Facultad Regional La Plata

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    Phase transformation during the zeolitization of fly ashes
    (Elsevier, 2017) Monzón, Jorge; Pereyra, Andrea; Conconi, Susana; Basaldella, Elena
    The reactivity of a fly ash discarded from a thermoelectric power station was evaluated in terms of its hydrothermal conversion into NaA-containing products. The influence of ash pretreatments and the effect of changes in the synthesis mixture composition on the evolution of the solid phase toward its conversion into zeolitic materials were studied. Activation by milling was not as effective as alkaline fusion. The highest levels of fly ash reactivity were obtained by applying an alkaline fusion treatment using sodium carbonate at 800 C. It was observed that this particular ash activatiorn induces a solid reordering that generates crystalline materials identified as NaAlSiO2 polymorphs that in turn are easily transformed into zeolite structures. Synthesis conditions for ash zeolitization as high as 60% were established.
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    Electrochemical characterization of nickel hydroxide nanomaterials as electrodes for NiMH batteries
    (Springer, 2016-08-23) Real, Silvia; Ortiz, Mariela; Castro, Élida Beatriz
    β-Nickel hydroxide was successfully synthesized by a hydrothermal method. Nano-nickel hydroxide material was characterized by X-ray diffraction, infrared absorption spectroscopy, and transmission electron microscopy. They were employed as additives to the positive electrode of Ni-MH batteries. Working electrodes, with mixtures of commercial nickel hydroxide and nano-nickel hydroxide (0–10 wt.%) as active material, were prepared. Cyclic voltammetry, charge discharge profiles, and electrochemical impedance spectroscopy studies were carried out to evaluate the electrochemical performance of the nickel electrode, in 7 M KOH electrolyte, at 25 °C. The presence of nano-nickel hydroxide improves the electrochemical behavior of the active material. The electrochemical impedance spectroscopy (EIS) results were analyzed employing a modified version of previously developed physicochemical model that takes into account the main structural and physicochemical parameters that control these systems.
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    Hydrothermal synthesis of cathode materials for rechargeable lithium ion battery
    (Annual Meeting of the International Society of Electrochemistry, 2014-08-31) Ortiz, Mariela; Real, Silvia; Visintin, Arnaldo
    The Lithium-ion batteries are electrochemical systems based on the use of intercalation compounds supported on porous structures with different characteristics. The Li-ion battery operates by intercalation of Li+ cations in materials, for migration from the cathode to the anode. Different materials are used as cathode, for example, mixed oxides of transition metals (LiMO2, where M: Mn, Co and / or Ni) [1-2], and lithium iron phosphate (LiFePO4) [3] or other materials [4-5]. In this paper the preparation of Li-Ni-Co-Mn oxides by hydrothermal synthesis is presented; being a simple, low cost and low temperatures process; that produces highly homogeneous materials. A solution containing nitrate of cobalt, nickel and manganese, sodium hydroxide and lithium are used as precursor solution; this is introduced into an autoclave at 180°C. Then the precipitates that have been obtained are combusted in an oxygen atmosphere. Optical techniques (as DRX, SEM and TEM) are used to characterize the prepared material. The electrochemical performance of mixed oxides as active cathode materials in lithium-ion batteries are studied by electrochemical techniques such as charge-discharge cycles, galvanostatic discharge at different currents, cyclic voltammetry and electrochemical impedance spectroscopy.