Synthesis of nanocrystilline ferrites by sol–gel combustion process: the influence of pH value of solution

Abstract

The dried nitrate–citrate gels exhibit auto-catalytic combustion behavior, which can be used to synthesize the nanocrystalline ferrite powders. In this study, NiCuZn ferrite nanocrystalline powders with composition of (Ni 0.25Cu 0.25Zn 0.5)O(Fe 2O 3) 0.98 were synthesized by a sol–gel auto-catalytic combustion process. The influences of pH value of the precursor solution on the gel morphology, combustion behavior and crystallite size of synthesized powders were investigated with the help of scanning electron microscopy observation, thermal analysis, infrared (IR) spectra and X-ray diffraction technique. The experiments showed that the pH value of the mixed precursor solutions has a significant influence on the morphology of dried gels. The high porous precursors with network structure can be formed at high pH values after the solutions were dried at 135°C. With increasing pH value, the combustion rate is increased significantly. The as-burnt powders become uniform in size and the crystallites size is increased from 26 to 48 nm with pH value increasing from 2 to 7. The combustion reaction mechanisms were put forward with the help of IR spectra and differential thermal analysis techniques.