Corrosion inhibition of copper by purine or adenine in sulphate solutions

The influence of the concentration of purine (PU) or adenine (AD) on the spontaneous dissolution of copper in 0.5 M Na2SO4 solutions (pH 6.8 and 1.0) was studied. The investigations involved weight loss measurements, quartz crystal microbalance (QCM) techniques and scanning electron microscopy (SEM). The inhibition efficiency increases with an increase in the concentration of PU or AD. An adherent layer of inhibitors are postulated to account for the protective effect. The adsorption of both inhibitors was found to occur on the surface of copper according to the Langmuir isotherm. The values of standard free energies of adsorption suggest the chemical adsorption of PU and AD on copper surface.