Sintering experiments were carried out in order to suppress the formation of large pores existed in the assimilated parts of sinter produced using pisolitic ores. A briquette consisted of disk-shaped pisolitic ore specimen as core particle and fine mixture of hematite ore and limestone as shell layer was used for the experiments. CaO concentration of the shell layer was varied in two levels, i.e., 10 and 26 mass%. The influence of CaO concentration of the shell layer and heating rate on the performance of large pore formation during heating were examined by a microscopic observation. The mean diameter and the area fraction of pores existed in the assimilated part of specimen were also measured. The results obtained were as follows: By increasing CaO concentration of the shell layer from 10 to 26 mass%, the suppression of the large pore formation was achieved in terms of the decrease in both of the diameter and amount of pores. The amount of pores decreased with decrease in heating rate over the temperature of melt-formation for both CaO concentration of the shell layer, but heating rate did not influence remarkably pore diameter. It is clear that the suppressible effect of the increase in CaO concentration of the shell layer on the formation of large pores is resulted from both of the promotion of coalescence of bubbles and decrease in the bubble size possible to move in the melt due to lowering apparent viscosity of the melt formed during heating.
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