Sacrificial anode

タイトルまたは説明

There are three main alloys used as galvanic anodes, magnesium, aluminium and zinc. They are all available as blocks, rods, plates or extruded ribbon. Each material has advantages and disadvantages.
Zinc and aluminium are generally used in salt water, where the resistivity is generally lower. Typical uses are for the hulls of ships and boats, offshore pipelines and production platforms, in salt-water cooled marine engines, on small boat propellers and rudders and for the internal surface of storage tanks.

Aluminium anodes have several advantages: they are much lighter in weight, and have a much higher capacity than zinc. Their electrochemical behaviors is not considered as reliable as zinc and greater care must be taken in how they are used. When aluminium strikes a rusty surface a large thermite spark may be generated, so its use is restricted in tanks where there may be explosive atmospheres and there is a risk of the anode falling.

Since the operation of a galvanic anode relies on the difference in electropotential between the anode and the cathode, practically any metal can be used to protect any other, providing there is a sufficient difference in potential. For example, iron anodes can be used to protect copper.