing, special coatings, and other fields, requiring extremely high purity and production efficiency. Currently, industrial-scale WF6 production processes mainly include direct fluorination with fluorine gas and fluorination with a mixture of chlorofluoride and hydrogen fluoride (Cl2·2HF). However, these methods generally suffer from problems such as complex processes, difficulties in raw material purification, and the potential for byproduct contamination.

[0003] To simplify the process, the direct electrolytic synthesis of WF6 has attracted attention. Current electrolytic technologies primarily utilize the electrolysis of molten salts. This method employs electrolyte systems with high melting points and strong corrosiveness, placing stringent demands on equipment. Furthermore, the anode surface is prone to uneven corrosion or passivation during electrolysis, leading to short anode life and reduced current efficiency. Simultaneously, the gas produced during electrolysis has a complex composition (potentially containing unreacted fluorine gas, electrolyte dust, etc.), requiring subsequent processing through complex gas purification tanks (including tungsten microsphere reaction layers, multi-stage filters, etc.). System integration and energy efficiency require further improvement.

[0004] Another existing technology involves producing fluorine gas (F2) through electrolysis, and then reacting the generated fluorine gas with metallic tungsten in another reactor to synthesize WF6. This two-step process is longer, requires more equipment, and presents challenges in the safe storage and accurate metering of fluorine gas, increasing the risk and complexity of the process.

[0005] Therefore, developing an integrated electrolytic production technology for WF6 that features high anode stability, a mild electrolysis process, and efficient product separation and purification is of great significance for reducing production costs and improving product purity and safety. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides an anode, apparatus, system, and method for the electrolytic production of tungsten hexafluoride.

[0007] According to an embodiment of the present invention, in a first aspect, an anode for electrolytic production of tungsten hexafluoride is provided, the anode being made of a tungsten-nickel alloy with a nickel content of 5-15 wt%, and having a NiF2-WF2 composite fluorination layer on its surface, the thickness of the composite fluorination layer being 10-50 μm.

[0008] Preferably, the tungsten-nickel alloy is prepared by powder metallurgy eutectic sintering.

[0009] Secondly, an electrolytic apparatus for the electrolytic production of tungsten hexafluoride is provided, comprising the aforementioned anode, a cathode, and an electrolytic cell, wherein KF·2HF is used as the electrolyte in the electrolytic cell, and 0.5-5 wt% LiF is added as an anode effect inhibitor.

[0010] Preferably, the anodic effect inhibitor also contains CsF.

[0011] Further preferably, the amount of LiF added is 0.5 wt%, and the amount of CsF added is 0.3 wt%.

[0012] Thirdly, a system for electrolytically producing tungsten hexafluoride is provided, comprising the aforementioned electrolytic apparatus and a gradient solidification separator for collecting the gas produced by the electrolytic apparatus.

[0013] Preferably, the gradient solidification separator is divided into a high-temperature zone, a transition zone, and a low-temperature zone along the gas flow direction, wherein a liquid HF discharge valve is provided at the bottom of the low-temperature zone.

[0014] More preferably, the temperature range of the high-temperature zone is 28-32℃, the temperature range of the transition zone is 20-25℃, and the temperature range of the low-temperature zone is -25~-30℃.

[0015] Fourthly, a method for electrolytically producing tungsten hexafluoride is provided, comprising the following steps:

[0016] Step 1: Electrolysis is performed using a tungsten-nickel alloy anode, wherein the anode surface has a NiF2-WF2 composite fluorination layer, and the electrolyte in the electrolytic cell contains additives of KF·2HF, 0.5-5wt% LiF and 0.1-2wt% CsF.

[0017] Step 2: Use a gradient solidification separator to separate the gas obtained in Step 1. The gradient solidification separator is divided into a high temperature zone of 28-32℃, a transition zone of 20-25℃ and a low temperature zone of -25~-30℃ along the gas flow direction, and collects WF6 crystals in the low temperature zone.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] Tungsten-nickel alloy anode. By introducing a specific proportion of nickel and using pretreatment to construct a NiF2-WF2 composite fluorination layer with a specific structure and composition on the surface, this layer forms ion-conducting channels at the microscopic level, achieving "self-protection" and "long lifespan" of the anode at the macroscopic level.

