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NISCAIR ONLINE PERIODICALS REPOSITORY (NOPR) >
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Research Journals >
Indian Journal of Chemical Technology (IJCT) >
IJCT Vol.12 [2005] >
IJCT Vol.12(6) [November 2005] >
| Title: | Synergistic effect of NTMP, Zn2+ and ascorbate in corrosion inhibition of carbon steel |
| Authors: | Rao, B V Appa
Rao, S Srinivasa
Babu, M Sarath |
| Keywords: | Synergism
ascorbate
carbon steel
NTMP
corrosion inhibition |
| Issue Date: | Nov-2005 |
| Publisher: | CSIR |
| IPC Code: | C23F11/00 |
| Abstract: | Nitrilotris(methylenephosphonic
acid) (NTMP) inhibits corrosion of carbon steel in presence of Zn2+
. However, in order to make the inhibitor more environment friendly, it is
necessary to reduce the levels of Zn2+ or phosphonate or both by
introducing an environment friendly organic salt as a second synergist. In this
paper, the inhibitive action of ascorbate as a second synergist in the presence
of relatively low concentrations of NTMP and Zn2+, is presented.
Addition of just 25 ppm of ascorbate to 20 ppm each of NTMP and Zn2+,
at pH=7, increased the inhibition efficiency markedly from 35 to 95%. In the pH
range of 6-4, the concentration of ascorbate required to bring up the
inhibition efficiency to 94%, is only 10 ppm. However, the alkaline region
demanded relatively higher concentration of ascorbate. This ternary system is
quite effective in a wide pH range, 4-10. This is the uniqueness of this new
synergistic formulation. Potentiostatic polarization studies indicated that
this synergistic formulation acts as a mixed inhibitor, predominantly cathodic
in nature. A large increase in charge transfer resistance and also a decrease
in double layer capacitance of the surface film, were observed from a.c.
impedance studies. X-ray photoelectron spectrum of the surface film indicated
the presence of the elements, viz.,
P, O, N, C, Zn and Fe in the film. The shifts in binding energies of these
elements indicated the presence of oxides and hydroxides of iron and zinc as
well as complexes of Fe(III) and Zn(II) with phosphonate and ascorbate. The
reflection absorption FTIR spectrum of the surface film also supported the
formation of insoluble complexes of phosphonate and ascorbate with metal ions
as well as presence of Zn(OH)2 on the metal surface. A suitable
mechanism of corrosion inhibition is proposed, which corroborates all the above
experimental results. |
| Page(s): | 629-634 |
| ISSN: | 0975-0991 (Online); 0971-457X (Print) |
| Source: | IJCT Vol.12(6) [November 2005]
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