Novel Engineering Route to Improve the Green Mechanical Properties of Nano-Bonded Refractory Castables

M. Nouri-Khezrabad1, F. Golestani-Fard1, H. R. Rezaie1, A. P. Luz2, V. R. Salvini2, V. C. Pandolfelli2

1 School of Metallurgy and Materials Engineering, Iran University of Science and Technology (IUST), Narmak, Tehran/Iran
2 Federal University of São Carlos (UFSCar), Materials Microstructural Engineering Group (FIRE Associate Laboratory, São Carlos, 13565-905 SP/Brazil

Revision 31.05.2014, 23.09.2014

Volume 7, Issue 1, Pages 83 - 87


The use of colloidal silica as a CaO-free binding system for refractory castables has been increasing recently. Nevertheless, the resultant low green mechanical strength of these castables has hindered their application in relevant areas. The current paper provides a novel engineering route to improve the green mechanical properties of colloidal silica bonded refractories. To attain this purpose, calcium aluminate cement (CAC) and/or hydratable alumina (HA) were used as gelling agents. Splitting tensile test showed that although using HA resulted in a more significant increase in the mechanical strength of the samples when compared to CAC, using a combination of both additives (CAC+HA) had the most positive impact on the green mechanical properties of the castables, leading to strength levels as high as the reference cement-bonded system (CAC-Ref). XRD and DTG tests were carried out to evaluate the hydration behaviour of the selected additives. The results indicated that CAC enhanced the hydration of HA based on the accelerated dissolution of the gel layer formed on HA particles, which was induced by the Al(OH)4 – common ion effect. Nevertheless, XHR-SEM results showed that HA on its own is an efficient gelling agent for colloidal silica bonded refractory castables, providing a unique hybrid gelled nanostructure in the matrix.


colloidal silica, refractory castables, green strength


[1] Lee, W.E.; et al.: Castable refractory concretes. Int. Mater. Rev. 46 (2001) [3] 145–167 [2] Krietz, L.: Refractory castables, in: Schacht, C.A. (Ed.): Refractories Handbook, New York 2004, 259–285 [3] Hongo, Y.: ρ-alumina bonded castable refractories. Taikabutsu Overseas 40 (1988) [4] 226–229 [4] Ismael, M.R.; et al.: Colloidal silica as a nanostructured binder for refractory castables. Ref. Appl. and News 11 (2006) 16–20 [5] Braulio, M.A.L.; et al.: Colloidal alumina as a novel castable bonding system. refractories WORLDFORUM 3 (2011) [3] 136–141 [6] Racher, R.: Improved workability of calcia-free alumina binder Alphabond for non-cement castables, In: Proceedings of UNITECR’05, Orlando, USA, (2005) 1–8 [7] Cardoso, F.A.; et al.: Drying behavior of hydratable alumina-bonded refractory castables. J. Europ. Ceram. Soc. 24 (2004) [5] 797–802 [8] Innocentini, M.D.M.; Pardo, A.R.F.; Pandolfelli, V.C.: Permeability of high-alumina refractory castables based on various hydraulic binders. J. Amer Ceram. Soc. 85 (2002) [6] 1517–1521 [9] Banerjee, S.; Connors, C.W.: Composition and method for manufacturing steel-containment equipment. US Patent 5147830. Sept. 15, 1992 [10] Nouri-Khezrabad, M.; et al.: Nano-bonded refractory castables. Ceram. Int. 39 (2013) 3479–3497 [11] Iler, R.K.: The chemistry of silica, solubility, polymerization, colloid and surface properties and biochemistry. New York (1979) 364–372 [12] Anjos, R.D.; et al.: Workability and setting parameters evaluation of colloidal silica bonded refractory suspensions. Ceram. Int. 34 (2008) [1] 165–171 [13] Parr, C.; Wöhrmeyer C.: The advantages of calcium aluminate cement as a castable bonding system. Presented at St Louis Section Meeting of American Ceramic Society (2006), 1–20 [14] Ma, W.; Brown, P.W.: Mechanisms of reaction of hydratable aluminas. J. Amer. Ceram. Soc. 82 (1999) [2] 453–456 [15] Mista, W.; Wrzyszcz, J.: Rehydration of transition aluminas obtained by flash calcining of gibbsite. Thermomechanica Acta 331 (1999) 67–72 [16] Huang, C.C.; Kono, H.: Granulation and rehydration of rehydratable alumina powders. Ind. Eng. Chem. Res. 28 (1989) [7] 910–919 [17] Wefers, K.; Misra, C.: Oxides and hydroxides of aluminum. Alcoa Technical Report, No. 19, 1978 [18] Iler, R.K.: Coagulation of colloidal silica by calcium ions, mechanism, and effect of particle size. J. of Colloid and Interface Sci. 53 (1975) [3] 476–488 [19] Zerrouk, R.; et al.: Study of Ca2+-induced silica coagulation by small angle scattering. J. of Colloid and Interface Sci. 139 (1990) [1] 20– 29 [20] Studart, A.R.; et al.: Reaction of aluminum powder with water in cement-containing refractory castables. J. Europ. Ceram. Soc. 25 (2005) 3135–3143 [21] Marshall, W.L.; Warakomski, J.M.: Amorphous silica solubilities: II. Effect of aqueous salt solutions at 25 °C. Geochimica et Cosmochimica Acta 44 (1980) 915–924 [22] Chan, S.H.: A review on solubility and polymerization of silica. Geothermics 18 (1989) [1/2] 49–56


Göller Verlag GmbH