Preparation and microstructure of spinel zinc ferrite ZnFe ₂O₄by Co-precipitation method

Spinel zinc ferrites ZnFe₂O₄, prepared by co-precipitation method using the zinc nitrate Zn(NO₃) ₂·6H₂O and ferric nitrate Fe(NO₃) ₃·2H₂O as the raw materials, were characterized by the thermo gravimetric analysis (TG) and differential scanning calorimeter (DSC), X-ray diffraction (XRD) and scanning electron microscope (SEM). The influence of synthesis conditions, such as Zn/Fe molar ratio, pH value, the sintering temperature and time, on the microstructures was detailedly investigated. The relationships between the microstructures and the synthesis conditions were discussed. The results show that the pure spinel zinc ferrites ZnFe₂O₄ are formed when the Zn/Fe molar ratio is 1.05: 2 at pH=8.5 or Zn/Fe molar ratio is 1 : 2 at Ph=9-10, and the precursors are sintered at 1100 °C for 4 h. Especially no other phases are observed when the Zn/Fe molar ratio is 1 : 2 at pH= 10 and the precursor is sintered above 700 °C for 4 h. The higher sintering temperature and longer sintering time contribute to grain growth.