The failure of ruthenium-iridium-titanium anode passivation's reasons

The ruthenium-iridium-titanium anode has a certain working life during the electrolysis process. When the voltage rises very high and there is actually no current flowing, the ruthenium, iridium, titanium anode loses its function. This phenomenon is called anode passivation.

There are several reasons for the passivation of mmo ruthenium-iridium-titanium anodes

1) Coating peeling

The titanium ruthenium iridium titanium anode is composed of a titanium substrate and a ruthenium iridium titanium active coating. The electrochemical reaction is only the ruthenium iridium titanium active coating. If the coating and the substrate are not firmly bonded, it will fall off the titanium substrate and fall off to a certain extent. To a certain extent, the titanium ruthenium iridium titanium anode loses its effect. (Divided into crushed peeling, belly-shaped layer peeling and cracked peeling)

2) There are cracks in the coating

During electrolysis, new ecological oxygen is generated on the ruthenium-iridium-titanium anode, some of which discharge at the interface between the active coating and the electrolyte, and then leave the anode surface to generate oxygen into the solution; due to cracks in the active coating, the other part of the oxygen is adsorbed on the anode On the surface, through the active coating through diffusion or migration, it reaches the interface between the coating and the titanium substrate, and then oxygen is chemically adsorbed on the surface of the titanium substrate to form a non-conductive oxide film (TiO2) with the titanium, resulting in reverse resistance; Or the electrolyte penetrates through the cracks of the coating, the titanium substrate is slowly oxidized, and the interface with the ruthenium-iridium-titanium active coating is corroded, causing the ruthenium-iridium-titanium active coating to fall off, resulting in an increase in the potential of the ruthenium-iridium-titanium anode. The increase in potential further promotes the dissolution of the coating and the oxidation of the titanium substrate.

3) RuO2 dissolves

Reducing the occurrence of oxygen can slow down the formation of oxide film. When the total current density of electrolysis increases, the increase in the rate of chlorine generation is much greater than the increase in the rate of oxygen generation, so the increase in current density is conducive to the decrease of the oxygen content in chlorine. The titanium substrate is pre-oxidized to form an oxide film, which can increase the binding force of the active coating of ruthenium, iridium, titanium and the titanium substrate, make the coating firm, and prevent the falling and dissolution of ruthenium, but it will also cause ruthenium, iridium, titanium Increase in anode ohmic drop.

4) Oxide saturation

The active coating is composed of non-stoichiometric RuO2- and TiO2, which are oxygen-deficient oxides. It is the non-stoichiometric oxide that really serves as the activation center of the chlorine discharge. The more such oxides, the more active centers, and the better the activity of the ruthenium-iridium-titanium anode. The conductivity of ruthenium-iridium-titanium-coated anodes is the performance of distorted n-type mixed crystals generated from isomorphic RuO2 and TiO2 after heat treatment. There are some oxygen vacancies. When these oxygen vacancies are filled with oxygen, the The potential rises rapidly, leading to passivation.