Flux Preparation Of Sheet Iron Oxide Crystal Growth Mechanism

The studies of flaky iron oxide via flux method were performed with FeCl₃·6H₂O as raw material.The effect on the properties of resulting product such as flaky morphology,mean particle diameter,and crystal form,was investigated by Laser-scattering Particle Sizing,Optical Microscope,SEM and XRD.It was found that the types and dosage of flux salt,calcined temperature and time,preparation method of precursor and doping were the key factors on the process of crystal growth.When the mixture flux system was Na₂SO₄:K₂SO₄=3:1,and the mole ratio of (Na₂SO₄+K₂SO₄) to FeCl₃·6H₂O is 4,with wt3%Al₂O₃ doped,then calcinated at 1100℃for 4h,flaky particles of hematiteα-Fe₂O₃ were obtained with 20～60μm in diameter,nearly 400nm in thickness,owing smooth surface and good dispersion property.It was found that a better flaky morphology of crystal was obtained in the mixture flux system,rather than in the simple flux system. Furthermore,the flaky crystal could be more readily obtained in a flux system in the presence of SO₄^2-,while in the flux system containing chloride only granule or plate crystal can be available.Moreover,the product with a mean particle size below 50μm,flown time of 75s,and best disperse property,can be prepared in the complex flux system of (Na₂SO₄+K₂SO₄) when the mole ratio of flux to Fe³⁺ is 4.The effect on the process of crystal growth was investigated by using different preparation method of precursor and doping.Several crystal defects,such as growth fringe,inclusion,cracking,and screw dislocation,were detected in the crystals obtained through different precursor preparation method.At the same time,it was found that when doped with Al₂O₃,the corresponding crystals always exhibit regular hexagon flaky shape,smooth surface and a particle size of 20～60μm, with decreased thickness from 0.7μm to 0.4μm.However,the crystals showed a cellular structure when doped with SiO₂ or P₂O₅.And the particles with 0.5～3μm in diameter were found in the obtained product when ZnO was doped.Therefore,the reason for the decreased thickness decreased could be acribed to that Al³⁺ has the same valence,similar crystal configuration but smaller ion radius when compared with Fe³⁺. Based on the analysis of the crystal morphology above,it was proposed that the produce process of flaky iron oxide crystal in the complex (Na₂SO₄+K₂SO₄) flux system was controlled mainly by interface mechanism,and fitted the model of Anion Coordination-Polyhedra and Dissolution-Ionization well.