The Hydration Behaviour of MgO–SiO2–H2O Gel Bonded MgO Castables

Hong Peng, Bjørn Myhre

Elkem Silicon Materials Kristiansand/Norway

Revision 25.11.2014, 02.02.2015

Volume 7, Issue 2, Pages 95 - 100


Although high-performance refractory castables play an essential role in state-of-the-art steel-making, magnesia castables have not been widely used yet. One of the major challenges is brucite formation during MgO hydration, which causes volume expansion and subsequent cracking – a phenomenon commonly called “slaking”. To overcome these problems, a new specialty product (SioxX-Mag) has recently been developed for cement-free MgO castables based on the MgO–SiO2–H2O bond. In this paper, systematic work has been carried out in order to understand the MgO hydration and to make crack-free MgO castables. Using SioxX-Mag in conjunction with microsilica, the cracking caused by the brucite formation is suppressed and crack-free dried large blocks can be made. Samples taken from the inner parts of the large blocks were investigated by XRD techniques after hydration during drying-out process. The results demonstrate that microsilica is an effective anti-hydration additive for MgO castables. When 8 % microsilica was used, MgO hydration was inhibited and no brucite phase was detected and crack-free large MgO castable blocks were made. With less microsilica (e.g. 6 %), brucite forms during drying-out process and cracks are observed in the blocks.


MgO castable, brucite formation, crack-free, gel-bonded, microsilica


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