Structure and application of the hottest metallogr

Structure and use of metallographic microscope

I. experimental purpose:

1 Understand the structure and principle of metallographic microscope

2. Familiar with the use and maintenance of metallographic microscope

II. Experimental overview:

(I) basic principle of metallographic microscope

optical microscope for studying the internal structure of metals and alloys is called metallographic microscope

convex lens can magnify and image objects, but the magnification of a single lens or a group of lenses is limited. If another group of lenses is used to magnify the first magnified image again, a higher magnification can be obtained. The metallographic microscope is designed according to this principle, and its amplification imaging principle is shown in the attached figure

there are two groups of magnifying lenses in the metallographic microscope. The group close to the object is called the objective lens, and the group close to the eye is called the eyepiece. The observed object AB is placed slightly away from the front focus F1 of the objective lens, and the light reflected by the object passes through the objective lens. After refraction by the objective lens, an enlarged inverted real image A1B1 is obtained, which is just within the front focus F2 of the eyepiece, so the eyepiece enlarges it again into an inverted virtual image a2b2, This is the image we observed under the microscope after two magnifications

(II) performance of metallographic microscope

measuring the increasingly scarce coal resources, microscope performance indicators mainly include magnification, resolution, depth of field and so on

(1) magnification M: refers to the product of objective magnification M1 and eyepiece magnification m2

M=M1 × M2

(2) resolution D: it reflects the ability of the microscope to clearly distinguish the minimum distance image between two points on the sample for the smallest tissue on the sample. The smaller the D value, the higher the discrimination rate. It is an important performance of microscope

where: λ—— Wavelength of incident light

a -- numerical aperture of objective lens

(3) depth of field refers to the vertical resolution of the microscope, which refers to the ability of the microscope to clearly image uneven objects

(III) structure of metallographic microscope

there are many types and forms of metallographic microscope, mainly including desktop, vertical and horizontal. But its basic structure is basically the same, which is usually composed of optical system, lighting system and mechanical system. Some microscopes are also equipped with a device for photographing this line, called an enhanced stage shadow device, polarized light accessories, etc., to expand the function of the microscope. The structure of domestic 4x desktop metallographic microscope is shown in Figure 2. This kind of microscope is widely used because of its light structure and simple operation

(IV) use of metallographic microscope

1. According to the magnification requirements required to observe the sample, the objective lens and eyepiece are correctly selected and installed on the objective lens base and eyepiece barrel respectively

2. Adjust the alignment between the center of the stage and the center of the objective lens. With the strong support of the state, put the prepared sample on the center of the stage with the observation surface of the sample facing down

3. insert the bulb of the microscope into the low-voltage transformer (6 ~ 8V), and then insert the transformer plug into the 220V power socket to make the bulb shine

4. turn the coarse focusing hand wheel, lower the stage, and make the observation surface of the sample close to the objective lens; Then turn the coarse focusing knob in reverse direction to raise the stage, so that the blurred image can be seen in the eyepiece; Finally, turn the fine-tuning focus hand wheel until the image is the clearest

5. Adjust the aperture diaphragm and field diaphragm appropriately, and select the appropriate filter to obtain the ideal object image

6. Move the stage back and forth, left and right, and observe different parts of the sample, so as to comprehensively analyze and find the most representative microstructure

7. After observation, the power supply should be cut off in time to prolong the service life of the bulb

8. After the experiment, remove the objective lens and eyepiece carefully, and check whether there is dust and other pollution. If there is pollution, wipe it gently with lens paper in time, and then store it in a dryer to prevent moisture and mildew. The microscope should also be covered with dust cover at any time. (end)