Hydration behavior and microstructural evolution of hydratable alumina with different particle size in alumina-spinel castables

Abstract

Considering the same chemical compositions, the particle size of hydratable alumina (HA) is the key property related to the large differences in their rheology, sintering and thermal shock resistance. It is reasonable to consider that the benefits promoted by HA, added as binder, would be affected by particle size changes. In this study, the design of alumina-spinel castables is optimized based on changing particle size to control HA hydration behavior. It is observed that the pH values and conductivities of HA slurry raise with decreasing particle size which indicates an increase in hydration rate of HA. The finer (d₅₀ 8.70 µm) HA are beneficial to motivate the hydration process and improve the mechanical properties of castables, and could also effectively enhance the thermal shock resistance as it can homogeneously hydrate in the matrix and significantly promote the sintering process. Accompanied with the dehydration and phase transformation of HA, the high density of matrix structure can be found in the castables, which is responsible for an increase of mechanical performance. However, smaller particle size and higher specific surface area can also lead to severe hydration and excessive volume expansion of matrix cracks which could induce more microdamage during the hydration and dehydration.