Excimer laser cleaning of black sulphur encrustation from silver surface

TL;DR

This study demonstrates that excimer laser cleaning effectively removes sulphur encrustation from silver surfaces with minimal substrate damage, optimizing parameters for maximum cleaning efficiency.

Contribution

The paper introduces a novel excimer laser-based method for localized removal of silver sulphide encrustation, detailing optimal parameters and surface effects.

Findings

Effective removal of sulphur encrustation at specific laser fluences.

Minimal damage to the silver substrate during cleaning.

Microhardness increased post-cleaning.

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/cm2), 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/cm2 was observed as above threshold value for removal of sulphide from the encrusted surface while a fluence of 384.85 mJ/cm2 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/cm2 of fluence value. The topography of the ablated surface showed a removal of 5-10 um of the sulphide layer from the surface whereas the thickness of the sulphide coating was around 8-10 um. 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.