Morphological Forms Control of α-Al_2O_3 Crystal Spontaneously Synthesized by Hydrothermal Method

The shape and the interface morphological forms of α-Al_2O_3 crystal synthesized by hydrothermal method at high temperature and high pressure were investigated. Under the hydrothermal conditions, the shapes of the α-Al_2O_3 crystal have a close correlation with synthesized temperature and mineralizer concentration.When the concentration of KOH and the temperature are rather low (eg.0.1M KOH,390℃),the exposed faces of crystal are faces c{0001},a {11-20},r{01-12},n{11-23}. With the increase of the mineralizer concentration and the temperature, the exposed areas of faces r｛01-12｝ and n｛11-23｝ become smaller and smaller, till disappeared(eg. 2M KOH, 400℃), then the crystal only exposes bottom faces c ｛0001｝ and prism faces a ｛11-20｝, and appears hexagonal prism.