Uniform Nanosized Goethite Particles Obtained by Aerial Oxidation in the FeSO4–Na2CO3 System
摘要
Pure goethite particles in the nanometer size range (from 
200 to 80 nm) with an elongated shape (axial ratio from 5 to 8) useful as iron precursors for magnetic recording have been prepared by oxidation of the suspensions resulting from the addition of sodium carbonate to Fe(II) sulfate aqueous solutions under a restrictive set of experimental conditions (Fe(II) concentration, carbonate/Fe(II) mole ratio, temperature, and air flow rate). In all cases, the goethite particles were formed by a dissolution–recrystallization mechanism through an intermediate green-rust phase. The particle size was determined by the carbonate/Fe(II) ratio (which controls the formation pH), the FeSO4 concentration, and the air flow rate. The smallest particles (length 80 nm) were obtained for a high carbonate/Fe(II) mole ratio (≥3), a low Fe(II) concentration (0.075 mol dm−3), and an air flow rate of 2 dm3 min−1. The goethite particles were also characterized by the electron diffraction and high-resolution TEM finding that they were monocrystalline, having the crystalline c axis parallel to the longest particle dimension.
200 to 80 nm) with an elongated shape (axial ratio from 5 to 8) useful as iron precursors for magnetic recording have been prepared by oxidation of the suspensions resulting from the addition of sodium carbonate to Fe(II) sulfate aqueous solutions under a restrictive set of experimental conditions (Fe(II) concentration, carbonate/Fe(II) mole ratio, temperature, and air flow rate). In all cases, the goethite particles were formed by a dissolution–recrystallization mechanism through an intermediate green-rust phase. The particle size was determined by the carbonate/Fe(II) ratio (which controls the formation pH), the FeSO4 concentration, and the air flow rate. The smallest particles (length 80 nm) were obtained for a high carbonate/Fe(II) mole ratio (≥3), a low Fe(II) concentration (0.075 mol dm−3), and an air flow rate of 2 dm3 min−1. The goethite particles were also characterized by the electron diffraction and high-resolution TEM finding that they were monocrystalline, having the crystalline c axis parallel to the longest particle dimension.