Synthesis of nanocrystalline Mn-Zn ferrite powders through thermolysis of mixed oxalates

Nanocrystalline Mn-Zn ferrite powders were synthesized by thermal decomposition of an oxalate precursor. Two polymorphs of a mixed Mn-Zn-Fe oxalate dihydrate were obtained by precipitation of metal ions with oxalic acid: monoclinic alpha-(Mn, Zn, Fe)(3)(C2O4)(3)center dot 6H(2)O is obtained after precipitation and ageing at 90 degrees C, whereas the orthorhombic beta-type is formed after precipitation at room temperature. The morphology of the oxalate crystals can be controlled by the precipitation conditions. The alpha-polymorph of the mixed oxalate consists of prismatic and agglomerated particles. The beta-oxalate forms non-agglomerated crystallites of submicron size. Thermal decomposition of the oxalate at 350 degrees C in air results in an amorphous product. Nanosize Mn-Zn ferrite powders are formed at 500 degrees C and a mixture of haematite and spinet is observed at 750 degrees C. The thermal decomposition of the mixed oxalate is monitored by thermal analysis, XRD and IR-spectroscopy. The morphology of the oxalate particles is preserved during thermal decomposition; the oxide particle aggregates display similar size and shape as the oxalates. The primary particles are much smaller; their size increases from 3 nm to 50 nm after decomposition of the oxalates at 350 and 500 degrees C, respectively. The powder synthesized by decomposition at 500 degrees C was sintered at 1150 degrees C to dense and fine-grained Mn-Zn ferrites. (c) 2010 Elsevier Ltd and Techna Group S.r.l. All rights reserved.