Chemical processes and composition of the gas and solid phases in the Al2O3-Mo system in the temperature range 2327–2500 K

The possibility of chemical reactions has been calculated and the composition of the gas and solid phases that are in equilibrium with an aluminum oxide melt is determined. It is shown that, for the Al 2 O 3 -Mo system in the pressure range 1−1 × 10 −5 bar, evaporation of Al 2 O 3 is incongruent, and the fraction of this component in the gas phase decreases from 51.5 mol % ( P = 1 bar) to 0.01 mol % ( P = 1 × 10 −5 bar). The presence of molybdenum-containing compounds in the gas phase changes the balance of oxygen and aluminum in favor of the latter (the aluminum partial pressure increases by a factor of 1.5–3), as a result of which there may be an aluminum deficit in the solid phase of Al 2 O 3 during crystal growth from a melt. The thermodynamic characteristics ( K p , Δ G , P tot ) of dominant chemical reactions have been calculated for the temperature range 2327–2500 K. Understanding of the chemical processes makes it possible to optimize the growth parameters of leucosapphire single crystals.