Summary Tris(dicarboxylate) complexes of iron(III) with oxalate, maleate, malonate and phthalate viz. K3[Fe(C2O4)3]×3H2O (1), K3[Fe(OOCCH2COO)3]×3H2O (2), K3[Fe(OOCCH=CHCOO)3]×3H2O (3), K3[Fe(OOC-1,2-(C6H4)-COO)3]×3H2O (4) have been synthesized and characterized using a combination of physicochemical techniques. The thermal decomposition behaviour of these complexes have been investigated under dynamic air atmosphere upto 800 K. All these complexes undergo a three-step dehydration/decomposition process for which the kinetic parameters have been calculated using Freeman-Carrol model as well as using different mechanistic models of the solid-state reactions. The trisoxalato and trismalonato ferrate(III) complexes undergo rapid dehydration at lower temperature below 470 K. At moderately higher temperatures (i.e. >600 and 500 K, respectively) they formed bis chelate iron(III) complexes. The trismalonato and trismaleato complexes dehydrate with almost equal ease but the latter is much less stable to decomposition and yields FeCO3 below 760 K. The cis-dicarboxylate complexes particularly with maleate(2-) and phthalate(2-) ligands are highly prone to the loss of cyclic anhydrides at moderately raised temperatures. The thermal decomposition of the tris(dicarboxylato)iron(II) to iron oxide was not observed in the investigated temperature range up to 800 K. The dehydration processes generally followed the first or second order mechanism while the third decomposition steps followed either three-dimensional diffusion or contracting volume mechanism.
The thermal decomposition behavior of hard coal fly ash (HCA2), obtained from the combustion of an Australian hard coal in
thermoelectric power plants, in different atmospheres (air, N2 and N2-H2 mixture), was studied using thermogravimetry (TG), infrared-evolved gas analysis (IR-EGA), differential scanning calorimetry
(DSC) and thermodilatometry (DIL) techniques. It was found that changing of the applied atmosphere affects the carbon content
of the ash which results in different thermal decomposition behaviors. In air, the carbon content was oxidized to carbon dioxide
before the decomposition of carbonate. In N2 or in N2-H2 atmospheres, the carbon content acts as a spacer causing a fewer points of contact between calcium carbonate particles, thus
increasing the interface area which results in a decrease of the carbonate decomposition temperature. Following the carbonate
decomposition, the iron oxide content of the ash undergoes a reductive decomposition reaction with the unburned carbon. This
oxidation-reduction reaction was found to be fast and go to completion in presence of the N2-H2 mixture than in the pure nitrogen atmosphere due to the reducing effect of the hydrogen.
The kinetics of the carbonate decomposition step, in air and N2-H2 mixture was performed under non-isothermal conditions using different integral methods of analysis. The dynamic TG curves
obeyed the Avrami-Erofeev equation (A2) in air, and phase boundary controlled reaction equation (R2) in N2-H2 mixture. The change in the reaction mechanism and the difference in the calculated values of activation parameters with the
change of the atmosphere were discussed in view of effect of the atmosphere on the carbon content of the ash.
Ironoxides play an important role in industry, such as semiconductive compounds, inorganic pigments, magnetic tapes, catalysis, and gas sensing [ 1 – 5 ]. The structure of most ironoxides can be described in
Authors:Bernadett Bajnóczi, Attila Demény, and László Korpás
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Authors:Ádám Csorba, Vince Láng, László Fenyvesi, and Erika Michéli
Schwertmann, U., 1993. Relations between ironoxides, soil color and soil formation. In: Soil Color, Special Publication. (Eds.: Bigham, J. M. & Ciolkosz, E. J.) 51–70. Soil Science Society of America. Madison, Wisconsin.
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, M. L., 1960. Ironoxide removal from soils and clay by dithionite-citrate system buffered with sodium bicarbonate. Clays and Clay Minerals.
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