The choice of a reliable anode, with an adequate life expectancy, is a complicated matter. The cathodic protection engineer can choose between massive anodes (graphite, silicon-iron, magnetite, ferrite) and composite anodes (platinized titanium / niobium or LIDA® ).

Massive anodes, especially graphite and silicon-iron alloys, are usually subject to high consumption rates, and even for a ten year life, must have a considerable mass and have a utilisation factor ranging between 0.6 and 0.85 depending upon the type of connection, whether it is end connected or centre connected, which is because the dissolution of anode material is not uniform. This results in increase of real quantity of massive anodes for desired life. in addition, these anodes are very brittle, which limits ease of handling in the field. Electrical connection failures are common for end or centre-connected massive anodes.

Composite anodes offer a good technical answer to these drawbacks and are dimensionally stable and retain their original size and shape during the entire life, hence for lida^® anodes operating life is not calculated on the basis of utilisation factor but on the basis of operating current density. This leads to equivalent utilisation factor of 1 (one) for MMO anodes. A ductile, corrosion resistant base metal provides for the overall toughness of the system. Titanium, or in some cases niobium, is a common choice. However, since the two materials tend to be covered by a layer of insulating oxide, their surface must be coated with a conductive film.

These electroconductive films may take on many compositions. They may be based on noble metals such as platinum, either clad or deposited. LIDA® anodes feature an electroconductive coating of mixed metal oxides (MMO), forming a solid solution with the titanium substrate and exhibiting electrical properties which allow the composite to function as an anode. The characteristics of the LIDA^® mixed metal oxide (MMO) coating are:

• Low and uniform wear rate.