No abstract

Foram realizados testes galvanostáticos em soluções de NaCl com magnésio puro e com a liga AZ91HP, tendo sido medido o volume de hidrogênio desprendido durante os testes. A fim de estudar o efeito da diferença negativa (NDE), uma idéia foi desenvolvida para separar o desprendimento de hidrogênio (H.E) na superfície passiva do desprendimento dentro dos pites. A análise dos dados volumétricos mostrou que a corrente de redução de hidrogênio dentro dos pites, sobre o Mg, é muito mais alta do que nos pites sobre a liga AZ91HP. Supondo que a razão entre a taxa de redução de hidrogênio e a taxa de dissolução de magnésio, expressa pelo fator k, não muda com a polarização, foi encontrado um valor de aproximadamente 0,5 para o Mg puro. Para a liga AZ91HP foi alcançado somente um valor em torno de 0,3.Galvanostatic tests with pure magnesium and with the AZ91HP alloy were performed in NaCl solutions, and the volume of hydrogen evolved during the tests was measured. In order to examine the negative-difference effect, a concept was developed to separate the hydrogen evolution (H.E.) on the passive surface and the H.E. inside the pits. An analysis of the volumetric data showed that the current density of H.E. inside the pits is much higher for Mg than for the AZ91HP alloy. With the assumption, that the ratio between the hydrogen reduction rate and the rate of the anodic metal dissolution, expressed by the factor k, does not change with the polarization, a k value of ca. 0.5 for pure Mg was found, while for the AZ91HP alloy this value was only ca. 0.3.

No abstract

not Available.

Thick nanoporous oxide films exhibiting interference colors were grown on AISI 304L stainless steel by triangular current scan method in 5 M H2SO4 + 2.5 M H2CrO4 using different electrolysis times. The nanocrystalline spinel oxide films thus obtained were electrochemically characterized by cyclic voltammetry at 1 mV•s-1 in 0.5 M Na2SO4. Strong anodic peaks are observed at the potential region where the transpassive peak of stainless steels is expected. Such behavior evidences not only the large active surface area of the films, but also that the cationic species are not fully oxidized. The effect of polarizing in 0.5 M Na2SO4 to a potential in the transpassive region on the morphology and the composition of these films was investigated.