Investigation of electropolishing characteristics of tungsten in eco-friendly sodium hydroxide aqueous solution

Abstract

In this study, an eco-friendly electrolyte for electropolishing tungsten and the minimum material removal depth on the electropolished tungsten surface are investigated using an electrochemical etching method. Using a concentrated acid electrolyte, the polarization curve and current density transient are observed. For a NaOH electrolyte, the effects of interelectrode gap and electrolyte concentration on electropolishing are investigated. The differences in electropolishing characteristics are compared among different electrolyte types. Microholes are etched on the electropolished tungsten surface to determine the minimum material removal depth on the tungsten surface. Experimental results indicate the color effect due to a change in the thickness of the oxide film on the tungsten surface after electropolishing with a concentrated acid electrolyte. The surface roughness decreases with the interelectrode gap width owing to the increased current density when using the NaOH electrolyte. However, the electropolishing effect is less prominent with a significantly smaller gap because the generated bubbles are unable to escape from the narrow working gap in time. A material removal depth of less than 10 nm is achieved on the tungsten surface in an area of diameter 300 µm, using the electrochemical etching method.

Keywords

Electropolishing / NaOH solution / Surface roughness / Tungsten / Etching

References

[1] Fan HG, Tsai HL, Na SJ. Heat transfer and fluid flow in a partially or fully penetrated weld pool in gas tungsten arc welding. Int J Heat Mass Transf, 2001, 44: 417-428.

[2] Tanaka M, Shimizu T, Terasaki H, et al. Effects of activating flux on arc phenomena in gas tungsten arc welding. Sci Technol Weld Join, 2000, 5: 397-402.

[3] Abyzov AM, Kidalov SV, Shakhov FM. High thermal conductivity composites consisting of diamond filler with tungsten coating and copper (silver) matrix. J Mater Sci, 2011, 46: 1424-1438.

[4] Ju BF, Chen YL, Fu M, et al. Systematic study of electropolishing technique for improving the quality and production reproducibility of tungsten STM probe. Sens Actuators A Phys, 2009, 155: 136-144.

[5] Kelsey GS. The anodic oxidation of tungsten in aqueous base. J Electrochem Soc, 1977, 124: 814-819.

[6] Han W, Kunieda M. A novel method to switch machining mode between micro-ECM and micro-EDM using oxide film on surface of tungsten electrode. Precis Eng, 2019, 56: 455-465.

[7] Wang J, Fang FZ, Yan G, et al. Study on diamond cutting of ion implanted tungsten carbide with and without ultrasonic vibration. Nanomanuf Metrol, 2019, 2: 177-185.

[8] Wang XL, Han LH, Geng YQ, et al. The simulation and research of etching function based on scanning electrochemical microscopy. Nanomanuf Metrol, 2019, 2: 160-167.

[9] Fang FZ, Zhang N, Guo D, et al. Towards atomic and close-to-atomic scale manufacturing. Int J Extrem Manuf, 2019, 1: 1-33.

[10] Fang FZ, Xu F. Recent advances in micro/nano-cutting: effect of tool edge and material properties. Nanomanuf Metrol, 2018, 1: 4-31.

[11] Suzuki N, Haritani M, Yang J, et al. Elliptical vibration cutting of tungsten alloy molds for optical glass parts. CIRP Ann Manuf Technol, 2007, 56: 127-130.

[12] Sarkar S, Sekh M, Mitra S, et al. Modeling and optimization of wire electrical discharge machining of γ-TiAl in trim cutting operation. J Mater Process Technol, 2008, 17: 525-536.

[13] Chen HC, Lin JC, Yang YK, et al. Optimization of wire electrical discharge machining for pure tungsten using a neural network integrated simulated annealing approach. Expert Syst Appl, 2010, 37: 7147-7153.

[14] Yang RT, Tzeng CJ, Yang YK, et al. Optimization of wire electrical discharge machining process parameters for cutting tungsten. Int J Adv Manuf Technol, 2012, 60: 135-147.

[15] Masuzawa T. State of the art of micromachining. CIRP Ann Manuf Technol, 2000, 49: 473-488.

[16] Reinhardt KA, Kern W. Handbook of silicon wafer cleaning technology, 2018, 3 Park Ridge: William Andrew

[17] Fang FZ, Zhang XD, Gao W, et al. Nanomanufacturing—perspective and applications. CIRP Ann Manuf Technol, 2017, 66: 683-705.

