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Lab_Report_Microstructure

Lab_Report_Microstructure - 1st YEAR COMMON ENGINEERING...

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1 st YEAR COMMON ENGINEERING COURSE LAB REPORT MICROSTRUCTURES OF MATERIALS Name: SHAFIQ SAMSUDIN Matric: 067437E03 Group: BL13 Date: 18.09.2006 1
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TABLE OF CONTENTS 1. Introduction Pg 3 - 4 2. Literature Review Pg 5 - 8 3. Experiment Setup Pg 9 - 10 4. Question & Answer Pg 11 - 12 5. Conclusion Pg 13 6. References Pg 14 2
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INTRODUCTION This experiment introduces the study of different microstructures in polymeric, ceramic and metallic materials. The microstructure of a material is important as it affects the final physical and mechanical properties of the material. Samples which have similar chemical compositions but different microstructures can have vastly different physical and mechanical properties. As most materials are microscopic in nature, it is difficult to view them with a naked eye and as such the study of microstructures of materials involves the use of microscopes at higher magnifications. Materials that are opaque to visible light (all metals and many ceramics and polymers), only the surface is subject to observation, and the light microscope must be used in a reflecting mode. As shown in Figure 1, a horizontal beam of light from some light source is reflected by means of a plane-glass reflector, downward through the microscope objective onto the surface of the material. Some of this incident light reflected from the material surface will be magnified in passing through the plane-glass reflector and be magnified again by the upper lens system, the eyepiece. The initial magnifying power of the objective and the eyepiece is usually engraved on the lens mount. In the case of polymers, it is more common to view the microstructure by focusing the light to go through the sample. As the light goes through the objective lens and eyepiece, the image observed from the sample surface is magnified to a given magnification. Transmitting light microscope utilizes the polarization of light. Natural sunlight and most forms of artificial illumination transmit light waves whose electric field vectors vibrate in all perpendicular planes with respect to the direction of propagation. When the electric field vectors are restricted to a single plane by filtration then the light is said to be polarized with respect to the direction of propagation and all waves vibrate in the same plane. Transmitting light microscope uses two crossed polarizer’s that the first polarizer is placed below the specimen in the light path and the analyzer is placed above the sample, between the objective and the eyepiece. Polarizer 1 is oriented vertically in the incident beam so it will pass only the waves that are vertical in the incident beam. The waves passing through polarizer 1 are subsequently blocked by the analyzer because the analyzer is oriented horizontally with respect to the electric field vectors in the light waves. With no sample on the microscopic stage, the light polarized by the polarizer is blocked by the analyzer and no light is visible. When a sample that is birefringent is viewed on the stage between the crossed polarizer’s, you can visualize the aspects of the sample through the light rotated by the sample and then able to pass through the analyzer.
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