Application And Performance Studies Of Organic Phosphine In Chrome-free Passivation

Galvanized sheet is widely used in industries such as transportation,construction and home appliance,but galvanized sheet tend to corrode in wet conditions,in order to improve the corrosion resistance of galvanized sheet,the zinc plate is often passivated with high chromium salt,but the high chromium element is carcinogenic to the human body and environmental pollution is serious,therefore it is forbidden to use,in order to find the passivation technology of environment-friendly,the chrome-free passivation of galvanized sheet has been paid more attention,now the study of chromium-free passivation include the passivation of phosphate,the passivation of silicate,the passivation of molybdate,the passivation of phytic acid and silane passivation.In the paper,the passivation technology of organic phosphine high polymer was studied based on galvanized sheet,the components of passivation liquid include organic phosphine polymer,organosilane KH560,fluorozirconic acid and vanadium sulfate,organic silane KH560 is a film agent,fluorozirconic acid and vanadium sulfuric acid are corrosion inhibitors and organic phosphine polymer is both a film agent and a corrosion inhibitor.The optimal formula was obtained through the DOE orthogonal experiment:3.5%KH560?0.3%organic phosphine polymer?0.2%H2ZrF6?0.005%VOSO4,the optimal process parameters are:pH value is 2.5,passivation temperature is 60?,passivation time 60s,curing temperature is 150?,curing time is 90s and the passivation solution was static for 24h without precipitation.The effect of organic phosphine polymer on the corrosion resistance of passivation film was studied after passivation of galvanized sheet,the organic phosphine polymer in passivated fluid increased the corrosion resistance of galvanized sheet by 82%,the corrosion rate decreased by 19%and the impedance value increased by 0.6 orders of magnitude,the improvement of the corrosion resistance of galvanized sheet is mainly due to the formation of covalent bonds between the-PO(OH)2 group and Zn-OH on the surface of the zinc layer,adsorbed on the surface of zinc layer to form a transformation film,in addition,the acid groups in the-PO(OH)2 can further enhance the densification of the passivation film by condensation polymerization,which make the zinc layer isolated from the external corrosion media,the adhesion of the paint film has been improved by one grade,indicating the high activity of acrylic groups in organic phosphine polymers,it can react with the paint film to increase the bonding force between the paint film and zinc layer,after testing by EDS and XRD found that the passivation film mainly contained elements Zn,C,O,Si,Zr,F and P,after the ATR-FTIR test found that in the passivation film contained-Si(OH)3,-CH3 and-CH2 groups and silane forms acovalent bond with the zinc layer,in addition,Si-O-Si bonds formed by the condensation of silanol.The elements contained in the passivation film show that the organic phosphine polymer can work together with other components to improve the corrosion resistance of the passivation film.