p-methoxy benzylidene malonitrile (MN1) and p-hydroxy benzylidene
malonitrile (MN2) were synthesized and tested as inhibitors for the corrosion
of mild steel in molar HCl. We have found that both of them inhibit the corrosion.
The maximum inhibition efficiency reached 100% for MN1 at 10-4 M and for
MN2 at 10-3 M. Current-voltage curves indicated that malonitriles act as mixed
type inhibitors. Their adsorption on the steel surface obeys to the Langmuir
isotherm model. The effect of temperature on the corrosion behaviour of steel
indicated that the inhibition efficiency of the two inhibitors decreases slightly
with the rise of temperature in the range 298-338 K. The apparent activation energies
for steel dissolution are greater than in the absence of inhibitors, which is
consistent with a chimisorption mechanism.