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Effects of Changing the Specific Surface Area in the Ceramic Matrix of CAC-Containing Refractory Castables on the Dispersion and Mixing Process
F. Holleyn1, T. Waldstädt2, J. Kasper2, L.T. Ibarra Plata1, C. Dannert2, O. Krause1
1 Koblenz University of Applied Sciences, Rheinstrasse 56, 56203 Höhr-Grenzhausen, Germany
2 Forschungsgemeinschaft Feuerfest e. V. at the European Centre for Refractories, Rheinstrasse 58, 56203 Höhr-Grenzhausen, Germany
received October 16, 2024, received in revised form April 24, 2025, accepted May 7, 2025
Vol. 16, No. 3, Pages 173-186 DOI: 10.4416/JCST2024-00023
Abstract
Beside the coarse and medium grain size distribution, the matrix components play a central role in the performance of refractory castables. On the basis of practical experience, it is evident that the particle size distribution (PSD) and the resulting specific surface area of the ceramic matrix exert a significant influence on the processing, setting and sintering properties of refractory castables, which in turn influence each other. However, there is a lack of detailed highly systematic studies regarding the extent to which the properties of refractory castables are influenced by changes in the PSD or specific surface area of the raw materials in the matrix. The objective is to gain a general understanding of this.
To shed more light on this issue, the ceramic matrices were varied, resulting in model castables with gradations in the specific surface area of the matrix. The refractory castables were dispersed using three different dispersing agents with different mechanisms of action (electrosteric and steric) at graded concentrations.
The findings of this study demonstrate that refractory model castables with variations in the specific surface areas of the ceramic matrix and different dispersing agents and their concentrations necessitate substantial differences in the required mixing energy. Castables with matrices containing larger quantities of highly sintered and (very) finely ground alumina raw materials (with high specific surface areas) require less mixing energy than mixtures with lower specific surface areas. An increase of the dispersing agent content also results in a reduction in the required mixing energy and lower temperature evolution, with due consideration of the respective water content. A clear correlation can be established between the mixing energy introduced and the temperature increase during mixing. Castables with higher specific surface areas of the matrix require less mixing energy and therefore heat up less during the mixing process than castables with lower specific surface areas. The findings of the measurements of the dynamic viscosity of matrix suspensions in high shear rate ranges support these observations.
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Keywords
Refractory castables, specific surface area, dispersing agents, mixing process, rheology.
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