An-Najah Staff

The detailed study of corrosion behaviour of copper in 2M nitric acid solution in the presence and absence of 2-(4-(2-ethoxy-2-oxoethyl)-2-p-tolylquinoxalin-1(4H)-yl)acetate (Q1) was investigated using weight loss method at various temperatures from 303 to 343 K. The inhibitor showed 97% inhibition efficiency at its optimum concentration 10-3M at 303K and decreased at higher temperatures. The thermodynamic parameters such as, equilibrium constant, adsorption heat and adsorption entropy were obtained. The various parameters of activation determining the kinetic data such as energy, enthalpy and entropy at different concentrations of the inhibitor were evaluated and discussed. The adsorptive behaviour of Q1 followed Langmuir-type isotherm. The standard free energies of adsorption were negative at different temperatures tested, reûecting better inhibition performance.

2Z)-1-(4-chlorophenyl)-2-[(3E)-3-[2-(4-chloropheny l)-2-oxoethylidene]-3,4dihydro quinoxalin- 2 (1H)-ylidene]ethanone (Q4) was tested as inhibito r for the corrosion of copper in 2M HNO 3 using gravimetric method at 303 – 343 K. The inhibi tor (Q4) showed about 90% inhibition efficiency (E (%)) at an optimum concentration of 1 0 -3 M. The inhibition efficiency increases with increase in inhibitor concentration but decrease wi th rise in temperature. Various parameters (Ea , ∆G ° ads , K ads ) for adsorption reveal a strong interaction betwee n inhibitor and copper surface. The negative values of ∆G° ads indicate the spontaneous adsorption of the inhibit or on copper surface. Kinetic parameters activation such as a E , aH °∆ , aS °∆ and pre-exponential factor have been calculated and discussed. Further, theore tical calculations were carried out and relations between computed parameters and experimen tal inhibition efficiency were discussed.