Institute of Mineral Engineering, RWTH Aachen mail: kieliba@ghi.rwth-aachen.de Ilona KIELIBA ESR Position 05 Thermal cyclic characteristic of alumina-spinel steel ladle brick Dr.-Ing. Thorsten TONNESEN, RWTH Aachen Prof. Marc HUGER, University of Limoges The study of the thermal cyclic characteristic of alumina-spinel steel ladle brick constitutes an initial part of the Ph.D. ATHOR project dedicated to monitoring of gradual fatigue to thermal cycling. Within the framework of this project alumina – spinel refractories, both brick and monolithic solutions will be characterized under thermal cycling conditions. Obtained results will contribute to a better understanding of the microstructural and thermomechanical degradation phenomena taking place in industrial processes and support modeling surveys by providing valuable data regarding damage kinetics. EXPERIMENTAL PROCEDURE: • Resonant frequency and damping measurements have been utilized for the continuous monitoring of microstructural changes taking place in alumina – spinel brick exposed to heating-cooling cycling. • Temperature dependence of the Young’s modulus has been shown to exhibit typical for refractories hysteresis shape. • As expected high temperature damping measurement has been proven to be more sensitive to microstructural alterations and therefore reveals some phenomena that are undetectable by Young’s modulus measurements. • Two step evolution of microstructural changes in the temperature range 1000 -1500°C should be further investigated, but it is very likely that complex alumina spinel solid- state reactions determine material behaviour at this heating and cooling stage. Supervisors & Industrial mentors Acknowledgments This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement no.764987 Consortium of 15 European Partners Dr. Erwan GUÉGUEN, RHI MAGNESITA References: 1. Tonnesen, T. & Telle, R. Thermal shock damage in castables: microstructural changes and evaluation by a damping method. Ceramic Forum Int. 84, 1–5 (2007). 2. Tessier-Doyen, N., Glandus, J. C. & Huger, M. Untypical Young’s modulus evolution of model refractories at high temperature. J. Eur. Ceram. Soc. 26, 289–295 (2006). Alumina-spinel brick is being increasingly used in steel industry applications, especially in steel ladles mainly due to growing need of ultralow carbon metallurgy. Damage of refractories in secondary furnaces is induced by several factors like corrosion and abrasion but also thermal spalling and extensive thermal cracking, originated from prolonged thermal cycling, constitute a serious concern. For the design of the cyclically loaded material, knowledge of the elastic properties and their evolution with temperature and thermal history is a fundamental requirement. Continues monitoring of Young's modulus value and damping behaviour versus temperature provide a substantial information about the microstructural alterations taking place in the material exposed to thermal cycling conditions. Especially damping measurements, which have been proven to be very sensitive in detecting and following microstructural phenomena as: crack initiation and propagation1, stress relaxation, phase transition, diffusion and precipitation, should by increasingly implemented in the microstructural studies. Determination of damping temperature dependency can deliver information undetectable by other techniques, which will constitute an additional scientific basic for further development and microstructural material optimization. Young's modulus behaviour under thermal cycling conditions Prof. Rainer TELLE, RWTH Aachen In the literature2 typical hysteresis curve and stages observed during heating and cooling of the refractory material are described and explained as follow: • At intermediate temperatures because of CTE mismatches between the phases a crack closure and therefore, an increase in Young's modulus is observed. During cooling an