Thunbergia Fragrans extract as green inhibitor for mild steel in acidic medium

• K. Muthukumarasamy¹, S. Pitchai², K. Devarayan³ and L. Nallathambi⁴

¹ Department of Physics, Government Arts and Science College, Srirangam, Tiruchirappalli 620027, Tamil Nadu, India
² Department of Chemistry, Government Arts and Science College for Women, Orathanadu 614625, Tamil Nadu, India
³ Tamil Nadu Dr. J.Jayalalithaa Fisheries University, College of Fisheries Engineering, Nagapattinam 611002, India
⁴ Department of Physics, St. Joseph’s College (Autonomous), Tiruchirappalli 620002, Tamil Nadu, India

Abstract: The present study focuses on the formulation of a green inhibitor against the corrosion of mild steel in 1 M H₂SO₄. At first, the ethanolic extract of Thunbergia fragrans was prepared. Then the inhibitor solution was formulated at different concentrations such as 100, 200, 300, 400, and 500 ppm. The inhibitory effect on the corrosion of the mild steel and the effect of concentration was studied using weight loss measurements at 303 K. The green inhibitor inhibited about 82% of corrosion of mild steel in acid medium. Also, the results indicated that inhibitor concentration and inhibition efficiency are directly proportional to each other. The mechanism of inhibition was analysed through an adsorption isotherm. Langmuir and Temkin adsorption isotherm plots revealed the nature of adsorption behaviour. The data obeyed Langmuir adsorption isotherm as the correlation coefficient value was 0.98. The adsorption process was spontaneous in nature. Furthermore, the thermodynamic behaviour (ΔG_ads) confirms that the inhibitor was adsorbed on the steel surface in 1 M H₂SO₄ through physisorption processes. The metal surface protection was also observed under a scanning electron microscope. The results indicated adsorption of inhibitor on the metal surface.

Keywords: mild steel, plant extract, SEM, Thunbergia fragrans

Int. J. Corros. Scale Inhib., 2022, 11, no. 2, 686-694
doi: 10.17675/2305-6894-2022-11-2-16

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