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Non Consumable Anodes

This type of anode supports other anodic reactions on their surfaces. In environments where water and chloride ions are present, chlorine evolution and oxidation of water are possible.

Platinized titanium is often used in marine environments. To avoid the dissolution of titanium at unplatinized locations on the surface, the operating voltage of the anode is limited by the anodic breakdown potential of titanium which is in the range of 9 to 9.5 V in the presence of chlorides. Hence the maximum recommended operating voltage of platinized titanium anodes is 8 V. The corresponding maximum current density output is approximately 1 kA m-2. For cathodic protection systems where operating voltages are relatively high, niobium and tantalum based anodes are generally selected. This is because these two substrates have anodic breakdown potentials greater than 100 V in chloride containing electrolytes. The wastage rate of platinized anodes is approximately 8 mg A-1 y-1.

The rate of platinum consumption has been found to accelerate in the presence of AC current ripple. Most wastage was observed to occur with AC frequencies of less than 50 Hz. The repeated oxidation/reduction processes result in the formation of a brownish layer of platinum oxide. To avoid the occurrence of this phenomenon, a single or a three phase full-wave rectification is recommended. The consumption rate of platinized anodes is also adversely affected by the presence of organic impurities such as sugar and diesel fuel.