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Author: ANYIAM, CHIOMA KEZAIAH

Title:    Use of Modified Sweet Potato Starches as Corrosion Inhibitors of Selected Metals  

Affiliation: POLYMER SCIENCE Department 

School of Engineering and Engineering Technology

Federal University of Technology, Owerri Imo State

 

Date: July, 2016

 

ABSTRACT

Sweet potato starch was modified via extrusion, alkaline steeping and acid steeping to yield physically modified starch (PMS), alkaline treated sweet potato starch (ASS) and acid treated sweet potato starch (ATS). The unmodified and modified starches were characterized using the Fourier transform infrared spectroscopy and assessed for corrosion inhibition efficacy on mild steel and galvanised steel in 0.25 M H2SO4 and 1 M HCl using  gravimetric (weight loss) measurements and potentiodynamic polarization techniques. All the starch samples inhibited corrosion of the metals in the acidic media, with maximum efficiency ranging from 22.86 to 62.76 % for mild steel and 24.27 to 63.48 % for galvanised steel. Introduction of potassium iodide notably increased inhibition efficiency up to 85.59 %, 85.09 %, 83.64 %, 87.72 % for NS, PMS, ASS, and ATS respectively for mild steel and for galvanised steel 92.60 %, 95.62 %, 93.67 % and 93.94 % respectively for NS, PMS, ASS and ATS. Fourier transform infrared spectroscopy was used to analyse the scrapped metal after corrosion in presence and absence of the additives in the acidic media. Atomic force microscopy was used to analyse the surface morphology of the corroded metals in the presence and absence of the additives in the acidic media. The inhibitor adsorption characteristics were found to obey Langmuir isotherms. Temperature studies (30-60OC) investigated showed higher inhibition efficacy at lowest temperatures, thus suggesting physiosorption adsorption mechanism. These results were in agreement with the kinetic and activation energy parameters investigated. Potentiodynamic polarization measurements showed that NS, PMS, ASS and ATS are mixed-type inhibitors.