The invention provides a process for the activation by oxyfluorination of at least part of a surface of a solid, which process includes exposing, under selected conditions of temperature and pressure and for a selected reaction time, at least part of the surface of the material of the solid to an oxfluorinating atmosphere. The oxyfluorinating atmosphere is a gas/vapor mixture which includes at least one fluorine-containing gas which reacts with the material of the exposed surface, at least one oxygen-containing gas which reacts with the material of the exposed surface, and water vapor. The gases in the oxyfluorinating atmosphere act to oxyfluorinate the exposed surface, thereby to activate it, and the water vapor acts to enhance the activation.