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Title: Ternary inhibitor system containing phosphonate, molybdate and Zn<sup>2+</sup> in corrosion control of carbon steel
Authors: Rao, B V Appa
Christina, K
Keywords: N-(2-hydroxyethyl)imino-bis(methylphosphonic acid)
Corrosion inhibition
Issue Date: May-2006
Publisher: CSIR
Series/Report no.: C23F13/00
Abstract: With the objective of developing a new environmental friendly inhibitor formulation for corrosion of carbon steel in nearly neutral aqueous environments, phosphonic acid <i style="">viz</i>., N-(2-hydroxyethyl) imino-bis(methylphosphonic acid) [HEIBMPA] was chosen as the inhibitor. Zn<sup>2+</sup> was chosen as the first synergist. A maximum inhibition efficiency of 99.3% was obtained with the binary system containing 70 ppm HEIBMPA and 80 ppm Zn<sup>2+</sup>. Molybdate ion, which is inorganic in nature but environmental friendly, was used as the second synergist. The binary inhibitor formulation containing relatively low concentrations, <i style="">viz</i>., 30 ppm HEIBMPA and 40 ppm Zn<sup>2+</sup> offered an inhibition efficiency of only 23%. To the above combination, when 200 ppm molybdate was added, the inhibition efficiency was found to increase to 95%. The potentiostatic polarization studies revealed that this ternary inhibitor system controlled the anodic reaction predominantly. A large increase in the polarisation resistance (<i style="">R</i><sub>p</sub>) value indicated the formation of a non-porous protective film on the metal surface. The reflection absorption FT-IR spectrum and X-ray photoelectron spectra of the film suggested that the film consisted of [Fe(III)-HEIBMPA-molybdate] complex, [Fe(III), Zn(II)-HEIBMPA-molybdate]complex, oxides and hydroxides of iron and Zn(OH)<sub>2</sub>. A plausible mechanism of inhibition of corrosion is proposed, which explains all the above experimental results.
Description: 275-282
ISSN: 0975-0991 (Online); 0971-457X (Print)
Appears in Collections:IJCT Vol.13(3) [May 2006]

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