Heat Treatment of Dark Blue Sapphire from Australia

In this paper, by changing the condition of heat treatment parameters, such as temperature, atmosphere and additives, the process of heat treatment of dark blue sapphire from Australia is studied. The heat treatment results show that the temperature of 600-800 ℃ under reduced environment for 12 hours is not efficient for improving the dark blue tone of sapphire. The dark blue tone of the sapphire can be improved at the temperature of 600-1 300 ℃ for 12 hours under the environment with addition of carbon powder or open environment. When the temperature is higher than 1 400 ℃, the dark blue tone of sapphire can be enhanced, but the atmosphere environment created by carbon powder is difficult to control. The improvement effect of adding Al(OH)₃ and TiO₂ powder at the temperature of 1 300 ℃ for 12 hours in open environment is the most obvious. Under that circumstances, sapphire's dark blue tone has weakened and the colour has brightened. The variety, content and lattice position of Fe²⁺, Fe³⁺, Ti⁴⁺ and other colorized trace elements in the lattice are related to the colour change of Australian sapphire. However, the relationship between the change of absorption peak and band in UV-Vis spectrum is complicated.