Shrinkage in compacts of iron oxides and ores

Compacts have been pressed from (i) four, finely ground, iron ores and (ii) mixtures of subsieve ferric oxide with up to 40 wt % of either lime, alumina, silica, or water, and have been sintered in oxygen at temperatures in the range 1000 to 1400 C. Shrinkage, macro- and micro-appearance were recorded at each sintering stage.The iron ores were classified into two groups: one was characterised by the red ferric oxide appearance and by significant shrinkage at 1000 C; the other was predominantly black and required a temperature of 1200 C to initiate shrinkage in 1 h. The shrinkages of the ores are discussed in terms of the presence of black ferric oxide, particle size, lime content, and dilution of the iron-bearing grains with inert oxides.The mixtures were used to study the effect of inert oxides on the sintering of ferric oxide. The reduction in shrinkage in the case of alumina and silica is shown to be largely a consequence of dilution; the abnormally high shrinkage at 1000 C induced by 5 wt % of lime is probably due to the presence of low-melting-point ferrites.