S.S. Abd El Rehim

Electrodeposition of noncrystalline cobalt-tungsten alloys from citrate electrolytes

Induced electrodeposition of Co–W alloys onto steel substrates from acid citrate baths has been investigated. The effects of some plating parameters, such as current density, pH and temperature on the potentiodynamic cathodic polarization curves, cathodic current efficiency of the alloy and the percentage tungsten in the alloy were studied. Highly adherent and compact Co–W alloys codeposited from citrate baths containing up to 28 mass % tungsten were obtained. The percentage W (w/w) in the alloy increases with increasing pH, bath temperature and Co2+ ion concentration. On the other hand, the percentage W in the alloy decreases with increasing current density. Anodic linear stripping voltammetry (ALSV) indicated that the alloy might consist of one phase solid solution. These alloys were determined to be noncrystalline by X-ray diffraction analysis.

ELECTROPLATING OF ZINC-NICKEL BINARY ALLOYS FROM ACETATE BATHS

Zinc-nickel binary alloys have been successfully electrodeposited onto steel sheets from baths containing zinc acetate, nickel acetate and acetic acid (pH 4.4–4.6). The potentiodynamic cathodic polarization, cathodic current efficiency, morphology and composition of the deposits were determined for a variety of bath composition, temperature, current density and superimposed ac on dc. The baths are characterized by high cathodic current efficiency for co-deposition. The co-deposition shows an anomalous behaviour with zinc being the preferentially deposited metal. X-ray tests revealed the presence of a single γ-phase (rich-zinc alloys) with body centered cubic structure.

Pitting corrosion of zinc in Na2SO4 solutions and the effect of some inorganic inhibitors

Abstract The pitting corrosion behaviour of Zn in neutral (pH 6.8) Na2SO4 solutions was studied by using potentiodynamic and cyclic voltammetry techniques and complemented by X-ray analysis under the effect of electrolyte concentration, scan rate, temperature and pH. The voltammograms involve active/passive transition prior to the initiation of pitting corrosion. The active region displays one anodic peak. The passivity is due to the formation of ZnO film on the anode surface. The critical pitting potential decreases with increasing sulphate ion concentration and temperature but decreases with scan rate. Increasing the acidity or alkalinity of the medium enhances the pitting corrosion. The effects of adding increasing concentrations of Cr 2 O 2− 7 , CrO 2− 4 , WO 2− 4 , MoO 2− 4 and NO − 2 anions on sulphate pitting corrosion of Zn were investigated. These anions inhibit the active dissolution and pitting corrosion and the extent of inhibition depends upon the type and concentration of the inhibitors. The adsorption characteristics of these anions on the electrode surface plays a significant role in inhibition.

Inhibition of chloride pitting corrosion of tin in alkaline and near neutral medium by some inorganic anions

Abstract The effect of dichromate, chromate, molybdate, nitrite and nitrate anions on the chloride pitting corrosion of tin in each of the following solutions: Na 2 CO 3 ( pH = 10.9), Na 2 B 4 O 7 ( pH = 8.35) and Na 2 SO 4 ( pH = 6.8) (each solution containing 0.1 M NaCl) has been studied. The potentiodynamic technique was used, complemented by X-ray and SEM. Addition of increasing concentrations Cr 2 O 7 2− , CrO 4 2− or MoO 4 2− caused a shift of the pitting potential ( E pit ) in the positive direction indicating the inhibitive effect of the added anions on the pitting corrosion. The absorption characteristics of these anions on the metal surface plays a significant role in inhibition. The NO 2 − anion has a little inhibitive effect of pitting corrosion but the NO 3 − anion is ineffective as an inhibitor, and actually increases pitting corrosion. The pitting corrosion of chloride ions and other aggressive anions in the solutions is completely suppressed at concentration

Electroplating of copper films on steel substrates from acidic gluconate baths

/0.01 M sodium dichromate. The MoO 4 − species limits the growth of the passive film, restricts Cl − anions and inhibits the pitting corrosion.

Electrodeposition of cobalt from gluconate electrolyte

Abstract Electroplating of thin films of copper onto steel substrate from acidic gluconate bath has been investigated under different conditions of bath composition, pH, current density, and temperature. A detailed study has been made about the effect of these parameters on potentiodynamic cathodic polarization, cathodic current efficiency (CCE%), and throwing power (TP) of the bath. Fine grained, highly adherent and smooth bright deposits were produced. X-ray diffraction analysis showed that these deposits were produced in one phase with crystalline cubic structure. The optimum conditions are: 10 g l−1 CuSO4·5H2O, 30 g l−1 C6H11O7Na, 10 g l−1 K2SO4, pH=2.2, I=2.8 mA cm−2, and temperature range between 22°C and 31°C. The TP of the bath is greatly improved by increasing the current density.

