The Inhibited Effect of Cysteine Towards the Corrosion of Copper in Nitric Acid Solution
The detailed study of cysteine (Cys) as corrosion inhibitor for copper in nitric acid solution has been performed through weight loss, electrochemical polarization, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) measurements. The effect of inhibitor concentration, temperature and immersion time against inhibitor action was investigated. Results show that Cys may be used as an efficient inhibitor for copper in nitric acid at higher temperatures (98% at 50°C). Potentiodynamic polarization studies reveal that Cysteine acts as a mixed-type inhibitor without any change in the mechanism of hydrogen evolution. The adsorption of this compound on copper surface obeys Langmuir's adsorption isotherm and has a chemisorptions mechanism.
Cysteine as a green corrosion inhibitor for Cu37Zn brass in neutral and weakly alkaline sulphate solutions
The aim of this study was to investigate electrochemical properties of brass in neutral and weakly alkaline solutions in the presence of cysteine as a nontoxic and ecological corrosion inhibitor. Potentiodynamic measurements, open circuit potential measurements, as well as chronoamperometric measurements were the methods used during investigation of the inhibitory effect of cysteine on the corrosion behaviour of brass. Potentiodynamic measurements showed that cysteine behaves as a mixed-type inhibitor in the investigated media. Based on polarization curves for brass in a weakly alkaline solution of sodium sulphate at varying cysteine concentrations, an interaction occurs between Cu+ ions and the inhibitor, resulting in the formation of a protective complex on the electrode surface. The results of chronoamperometric measurements confirm the results obtained by potentiodynamic measurements. Optical microphotography of the brass surface also confirms the formation of a protective film in the presence of a 1 × 10−4 mol/dm3 cysteine. Adsorption of cysteine on the brass surface proceeds according to the Langmuir adsorption isotherm.
THE INFRARED SPECTRA OF 4-SUBSTITUTED-THIOSEMICARBAZIDES AND DIAZOTIZATION PRODUCTS
The infrared absorption spectra of 4-substituted-thiosemicarbazides, 5-(substituted)amino-1,2,3,4-thiatriazoles, and the corresponding isomeric tetrazolinethiones have been studied and structural assignments of importance to these systems made or suggested. Important conclusions drawn from the spectral data are: there is no suggestion of any thiol–thione tautomerism for the solid 4-substituted-thiosemicarbazides and that the thione structure predominates for these substances; that the so-called 5-thiol-tetrazoles also exist as thiones; and that the diazotization products of the 4-substituted-thiosemicarbazides yield 1,2,3,4,-thiatriazoles rather than the isomeric open chain thiocarbamyl azides. The C==S, —N—C==S, and cyclic —N—N==N— configurational assignments, which are of importance to the classes of compounds studied, are discussed.