A coating composition comprising an aqueous mixture containing inorganic particles, a catechol compound, and one or more fluoroacids. The preferred fluoroacids are selected from fluorotitanic acid, fluorozirconic acid, fluorosilicic acid, fluoroboric acid, fluorostannic acid, fluorogermanic acid, fluorohafnic acid, fluoroaluminic acid or salts of each thereof. The invention is also directed to a coating on a metal substrate. The coating comprises silica particles attached to the metal substrate through a metal-oxide matrix. The metal-oxide matrix comprises a metal selected from titanium, zirconium, silicon, hafnium, boron, aluminum, germanium, or tin, and a catechol compound.