Corrosion and Corrosion Protection of Aluminum in Hydrochloric Acid by Using Piperidine

The corrosion and corrosion inhibition of aluminum in different concentrations of HCl solutions in the absence and presence of piperidine was investigated using weight loss method and thermometric technique which complemented with surface examination using scanning electron microscopy (SEM). It has been found that piperidine acts as a good corrosion inhibitor for aluminum and the action depends on the concentration of both acid and inhibitor. The concentration of 2.25 M HCl was chosen to carry out the tests of additives either separately or in pairs. Results for weight loss and thermometric measurement indicated that inhibition efficiency increases with increasing inhibitor concentration. It was found that adsorption of piperidine on aluminum surface follows Langmuir adsorption isotherm with a spontaneous process. On the other hand, addition of increasing amounts of NaNO3 to 2.25 M HCl showing that, at lower nitrate concentration there are a decrease in the induction period which is accompany by a rise in the maximum temperature Tm. While at higher ones C > 0,1, an increase in the induction period is manifested. The high dissolution rates of metals in acidic NO3 solution are the result of an autocatalytic process involving the partial reduction of the NO3- ion to NO2