Investigation of electropolishing characteristics of tungsten in eco-friendly sodium hydroxide aqueous solution
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Investigation of electropolishing characteristics of tungsten in ecofriendly sodium hydroxide aqueous solution Wei Han1 • Feng-Zhou Fang1,2
Received: 2 February 2020 / Revised: 17 March 2020 / Accepted: 4 May 2020 The Author(s) 2020
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 lm, using the electrochemical etching method.
& Feng-Zhou Fang [email protected] 1
Centre of Micro/Nano manufacturing Technology (MNMTDublin), University College Dublin, Dublin 4, Ireland
2
State Key Laboratory of Precision Measuring Technology and Instruments, Centre of Micro/Nano Manufacturing Technology (MNMT), Tianjin University, Tianjin 300072, People’s Republic of China
Keywords Electropolishing NaOH solution Surface roughness Tungsten Etching
1 Introduction Tungsten has the highest melting point of all available metals with a melting temperature at 3 422 C and is applied extensively in various fields, such as arc-welding electrodes [1, 2] and heat-resistant coatings [3]. Furthermore, it is the most typically used material for preparing scanning probe microscopy and scanning tunneling spectroscopy probes owing to its good physical and chemical properties [4, 5]. Moreover, tungsten has high stiffness and good electrical conductivity and is generally used as tool electrodes in electrical discharge machining [6] and electrochemical machining (ECM) [7, 8]. As a hard-brittle material, tungsten is difficult to machine using conventional machining methods, such as cutting and grinding, owing to its low machinability [9, 10]. It has been reported that the ultraprecision diamond cutting of tungsten is significantly affected by the adhesion of tungsten to the tool, rapid tool wear, and brittle fracture [11]. Hence, tungsten is typically machined using nonconventional machining methods. Wire electrical di
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