Physico-chemical processes in single crystal growing of calcium aluminates by zone melting

The growing of single crystals of calcium aluminates of compositions 12 CaO · 7 Al₂O₂, CaO · Al₂O₃, and CaO · 2 Al₂O₃ by zone melting under vacuum of 10⁻⁵ mm Hg permitted to establish that some of the Al³⁺ ions in octahedral coordination have been driven back by the moving crystallization front. Energetically, this process can be represented on the basis of the viscous flow model with the activation energy of −45 kcal/mole. The possible mathematical models have been considered for the processes of preparation of single phase crystals of the aluminates mentioned above which take account of incongruent vaporization of the component oxides and refining of the melt from structural impurities by the moving crystallization front.