Metallographic microscope principle, optical application and precautions for use

Metallographic microscope principle

Metallographic analysis is a method by which metallographic microscopes are used to study the size, morphology, distribution, quantity and properties of metals and alloys. Microstructure refers to characteristic structures such as grains, inclusions, inclusions, and phase change products. This method is used to examine the relationship between alloying elements, compositional changes and changes in microstructure: changes in the introduction of cold and hot processing to the tissue; metallographic testing can also be used for quality control and product inspection and failure analysis. Wait.

Application field

Metallographic microscope electronic eyepieces are suitable for any standard biological, stereoscopic, and metallographic microscopes. They can be widely used in medical and health institutions, laboratories, research institutes, and universities for biology, pathology, bacteriology, and teaching. And research, clinical trials and routine medical testing; analysis and identification of materials in factories and laboratories.

Metallographic microscopes are still the most commonly used instruments in routine inspection and research work due to their ease of operation, large field of view, and relatively low cost.

In recent years, the improvement of metallographic microscopes has the following main points:

Infinity optical system

The objective lens is designed according to the infinity image distance rather than the finite image distance as in the conventional objective lens. This optical system is called an infinity chromatic aberration and aberration correction optical system or simply an infinity optical system. When using this optical system When the incident light is reflected from the surface of the sample and enters the objective lens again, it does not converge but remains as a parallel beam until it passes through the lens barrel and converges to form an intermediate image, that is, the image is magnified once, and then the eyepiece is amplified again. The advantages of an infinity optical system are the various optical accessories in the microscope (such as dark field beam splitters, polarized light splitters, prisms for differential interference contrast), polarisers, and other additional color filters). The space of the parallel beam between the objective lens flange and the mirror lens can be placed. Since the imaging beam is not interfered by the above optical accessory, the quality of the object image is not impaired, thereby simplifying the correction of chromatic aberration and aberration in the objective lens design. In addition, in an infinity optical system, the barrel length factor remains one, no matter how far the objective lens is from the eyepiece, a fixed relay lens system is not required. At present, German companies and companies, Japanese companies and metallographic microscopes produced by olympus have adopted infinity optical system design.

Flat field achromatic objective

Today's new microscopes have used flat-field achromatic objectives and even more advanced flat-field apochromat objectives. The diameter of the first-time magnified image of the old-fashioned objective lens is only 18mm~20mm, while the flat-field achromatic objective lens specifies that the height-corrected initial magnification plane image has a diameter of 28mm, that is, the image field area is doubled, and the image field curvature is obtained. Very good correction.

Wide field eyepiece

The structural feature of the wide-field eyepiece is that the field pupil is significantly increased, generally 22mm to 26.5mm (the field pupil diameter of the old eyepiece is only 16mm), making full use of the enlarged field area of ​​the flat field objective.

In addition, some microscopes are also equipped with high-eye eyepieces, so that people with defective eyes (such as astigmatism) can wear glasses to observe, the quality of the object can be protected from eye defects. Due to the popularization of the afield achromatic objective lens and the wide-field eyepiece, the field of view of the microstructure observation is greatly expanded, which correspondingly increases the processing precision and sample preparation quality of the microscope stage.

Long working distance objective

Some microscope manufacturers have also introduced some objective lenses with long working distances, which are designed to meet production inspections or special needs (such as high temperature stations). In general, the higher the magnification of the objective lens, the working distance (ie, when the object is focused). The shorter the distance between the objective lens and the sample, the special objective lens is designed to prevent the objective lens from being damaged due to accidental contact with the sample during work or heat. For example, in the objective lens series of the NikonEPIPHOT300 metallographic microscope, there are 50× and 100× long working distance objective lenses with working distances of 8.7mm and 2.0mm respectively, and the NA values ​​are 0.55 and 0.8 respectively; another example is the olympusGX series microscope. With a working distance of 50× and 100× working distances of 10.6 mm and 3.4 mm, respectively, the NA values ​​are 0.55 and 0.8, respectively, while the working distances of 50× and 100× ordinary objectives are only 0.54 mm and 0.3 mm, respectively. However, their NA values ​​are 0.8 and 0.95, respectively. It can be seen that the numerical aperture of the objective lens with a long working distance has a reduced resolution, but the image quality is still good.

Metallographic microscope use precautions

1. Under the condition of permission, it is recommended that your laboratory should have three prevention conditions: shockproof (away from the source), moisture proof (using air conditioner, dryer), dustproof (floor laying on the floor); power supply: 220V ± 10%, 50HZ ; Temperature: 0 ° C - 40 ° C.

2. When focusing, be careful not to let the objective lens touch the sample to avoid scratching the objective lens.

3. When the position of the center of the circular hole of the stage gasket is away from the center of the objective lens, do not switch the objective lens to avoid scratching the objective lens.

4, the brightness adjustment should not be too big and small, and not too bright, affecting the life of the bulb, but also damage the vision.

5, all (function) switch, the action should be light, to be in place.

6. Turn off the brightness to a minimum when shutting down.

7. Non-professionals should not adjust the lighting system (filament position light) to avoid affecting the image quality.

8. Pay attention to high temperature when replacing the halogen lamp to avoid burns; be careful not to touch the glass body of the halogen lamp directly by hand.

9. When the machine is not used for shutdown, adjust the objective lens to the lowest state through the focusing mechanism.

10. When the machine is not used for shutdown, do not cover the dust cover immediately. After cooling, cover it again and pay attention to fire prevention.