Change in Structure of Fe3O4 Precipitate by Heat Treatment

Abstract

By the addition of KOH solution to FeSO4-Cr2(SO4)3 mixed solution, Fe(OH)2 was formed and it was oxidized to Fe3O4 by air. The heat treatment of formed Fe3O4 precipitate was carried out in vaccum (10-5 Torr) and in H2-H2O mixed gas (H2O/H2=2) at 200~500°C for 5 hrs. The effects of the heating temperature on particle size, surface area and pore structure (pore distribution, pore diameter, pore volume) were investigated by means of X-ray diffraction, electron microscopy and gas adsorption. Addition of Cr(III) suppressed the particle growth of Fe3O4 and also increased the surface area remarkably. By the heat treatment of the precipitate; 1) The particle growth of Fe3O4 occurred slightly at temperatures above 400°C, 2) The surface area changed with rise in temperature, that is, the area increased with temperature up to about 300°C and showed a maximum at this temperature. Above 300°C, however, the area decreased. The increase in surface area was caused by micropore (diameter <50 Å) resulting from the removal of water contained, and the decrease was caused by the pore-widening process resulting from sintering of the precipitate at temperatures above 400°C, 3) The changes of particle size, surface area and pore structure were also affected by heating atmosphere. © 1974, The Chemical Society of Japan. All rights reserved.