Phosphatization Coating-forming Mechanism Based on Green Phosphating Accelerator Rare Earth Nitrate

摘要

Experimental results show that the samples gained in bath added Rare earth nitrate (REN), relative to the sample got in bath without REN, improve the anti-corrosion power of the coating because of increasing of covering rate of formless crystal Zn_2Fe(PO_4)_2·4H_2O (marked P) crystals and the ratio of P/(P+H) (H is the mark of Zn_3(PO_4)_2 crystal) in the coating, combination of which with components parsing by EDS indicates that the sequence of contribution elements P and Zn to erosion resistance of coatings is P>Zn. And the correlative mechanism was discussed, which has it clear that RE is materially a catalyst holding excellent ability of carrying oxygen and cathode depolarization, its concentration gets so constant in certain range that it is much steadier and more efficient than the usual consumptive oxidants like nitrates. In a word, REN plays the role of surface regulator, accelerant and densification agent, which speeds up the phosphating, and bids it effective to enhance the anti-corrosion power of the coating. The addition of REN, not only promote the phosphating film formation and substantial reduction or exemption of nitrite. So, REN is a green phosphating accelerator of live up to one's name.