Mechanism of Auto Combustion Method in Synthesis of Nanocrystalline NiFe2O4 Powders

Nanocrystalline NiFe2O4 powders were synthesized by citrate. Nitrate Sol-Gel auto combustion method at room temperature. Various xerogels were obtained by adding different amounts of ammonia into precursor solution. The corresponding auto combustion powders were prepared through subsequent auto combustion process. The variation regularity of crystallinity of auto combustion powders, properties and thermal decomposition process of xerogel were investigated by XRD, TEM, IR and TG-DTA techniques. The mechanism of auto combustion method was further studied. The results indicate that auto combustion powders are mainly composed of NiFe2O4 phase with small amout impurity phase of alpha-Fe2O3 and FeNi3. The crystallinity of auto combustion powders are enhanced with increasing the amount of ammonia. The xerogel contains amorphous phase and NH4NO3 crystallization phase. The amount of ammonia exerts appreciable effects on the quantity of NH4NO3 and properties of xerogel. The mechanism of auto combustion is a chain reaction which is formed by mutual promotion of NH4NO3 decomposition and citric acid combustion.