  A growing interest in designing high-alumina MgO-bonded refractory castables
has been identified in recent years due to the magnesia ability to react: (i)
with water at the initial processing stages of these materials (inducing the
precipitation of brucite phase) or (ii) with alumina, giving rise to in situ
MgAl2O4 generation at high temperatures. Nevertheless, despite the great
potential of caustic magnesia to be used as a binder in such systems due to its
high reactivity, it is still a challenge to control the hydration reaction rate
of this oxide and the negative effects derived from the expansive feature of
Mg(OH)2 formation. Thus, this work evaluated the incorporation of different
contents of aluminum hydroxyl lactate (AHL) into caustic magnesia-bonded
castables, aiming to control the brucite precipitation during the curing and
drying steps of the prepared samples, resulting in crack-free refractories. The
designed compositions were characterized via flowability, setting behavior,
X-ray diffraction, cold flexural strength, porosity, permeability and
thermogravimetric measurements. According to the results, instead of Mg(OH)2,
hydrotalcite-like phases [Mg6Al2(OH)16(OH)2.4.5H2O and Mg6Al2(OH)16(CO3).4H2O]
were the main hydrated phases identified in the AHL-containing compositions.
The addition of 1.0 wt.% of aluminum hydroxyl lactate to the designed castable
proved to be, so far, the best option for this magnesia source, resulting in
the development of a crack-free refractory with enhanced properties and greater
spalling resistance under heating.
