MMO anodes comprise a base metal and a coating. Titanium is used as the substrate because it provides the properties needed to receive a coating for aggressive chemical environments and is suitable for current transfer.
Titanium is also lightweight and can be used in tubular, ribbon, wire, mesh and plate forms.
The MMO coating is only a few microns thick and can be applied by different methods. Depending on the application, it combines two or more oxides of iridium, tantalum, ruthenium and titanium.
Cross-section of Borna Electronic MMO anodes
Microstructure of the Borna Electronic MMO anode coating
The activating coating substantially reduces the overpotential for anodic chlorine and oxygen evolution. Its catalytic action gives the anode very low resistance, resulting in low consumption over its service life. MMO anode consumption is very low, below approximately 1 mg/A·year, depending on environment and application.
MMO anodes are used in impressed current systems to protect metal-based structures. Major applications include bridge maintenance, marine structures and platforms, storage tank bottoms, buried or submerged pipelines and reinforced concrete.
General advantages of MMO anodes include:
- Easy use
- Manufacture in different shapes
- Easy transport
- Low weight
- High current output
- Long life at very high current densities
- Dimensional stability
- Recoating capability
- Reliability
Maximum Current Density and Service Life of MMO Anodes
| Environmental conditions | Maximum output current density (A/m²) | Service life (Year) |
| Carbonaceous backfill | 50 | 25 |
| Petroleum coke | 100 | 25 |
| Fresh water | 100 | 25 |
| Saline water | 100-300 | 25 |
| Seawater | 600 | 25 |
Common MMO cathodic protection anode shapes, applications and specifications are described below.
Tubular MMO Anodes
Tubular MMO anodes protect buried or submerged metal structures. The titanium substrate meets ASTM B338 Grade 1 or 2. Coke backfill is normally used in groundbeds to improve current output, or the anodes are installed in canisters containing carbonaceous coke backfill.
Part of Borna Electronic’s MMO anode production line
Maximum Output Current and Life of Tubular MMO Anodes by Dimensions and Environment
| Environmental conditions | Anode Dimensions (Length×Diameter) | Output Current(A) | Life time(Year) |
| Soil, Cock and Fresh water | (3.4 in×48 in)19 mm×1220 mm | 7 | 25 |
| (1 in×19.7 in)25 mm×500 mm | 4 | 25 | |
| (1 in×39.4 in)25 mm×1000 mm | 8 | 25 | |
| (1 in×48 in)25 mm×1220 mm | 3.5 | 25 | |
| (1 in×60 in)25 mm×1500 mm | 4.5 | 25 | |
| (1.25 in×48 in)31.75 mm×1220 mm | 12 | 25 | |
| Sea water | (3.4 in×48 in)19 mm×1220 mm | 45 | 25 |
| (1 in×19.7 in)25 mm×500 mm | 25 | 25 | |
| (1 in×39.4 in)25 mm×1000 mm | 50 | 25 | |
| (1.25 in×48 in)31.75 mm×1220 mm | 75 | 25 |
Ribbon MMO Anodes
Ribbon MMO anodes protect pipelines and tanks. Their titanium substrate meets ASTM B265 Grade 1. Conductor bars connect the ribbons and supply current to the anode network. These bars are pure titanium to ASTM B265 Grade 1. Beneath tank bottoms, ribbon anodes and conductor bars form intersecting grids connected by spot welding.
A titanium power feed connects the positive transformer rectifier cable to the tank-bottom anode grid. It is spot-welded to the grid.
Dimensions and Weight of Common Ribbon MMO Anodes
| Width | 6.35 mm (0.25 in) |
| Thickness | 0.635 mm (0.025 in) |
| Standard coil length | 100 m |
| Standard coil weight | 1.5 kg |
| Ribbon surface area | 0.014 m²Per/m |
Maximum Output Current and Life of Common Ribbon MMO Anodes
| Environmental conditions | Output current (mA/m) | Approximate life (Year) |
| Fine sand | 42 | 50 |
| Concrete | 1.5 | 100 |
MMO Mesh Ribbon Anodes
MMO mesh ribbon anodes protect reinforced concrete structures. Their titanium substrate meets ASTM B265 Grade 1.
Maximum Output Current and Life of MMO Mesh Ribbon Anodes in Concrete by Width
| Width (mm) | Output current (mA/m) | Approximate life (Year) |
| 10 | 2.75 | 75 |
| 13 | 3.7 | 50 |
| 3.5 | 100 | |
| 15 | 4.1 | 50 |
| 3.9 | 75 | |
| 20 | 5.6 | 50 |
| 4.9 | 75 | |
| 4.7 | 100 |
MMO Wire Anodes
MMO wire anodes protect buried metal structures such as pipelines and tank bottoms. Their titanium substrate meets ASTM B863 Grade 1. They may be supplied with carbonaceous coke backfill. Assemblies comprising MMO wire, cable, coke and a protective covering are known as piggyback anodes.
Borna Electronic MMO wire anodes
Maximum Output Current of MMO Wire Anodes by Size
| Wire diameter (mm) | Output current A/m | ||
| Seawater | Fresh water | Soil with backfill | |
| 1.5 | 3 | 0.5 | 0.5 |
| 3 | 6 | 1 | 1 |
Connection of an MMO wire anode to HMWPE/PVDF covered cable
Other MMO Anodes
Other forms include disc, probe, rod, strip, mesh and tubular mesh anodes, each with specific applications according to the conditions.
Borna Electronic can design and manufacture MMO anodes to meet customer requirements or project needs.