31-05-2013, 12:28 PM
Optical Microscopes
[attachment=54553]
Introduction:
The use of "Optical Microscopes" in "Materials Evaluation" is very popular since it enables the researcher to observe the "internal structure" of materials. This information can then be used to improve material processing and properties which form the foundation of materials science and engineering (MSE).
The microstructure generally ranges from the atomic scale (0.1nm) to 1mm(1000µm) with the most widely used scale of 1-1000 µm. Practically the optical microscopes can be used up to 2000x at which the resolution becomes so poor that objects smaller than 1 µm cannot be distinguished. But since most materials have grain sizes in the range 1-100µm optical microscope (OM) is a perfect low cost tool. Typical microstructural features are grains(single crystal), precipitates, inclusions, pores, whiskers, defects, twin boundaries, etc. Most of the manufacturers use OMs for process control and R&D.
There are mainly two types of optical microscopes (OM): Reflected Light (RL) and Transmitted Light (TL). In the former the light is reflected from the surface of the specimen while in the latter the sample is so thin (20-50µm) that light passes through it. A third but less important type may be the stereo microscopes that do not require any sample prep and are generally used to observe fracture surfaces, electronic circuit boards, etc. Reflected Light Optical Microscopes are the most widely used machines in materials science. Because they involve light reflection the specimen surface must be very well polished to a "mirror finish". In order to have a mirror finish the sample goes through a number of "sample preparation treatments":
BF Illumination is used in the following modes:
(1) Plane polarized light (PP): Most widely used illumination technique in MSE. Grain size measurements, precipitates, inclusions, are all observed in this mode. PP is achieved by inserting a polarizing filter into the incoming light path. This filter kills the wave's electrical wave component's vibration in all directions except in one direction. This direction corresponds to that of the filter orientation. E.g. light passing through the window through the blinds (jaluzi).
[attachment=54553]
Introduction:
The use of "Optical Microscopes" in "Materials Evaluation" is very popular since it enables the researcher to observe the "internal structure" of materials. This information can then be used to improve material processing and properties which form the foundation of materials science and engineering (MSE).
The microstructure generally ranges from the atomic scale (0.1nm) to 1mm(1000µm) with the most widely used scale of 1-1000 µm. Practically the optical microscopes can be used up to 2000x at which the resolution becomes so poor that objects smaller than 1 µm cannot be distinguished. But since most materials have grain sizes in the range 1-100µm optical microscope (OM) is a perfect low cost tool. Typical microstructural features are grains(single crystal), precipitates, inclusions, pores, whiskers, defects, twin boundaries, etc. Most of the manufacturers use OMs for process control and R&D.
There are mainly two types of optical microscopes (OM): Reflected Light (RL) and Transmitted Light (TL). In the former the light is reflected from the surface of the specimen while in the latter the sample is so thin (20-50µm) that light passes through it. A third but less important type may be the stereo microscopes that do not require any sample prep and are generally used to observe fracture surfaces, electronic circuit boards, etc. Reflected Light Optical Microscopes are the most widely used machines in materials science. Because they involve light reflection the specimen surface must be very well polished to a "mirror finish". In order to have a mirror finish the sample goes through a number of "sample preparation treatments":
BF Illumination is used in the following modes:
(1) Plane polarized light (PP): Most widely used illumination technique in MSE. Grain size measurements, precipitates, inclusions, are all observed in this mode. PP is achieved by inserting a polarizing filter into the incoming light path. This filter kills the wave's electrical wave component's vibration in all directions except in one direction. This direction corresponds to that of the filter orientation. E.g. light passing through the window through the blinds (jaluzi).