High power diode laser modification of the wettability characteristics of an Al₂O₃/SiO₂ based oxide compound for improved enamelling

High power diode laser (HPDL) surface melting of a thin layer of an amalgamated Al₂O₃/SiO₂ oxide compound (AOC) resulted in significant changes in the wettability characteristics of the material. This behaviour was identified as being primarily due to: (1) the polar component of the AOC surface energy increasing after laser melting from 2.0 to 16.2 mJ m^-2, (2) the surface roughness (Ra) of the AOC decreasing from 25.9 to 6.3 μm after laser melting and (3) the relative surface oxygen content of the AOC increasing by 36% after laser melting. HPDL melting was consequently identified as affecting a decrease in the enamel contact angle from 118° prior to laser melting to 33° after laser melting, thus allowing the vitreous enamel to wet the AOC surface. The effective melt depth for such modifications was measured as 50 to 125 μm. The morphological, microstructural and wetting characteristics of the AOC were determined using optical microscopy, scanning electron microscopy, energy disperse X-ray analysis, X-ray diffraction techniques and wetting experiments by the sessile drop technique. The work has shown that laser radiation can be used to alter the wetting characteristics of the AOC only when surface melting occurs.