The inhibition effect of phosphonic acids such as amino(trimethylenephosphonic acid) (ATMP), diethylenet riaminepenta(methylenephosphonic acid) (DTPMP) and phenyl phosphonic acid (PhPA) on the corrosion of carbon steel in rain water collected from rooftop was studied by weight loss, potentiostatic polarization and electrochemical impedance spectroscopy methods. The results show that the inhibition efficiency (IE) of the phosphonic acids used were in the order of ATMP > DTPMP > PhPA in the presence of Zn2+. A synergistic effect exists between the phosphonic acids and Zn2+. The protective film formed on the metal surface was confirmed by FTIR spectroscopy, Atomic Force Microscopy and Scanning Electron Microscopy.
carbon steel, phosphonic acids, corrosion inhibition, synergistic effect, electrochemical
