Key words: aluminum oxide, group II metal compounds, water fluid, ammonia, aluminates, heat treatment
The formation of mixed oxides in the Al2O3—MO (M — Mg, Ca, Sr, Ba) system during
heat treatment and treatment with water fluids (WF) has been studied. It is shown that
during high-temperature treatment of mixtures of aluminum hydroxide Al(OH)3 with
nitrates of metals of group II, aluminates of the composition MAl2O4 are formed mainly,
sometimes with an admixture of aluminates of a different composition. If the same mixtures
undergo preliminary treatment in a water fluid (400 °C, fluid density 0,2 g/cm3), then the
sample is more complex, which is associated with dehydration and partial structuring of
the Al-containing component during processing in a WF medium. It is shown that the
addition of ammonia to WF has a stimulating effect on the formation of double oxides,
first of all, due to the alkaline hydrolysis of salts of II group metals and the formation of
corresponding hydroxides; the reduction of nitrates and nitrites with ammonia is apparently
a secondary process.