Portugaliae
Electrochimica Acta

A new alkaline electrolytic solution based on ammonia for copper electroplating has been investigated. Upon addition of alkaline metal hydroxide solution and ammonia followed by the immediate addition of a strong inorganic acid, a highly exothermic reaction takes place. At optimum solution condition ammonia remains in solution as NH2 and forms a complexing agent.

The corrosion behaviour of 1018, 410 and 800 steels exposed to synthetic wastewater has been studied using linear polarization resistance (LPR), cyclic potentiodynamic curves (CPC), electrochemical noise (EN), and electrochemical impedance spectroscopy (EIS) tests. The conditions were: biochemical oxygen demand (BOD) of 776 ppm, a chemical oxygen demand (COD) of 1293 ppm, pH = 8 and the cell temperature was 24 °C. From the CPC and EN results, no localized corrosion was found for the stainless steels. However, the reverse was true for the 1018 steel. The EIS results showed that different corrosion mechanism occurred for the carbon steel compared with the stainless steels. This shows that the corrosion mechanism strongly depends on the type of steel. Overall, the 1018 steel exhibited the highest corrosion rate, followed by the 410 alloy. The highest corrosion resistance was achieved by the 800 alloy. In addition, SEM analyses were carried out to explain the experimental findings.

Electroless nickel (EN) process is the controlled auto catalytic reduction of nickel ions using suitable reducing agent such as sodium hypophosphite on certain catalytic surfaces, which results in the production of sound, coherent coatings for a number of applications. Frequently the rate of deposition of EN with hypophosphite as reducing agent is below 20 microns per hour. Hence the deposition of the electroless nickel with hypophosphite solution in the presence of small concentration of thiourea and its derivatives as accelerators is investigated. The mechanism of accelerated deposition is studied by impedance measurements. The performance of various additives during the plating process is being evaluated by increased Constant Phase Element (CPE) and decreased charge transfer resistance values. A model is proposed for the adsorptive behavior of additives.

The effect of different concentrations of 1,3-dihydroxypropane (DHP) on the electrodeposition of copper powder from acidified copper sulphate solution has been studied at different temperatures and different speeds of rotation. Copper powder was electrodeposited onto rotating cylinder electrode (RCE) that made of pure copper. The inhibition percentage, P, in the electrodeposited copper powder was 0.00 – 92.91%, depending on the experimental variables. P was affected by temperature and mole fraction of DHP, while rotation did not show any influence whatsoever. Values of the activation energy of electrodeposition process, Ea, were found to be less than 28 k J mol-1 indicating diffusion controlled process. The overall mass transfer correlations under the present conditions have been obtained using the dimensional analysis method. The data were valid for 80 < Sh (Sh = Sherwood number) < 3970, 290 < Sc (Sc = Schmidt number) < 59284 and 271 < Re (Re = Reynolds number) < 52705 and the results agreed with the previous studies of mass transfer to rotating cylinders in turbulent flow regimes. Experimental determination of the solution critical velocity was obtained for blank and 20% (v/v) DHP solutions at 298 K. The effect of time, DHP content, temperature and the speed of rotation on the morphological changes of the electrodeposited copper powder as well as deposits composition and particle size have been studied. Various particle sizes ranged 60.5 – 203.4 nm were obtained, characterized by EDS and XRD and found to be pure copper with small amount of oxygen. Different topographs proved that the rate of copper electrodeposition increased by increasing time, temperature and the speed of rotation. In addition, they proved that the deposition rate decreased by adding DHP to the solution. Therefore, the results obtained by SEM supported those results obtained by electrochemical measurements. The morphological structure of deposited copper powder from 20% (v/v) DHP at 1000 rpm and 298 K was unique, rounded-crystalline aggregates with voids.

This work presents the results of corrosion inhibition of muntz alloy (63% Cu,  37% Zn) in 1.0 M HCl by water extracts of some naturally occurring plants. These are: outer brown skin of onion (A), onion bulb (B), the cloves of garlic bulb (C), orange peels (D), and henna leaves (E). The techniques of measurements for the determination of the amount of each zinc and copper dissolved from the alloy in the aggressive solution were: weight-loss, galvanostatic polarization, linear polarization and atomic absorption spectroscopy. From these measurements the values of surface coverage, , and inhibition efficiency were calculated. It was found that the investigated extracts have high inhibition efficiency on the corrosion of muntz alloy in 1.0 M HCl. Their inhibition efficiency decreases according to the order: C > D > E > B > A. These extracts behave as mixed inhibitors, i.e., they affect both the cathodic and anodic processes. The activation energy of corrosion was calculated in absence and in presence of extracts. It was found that the presence of extracts in 1.0 M HCl solutions increases the values of activation energy of corrosion in that order of their inhibition efficiency. The inhibiting effect of these extracts results from their adsorption on the electrode surface via the adsorption centers of the compounds present in the extracts. The adsorption of these extracts onto the surface of muntz follows Frumkin,s isotherm. The atomic absorption spectroscopic measurements showed that the presence of these extracts greatly inhibits the preferential dissolution of zinc from the alloy and the occurrence of simultaneous dissolution of both zinc and copper.

The effect of natural occurring extract of artemisia on the corrosion of steel in 0.5 M H2SO4 in the temperature range 298 – 353 K is studied by weight loss method, electrochemical polarisation and linear polarisation Rp measurements. Results obtained reveal that extract reduces the corrosion rate. The inhibition efficiency increases with the increase of artemisia content at 10 g/L to reach 95% and 99% at 298 and 353 K, respectively. Results obtained by gravimetric and electrochemical polarisation are in good agreement. Polarisation studies clearly reveal that the presence of the natural artemisia does not change the mechanism of the hydrogen evolution reaction and acts as a mixed type inhibitor. The inhibition efficiency increases with temperature. The adsorption of artemisia on the steel follows Langmuir adsorption isotherm.