Naturally occurring organic substances as corrosion inhibitors for mild steel in acid medium: Concentration and temperature effects

Potentiodynamic cathodic and anodic polarization technique was used to study the effect of some common amino acids concentration on the corrosion inhibition of mild steel in H2SO4. A value of 1.0 x 10(-4) M represents a critical concentration, for the aliphatic amino acids, above which the corrosion rate increases. The increase of the sulphur-containing amino acids concentration largely decreases the corrosion rate. A mono-layer adsorption of the amino acid molecules on the metal surface was proposed with the adsorption behaviour following the Temkin isotherm at 30 degrees C. The effect of temperature on the corrosion inhibition of amino acids was also studied over the temperature range 25 to 60 degrees C. Values of the apparent activation energy in the range of 42-49 kJ mol(-1) were estimated for the steel corrosion in the inhibited acid solutions.