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To assess the effect of polymeric substances on the biomineralization and stabilization of green rust (GR), the effect of two organic polymers on the transformation of lepidocrocite (γ-FeOOH) to GR vs. magnetite in presence ofShewanella putrefacienswas investigated. These two polymers, generally used as flocculants, are polyacrylic acid (PAA), which bears negatively charged carboxylic groups at neutral pH and is expected to react with cationic hydrolyzed iron species, and polyacrylamide (PAM), which is a neutral polymer that may develop hydrogen bonds with iron nanocolloids. The bioreduction of lepidocrocite byS. putrefacienswas performed under conditions known to yield either magnetite or GR. Each operational condition of interest was investigated with various polymer concentrations from 0.6 to 60 mg g−1Fe (10 to 1000 mg l−1). The final product was characterized using X-ray diffraction and electronic microscopy. The results showed that the formation of GR is favored, with respect to magnetite, to a lesser extent with PAM than with PAA. These results indicated that polymers influence the chemical stability of GR and/or guide the route of biomineralization. Polymer properties, in addition to silica and phosphate concentrations, are then critical parameters that control the secondary iron mineral biomineralization from iron-reducing bacteria. Supplemental materials are available for this article. Go to the publisher's online edition ofGeomicrobiology Journalto view the supplemental file. [ABSTRACT FROM AUTHOR]

We have characterized by transmission electron microscopy several new phases that we have discovered in bulk alloys of the Al–Cr–Fe system. These structures are an icosahedral compound and several approximants of the decagonal phase. According to the indexation of the electron diffraction patterns (EDPs), some of the approximants are not of Fibonacci type. These EDPs correspond to nanodomains, which are due to disorder introduced by quenching the alloys after melting the pure constituent metals. For these new types of approximant, we propose a crystallographic description related to the usual Fibonacci description. In addition, we suggest a construction of the corresponding tilings. The orientation relationships between these structures are described. [ABSTRACT FROM AUTHOR]

We have identified two ?-brass phases in the Al–Cr–Fe system by X-ray diffraction and transmission electron microscopy. These structures (rhombohedral and cubic) are closely related to each other and can co-exist in the same alloy together with approximants of quasicrystals. In particular, a long-period superlattice, typical of ?-brass phases, was characterized in the cubic structure. This superstructure is constituted of inversion domains separated by boundaries lying at (10) planes. The displacement vector between like domains was determined from high resolution microscopy data. This study deals also with a description of some structural links between ?-brass phases and approximants of decagonal and icosahedral quasicrystals. [ABSTRACT FROM AUTHOR]

We introduce a new method for the synthesis of Al-Ni nanosized particles. After partial oxidation, this technique is able to produce ultrafine sub-nanometric nickel clusters dispersed with an amorphous aluminium oxide. Such clusters consist of about 15 nickel atoms which exhibit discrete electronic energy levels and superparamagnetism. A very significant enhancement of the catalytic properties is observed. We expect that division of metals down to such a reduced scale will lead us to new properties and to a technological breakthrough since upscaling this method to industrial production rate is straightforward. [ABSTRACT FROM AUTHOR]

Finely dispersed Ni powders were obtained after chemical reduction of Ni(II) salts by activated sodium hydride in organic solvents. This process allows one to prepare particles in the nanometre range. The particles with sizes smaller than 4 nm were found to be hcp whereas larger particles were fcc. To the best of our knowledge, this is the first observation that unsupported Ni powder may crystallize in the hcp system and that the phase stability of this metallic element is particle size dependent. [ABSTRACT FROM AUTHOR]