3.1 Magnesium oxide (MgO)

The dried powder of Mg-dissolved solution was run for DTA/TG characterization where the associated plot is given in Figure 2. A significant drop of the mass of the powdered sample between RT and approximately 600°C is related to some thermodynamic phenomena recorded as endothermic peaks. The peaks between RT and 300°C are attributed to release water molecules with a mass loss of approximately 50%, while the peak at �500°C is due to the liberation of chloride ions and molecules. The last release is also indicated by some mass drop up to 600°C. The DTA/TG observations led the synthesis of MgO. A calcination temperature range of 400–800°C was then selected. The success of the syntheses was examined mainly using XRD measurements (Figure 3).

The XRD patterns of the calcined Mg-dissolved powders clearly show the phase evolution with calcination temperature. At 400°C, only bischofite (MgCl2�6H2O) was detected. Increasing the temperature to 500°C resulted in the formation of MgO, and further calcination at 700°C gave pure MgO. This result indicates that between 400 and 700°C, there was a reaction of MgCl2�6H2O (s) ! MgO (s) + H2O (g) + Cl2 (g). As implied by the DTA/TG data, there is a drop of mass and exothermic phenomena which can be ascribed to this reaction. Further analysis shows that the composition and crystallite size of the products change subsequently (Table 4). Therefore, the Mg metal-dissolved method can produce nanocrystalline, pure MgO powder after calcination at 700°C. Calcination at 800°C does not significantly alter the phase characteristics of the powder.
