Effect of atmosphere and basicity on softening-melting behavior of primary slag formation in cohesive zone

The softening-melting characteristics of ferrous burden play a crucial role in the thickness and position of the cohesive zone.The influence of the basicity and experimental atmosphere on the softening-melting behavior of primary slag under slag-coke interaction was investigated using in situ visualization method.The mechanism was analyzed using the FactSage software,X-ray diffraction,and electron probe microanalysis.The softening and melting temperatures of the samples increased with increasing basicity under different atmospheres.The difference between softening and melting temperatures is smaller in a H_(2) atmosphere than in a CO atmosphere;in H_(2) atmosphere,the range of softening zone in the cohesive zone was significantly thinner.The formed low-melting-point FeO-bearing phases decrease when H_(2) was used as the reducing agent.In addition,according to FactSage calculations,the high content of metallic iron reduced in the H_(2) atmosphere raised the softening temperature of the primary slag.It also narrowed and moved downward the cohesive zone due to an increase in softening and melting temperatures.Meanwhile,the increase in basicity promoted the decrease in liquid ratio and improved the permeability of cohesive zone.

Primary slag formation behavior during reduction process of SFCA-I and SFCA

Because the formation behavior of primary slag which decomposed from complex calcium ferrite(SFCA-I and SFCA)is not quite clear,the migration behavior of CaO and Al_(2)O_(3) derived from high basicity or high alumina sinter is always worth studying.The reducibility of three representative sinter samples and the formation behavior of primary slag during reduction process were investigated via X-ray diffraction,scanning electron microscopy,and energy-dispersive spectroscopy characterization.The results show that the reducibility of high basicity sinter is superior to that of high alumina sinter.Minerals with poor reducibility like hercynite and brownmillerite and with large-grained particles like free alumina and silica form in sinters with basicity of 2.4 and Al_(2)O_(3) content of 4 wt.%,respectively.The appearance of these minerals can well explain the reduction stagnation phenomenon occurring in these sinter samples.The migration behavior of CaO and Al_(2)O_(3) during slag formation process is different.CaO can easily combine with SiO2 to form silicate phase or firstly form calcium-rich ferro-aluminate solid solution and then transform to silicate phase,while Al_(2)O_(3) firstly combines with CaO and FeO to form solid solution and then,gradually combines with SiO2 to form calcium aluminum silicate phase.

Effect of quaternary basicity on softening-melting behavior of primary slag based on magnesium flux pellet

It is generally accepted that the softening-melting properties of ferrous burden play a vital role in optimizing the shape and position of cohesive zone.The effect of quaternary basicity and atmosphere on softening,melting and permeation temperatures of primary slag based on magnesium flux pellet was investigated by visualization method.The mechanisms were analyzed utilizing thermodynamic calculation,X-ray diffraction analysis and electron probe microanalysis.The results indicated that the softening and melting temperatures of oxide samples increased by approximately 120℃with increasing quaternary basicity from 0.3 to 1.2 owing to the formation of slag phases with high melting point and solid Fe.Meanwhile,the difference between softening and melting temperatures decreased from 21 to 11℃.The permeation temperature was not affected by the quaternary basicity and fluctuated around a level of 1250 C,given that the permeation temperature depends on the wettability between slag and coke bed.On the other hand,as the ratios of CO/CO_(2) varied from 3/7 to 7/3,there were no significant differences in either the softening or melting temperatures,whereas the permeation temperature was increased from 1239 to 1271℃ since the reduction of FeO-bearing phases to solid Fe could decrease the wettability between slag and coke bed.