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The inhibition of carbon steel corrosion induced in 1 M H 2 SO 4 by soy polymer (SP) from an extract of Glycine Mac-L and polyvinylpyrrolidone (PVP) respectively was investigated at 30-60 °C using hydrogen gas evolution, potentiodynamic polarization and quantum chemical computation technique respectively. Results obtained from hydrogen gas evolution technique revealed that SP and PVP respectively acted as an inhibitor for corrosion of carbon steel in 1 M H 2 SO 4 solution. The increase in inhibition efficiency (IE%) of SP and PVP reached a maximum at 89.5% and 84.36% respectively, and the increment was found to be dependent on inhibitor concentration. The combination of mixture of SP and PVP as single inhibitor showed better inhibition improvement compared to individual inhibitor. Temperature study reveals that inhibition efficiency decreased with a rise in temperature suggesting physical adsorption. The computed parameters for the activation energies and heat of adsorption of the corrosion process supported the physical adsorption mechanism proposed. Regression analysis (adsorption isotherm model) was used to approximate the adsorption characteristics of the SP and PVP. Polarization data revealed that SP and PVP respectively adsorption acted as a mixed type inhibitor and also affected the anodic and cathodic partial reactions process. Quantum chemical computations were performed using the density functional theory to establish a clear link existing between the effectiveness of the inhibitor and its electronic properties.

Native starch extracted from sweet potato tubers was modified via extrusion. The native starch and modified starch were characterized by Fourier transform infrared (FTIR) spectroscopy, which revealed slight modifications in peak position and intensities on starch modification. The modified starch was evaluated as a corrosion inhibitor of galvanized steel in 1 M HCl solution by gravimetric and potentiodynamic polarization measurement techniques. Results obtained from gravimetric measurement reveals that the modified starch inhibition efficacy was dependent on time, concentration and temperature, increasing with increase in concentration and decreasing with increase in time of immersion and temperature of the system. Maximum inhibition efficiency of 64.26% was obtained at a concentration of 0.7 g/L PMS. Also, result from polarization technique indicated that the modified starch belonged to a mixed-type inhibitor. Adsorption of the inhibitor on the galvanized steel surface was found to obey the Langmuir adsorption isotherm.

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The adsorption and inhibition performance of hydroxypropyl cellulose (HPC) on aluminium corrosion in 0.5 M HCl and 2 M H 2 SO 4 were investigated at 30-65 °C using potentiodynamic polarization, gravimetric measurement and quantum chemical computation technique respectively. Potentiodynamic polarization results confirmed that HPC acted as a mixed-type inhibitor in both aggressive solutions with a more dominant anodic effect. Results of gravimetric measurement revealed that HPC displayed significant regulatory action on the corrosion of aluminium within the condition studied. Also, aluminium was observed to exhibit higher resistance to dissolution in sulphuric compared to hydrochloric acid. Also, improvement in inhibition efficiency was recorded with an increase in the concentration of inhibitor, but its sustainability was altered with an increase in temperature. The trend of adsorption mechanism proposed was based on the relationship between temperature and inhibition efficiency and computed results of the energy of activation. The adsorption of HPC molecules onto aluminium surface followed the Langmuir adsorption isotherm. Quantum chemical calculations through the aid density functional theory were used to reveal the adsorption strength attractiveness of HPC molecules towards aluminium surface.