Insight into the Effect of Mg(OH)2 Films versus Nobel Element Enrichment on the Global and Local Cathodic Activation of Corroding Mg

The anodically enhanced cathodic activation of high purity Mg was studied by global and local electrochemical measurements in unbuffered 0.6 M NaCl, 0.6 M NaCl saturated in Mg(OH)2, 0.1 M MgCl2, 0.1 M Na2SO4 and 0.1 M Tris(hydroxymethyl)aminomethane hydrochloride (TRIS). The selection of diverse aqueous environments was deliberate, in order to explore the effect of dissolution product upon subsequent cathodic activation. Cathodic activation was found to be strong in all of the chloride-containing environments where a porous hydroxide forms, weak in Na2SO4 where a denser more compact hydroxide forms, and negligible in TRIS where no hydroxide forms. Elemental enrichment, mapped using micro particle induced X-ray emission (PIXE), revealed the enrichment of Fe only in Cl- containing environments suggesting that noble metal enrichment provides a stronger influence on cathodic activation than that of Mg(OH)2 films.

The Origin of Dissolved Sulphate in the Thermal Waters of Budapest Inferred from Stable S and O Isotopes

The thermal waters produced by wells and springs from the Buda Thermal Karst in Budapest and its surroundings are rich in dissolved sulphate. Radiocarbon ages indicate that waters of T >45 ℃ were infiltrated during the Ice Age (more than 11 thousand years ago), on the higher elevations of the Buda-Pilis Hills, whereas waters of lower temperatures were infiltrated during the Holocene. For the origin of dissolved sulphate, two hypotheses can be set up: (1) the dissolved sulphate originates from the oxidation of the sulphide (pyrite) of Oligocene Clay Formation; (2) it is the dissolution product of the sulphate minerals (gypsum and anhydrite) of older carbonaceous rocks (limestone and dolomite). The isotopically stable sulphur composition of the dissolved sulphate in the thermal water (δ34S = 9.7‰ to 17.7‰) indicates its marine origin, so likely it dissolved from the older Permian evaporites.