Reasons for the failure of ruthenium iridium titanium anode passivation?
The ruthenium iridium titanium anode has a certain period of working life in the process of electrolytic operation. When the voltage rises so high that there is no current passing through it, the ruthenium iridium titanium anode loses its function.
This phenomenon is called anode passivation.
Ruthenium iridium titanium anode passivation has the following reasons.
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,
If it falls off from the titanium substrate, and falls off to a certain extent, the titanium ruthenium iridium titanium anode will lose its function. (Divided into pulverized exfoliation, convex belly exfoliation and cracked exfoliation)
2) There are cracks in the coating
During electrolysis, nascent oxygen is generated on the ruthenium iridium titanium anode, a part of which is discharged on the interface between the active coating and the electrolyte, and then leaves the surface of the anode to generate oxygen and enter the solution;
There are cracks in the active coating, and another part of oxygen is adsorbed on the surface of the anode, and passes through the active coating to reach the interface between the coating and the titanium substrate by diffusion or migration.
After that, oxygen is chemically adsorbed on the surface of the titanium substrate, forming a non-conductive oxide film (TiO2) with titanium, resulting in reverse resistance; or the electrolyte penetrates through the cracks in the coating, and the titanium
The 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
into 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 rate of chlorine generation increases much more than the rate of oxygen generation, so the electrolysis
The increase of flux density is beneficial to the reduction of oxygen content in chlorine. The titanium substrate is pre-oxidized to form a layer of oxide film first, which can increase the contact between the ruthenium iridium titanium active coating and the titanium substrate.
The binding force makes the coating firm, which can prevent the ruthenium from falling off and dissolving, but it will also cause the ohmic drop of the ruthenium-iridium-titanium anode to increase.
4) Oxide Saturation
The active coating is composed of non-stoichiometric RuO2 and TiO2, which belong to oxygen-deficient oxides. It is the non-stoichiometric oxide that really serves as the chlorine discharge activation center, and this oxygen
The more compounds, the more active centers, the better the activity of ruthenium iridium titanium anode. The conductivity of ruthenium-iridium-titanium coating anode is obtained from isomorphic RuO2 and TiO2 after heat treatment.
The properties presented by distorted n-type mixed crystals, in which there are some oxygen vacancies, when these oxygen vacancies are filled with oxygen, the overpotential rises rapidly, leading to passivation.
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