Inhibition effect of plant distillates on 90/10 Cu-Ni alloy in acidic chloride media

Abstract

Citrus paradisi and Cymbopogon distillates were admixed in ratio 1:1 and assessed for their inhibition effect on Cu-Ni cupronickel alloy in 0.25 M H 2 SO 4 –3.5% NaCl electrolyte. Results revealed the distillates effectively inhibited the Cu-Ni alloy at 2–5% CPC concentrations. The degradation rate of Cu-Ni alloy without distillate is 0.373 mm/y whereas at 1% concentration, the degradation rate decreased to 0.140 mm/y (1.37 × 10 −5 A/cm 2 ) corresponding to inhibition efficiency of 62.46%. At 2–5% concentration, inhibition efficiency ranged between 80.47 and 95.58%. The distillate displayed mixed-type inhibition performance coupled with significant suppression of cathodic reduction reactions. Thermodynamic calculations showed the distillates adsorbed unto the Cu-Ni alloy by chemisorption according to Langmuir and Freundlich adsorption isotherms (correlation coefficients above 0.8). Gibbs free energy indicate increase lateral attraction effect among the distillate molecules with respect to #concentration. Open circuit potential curves showed the distillates increased the thermodynamic instability of Cu despite effective inhibition performance.