Preparation of akaganeite nanorods and their transformation to sphere shape hematite

Akaganeite (beta-FeOOH) nanorods were synthesized through hydrolysis of FeCl3 and FeCl2 solutions containing urea in the temperature range from 90 to 95 degrees C under reflux condition for 8 h. The average diameters and lengths of nanorods were impacted by FeCl2 and urea. Upon heating the solution containing FeCl3, FeCl2 and urea, the average diameters were about 80 nm and lengths of nanorods were about 1.2 microm. The morphologies of beta-FeOOH nanorods in different growth times were shown by TEM images. More interestingly, in the growth process of nanorods, they can self-assemble and form cross structure. The ultrasonic might promote effectively the formation of the nano-cross structure. beta-FeOOH nanorods were calcined and the influence of the calcining temperature and time about the morphology and size of the powder was studied. By heating beta-FeOOH nanorods at 800 degrees C for 6 hours, the hematite in sphere shape was obtained and the forming mechanism was discussed.