缅甸抹谷Baw⁃mar矿区蓝宝石的热处理及谱学研究

Study on heat treatment and spectroscopy of sapphire from Baw⁃mar Mine,Mogok,Myanmar

目前缅甸抹谷矿区开采的蓝宝石原石约80%都要经过优化处理才能投入市场,其中主要为热处理。本文对缅甸抹谷Baw⁃mar矿区蓝宝石进行不同温度制度的热处理,并利用电子探针、X射线粉晶衍射仪(XRD)、紫外-可见-近红外光谱仪、傅里叶红外光谱仪和激光拉曼光谱仪对其热处理前后的谱学特征进行了对比研究。结果表明,1300℃热处理后所有样品2θ<60°的XRD衍射峰开始向低角度方向偏移,晶胞参数c/a值随热处理温度升高而降低,推测与其晶体结构在高温下发生畸变有关;Baw⁃mar矿区蓝宝石的主要致色元素是Fe、Ti和V,其中Fe和Ti共同导致其呈蓝色,V使其略带绿色调,部分样品的灰色调主要由Ni所致;热处理后样品中Fe^(2+)⁃Ti^(4+)荷移增强,Fe^(2+)⁃Fe^(3+)荷移减弱,导致585 nm紫外吸收带增强,746和764 nm吸收峰减弱,同时样品颜色变蓝且灰色调减弱;红外光谱中,样品出现1988、2123 cm^(-1)硬水铝石羟基倍频振动吸收峰和3619、3696 cm^(-1)高岭石外羟内羟振动吸收峰,热处理后由于硬水铝石和高岭石完全脱水,晶体结构被破坏导致羟基吸收峰全部消失;1100℃热处理后出现1324 cm^(-1)拉曼谱峰并随温度升高逐渐增强,推测其为高温下熔融硼砂和Al_(2)O_(3)反应形成玻璃态物质沿裂隙进入蓝宝石内部所致。本文的研究也为进一步探讨其改色工艺提供了思路和依据。

At present,about 80 percent of rough sapphire mined from the Mogok mine in Myanmar must be optimized before being put into the market,mainly heat treatment.In this paper,the sapphire from Baw⁃mar mine,Mogok,Myanmar is heat treated with different temperature regimes,and electron microprobe,X⁃ray powder crystal diffractometer(XRD),ultraviolet⁃visible⁃near infrared spectrometer,fourier infrared spectrometer and laser raman spectrometer were used to compare the spectroscopic characteristics before and after heat treatment.The results show that after heat treatment at 1300℃,all XRD peaks of sapphire with 2θ<60°begin to shift to low angle direction,and the ratio of unit cell parameter c/a decreases with the increase of heat treatment temperature,which is presumed to be related to the distortion of its crystal at high temperature.The main chromogenic elements of sapphire in Baw⁃mar mining area are Fe,Ti and V,among which Fe and Ti together cause it to be blue,V makes it slightly green,and the gray color of some samples is mainly caused by Ni.After the heat treatment,the charge transfer of Fe^(2+)⁃Ti^(4+) is enhanced,and the charge transfer of Fe^(2+)⁃Fe^(3+) is weakened,resulting in an enhanced 585 nm ultraviolet absorption band and a weakened absorption peak at 746 and 764 nm.At the same time,the color of the sample turns blue and the gray tone weakens.In the infrared spectra,the sample appears at 1988,2123 cm^(-1) diaspore hydroxyl frequency doubled vibration absorption peaks and 3619,3696 cm^(-1) kaolinite outer hydroxyl and inner hydroxyl vibration absorption peaks.After the heat treatment,the diaspore and kaolinite are completely dehydrated,and the crystal structure is destroyed,resulting in the disappearance of all the hydroxyl absorption peaks.After heat treatment at 1100℃,the Raman peak at 1324 cm^(-1) appeared and gradually increased with the increase of temperature.It is speculated that it is caused by the reaction of molten borax and Al_(2)O_(3) at high temperature to form glassy substances along the cracks and enter the interior of the sapphire.The research in this paper also provides ideas and basis for further discussion of its color changing process.