High Temperature Slag

Name: High Temperature Slag
Diagram No.: 1158
Type of diagram: TTT
Chemical composition in weight %: See the table
Group: Slags
Note: TTT curves of the different samples.
The TTT curves of different samples were presented in Figure. As can be seen, these TTT curves showed a similar shape, that is a double C from high temperature to low temperature, which suggested that two different crystallization events occurred. As the slag melt was quenched from 1500 C, the crystallization was not observed when it was higher than the break temperature (the highest temperature at which crystallization could appear), indicating that the waste heat recovery from the slags can last a long time during this temperature interval. It can be seen that the break temperature increased from sample A1 to A3, which suggested that the crystallization was enhanced by Al2O3 addition.

As the temperature decreased lower than the break temperature, crystals may precipitate after an incubation time. The incubation time decreased with the decrease of isothermal temperature until the nose position, then it increased with further decreasing temperature to the separate temperature between these two C shapes. With the decrease of temperature, the undercooling degree was increased, which was beneficial for crystal formation, whereas the viscosity increased at the same time, which suppressed the crystal formation. These two factors caused by temperature decrease influenced the crystal precipitation in opposite directions and caused the appearance of a shortest incubation time, i.e., at the nose position. The shortest incubation time at the nose position suggested that the waste heat recovery time with medium must be very quick at this temperature in order to avoid crystallization.

With further decreasing temperature, a similar variation tendency as with the first C shape was observed in the crystallization temperature range. Finally the temperature was decreased to a low temperature zone where no crystallization was observed due to the high resistance of mass transfer caused by the higher viscosity. These results indicated that the waste heat recovery time from slags could be set up with temperature, and the cooling process was therefore determined based on the TTT curves. An apparent trend was observed in that the TTT curves moved to the left side in high temperature zones with increasing Al2O3 content, which indicated that the crystallization was enhanced by Al2O3. This suggested that an increasing Al2O3 content resulted in a lower waste heat recovery time in this temperature interval. It is also noted that the second C shape in low temperature zones did not show an apparent variation tendency for different samples, which might be because that the effect of undercooling on the crystallization was greater than that of the Al2O3 content.

Reference: Not shown in this demo version.

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