Electrochemical polishing solution for superconducting niobium material and application of electrochemical polishing solution

Abstract

The invention relates to the technical field of superconducting material surface treatment, and particularly discloses an electrochemical polishing solution for a superconducting niobium material and application of the electrochemical polishing solution. The polishing solution is formed by mixing 98wt% of concentrated sulfuric acid, 40wt% of hydrofluoric acid and absolute ethyl alcohol according to the volume ratio of 5: 1: 1. Compared with a traditional 9: 1 binary system, absolute ethyl alcohol is introduced to serve as a key third component, the acid-base ratio is optimized, and a ternary synergistic system is constructed. The absolute ethyl alcohol plays multiple functions of inhibiting pitting corrosion, improving the wettability and mass transfer process, controlling reaction kinetics and the like in a system, and has a synergistic effect with the adjusted acid proportion, so that the problems that pitting corrosion is easy to generate, the surface uniformity is poor and a process window is narrow in a traditional formula are effectively solved. The polishing solution is particularly suitable for carrying out 30-second short-time efficient polishing on the superconducting niobium plate under the condition of 15V direct-current voltage, and a pitting-corrosion-free and low-roughness ultra-smooth surface can be stably obtained.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of superconducting material surface treatment, and particularly relates to an electrochemical polishing solution and application thereof in superconducting niobium material surface treatment, and is particularly suitable for efficient and high-precision electrochemical polishing of superconducting niobium plates in a laboratory environment. BACKGROUND

[0002] Metallic niobium is widely used in the manufacture of superconducting RF cavities due to its excellent superconducting performance. In the superconducting state, the current is only distributed in a very shallow depth of the material surface, and this skin effect makes the performance of superconducting devices extremely sensitive to the surface quality. Any micro-scale surface roughness, defects or contamination will cause a significant increase in RF loss, thereby reducing the quality factor and accelerating gradient of the superconducting cavity.

[0003] Currently, electrochemical polishing is a standard process for obtaining super-smooth niobium surfaces. The electrolyte system commonly used in the industry is a binary solution composed of concentrated sulfuric acid and hydrofluoric acid, and the typical ratio is 98wt% concentrated sulfuric acid and 40wt% hydrofluoric acid mixed at a volume ratio of 9:1. Although this traditional system can achieve basic polishing effect, it has several inherent defects in actual application.

[0004] Firstly, hydrofluoric acid shows a clear selective corrosion tendency to the grain boundaries and defect regions of niobium, and this localized corrosion behavior is prone to form pitting on the polished surface, which becomes a potential failure source of superconducting performance. Secondly, the high viscosity of concentrated sulfuric acid leads to uneven wetting of the electrolyte on the niobium surface, making it difficult to form a uniform and stable anodic diffusion layer, resulting in inconsistent surface roughness after polishing. In addition, the reaction kinetics of this binary system is difficult to accurately control, especially when a higher material removal rate is pursued, the process window is narrow, and it is easy to change from the ideal polishing state to the excessive erosion state, which seriously affects the final surface quality.

[0005] To overcome these limitations, existing technologies often need to compensate through complex tool design or extremely strict process parameter control, which not only increases the process complexity and implementation cost, but also reduces the stability and repeatability of the process. Therefore, it is particularly urgent to develop a new type of electrolyte system that can fundamentally improve the polishing quality and broaden the process window. SUMMARY

[0006] The purpose of the present application is to provide a completely new electrochemical polishing solution, which fundamentally reconstructs the traditional formula system, effectively solving key technical problems such as pitting control, surface uniformity and process stability.

[0007] The electrochemical polishing solution provided by the present application is composed of the following components in volume ratio: 98wt% concentrated sulfuric acid, 40wt% hydrofluoric acid and anhydrous ethanol mixed in a ratio of 5:1:1. This ratio design is based on the optimization scheme obtained from in-depth analysis of the traditional system and a large number of experimental verification.

[0008] Compared with the traditional 9:1 binary system, the innovation of the present application mainly lies in two aspects. First, the fundamental change of the system composition, by introducing anhydrous ethanol as the key third component, the original binary system is upgraded to a ternary synergistic system. Anhydrous ethanol plays multiple important roles in the system, its function far beyond a simple diluent. Ethanol molecules can preferentially adsorb on the high-energy active sites on the surface of niobium anode, such as grain boundaries and defect areas, forming a dynamic molecular protective layer. This adsorption behavior effectively blocks the direct attack of hydrofluoric acid on these sensitive areas, thereby converting local corrosion into uniform dissolution, fundamentally inhibiting the occurrence of pitting.

[0009] In terms of physical properties, the addition of anhydrous ethanol significantly improves the transport performance of the electrolyte. It can effectively reduce the inherent high viscosity and high surface tension of concentrated sulfuric acid system, greatly improve the wetting ability of the electrolyte to the surface of niobium. This improvement enables the metal ions and reaction heat generated during the anodic dissolution process to diffuse more efficiently to the bulk solution, which is beneficial to the formation of a thinner and more stable anodic diffusion layer, which is an important prerequisite for obtaining an atomic-level smooth surface.

[0010] At the level of reaction kinetics, the introduction of anhydrous ethanol has a profound impact on the chemical environment of the system. By reducing the water activity in the system, it effectively inhibits the excessive ionization of hydrofluoric acid, thereby mitigating its non-selective chemical corrosion. This regulation makes the metal removal process more dependent on the anodic potential-controlled electrochemical dissolution rather than uncontrollable chemical reaction, significantly improving the controllability and predictability of the polishing process.

