泥页岩样品自然断面与氩离子抛光扫描电镜制样方法的比较与应用

Application and comparison of fresh fracture secondary electron SEM and ion-milled backscatter SEM for shale sample preparation

根据不同的研究目的,泥页岩的扫描电镜实验常用自然断面和氩离子抛光两种制样方法。自然断面的样品一般利用二次电子(SE)信号成像,反映样品表面原始形貌,图像立体感强,是最常用的制样方法。自然断面方法适合观察较大的孔隙结构,矿物及有机质形态特征,有机显微组分等。氩离子抛光样品一般利用背散射(BSE)信号成像,反映样品原子序数差异,容易区分有机质与矿物质。氩离子抛光样品表面光滑平整,适合观察泥页岩中纳米级孔隙,能直观地观察到矿物及有机质的颗粒大小及分布情况,但经过切割、研磨和抛光等一系列复杂的处理过程,样品原始形貌受到一定的破坏,会损失掉一些有用信息。本文详细比较了自然断面与氩离子抛光两种制样方法的特点及适用条件,指出如何根据样品特征及研究目的选择合适的制样方法。

There are two ways to prepare SEM samples of shale： fresh fracture secondary electron method and ion-milled backscatter method. Secondary electron SEM shows 3-D image,which can provide the original morphology and is suitable for observing large pores（larger than 1 μm）. In Secondary Electron SEM,we can identify mineral with crystal morphology and recognize organic matters（OM）in fresh fracture surface based on its macerals and occurrence. Ion-milled backscatter samples have very flat surface. The grayscale is proportional to density,so it is easy to distinguish OM and mineral. Visible pores have well-defined outlines,so it is suitable for observing small pores. Because the fragments of shale tend to block the large pores（larger than 1 μm） during sample preparation,so it is difficult to observe the whole actual pores. During the processing of samples,the surface of sample is damaged to certain extent,and some information will be lost. So the ion-milled backscatter method is not suitable for mineral and OM observation,but it is easy to observe the distribution of mineral and OM. In conclusion,the sample preparation method should be chosen according to our purpose and the feature of samples.