Excimer laser cleaning of black sulphur encrustation from silver surface. (May 2019)

• Record Type: Journal Article
• Authors: Raza, Mohammad Shahid; Das, Sankha Shuvra; Tudu, Parimal; Saha, Partha
• Is Part Of: Optics & laser technology. Volume 113(2019)
• Page Start: 95
• Page End: 103
• Publication Date: 2019-05
• Subjects: Excimer laser -- Silver sulphide coating -- Ablation mechanism -- Threshold fluence -- Surface topography -- Microhardness; Optics -- Periodicals; Lasers -- Periodicals; Electronic journals; 621.366
• DOI: 10.1016/j.optlastec.2018.12.012
• Languages: English
• ISSNs: 0030-3992

Abstract

Highlights: Localized cleaning of black encrustation of silver sulphide by KrF excimer laser. Laser fluence and number of pulses were used as the process parameters. Fluence of 260.48 mJ/cm 2 was well above the threshold fluence value for removal. Fluence of 384.85 mJ/cm 2 resulted more sulphide removal but formed peripheral rim. 5–10 µm of the sulphide layer could be removed without affecting silver substrate. Abstract: The process of localized cleaning of silver sulphide from the silver surface has been investigated in this work. An artificial black encrustation was generated on the silver surface and its laser cleaning was performed using an excimer laser (KrF based) working at a wavelength of 248 nm and pulse width 25 ns. Laser process parameters i.e. laser fluence and number of pulses were used to perform the experiment and after different optical, microstructural, elemental, microhardness and surface topography analysis of the laser ablated zone was performed. The parametric window selected for the excimer laser cleaning were laser fluence (200–400 mJ/cm 2 ), repetition rate 4 Hz and number of pulses (60–300). It was observed that excimer laser is very effective in the cleaning of black encrustation having ∼6 wt% of sulphur from the surface without any significant removal of the silver substrate. The fluence value of 260.48 mJ/cm 2 was observed as above threshold value for removal of sulphide from the encrusted surface while a fluence of 384.85 mJ/cm 2 and 220 pulses showed the maximum removal of sulphur encrustation (∼0.38 wt% of sulphur remaining). Formation of the peripheral rim was observed to occur above 280.17 mJ/cm 2 of fluence value. The topography of the ablated surface showed a removal of 5–10 µm of the sulphide layer from the surface whereas the thickness of the sulphide coating was around 8–10 µm. Microhardness value showed a change of microhardness of the silver surface from 75.12 HV0.5 (uncoated parent silver) to 96.07 HV0.5 (centre of the ablated zone). Finally, it was concluded that excimer laser cleaning is a novel method for localized removal of silver sulphide encrustation from silver surface.