Computer simulations for the growth process of peanut-type hematite particles

The growth process of a monodispersed peanut-type hematite particle consisting of much smaller elongated subcrystals has been reproduced by computer simulation. On the basis of the microscopic internal structure, the simulation was performed by replacing the sequential events of surface nucleation and the subsequent growth of each subcrystal in the actual process with an arranged deposition of rectangular segments of fixed dimensions under different conditions in their site-dependent deposition rate and in the flexibility of their tilt angles. The most successful simulation model was obtained on the assumptions of a relatively fast deposition of the segments on the outermost side-surface of the ellipsoidal particle and the flexible tilt angle of each segment depending on the position of a neighboring new segment placed afterward. The result of the simulation strongly supported the previous elucidation of the growth mechanism in terms of the outward bending of adjoining subcrystals by nucleation and growth of a new subcrystal in each space between them. Enhancement of the outward bending of subcrystals by a large amount of sulfate ions adsorbed to the growing subcrystals was also suggested.