Submicron MgO powders have been synthesized from thermal decomposition
of magnesium chelates or acetate at around 200 degrees C in liquid al
cohol or supercritical alcohol-CO2 mixtures. Because of a similar coor
dination of the magnesium atom in both types of precursors, a common a
morphous alkoxy-hydroxy derivative is first obtained. When the reactio
n occurs in a supercritical medium with carbon dioxide as cosolvent, t
he microstructure of the solid is quite different and a CO2 group is i
ncorporated into the alkoxy bond. In all cases, the intermediate compo
und crystallizes into cubic magnesium oxide under thermal treatment be
tween 400 and 600 degrees C; the elementary particle size in the powde
rs obtained is less than 100 nm.