In this work we studied the mechanism of formation and phase transformations of iron sulfides in diverse anoxic environments. The transformation of precipitated FeS was followed in both aqueous and dry aging experiments using X-ray powder diffraction (XRD) and scanning and transmission electron microscopy (SEM/TEM) and selected-area electron diffraction (SAED). The initial precipitate is commonly referred to as nanocrystalline mackinawite (FeS) or amorphous FeS. We have found that at room temperatures, amorphous FeS transforms to mixture of mackinawite and greigite (Fe3S4) in about 2 months, and completely converted to platy greigite after about 10 months. In order to accelerate phase transitions, the initial FeS precipitate was heated to 120 °C, resulting in the formation of crystalline mackinawite within 2 h at 150 °C, the material converted directly to pyrrhotite. Finally, when stored in a dry state at room temperature, crystalline mackinawite converted to greigite in 3 months.
COBISS.SI-ID: 25570343
Organizers of the joint MSCC-SEMC 2012 conference (5th Mineral sciences in the Carpathians conference and 3rd Central European mineralogical conference) invited dr. Nina Daneu to present the results in the field of atomic-scale investigations of twinning in minerals and the correlation between twinning and epitaxies between structurally related minerals in the form of a plenary lecture. In the lecture she described the results of nanostructural analyses of twins in spinel, rutile, sphalerite and bixbyite. Besides, special techniques of electron microscopy which were developed and applied to different materials/minerals by the author and her co-workers were presented. The results were described also in a paper, published in Acta Mineralogica-Petrographica (Abstract series).
COBISS.SI-ID: 25754407
Maghemite (γ-Fe2O3) is a common product of magnetite oxidation in natural environments. In the present work we have studied synthesis pathways to produce nanosized maghemite crystals. They can be formed via magnetite at relatively low temperatures (70°C) from Fe(II) oxalate or Fe(II) sulfate and consequent oxidation to maghemite. We have studied effects of ethylene glycol and tetraethylene glycol on the morphology of the crystals. The magnetite crystals formed from different precursors showed diverse morphological and textural features. Octahedral magnetite crystals were produced from Fe(II) oxalate via a simple co-precipitation process. These crystals often show spinel-type {111} twin boundaries, {110} stacking faults and {111} epilayers of feroxyhyte on the octahedral faces of former magnetite nanocrystals. Formation of twin boundaries was related to short-range ferromagnetic attraction among the nanocrystal seeds.
COBISS.SI-ID: 26132775