Titanium anodes have excellent conductivity and corrosion resistance. Their service life is much higher than lead anodes. They can work steadily for more than 4000 hours. The cost is low. It will be an inevitable trend for the development of electroplating zinc and tin production at home and abroad. Titanium electrodes are currently used in Japan, the United States, Germany, and China, which not only greatly saves the energy consumption of electroplating, but also creates conditions for the production of thick galvanized and tin steel plates because of the increased electroplating current density.
Titanium anode classification:
- 1. According to the anode gas evolution in the electrochemical reaction, the chlorine gas is called the chlorine anode, such as the ruthenium-coated titanium electrode: the precipitated oxide is called the oxygen evolution anode, such as the iridium-coated titanium electrode and the platinum titanium mesh /board. Chloride anode (ruthenium-coated titanium electrode): high chloride ion content in the electrolyte, generally in hydrochloric acid environment and electrolyzed seawater, electrolyzed salt water environment. The corresponding products of our company are ruthenium-iridium-titanium anode, ruthenium-iridium-tin-titanium anode.
- 2. Oxygen evolution anode (Iridium-coated titanium electrode): The electrolyte is generally sulfuric acid environment. Corresponding to our company’s products are iridium tantalum anode, iridium tantalum tin titanium anode, high iridium titanium anode.
- 3. Platinum-coated anode: Titanium is the base material. The surface is coated with platinum, the thickness of the coating is generally 0.5-5μm, and the specifications of the platinum titanium mesh are generally 12.5 × 4.5mm or 6 × 3.5mm.
The ruthenium-iridium-titanium anode has a certain life span during the electrolytic operation. When the voltage rises so high that no current actually passes, the ruthenium-iridium-titanium anode loses its function. This phenomenon is called anode passivation.
There are several reasons for the passivation of ruthenium-iridium-titanium anode.
A. Coating peeling
The titanium ruthenium-iridium-titanium anode consists of a titanium substrate and a ruthenium-iridium-titanium active coating. Only the ruthenium-iridium-titanium active coating plays the role of electrochemical reaction. If the coating and the substrate are not firmly combined, they will fall off the titanium plate substrate To a certain extent, the titanium ruthenium-iridium-titanium anode becomes useless. (Divided into crushed peeling, convex belly peeling and cracking peeling)
Reducing the generation of oxygen can slow down the formation of oxide film. When the total current density of electrolysis increases, the chlorine generation rate increases much more than the oxygen generation rate, so the increase in current density is beneficial to the reduction of oxygen content in chlorine. The titanium substrate is pre-oxidized to form an oxide film first, which can increase the binding force of the ruthenium-iridium-titanium active coating and the titanium substrate to make the coating firm and prevent ruthenium from falling off and dissolving, but it can also cause ruthenium-iridium-titanium Increase in anode ohmic drop.
C. Oxide saturation
Active coating is composed of non-stoichiometric RuO2- and TiO2, which is an oxygen-deficient oxide. It is the non-stoichiometric oxide that really acts as the activation center for 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 exhibited by the distortion of n-type mixed crystals from isomorphous 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.
D. The coating has cracks
During the electrolysis, new ecological oxygen is generated on the ruthenium-iridium-titanium anode, part of which is discharged at the interface between the active coating and the electrolyte, and then leaves the anode surface to generate oxygen into the solution; due to cracks in the active coating, the other part of oxygen is adsorbed on the anode On the surface, through the active coating through diffusion or migration to the interface between the coating and the titanium substrate, then oxygen is chemically adsorbed on the surface of the titanium substrate, and a non-conductive oxide film (TiO2) is formed with the titanium, resulting in reverse resistance Or, the electrolyte invades through the coating crack, 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 matrix.