Effects of hydrothermal reaction temperature and time on the microstructure evolution of Fe_3O_4

The extremely dispersed Fe3O4powders were prepared by hydrothermal reaction of FeSO4·7H2O and NaOH with aid of ultrasonic treatment. Phase identification was accomplished by XRD, and micromorphology was observed by FE-SEM. The results show that under the condition of strongly alkaline environment, poorly crystallizedα-FeOOH phase is synthesized at 120 ℃ and the Fe2O3phase is synthesized at 140 ℃. When the hydrothermal temperature is over 160 ℃, Fe3O4is formed. The grain size of the prepared Fe3O4increases with the increasing of hydrothermal temperature. Effect of holding time on the crystalline phase of the product is not obvious. However, with the extension of holding time, the particle size of prepared samples grows larger, with higher phase purity and crystallinity.