What is the process of MMO coating?

MMO (Mixed Metal Oxide) coating is a specialized process used to apply a corrosion-resistant and conductive layer onto substrates, typically titanium or other metals. These coatings are widely used in industrial applications like anodes for cathodic protection, electrolysis, and other electrochemical processes. The general process of MMO coating is as follows:

1. Substrate Preparation

Material Selection: The substrate is usually titanium (Grade 1 or 2).

Surface Cleaning: The substrate is degreased and etched (using acid solutions like oxalic or hydrochloric acid) to remove oxides and contaminants, ensuring good adhesion.

Roughening (Optional): Some processes involve sandblasting or mechanical abrasion to increase surface area.

2. Coating Application

The coating consists of precious metal oxides (e.g., ruthenium, iridium, platinum) mixed with metal oxides (e.g., titanium).

The uniformity and thickness of the coating directly affect the performance of the anode. Commonly used coating methods include brush coating, spray coating, and dip coating. Brush coating is suitable for anodes with small areas or complex shapes, while spray coating and dip coating are suitable for large areas or mass production.

3. Drying

The coated substrate is dried at moderate temperatures to evaporate solvents.

4. Thermal Decomposition

The dried coating is fired in a furnace at high temperatures (350–550°C) in an oxidizing atmosphere.

5. Repetition of Coating & Firing

Multiple layers (5–20 cycles) are applied to achieve the desired thickness (typically 8–10 microns).

Each layer is dried and fired before the next is applied.

6. Post - treatment

Sintering hardening is the process of heat-treating the coated titanium anode in a high-temperature environment. Through high-temperature sintering, a chemical reaction occurs between the coating material and the titanium substrate, forming a strong bonding layer. Additionally, the high-temperature treatment enhances the density and hardness of the coating, thereby improving the anode's corrosion resistance and mechanical strength.