Half-cell . A conducting material (usually metallic), in contact with, an 

 electrolyte. It is used as a standard reference in potential tests. 

 For further explanation, reference is made to paragraph 8-01 £_. in this 

 manual . 



Hydrogen embrittlement . Hydrogen emhrittlement is caused by the entrance 

 of hydrogen into the metal, for example, through pickling or cathodic 

 polarization. 



Hydrogen overvoltage . Overvoltage associated with the liberation of 

 hydrogen gas is termed hydrogen overvoltage. 



Impingement attack . Corrosion associated with turbulent flow of a liquid. 

 For some metals the action is considerably accelerated by entrained 

 bubbles in the liquid. 



Inactive . (See passivity. ) 



Inhibitor . As applied to corrosion, an inhibitor is a chemical substance 

 or mixture that if added to an environment (usually in small concentration] 

 effectively decreases corrosion. 



Intercrystalline corrosion . (See intergranular corrosion.) 



Intergranular corrosion . Preferential corrosion at grain boundaries of 

 a metal or alloy. It is also called intercrystalline corrosion. 



Internal oxidation . The precipitation of one or more oxides of alloying 

 elements beneath the external surface of an alloy as a result of oxygen 

 diffusing into the alloy from the external source. It is also known as 

 subscale formation. 



Ion . An electrically charged atom or group of atoms. 



Local action . Corrosion caused by local cells on a metal surface. 



Local cell . A cell the e.m.f. of which is due to difference of potential 

 between areas on a metallic surface in an electrolyte. 



Long-line current . Current flowing through the earth, from an anodic to 

 a cathodic area that returns along an underground metallic structure. 

 Usually occurs where the areas are separated by considerable distances 

 and where the current results from concentration cell action. (See 

 positive electricity. ) 



Matte surface . A surface of low specular reflectivity. 



Metallizing . The process of spraying a surface with a metal. 



Metal replacement . The deposition of a metal from a solution of its ion 

 on a more anodic metal accompanied by the solution of the latter metal. 

 It is also called "immersion plating." 



B-6 



