Study on Phenomena of Separating Fe Ion out from Yunnan Ruby in Heat Treatment

Most rubies on market have been heat-treated to some extent.The longest time on the research and the most prominent effect of treatment are in Thailand,thus it is very important to study the treatment technology of Thailand in order to enhance the quality of ruby from Yunnan Province. The ruby samples are tested by using EPMA,showing that besides Cr³⁺,high content of Fe ion exists in the ruby,which is the main factor for parti-colour.Bying heat treatment on the rubies respectively in Thailand(sealed,1 500~1 700(°C),t=8~15 h) and in the Gemstone Testing Centre,East China University of Science and Technology(open,1 400~1 600(°C),t=15~24 h),the parti-colour of the ruby samples are declined,with purer red and higher transparency.The reagents on the surface of the samples after heat treatment in the Gemstone Testing Centre appear yellowish-brown to some extent.Tested by ICP-AES,it is found that the yellowish-brown substance is bearing the high content of Fe ion,showing that partial Fe ion has been separated out from the samples.By contrasting and analysing the UV-VIS absorption spectra of the samples treated respectively in Thailand and in the Centre,it is shown that partial Fe ion could be separated out from the samples by the treatment in Thailand and in the Centre.The absorption of parti-coloured ions weakened is the main factor of the relative absorption of Cr³⁺ strengthening and the colour more vivid.