Hydrothermal Synthesis and Microstructural Control of Hematite Particles

Abstract

Hematite particles of various shapes and sizes have been prepared h ,drotherntally at different pHs and temper-atures from ferric chloride solution. Particle size decreases with increase in pH and decrease in residual iron concentration during precipitation as observed from Transmission Electron Microscope (TEM). A comparison of particle size from TEM and mean crystalline diameter (MCD) from XRD data reveals that the particles prepared are polycrystalline in nature with different degree of poly- crystallinity The degree of polycrystallinity decreases with increase in the pH of precipitation. Monodispersed pseudocubic polycrystalline particles obtained at lower pH exhibit very high coercivity. Various sizes of pseud-ocubic particles have also been prepared by varying the synthesis temperature, the coercivity of which is linearly increasing with increase in the size of the particles. By the developed process iron oxide of required size, shape and magnetic properties can be engineered. Formation of polycrystalline nature of particles is explained in terms of aggregation of very fine particles formed as an intermediate during conversion to hematite.