Reaction of aluminum powder with water in cement-containing refractory castables

Aluminum powder is quite often used in refractory castables either to minimize explosive spalling during castable de-watering or to inhibit the oxidation of coke/graphite at high temperatures in carbon-containing materials. In the first case, the aluminum powder is expected to increase the permeability of castables by generating H2 gas during reaction with H2O and forming open porosity within the microstructure. In the latter application, on the other hand, it is desirable that a minimum amount of aluminum reacts with H2O during castable processing, so that most of the metal remains in the microstructure to prevent carbon oxidation. Therefore, the understanding of the mechanisms involved in the Al–H2O reaction in refractory castables is of crucial importance for an appropriate use of aluminum powder in either of these applications. This article aims at investigating the factors that determine the kinetics of the Al–H2O reaction in cement-based castables. The chemistry of the castable aqueous solution was observed to play a major role on the kinetics of this reaction. A comprehensive qualitative model is proposed in the paper to describe the rate-limiting steps and the driving forces that trigger the Al–H2O reaction in cement-based refractory castables.