光谱学与光谱分析, 2021, 41(2): 629, 网络出版: 2021-04-08
Spectral Characteristics of Dark-Blue Corundum From Fangshan Mine, Shandong, China and Le-Shuza-Kone Mine, Mogok, Burma
为对比研究中国山东昌乐方山矿区与缅甸抹谷Le-shuza-kone矿区所产暗蓝色刚玉的光谱学特征, 并确定方山矿区和Le-shuza-kone矿区刚玉中铁元素的价态及致色机理, 采用X射线粉晶衍射(XRD)、 显微拉曼光谱(RAMAN)、 显微傅里叶红外光谱(FTIR)测试、 电子探针(EPMA)及穆斯堡尔谱(CEMS)等方法, 对产于方山矿区和Le-shuza-kone矿区暗蓝色刚玉的物相、 光谱学特征及成分开展深入研究。 X射线衍射结果表明, 两个矿区所产的刚玉在2θ=25°~45°之间以3.408 8 ?(012), 2.551 8 ?(104), 2.380 7 ?(110)和2.085 0 ?(113)四个衍射峰为特征。 缅甸抹谷Le-shuza-kone矿区刚玉在2θ=22°~23°之间有3.981 5 ?(110)的弱衍射峰, 在2θ=38°~40°之间有2.314 9 ?(111)的弱衍射峰, 分别为硬水铝石和勃姆矿(一水软铝石)的特征。 拉曼光谱散射峰主要分布于350~450和550~850 cm-1两个区间。 416和378 cm-1为刚玉的特征峰, 测试结果中415和377 cm-1的强峰属于内部结构变形导致的拉曼位移, 749 cm-1处的拉曼散射峰归属于Al-O伸缩振动。 方山矿区刚玉的793和811 cm-1拉曼峰和Le-shuza-kone矿区刚玉707, 793, 1 239和1 247 cm-1拉曼峰可作为区分产地的依据。 红外光谱表现为两个矿区样品共有指纹区451, 603, 640, 779和1 088 cm-1的吸收峰, 缅甸抹谷Le-shuza-kone矿区刚玉在官能团区有结构水(—OH)1 981, 2 110和3 311 cm-1的吸收峰, 可作为特征峰与中国山东昌乐方山矿区刚玉相区别。 缅甸抹谷Le-shuza-kone矿区暗蓝色刚玉含结构水, 其形成过程中有水的参与, 而山东昌乐方山矿区的刚玉中没有结构水。 经电子探针测试和电价差法计算, 中国山东昌乐方山矿区刚玉中铁元素的存在形式为Fe2+, Fe3+的含量为0, Le-shuza-kone矿区刚玉中Fe2+占Fe总量的91.9%, Fe3+占Fe总量的8.1%。 创新性的在刚玉中铁元素的研究中引入了穆斯堡尔谱仪测试测得中国山东昌乐方山矿区刚玉内铁的赋存形式为Fe2+, 而非Fe2++Fe3+, 其深蓝色的体色是由Fe2+致色的, 而非前人推测的Fe2++Fe3+或Fe2++Ti4+价间电荷转移致色。
To analyze spectral characteristics of dark-blue corundum from Fangshan mine, Changle, Shandong, China and Le-shuza-kone mine, Mogok, Burma comparatively, and to find out the valence state of iron and coloring mechanism of corundum from both of the mines, in this paper, we did research with the help of X-ray powder diffraction (XRD), microscopic laser RAMAN spectroscopy, microscopic Fourier infrared spectrum (FTIR), electron microprobe (EPMA), Mossbauer spectroscopy (CEMS) and other methods. The phase, spectral characteristics and composition of dark-blue corundum produced in Fangshan mine and Le-shuza-kone mine were studied. The X-ray diffraction results show that the corundum produced in the two mines is characterized by four diffraction peaks of 3.408 8/3.477 0 ? (012), 2.551 8/2.549 9 ? (104), 2.380 7/2.378 1 ? (110) and 2.085 0/2.089 4 ? (113) between 2θ angles of 25° and 45°. In addition, The corundum from Le-shuza-kone mine has a weak diffraction peak of 3.981 5 ? (110) between 2θ angles of 22° and 23°, and a weak diffraction peak of 2.314 9 ? (111) between 2θ angles of 38° and 40°, which are the characteristics of diaspore and boehmite, respectively. Raman spectral scattering peaks are mainly distributed in the two ranges of 350 to 450 and 550 to 850 cm-1. The 416 and 378 cm-1 are characteristic peaks of corundum. In the RAMAN results, the strong peaks of 415 and 377 cm-1 are displacements caused by internal structural deformation, and the Raman scattering peak at 749 cm-1 is attributed to Al—O stretching vibration. The 793, 811 cm-1 Raman peaks of corundum from Fangshan mine and the 707, 793, 1 239, 1 247 cm-1 Raman peaks of corundum from Le-shuza-kone mine can be used as the basis for distinguishing the origins. The infrared spectrum shows that the absorption peaks of 451, 603, 640, 779 and 1 088 cm-1 in the fingerprint region are common of the samples from the two mines, and in the functional group region, the absorption peaks of corundum of Le-shuza-kone mine has constitution water (—OH) peaks of 1 981, 2 110 and 3 311 cm-1, which can be distinguished from the characteristic peaks of corundum from Fangshan mine, Changle, Shandong, China. The dark-blue corundum from Le-shuza-kone mine, Mogok, Burma contains constitution water (—OH), which was involved in its formation, while the corundum from Fangshan mine, Changle, Shandong has no constitution water (—OH). According to the electron probe results and the electrovalence difference method, the iron element in the main crystal of corundum from Fangshan mine is Fe2+, and the Fe3+content of is zero. In the sample from Le-shuza-kone mine, Fe2+ accounts for 91.9% while Fe3+ accounts for 8.1% of the total amount of iron. Furthermore, the Mossbauer spectra were creatively applied in the research of Fe valence state in Fangshan-mine corundum, and the results show that the occurrence form of iron in corundum from Fangshan mine is Fe2+, and the dark-blue body color is caused by Fe2+, which is neither Fe2++Fe3+ nor Fe2++Ti4+ inter-valence charge transfer reported before.