The electrochemical behaviour of coated Cr3C2-NiCr steel in aerated 0.5 M H2SO4 solution was studied by means of electrochemical ac and dc measurements. The structural characterisation of the coated steel, before and after electrochemical tests, was also performed in order to identify the mechanism of the electrolyte penetration through the coating up to the steel substrate, causing its corrosion. This characterisation may also help to explain electrochemical results. Three types of Cr3C2-NiCr coatings performed by a High Velocity Oxy-Fuel Spraying system (HVOF) were analysed. The facility for the electrolyte penetration through the coating and the corresponding electrochemical behaviour of the samples were strongly influenced by the spray parameters used and heat treatment applied. It was observed that heat-treated coatings (Q1 and Q3) showed better corrosion resistance than the as-sprayed coating (A). For coatings Q1 and Q3, the electrolyte did not reach the steel substrate during the measurement, leading to a better protection of the steel substrate against corrosion.

The electrochemical behavior of Cu-(0.5-13 wt.%)Al alloys in K2SO4 0.5 mol dm-3 (m = 1.5 M, pH 2-5) was studied using open-circuit potential (Eoc) measurements and polarization curves, in order to know the conditions of copper oxides formation, influence of Al concentration and solution pH on the electrode processes. The open-circuit potential measurements with time indicated that the Eoc decreases with the Al content, due to the lower Al potential compared to Cu. The electrode potentials decrease ca. 20 mV per unity of solution pH as increase pH of the solution. The polarization curves showed changes with the increase of Al concentration. For alloys with up to 3 wt.%Al the obtained Tafel anodic coefficient was 40 mV/decade for low potentials region (E < -320 mV) and 130 mV/decade for the other region (-320 < E/mV < -250), indicating that up to this concentration there is no considerable change in the electrochemical behavior of the alloys, when compared to pure Cu. For alloys with an Al content from 8 to 13 wt.% the Tafel anodic coefficient was 60 mV/decade. No influence of the solution pH on the Tafel anodic coefficient was observed.

Preparação, caracterização e o comportamento eletroquímico dos complexos: [Cu(N3)2(N,N-diEten)]2, [Cu(N3)2(tmeen)]2, [Cu(N3)(NCO)(N,N-diEten)]2, [Cu(N3)2(N,N’-diMeen)]2 e [Cu(N3)(NCO)(tmeen)]2 são apresentados e discutidos. Os estudos eletroquímicos foram realizados utilizando-se as técnicas de voltametria cíclica e eletrólise a potencial controlado. Os voltamogramas cíclicos de todos complexos são semelhantes e apresentam um par de picos de corrente entre -0,65 e 0,0 V. A eletrólise a potencial controlado, em @ -0,55 V, forneceu 1,8 < n < 2,1 para todos os compostos, indicando a redução de Cu(II) a Cu(I) em ambos os centros metálicos. A comparação dos valores dos potenciais de pico do par Cu(II)/Cu(I) desses complexos mostra que esse processo redox é fracamente influenciado pela basicidade dos ligantes.

The complexes: [Cu(N3)2(N,N-diEten)]2, [Cu(N3)2(tmeen)]2, [Cu(N3)(NCO)(N,N-diEten)]2, [Cu(N3)2(N,N’-diMeen)]2 and [Cu(N3)(NCO)(tmeen)]2 were prepared, characterized and their electrochemical behavior was investigated by cyclic voltammetry and controlled potential electrolysis. Cyclic voltammograms for all complexes studied are similar and exhibit one pair of current peaks in the range of -0.65 to +0.0 V. The number of electrons obtained from controlled potential electrolysis at ca. -0.55 V for all compounds was 1.8 £ n £ 2.1, indicating that both copper(II) metallic centres in the molecule were reduced to copper (I). Comparing the peak potential values for these complexes one can observe that the redox process corresponding to copper(II)/copper(I) couple is slightly influenced by the s-basicity of the ligands.