Dispersants and their Effects on Hydratable Alumina Containing Castables
Volume 1, Issue 1, Pages 103 - 109
Alternative hydraulic binders such as hydratable alumina (HA) have been used in refractory castables. However, the drying step of these materials is usually slower when compared to the calcium aluminate cement containing compositions. This aspect can lead to water vapor pressurization in the structure and the explosion of refractories, due to the permeability reduction, which increases the difficulty of vapor migration from the inner part of the body to its surface. Additives used in refractory castable processing to disperse the matrix usually affect the reactive alumina hydration mechanism. The dispersion of the binder particles plays an important role in the development of hydratable phases but the coating of the particle surfaces by the additive, may hinder the hydration. This behavior was observed using citric acid which resulted in higher water loss with the curing time and large pores in castable macrostructure. Polymeric additives, in turn, presented a high steric effect favoring the formation of the binding phases and allowing better processing properties for HA containing castables.
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