Process Exploration of Heat Treatment on Ruby and Sapphire from Madagascar

Some pieces of Madagascar colourful corundum were chosen as samples．According to the colour characteristics，they were divided into three categories：red，yellow-green and blue-green．By changing temperatures，atmosphere and adding auxiliary agent in the heat treatment，the authors explored the best heat treatment plan.
According to the resuit of heat treatment at different temperatures，it can be found that the heat treatment of red Madagascar ruby samples should be conducted in oxidizing atmosphere at the temperature of 1 500℃.After the treatment，the tone of red Madagascar ruby samples turned brighter and the blue-violet colour was eliminated.
According to the resuit of heat treatment at different atmosphere，it can be found that the heat treatment of yellow-green and blue-green sapphires should be conducted in reducing atmosphere at the temperature 0f 1 500℃.After treatment，yellow-green tone of the samples was weakened and blue tone was deepened.The treatment can produce pure and uniform blue colour.In the experiment，the carbon power for reducing atmosphere should be avoid to contact with the samples directly，which may be difficult to remove from the samples.
It’s worth to mention that，in both oxidizing and reducing atmosphere of heat treatment，the brown stripes of samples can be eliminated effectively.So the eliminating of brown stripes is unrelated to atmosphere，but the temperature.High temperature can make the structure become loose and more conducive to the spread of Fe²⁺，thereby reducing the transition of 0^2-→Fe²⁺.eliminating the brown colour.
Additional，since these ruby and sapphire samples from Madagascar have few fissures and good transparency，it is no need to add borax as an auxiliary for heat treatment.The result of heat treatment shows that borax added as auxiliary agent does not improve the colour and it turns into white crystalline material at high temperature，which finally covers the surface of the sample and affects the transparency.