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    Thermodynamics and kinetics of the dehydration reaction of FePO4·2H2O
    (2010-05-01)
    Boonchom, Banjong
    ;
    Puttawong, Spote
    The thermal decomposition kinetics of FePO<inf>4</inf>·2H<inf>2</inf>O in dynamical air atmosphere was studied by mean TG-DTG-DTA. The stage and product of the thermal decomposition were determined. A number of kinetic models and calculation procedures were used to determine the kinetic triplet and thermodynamic parameters characterizing the dehydration process. The obtained activation energy and most kinetic model indicate the single kinetic mechanism and three-dimension diffusion as "Ginstling-Brounstein equation (D4 model)", respectively. The thermodynamic functions (ΔH*, ΔG* and ΔS*) of the dehydration reaction are calculated by the activated complex theory and indicate that the process is non-spontaneous without connecting with the introduction of heat. The kinetic and thermodynamic results were satisfactory which present good correlation with a linear correlation coefficient close to unit a low standard deviation. © 2010 Elsevier B.V. All rights reserved.
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    Flower-like microparticles and novel superparamagnetic properties of new binary Co1/2Fe1/2(H2PO4) 2·2H2 O obtained by a rapid solid state route at ambient temperature
    (2009-12-01)
    Boonchom, Banjong
    ;
    Thongkam, Montree
    ;
    Kongtaweelert, Samart
    ;
    Vittayakorn, Naratip
    A new binary Co<inf>1/2</inf>Fe<inf>1/2</inf>(H<inf>2</inf>PO<inf>4</inf>) <inf>2</inf>·2H<inf>2</inf>O was synthesized by a simple, rapid and cost-effective method using CoCO<inf>3</inf>-Fe(c)-H<inf>3</inf>PO<inf>4</inf> system at ambient temperature. Thermal treatment of the obtained Co<inf>1/2</inf>Fe<inf>1/2</inf>(H<inf>2</inf>PO<inf>4</inf>) <inf>2</inf>·2H<inf>2</inf>O at 600 °C yielded as a binary cobalt iron cyclotetraphosphate CoFeP<inf>4</inf>O<inf>12</inf>. The FTIR and XRD results of the synthesized Co<inf>1/2</inf>Fe<inf>1/2</inf>(H<inf>2</inf>PO<inf>4</inf>) <inf>2</inf>·2H<inf>2</inf>O and its final decomposed product CoFeP<inf>4</inf>O<inf>12</inf> indicate the monoclinic phases with space group P2<inf>1</inf>/n and C2/c, respectively. The particle morphologies of both binary metal compounds appear the flower-like microparticle shapes. Room temperature magnetization results show novel superparamagnetic behaviors of the Co<inf>1/2</inf>Fe<inf>1/2</inf>(H<inf>2</inf>PO<inf>4</inf>) <inf>2</inf>·2H<inf>2</inf>O and its final decomposed product CoFeP<inf>4</inf>O<inf>12</inf>, having no hysteresis loops in the range of ±10,000 Oe with the specific magnetization values of 0.045 and 12.502 emu/g at 10 kOe, respectively. The dominant physical properties of the obtained binary metal compounds (Co<inf>1/2</inf>Fe<inf>1/2</inf>(H<inf>2</inf>PO<inf>4</inf>) <inf>2</inf>·2H<inf>2</inf>O and CoFeP<inf>4</inf>O<inf>12</inf>) are compared with the single compounds (M(H<inf>2</inf>PO<inf>4</inf>)<inf>2</inf>·2H<inf>2</inf>O and M<inf>2</inf>P<inf>4</inf>O<inf>12</inf>; where M = Co, Fe), indicating the presence of Co ions in substitution position of Fe ions. © 2009 Elsevier Ltd. All rights reserved.