The titanium merely acts as a conductor.įor MMO wire anodes, some suppliers utilize a bimetallic substrate with a thin layer of titanium extruded over a copper core. Unless the catalytic coating is significantly damaged or consumed, the titanium substrate never sees sufficient polarization to reach the break down voltage for dissolution. This does not take into consideration the role of the highly conductive electrocatalytic oxide and the protective oxide films that make up the MMO coating. The concerns led some to believe that any anode operating with more than 8-10 volt power supplies could be at risk of damaging the anode. Bare titanium when polarized above 8 to 9 volts in seawater (or above 10 volts in soil or coke backfill) is subject to intense oxygen evolution of the titanium surface resulting in passive film break-down and dissolution (pitting corrosion) of titanium. When first used as an anode substrate, there were significant, although unfounded, concerns over the potential for the titanium to exceed its “break down” voltage. There is no “better” between Grade 1 and Grade 2 – they can be used interchangeably with no impact on performance. The specifications for Grade 1 and Grade 2 are very similar and overlap so that often the same material meets the requirements of both Grade 1 and Grade 2 and can be dual certified. Grade 1 titanium is slightly more malleable than Grade 2 titanium but is also less commonly used in industry. For MMO anodes, Grades 1 and 2 are used for MMO anodes. Outstanding chemical resistance to highly acidic conditions – typical for oxygen and chlorine evolving environments common in many cathodic protection applicationsĬommercially pure titanium is available in a range of grades.Excellent adherence properties with proper surface preparation.Titanium is readily available in commercially pure form. Titanium offers several key advantages as a substrate: Titanium MMO Anode Advantages Mixed metal oxide anodes are applied over a commercially pure titanium substrate. Their primary purpose is to provide an oxide film over the substrate material to prevent corrosion of the substrate. The bulk oxides are typically a mixture of Titanium Dioxide (TiO 2) and Tantalum Oxide (TaO 5). Most CP manufacturers use Iridium Oxide based mixed metal oxide for their cathodic protection anodes because it is suitable for both chlorinating and oxygenating environments. The catalytic life is significantly reduced when the primary reaction is the evolution of oxygen (fresh water, soil, coke backfill and concrete environments). Ruthenium oxide, which is the cheaper of the two electrocatalysts, should only be used in chlorinated environments (sea water). For cathodic protection applications two primary electrocatalysts are used: The coating recipe consists of an electro catalytic conductive component that catalyzes the reaction to generate current flow, and bulk oxides (cheaper fill materials) that prevent corrosion of the substrate material. There is no precise industry definition for “mixed metal oxide.” Each supplier has a unique recipe for their mixed metal oxide coating. MMO anodes are quickly becoming the most popular impressed current anode gaining market share over conventional anodes such as graphite and high silicon cast iron. MMO anodes have imperceptibly low wear rates and are often referred to as Dimensionally Stable Anodes as they do not change geometry over time.
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