Mixed Metal Oxide Coated Titanium Anode
Mild steel Corrosion
Mild steel is the one of the most commonly used material in building structures on land and at sea. Steel, however, has a high corrosion rate - especially when exposed to fresh water and sea water. There are various methods in practice to protect steel structures from corroding away. The following article describes an economic and effective way of protecting steel structures by a process called cathodic protection.
Cathodic Protection (CP) is a process where a DC current is applied to a metal to slow or stop corrosion. In a marine environment, the structure to be protected connected to a metal that is more prone to corrosion using a DC current. The metal that needs to be protected acts as a cathode and the metal that is more prone to corrosion acts as the anode, and is often called the sacrificial anode.
Figure 1 – Illustration of an MMO-coated titanium anode that provides cathodic protection to a SeaPod.
Mixed Metal Oxides
Mixed metal oxides are compounds that are with high conductivity and corrosion resistance. They are used to as a surface coating to protect a steel structure from corrosion. Most commonly used MMOs are Ruthenium Oxide (RuO2) and Iridium Oxide (IrO2). Ruthenium Oxide (RuO2) is inexpensive and more suitable for marine environments.
MMO anodes have a very low wear rate and do not change shape 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. Some of the advantages of using mixed metal oxide anodes are
- Longevity (life span)
- Low cost
Titanium is one of the most sought-after metals in the manufacturing industry. It offers several key advantages as a building block for marine applications. The following are advantages of using Titanium.
- Abundant in nature and commercially available for manufacturing industries
- Light weight
- Incredible mechanical strength
- Highly resistant to chemical reactions, especially in highly acidic conditions like marine environments
Mixed Metal Oxide (MMO)-Coated Titanium Anode
An MMO-coated titanium anode is manufactured by coating a pure titanium structure with a mixed metal oxide, such as ruthenium oxide, which is ideally suited for marine environments.
A pure titanium anode (substrate) is cleaned and prepared by chemical etching and sometimes mechanical abrasion of the anode surface. Once the substrate is ready, a coating of ruthenium oxide is applied and thermally decomposed at temperatures ranging 400 to 600 °C. This creates an adherent layer of ruthenium oxide (mixed metal oxide).
The longevity of an MMO-coated titanium anode depends on the amount of current that is applied to the anode. Depending on the current, MMO-coated titanium anodes can last between 20 and 40 years.
MMO-coated titanium anodes have been used in the manufacturing sector for decades because of their cathodic protection properties, longevity, low cost and strength. When coated with a mixed metal oxide like ruthenium oxide, the anode is resistant to corrosion, especially in marine environments where corrosion rates are extremely high.