A synchrotron radiation study of the hydrothermal synthesis of layered double hydroxides from MgO and Al2O3 slurries

The hydrothermal reaction of slurries containing MgO and Cp3 alumina has been investigated in situ using energy dispersive X-ray diffraction (EDXRD). A range of temperatures ( 100, 150, 180 and 240 degrees C) were studied. Kinetic data for the formation of the hydrotalcite-like Mg - Al layered double hydroxide (LDH) have been determined. At 100 degrees C the LDH is the predominant phase that is formed but at higher temperatures the impurity phases brucite and boehmite become more significant. The rate of reaction increases with temperature in agreement with Arrhenius behaviour and the LDH growth curves exhibit sigmoidal kinetics. The rate of formation of the LDH phase was found to be approximately equal to the rate of consumption of MgO, indicating that the mechanism of LDH formation is unlikely to proceed via a long-lasting intermediate phase.