الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Corrosion is destructive and silent operating processes. It poses problems to big as Well as small industries. Since corrosion is impracticable to eliminate, the effective corrosion science and engineering lies in controlling rather than preventing it. Inhibition is a preventive measure against corrosive attack on metallic materials. Chemical compounds may be used which, when added in small concentrations to an aggressive environment, are able to decrease corrosion of the exposed metal. In the present investigation, the four expired pharmaceutical drugs taken for the corrosion inhibition of mild steel corrosion control in the HCl media, based on the present investigation reveals the following conclusions.• In the present investigation, four different non-toxic expired pharmaceutical drugs (Silymarine, Megavit zinc, Diax, No Plac) got from the local medical shops and utilized for this investigation.
• All the four expired drugs have been found as effective inhibitors of mild steel corrosion in hydrochloric acid media by weight loss and electrochemical methods like Tafel polarization and impedance techniques.
• The inhibitive action of all four drugs estimated on mild steel corrosion in 1.0 M HCl with the concentrations 5, 10, 15, 20 ppm. The inhibitive action at different immersion periods 1/2, 1, 1½ and 2 hours at temperatures 303 K, 313 K, 323 K, 333 K and 343 K was investigated.
• The parameters such as surface coverage (θ), inhibition efficiency (IE %) and corrosion rate (mpy) were estimated.
• In the weight loss technique, the inhibition efficiency increases with increasing time rapidly in the first times and then very slowly because at long time all the surface of the metal is fully saturated with the inhibitor.
• In HCl media, the inhibition efficiency of the inhibitors was found to follow the order: Silymarine> Megavit zinc> Diax> No Plac.
• from the weight loss technique as the concentration of inhibitor increases the corrosion rate decrease and hence the inhibition efficiency increase.
• The inhibition efficiency of all the four inhibitors following the above order because of first two have O atom which have lone pair of electrons which search for vacant orbital to make co-ordination bond. The molecular weights of the first two is high. Hence, high electrons reach atom and high molecular weight will give synergistic effect.
• The inhibitor Megavit zinc is having highest molecular weight along the four inhibitors, Megavit zinc and Silymarine also contain bulked groups and having electron reach atoms so they having highest inhibition efficiency comparing to other two inhibitors.
• The effective concentration of the inhibitor in suitable period of immersion for maximum efficiency was found for all the four inhibitors.
• The maximum inhibition efficiency 97% of Silymarine on mild steel corrosion in 1.0 M hydrochloric acid media was observed with optimum concentration (0.9%) and immersion period (2 hours) by weight loss method.
• The maximum inhibition efficiency 96% of Megavit zinc on mild steel corrosion in 1.0 M hydrochloric acid media was observed with optimum concentration (0.7%) and immersion period (2 hours) by weight loss method.
• The maximum inhibition efficiency 94% of Diax on mild steel corrosion in 1.0 M hydrochloric acid media was observed with optimum concentration (0.9%) and immersion period (2 hours) by weight loss method.
• The maximum inhibition efficiency 93% of No Plac on mild steel corrosion in 1.0 M hydrochloric acid media was observed with optimum concentration (0.9%) and immersion period (2 hours) by weight loss method.
• The inhibition efficiencies of inhibitors increase with increasing temperature. Therefore, it was proved that these are having highly temperature resistance, favorable to use in the high temperatures for corrosion control also.
• The negative values of free energy of adsorption (ΔGads) of inhibitors indicate that the adsorption of the inhibitors is spontaneous.
• The inhibitors are found to obey Frumkin adsorption isotherms with correlation coefficient almost unity (0.9835). These isotherms confirm the nature of adsorption of inhibitors. The isotherms confirm that they are participating in the chemical adsorption.
• The activation energies (Ea) decrease with addition of the inhibitor. The activation energy value less than that of the uninhibited solution decreases with an increase in inhibitor concentration confirming the inhibition action of it via chemical adsorption.
• The positive values of enthalpy of adsorption (ΔHads) of inhibitor at various temperatures indicate the reaction is endothermic and suggesting that a high temperature favor in the complexation process and it is in good agreement with increasing stability with the temperature.
• Change in the entropy of adsorption (ΔSads) indicating association of chemical constituent is present in the inhibitors at rate determining step. The negative values of entropy of adsorption (ΔSads) pointed to a greater order produced during the process of activation because of the formation of active complex and represents association or fixation with consequent loss in the degrees of freedom of the system during the process. .