Morphology control and texture of hematite particles by dimethylformamide in forced hydrolysis reaction

The effects of dimethylformamide (DMF) on morphology and texture of hematite particles produced from a forced hydrolysis reaction of FeCl₃–HCl solution were investigated by transmission electron microscopy (TEM), x-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), thermogravimetry and differential thermal analysis (TG-DTA), N₂and H₂O adsorption, and zeta potential measurements. The morphology of synthetic hematite particles was concentration dependent; they changed from large sphere with a diameter of ca. 600 nm to diamond-like shape with increasing DMF concentration in the aging solution accompanying a reduction of their size to 80 nm without incorporation of DMF in the particles. This fact was explained by an acceleration of phase transformation from β–FeOOH to hematite with an elevation of the solution pH owing to dimethylamine produced from a hydrolysis of DMF at an elevated temperature. TEM and XRD suggested that the diamond-like hematite particles formed above 6–10 vol% DMF possess a single-crystal nature. Gas adsorption technique revealed that the particles produced above 10 vol% DMF possess a high thermal stability. TG and FTIR indicated that the hematite particles produced with DMF contained small amounts of OH^_ions in the lattice though they provided a single-crystal nature.