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Crystallization Control in Metallurgical Slags Using the Single Hot Thermocouple Technique
Author(s) -
Klug Jeferson L.,
Hagemann René,
Heck Nestor C.,
Vilela Antônio C. F.,
Heller Hans P.,
Scheller Piotr R.
Publication year - 2013
Publication title -
steel research international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.603
H-Index - 49
eISSN - 1869-344X
pISSN - 1611-3683
DOI - 10.1002/srin.201200093
Subject(s) - liquidus , thermocouple , continuous cooling transformation , isothermal transformation diagram , materials science , isothermal process , crystallization , metallurgy , slag (welding) , nucleation , precipitation , analytical chemistry (journal) , thermodynamics , microstructure , chemistry , composite material , alloy , chromatography , meteorology , austenite , bainite , physics
With 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–Al 2 O 3 slag – 44% CaO, 56% Al 2 O 3 (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–SiO 2 slag – % CaO/% SiO 2 (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–SiO 2 slag when increasing the temperature after reaching lower temperatures (<1000°C), where probably the conditions for nucleation are better.