关键词: 二乙烯三胺五甲叉膦酸, 化学转化膜, 螯合作用, 腐蚀防护性能, pH, 锌离子

Abstract:

Novel diethylene triamine penta(methylene phosphonic acid) (DTPMPA)-zinc ion (Zn²⁺) conversion coatings with uniform blue color and excellent corrosion protection were directly formed on the cold rolled steel (CRS) substrates by immersing a CRS plate into the film-forming solutions containing the appropriate concentrations of DTPMPA and Zn²⁺ ion at the proper pH. In this paper, surface morphologies and elemental compositions of DTPMPA-Zn²⁺ conversion coatings were characterized by SEM and EDS, respectivey. The surface functional groups, chemical constituents and binding modes to the substrates were investigated by means of FTIR and XPS methods. The influences of DTPMPA concentrations and pH values on the corrosion protection properties of the DTPMPA-Zn²⁺ conversion coatings were studied using electrochemical impedance spectroscopy (EIS) and polarization measurements. The results revealed that DTPMPA reacted with Zn²⁺ ions, forming the DTPMPA-Zn²⁺ chelate under the coexistence condition of both substances. Moreover, the chelate would be deposited onto the CRS substrate through the cross-linking of Zn²⁺ ions and form three-dimensional DTPMPA-Zn²⁺ thin films with uniform blue color and thickness. This kind of conversion coating exhibited the best corrosion resistance performance with the protection efficiency of 91.6% when the concentrations of DTPMPA and Zn²⁺ ion were 0.2wt% and 0.044wt%, respectively, in the film-forming solutions at pH = 3.0.

Key words: DTPMPA, chemical conversion coating, chelation, corrosion protection, pH, zinc ion