Sunil, Dhanya and Kumari, Preethi P and Shetty, Prakash and Rao, Suma (2021) Indole Hydrazide Derivatives as Potential Corrosion Inhibitors for Mild Steel in HCl Acid Medium: Experimental Study and Theoretical Calculations. Transactions of the Indian Institute of Metals. ISSN 0972-2815

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Abstract

The present work highlights the corrosion inhi�bition action of two indole-3-hydrazides with varying alkyl chain lengths: 2-(1H-indol-3-yl)acetohydrazide (IAH) and 4-(1H-indol-3-yl)butanehydrazide (IBH) against mild steel (MS) in 0.5 M hydrochloric acid (HCl) solution using electrochemical and gravimetric measurement methods. Both IAH and IBH behaved as mixed-type inhibitors, and their anticorrosion behaviour was due to a protective film formation on MS surface through physisorption, in agree�ment with Langmuir’s adsorption model. The surface morphologies of the inhibited specimens examined using SEM and AFM images showed distinctive improvement against acid corrosion. The quantum mechanical calcula�tions indicated the contribution of delocalized p-electrons in the indole unit and the lone-pair electrons in the car�bonyl group for improved adsorption of the studied hydrazides onto the metal surface, supporting the experi�mental results. IAH and IBH showed maximum inhibition efficiency of 80.4 and 94.1% at 30 �C in MS exposed to 0.5 M HCl medium at its optimum concentration. The better resistance to MS corrosion was exhibited by the acid system-containing IBH bearing three methylene groups and hence having higher molar volume and surface coverage in comparison with IAH that incorporated only one methy�lene group in its chemical structure

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