## 4 Discussion
The change in color is equivalent to the concentration of the sample. The antioxidant ability of flavonoids such as quercetin and rutin had been extensively reported, conferring protection of liver cells, inflammation, carcinogenesis and smooth muscles [68; 69]. The anti-corrosive property of ginseng was confirmed due to the presence of phenolic compounds present in the extract, which are very active compounds adsorbed on the surface of the specimen, forming a protective film around the surface of the metal [70]. A thick, stable and well-bonded layer formed by the inhibitor was the reason for attaining higher efficiency at 1000-ppm concentration [26]. Due to high temperature, the stable compounds adsorbed on the surface are desorbed at some points and bring down the corrosion efficiency [71]. From SEM images, it was observed that without ginseng extract, the surface of the copper metal was seriously attacked by the HCl medium and formed severe roughness, pits and scratches. At the same time, a smooth copper surface without any damages was noted; due to the physical adsorption of ginseng extract molecules, a protective layer was formed over the metal surface and confirmed that the copper is well protected from corrosive ions. From the EDX spectra of copper metal after attack of HCl solution without inhibitor, it is noted that due to the surface contamination, there are some residual elements; C--7.13%, O--13.54% and Cl--1.01% were present on the surface of the copper specimen, which are more than that on the specimen with inhibitor, and there was no existence of Cl on the inhibited specimen. Presence of Cu is about 9% lower in the corroded specimen without the inhibitor because of removal of copper from the surface due to corrosion. Furthermore, 37% less O content represents that there was less oxidation in the inhibited specimen, which is the root cause for corrosion. The plant extract as a corrosion inhibitor formed a shielding layer on the metal surface which protected the copper from getting delaminated and removal of layer of metal surface. Furthermore, the presence of carbon and oxygen on the inhibited metal surface proves that the active chemical compounds are adsorbed on the copper surface by a synergistic effect and shows a higher inhibition efficiency. There are three ways of achieving adsorption--physical, chemical and combined [72]. Physical adsorption is nothing but the phenomenon of electrostatic interaction of protonated molecules with already adsorbed sulfur ions; chemical adsorption is the interaction between unshared electron pairs of oxygen atoms or \(\pi\)-electrons of aromatic ring copper surface (Figure 7). The inhibition process is executed, hindering the plant extract solution from forming a film around the metal surface, and by the action of adsorption, the available cathodic and anodic sites which activate corrosion are minimized [73; 74]. The roughness and damage on the corroded copper specimen under the exposure of HCl medium are due to the absence of the inhibitor. In the presence of the inhibitor, it is very clear from the topography of the AFM image that there was no corrosion initiation and the smooth surface without any pits and damage confirms that the thin film that formed on the surface of the copper metal protected it from corrosion (Figure 7). The surface roughness value is high in the blank solution (329 nm), that is, in HCl medium without the inhibitor, because of the corroded surface of the copper metal, whereas the roughness value decreased to about 55 nm in copper exposed to same acid environment with the inhibitor which is 16.7% less than that of the uninhibited corroded specimen [75; 76; 77; 78; 79; 80; 81].