Critical features of sol-gel coatings for corrosion protection

Metals and their alloys, such as iron, almninum, copper and magnesium, have a nafitral tendency to form a thin layer of oxide/hydroxide on their surface. Oxide/ hydroxide layers provide snfficient corrosion resistance to the metal in dry ambient conditiorrs. Under continued exposure to moisture, these layers become thick but more porous, which makes them (oxide/hydroxide layers) no longer protective for the metal beneath. Rust formation on iron, white oxide formation on alrrminrrm and magnesitrm, and tarnishing of copper are examples of corrosion. Coating is one of the most frequently ttsed methods to barricade the metal from moistme and other corrosive enviromnental factors. 

The primary role of coatings in corrosion protection is to retard or prevent the diffusion of corrosive solution to the metal beneath the coating. Sol-gel coatings have the ability to imdeigo chemical reaction with natural oxide/hydroxide films on the metal substrate (Fig. 12.5 and Table 12.1) and passivate the metal surface. The hydroxyl group of hydrolyzed metal alkoxides (M(OH)x (OR)n-x or M-OH M = Si, Ti, Zr) in coating sol forms a covalent bond with the hydroxyl group of natural oxide/hydroxide layers on the metal surface. The chemical 

Substrate Anodic reaction Natural surface oxide/ corrosion product Reaction with substrate sol 

Sol-gel based superhydrophobic coatings exhibit extreme water repellence, with water droplets rolling off at high contact angles. Different approaches have 

Kiruthika et alJ reported the formation of hybrid coatings, derived from 3-glycidoxypropyltrimethoxysilane, zirconium-n-propoxide and methacrylic acid (MAA) based sol coatings, on mild steel. 

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