Machinery Lubrication magazine published by Noria Corporation
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36 | July - August 2021 | www . machinerylubrication.com which can be manipulated to different positions and rotations to help enhance observations of surface features as needed. e resulting image will be monochrome (grayscale) since the objects are being observed with electrons, rather than how we observe color within the visible light spectrum. Contrast in an SEM image can be caused by physical features, differences in atomic number between materials or differences in conduc- tivity of the materials. SEM images of particles can appear differ- ently from optical images of the same particles because the electrons will penetrate the surface of the material during imaging, rather than just reflecting off the surface like light waves. Operating conditions will affect the depth of penetration of the electrons. An electron beam with a lower operating voltage will have less penetration depth but will more clearly show surface features such as oxide layers. Two major advantages of SEM over a light microscope are greater magnification and an increased depth of focus. Like a light micro- scope, the beam of electrons is focused more narrowly at higher magnifications, resulting in a clearer image but a reduced depth of focus. With an SEM, however, because the electron beam is narrower and has a smaller wavelength relative to light, it is often possible to get very high magnification and highly focused images of entire particles. Because of the larger depth of focus, we can see tall features and back- ground features simultaneously. Scanning electron microscopy is commonly used for applications like failure analysis and particle analysis. Because the SEM provides images at high magnifications, we can quan- tify the sizes and topography of particles in the sample. e higher depth of focus allows us to image large particles and small particles in the same area simultaneously, giving a better understanding of particle size distribution. We can also observe features such as wear patterns or evidence of fatigue which will provide clues to the formation of the features. Energy-Dispersive X-Ray Spectroscopy In addition to the high-resolution images of very small surfaces and features with high magnification, the SEM is typically arranged with an additional technology that can determine the particle elemental Steel debris (Fe, Si~1-2%) Spherical Wear Particles Steel debris (Fe, Si~1-2%) Fibers and Abrasive Wear From Filter Debris Flake-like Surface Fatigue Particles Zinc/Aluminum Particle from Engine Cutting Wear Iron/Zinc Particle from Engine CONDITION MONITORING, LUBRICANT ANALYSIS AND TROUBLESHOOTING