Portugaliae
Electrochimica Acta

The corrosion products formed on weathering steel and pure iron exposed to a wet-dry cycled SO2~atmosphere have been studied by means of reflection (CEMS) and transmission Mossbauer spectroscopy and X-ray diffraction. After 48 days of exposure, rusts of both materials exhibit different morphologies. FeS03.3H20, FeS04.nH20 and amorphous ferric oxyhydroxides (probably ferrihydrite and/or a-FeOOH of small particle size) are the constituents of both rusts. The main differences between the corrosion products of both materials are related with the concentration of Fe2* species and the crystallinity and/or particle size of ferric oxyhydroxides. The presence of Fe?+ species in 48 day-old rusts is attributed to the effect of the wet-dry cycling conditions.

The effect o-f the imidazoles I-III (1) on the deposition velocity o-f cooper on phenolic and epoxy resins has been studied. It is shown that these substances affect the stability of the cooper electroless baths in the temperature interval 25-52 ºC.

In solution containing chloride anions, the pitting corrosion can be obtained when the electrode potential exceeds a certain critical value (Ep). The initiation of pitting corrosion has been considered as a rare even both in space and time and consequently, it can be treated as a statistical phenomenon (1-4). The pitting corrosion of. 304 stainless steel (304 SS) in a strong buffered chloride ions containing medium has been studied by using the potentiodynamic and potentiostatic techniques complemented with scanning electron microscopy observations.

Differential pulse polarography (DPP) has been used to elucidate the interaction of adenine with copper and the interaction of 6-dimethyladenine with copper using sulphuric acid 0.1 M as supporting electrolyte. As has been verified with other purines in this and other media, copper (II) ions are reduced at the mercury electrode in two stages via an intermediate valency state, and two reduction peaks may be observed. Taking into account the variation of the differences (AEp) between the peak potential of each complex and the metal ion with the logarithm of concentration of adenine and the 6-dimethyladenine, respectively, we can conclude that the numbers of the ligands are equal in the two cases and the stability constants are of the same order of magnitude

A fim de automatizar a aquisição de dados de uma microbalança, desenvolveu-se e construiu-se uma interface a um computador PC compatível. Os resultados recebidos no computador são armazenados num ficheiro, a intervalos de tempo seleccionáveis por "software". Este programa, escrito em linguagem C, permite ainda o tratamento dos dados de molde a terminar automaticamente a aquisição uma vez verificado um critério de estabilidade pré-definido.