Protection Of Metal Coatings
- Jul 05, 2018 -
Protection of metal coatings
Metal plating on the surface of the steel plate is equivalent to the steel plate wearing protective clothing.The basic composition of steel plate is iron, the protective effect of coating on steel base should be divided into two cases.
The first case.Some metal coatings, such as galvanized coatings (whether hot galvanizing or electrogalvanizing), are anodic to the steel substrate, and the protective effect of the coating on the steel substrate is divided into two stages.,
In the first stage, when the coating remains intact, the coating ACTS as a "circular protection ", that is, the steel base is separated from the outside corrosive medium to protect the steel base from corrosion.At this time, the surface of the galvanized layer is exposed to impure water and other corrosive media, and the surface is corroded to form non-soluble compounds such as zinc hydroxide (Zn (OH) 2, zinc oxide (Zno) and zinc carbonate (ZnCos).These corrosion products are precipitated in the form of precipitation and merged into a dense film, which has a retarding effect on the development of corrosion to the deep. Therefore, the corrosion loss of galvanized layer is relatively slow.As long as the galvanized layer is not corroded through, it will continue to act as an isolation protection to the steel base.When the local corrosion of the galvanized layer penetrates, there is no isolation protection.
Happened in the second stage, when the coating after local damage, whether caused by corrosion penetration damage or mechanical scratch injury, because of the zinc electrode potential is lower than iron, when the corrosive medium, such as not pure water cover, micro battery formation, as anode, the galvanized layer of steel base as the cathode, anode oxidation reaction, to produce zinc corrosion;The corrosion of iron was inhibited by the reduction of cathode.This is the "sacrificial anode protection" of zinc. As an anode, zinc sacrifices itself to protect itself from corrosion by its own corrosion loss.