Anode Efficiency

A prospective sacrificial anode must possess a large number of electrons per unit mass and should deliver these electric charges efficiently. Thus the electrical output of an anode is given by current capacity which is expressed in Ah kg^-1 or kg A^-1 y^-1. The value of the current capacity is determined by the electrochemical equivalent, the density and the efficiency of the anodic material. The electrochemical equivalent, which is dependent on the atomic weight and valence, is a characteristic of the anode material. However efficiency is determined by a number of factors including nature of the environment, operating current density and metallurgical microstructure. It is apparent that if the cathode reaction rate on the anode is low then the efficiency will be high, so that there is minimum self corrosion. Similarly large operating currents will yield high anode efficiency. It should be added that the type of corrosion attack experienced by the anode also significantly affects the magnitude of the anode efficiency. For instance, severe pitting and intergranular attack may result in a chunk of the anode to become detached without complete consumption of the electric charge in that piece.