AC LEC 13-09

AC LEC 13-09 - Lecture 13 Microstructure and Microscopy OM...

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Lecture 13 – Microstructure and Microscopy Microstructure Optical microscopy Scanning Electron Microscopy (SEM) Transmission Electron Microscopy (TEM) Atomic Force Microscopy (AFM) SEM SPM TEM OM
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Materials Science and Engineering Structure-Property Relationship Requires Microstructural Characterization Inter-relationship between Structure Atomic Bonding Microstructure Properties Physical Engineering Processing Manipulate Microstructure
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Optical Microscopy and Metallography Generally done below 2000x Uses reflection of visible light Inverted microscope Specimen is ground, polished and etched Can find Grain Size Distribution of phases Manufacturing defects Limited in resolution
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Contrast in OM
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Resolution, Magnification and Depth of Field Resolution: Ability to resolve detail; the closest spacing of two points that can be seen clearly through the microscope to be separate entities Magnification: Size of a feature on the image divided by the size of the same feature on the actual specimen being studied Depth of Field: Distance along the optical axis over which details of the object can be observed with adequate sharpness. i.e. it is the range of positions of the object for which the eye can detect no change in the sharpness of the image
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Resolution Resolving Power is a distance; it is a measure of resolution - it should be SMALL RP = Resolving Power = (0.612 λ ) / (NA) where: NA = Numerical Aperture = η sin α λ = wavelength of light being used η = index of refraction α = light gathering angle Hence: for better Resolution (low RP) : low λ (e.g. green filter) high ηΠ (e.g. oil immersion lens) Large α (lens design)
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Resolution and the Human Eye Resolution of human eye: 0.01 cm at 25 cm Resolving power of metallurgical microscope is dependent on Objective magnification (see Table) Suppose sample has two features 10,000Å
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AC LEC 13-09 - Lecture 13 Microstructure and Microscopy OM...

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