The Hydration Behaviour of MgO–SiO2–H2O Gel Bonded MgO Castables
Elkem Silicon Materials Kristiansand/Norway
Revision 25.11.2014, 02.02.2015
Volume 7, Issue 2, Pages 95 - 100
Abstract
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.
Keywords
MgO castable, brucite formation, crack-free, gel-bonded, microsilica
References
[1] Watanabe, Y.; et al.: Development and application of Monolithic Refractory Containing Magnesia Clinker. Proc. 2nd Int. Conf. Refractories. Tokyo, Japan (1987) 494–506 [2] Silva, W.M.; Aneziris, C.G.; Modestino, A.M.B.: Effect of alumina and silica on the hydration behavior of magnesia-based refractory castables. J. Amer. Ceram. Soc. 94 (2011) [12] 4218–4225 [3] Souzaa, T.M.; et al.: Phosphate chemical binder as an anti-hydration additive for Al2O3-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” castables. Advances in Refractories Technology 4 (1989) 245–258 [5] Myhre, B.: Cement-free castables in the system MgO-SiO2: The effect of bond phase modifiers on strength. Presented at 93rd Annual Meeting, Amer. Ceram. Soc. (1991) [6] Odegard, C.; Feldborg, H.; Myhre, B.: Magnesia- silica-hydrate bonded MgO castables”. Proc. UNITECR’01, Mexico, 4–8th Nov. 2001 [7] 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 [8] Salomão, R.; Pandolfelli, V.C.: Microsilica addition as an antihydration technique for magnesia- containing refractory castables. Amer. Ceram. Soc. Bull. 86 (2007) [6] 9301–9306 [9] Salomão, R.; Bittencourt, L.R.M.; Pandolfelli, V.C.: A novel approach for magnesia hydration assessment in refractory castables. Ceram. Int. 33 (2007) [5] 803–810 [10] 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 [11] Souza, T.M.; et al.: Systemic analysis of MgO hydration effects on alumina-magnesia refractory castables. Ceram. Int. 38 (2012) [5] 3969– 3976 [12] Sako, E.Y.; Braulio, M.A.L.; Pandolfelli, V.C.: Microstructural evolution of magnesia-based castables containing microsilica. Ceram. Int. 38 (2012) [7] 6027–6033 [13] 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 [14] Myhre, B.; Peng, H.; Luo, M.: Cement free MgO castables Part I, flow, setting and slaking. Proc. UNITCER’13, Canada 2013 [15] EMMA (Elkem Materials – Mixture Analyzer) software, free download at: http://www.materials.elkem.com/
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