An-Najah Staff

The behaviour of C-steel in molar hydrochloric acid solution in the presence of Extract (CAE) was investigated using weight loss measurements, potentiodynamic polarization curves and electrochemical impedance spectroscopy. The results obtained reveal that the aggressiveness of hydrochloric solution was considerably decreased in the presence of the CAE. The inhibition efficiency was found to increase with increase in the concentration of the natural substances tested. Potentiodynamic polarization studies clearly reveal that the presence of CAE does not change the mechanism of the hydrogen evolution reaction and they act essentially as cathodic inhibitors. The temperature effect on the corrosion behaviour of C-steel is studied in the range from 298 to 328K without and with at 0.1 g/l. The adsorption isotherm of natural product on the steel has been determined. The apparent activation energies, enthalpies and entropies of the dissolution process were discussed.

The inhibition of ethyl 2-(4-(2-ethoxy-2-oxoethyl)-2-p-tolylquinoxalin-1(4H)-yl) acetate (Q3) on the corrosion of carbon steel in 1.0 M HCl at 308-343 K was studied by gravimetric method. Results obtained show that Q3 acts as inhibitor for carbon steel in hydrochloric solution. The inhibition efficiency was found to increase with increase in Q3 but decreased with temperature, which is suggestive of physical adsorption mechanism although chemisorption may play a part. The adsorption of Q3 onto the carbon steel surface was found to follow the Langmuir adsorption isotherm. Both kinetic parameters (activation energy, pre-exponential factor, enthalpy of activation and entropy of activation) and thermodynamics of adsorption (enthalpy of adsorption, entropy of adsorption and Gibbs free energy) were calculated and discussed.

A new corrosion inhibitor, namely diethyl 2-(2-oxop yrrolidin-1-yl) ethyl phosphonate (P1) was synthesized and its action on the corrosion of stee l in 0.5 M H 2 SO 4 solution has been studied. Weight loss measurements, potentiodynamic polarisat ion and linear polarisation resistance (Rp) and impedance spectroscopy (EIS) methods have been used. The inhibition efficiency increases with the concentration of P1 to attain 86% at 5.10 -3 M. We have noted a good agreement between gravimetric and electrochemical methods (po tentiodynamic and Rp polarisation and impedance spectroscopy (EIS)). Polarisation measure ments show also that the pyrrolidone derivative acts essentially as a cathodic inhibitor . The cathodic curves indicate that the reduction of proton at the steel surface is an acti vating mechanism. P1 adsorbs on the steel surface according to Langmuir adsorption model. Eff ect of temperature is also studied in the 298-353 K range.

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.

A new corrosion inhibitor, namely diethyl 2-(2-oxop yrrolidin-1-yl) ethyl phosphonate (P1) was synthesized and its action on the corrosion of stee l in 0.5 M H 2 SO 4 solution has been studied. Weight loss measurements, potentiodynamic polarisat ion and linear polarisation resistance (Rp) and impedance spectroscopy (EIS) methods have been used. The inhibition efficiency increases with the concentration of P1 to attain 86% at 5.10 -3 M. We have noted a good agreement between gravimetric and electrochemical methods (po tentiodynamic and Rp polarisation and impedance spectroscopy (EIS)). Polarisation measure ments show also that the pyrrolidone derivative acts essentially as a cathodic inhibitor . The cathodic curves indicate that the reduction of proton at the steel surface is an acti vating mechanism. P1 adsorbs on the steel surface according to Langmuir adsorption model. Eff ect of temperature is also studied in the 298-353 K range

N-1-Naphthylethylenediamine dihydrochloride monomethanolate (N-NEDHME) was tested as a corrosion inhibitor for copper in 2 M HNO3 solution using the standard gravimetric technique at 303–343 K. N-NEDHME acts as an inhibitor for copper in an acidic medium. Inhibition efficiency increases with increase in concentration of N-NEDHME but decreases with a rise in temperature. Thermodynamic parameters such as adsorption heat ( \UpdeltaH∘ads ), adsorption entropy ( \UpdeltaS∘ads ) and adsorption free energy (\UpdeltaG∘ads) were obtained from experimental data of the temperature studies of the inhibition process at five temperatures ranging from 303 to 343 K. Kinetic parameters activation such as Ea , \UpdeltaH∘a , \UpdeltaS∘a and pre-exponential factors have been calculated and are discussed. Adsorption of N-NEDHME on the copper surface in 2 M HNO3 follows the Langmuir isotherm model.

The effect of adding 2-phenylimidazo[1,2-a]pyridine-3-carbaldehyde derivative named (P2), newly synthesized on the electrochemical behavior of C38 steel in molar hydrochloric acid was investigated by using the weight-loss method, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) measurements. EIS results show that the transfer resistance increases with the increase of concentration of P2 and it also had an inhibiting effect on C38 steel corrosion in HCl solutions. Weight-loss essays confirm that the corrosion rate decreases as the P2 concentration increases. The inhibition efficiency for this compound studied increased with the increase in the inhibitor concentrations to attain 91.7 % at the 10−3 M of P2. The potentiodynamic polarization curves indicated that P2 acted as a mixed-type inhibitor in hydrochloric acid.

The effect of temperature on the corrosion behavior of copper in 2M nitric acid solution in the presence and absence of 5-(2,6-dichlorobenzyl)-6-methylpyridazin-3(2H)-one (P3) has been investigated by weight loss method. The inhibitory effect increases with increasing inhibitors concentration and decreases with rise of temperature from 303 to 343K. Adsorption follows the Langmuir isotherm with negative values of free enthalpy suggesting a spontaneous adsorption process. Other 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.

A brief review is given to study inhibitive action of Poly (4-vinylpyridine) – Graft - Bromodecane (P4VPBrD) at three degrees of quaternisation (25%, 45% and 60 %) on the corrosion behaviour of pure iron was investigated in desaerated molar sulphuric acid solution using weight loss measurements, potentiodynamic polarisation, and impedance spectroscopy (EIS) methods at free corrosion potential. A polarisation measurement shows also that the compound acts as a mixed-type inhibitor and was adsorbed on the iron surface according to the Langmuir adsorption isotherm model. The parameters, which characterise the corrosion behaviour, can be determined from plots and diagrams of Nyquist. There inhibition efficiency (E %) increases with the all inhibitors concentration. Trends in the increase of charge transfer resistance and decrease of capacitance values also shows the molecular adsorption on the metal surface. The temperature effect on the corrosion, behaviour iron metal in 1M H2SO4 without and with inhibitor at 510 -5 M was studied at the temperature range from 298 to 338 K, the associated activation energy have been determined and proved that the adsorption is a spontaneous process.