Abstract
The formation process of magnesium aluminate (MgAl2O4) due to the solid-state reaction of highly-dispersed and nanometer-sized aluminum and magnesium compounds has been examined by high-temperature X-ray diffractometry (HT-XRD), synchrotron radiation diffractometry (SRD) and X-ray photoelectron spectroscopy (XPS). The starting compounds were α-and γ-aluminum oxide (α-and γ-Al2O3; primary particle sizes, 105 and 31.6 nm, respectively) as aluminum sources, and magnesium oxide (MgO; 41.3 nm) and magnesium hydroxide (Mg (OH) 2; 61.1 nm) as magnesium sources. Through the combination of these compounds, four powder mixtures were prepared, namely, (i) α-Al203 and MgO, (ii) γ-Al2O3 and MgO, (iii) α-Al2O3 and Mg (OH) 2, and (iv) γ-Al2O3 and Mg (OH) 2. Phase change investigation during the heating of these mixtures indicated that the formation of MgAl2O4 due to the reaction of γ-Al2O3 with Mg (OH) 2 was faster when compared to the other combinations; almost single phase of MgAl2O4 could be obtained when this mixture was heated at 1200°C for 1 h. More detailed investigation on the formation process of MgAl2O4 was conducted using the precursor mixture of γ-Al2O3 and Mg (OH) 2 heat-treated at 800°C for 1 h. The data obtained from SRD and XPS suggested that small amounts of MgAl2O4 and ce-Al2O3, together with γ-Al2O3 and MgO, were present in this precursor. The formation of MgAl2O4 due to the reaction of γ-Al2O3 with Mg (OH) 2 was found to occur readily due to active mass transfer as a result of the very small primary particle and agglomerate sizes.
