Portugaliae
Electrochimica Acta

Compared to pure zinc plating, zinc alloys provide several advantages. A zinc alloy generally offers superior sacrificial protection to steel as since it corrodes more slowly than pure zinc. A search for a non-cyanide zinc plating bath resulted on the development of a zinc nickel sulphamate bath. To obtain better quality zinc-nickel deposits triethanolamine was added to the bath. In this paper the influence of triethanolamine in zinc-nickel plating from sulphamate bath, has been investigated through current efficiency measurements, cyclic voltammetry, scanning electron microscope, and X-ray diffraction techniques. In the presence of triethanolamine in the zinc-nickel sulphamate bath the current efficiency of alloy deposition increased to a maximum of 99% at the current density of 1.5Adm-2 and thereafter decreased. TEA adsorbed on the electrode surface obeying Henry’s isotherm. On mild steel surfaces, uniform smooth slate gray deposit with smaller crystallites was produced, in presence of TEA in solution, and the electrodeposits exhibited additional Zn(OH)2 and gamma-Ni3Zn22 phases. Hydrogen evolution was suppressed by TEA and thereby current efficiency is increased for alloy deposition.

Electrochemical response of glass carbon (GC) and edge plane pyrolytic graphite (EPPG) electrodes was investigated using electrochemical impedance spectroscopy (EIS) method in three kinds of electrolytes, i.e., 0.1 M Na2SO4 (aqueous solution), 0.1 M tetraethylammonium perchlorate (TEAP) (acetonitrile solution) and pure room temperature ionic liquids (RTILs) of 1-ethyl-3-methylimidazolium tetrafluorobroate (EMIBF4). The marked difference in the admittance plots was exhibited by the GC electrode, suggesting that the double layer occurring on GC electrode differed from each other when immersed in different electrolytes, indirectly proving the meso-porosity structure of GC electrode. While for EPPG electrode, similar results were obtained in these three selected electrolytes, which were interpreted by the “defects” in EPPG electrode.

In the past, mechanical properties have been the main criteria for selecting materials at the Miravalles Geothermal Field. Consideration of the corrosion resistance has been a secondary concern. The goal of this study was to determine the uniform corrosion rate of carbon steels currently used on pipelines (ASTM A 53, ASTM A515, ASTM A234 and API-5L) and compare this rate with the ASTM A-36 standard. The first step was the development of laboratory electrochemical and weight loss experiments. Ultrasonic thickness measurements of pipes for brine, steam and liquid-steam lines, in both straight and curve sections, showed negligible lost in material over the seven year period they have been on operation. The electrochemical study involved polarization curve analysis and corrosion rate measurements by Linear Polarization Resistance (LPR) and Electrochemical Noise Measurements (ENM). Electrochemical cells include triple and conventional testers (SCE as reference and platinum electrode as auxiliary) using brine degassed with nitrogen at 93 ± 2 ºC. According to the results, the ASTM-A36 has a similar general corrosion rate to those currently used on pipelines.

2-amino-1, 3, 4-thiadiazoles (AT), 2-amino-5-methyl-1, 3, 4-thiadiazoles (AMT), 2-amino-5-ethyl -1, 3, 4-thiadiazoles (AET) and 2-amino-5-propyl -1, 3, 4-thiadiazoles (APT) were synthesized. FT-IR and NMR studies were done in order to confirm the composition of the synthesized inhibitors. These compounds were evaluated as inhibitors for mild steel in 20% formic acid and 20% acetic acid by weight loss, potentiodynamic polarization and electrochemical impedance techniques. Scanning electron microscopic study (SEM) was also used to investigate the surface morphology of inhibited and uninhibited metal samples. The inhibition efficiency of these compounds was found to vary with the inhibitor concentration, immersion time, temperature and acid concentration. The adsorption of these compounds on the steel surface from both acids were found to obey Langmuir’s adsorption isotherm. These compounds are mixed type inhibitors in both acid solutions. Various thermodynamic parameters (Ea, ΔGads, ΔQ, ΔH, ΔS, t1/2) have also been calculated to investigate the mechanism of corrosion inhibition. Electrochemical impedance study was used to investigate the mechanism of corrosion inhibition.

Electrochemical oxidation of phenol, 4-aminophenol, 2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol, 2-hydroxybenzoic acid, 2-tert-butylphenol and 2-tert-butyl-4-methoxyphenol has been carried out at sacrificial zinc anode. The products of these reactions have been identified by elemental analysis and infrared spectral data and are found to be zinc(II) phenoxides. Though these compounds do not form coordination compounds on refluxing with 1,10-phenanthroline or 2,2'-bipyridyl, yet the coordination compounds of these phenoxides with these ligands have been synthesized electrochemically. Current efficiencies of these system are quite high.

The inhibition effect of tetra-N-butylammonium iodide (TBAI) on mild steel in 1 N H2SO4 has been studied by using weight loss, electrochemical polarization, Fourier Transform Infrared (FTIR) and scanning electron microscopic (SEM) techniques. It has been concluded that the percentage inhibition increases with increasing the concentration of the inhibitor. The adsorption of TBAI on mild steel surface in 1 N H2SO4 obeys Langumir adsorption isotherm; surface analysis and IR studies are also carried out to establish the mechanism of corrosion inhibition.

Electrochemical methods were used to investigate the abilities of the homologous straight chain monocarboxylates (CnH2n+1COO-,n=1-13) to inhibit the pitting corrosion of two types of copper alloys in aerated, saline and near neutral aqueous solutions. The copper alloys were alloy (I) (Cu + 4.47% Fe) and alloy (II) (Cu + 10.67% Al + 5.02% Fe). It was found that these were susceptible to pitting corrosion in NaCl solutions, with increase of Cl- ions concentration. Alloy (II) was more susceptible to pitting corrosion than alloy (I). The performance of monocarboxylates was shown to be critically dependent upon their chain length. The range of chain lengths producing optimal inhibition was (6  n  10). These carboxylates showed abrupt decreases in inhibitor ability outside the optimal range. The dramatic variations in inhibition efficiencies probably resulted from competing reactions such as adsorption, solubility and micelle formation.

The comparative study of corrosion behaviour of brasses 70Cu30Zn and 60Cu40Zn in HNO3 solution in absence and in presence of 1-phenyl-5-mercapto-1,2,3,4-tetrazole (PMT) was studied by gravimetric and electrochemical methods. Results obtained are in good agreement and reveal that the corrosion rate depends on immersion time and zinc content in the alloy. Copper and zinc losses from each specimen studied, at various immersion times, were estimated by Atomic Adsorption Spectroscopic analysis. This shows that the inhibition efficiency of the inhibitor towards copper is more significant than zinc. PMT was adsorbed preferentially on the copper surface and inhibits the process of corrosion of brasses in the nitric acid medium.

Electrodeposition of Ni-Ce alloy on steel was studied and an electroplating bath was optimized for maximum cathodic current efficiency. Cerium sulphate content in the bath decreased the cathodic current efficiency. Hydrogen evolution reaction from NaOH solution was catalysed by cerium in the alloy and also the increase of cerium content increased the catalytic activity. Among the various Ni-Ce alloys, Ni77Ce23 alloy offered the maximum catalytic activity.