MMO Anodes for Cathodic Protection (Mixed Metal Oxides)

Originally developed for the production of chlorine gas by seawater electrolysis, MMO Anodes have been used for cathodic protection (CP) applications since the 1980s. They continue to gain acceptance in a wide range of applications due to their significant advantages.

MMO anode advantages：

Proven reliability

Extremely long life

Multiple anode configurations available

Lightweight

Low cost

MMO anodes have a very low wear rate and are often referred to as dimensionally stable anodes because they do not change geometry over time.MMO anodes are quickly becoming the most popular applied current anode, surpassing the market share of traditional anodes such as graphite and high-silica cast iron.

MMO Anodes

Titanium MMO Anode advantages:

Titanium is readily available in commercially pure form

Excellent adhesion through proper surface treatment

Lightweight

Outstanding mechanical strength

Excellent chemical resistance to highly acidic conditions - typical for oxygen and chlorine release environments common to many cathodic protection applications

For MMO wire anodes, some suppliers use a bimetallic substrate with a thin layer of titanium extruded over a copper core. The use of copper-core titanium wire is primarily due to cost considerations, as most of the titanium content in solid titanium wire has been replaced by less costly copper materials. In addition, the conductivity of the wire is slightly improved because copper is a better conductor. However, using copper core wire increases the susceptibility of anode substrates to corrosion and chemical attack in highly acidic environments because copper does not have the same high resistance as titanium.

MMO Anode Manufacturing Process

A typical manufacturing process for MMO anodes begins with a surface preparation of the substrate by thoroughly cleaning commercially pure titanium. This is followed by chemical etching and, in some cases, mechanical abrasion of the surface. After the surface treatment of the substrate is completed, the coating is applied in the form of a mixture of metal salts and then thermally decomposed at temperatures between 400 and 600 °C. This forms an adhesive layer of mixed metal oxides. MMO coatings can be applied in multiple layers and heat treated after each coat to achieve the required coating load to meet the current capacity requirements of the application.

Electrocatalytic anodes based on mixed metal oxides are a different type of anode compared to conventional anodes. These anodes are dimensionally stable, long-life anodes that are not consumed in the process of generating cathodic protection current. For all cathodic protection applications, the use of iridium oxide is preferred. Ruthenium-based MMOs should be avoided for cathodic protection applications, except in highly chlorinated environments. Concerns about substrate failure due to titanium polarization exceeding the substrate breakdown voltage have proven unfounded. Mmo Cylindrical Anode continue to gain market acceptance and are rapidly replacing conventional anodes in a wide range of applications.