Abstract

The dispersion of calcium aluminate (CAC) in water is considered a challenge due to the hydration step which takes place when their particles are exposed to the aqueous media. In order to induce the dispersion, a new technology to stabilise CAC aqueous slurries, was developed. Based on this, suspensions containing up to 75 wt% of CAC and fillers, such as alumina, can be produced. After stabilisation, they can be easily reactivated by changing the pH, allowing the CAC particles to hydrate. The kinetics of hydration can be adjusted by adding some lithium source, so the time of solidification can be adjusted for different applications, such as feedstock for additive manufacturing techniques or for the production of dense and insulating refractories. In this work, the activation of stabilised slurries containing 75 wt% of Secar 71 or 15 wt% of Secar 71 and 60 wt% of alumina, was carried out. Sodium hydroxide and lithium sulphate solutions were selected to adjust the pH and the lithium content, respectively. The effect of the temperature was characterised in the range between 20°C and 50°C. Oscillatory rheometry, ultrasound speed evolution and temperature measurements were carried out in order to evaluate the microstructural changes in the reactivated slurries. According to the results, increasing the pH and the amount of lithium sulphate induced a faster solidification of the systems, which was followed by heat release associated with the precipitation of CAC hydrates. The temperature increase had a similar effect, speeding up the solidification. As it was observed in this study, CAC-stabilised slurries could be reactivated and the time of solidification could be tailored. Due to this flexibility to adjust the liquid-solid transition and the advantages of having dispersed CAC particles in an aqueous and non-toxic media, these slurries have a great potential to be used in different refractory applications.