The influence of some sulphur-containing anions on the anodic behaviour of zinc in an alkaline medium

Cobalt electrodeposited onto steel substrate was carried out from solutions containing cobalt sulfate, boric acid and sodium gluconate. The study dealt with the influence of bath composition, current density, pH and temperature on the potentiodynamic cathodic polarization curves, cathodic current efficiency, and throwing power, as well as the throwing index of these baths. The microhardness of cobalt electrodeposited from gluconate baths is generally high and higher than that of cobalt deposited under similar conditions from sulfate, chloride, bromide and acetate baths. The surface morphology of the as-deposited cobalt was investigated using scanning electron microscopy (SEM) while the structure was studied using X-ray diffraction analysis. Cyclic voltammetric, as well as current-transient, techniques recorded on a glassy carbon electrode suggested that the deposition of cobalt from gluconate bath occurs via a nucleation process under charge transfer control.

Electroplating of iron from alkaline gluconate baths

Abstract The anodic behaviour of Zn in 0.1 M NaOH containing various concentrations of Na2SO4, Na2SO3, Na2S, Na2S2O3 or NH4SCN was studied by means of the potentiodynamic technique, complemented by X-ray diffraction analysis and scanning electron microscopy. In the absence of sulphur-containing anions in solution, the cyclic voltammogram displays two anodic peaks in the forward scan prior to reaching the oxygen evolution potential. The first anodic peak A1 is related to the electroformation of Zn(OH)2, while the more positive peak A2 is assigned to the formation of ZnO2. The reverse scan exhibits a reactivated anodic peak A3 and one cathodic peak C1 prior to reaching the hydrogen evolution potential. The presence of either SO2−4 or SO2−3 stimulates the active dissolution of Zn while the presence of S2− (and/or SH−), S2O2−3 or SCN− inhibits it, presumably as a result of electroformation of sulphur-containing solid phases preceding the formation of Zn(OH)2. Also, the presence of one of the cited anions studied in the alkali solution produces pitting of Zn at a certain specific pitting potential. The existence of pitting is confirmed by scanning electron microscopy. The aggressiveness of the sulphur species decreases in the order SCN− > SO2−4 > SO2−3 > S2O2−3 > S2−. The pitting potential decreases with increasing concentration of the sulphur species.

Electrodeposition of Sn-Co alloys from gluconate baths

Abstract Electroplating of iron onto copper substrates from non-polluting baths containing ferrous sulfate and sodium gluconate has been investigated under different bath composition, pH, temperature and current density conditions. A detailed study has been made on the influence of these parameters on potentiodynamic polarization curves, cathodic current efficiency and throwing power of the baths. The optimum plating bath has been found to be: 0.072 mol/l FeSO4·7H2O, 0.23 mol/l sodium gluconate, pH 12, current density of 0.167 A dm−2 and at 25 °C. This bath is characterized by an excellent throwing power. The surface morphology of the as-deposited iron was investigated by using scanning electron microscope (SEM) while the crystal structure was examined by using X-ray diffraction analysis.

Studying the corrosion inhibition of carbon steel in hydrochloric acid solution by 1-dodecyl-methyl-1H-benzo[d][1,2,3]triazole-1-ium bromide

Electrodeposition of Sn-Co alloys was carried out from baths containing 2–20 g dm−3 SnSO4, 4–18 g dm−3 CoSO4.7H2O, C6H11O7Na and K2SO4 under different conditions of bath composition, pH, current density and temperature on to copper substrates. The influence of these variables on the cathodic potential, cathodic current efficiency and composition of the deposit were studied. The results show that the deposition of Sn-Co alloys from gluconate baths depends greatly on the concentration of tin. At high tin concentrations, tin is the more noble component. At low tin concentrations, tin reduction is strongly suppressed due to the formation of a more stable Sn-gluconate complex species and tin becomes the less noble component. The codeposition of Sn-Co alloy from these baths can be classified as an irregular plating system. The surface morphology of deposits was examined by scanning electron microscopy and crystal structure by X-ray. The results show that the structure of the deposits was controlled by the alloy composition.