Article ID: TETSU-2020-072
The formation of acicular silico-ferrite of calcium and aluminum (SFCA) with fine pores has been investigated from the perspectives of sintering temperature, cooling rate and Al2O3 concentration. Two types of hematite iron ore, lime stone, burnt lime and reagent grade Al2O3 powders were mixed so that the Al2O3 concentration was 0.8 mass% and 2 mass%. The mixed powders were uniaxially pressed into a shape of tablet, which was subjected to sintering. Both samples with low and high Al2O3 concentrations (LA and HA samples, respectively) were sintered for 10 min at constant temperatures in the range between 1215ºC and 1325ºC, and then cooled down in air. For LA samples sintered at 1255ºC, the effect of cooling rate (5ºC/min, 50ºC/min and 350ºC/min) was also examined. The samples after sintering were characterized by XRD and EPMA. XRD profiles indicated that only hematite and acicular SFCA existed above 1240ºC for LA sample and above 1230ºC for HA sample. For LA sample, in addition, EMPA indicated:
(i) the acicular SFCA melted above 1305ºC, and probably recrystallized from slag melt during the cooling cycle. The melting temperature increased with additions of Al2O3.
(ii) the fraction of fine pores except macro pores in the sinter increased with decreasing sintering temperature and decreasing cooling rate.
Hence, it is concluded that sintering at lower temperatures, more moderate cooling and higher Al2O3 concentration provide conditions suitable for formation of acicular SFCA with fine pores.