Surface and outgassing properties of 304 stainless steel samples were studied after electropolishing by a wiping method (WiEP) using felt that is attached to a cathode electrode and impregnated with an electrolyte. Surface morphology observed with an atomic force microscope suggests that WiEP yields a smoother surface with fewer pits compared with the conventional electropolishing method of immersing the samples in an electrolyte. The thickness of the oxide layer after either of the electropolishing processes was 3–4 nm as estimated by x-ray photoelectron spectroscopy, transmission electron microscopy, and energy-dispersive x-ray spectroscopy. Furthermore, no significant difference was found in the chemical state of the surface and oxide film in the two cases. Thermal desorption spectroscopy of the samples revealed that the amount of desorbed H2O and H2 was significantly low in the case of WiEP. The low outgassing was attributed to the formation of a smooth and dense oxide film on the sample surface after electropolishing by WiEP.
Electrolyte additives, applied voltage, and wiping speed were investigated to elucidate the optimum conditions for electropolishing of stainless steel (SUS304) using a wiping method with an electrolyte-solution-impregnated felt wiper cathode. Adding a viscosity improver and a surfactant to the electrolyte solution (mixed acid of 98% sulfuric acid and 85% phosphoric acid (1 : 3, v/v) ) reduced the evolution of pits on the electropolished SUS304 surfaces caused by the wiping method, but it reduced the polishing rate. Conditions of higher applied voltage and lower wiping speed led to an increased polishing rate and decreased pit evolution on the SUS304 surface. Electropolishing by the wiping method using the electrolyte containing the viscosity improver and 8 V of applied voltage and 10 mm s -1 wiping speed produced extremely smooth and high-gloss surfaces. Analysis by glow discharge optical emission spectroscopy revealed that the depth profile of the surface composition had a Cr-rich layer formed on the electropolished SUS304 surface by the wiping method. The pitting potential of SUS304 surface shifted to a more positive value after electropolishing using the wiping method. That value was comparable to that obtained after conventional electropolishing.
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