[0020] A composite functional additive electrolyte system. A binary additive consisting of LiF and CsF is introduced into the KF·2HF base molten salt. Li + With Cs +Through the synergistic effect of different physicochemical mechanisms, the properties of the electrode / electrolyte interface are improved at the microscopic level, while the anodic effect is suppressed and the electrolysis process is stabilized at the macroscopic level.

[0021] Solidification Separator. Based on the significant difference in vapor pressure between impurities such as WF6 and HF, a separation device with a precise spatial temperature field is designed. Continuous, high-purity separation of products is achieved through non-isothermal condensation, replacing complex chemical adsorption purification processes. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the gradient solidification separator in a system for the electrolytic production of tungsten hexafluoride according to the present invention.

[0023] In the above figures: 1, high temperature zone; 101, high temperature medium; 2, medium temperature zone; 3, low temperature zone; 301, low temperature medium. Detailed Implementation

[0024] The technical solutions of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] The gradient solidification separator in the electrolytic production of tungsten hexafluoride of this invention is a multi-layer concentric cylinder, such as... Figure 1 As shown, the area is divided into a high-temperature zone 1, a transition zone 2, and a low-temperature zone 3 along the gas flow direction. The high-temperature zone 1 has a high-temperature medium 101 inside its outer jacket, and the low-temperature zone has a low-temperature medium 301 inside its outer rubber sleeve. A liquid HF discharge valve is provided at the bottom of the low-temperature zone 1.

[0026] Example 1, baseline optimal conditions;

[0027] Anode preparation: 92 wt% tungsten powder, 8 wt% nickel powder. Hot pressing and sintering at 1500℃ / 30MPa. Treatment with 40% HF acid at 60℃ for 60 minutes to obtain a composite layer with a thickness of ~30μm.

[0028] Electrolyte: KF·2HF + 0.5wt% LiF + 0.3wt% CsF.

[0029] Separator temperature: 30℃ (high temperature zone); 22℃ (transition zone, residence time 10 min); -28℃ (low temperature zone).

[0030] Results after 800 hours of continuous operation:

[0031] Anode stability: The electrolysis voltage remained stable at 9.5±0.3V. After operation, the thickness of the anode composite layer was 32±5μm, with a smooth surface and no cracking or peeling.

[0032] Current efficiency: Based on dissolved tungsten, the average current efficiency reaches 94.7%.

[0033] Product purity: The collected WF6 crystals were analyzed by online mass spectrometry and infrared spectroscopy, and the purity was 99.72%. The key impurity HF content was 0.08 ppm, the O2 equivalent oxygen content was <5 ppm, and the total metal impurities were <1 ppm. After subsequent purification, the purity was 99.9995%.

[0034] HF recovery rate: Liquid HF is recovered from the transition zone with a purity of 99.1%, and the recovery rate is 98.5% of the input HF.

[0035] Anode effect, did not occur;

[0036] Example 2, verifying the component range;

[0037] Anode: Nickel content adjusted to 12wt%, pre-fluorinated layer thickness 25μm.

[0038] Electrolyte: The additives are 2.0wt% LiF + 1.0wt% CsF.

[0039] Results (300 hours): Voltage stable (9.8±0.4V). WF6 purity 99.68%, HF content 0.12ppm. The final purity after subsequent purification was 99.9995%, indicating that the higher nickel content and additive ratio were still effective, but the voltage was slightly higher, possibly related to the slight increase in layer resistance caused by the excessive NiF2 phase.

[0040] Example 3: Verifying stability;

[0041] Simulates fluctuations in actual production: the electrolysis temperature changes periodically between 90-110℃, and the current density jumps between 0.3-0.7 A / cm².

[0042] Results: The system exhibited good adaptability. Voltage varied with current but without abrupt changes. The final purity of WF6 remained at 99.70%, demonstrating the system's strong anti-interference capability. Subsequent purification yielded a final purity of 99.9995%.

