Study On Color And Change Of Sapphire In Shandong Province

The theme of this paper is to study and change the color of Shandong sapphire. It firstly expounds some background knowledge such as the origin of modern science of gemstones’ color, Shandong sapphire’s output condition, the reason of its coloration, principle of its colour changing. And then, on the common colour, brown and dark blue varieties of Shandong sapphire, using the method of thermal diffusion in the additive to change its colour. That is, incorporating titanium, beryllium, magnesium and other elements to do the treatment in a high temperature furnace. Study on the color causing part is mainly by using electron probe X-ray micro analyzer to test its containing element type and content.Sapphire has output in many countries around the world. The most famous is the "cornflower" blue sapphire from Kashmir, India. But now, it is almost extinct. In addition, it is also found many excellent quality of sapphire in Sri Lanka, Burma, Thailandand, Australia and other countries. Sapphire from Shandong is a special one in all kinds of sapphires. Shandong sapphires’ colour is different from other areas’. Unlike the sapphires that have bright, gorgeous and translucent colour from Burma, Sri Lanka, Thailand and other areas, Shandong sapphires’main colours are ink blue, dark bule, and different shades of brown. A few of them are yellow or have green tone. So its colour affects its commercial value a lot. Therefore, changing the colour of Shandong sapphire becomes more and more scholars’ research direction at the same time.Colour changing experiment on Shandong sapphire is mainly through adding agents such as TiO2、BeO and MgO, to do the thermal diffusion under different temperature and holding time. Thus improve the not ideal colour. Using conventional gemmological testing and a variety of spectroscopic analysis on samples before and after colour change treatment, it has been found that after treatment, samples’ colour is more bright and lively, and the transparency is also improved. In the experimental temperature range, the higher the temperature, the better the results:temperature of 1200℃ heat diffusion treatment is not enough to improve the samples’ color. Above 1400℃ makes samples’features such as color, transparency etc improved significantly. Samples’ dark inner core, and impurities in open fractures are weakened or disappeared. Diffusion treatment with beryllium oxide can make Shandong sapphire’s originally light or almost colorless parts become yellow. Compared the purely α-Al2O3 corundum diffraction data to the sample’s diffraction data before experiment, can explain from the side that natural Shandong sapphire itself contains many large radius of trace element ions, and they make a isomorphous substitution with aluminum ion. After diffusion treatment, there have some changes in the diffraction pattern than before, including the changing of diffraction peak’s position and intensity. That illustrates the adding ions went into the internal of samples after experiment. Due to the high temperature heat treatment, which makes the samples’ inside atoms rearrange, leading to the change of some peaks on strength.Study on mechanism of coloration is accomplished by the composition analysis of electron probe. Comparing and calculating sample’s composition measured by the electron probe, we found that the content of various trace elements in Shandong sapphire showed a consistent fluctuation tendency. The rule of fluctuation is mainly due to the ring of samples’. And the content of ferric iron led to very high in all the ions. We can see proportion of bivalent iron and ferric iron ions at the same time. Result of sample’s composition testing by electron probe after colour changing experiment also indicates that the adding ions go into samples during experiment. However, where there is a high content of magnesium, there is a relatively low content of iron. It could be speculated that magnesium ions are also involved in isomorphous substitutionin.Through the composition and spectroscopic studies of Shandong sapphire, we can know that the iron content is very high. After colour changing treatment, diffusion agents went into the samples and the iron content in them decreased correspondingly. Only when the temperature of colour changing treatment over 1400℃, it could emerge obvious effect. And the diffusion of Be and Mg can produce a richer color than Ti.