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Composition and anti-rust mechanism of Dacromet coating

Posted on 2018-12-22
  The Dacromet treatment solution is a dispersible aqueous solution composed of zinc flakes, aluminum flakes, anhydrous chromic acid, ethylene glycol, zinc oxide, etc., having a diameter of four to five micrometers and a thickness of four to five micrometers. After the treated workpiece is immersed or sprayed in the treatment liquid, the surface of the workpiece is thinly adhered with a coating liquid, and then heated to about 300 ° C in the curing furnace to make the hexavalent chromium in the coating layer The organic matter such as ethylene glycol is reduced to form water-insoluble, amorphous nCrO3 and mCr2O3. Under its action, the zinc sheet and the aluminum sheet are bonded together, and dozens of layers are stacked on the surface of the workpiece. The coating, together with the anhydrous chromic acid in the Dacromet coating, oxidizes the surface of the workpiece to enhance the adhesion of the coating to the surface of the workpiece.
  The rust prevention mechanism of Dacromet coating is generally considered to be the following:
  1. Controlled self-sacrifice protection of zinc powder;
  2. The chromic acid forms a dense oxide film on the surface of the workpiece that is not easily corroded during processing;
  3. The coating consisting of tens of layers of zinc and aluminum sheets forms a shielding function, which increases the intruder's arrival on the surface of the workpiece.
  The path that has passed. Electro-galvanizing is directly coated with a layer of zinc on the surface of steel. Corrosion current is easy to flow between layers. Especially in salt spray environment, the protective current is greatly reduced to make zinc easy to consume. White rust is produced in the early stage of processing. Or red rust. The Dacromet treatment consists of a piece of zinc sheet covered with chromic acid compounds, and the conductivity is moderate, so it has excellent corrosion resistance. The zinc sheets covered by the layers are superimposed to form a shield, and the precipitation rate of zinc is controlled even in the salt spray test. Moreover, since the chromic acid compound in the Dacromet dry film does not contain crystal water, its high temperature resistance and corrosion resistance after heating are also good.