occluded cell—an electro-chemical cell created at a localized site on a metal surface that has been partially obstructed from the bulk environment.
opacity—the degree of obstruction to the transmission of visible light or to which a material obscures a substrate.
open-circuit potential—see corrosion potential.
orange peel—(1) the dimpled appearance of a dried coating resembling the surface of a navel orange. (2) The rough appearance of a metal surface resulting from large grain size and deformation.
organic zinc-rich coating—coating containing a metallic zinc pigment (typically 75 mass percent zinc or more in the dry film) in an organic vehicle.
over voltage—the difference in potential of an electrode between its equilibrium and steady-state values when current is applied.
oxidation—(1) loss of electrons by a constituent of a chemical reaction. (2) corrosion of a material that is exposed to an oxidizing gas at elevated temperatures.
oxidation-reduction potential—the potential of a reversible oxidation-reduction reaction in a given electrolyte reported on the standard hydrogen electrode scale. [also called redox potential]
oxygen concentration cell—see differential aeration cell.