Effect of processing gas in high power diode laser ablation of tile grout

This work provides detailed information on the surface morphology, microstructure and thermohistory of the epoxy tile grout resulting from high power diode laser (HPDL) treatment using compressed air, Ar, N₂ and O₂. O₂ was found to effect the greatest removal rate, with the amount of removal with O₂ being up to twice as much as that with the other three gases. Such an occurrence is believed to be due to the fact that of the four gases used, O₂ is the most reactive. Microstructural analysis revealed differences in the grout surface structure before and after the laser treatment. The surface of the laser-treated samples had a collection of grouped particles with pores and gaps, whereas the untreated sample had a continuous mono-structured plane surface. Larger sized particles were observed with O₂ gas compared to compressed air, Ar and N₂. Both an EDX (energy-dispersive X-ray) and an XRD (X-ray diffraction) analyses showed changes in chemical composition before and after the laser treatment. CaO and CO₂ found in the laser-treated sample were considered to be the product of decomposition of CaCO₃ (limestone). A TG-DTA (thermogravimetric and differential thermal analysis) identified a sequence of thermal history for the epoxy grout in which reactions in the laser interaction can now be predicted.