Irene Llorente

Microbial stratification in low pH oxic and suboxic macroscopic growths along an acid mine drainage.

Macroscopic growths at geographically separated acid mine drainages (AMDs) exhibit distinct populations. Yet, local heterogeneities are poorly understood. To gain novel mechanistic insights into this, we used OMICs tools to profile microbial populations coexisting in a single pyrite gallery AMD (pH ∼2) in three distinct compartments: two from a stratified streamer (uppermost oxic and lowermost anoxic sediment-attached strata) and one from a submerged anoxic non-stratified mat biofilm. The communities colonising pyrite and those in the mature formations appear to be populated by the greatest diversity of bacteria and archaea (including ‘ARMAN’ (archaeal Richmond Mine acidophilic nano-organisms)-related), as compared with the known AMD, with ∼44.9% unclassified sequences. We propose that the thick polymeric matrix may provide a safety shield against the prevailing extreme condition and also a massive carbon source, enabling non-typical acidophiles to develop more easily. Only 1 of 39 species were shared, suggesting a high metabolic heterogeneity in local microenvironments, defined by the O2 concentration, spatial location and biofilm architecture. The suboxic mats, compositionally most similar to each other, are more diverse and active for S, CO2, CH4, fatty acid and lipopolysaccharide metabolism. The oxic stratum of the streamer, displaying a higher diversity of the so-called ‘ARMAN’-related Euryarchaeota, shows a higher expression level of proteins involved in signal transduction, cell growth and N, H2, Fe, aromatic amino acids, sphingolipid and peptidoglycan metabolism. Our study is the first to highlight profound taxonomic and functional shifts in single AMD formations, as well as new microbial species and the importance of H2 in acidic suboxic macroscopic growths.

Effect of Native Oxide Film on Commercial Magnesium Alloys Substrates and Carbonate Conversion Coating Growth and Corrosion Resistance

Possible relations between the native oxide film formed spontaneously on the AZ31 and AZ61 magnesium alloy substrates with different surface finish, the chemistry of the outer surface of the conversion coatings that grows after their subsequent immersion on saturated aqueous NaHCO3 solution treatment and the enhancement of corrosion resistance have been studied. The significant increase in the amount of aluminum and carbonate compounds on the surface of the conversion coating formed on the AZ61 substrate in polished condition seems to improve the corrosion resistance in low chloride ion concentration solutions. In contrast, the conversion coatings formed on the AZ31 substrates in polished condition has little effect on their protective properties compared to the respective as-received surface.

Accelerated leaching of ultra high performance concretes by application of electrical fields to simulate their natural degradation

When an electrical field is applied to a cementitious material, the ions of its pore solution move to the cathodic and anodic electrodes. As a consequence, an acceleration of the leaching degradation process may cause the dissolution of the solid phases. Several researchchers have applied this kind of method to the study of the leaching of cementitious materials, but mainly on cement paste. The study of leaching in concretes by this method is more difficult as, on the one hand, the high resistivity of these materials implies a quite low intensity passing through the concrete even at high voltage applied and characterisation of the degraded zones is doubtful. In this paper, electrical fields are applied to determine the ability of these methods to characterise and classify ultra high performance concretes (UHPC). Three different mixes of UHPC have been submitted to a migration test in galvanostatic conditions, using granitic water as electrolyte, and analysing the resulting electrolytes and the solid sample by different techniques. As a reference, the results have been compared with those obtained by following the standard ANSI/ANS-16.1-1986 “Measurement of the leachability of solidified low-level radioactive wastes by a short term procedure”. From this research, it could be deduced that the migration method accelerates very much the leaching process and gives a longer-term classification of different mixes of concretes against the degradation by natural water. The research presented in this paper has been carried out as part of the research project named “UNICORN”, supported by the Basic BRITE-EURAM Program of the EU.RésuméLorsque un champ électrique est appliqué à un matériel cimentaire, les ions de la solution qui se trouvent dans les pores se déplacent vers les cathodes et les anodes en provoquant une accélération des processus de dégradation par lixiviation. Plusieurs chercheurs ont appliqué ce type de méthode à l’étude de la lixiviation dans les matériaux cimentaires, mais surtout à la pâte de ciment. L’étude de la lixiviation dans les bétons en utilisant cette méthode est assez difficile, car d’une part, la grande résistivité de ces matériaux implique une faible intensité traversant le béton, même en appliquant des voltages élevés, et la caractérisation des zones dégradées est incertaine. Dans cet article, les champs électriques sont appliqués afin de déterminer la capacité pour cette méthode de caractériser et classifier les bétons d’ultra-haute performance (UHPC). Trois mélanges différents de UHPC ont été soumis à des essais de migration dans des conditions galvanostatiques, en utilisant de l’eau granitique comme électrolyte, et en analysant les électrolytes en résultant et les échantillons solides par diverses techniques. Comme référence, les résultats ont été comparés avec ceux obtenus selon la norme ANSI/ANS-16.1-1989. De cette étude, on pourrait déduire que la méthode de migration accèlère beaucoup les processus de lixiviation et donne à long terme une classification des différents mélanges de bétons en fonction de la dégradation par l’eau naturelle. La recherche présentée dans cet article fait partie d’un projet de recherche nommé UNICORN, et est supporté par le programme basique BRITE-EURAM de l’Union Européenne.

Effect of heat treatment of magnesium alloy substrates on corrosion resistance of a hybrid organic–inorganic sol–gel film

The influence of heat treatment of magnesium alloy substrates on corrosion resistance of a sol–gel coating has been assessed during immersion tests in 0.6 M NaCl aqueous solution. Relative differences in the chemical nature of the layers were quantified by scanning electron microscopy (SEM) and energy dispersive analysis of X-ray (EDX). Corrosion behaviour was evaluated by Electrochemical Impedance Spectroscopy (EIS) and hydrogen evolution measurement. Long-term immersion testing show that the sol–gel/heat treated AZ61 substrate exhibits a superior anti-corrosion property in comparison with the sol–gel/non-heated substrate. In contrast, no significant changes have been observed between the heated and non-heated samples in the case of the sol–gel coated AZ31 substrates. A link was found between lower O/Si atomic ratios observed by EDX analysis on the sol–gel coatings after the preparation process and reduced corrosion upon the coated substrates. Heat-treatment increased the protective properties of the passive film on the surface of the AZ61 substrate and hence inhibited magnesium dissolution and hydrophilic group formation during coating preparation.