Studies on the Influence of Temperature on the Adsorption of Some Cationic Surfactants on to Steel

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 H₂SO₄ 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 ΔG⁰_ads., ΔH⁰_ads. and ΔS⁰_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.