热处理宝石级黄色榍石的光谱特征与颜色成因初探
Spectral Characteristics and Color Mechanism of Heat-Treated Gem-Quality Yellow Sphene
王沛炼 1岳素伟 2李嘉妍1
作者信息
- 1. 广州城市理工学院珠宝学院,广东广州 510800
- 2. 广州番禺职业技术学院珠宝学院,广东广州 511400
- 折叠
摘要
榍石是钙钛岛状硅酸盐矿物,晶莹剔透者可作宝石,其中Ca2+、Ti4+、Si4+可被其他元素所替代.选取黄色榍石进行热处理,结果显示样品在700 ℃及以上的氧化气氛中加热,变为棕红色,还原气氛再次加热可褪回黄色.电子探针成分分析显示,样品成分与标准榍石成分一致,含少量FeO(均值0.601 wt％)、Al2O3(均值0.210 wt％).中红外反射光谱1 600～400 cm-1与标准榍石一致,可见由O—Si—O和Si-O振动引起的吸收;中红外透射光谱4 000～2 000 cm-1处可见O—H振动引起的吸收,并伴有3 450 cm-1为中心的吸收宽带;近红外光谱10 000～4 000 cm-1处可见O—H振动引起的吸收.紫外-可见吸收光谱显示,榍石样品(未加热)的黄色是Fe2+类质同象替代Ti4+占据八面体位产生Fe2+→Ti4+(IVCT)电荷转移形成的420 nm吸收带,及由O2-→Fe2+和O2-→Fe3+间电荷转移所致450 nm向紫外的强吸收边所致;氧化热处理变棕红是因为部分Fe2+变为Fe3+,产生Fe2+→Fe3+(IVCT)所致的540与450 nm向紫外强吸收边的叠加.
Abstract
Sphene is known as titanite,which is a transparent neosilicate mineral that can be used as a gem.Other elements can substitute the cations Ca2+,Ti4+,and Si4+in sphene.Yellow sphene was selected for heat treatment to explore the heat treatment process of sphene.The results showed that the yellow sphene samples were heated in an oxidizing atmosphere at 700 ℃ and turned brown-red above,whereas,the reducing atmosphere heated again to turn yellow again.The composition analyzed by the electron microprobe analysis(EMPA)shows that the samples are consistent with the standard sphene composition,and also contain a small amount of FeO(average 0.601 wt％)and Al2O3(average 0.210 wt％).The mid-infrared reflectance spectra 1 600～400 cm-1 are consistent with standard titanite,showing absorptions attributed to O—Si—O and Si—O vibrations.In the mid-infrared transmission spectra 4 000～2 000 cm-1,the absorption is caused by O-H stretching vibration and accompanied by 3 450 cm-1 centered absorptions broadband.In the near-infrared transmission spectra 10 000～4 000 cm-1,the absorption is caused by O—H stretching vibration.The UV-visible absorption spectrum illustrates that the yellow color of the untreated titanite sample is due to the substitution of Fe2+as an isomorphic counterpart for Ti4+in the octahedral site,leading to the charge transfer forms of Fe2+to Ti4+(IVCT),generating an absorption band at 420 nm.The charge transfer between O2-→Fe2+and O2-→Fe3+causes the strong absorption towards the ultraviolet at 450 nm.The brownish-red color after oxidation treatment is attributed to the partial conversion of Fe2+to Fe3+,resulting in the overlapping of the strong absorption edge at 540 and 450 nm towards the ultraviolet respectively,caused by the charge transfer forms of Fe2+to Fe3+(IVCT).
关键词
电子探针/红外光谱/紫外-可见光谱/热处理/榍石Key words
EMPA/Infrared spectrum/Ultraviolet-visible spectrum/Heat treatment/Sphene引用本文复制引用
基金项目
国家自然科学基金项目(41403032)
广东省普通高校特色创新类项目(2022KTSCX184)
出版年
2024
NETL
NSTL
万方数据