Crystallization Control in Metallurgical Slags Using the Single Hot Thermocouple Technique

Abstract

AbstractWith the single hot thermocouple technique (SHTT) the solidification behavior of metallurgical slags has been studied by in situ observation, constructing time–temperature–transformation (TTT) or continuous‐cooling‐transformation (CCT) diagrams. The SHTT is a unique apparatus that enables measurement of the slag sample temperature using a thermocouple while the sample is heated or cooled simultaneously. Due to the low heat capacity of the system sample/thermocouple high heating or cooling rates can be easily obtained (>3000°C/min). The following findings are reported in the present paper: (i) For the CaO–Al2O3 slag – 44% CaO, 56% Al2O3 (wt%) – the CCT diagram shows large differences between liquidus and the temperature for first crystals precipitation, even at low cooling rates, for example, 168°C below the liquidus when cooling at a rate of 6°C min−1. (ii) For the CaO–SiO2 slag – % CaO/% SiO2 (wt%) = 0.7 – no crystal is observed for continuous cooling, even at low cooling rates, such as 10°C min−1. During isothermal experiments crystallization was observed only at 1000°C with an incubation time of 76 s (average of six experiments, standard deviation 27 s). However, crystallization becomes much more intense for the CaO–SiO2 slag when increasing the temperature after reaching lower temperatures (<1000°C), where probably the conditions for nucleation are better.