4. Modes of action of sol-gel treatments

Oxide films obtained by the sol-gel process are of potential interest for the protection of metals against corrosion due to:

• the chemical and thermal inertia of the mineral oxide network;

• the barrier effect of the sol-gel deposit, which limits the access of aggressive environmental species (H ₂ O, ions...) to the metal substrate ;

• strong interactions between the metal oxide layer and the inorganic layer, linked in particular to the formation of covalent bonds of the ${\text{M—O—M}}^{\prime }$ type during film formation, where M is the metal to be protected (M = Fe, Al...) and