Behaviour of α-Fe2O3 (hematite), prepared by oxidation precipitation of ferrous sulphate, on heating

The effects of heatingα-Fe2O3 (hematite) prepared by oxidation precipitation of ferrous sulphate, at temperatures up to 700° C were studied. It was found that, in the course of heating, losses of structurally-bound water occured, accompanied by the formation and removal of pores, the lattice constants changed and the optical properties were modified, an effect which is important from the standpoint of the use of hematite as ferric pigment. With increasing annealing temperature, the complementary wavelength was shifted to higher values and the spectral purity of the pigment colour was decreased.