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

H. R. Rezaie1, A. P. Luz2, V. R. Salvini2, M. Nouri-Khezrabad3, F. Golestani-Fard3, V. C. Pandolfelli4

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
3 School of Metallurgy and Materials Engineering, Iran University of Science and Technology (IUST), Narmak, Tehran/Iran
4 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

Abstract

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.

Keywords

colloidal silica, refractory castables, green strength

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