Effects of vinyl series polymers on the formation of hematite particles in a forced hydrolysis reaction.

The influence of polymers on the formation of hematite particles from forced hydrolysis of acidic FeCl(3) solution was investigated using vinyl series polymers with different functional groups. The disk-like hematite particles were produced from forced hydrolysis of acidic FeCl(3) solution in the presence of polyvinyl alcohol (PVA: 0-1 wt%). On the other hand, spherical particles were produced by addition of very small amounts of polyacrylamide (PAAm: 0-0.004 wt%). The size of spherical particles was slightly decreased with increase in the concentration of PAAm. The ellipsoidal particles were precipitated by addition of a very low concentration of polyacrylic acid (PAAc: 0-0.004 wt%). The effect of polymers on the hematite particle formation was expressed in the order of PVA<PAAm<PAAc that is in the reverse order from their average molecular weight. Therefore it was concluded that the effects of polymer molecules strongly depend on the functional groups of polymers. The secondary reduction steps of the concentration of Fe(3+) ions ([Fe]) were observed during aging. This secondary step of [Fe] corresponded to the time of the complete phase transformation from beta-FeOOH to hematite. Thus one was forced to conclude that the dissolution of beta-FeOOH particles is a rate-determining step in the reaction sequence for the systems with polymers. A rotational particle preparation procedure suggested that the morphology of hematite particle is governed by the mode and strength of polymer adsorption onto beta-FeOOH and polynuclear primary particles.