Abstract
The corrosion inhibiting efficiencies of guanidine carbonate and some of its condensation products have been demonstrated for aluminium (1060) in 20% nitric acid at 25° and 35°C. The percentage inhibitive efficiencies (IE, %) have been found to increase with a rise in temperature and also with an increase in concentration of the inhibitors up to 500 ppm. All the condensation products exhibit greater inhibitive efficiency than the parent compound (guanidine carbonate). 1-p-Methoxyphenyl-3-formamidino-thiocarbamide was found to be the most effective inhibitor followed by 1-p-Methylphenyl-3-formamidino-thiocarbamide, 1-p-Chlorophenyl-3-formamidino-thiocarbamide, 1-m-Chlorophenyl-3-formamidino-thiocarbamide and guanidine carbonate. In each case the steady state potential attained a more negative value with increase in concentration of the additives. Potentiostatic (anodic and cathodic) polarisation studies revealed that the inhibitors are predominantly effective on local cathodes, although partially effective on anodes also. Cathodic Tafel slope values for different inhibitors are fairly in accordance with their inhibitive efficiencies. The critical current density for the passivation of aluminium decreases roughly in the same order as the increase in the efficiency of the inhibitor.
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