Electrical conductivity and sintering in iron oxides at high temperatures

Abstract

Two raw materials were chiefly used, namely laboratory ferric oxide and a high grade hematite. All experiments were carried out in an oxygen atmosphere, in the range 600 to 1300° C.

The conductivity/temperature determinations described are of two kinds,viz those on loose powders and those across fractures in previously compacted and sintered material. In the former, indications were obtained of differences in electrical behaviour above 1100° C which could be correlated with the appearance (red or black) of the powder. In the latter, unstable electrical behaviour was noted above the Tammann temperature in the hematite, but not in the ferric oxide.

Additionally, isothermal sintering experiments were carried out, at 975 to 1200° C on red ferric oxide, and at 1350 to 1400° C on black ferric oxide. The temperature dependence was approximately the same for both materials and the results are compatible with the electrical data, on the assumption that conductivity in general reflected particle surface conditions, whereas shrinkage was dependent on internal lattice movements.