Study On Artificial Synthetic Jade And Its Gemological Characteristics

Synthetic jadeite lacks of detailed research in the jadeite gemological field. In this thesis, we tried to synthesize jadeite by traditional solid-state reaction method. In addition,we researched the process which making raw material of sythetic jadeite by sol-gel method in detail, and the technological parameters of sol-gel method were determined through orthogonal experiments. Meanwhile, we researched the subsequent sintering and repeated sintering experiment to synthetize jadeite samples. The conventional gemological research methods, XRD, SEM, FTIR, TG-DTA, absorption spectra and colorimetric test were utilized to research and analysis the preparation of raw material, the sintering experiment, and the mineral gemological characteristics of the synthetic jadeite.The experimental results indicate that the synthetic jadeite samples by solid-state reaction method had a large number of irregular holes, and the diameter of hole is larger. Although the elements content percentage of samples is close to the nature jadeite, there were Al2O3 and SiO2 hybrid compound formed in the samples, and the samples exhibited the mixture color of green and pink-purple because of that Cr3+ doped into crystal lattice of two phases.The best preparation parameters of sol-gel experiment which made raw material of synthetic jadeite was with the TEOS density of 1.0 mol/L, the amount of deionied water (H2O/ [Si] mole ratio) of 20:1, pH value of 2, water-bath temperature of 60℃, the content of Cr(NO3)3 · 9H2O of 0.75 wt%. The order of these factors which influence the result of sol-gel experiment was:pH value> the TEOS density and water-bath temperature> the amount of deionied water> the content of Cr(NO3)3 · 9H2O. The powder precursors of synthetic jadeite were prepared by the best preparation parameters of sol-gel experiment.The raw material of synthetic jadeite by sol-gel method were sintered in the high temperature to get synthetic jadeite samples. The color of the samples are dark green, and there are a lot of holes in the samples. The phenomenon is because of the impurity element oxided to volatile gas, but part of the gas residued in the samples to form the holes, and the experimental results point out that adding flux could help to reduce holes. At the same time, the raw material of synthetic jadeite by sol-gel method repeated heat preservation at 1000℃, which is the crystallization temperature, got the structure of nepheline (NaAlSiO4), rather than the structure of jadeite. This is due to the jadeite is a typical high-pressure mineral, which is metastable at ordinary pressure. And it would decompose into NaAlSiO4 and SiO2 easily, namely NaAlSi2O6â†'NaAlSiO4+SiO2. Sol-gel method is more suitable for synthesizing jadeite than solid-state reaction method, by comparing the color and appearance, basic gemological properties, phase and structure of the synthetic jadeite samples made by the different way.In order to achieve the experimental effect, we conducted the repeated sintering experiment of synthetic jadeite by sol-gel method, on the basis of the sintering experiments. The results show that the density of repeated sintered samples increased significantly, and lots of small holes distribute in the samples uniformly. The samples are yellow-green, with high color saturation and low lightness slightly. There is NaAlSiO4 crystal in the repeated sintering samples, and the elements content percentage of samples is very close to the nature jadeite. Though the infrared spectrum of repeated sintering samples is similar to nature jadeite, the absorption band of synthetic jadeite is wide and the fissility is poor.