[18] Bielmann M, Mahajan U, Singh RK. Effect of particle size during tungsten chemical mechanical polishing. Mater Res Soc Symp Proc, 1999, 2: 401-403.

[19] Larsen-Basse J, Liang H. Probable role of abrasion in chemo-mechanical polishing of tungsten. Wear, 1999, 233(235): 647-654.

[20] Nanz G, Camilletti LE. Modeling of chemical—mechanical polishing: a review. IEEE Trans Semicond Manuf, 1995, 8(4): 382-389.

[21] Wang F, Zhang X, Deng H. A comprehensive study on electrochemical polishing of tungsten. Appl Surf Sci, 2019, 475: 587-597.

[22] Han W, Fang FZ. Investigation of electrochemical properties of electropolishing Co-Cr dental alloy. J Appl Electrochem, 2020, 50: 367-381.

[23] Han W, Fang FZ. Two-step electropolishing of 316L stainless steel in a sulfuric acid-free electrolyte. J Mater Process Technol, 2020, 279: 116558.

[24] Han W, Fang FZ. Fundamental aspects and recent developments in electropolishing. Int J Mach Tools Manuf, 2019, 139: 1-23.

[25] Schubert N, Schneider M, Michaelis A, et al. Electrochemical machining of tungsten carbide. J Solid State Electrochem, 2018, 22: 859-868.

[26] Han W, Fang FZ. Electropolishing of 316L stainless steel using sulfuric acid-free electrolyte. J Manuf Sci Eng, 2019, 141: 101015.

[27] Hu YN, Zhou H, Liao LP, et al. Surface quality analysis of the electropolishing of cemented carbide. J Mater Process Technol, 2003, 139: 253-256.

[28] Holstein N, Krauss W, Konys J, et al. Advanced electrochemical machining (ECM) for tungsten surface micro-structuring in blanket applications. Fusion Eng Des, 2016, 109: 956-960.

[29] Lee ES, Shin TH. An evaluation of the machinability of nitinol shape memory alloy by electrochemical polishing. J Mech Sci Technol, 2011, 25: 963-969.

[30] Rajurkar KP, Zhu D, McGeough JA, et al. New developments in electro-chemical machining. CIRP Ann Manuf Technol, 1999, 48: 567-579.

[31] Piotrowski O, Madore C, Landoly D. The mechanism of electropolishing of titanium in methanol-sulfuric acid electrolytes. J Electrochem Soc, 1998, 145: 2362-2369.

[32] Anik M. Effect of concentration gradient on the anodic behavior of tungsten. Corros Sci, 2006, 48: 4158-4173.

[33] Anik M, Osseo-Asare K. Effect of pH on the anodic behavior of tungsten. J Electrochem Soc, 2002, 149: B224-B233.

[34] Di PA, Di QF, Sunseri C. Anodic oxide films on tungsten-I. The influence of anodizing parameters on charging curves and film composition. Corros Sci, 1980, 20: 1067-1078.

[35] Evans TE, Hart AC, Skedgell AN. The nature of the film on coloured stainless steel. Trans IMF, 1973, 51: 108-112.

[36] Shimasaki T, Kunieda M. Study on influences of bubbles on ECM gap phenomena using transparent electrode. CIRP Ann Manuf Technol, 2016, 65: 225-228.

[37] Zhang R, Ivey DG. Preparation of sharp polycrystalline tungsten tips for scanning tunneling microscopy imaging. J Vac Sci Technol B Microelectron Nanom Struct, 1996, 14: 1-10.

[38] Krauss W, Holstein N, Konys J. Strategies in electro-chemical machining of tungsten for divertor application. Fusion Eng Des, 2007, 82: 1799-1805.

[39] Park JJ, Il PS, Lee SB. Growth kinetics of passivating oxide film of Inconel alloy 600 in 0.1 M Na₂SO₄ solution at 25–300 °C using the abrading electrode technique and ac impedance spectroscopy. Electrochim Acta, 2004, 49: 281-292.

[40] Schuster R, Kirchner V, Allongue P, et al. Electrochemical micromachining. Science, 2000, 289: 98-111.

Funding

Science Foundation Ireland (15/RP/B3208)

National Natural Science Foundation of China http://dx.doi.org/10.13039/501100001809(61635008)

Enterprise Ireland http://dx.doi.org/10.13039/501100001588(713654)

H2020 Marie Skłodowska-Curie Actions http://dx.doi.org/10.13039/100010665(713654)