Bogdan Tutunaru

Surface Analysis of Inhibitor Film Formed by 4-Amino-N-(1,3-thiazol-2-yl) Benzene Sulfonamide on Carbon Steel Surface in Acidic Media

ABSTRACT Inhibitive properties of the antibacterial sulfa drug sulfathiazole—IUPAC name being 4-amino-N-(1,3-thiazol-2-yl) benzene sulfonamide—on the corrosion of carbon steel in 1.0 M HCl solution were investigated using weight loss measurements, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Sulfathiazole is a good adsorption inhibitor, and the inhibition efficiency increases with increasing concentration. Adsorption is spontaneous and is best described by Temkin isotherm. XPS analysis showed, at this stage, that the main product of corrosion is a nonstoichiometric Fe3+ oxide/oxyhydroxide consisting of a mixture of Fe2O3, α, and γ-FeO(OH) and/or Fe(OH)3, where α, γ-FeO(OH) is the main phase.

Thermal analysis of corrosion products formed on carbon steel in ammonium chloride solution

The influence of different ions NO3− and SO42− on the carbon steel corrosion in ammonium chloride was investigated using mass loss measurements and potentiodynamic polarization. Corrosion products were analyzed using X-ray photoelectron spectroscopy (XPS) and simultaneous thermal and differential scanning calorimetry (TG/DSC). XPS analysis shows that the main product of corrosion is a non-stoichiometric Fe3+ oxyhydroxide, consisting of a mixture of FeO(OH) and FeO(OH) containing inclusions of these anions, species such as Fe3+O(OH,Cl−); Fe3+O(OH,SO42−); and Fe3+O(OH,NO3−). TG/DSC confirms the decomposition of the rusty products formed by chemical corrosion, compounds like Fe3+ oxyhydroxides, with β-FeOOH as the major phase, crystal structure of which may contain Cl−, NO3−, and SO42−—e.g., akaganeite [Fe3+O(OH,A)].

Adsorption and inhibitive properties of a Schiff base for the corrosion control of carbon steel in saline water.

A Schiff base, namely N-(2-hydroxybenzylidene) thiosemicarbazide (HBTC), was investigated as inhibitor for carbon steel in saline water (SW) using electrochemical measurements such as: potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The morphology of the surfaces before and after corrosion was examined by Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM/EDS). The results showed that HBTC acts as corrosion inhibitor in SW by suppressing simultaneously the cathodic and anodic processes via adsorption on the surface which followed the Langmuir adsorption isotherm; the polarization resistance (Rp) and inhibition efficiency (IE) increased with each HBTC concentration increase. SEM/EDS analysis showed at this stage that the main product of corrosion is a non-stoichiometric amorphous Fe3+ oxyhydroxide, consisting of a mixture of Fe3+ oxyhydroxides, α-FeOOH and/or γ-FeOOH, α-FeOOH/γ-FeOOH and Fe(OH)3.

Quinine sulfate: a pharmaceutical product as effective corrosion inhibitor for carbon steel in hydrochloric acid solution

Quinine sulfate dihydrate (QNS), IUPAC name: (8S,9R)-6-methoxy-4-quinolenyl-5-vinyl-2-quinuclidinyl methanol sulfate dihydrate, was tested as corrosion inhibitor for carbon steel in 1.5 mol L−1 HCl solution using the potentiodynamic polarization and the electrochemical impedance spectroscopy (EIS) associated with UV-Vis spectrophotometry. The electrochemical results showed that, the inhibition efficiency (IE) increased with the increase in QNS concentration, reaching a maximum value of 93.35±0.25%. The polarization resistance (Rp) followed the same trend, obtaining the highest value of 659.7 Ω cm2, while the corrosion current density (icorr) reached the lowest level of 195 µA cm−2. The action mechanism of QNS was proposed considering the ability of quinine (QN) to be adsorbed on the metal surface via the lone pairs of electrons from hydroxyl oxygen atom, and/or from quinoline and quinuclidinic nitrogens. The occurrence of the complexes between inhibitor and iron ions was considered an additional process, which may contribute to protective layer formation. The Temkin adsorption isotherm was found as the best fitting for the degree of surface coverage (θ) values. In order to elucidate the mechanism of protective layer formation, the free energy of adsorption (ΔGoads) value was calculated. This indicates that the inhibitor acts by chemical adsorption on the steel surface.

Catalytic Activity of Thallium on Electrochemical Degradation of Metronidazole from Aqueous Solutions

The platinum/thallium electrode was prepared by thallium electrodeposition on platinum substrate in order to use it for the increase of the electrochemical degradation rate of some drugs, such as, in our study, metronidazole (MNZ). The platinum/thallium electrode was characterized by chronoamperometry, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. 2D progressive nucleation mechanism of thallium layer development was found by chronoamperometry. The value of charge transfer resistance of 537.2 Ω cm2 and the double-layer capacitance value of 2.9 mF cm−2 were deduced by EIS. The scanning electron microscopy showed a relatively fine-grained structure and the uniform distribution of the thallium granules. The electrochemical degradation of metronidazole has been performed using galvanostatic technique associated with UV-Vis spectrophotometry. The degradation degree of metronidazole reached a higher level on platinum/thallium electrode than that on platinum plate, indicating its improved performance and electrocatalytic activity of thallium coating. Moreover, the electrochemical degradation mechanism of this drug was proposed, the best way to fit the experimental data being the kinetics model of the first-order reactions.