Corrosion Terminology - I's

immunity—a state of resistance to corrosion of a metal in which the metal itself is more thermodynamically stable than its possible corrosion products. (In practical situations, immunity is assumed when the equilibrium concentration of corrosion products is negligible [typically less than 10-6 mol/L].)

impact resistance—ability of a material to resist damage from impact.

impingement corrosion—a form of erosion-corrosion generally associated with the local impingement of a high-velocity, flowing fluid against a solid surface.

impressed current—an electric current supplied by a device employing a power source that is external to the electrode system. (An example is direct current for cathodic protection.)

impressed current anode—an electrode, suitable for use as an anode when connected to a source of impressed current. (It is often composed of a substantially inert material that conducts by oxidation of the electrolyte and, for this reason, is not corroded appreciably.)

impulse dielectric test—a method of applying voltage to an insulated wire through the use of electric pulses (usually 170 to 250 pulses per second) to determine the integrity of the wire’s insulation.

inclusion—a nonmetallic phase such as an oxide, sulfide, or silicate particle in a metal.

inorganiczinc-rich coating—coating containing a metallic zinc pigment (typically 75mass percent zinc or more in the dry film) in an inorganic vehicle.

instant-off potential—the polarized half-cell potential of an electrode taken immediately after the cathodic protection current is stopped, which closely approximates the potential without IR drop (i.e., the polarized potential) when the current was on.

intentiostatic—see galvanostatic.

intercrystalline corrosion—see intergranular corrosion.

interdendritic corrosion—corrosion of cast metals that progresses preferentially along paths between dendrites.

interference bond—an intentional metallic connection, between metallic systems in contact with a common electrolyte, designed to control electrical current interchange between the systems.

interference current—see stray current.

intergranular corrosion—preferential corrosion at or adjacent to the grain boundaries of a metal or alloy.

intergranular stress corrosion cracking—stress corrosion cracking in which the cracking occurs along grain boundaries.

internal oxidation—the formation of isolated particles of oxidation products beneath the metal surface.

intumescence—the swelling or bubbling of a coating usually caused by heating. (The term is commonly used in aerospace and fire-protection applications.)

ion—an electrically charged atom or group of atoms.

IR drop—the voltage across a resistance when current is applied in accordance with Ohm’slaw.

iron rot—deterioration of wood in contact with iron-based alloys.

isocorrosion curve—a line drawn linking all points on a graph that have equal corrosion rates.

isocorrosion diagram—a graph on which the axes represent environmental parameters (e.g.,concentration, temperature, pressure, velocity) and on which one or more isocorrosion curves are drawn.