SEM/X-ray imaging of cement-based materials

Next: Imaging Processing Up: Sample Preparation and Imaging Techniques Previous: Sample Preparation

2.2 Image Acquisition

The specimen is placed in the SEM viewing chamber, and signals are collected for the backscattered electrons and X-rays. Typical accelerating voltage and probe current for the backscattered electron images are 12 kV and 2 nA, respectively. For the X-ray images, the probe current is increased to about 10 nA. For cements, in addition to the backscattered electron signal, X-ray images are collected for Ca, Si, Al, Fe, S, K, and Mg. For fly ash, other X-ray signals may be desirable such as Cl, Zn, or Pb. Because these X-ray images are collected at the same location as the backscattered electron image, this series of images can be combined to determine the mineral phase present at each location (pixel) in the two-dimensional image (typically 512 pixels by 400 pixels in size). Typically, magnifications of 250X or 500X are employed for obtaining the SEM images.