Sacrificial Anode Research Paper

Aluminium metal is highly preferred for sacrificial anode mainly because of its high current capacity. However, pure aluminium is not useful as an anode because it immediately forms a passive oxide film on its surface when it is exposed to the environment. The development of an aluminium anode is always dependent upon the activation of aluminium by diminishing the detrimental effects of the oxide films. As well known alloying additions in aluminium exert great effects on its electrochemical performance, especially its potential, which is one of the most important characteristics for sacrificial anodes. In order to promote surface activation, aluminium is usually alloyed with small quantities of one or more of such elements as mercury, tin,

The yield efficiency also increases over 90% compared with 50% the efficiency of pure aluminium in synthetic sea water. Impurities like iron and copper have a remarkable effect on the anode efficiency. The type and concentration of alloying elements have great effects on the efficiency of aluminium anode. One study concluded that even a small amount of iron or copper would lower the efficiency, whereas another demonstrated that in an Al-Zn-In alloy iron is beneficial but copper is detrimental even at low level of 0.019%. In other study it is found that indium is cathodic to Al, the indium precipitates will be cathodically protected by the aluminium matrix and lead to the formation of a local action cell where the anode consumes itself and provides no useful energy. The precipitates accumulated along the grain boundary to dissolve first and cause the whole grain to separate from anode. The efficiency is reduced by self corrosion in the form of intergranular corrosion. The current efficiency is decreased greatly

The corrosion resistance of these alloys is related to the formation of an oxide (passive) film, which naturally develops on the alloy surface under normal atmospheric conditions. The oxide film formed on the aluminium alloy surface is non-uniform, thin and non-coherent. Therefore, it imparts a certain level of protection under normal conditions. When exposed to the environments containing halide ions, of which the chloride (Cl-) is the most frequently encountered in service, the oxide film breaks down at specific points leading to the formation of pits on the aluminium surface. This type of corrosion is known as pitting corrosion. The structural characteristics of the film formed on the aluminium surface, and the intensity of the corrosion attack are influenced