Synergistic inhibition effect of walnut green husk extract and potassium iodide on the corrosion of cold rolled steel in trichloroacetic acid solution

Abstract

Plant extract inhibitor is of low price, rich natural raw resources, eco-friendly and biodegradable. To further strengthen inhibition stability and efficiency, halide ion is always mixed with plant extract so as to produce synergism. In the present work, the synergistic inhibition effect of walnut green husk extract (WGHE) and potassium iodide (KI) on the corrosion of cold rolled steel (CRS) in trichloroacetic acid (Cl3CCOOH) solution was studied by weight loss, electrochemical techniques and surface analysis. Results show that WGHE moderately inhibits the corrosion of CRS in Cl3CCOOH media. However, WGHE/KI mixture has pleasant inhibitive ability with the maximum inhibition efficiency of 97.2% in 0.10 M Cl3CCOOH from weight loss method. There is a synergism for WGHE mixing with KI, and all corresponding synergism parameters are high than unity. The adsorption of WGHE either in the absence or presence of KI obeys Langmuir adsorption isotherm, and the external addition of KI facilitates the adsorption of WGHE on steel surface. Individual WGHE mainly retards cathodic reaction, while WGHE/KI mixture drastically inhibits both anodic and cathodic reactions simultaneously. Nyquist appears a capacitive loop at high frequencies followed by an inductive loop at low frequencies. The charge transfer resistance follows the order: WGHE/KI > KI > WGHE. SEM and AFM clearly proves the corrosion degree and surface roughness of CRS surface were dropped to more extent with the synergistic WGHE/KI mixture. Moreover, the synergistic inhibition of two main components of juglone and kaempferol with KI was discussed in detail under same conditions.