A. S. Fouda

Inhibition of the corrosion of iron by oxygen and nitrogen containing compounds

SummaryCorrosion inhibition by quinine, ephedrine, brucine, cinchonine, codeine, and harmaline with respect to the dissolution of iron in 2M sulphuric acid was measured using electrochemical methods. Polarization curves indicated that these compounds act as mixed-type inhibitors,i.e. both the cathodic and anodic curves are affected. The observed effect follows theTemkin adsorption isotherm. The effect of the different structural features of these compounds on their inhibition efficiency has been studied. Results indicate that the rate of corrosion of iron increases with increasing temperature over the range 30–50 °C both in the absence and in the presence of inhibitors. Some thermodynamic functions were also computed and are discussed.ZusammenfassungDie von Chinin, Ephedrin, Brucin, Chinchonin, Codein und Harmalin ausgeübte Korrosionshemmung bei der Auflösung von Eisen in 2M Schwefelsäure wurde mittels elektrochemischer Methoden untersucht. Polarisationskurven zeigen, daß die erwähnten Verbindungen als Inhibitoren gemischten Typs fungieren, d. h. sowohl die kathodische als auch die anodische Kurve wurde beeinflußt. Der beobachtete Effekt folgt derTemkinschen Adsorptionsisotherme. Die Auswirkung von Strukturänderungen auf die Effizienz der Hemmung und einige thermodynamische Funktionen werden diskutiert. Die Korrosionstrate von Eisen steigt sowohl in Gegenwart als auch in Abwesenheit der Inhibitoren im Bereich von 30–50°C mit steigender Temperatur.

Standard potentials of the (silver+silver chloride) electrode and the thermodynamic behaviour of hydrochloric acid in (ethanol+water) at 288.15 to 328.15 K

Abstract Electromotive-force measurements of cells of the type: Pt|H 2 (g)z.sfnc;HCl (m) in (ethanol + water)z.sfnc;AgClz.sfnc;Ag , at nine temperatures from 288.15 to 328.15 K have been used to determine the standard e.m.f. of the cell in 20 (ethanol + water) solvents containing up to 100 mass per cent ethanol. The standard e.m.f. was determined by an extrapolation method making use of the extended terms of the Debye-Huckel theory. In solvents of high alcohol content, where the dielectric constant is small, it was necessary to correct for ion-pair formation. The molality m of HCl ranged from 0.005 to 0.1 mol kg −1 . The temperature variation of the standard e.m.f. was used to calculate the standard thermodynamic functions for the cell reaction, the primary medium effects of various solvents upon HCl, and the standard quantities for the transfer of HCl from the standard state in water to the standard states in the respective (ethanol + water) solvents.

Thermodynamic properties of hydrobromic acid in ethanol + water solvent mixtures from electromotive force measurements at 15–55°C

Abstract From the electromotive force measurements of cells of the type: Pt, H 2 (gas, 1 atm); HBr ( m ), ethanol + water solvent mixtures; AgBr, Ag, at nine different temperatures in the range 15–55°C and in the molality range of HBr from 0.005 to 0.1 mol kg −1 , the standard potentials of silver—silver bromide electrode have been determined in twenty ethanol + water solvent mixtures covering the whole range of solvent composition. The temperature variation of the standard potential was utilized to calculate the standard thermodynamic functions for the cell reaction, the primary medium effects of various solvents upon HBr, and the standard quantities for the transfer of HBr from the standard state in water to the standard states in the respective solvent media. The results have been interpreted in regard to the acid-base properties and structure of the solvents.

Efficiency of some phenylthiosemicarbazide derivatives in retarding the dissolution of Al in NaOH solution

Five derivatives of phenylthiosemicarbazide have been prepared and treated as inhibitors for the corrosion of aluminium in 2M sodium hydroxide. All the five substances afford 98.5 to 75% protection to aluminium in sodium hydroxide. 1(-Methoxybenzoyl)-4-phenyl-3-thiosemicarbazide being the most efficient inhibitor. Thermometric and weight loss methods indicate that the inhibition is principally governed by the adsorption of these compounds on the surface of the aluminium metal and the adsorbability of inhibitors is dependent on the basicity of the oxygen and sulphur sites involved.ZusammenfassungEs wurden fünf Derivate von Phenylthiosemicarbazid hergestellt und als Inhibitoren für die Korrosion von Aluminium in 2M NaOH eingesetzt. Die Substanzen ergaben 98.5 bis 75% Schutz für Aluminium in NaOH. Dabei war 1-(Methoxybenzoyl)-4-phenyl-3-thiosemicarbazid der effizienteste Inhibitor. Thermometrische und Gewichtsverlustmethoden zeigten, daß die Inhibition prinzipiell von der Adsorption dieser Verbindungen auf der Metalloberfläche gesteuert wird, wobei die Adsorbierbarkeit der Inhibitoren von der Basizität der teilnehmenden Sauerstoff- und Schwefelfunktionen abhängt.

