Novel low temperature synthesis method for nanocrystalline zinc and magnesium chromites

In this paper we report a study regarding the preparation of zinc and magnesium chromites nanopowders starting from Zn(NO3)(2)center dot 6H(2)O, Mg(NO3)(2)center dot 6H(2)O, Cr(NO3)(3)center dot 9H(2)O and 1,3-propanediol (1,3PG). The used method consists in two steps: (i) the synthesis of the precursors (M(II)/M(III) carboxylate/hydroxycarboxylate compounds) by the redox reaction at 140 degrees C between the metal nitrates and 1,3PG and (ii) the controlled thermal decomposition of the precursors followed by the annealing at different temperatures. According to the thermal analysis, the precursors decompose in the temperature range 250-300 degrees C leading to the formation of the primary oxidic system (Cr2O3+x + MO; M = Zn, Mg). XRD patterns of the powders annealed at different temperatures (400,500, 600, 1000 degrees C) showed that ZnCr2O4 formed in the reaction (Cr2O3 + ZnO) crystallizes at 400 degrees C, while MgCr2O4 crystallizes starting with 500 degrees C, as a result of MgCrO4 thermal decomposition. Both chromites were obtained as nanocrystallites. (C) 2011 Elsevier B.V. All rights reserved.