Titanium anode has excellent conductivity and corrosion resistance, with a much longer service life than lead anode. It can work stably for more than 4000 hours and has low cost. It will be an inevitable trend in 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 electroplating energy consumption, but also creates conditions for the production of thick galvanized and tin steel plates by increasing electroplating current density.
Classification of titanium anodes:
1. According to the anodic gas evolution in electrochemical reactions, those that precipitate chlorine gas are called chlorine evolution anodes, such as ruthenium based coated titanium electrodes; those that precipitate oxidation are called oxygen evolution anodes, such as iridium based coated titanium electrodes and platinum titanium mesh/plates. Chlorination anode (ruthenium coated titanium electrode): The electrolyte has a high content of chloride ions and is generally used in hydrochloric acid environments, electrolytic seawater environments, and electrolytic saline environments. Our company's corresponding products are ruthenium iridium titanium anode and ruthenium iridium tin titanium anode.
2. Oxygen evolving anode (iridium coated titanium electrode): The electrolyte is generally in a sulfuric acid environment. Our company's corresponding products are iridium tantalum anode, iridium tantalum tin titanium anode, and high iridium titanium anode.
3. Platinum coated anode: titanium as the substrate. The surface is coated with platinum, and the coating thickness is generally 0.5-5 μ m. The mesh size of platinum titanium mesh is generally 12.5 × 4.5mm or 6 × 3.5mm
The working life of ruthenium iridium titanium anode during electrolysis operation has a certain limit. When the voltage rises very high and there is actually no current passing through, the ruthenium iridium titanium anode loses its function, and this phenomenon is called anode passivation.
There are several reasons for ruthenium iridium titanium anode passivation:
a. Coating peeling off
The titanium ruthenium iridium titanium anode consists of a titanium substrate and a ruthenium iridium titanium active coating. The ruthenium iridium titanium active coating is the only one that plays an electrochemical reaction role. If the coating is not firmly bonded to the substrate and falls off from the titanium plate substrate to a certain extent, the titanium ruthenium iridium titanium anode loses its function. (Divided into crushing shedding, bulging layer shedding, and cracking shedding)
b. RuO2 dissolution
The occurrence of low oxygen can slow down the formation of oxide film. When the total current density of electrolysis increases, the rate of chlorine generation increases much faster than the rate of oxygen generation, so an increase in current density is beneficial for reducing the oxygen content in chlorine. Pre oxidation treatment is carried out on the titanium substrate to form a layer of oxide film, which can increase the bonding strength between the ruthenium iridium titanium active coating and the titanium substrate, making the coating firm and preventing the detachment and dissolution of ruthenium. However, it can also cause an increase in the ohmic drop of the ruthenium iridium titanium anode.
c. Oxide saturation
The active coating is composed of non stoichiometric RuO2- and TiO2, which belong to oxygen deficient oxides. The truly active centers for chlorine discharge are non stoichiometric oxides. The more such oxides there are, the more active centers there are, and the better the activity of the ruthenium iridium titanium anode. The conductivity of ruthenium iridium titanium coated anodes is the performance exhibited by distorted n-type mixed crystals generated from the same crystal form of RuO2 and TiO2 through heat treatment, which contain some oxygen vacancies. When these oxygen vacancies are filled with oxygen, the overpotential rapidly increases, leading to passivation.
d. There are cracks in the coating
During electrolysis, new ecological oxygen is generated on the ruthenium iridium titanium anode, with a portion of it discharging at the interface between the active coating and the electrolyte, and then leaving the anode surface to generate oxygen that enters the solution; Due to the presence of cracks in the active coating, another portion of oxygen is adsorbed on the anode surface and diffuses or migrates through the active coating to reach the interface between the coating and the titanium substrate. Then, oxygen is chemically adsorbed on the surface of the titanium substrate, forming a non-conductive oxide film (TiO2) with titanium and generating reverse resistance; Alternatively, the electrolyte may penetrate through cracks in the coating, causing the titanium substrate to slowly oxidize and corrode the interface with the ruthenium iridium titanium active coating, resulting in the detachment of the ruthenium iridium titanium active coating and an increase in the anode potential of the ruthenium iridium titanium. The increase in potential further promotes the dissolution of the coating and the oxidation of the titanium substrate.
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