Anisotropic Dissolution of α-Alumina (0001) and (1120) Surfaces into Adjoining Silicates

The dissolutions of the (0001) and (1120) orientations of α-Al ₂O₃ into calcium silicate, aluminosilicate, and calcium aluminosilicate melts were modeled using molecular dynamics simulations. In all cases, it was found that the (1120) surface of the crystal destabilizes and melts at a lower temperature than does the (0001) surface. This anisotropy in dissolution counters the anisotropy in grain growth, in which the outward growth of the (1120) surface occurs more rapidly than that on the (0001) surface, causing platelets. However, anisotropic dissolution occurred only at a certain temperature range, above which dissolution behavior was isotropic. The presence of calcium in the contacting silicate melt plays an important role in this anisotropic dissolution, similar to its role in anisotropic grain growth observed previously. However, anisotropic dissolution also occurs in the silicate melts not containing calcium, indicating the importance of the different surface energies. In combination with previous simulations of anisotropic grain growth in alumina, these simulations reveal a complex kinetic competition between preferential adsorption and growth versus preferential dissolution of the (1120) orientation in comparison with the (0001) orientation as a function of temperature and local composition. This, in turn, indicates potential processing variations in which to design morphology in alumina.