[0043] Comparative Example 1: Pure tungsten anode, without additives;

[0044] Anode: Pure tungsten plate (99.95%).

[0045] Electrolyte: Pure KF·2HF, without any additives.

[0046] Results: After electrolysis was started, the voltage began to fluctuate drastically after 2 hours, exhibiting typical anodic effects intermittently and periodically. After 10 hours of operation, disassembly of the electrolytic cell anode revealed a loose, grayish-white powder layer approximately 200 μm thick covering its surface, which was easily peeled off. The electrolysis process was interrupted several times due to high anode pressure, forcing the normal experiment to be suspended.

[0047] Comparative Example 2: Tungsten-nickel anode, but without pre-fluorination layer;

[0048] Anode: Same as W-Ni alloy in Example 1, but without HF pretreatment.

[0049] Electrolyte: Same as in Example 1 (including additives).

[0050] Results: The voltage was high (12V) during the initial electrolysis phase (0-2 hours), then gradually decreased and stabilized at around 10V. However, after 200 hours of operation, uneven corrosion was observed on the anode surface, with localized pitting. The purity of WF6 fluctuated greatly (99.0-99.5%), and the HF content ranged from 2-10 ppm. This demonstrates that the pre-formed composite fluorinated layer is crucial for ensuring long-term uniform dissolution, and its "guiding" and "buffering" functions cannot be replaced by the disordered fluorinated layer naturally formed during the initial electrolysis phase.

[0051] Comparative Example 3 uses the anode and electrolyte of the present invention, but the separator is a single-stage cold trap;

[0052] The initial process is the same as in Example 1.

[0053] Separation: The product is collected using only a single-stage cold trap at -30°C.

[0054] Results: The amount of WF6 crystals collected was the same, but the purity was only 99.4%, with an HF content as high as 85 ppm. Segmented heating analysis of the material in the cold trap revealed that a large amount of HF co-condensed with WF6. This proves that a single-stage low-temperature process cannot achieve effective separation, and the multi-temperature gradient design of this invention is a necessary step to obtain high-purity products.

[0055] Comparative Example 4, simulating existing technology;

[0056] Using an impregnated and reinforced carbon anode, fluorine gas is generated by electrolysis and reacts with tungsten powder in a cylindrical reactor to produce tungsten hexafluoride.

[0057] Results: The overall yield of this scheme was low (85%), the reactor was severely corroded, the process control was complicated, and the removal of HF was difficult.

[0058] The results and related data of the examples and comparative examples are summarized in the table below:

[0059]

[0060] By employing an "alloying + pre-fluorination" strategy, a dynamically stable electrode / electrolyte interface is creatively designed, transforming the passivation layer that hinders the reaction into a conductive layer that promotes the reaction.

[0061] NiF2 exhibits a fluoride ion conductivity 2–3 orders of magnitude higher than WF2 at the electrolysis operating temperature (100℃). Interstitial NiF2 contains F... -The rapid migration provides a low-resistance path, increasing the overall ionic conductivity of the composite layer by more than 100 times compared to a pure WF2 layer. This fundamentally solves the anodic passivation problem.

[0062] The thermal expansion coefficients of WF2 and NiF2 differ, with α_WF2 < α_NiF2. During electrolysis temperature cycling, this difference induces microscopic compressive stress, which in turn makes the composite layer bond more tightly to the alloy matrix, avoiding the problem of pure WF2 layers being prone to peeling due to high internal stress.

[0063] In subsequent electrolysis, the WF2 framework, acting as a "reservoir" of tungsten, is gradually fluorinated to WF6 under anodic polarization: WF2(solid) + 4F - → WF6 (gas) + 4e - The reaction begins at the WF2 / NiF2 interface, while the NiF2 phase continuously provides F. - Transport channels. This "sacrifice the skeleton, perpetual channel" mechanism allows the composite layer thickness to remain dynamically balanced (approximately 50 μm) over hundreds of hours of operation, rather than increasing indefinitely, thus achieving long-term stable dissolution of the anode.

