绿色蓝晶石的宝石学特征及颜色成因分析

蓝晶石化学式Al_(2)SiO_(5),属岛状硅酸盐,宝石级蓝晶石常见蓝色、绿色、黄色、橙色、褐色和无色。由于绿色蓝晶石的颜色成因存在争议,选取宝石级绿色蓝晶石,利用X射线荧光光谱(XRF)、中红外光谱(Mid FT-IR)、紫外-可见光谱(UV-Vis)和电子顺磁共振波谱(EPR)等相关谱学测试,对其致色离子配位与颜色成因进行分析。结果表明,蓝晶石样品中Fe^(2+)、Fe^(3+)和Cr^(3+)类质同象替代和离子电荷转移的方式广泛;Fe^(3+)和Cr^(3+)类质同象替代Al―O八面体,Fe^(3+)在可见光区引起432 nm和446 nm吸收峰,Cr^(3+)导致600 nm中心宽吸收带,形成530 nm附近的绿色光透过窗,而使样品呈绿色;在垂直于c轴方向,上述现象尤为明显,可使样品在该方向出现绿色-黄绿色多色性;平行于c轴方向上,Cr^(3+)与Al―O八面体位类质同象替代与蓝色调有关,过量的Fe^(2+)―Fe^(3+)电荷转移则会使蓝晶石带有黄色调。

Machining of Single‑Crystal Sapphire with Polysaccharide‑Bonded Abrasive Tool

A novel polysaccharide-bonded abrasive tool is proposed for the green machining of single-crystal sapphires.The prescription and manufacturing process of the proposed tool is designed,and the gelation property of polysaccharide by microwave treatment is investigated.Abrasive tool samples are fabricated,and a machining experiment on a single-crystal sapphire is performed.It is found that the crystallinity of polysaccharide gel decreases as the proportion of cross-linked polysaccharide increases.Abrasive tool samples with cross-linked polysaccharide present higher surface hardness.With the new abrasive tool,the surface quality of sapphire wafer can be significantly improved.This new tool with an abrasive to binder ratio of 2∶1 attains a material removal rate of 0.68μm/min.It is found that increasing the abrasive to binder ratio leads to better self-dressing performance but worse material removal ability and greater loss of abrasive tool materials.The validity of polysaccharide as an abrasive tool binder is preliminarily verified.