New Insight on Developing MgO–SiO 2 –H 2 O Gel Bonded MgO Castables

Hong Peng, Bjørn Myhre

Elkem Silicon Materials, Kristiansand/Norway


Volume 6, Issue 3, Pages 83 - 88


It is well known that brucite forms during MgO hydration and this causes volume expansion and subsequent cracking – a phenomenon commonly called “slaking”. Although much research on lab-scale small prisms has demonstrated that the interaction between MgO and SiO 2 prevents slaking, the mechanism of MgO hydration has not been well understood. Hence, magnesia castables have not been widely used. To overcome problems related to slaking, a new specialty product, SioxX-Mag, has recently been developed for cement-free MgO castables based on MgO–SiO 2 –H 2 O bond. Samples from larger, dried blocks were characterized by XRD. Using SioxX-Mag in combination with microsilica, cracking caused by brucite formation is suppressed. The results demonstrate that the dosage of microsilica and the type of dispersant play essential roles in the crack formation in large specimens. Furthermore, the compatibility of SioxX-Mag with different types of MgO aggregates, medium to high-grade dead burned magnesia and olivine, has been evaluated. High-performance, self-flowing MgO–SiO 2 –H 2 O gel bonded MgO castables have been developed, exhibiting good workability and setting behavior while hot-properties are maintained.


microsilica gel-bond, MgO hydration, MgO castables, slaking


[1] Watanabe, Y.; et al.: Development and application of monolithic refractory containing magnesia clinker. Proc. 2 nd Int. Conf. Refr. Tokyo, Japan (1987) 494–506 [2] Silva, W.M.; Aneziris C.G.; Brito, M.A.M.: Effect of alumina and silica on the hydration behavior of magnesia-based refractory castable. J. Amer. Ceram. Soc. 94 (2011) [12] 4218–4225 [3] Souzaa, T.M.; et al.: Phosphate chemical binder as an anti-hydration additive for Al 2 O 3 -MgO refractory castables. Ceramics Int. 40 (2014) 1503–1512 [4] Sandberg, B.; Mosberg, T.: Use of microsilica in binder systems for ultra-low cement castables and basic, “cement-free” castablesx. Advances in Refractories Technol. 4 (1989) 245–258 [5] Myhre, B.: Cement-free castables in the system MgO-SiO 2 : The effect of bond phase modifiers on strength. Presented at 93 rd Annual Meeting. Amer. Ceram. Soc. 1991 [6] Odegard, C.; Feldborg, H.; Myhre, B. Magnesiasilica-hydrate bonded MgO castables. Proc. of UNITECR’01, Mexico, 4–8 Nov. 2001 [7] Odegard, C.; et al. MgO-SiO 2 -H 2 O bonded MgO castables. Part 1: Effect on flow, set and hot properties when substituting microsilica with alumina in pumpable MgO castables. 4 th Int. Symposium on Refractories (Dalian, China), (2003) 148–156 [8] Ghanbari Ahari, K; Sharp, J.H.; Lee, W.E.: Hydration of refractory oxides in castable bond systems II: alumina-silica and magnesia-silica mixtures”. J. Europ. Ceram. Soc. 23 (2003) [16] 3071–3077 [9] Salomão, R.; Pandolfelli, V.C.: Microsilica addition as an antihydration technique for magne- sia-containing refractory castables. Amer. Ceram. Soc. Bull. 86 {2007) [6] 9301–9306 [10] Salomão, R.; Bittencourt, L.R.M.; Pandolfelli, V.C.: A novel approach for magnesia hydration assessment in refractory castables. Ceram. Int. 33 (2007) [5] [11] Durán, T.; et al: Interactions in calcium aluminate cement (CAC)-based castables containing magnesia. Part I: Hydration-dehydration behavior of MgO in the absence of CAC. J. Amer. Ceram. Soc. 94 (2011) [3] 902–908 [12] Souza, T.M.: Systemic analysis of MgO hydration effects on alumina-magnesia refractory castables”. Ceram. Int. 38 (2012) [5] 3969–3976 [13] Sako, E.Y.: Braulio, M.A.L.; Pandolfelli, V.C.: Micro structural evolution of magnesia-based castables containing microsilica. Ceram. Inter. 8 (2012) [7] 6027–6033 [14] Peng, H.; Myhre, B.; Luo, M.: New additive packages for self-flowing high-alumina and MgO based refractory castables. Proc. ALAFAR 2012, Cancùn, Mexico, 5–8 Nov. 2012 [15] Peng, H.; Myhre, B.; Luo, M.: Cement free MgO castables Part I, flow, setting and slaking. Proc. UNITCER’13, Canada (2013) [16] EMMA (Elkem Materials – Mixture Analyzer) soft ware, free download at:


Göller Verlag GmbH