Combustion synthesis: Effect of urea on the reaction and characteristics of Ni-Zn ferrite powders

The purpose of this study was to evaluate the effect of the urea content (fuel) on the reaction and the characteristics of Ni-Zn ferrite powders obtained by combustion synthesis. Several batches were prepared with different fuel contents, ranging from the stoichiometric composition between 20 and 100% (excess), while the desired molar proportion of the metal precursors was kept constant. The solutions were heated on a hot plate and then transferred to a muffle furnace preheated to 700degreesC, in which ignition took place. The resulting powders were characterized by XRD, BET, SEM, and sedimentation, aided by rotation measured through an optic light. The crystalline hematite (alpha-Fe2O3) and Ni-Zn ferrite phases were present in all the compositions studied, and the appearance of the agglomerates varied from soft to hard with increasing urea content. The increased urea content, which promoted a longer flame time, influenced the growth and/or formation of hard agglomerates. After sintering at 1200degreesC/2 h using the stoichiometric composition, only the spinel structure Ni-Zn ferrite, with homogeneous microstructure, was present.