Effectiveness and harmful effects of removal sulphated black crust from granite using Nd:YAG nanosecond pulsed laser

• Published in: Applied surface science Vol. 302; pp. 309 - 313
• Main Authors: Pozo, S., Barreiro, P., Rivas, T., González, P., Fiorucci, M.P.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 30.05.2014; Elsevier
• Subjects: Black crust; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Cultural heritage; Exact sciences and technology; Granite; Laser cleaning; Physics; Cultural heritage; Black crust; Laser cleaning; Granite; Pulsed lasers; YAG laser
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2013.10.129

•First contribution to the study of Nd:YAG laser capacity for black crust removal on granites.•Effectiveness of different fluences and wavelengths (1064, 532, 355 and 266nm) on removing black crusts are evaluated.•Gypsum is not completely eliminated even at the highest fluence.•Only the carbonaceous particles are totally removed with 1064nm with fluence greater than 20.16Jcm−2. Sulphated black crust is a common form of deterioration affecting stone used in monuments, usually occurs in contaminated atmospheres or urban environments. Its origin and cleaning have been studied extensively, for decades, in the case of carbonate rocks. Recent studies show that this form of alteration also affects granites. Scientific research on laser removal effectiveness of gypsum-rich black crust on granites needs to be scientifically addressed considering the inexistent references. This paper assesses the removal by laser of sulphate-rich black crusts on granite using the different harmonics of a Nd:YAG nanosecond pulsed laser (266nm, 355nm, 532nm and 1064nm). Effectiveness was evaluated using Scanning Electron Microscopy with Energy Dispersive X-ray Spectrometry (SEM–EDS), X-Ray Diffraction (XRD) and Attenuated Total Reflection-Fourier Infrared Transform Spectroscopy (ATR-FTIR). We also evaluated the effect of the radiation on granite-forming minerals and on the colour of the stone using Scanning Electron Microscopy and spectrophotometry colour measurements respectively. SEM–EDS, XRD and ATR-FTIR analyses show that the higher the wavelength, the more efficient the cleaning, so samples cleaned using 1064nm pulsed laser recovered its original colour. Nevertheless, the Nd:YAG laser did not completely eliminate the crust, and gypsum crystals remaining on the rock surface are observed, even at the most effective wavelength.