[0011] Ratio optimization is another important feature of the present application. Compared with the traditional 9:1 ratio, the present application adjusts the volume ratio of sulfuric acid and hydrofluoric acid to 5:1. This adjustment forms a good synergistic effect with the introduction of anhydrous ethanol. Under the premise that ethanol effectively inhibits the negative effects of hydrofluoric acid, appropriately increasing the relative proportion of hydrofluoric acid can ensure that its functions of dissolving oxide film and complexing metal ions are fully exerted, while a higher proportion of sulfuric acid maintains the necessary conductivity and oxidation potential. The three together constitute a new polishing system that is thermodynamically stable and dynamically synergistic.

[0012] This invention also provides a specific method for applying the above-mentioned electrochemical polishing slurry in the electrochemical polishing of superconducting niobium materials. The preferred operating parameters are: constant-voltage polishing of the superconducting niobium plate, serving as the anode, for 30 seconds under a 15V DC voltage. The successful implementation of this efficient process parameter fully demonstrates the superior performance of the polishing slurry of this invention in terms of reaction controllability and surface quality assurance. Attached Figure Description

[0013] Figure 1 The microstructure of the original niobium surface;

[0014] Figure 2 The microstructure of the niobium plate surface after polishing using the traditional 9:1 binary system is shown, revealing obvious pitting corrosion distribution.

[0015] Figure 3 The microstructure of the niobium plate surface after polishing using the 5:1:1 ternary system of this invention exhibits uniform smoothness. Detailed Implementation

[0016] The present invention will be described in detail below through specific embodiments and comparative experiments, but the scope of protection of the present invention is not limited to these embodiments.

[0017] Comparative Example 1

[0018] Measure 22.5 mL of 98wt% concentrated sulfuric acid and 2.5 mL of 40wt% hydrofluoric acid into a polytetrafluoroethylene beaker, and slowly mix and stir evenly under ice-water bath conditions to prepare a conventional electropolishing solution with a volume ratio of 9:1. Use a pretreated standard 10mm×10mm×1mm superconducting grade niobium plate as the anode and a 30mm×50mm×0.2mm aluminum sheet as the cathode, and perform polishing for 30 seconds under 15V DC constant voltage and room temperature conditions.

[0019] After polishing, the sample was characterized in detail. Laser confocal microscopy revealed unevenly distributed pitting on the niobium plate surface, with the size of these micro-defects ranging from 1 to 5 micrometers. Quantitative analysis by surface roughness profilometry showed that the arithmetic mean roughness (Ra) value was 85 nm, and the surface quality failed to meet the high standards required for superconducting applications.

[0020] Example 1

[0021] 25 mL of 98 wt% concentrated sulfuric acid, 5 mL of 40 wt% hydrofluoric acid, and 5 mL of anhydrous ethanol were accurately measured into a polytetrafluoroethylene beaker. The mixture was slowly mixed and thoroughly stirred under ice-water bath protection to prepare the electrochemical polishing solution of this invention with a volume ratio of 5:1:1. A comparative experiment was conducted using a superconducting niobium plate sample, electrode configuration, and polishing parameters identical to those in Comparative Example 1.

[0022] Throughout the polishing process, the anolyte current remained stable, and the bubble precipitation was uniform and orderly, without any violent reactions. After polishing, the niobium plate surface exhibited a good mirror-like luster. Further microscopic characterization showed that no pitting defects were observed under a laser confocal microscope, and the arithmetic mean roughness (Ra) value measured by a surface roughness profilometer was significantly reduced to 28 nm. This result fully demonstrates the superior performance of the polishing solution of this invention in improving surface quality.

[0023] Through systematic experimental verification, the 5:1:1 ternary electrochemical polishing slurry provided by this invention achieves a synergistic effect of multiple functions, including inhibiting pitting corrosion, optimizing mass transfer, and controlling the reaction, through the introduction of anhydrous ethanol and the optimized adjustment of the acid-base ratio. This system can achieve short-time and efficient polishing under high power input conditions, stably obtaining a superconducting niobium surface with no surface defects and extremely low roughness, effectively solving the process challenges faced by traditional binary systems in high-power short-time polishing.

Claims

1. An electrochemical polishing slurry for superconducting niobium materials, characterized in that, It is composed of a mixture of 98wt% concentrated sulfuric acid, 40wt% hydrofluoric acid and anhydrous ethanol in a volume ratio of 5:1:

1.

2. The method for preparing the electrochemical polishing solution according to claim 1, characterized in that, Accurately measure 98wt% concentrated sulfuric acid, 40wt% hydrofluoric acid, and anhydrous ethanol, and slowly mix and stir them thoroughly under ice-water bath protection to prepare an electrochemical polishing solution with a volume ratio of 5:1:

1.

3. The application of the electrochemical polishing slurry according to claim 1, for the electrochemical polishing of superconducting niobium materials.

4. In the application according to claim 3, superconducting niobium material is used as the anode for electrochemical polishing.

5. According to the application of claim 4, the operating parameters are: under a DC voltage of 15V, the superconducting niobium plate serving as the anode is subjected to constant pressure polishing for 30 seconds.

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