Copper reduction and hydroxyl formation by hydrogen process in alumino-silicate glasses

The process of nanometric copper (Cu⁰) precipitation by hydrogen in alumino-silicate glasses was studied regarding the simultaneous formation of hydroxyl bonding. Firstly, copper-ion-doped alumino-silicate glasses were melt-quenched and then heat-treated in the presence of hydrogen gas, which allowed copper ions to be reduced into nanometric metal particles. Along with the metallic copper formation, there was also formed the hydroxyl groups as a byproduct of the reaction. From spectroscopic studies, it was revealed that the reduction process was kinetically controlled by the hydrogen diffusion into the glasses. After the Cu⁰ precipitation, in particular, at temperatures higher than 700 °C or for reduction times longer than 5 h the copper metal was found to move towards the surface, creating a copper metal rich surface. Moreover, an increase in hydrogen permeation with the treatment time was also observed and this tendency was more intense for the matrix, which allowed higher copper reduction.