Cefixime, a third-generation semi-synthetic cephalosporin antibiotic was used as a copper corrosion inhibitor in 1M HNO 3 solution. The study was conducted through the weight loss technique at 298 -318 K and theoretical studies based on quantum chemistry. The studied drug inhibited the corrosion of copper in 1M HNO 3 over the cefixime concentration range (0.02 -2 mM). The inhibition efficiency increased with an increase in the inhibitor concentration to reach 91.07% at 2 mM, but decreased with an increase in temperature. The thermodynamic functions related to the adsorption of cefixime on the copper surface and that of the metal dissolution were computed and analyzed. The results point out spontaneous adsorption, mainly through a physisorption mechanism following Langmuir adsorption isotherm model and an endothermic dissolution process. Quantum chemical calculations were also performed at B3LYP level with 6-31G (d, p) basis set and lead to molecular descriptors such as E HOMO (energy of the highest occupied molecular orbital), E LUMO (energy of the lowest unoccupied molecular orbital), ΔE (energy gap) and μ (dipole moment). The global reactivity descriptors such as χ (electronegativity), χ (global hardness), S (global softness), and ω (electrophilicity index) were derived using Koopman's theorem and analyzed. The local reactivity parameters, including Fukui functions and dual descriptors were determined and discussed. Experimental and theoretical results were found to be in good agreement.

This work reports the inhibition properties of nicotinic acid (NAC) for copper protection during its applications in seawater systems such as water pipelines, shipbuilding, seawater desalination operations and heat exchange systems. The efficiency of nicotinic acid (NAC) as a copper corrosion inhibitor in 3.5 wt % NaCl solution was investigated by Tafel extrapolation and electrochemical impedance spectroscopy (EIS) methods in the temperature range from 20 to 50 °C. The corrosion parameters and the adsorption isotherms were determined from the potentiodynamic polarization curves. It was found that the inhibitory efficiency (%) and the coverage rate () increase to a maximum of 87.97 at 25 °C in 10 mM of nicotinic acid at fixed temperature but decrease as the temperature of the solution increases. Nicotinic acid acts is a purely cathodic inhibitor. Moreover, the obtained thermodynamic parameters using Langmuir model suggested a physical adsorption type. A correlation was found between the corrosion inhibition efficiency and the theoretical parameters obtained by the functional density method B3LYP/ 6-31 + G (d, p). All these results indicate that the addition of NAC in the corrosive solution significantly decreases the corrosion rate.

Pickling with nitric acid is commonly practiced in industry for finishing metal surfaces. The use of inhibitors during the pickling operation is of very recent origin. The TBNBI inhibition effect on copper corrosion in 2M nitric acid solution was investigated by weight loss method in relation to the temperature (25 to 40°C) and inhibitor concentration range 10-4 to 5.10-3 M. The results show that TBNBI is a good inhibitor for copper and the inhibition efficiency increases with concentration of TBNBI but decreases with increase in temperature. The adsorption parameters 0 00(G H Sads ads a, ,)ds∆∆∆ and the activation ones **a aa(E,H,S)∆∆ for the corrosion process in inhibited and uninhibited nitric acid solution were also calculated using Arrhenius equations. It can be con-cluded that the adsorption of the compound is spontaneous and found to occur through both physisorption and chemisorption processes. The adsorbed film on copper surface was characterized using optic microscopy and Raman spectroscopy. The surface analysis confirmed the inhibition action of TBNBI. Quantum chemical calculations using Gaussian 09 at B3LYP level with 6-31G (d,p) basis set lead to obtain molecular descriptors such as EHOMO (energy of the highest occupied molecular orbital), ELUMO (energy of the lowest unoccupied molecular orbital), ∆E (energy gap) and μ (dipole moment). The global reactivity descrip-tors such asχ (electronegativity), η (hardness), S (softness) and ω (electrophilicity index) were derived using Koopman’s theorem and analyzed. We used the condensed Fukui function and softness indices, Mulliken population analysis for local reactivity study. The calculated results are consistent with the experimental data.

The corrosion inhibition of mild steel by 7-(ethylthiobenzimidazolyl) theophylline (7-ETBT) in 1 M HCl medium was investigated through weight loss and Tafel polarization techniques within a temperature range of 298 to 318 K. The inhibition efficiency depends on the concen­tration of 7-ETBT and reaction system temperature. The maximum inhibition efficiency values of 90.73 and 87.06 %, respectively, were estimated using both weight loss and Tafel polarization techniques at 298 K. The results suggest spontaneous and predominant physical adsorption of 7-ETBT on the metal surface which obeys Langmuir isotherm model. Furthermore, Tafel polarization method revealed that 7-ETBT is a mixed-type inhibitor. Po­tentiodynamic polarization results are in accordance with weight loss data to a good extent.