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Scanning Electron Microscope

electron microscope
Information about materials can often be found from visual examination; however, it is frequently necessary to go to higher magnification to observe important features of a fracture surface or the distribution and morphology of different phases. Conventional optical microscopy typically magnifies from 1 to 400 times the original size; 1000 times magnification is the upper limit. When greater magnification is required, an electron microscope can be used. The SEM is a common instrument that provides images which are intuitive and easy to understand. Magnification ranges from 20 to above 20,000 times the original size.
low magnification
Low magnification image (50X, scanning electron microscope) of stainless steel welded to cast iron. The black spots are carbon particles, and the interface between the steel and cast iron shows the heat affected weld zone.
medium magnification
Medium magnification image (500X) of an inclusion particle in zinc. In the SEM, the image is created by bombarding the specimen surface with electrons. Electrons are reflected back or ejected from the sample surface. These emitted signals are collected by a detector and converted into a gray scale image which is displayed on a computer monitor.
high magnification
High magnification image (8000X) of 4130 steel. At this magnification, the fine lamellar structure of the pearlite region can be seen.
x-ray chart
Characteristic x-rays, which are specific to the elements present, are a by-product of scanning electron microscopy. The identity and amount of the elements present can readily be determined.