Portugaliae
Electrochimica Acta

Aromatic nitrones have been synthesized and investigated for their function as inhibitor for the corrosion of mild steel in the organic acid media – 20% formic acid and 20% acetic acid at various inhibitor concentrations in the range of 50 - 150 ppm. Weight loss measurements and potentio-dynamic polarization studies reveal that the nitrones behave as mixed type inhibitors. Among the nitrones tested, para-methyl substituted derivatives perform better as inhibitors than the un-substituted nitrones.

The inhibitive effect and adsorption properties of petiole extract obtained from destructive distillation of cocos nucifera for the corrosion of mild steel in 0.5 M H2SO4 and 1 M HCl were investigated using mass loss, polarization and electrochemical impedance techniques of monitoring corrosion. The results obtained indicate that petiole extract of cocos nucifera behaves as good inhibitor for the corrosion of mild steel in 0.5 M H2SO4 and 1 M HCl. Activation energy of thermodynamic parameter was evaluated from temperature studies result. The adsorption of the inhibitor on mild steel surface was found to be spontaneous, endothermic and consistent with the assumptions of Langmuir adsorption isotherm. The electrochemical measurements reveal that the petiole extract behaved like mixed type inhibitor. Efforts are made to analyze the effectiveness of petiole extract of coconut palm in industrial processes.

Properties of electrodeposited Ni-composite coatings containing ceramic particles are very much dependant on the bath used, current density, duration of deposition, particle content in the bath, etc. In the present study, the influence of process parameters like the concentration of particles, current density and time of deposition on the area fraction of yttria stabilized zirconia (YSZ), the microhardness and the thickness of the electrodeposited nickel (Ni)-YSZ composite coating was analyzed by Taguchi Design method and analysis of variance (ANOVA). According to the experimental results and ANOVA, the interaction of current and time are the most significant factors influencing the thickness of the coating; interaction of concentration of particles in the electrolyte bath and current are the most significant factors influencing the microhardness; and concentration of particles in the electrolyte bath is the most significant factor affecting the area fraction of particles in the Ni matrix. Models were developed for predicting the microhardness and thickness of the composite coating and area fraction of particles incorporated in the nickel matrix. They were found to be in good agreement with the experimental results. The models were tested for experimental conditions and were found to be close to predicted values. The thickness of the deposit was mainly dependent on the current density and duration of plating. On the other hand, the microhardness of the coating and area fraction of particles present in the nickel matrix were mainly dependent on the amount of particles present in the bath.

The inhibition efficiency of natural phosphate and kaolin systems in controlling corrosion of stainless steel in HClO4 (0.1 M) solution has been evaluated by electrochemical polarization methods, and electrochemical impedance spectroscopy. The electrochemical data show that the corrosion resistance is greatly enhanced after surface modification. The best protection is obtained with natural phosphate. The uniform coatings of phosphate and kaolin on iron substrates were obtained by electro deposition.

The effect of N-[N`-(4-methoxyphenyl)benzenesulphonamido]-3-carboxy-4-methyl-4-(4-methylphenyl)-3-butenamide 1, N-(N`-phenylbenzenesulphonamido)-3-carboxy-4-methyl-4-(4-methylphenyl)-3-butenamide 2, and N-[N`-(4-chlorophenyl)benzenesul-phonamido]-3-carboxy-4-methyl-4-(4-methylphenyl)-3-butenamide 3, on the corrosion of low carbon steel in 1 M hydrochloric acid solution has been studied by weight loss measurements and potentiodynamic technique over the temperature range 30-60 °C. Results obtained showed that protection efficiency increased with the increase in concentration of the different organic compounds used and decreased with the increase in temperature. Langmuir adsorption isotherm at all temperatures was studied. The phenomenon of physical adsorption is proposed from the values of Ea and ∆G˚ads. Results obtained showed that compound 1 is the best inhibitor, and the protection efficiency follows the order: 1 > 2 > 3.

The influence of 2-[3-(2-oxo-2-phenylethylidene)-1,4-dihydroquinoxaline-2(1H)-ylidene]-1-phenylethanone (Qx1) and amino-2-aniline (Diam1) on the corrosion of steel in 1 M HCl solution has been investigated by weight loss measurements, potentiodynamic polarisation and impedance spectroscopy (EIS) methods. The inhibiting action increases with the concentration of Qx1 and Diam1. The highest efficiency (85%) is obtained at the 10-4 M Qx1. There is good agreement between gravimetric and electrochemical methods (potentiodynamic polarisation and EIS). Polarisation measurements also show that Qx1 and Diam1 act as mixed inhibitors. The cathodic curves indicate that the reduction of proton at the steel surface happens with an activating mechanism. Qx1 adsorbs on the steel surface according to Langmuir adsorption model. Effect of temperature is also studied between 308 and 353 K.