Abstract
Morphological control of goethite particles by various operation conditions in a bench scale was devised in an attempt to improve magnetic properties of the end products. Reaction parameters were systematically varied and the detailed crystallographical analyses based on X-ray diffractometry and electron micrographs were employed as principal analytical tools.
When ferrous sulfate and sodium hydroxide were used, precursors immediately before goethite were Fe(OH)2 or Green rust (II), at excess or deficiency of alkali, respectively. The superiority of goethite particles is mainly attributed to adequate lateral growth along (110) as compared to the growth rate in (010). Preferential lateral growth, in turn, was predominated by the concentration of FeOH+ complex ions. Green rust (II) was stabilized by the buffering function of Fe2+ in the solution. Coexistence of green rust (II) with goethite enables steady growth of goethite preferentially in the axial direction, resulting in an increase in the aspect ratio.
Since morphology of those magnetic materials is sustained from those of goethite, it is safe to conclude that proper choice of the starting ferrous source, extent of alkali excess and concentration of dissolved oxygen are the key factors for better goethite particles and, hence, better materials for magnetic recording.
