Abnormal Swelling on Pellet during Prereduced Process

　An investigation was made on the abnormal swelling during prereduced pellet firing. Ten kinds of iron ore and three kinds of solid reductant were tested. When pellets contained a reactive reductant, abnormal swelling occurred in some kinds of ore. This was found to be due to the growth of metallic filaments in the pellet, that grew abruptly in reduction at about 1000℃.
　The swelling was related to the unstable phase during reduction, or this may be attributed to (1)the laminated structure, (2)strain within crystals, (3)weathering of ore, (4)incomplete recrystallization and so forth.
　In experiments in which 2% of pyrite or 1% of sulphonic acid(S 15.9%) was mixed with ores, an it was found that sulphur addition was effective to prevent from swelling. However, sulphur addition was detrimental to pellet quality, because the sulphur remains in the pellet after reduction.