Thermodynamic studies of hydrobromic acid in (ethylene glycol + water) from electromotive-force measurements

Standard potentials of the (silver + silver bromide) electrode in 20 (ethylene glycol + water) solvents, covering the whole range of solvent composition, have been determined from electromotive-force measurements of cells of the type: Pt|H2(g)|HBr(m) in solvent &.sfnc;AgBr|Ag at 9 different temperatures from 288.15 to 328.15 K. The molality m of the acid ranged from 0.004 to 0.1 mol · kg−1. The temperature variation of the standard e.m.f. was used to calculate the standard thermodynamic functions for the cell reaction, the primary medium effects of various solvents upon HBr, and the standard quantities for the transfer of HBr from water to the solvents, and the results have been discussed.

Standard potentials of the silver—silver bromide electrode in dioxane—water mixtures and related thermodynamic functions

Abstract The standard potentials of AgAgBr electrode in eighteen dioxane + water solvent mixtures containing up to 90 wt % dioxane, have been evaluated from the emf measurements of the cell Pt, H 2 (g, 1 atm); HBr (m), X % dioxane, Y % water: AgBr, Ag at nine different temperatures in the range 15–55°C. The standard molal potentials in each solvent have been represented as a function of temperature. The standard thermodynamic functions for the cell reaction, the primary medium effects of various solvents upon HBr and the standard thermodynamic quantities for the transfer of one mole of HBr from water to the respective dioxane + water media have been computed and discussed in the light of ion—solvent interactions as well as the structural changes of the solvents.

Standard potentials of the silver, silver bromide electrode in tetrahydrofuran and tetrahydrofuran + water mixtures at different temperatures and related thermodynamic quantities

The standard potentials of the Ag, AgBr electrode have been determined in tetrahydrofuran (THF) and in nineteen THF + water solvent mixtures from the e.m.f. measurements of the cell Pt|H2(g, 1 atm)| HBr(m), solvent|AgBr (s)|Ag at intervals of 5 °C from 5 to 45 °C. In solvents of high THF content, where the dielectric constant is small, it was necessary to correct for ion-pair formation. The temperature variation of the standard potential has been utilized to evaluate the standard thermodynamic functions for the cell reaction and the standard thermodynamic quantities for the transfer of HBr from water to the respective solvents. The results are discussed in the light of ion–solvent interactions as well as the structural changes of these solvents.

Standard potentials of the silver/silver bromide electrode and related thermodynamic quantities in propan-2-ol + water mixtures

Standard potentials of the Ag, AgBr electrode in eighteen propan-2-ol + water mixtures have been determined from e.m.f. measurements on the cell Pt|H2(g, 1 atm)|HBr (m), solvent|AgBr|Ag at nine temperatures from 15 to 55°C at 5°C intervals. These values were used to evaluate the standard thermodynamic functions for the cell reaction, the primary medium effects of various solvents upon HBr and the standard thermodynamic quantities for the transfer of one mole of HBr from water to propan-2-ol + water solvents. The results have been discussed in the light of ion–solvent interactions as well as the structural changes of these solvents.

Unused clopidogrel drug as eco-friendly corrosion inhibitor for carbon steel in aqueous media

Effect of Clopidogrel drug on the corrosion of carbon steel in 2 M HCl solution has been investigated by various corrosion monitoring techniques. Results obtained reveal that this drug is very good inhibitor. Polarization studies clearly reveal the type of the inhibitor. Changes in impedance parameters (Rct and Cdl) are indicative of adsorption of the drug on the C-steel surface leading to the formation of a protective film. The adsorption of the drug on the C-steel surface follows Temkin adsorption isotherm. The morphology of inhibited carbon steel surface was analyzed and characterized by Fourier transform–infrared (FT-IR) and (UV/vis) spectroscopy. The mechanism of protection process was discussed in terms of the adsorption of Clopidogrel on the metal surface.

Electrochemical assessment of inhibitive behavior of some antibacterial drugs on 316 stainless steel in acidic medium

In this work, the inhibitive effect of some antibacterial drugs against the corrosion of 316 stainless steel in 1M HCl has been studied by weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The inhibiting effect explained by adsorption of the additives on steel surface. The inhibition efficiency increases with increasing the inhibitors concentrations and decreases with increasing the temperature. The data obtained fit well to Langmuir adsorption isotherm and the kinetic-thermodynamic model. The results of polarization studies indicate that the investigated antibacterial drugs are mixed type inhibitors. Increasing the inhibition efficiency of the investigated inhibitors with the addition of iodide ions indicates that iodide ions play important role in the adsorption process. The efficiencies obtained from the different electrochemical techniques were in good agreement which prove the validity of these tools in the measurements of the tested inhibitors.