Abstract
The inhibition of steel corrosion by cationic surfactants has been investigated in acidic media. The study demonstrates a correlation between the inhibition action towards corrosion and increasing numbers of methylene groups per surfactant molecule. The mode of adsorption of inhibitor molecules on the steel surface in H
2
SO
4
solutions containing different concentrations of cetyltrimethylammonium bromide (CTABr), n-tetradecyl- N,N,N-trimethylammonium bromide (TDTABr), n-dodecyl-trimethylammonium bromide (DDTABr) and n-decyltrimethylammonium bromide (DTABr) has been investigated. Measurements have been conducted at temperatures ranging from 10°C to 50°C for all surfactants studied. The activation parameters E
a
and ΔS, and the thermodynamic parameters ΔG
0
ads.
, ΔH
0
ads.
and ΔS
0
ads.
, have been determined and their values discussed. The Temkin adsorption isotherm and a recent kinetic–thermodynamic model fit the process of surfactant adsorption on to a steel surface well. The binding constant, the free energy of adsorption, the lateral interaction and the number of active sites are reported.