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The aim of this paper was to investigate the corrosion inhibition potential of two synthesized benzothiazines, namely, 3,4-dihydro-2-methoxycarbonylmethyl-3-oxo-2H-1,4-benzothiazine (1) and ethyl 3-oxo-3,4-dihydro-2H-1,4-benzothiazine-2-carboxylate (2) on mild steel corrosion in 1M H₂SO₄.

Corrosion inhibition efficiency (IE%) was studied by weight loss measurements, potentiodyanmic polarization method, alternating current (AC) impedance spectroscopy, fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy. Quantum chemical approach was used to complement the experimental results.

The results obtained show that the IE% increased with inhibitor concentration and follow the order 2 > 1, obeying Langmuir adsorption isotherm. The calculated quantum chemical indices were consistent with experimental results.

This paper provides information on the inhibitive properties of new set of benzothiazines on mild steel corrosion in 1M H₂SO₄.

Over the past decade, plant extracts are ultimate green candidatures to substitute the expensive and noxious synthetic corrosion inhibitors. In this regard, this study aims to focus on evaluating anti-corrosion properties of green inhibitor Cyperus rotundus (C. rotundus), a perennial herb found throughout India.

The biocompatible components present in C. rotundus extract was analyzed by gas chromatography–mass spectroscopy analysis. The corrosion inhibitory effect of C. rotundus was assessed by impedance, polarization and surface morphometric study [atomic force microscopy (AFM)]. Density functional theory (DFT) study was carried using DFT/B3LYP, and basis set used for calculations was 6-31G (d, p) using Gaussian 03 program package.

Predominant components such as octadecanoicacid, ethylester, n-hexadecanoic acid, pentanoicacid-4-oxoethyl ester, cyclotrisiloxane, hexamethyl, cyclotetrasiloxane and octamethyl were identified from the extract of C. rotundus. Impedance study demonstrated that the addition of inhibitor reduces the double-layer capacitance and increases the charge transfer resistance. Furthermore, polarization studies indicated that the extract of C. rotundus acted as a mixed-type inhibitor with decrease in corrosion current density with increase in concentration. AFM study evinced the formation of inhibitor film on mild steel surface. The donor–acceptor interactions of active sites of predominant phytoconstituents were substantiated by computational analysis (DFT).

This paper deals with the inhibition effect of extract of C. rotundus on mild steel in 0.5M H₂SO₄. C. rotundus has a capability to adsorb on the metal surface, thus hindering corrosion.