A. Gomes

Potentiostatic and AFM morphological studies of Zn electrodeposition in the presence of surfactants

Zinc electrodeposition onto a steel substrate in the presence of surfactants with different charged head groups, namely, anionic sodium dodecylsulfate (SDS), cationic dodecyltrimethylammonium bromide (CTAB), and nonionic octylphenolpoly(ethyleneglycolether) n , n = 10 (Triton X-100), was studied by both chronoamperometric and atomic force microscopy (AFM) techniques. AFM analysis shows that Zn electrodeposition, in the absence of surfactants, begins in the underpotential deposited (UPD) region with the formation of different-sized circular aggregates with a random distribution, which indicates that progressive nucleation takes place. In the presence of SDS, CTAB, and Triton X-100 no change of the electrodeposit morphology is observed as a function of the surfactant presence. The Zn UPD deposition is confirmed by chronoamperometric measurements performed in this potential region. In what concerns the bulk deposition region, where the hydrogen evolution that goes together with the zinc deposition, the analysis of the current-time transients indicates that the Zn electrodeposition occurs by instantaneous nucleation and three-dimensional growth controlled by diffusion in the surfactant-free solution and in the presence of SDS. When the CTAB and Triton X-100 were added to the bath, change from instantaneous to progressive nucleation arises as a consequence of the simultaneous adsorption of the surfactant that inhibits the nucleation sites. The kinetic parameters values obtained from the Heerman and Tarallo model are in accordance with the dimensionless analysis of the transients. AFM confirms the effect of surfactants on the zinc bulk deposition.

Effect of the substrate on the electrodeposition of iron sulphides

The electrodeposition of iron sulphides films on titanium and Ebonex®, in aqueous solutions containing iron(II) ions and colloidal sulphur, has been assessed at 333 K, using periodic pulse electrolysis. Mackinawite was the only crystalline iron sulphide phase identified on the deposit. The structural and morphological characterization of the sulphide films obtained on both substrates was accomplished by X-ray powder diffraction (XRD) and scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM/EDS). The results show that the film structure and morphology are sensitive to the substrate material.

Voltammetric study of the Fe-S-Ebonex® system

A voltammetric study of the Fe-S-Ebonex® system at pH 3 is reported. Aqueous solutions of Na2S2O3 and (NH4)2Fe(SO4)2 were used as sources of sulphur and iron, respectively. The influence of the starting potential on the electrochemical behaviour of the system is analysed. Deposits obtained at −1.1 V vs SCE, by potentiostatic methods, show X-ray diffraction peaks of the pyrite structure. Troilite and mackinawite phases are also identified.

Studies on the Stability of Zn and Zn – TiO2 Nanocomposite Coatings Prepared by Pulse Reverse Current

Zn―TiO 2 nanocomposite thin films were obtained from the occlusion electrodeposition method using pulsed reverse current electrolysis, from acidic zinc sulfate solutions, on a Ti support. According to the glow discharge optical emission spectrometry analysis, the TiO 2 nanoparticles are incorporated and uniformly distributed through out the metallic matrix. The 24 h stability of these coatings, in neutral sulfate solutions, has been investigated and compared with the behaviorof the Zn electrodeposits. The stability of the films is strongly dependent on their morphologic and structural characteristics, namely the crystallite size and texture of the matrix. It has been found that a protective layer, mainly composed by Zn 4 SO 4 (OH) 6 and ZnS0 4 , is easily formed on the Zn―TiO 2 films than on the Zn electrodeposits. Such protective layer acts as a barrier against further metal dissolution, proved by the solution analysis using atomic absorption spectrophotometry and anodic stripping voltammetry of the solution.

Morphological Characterization of Electrodeposited Zinc-based Matrix Composites

Research at the nanometer scale, aiming to create novel materials and devices offering better performance than those of macro/micro systems, is currently of great relevance in many topics of modern science, technology and engineering. In what concerns coatings technology, the nanocomposite films can offer excellent properties in different applications, representing their morphological characterization a great challenge.