Effect of laser induced rapid solidification structures on adhesion and bonding characteristics of alumina/silica based oxide to vitreous enamel

The present work is concerned with investigating the effects of high power diode laser (HPDL) radiation on the microstructure of an amalgamated alumina/silica based oxide compound (AOC). The main rapid solidification theories, namely constitutional supercooling and the theory of morphological stability, are used to explain the observed microstructural changes in the AOC resulting from HPDL interaction. Without laser treatment of the AOC surface it was impossible to fire the enamel onto the AOC. However, wetting experiments, using a number of control liquids and the sessile drop technique, revealed that laser treatment of the AOC surface significantly altered the wetting characteristics of the AOC and allowed the enamel to bond to the AOC. Accordingly, HPDL treatment was identified as allowing the vitreous enamel to wet the surface by causing a decrease in the enamel contact angle from 118° to 33°. Moreover, no discernible difference was seen in the change in contact angle across the range of rapid solidification microstructures obtained. The actual incidence of rapid surface resolidification, and not the degree of rapid surface resolidification, was therefore identified as being the primary factor governing changes in contact angle. The bonding mechanisms were identified as being principally owing to van der Waals forces, however, some evidence of chemical bonding was also observed. The work has clearly shown that laser radiation can be used to alter the wetting characteristics of the AOC.