Comparative Corrosion Inhibition Performance of Rice Husk and African Breadfruit Husk Extracts on Mild Steel in Nitric Acid Medium

Abstract

The increasing demand for environmentally friendly corrosion inhibitors has promoted the investigation of agro-waste biomass as a sustainable alternative to harmful synthetic chemicals. In this study, the corrosion inhibition capabilities of rice husk extract (RHE) and African breadfruit husk extract (ABHE) on mild steel in a nitric acid medium were compared. The extracts were obtained through ethanol extraction and characterised by Fourier transform infrared spectroscopy (FTIR) and gas chromatography–mass spectrometry (GC-MS) to identify active phytochemical components. Corrosion behavior was assessed using potentiodynamic polarisation (PDP), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) for surface morphology analysis. Both extracts significantly reduced the corrosion rate of mild steel in nitric acid, with inhibition efficiency increasing with increasing inhibitor concentration. RHE achieved a maximum inhibition efficiency of 91%, while ABHE showed a slightly higher efficiency of 93% at optimal levels. Electrochemical results indicated that both extracts acted as mixed-type inhibitors, reducing both anodic metal dissolution and cathodic reduction reactions. Adsorption of inhibitor molecules followed the Langmuir adsorption isotherm, implying monolayer coverage on the steel surface. SEM analysis confirmed improved surface smoothness and fewer pits compared to the uninhibited system. The results show that rice husk and African breadfruit husk extracts are a complex mixture of phytochemical based green corrosion inhibitors for mild steel in aggressive nitric acid environments. The comparative evaluation provides insight into the dominant inhibition mechanisms and serves as a basis for selecting suitable agro-waste inhibitors before developing synergistic formulations.