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www.ireng.org 100


10 20 30 40 50 60 70 80 90


0 0 10 20 30 40 50 amount of Fe2 O3 60 (wt% )


Figure 5: Evolution of the phase distribution of C5S26 refractory (matrix) in reaction with iron oxide in air calculated at 1600°C


100 L iquid


10 20 30 40 50 60 70 80 90


0 0 10 20 30 40 50 wt% of Fe2 60 O3


Figure 6: Evolution of the phase distribution of C5S26 refractory (matrix) in reaction with iron oxide in air calculated at 1700°C


system of Al2 O3 -MgO-Fe2 O3 and spinel ss. By increasing the Fe2 O3


. The co-existing solid phases are corundum ss O3


content the above stability range of


both solid solutions with regard to melting decreases. At a fixed amount of 50 wt% Fe2


(red line in Figure 7), spinel ss and corundum ss will co-


exisit below 1454°C. From 1454°C to 1665°C, spinel ss is the single phase in the system, meaning the corundum reacts with iron oxide to form spinel solid solution. Above 1665°C, liquid starts to appear. As the temperature increases to 1758°C, spinel ss becomes completely molten.


2000 1900 Liquid (L) 1800 1758o L + Spinel 1700 1600 Spinel 1500 Spinel + CorS.S. 1400 0 20 wt % Fe2 O3 40 /((Al2 O3 )0.789 60 (MgO)0.211 +Fe2 Figure 7: Calculated phase diagram of the system Fe2O3 O3 - Al2 ) O3 -MgO in air


simulating the chemical reaction between A4S26 refractory (matrix) and iron oxide


July 2018 Issue 80 100 1454o C 1665o C


Onset temperature of liquid phase at 50 wt% Fe2


O3


Liquid phase content at 1600°C and 50 wt% Fe2


O3 O3


Liquid phase content at 1700°C and 50% Fe2


O3 -MgO-CaO and Al2 O3 (refractory matrix as basis, see text) ENGINEER THE REFRACTORIES 19 C 70 80 90 100 S pinel Ca(Al,Fe)12 O19


10 20 30 40 50 60 70 80 90


0 0 10 20 30 40 50 wt% of Fe2 60 O3


Figure 9: Evolution of the phase distribution of A4S26 refractory (matrix) in reaction with iron oxide in air calculated at 1700°C


As with the lime containing system earlier, the phase diagram is plotted at 1600°C (Figure 8) and at 1700°C (Figure 9). At 1600°C, there is no liquid phase in the system. Corundum ss and spinel ss coexist until the Fe2


O3


content increases above 21 wt%, because the corundum ss forms spinel ss by reaction with iron oxide.


At 1700°C (Figure 9), the corundum phase disappears at Fe2O3 8 wt%. In this case, spinel ss starts melting at 37.5 wt%Fe2


O3 O3 wt% Fe2 O3 .


In order to compare the two systems of Al2O3 MgO-Fe2


O3 -MgO-CaO-Fe2 O3 and Al2 O3 - , table 2 consolidates important results from the thermodynamic


evaluation. It shows the calcia-free system has a clear advantage to the system with calcia. The onset temperature of liquid phase for the calcia-free


Al2 O3 -MgO-CaO 1575°C 28 wt% 75.5 wt% Al2 O3 -MgO 1665°C 0 50 wt%


Table 2: Thermodynamic analysis on the effect of iron oxide to the system Al2


-MgO in air at a defined chemical composition


content of . At an iron


oxide content of wt50%, there is 50 wt% liquid phase in the system. Further increase in Fe2


content leads to complete melting of the spinel ss at 63.5 70 80 90 100 70 80 90 100 100 S pinel CaMg2 Al16 O27 S pinel Ca(Al,Fe)12 O19 L iquid CorS .S .


10 20 30 40 50 60 70 80 90


0 0 10 20 30 40 50 wt% of Fe2 60 O3


Figure 8: Evolution of the phase distribution of A4S26 refractory (matrix) in reaction with iron oxide in air calculated at 1600°C


100 S pinel S lag 70 80 90 100


Technical Paper


CorS .S .


CorS .S .


T emperature, o


C


phase distr ibution (wt %)


phase distr ibution (wt%)


phase distr ibution (wt%)


phase distr ibution (wt%)


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