Microscope micrometer to determine the degree of dust dispersion (objective micrometer / eyepiece micrometer)
Dust dispersion refers to the degree of solid particles of different sizes, expressed in% composition.
Principle of membrane filtration method:
The filtered membrane is dissolved in an organic solvent to form a suspension of dust particles. After the smear is made, the size of the dust particles (um) is measured under the microscope with an eyepiece micrometer.
[Equipment and reagents] Dust filter, micrometer for eyepiece and micrometer for objective lens; small test tube, small glass rod, one dropper, several slides; butyl acetate or ethyl acetate.
Steps:
Preparation of Dust Specimen (1) Put the filter membrane with dust in a small test tube, add 1 ~ 2ml of butyl acetate, dissolve the filter membrane, and stir it with a glass rod to make it into a uniform dust suspension.
(2) Take one drop of the suspension on the slide glass to make a smear. After one minute, a layer of dust film will appear on the slide glass.
Selection of microscope eyepiece and objective lens The ability of the microscope to distinguish small objects depends mainly on the objective lens. Under normal circumstances, to determine the degree of dispersion, a high-power objective lens can be used in conjunction with a 10-fold eyepiece. For special requirements, an oil lens can be used.
The size of the calibrated dust particles in the eyepiece micrometer is measured with the eyepiece micrometer placed in the eyepiece. When the magnification of the objective lens of the microscope changes, although the size of the uranium ruler in the field of view of the eyepiece does not change, the size of the measured object in the field of view also changes accordingly. Perform calibration.
For the calibration method, please refer to C2 type √2n mesh eyepiece ruler scale calibration measurement. Take off the objective micrometer and replace it with the prepared dust specimen. Under the high magnification lens, use the calibrated eyepiece micrometer to measure the size of the dust particles in sequence. When measuring the long diameter with the long diameter and the short diameter with the short diameter, each specimen should measure at least 200 dust particles, and follow the table below Group records.
Precautions
1. The glassware used should be kept clean to avoid dust pollution.
2. If the dust particles on the smear are too many and overlap, which affects the measurement, you can add an appropriate amount of acetic acid to the ester to dilute to prepare a smear; if the dust particles are too small, the two filters at the same sampling point can be dissolved together , And then make the film for measurement, the results are not affected.
3. Before each batch of filter membranes is used, it is necessary to conduct a photo experiment to measure the contamination. If the filter membrane itself contains only a small amount of dust, it will have little effect on the results.
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