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)2·6H2O, Mg(NO3)2·6H2O, Cr(NO3)3·9H2O 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 °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 °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 °C) showed that ZnCr2O4 formed in the reaction (Cr2O3 + ZnO) crystallizes at 400 °C, while MgCr2O4 crystallizes starting with 500 °C, as a result of MgCrO4 thermal decomposition. Both chromites were obtained as nanocrystallites.