[0064] In the electrolyte system of this invention, the role of LiF is to lower the liquidus temperature and improve wettability. Li + With a small ionic radius (0.76 Å) and high charge density, it can effectively disrupt the original -[F…HF…F]- hydrogen bond network in the KF·2HF melt, reducing the melt viscosity by 15-20%. This brings two major benefits: (1) improved electrolyte conductivity; (2) and more importantly, a significant reduction in the wetting angle of the melt on the anode (especially the composite fluorinated layer). Good wetting ensures tight contact at the electrode / electrolyte interface, allowing gaseous products (WF6) to detach from the electrode surface at a smaller bubble size and faster speed, significantly reducing concentration polarization.

[0065] The role of CsF: to suppress the anodic effect. Utilizing large-size CsF... + The reconstruction of the melt structure creates a highly efficient fluoride ion conductive network in both the bulk phase and the interface. Through field-induced adsorption and polarization shielding, the microscopic electric field distortion on the anode surface is dynamically smoothed, eliminating "hot spots" that trigger the anode effect. Functionally complementary to LiF and coupled with the anode composite layer structure, a complete optimized system is formed from the electrode bulk phase to the reaction interface.

[0066] LiF and CsF do not act independently. Experiments showed that the synergistic effect was strongest when 0.5 wt% LiF and 0.3 wt% CsF were added. + Improved overall wettability Cs + The specific adsorption of Cs provides a more uniform interfacial basis; while Cs + Suppressing the anodic effect ensures the Li+ The effect of reducing surface tension is not interrupted by a sudden gas film.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. An anode for the electrolytic production of tungsten hexafluoride, characterized in that, The anode is made of a tungsten-nickel alloy with a nickel content of 5-15 wt% and has a NiF2-WF2 composite fluorination layer on its surface with a thickness of 10-50 μm.

2. The anode for electrolytic production of tungsten hexafluoride according to claim 1, characterized in that, The tungsten-nickel alloy was prepared by powder metallurgy eutectic sintering.

3. An electrolytic apparatus for the electrolytic production of tungsten hexafluoride, characterized in that, The device includes an anode as described in claim 1 or 2, and further includes a cathode and an electrolytic cell, wherein the electrolytic cell uses KF·2HF as the electrolyte and adds 0.5-5 wt% LiF as an anode effect inhibitor.

4. The electrolytic apparatus for producing tungsten hexafluoride according to claim 3, characterized in that, The anodic effect inhibitor also contains CsF.

5. The electrolytic apparatus for producing tungsten hexafluoride according to claim 4, characterized in that, The amount of LiF added was 0.5 wt%, and the amount of CsF added was 0.3 wt%.

6. A system for electrolytically producing tungsten hexafluoride, characterized in that, Includes the electrolysis device as described in claim 5, and a gradient solidification separator for collecting the gas produced by the electrolysis device.

7. The system for electrolytic production of tungsten hexafluoride according to claim 6, characterized in that, The gradient solidification separator is divided into a high-temperature zone, a transition zone, and a low-temperature zone along the gas flow direction, with a liquid HF discharge valve at the bottom of the low-temperature zone.

8. The system for electrolytic production of tungsten hexafluoride according to claim 7, characterized in that, The temperature range of the high-temperature zone is 28-32℃, the temperature range of the transition zone is 20-25℃, and the temperature range of the low-temperature zone is -25~-30℃.

9. A method for electrolytically producing tungsten hexafluoride, characterized in that, Includes the following steps: Step 1: Electrolysis is performed using a tungsten-nickel alloy anode, wherein the anode surface has a NiF2-WF2 composite fluorination layer, and the electrolyte in the electrolytic cell contains additives of KF·2HF, 0.5-5wt% LiF and 0.1-2wt% CsF. Step 2: Use a gradient solidification separator to separate the gas obtained in Step 1. The gradient solidification separator is divided into a high temperature zone of 28-32℃, a transition zone of 20-25℃ and a low temperature zone of -25~-30℃ along the gas flow direction, and collects WF6 crystals in the low temperature zone.

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