Mechanism and prediction of laser wet cleaning of marble encrustation

During the removal of encrustation from marble with 355 nm laser pulses, the effects of the thin liquid layer covering the encrustation are experimentally and numerically investigated. The working mechanism of the liquid layer is analyzed. A two-dimensional axial symmetric model is proposed to simulate the changes in the temperature, liquid volumetric fraction, and vapor pressure in the irradiated encrustation. To model the conservation of mass, momentum, and energy, three coupled nonlinear partial differential equations are numerically solved. The measured porosity of the encrustation is incorporated into the model. Marble cleaning with three different liquids having different thermodynamic properties, distilled water, ethanol, and acetone, are compared in terms of the cleaning efficiency at different fluence levels. With the liquid layer, the surface color of cleaned marble is also studied. In addition, surface-enhanced raman spectroscopy and a chromameter are used to identify the chemical constituents and measure the color of the cleaned marble, respectively.