An MMO coated titanium anode is a titanium substrate coated with a mixed metal oxide layer, also called a dimensionally stable anode (DSA). The titanium base gives mechanical strength and corrosion resistance, and the oxide coating carries the electrochemical reaction without the anode dissolving. This guide covers the coatings, substrate, forms and applications, and what to specify on an enquiry.
Coating types and when to use them
The coating is chosen for the reaction and the electrolyte. A ruthenium-iridium oxide (Ru-Ir) coating favours chlorine evolution and holds up in seawater, brine and other chloride-bearing or severe environments. An iridium-tantalum oxide (Ir-Ta) coating favours oxygen evolution and is used in acid sulphate electrolytes and low-chloride or fresh water service.
| Coating | Main reaction | Typical electrolyte |
|---|---|---|
| Ru-Ir oxide | Chlorine evolution | Seawater, brine, chloride solutions |
| Ir-Ta oxide | Oxygen evolution | Acid sulphate, low-chloride, fresh water |
Substrate and forms
The substrate is usually commercially pure Grade 1 titanium for its corrosion resistance and coating adhesion. Anodes are supplied as plate, expanded or woven mesh, tube, rod and wire, so the form can match the cell or process. State the form and dimensions, and the working area.
| Point | What the guide states |
|---|---|
| Substrate | Usually commercially pure Grade 1 titanium, for its corrosion resistance and coating adhesion |
| Forms | Plate, expanded mesh and the other forms the guide lists |
Common applications
MMO coated titanium anodes are used in chlor-alkali and on-site chlorine generation for municipal water, swimming pools and disinfection, in electrowinning and electrorefining of copper, zinc and nickel, in copper foil and electroplating lines, in electrodialysis, and in wastewater and electrochemical water treatment. For impressed current cathodic protection, see the titanium anode for cathodic protection guide.
For cell-specific duty, the titanium in chlor-alkali cells guide separates coating families, cell type and the operating fields that belong on the enquiry.
For a reproducible company-page shortlist, use the titanium anode manufacturers list; it keeps Beiyu outside the ranked set and separates published coating fields from RFQ checks.
What to specify on an MMO anode RFQ
State the application and electrolyte, the coating type, the substrate grade and form, the dimensions and working area, the operating current density and design life, and the certificate scope. Coating composition and loading are specified to the duty by order scope. Browse the titanium anode range or send requirements to [email protected].
| Field to state on an MMO anode RFQ | Detail |
|---|---|
| Application and electrolyte | The application and the electrolyte |
| Coating | The coating type |
| Substrate | Substrate grade and form |
| Geometry | Dimensions and working area |
| Duty | Operating current density |
Recoating a spent anode instead of replacing it
A coated titanium anode reaches end of life when the coating loses activity, not when the metal fails. Titanium is a valve metal: where the coating flakes off, the exposed titanium passivates instead of corroding. That is why the same substrate can normally be stripped and recoated rather than scrapped, and why the decision is commercial rather than metallurgical.
| Question | What settles it |
|---|---|
| Is the substrate still usable | Whether the titanium is intact and dimensionally sound, since the coating rather than the metal is what wore out |
| Is recoating worth it | When the loss caused by the risen cell voltage exceeds the cost of stripping and recoating, recoating is the reasonable option |
| How the old coating comes off | Molten salt stripping, acid boiling or sulphate electrolysis, chosen against the coating that is being removed |
| What the new coating should be | The duty may have changed since the anode was first bought, so the coating family is reconfirmed rather than repeated |
The stripping step matters more than it looks. The failed layer is removed down to clean titanium before the new coating is applied.
A recoating enquiry carries different information from a new anode enquiry. State the anode form and dimensions, the coating currently on it, the duty it has been running, the cell voltage now compared with when it was new, and whether the duty is changing. Beiyu Titanium reviews those fields before quotation, and the substrate condition is assessed on receipt rather than assumed from the description.
Specification detail with sources
ASTM B265 quantifies why Grade 1 is the default MMO substrate: UNS R50250 is the softest commercially pure grade, with oxygen capped at 0.18 percent by weight and a 240 MPa minimum tensile strength, the low-interstitial surface an oxide coating keys onto. The substrate standards then follow the form, B265 for the plate and mesh stock and B348 for rod, while the coating split tabled above is electrochemical, ruthenium-iridium oxide toward chlorine evolution against iridium-tantalum oxide toward oxygen evolution.
Beiyu Titanium’s part of an MMO anode is the substrate: Beiyu supplies Grade 1 and Grade 2 titanium as plate from 0.5 mm thick, bar from 1 to 500 mm diameter and wire from 0.8 to 6.0 mm for the plate, rod, mesh and wire anode forms this page lists. The mixed metal oxide coating itself is applied by a specialist coating stage to the duty the order defines, not at the titanium mill, so a Beiyu quotation carries the substrate grade, form and dimensions with an EN 10204 3.1 certificate for the titanium, and the coating type, loading and design life as separate order lines.