Preparation of high acicular and uniform goethite particles by a modified-carbonate route

A procedure for the synthesis of high acicular and uniform goethite particl es based on a modified-carbonate route is reported. It essentially consists of the oxidation-precipitation of iron sulfate solutions through a two-oxi dation process, which involves the formation of primary particles and their subsequent growth. XRD, TEM, colour evolution and pH monitoring have been used to determine the mechanism responsible for the formation of goethite p articles with well-controlled morphology. Single-phase goethite particles a re formed from initial suspensions with OH/Fe equivalent ratios from 0.05 t o 0.35, which determine the supersaturation level of the solution and conse quently, the length of the particles. The best conditions to prepare unifor m goethite particles of 250 nm in length and high axial ratio (8), adequate as high-density audio/video media precursors, have been established.