HPHT Synthesis And Characterization Of NaAlSi₂O₆ Jadeite Doped With Different Oxides

Jadeite is a kind of precious gem.It is a polycrystalline mineral aggregate mainly composed of NaAlSi₂O₆.Many experts and scholars have expressed their opinions on the formation mechanism of jadeite,mainly including magmatism,metamorphism and metasomatism.In a word,the formation of jadeite is closely related to the for-mation of rocks and magmatic activities in the earth.Through the field investigation and research of many scholars,it is found that the formation of jadeite can't be sepa-rated from high-temperature and high-pressure?HPHT?environment.The natural jadeite resources are nearly exhausted due to the scarcity and wanton exploitation of jadeite deposits.Therefore,the study of synthetic jadeite has attracted more and more attention.The GE company of American announced the success of synthetic jadeite in 1985,but the company did not report the synthetic process.In consideration of cost and commercial value,GE company did not implement large-scale production and sales.At the same time,many scientific research institutes,such as Changchun Institute of Applied Chemistry,have also begun to research on the synthesis of jadeite.According to the research results of Shen Caiqing and others,the jadeites synthesized in our country are far from the standard of gem quality of jadeite at present.The main characteristics are poor light transmittance,dry quality,poor col-or,poor crystallinity,and no fine and dense fiber woven structure of natural jadeite.In recent years,our group has also carried out a lot of researches,but because the assem-bly materials have not been optimized appropriately,the synthetic samples are easy to adhere to the cavity materials and fracture,and only the doping researches of MnO and Cr₂O₃ were carried out.The synthesis of NaAlSi₂O₆ jadeite in a series of oxide doping and the synthesis process of high-quality jadeite and the coloration mechanism need to be further studied.In this paper,the synthesis of NaAlSi₂O₆ jadeites under HPHT have been further studied using Al₂?SiO₃?₃ and Na₂SiO₃?9H₂O as experimental materials doped eight kinds of main gem color causing oxides on the basis of optimizing the experimental assembly.And the gemological characteristics of the samples of NaAlSi₂O₆ jadeite have been characterized in detail.The innovative research results are as follows:?1?Adding a small amount of different color causing oxides to the mixed raw materials of Al₂?SiO₃?₃ and Na₂SiO₃?9H₂O,through the process of mixing-drying-multiple quenching,the high-quality amorphous NaAlSi₂O₆ glass material were ob-tained.This preparation of raw materials solved the problem of black spots and color spots of synthetic doped NaAlSi₂O₆ jadeite.The composite material of NaCl-ZrO₂was used in the assembly process,which not only ensured the stability of pressure and temperature of the cavity,but also solved the problem of samples fracture.The opti-mization of the two processes provided an important experimental basis for the syn-thesis of high-quality NaAlSi₂O₆ jadeite.?2?The color of undoped synthetic NaAlSi₂O₆ jadeites are milky white with uniform and dense texture.It was concluded that the pressure and temperature range of the synthesis of NaAlSi₂O₆ jadeite is:2.5-5.5 GPa,900-1530?within the maxi-mum pressure selected in this experiment and the optimum synthesis temperature at different pressure was determined through a large number of experiments.The X-ray diffraction analysis shown that the synthesized samples are pure jadeite,the peak val-ue of X-ray diffraction is the strongest at 2.93?,and the peaks at 2.84?and 2.5?are also generally strong.The results of field emission electron scanning electron mi-croscopy?FESEM?shown that the microstructures of the synthesized NaAlSi₂O₆jadeites consist of granular,columnar and felt and fiber weave structures of high-quality natural jadeite.The results of Raman spectra shown that the synthesized undoped NaAlSi₂O₆ jadeites have a typical coordination structure of jadeite.The four strong peaks of 1036 cm^-1,989 cm-¹,698 cm^-1 and 373 cm^-1 are Si-O vibration peaks.The Raman bands of 201 cm^-1,326cm^-1 and 522cm^-1 are the vibration peaks of Na⁺and Al³⁺with O.With the increased of pressure,the hardness and density of the best synthesized samples increased,and the hardness and density of the samples synthe-sized under 5.0 GPa,1450?are close to those of the natural jadeite.?3?The colors of NaAlSi₂O₆ jadeites synthesized doped with 0.4 wt%TiO₂,V₂O₅,Cr₂O₃,MnO,Fe₃O₂,CoO,NiO and CuO of eight common gem coloring oxides are gray,apple green,emerald green,pink purple,light yellow green,cobalt blue,yellow and sky blue respectively and the shapes are cylinder with height of about 3mm and diameter of about 8 mm.The colors of the synthesized samples are pure and the texture are uniform and dense.In this paper,the X-ray diffraction analysis of NaAlSi₂O₆ jadeites doped with eight kinds of oxides synthesized at 1450?and 5.0GPa were introduced.The results show that the eight samples are pure jadeite.The synthesized samples doped with 1.0 wt%MnO are a single component of violet NaAlSi₂O₆ jadeite.Only SiO₂ was detected in the samples synthesized in the low pressure and high temperature environment below 2.0 GPa.?4?The lattice parameters of doped 0.4wt%MnO NaAlSi₂O₆ jadeite under 5.0GPa,1450?were analyzed and fitted.The results show that the synthesized samples are monoclinic,the space group are C2/c,the lattice parameters are:a=9.423?,b=8.578?,c=5.232?,Beta=107.546?.At the same time,transmission electron mi-croscopy?HRTEM?shown a highly ordered lattice arrangement.The comparison of the microstructures of the samples synthesized by three kinds of optimum temperature under different pressures shown that the samples synthesized by higher pressure have more fiber woven structure of high-quality jadeite.The infrared spectra shown that the synthesized samples have the molecular vibration characteristics of natural jadeite and the hydroxyl group(OH^-1)was detected,which is due to the water absorption of the synthesized NaAlSi₂O₆ jadeite.The doped trace elements have no effect on the Raman spectra of the synthesized samples.The samples are single jadeite.Through the analysis of density and hardness of the samples synthesized under different pres-sures,the density and hardness of the synthesized doped NaAlSi₂O₆ jadeite increased with the increased of pressure.The hardness and density value of the synthesized jadeite are similar to those of the natural jadeite under 5.0 GPa,1450?.Combining with the microstructures,it was concluded that the synthesized NaAlSi₂O₆ jadeite un-der 5.0 GPa and above is better.?5?The coloration mechanism of several kinds of oxide doped NaAlSi₂O₆ jade-ites were studied by EDS,X-ray electron spectroscopy and UV-Vis absorption spec-troscopy.The content of elements in each color sample was consistent with the theo-retical value.XPS spectra shown that the binding energy of Na-O was 1072.3 eV for Na_1s,74 eV for Al_2p,102.3 eV for Si_2p,652.8 eV for Mn_2p,respectively.The UV-Vis absorption spectra of doped NaAlSi₂O₆ jadeites shown specific ion absorption.The analysis shown that the trace color-causing ions replaced the Al³⁺in jadeite and caused the Al-O octahedron to be distorted and colored,and the coloration mechanism was consistent with the ion chromogenic theory of mineral.