Abstract
Some characteristics of sponge-irons reduced from ferric oxide and iron-ores were studied. They were reduced by hydrogen in the temperature range 400 to 800°C and re-oxidized by N2-O2 mixed gases at 400°C. The results were as follows.
1) In most cases, sponge-irons reduced in the range 600 to 700°C showed maximum re-oxidation degrees.
2) The re-oxidation degree of those sponge-irons was increased with increasing the oxygen concentration of oxidizing atmosphere.
3) When the sponge-irons reduced at 600°C were reheated at 700°C, re-oxidation showed lower values than that reduced at 700°C.
4) The behaviors of the re-oxidation were studied for several kinds of iron-ores. The sponge-irons reduced from limonite ores which have large surface areas, showed high re-oxidation degrees up to 90%.
Those from hematite ores were also re-oxidized up to 40-60%, those from magnetite ores, however, have small surface areas and lower re-oxidation degrees up to 10-20%. Although pyrite cinders have generally small surface areas, those sponge-irons showed high re-oxidation degrees.
5) Re-oxidation degrees of sponge-irons could be considered to be controlled by such factors as specific surface area, lattice strain, pore distribution and temperature rise by the heat of re-oxidation.
The factor of temperature is particularly important for low temperature re-oxidation.
