P

passivity
The state of the surface of a metal or alloy susceptible to corrosion where its electrochemical behaviour becomes that of less reactive metal and its corrosion rate is reduced.

NOTE: This is generally the result of protective film formation.

pH:

pH value
A logarithmic index for the concentration of hydrogen ions in an electrolyte.

NOTE: See A.1.

acid
Containing an excess of hydrogen ions over hydroxyl ions.

alkaline
Containing an excess of hydroxyl ions over hydrogen ions.

neutral
Containing equal concentrations of hydrogen ions and hydroxyl ions

pitting
A non-uniform corrosion of a metal whereby a number of cavities, not in the form of cracks, are formed in the surface.

polarisation
Change in the potential of an electrode as the result flow.

polarisation cell
A device inserted in the earth of a structure that drains only a small current from the source used to provide cathodic protection for the structure, but provides a low resistance path to currents from high d.c. voltages and all a.c. voltages carried by the structure.

protection current
The current made to flow into a metallic structure from its electrolytic environment in order to effect cathodic protection of the structure.

protection potential
The more negative level to which the potential of a metallic structure, with respect to a specified reference electrode in an electrolytic environment, has to be depressed in order to effect cathodic protection of the structure.

protective coating
A dielectric material adhering to or bonded to a structure to separate it from its environment in order to prevent corrosion.