Abstract
Gravimetric method was used to study the temperature effects on mild steel corrosion in 2.0M of HCl and H2SO4 in the absence and presence of aqueous extract for fenugreek leaves (AEFL). In 2.0 M HCl, the results revealed that the inhibition efficiency of AEFL increases with increasing concentration, but an increase or decrease in the inhibitor efficiency depending on its concentration is detected with increasing temperature. On the other hand, in 2.0 M H2SO4, the inhibition efficiency of AEFL was found to increase with increasing both the inhibitor concentration and solution temperature. However, the AEFL inhibited mild steel corrosion in HCl more than in H2SO4 at all inhibitor concentrations and solution temperatures. The inhibition action of AEFL was performed via adsorption of the extract species on mild steel surface. The adsorption was spontaneous and followed Langmuir adsorption isotherm in HCl, while followed Temkin adsorption isotherm in H2SO4 at all studied temperatures. Thermodynamic data for both inhibitor adsorption and mild steel corrosion led to suggest the occurrence of (a) comprehensive adsorption (physical and chemical adsorption) for the inhibitor species on mild steel from HCl solution and (b) chemical adsorption for the inhibitor species on mild steel from H2SO4 solution. The inhibition mechanism for the adsorption of AEFL species on mild steel surface from both acids was discussed with the light of some AEFL constituents.