硝酸镧改性无铬达克罗涂层的腐蚀行为与防腐机理

Corrosion Behavior and Anti-corrosion Mechanism of Lanthanum Nitrate Modified Chromium-Free Dacromet Coating

以锌粉、铝粉为原料,硝酸镧为添加剂,制备了硝酸镧改性无铬达克罗涂层,研究了改性涂层在质量分数5%NaCl溶液中浸泡后的腐蚀产物物相组成和微观形貌,探究了涂层的腐蚀行为和防腐机理。结果表明:在NaCl溶液中浸泡10 d后,涂层中部分富锌相优先腐蚀形成Zn_(5)(OH)_(8)Cl_(2)·H_(2)O,表面呈蜂窝状形貌;浸泡30 d后,腐蚀产物增多,生成Zn_(5)(OH)_(6)(CO_(3))_(2),表面呈海绵状结构;浸泡60 d后,腐蚀产物逐渐溶解、剥落,表面呈三维多孔网络结构。涂层的防腐机理包括腐蚀产物和稀土钝化膜的自修复作用、有机硅烷钝化膜和片状锌铝粉分层堆叠的物理屏蔽作用、锌和铝金属的牺牲阳极作用以及稀土钝化作用和缓蚀剂的缓释作用。

With zinc powder and aluminum powder as raw materials and lanthanum nitrate as additive,lanthanum nitrate modified chromium-free Dacromet coating was prepared.The phase composition and micromorphology of the corrosion products of the coating after immersion in 5wt%NaCl solution were studied,and the corrosion behavior and anti-corrosion mechanism of the coating were investigated.The results show that after immersion in NaCl solution for 10d,some zinc-rich phases in the modified coating were preferentially corroded to form Zn_(5)(OH)_(8)Cl_(2)·H_(2)O,and the surface showed a honeycomb morphology;after immersion for 30d,the corrosion products increased and Zn5(OH)6(CO_(3))_(2)was formed,and the surface showed a sponge-like structure;after immersion for 60d,the corrosion products gradually dissolved and peeled off,and the surface showed a threedimensional porous network structure.The anti-corrosion mechanism of the coating included the self-repairing effect of corrosion products and rare earth passivation film,the physical shielding effect of organic silane passivation film and lamellar zinc-aluminum powder overlapping,the sacrificial anodization effect of zinc-aluminum metal,the passivation effect of rare earth and the slow-releasing effect of corrosion inhibitor.