Inhibition Effect of Walnut Green Husk Extract on Aluminum in HNO₃ Solution

Walnut green husk extract (WGHE) was prepared from walnut skin with 10%~60% (volume fraction) ethanol solution. The corrosion inhibition effect of WGHE on aluminum in HNO₃ solution was studied by weight loss method, potentiodynamic polarization curve and scanning electron microscopy (SEM). The results showed that the yield and inhibition rate of WGHE prepared by 40% ethanol aqueous solution were relatively higher. WGHE had a significant inhibitory effect on the corrosion of aluminum in HNO₃ solution. The corrosion inhibition rate increased with the increase of WGHE addition, while decreased with the increase of temperature. The inhibition rate of 1.0 g·L^-1 WGHE for Al in 1.0 mol·L^-1 HNO₃ at 20℃ was higher than 85%. With the increase of corrosion immersion time and HNO₃ concentration, the corrosion inhibition rate first increased and then decreased. When the corrosion immersion time was 24 h or the concentration of HNO₃ was 1.0 mol·L^-1, the maximum value of corrosion inhibition rate appeared. In 1.0 mol·L^-1 HNO₃ solution at 20~50℃, the adsorption of WGHE on the aluminum surface was an exothermic process and obeyed the Langmuir adsorption isotherm. WGHE acted as an anode-type corrosion inhibitor to inhibit the corrosion of aluminum in HNO₃ solution.