Which microscope to use for observing dust particles
Dust analysis generally involves several aspects of research: observing the surface structure of dust, measuring the degree of dispersion of dust, studying the particle size of dust, counting dust particles, and so on.
Then for research in different directions, the size and state of the dust required to be seen are not the same. What kind of microscope should be used for observation when doing what kind of experiment, and what type of microscope is most suitable for the observation of dust samples , What software can be used to analyze, process and study dust particles. Ruike Zhongyi specializes in operating various types of microscopes, and can provide corresponding professional microscope products for different purposes of users.
First of all, dust needs to be classified, and there are multiple classification methods for dust.
1. Classification according to material composition: According to material composition, dust can be divided into organic dust, inorganic dust and mixed dust. Organic dust includes plant dust, animal dust, and processed organic dust; inorganic dust includes mineral dust, metal dust, and processed inorganic dust.
2. According to the particle size classification, according to the size of the dust particles or the degree of visibility under the microscope, the dust can be divided into: coarse dust, the particle size is greater than 40?m, which is equivalent to the minimum particle size of general screening; 40?m, visible to the naked eye under bright light; microscopic dust, with a particle size of 0.25~10?m, can be observed with an optical microscope; submicroscopic dust, with a particle size of less than 0.25?m, can only be observed with an electron microscope . Dusts of different particle sizes settle in different positions in the respiratory organs, and are divided into: respirable dust, which can be inhaled by respiratory organs, with a diameter greater than 10 μm; fine dust with a diameter of less than 2.5 μm, The fine dust will settle in the alveoli of the human body.
3. Classified by shape, dust of different shapes can be divided into: (1) Three-way equal-length particles, that is, particles with the same or close dimensions of length, width, and height, such as regular polygons and other similar irregular shapes (2) Sheet-shaped particles, that is, the length of two directions is much longer than the third direction, such as thin flakes and scales; (3) Fiber-shaped particles, that is, much longer in one direction Particles, such as columnar, needle-shaped, and dimensional particles; (4) spherical particles, round or oval in shape.
4. According to the classification of physical and chemical properties, the dust with different properties can be distinguished by the wettability, viscosity, combustion and explosiveness, electrical conductivity and fluidity of the dust. For example, according to the wettability of the dust, it is divided into a wet angle of less than 90°. The hydrophilic dust and wetting angle are greater than 90. Hydrophobic dust; according to the viscosity of the dust, it can be divided into non-sticky dust with a breaking force of less than 60Pa, slightly sticky dust with a breaking force of 60-300Pa, medium-sticky dust with a breaking force of 300-600Pa, and strong sticky dust greater than 600Pa; according to dust burning, Candle flower explosives are divided into flammable, explosive dust and general dust; according to the fluidity of powder, it can be divided into angle of repose less than 30. The dust with good fluidity has an angle of repose of 30. ~45. Medium fluidity dust and angle of repose greater than 45. Dust with poor mobility. According to the conductivity of the dust and the difficulty of electrostatic dust removal, it can be divided into high specific electric negative dust greater than 1011Ω?cm, 104~1011Ω?cm is called specific resistance dust, and low specific electric negative dust less than 104Ω?cm.
5. Other classifications include productive dust and atmospheric dust, fibrous dust and granular dust, primary dust and secondary dust, etc.
At present, the existing dust particle size measurement methods at home and abroad can be divided into three categories in principle: microscope method, sedimentation method and classification method. Among them, microscopy is the only method that can observe and measure individual particles, and is often regarded as the best method for particle analysis.
Example description: using a microscope to measure the dispersion of dust
(1) Membrane dissolution smear method
1. Principle Dissolve the dust-collected filter membrane in butyl acetate, stir evenly, make a dust sample, and measure it under a microscope.
2. Reagents and equipment Butyl acetate (CP), microscope, eyepiece and objective micrometer
3. Operation steps Put the dust collection filter membrane in a small beaker, add 1-2ml butyl acetate and stir evenly to make a dust sample. Under the magnification of 400 to 600 times, the size of dust particles is measured with an eyepiece micrometer. Only at least 200 particles are measured, and the long diameter is measured in case of long diameter, and the short diameter is measured in case of short diameter. Record according to <2μm, 2μm-, 5μm-, >10μm, and calculate the percentage (%).
(2) Natural settlement method
1. Principle The dusty air is collected in the settler, the dust particles are naturally settled on the cover glass, the specimen is prepared and measured under the microscope.
2. Equipment Green settler, microscope, eyepiece and objective micrometer
3. Operation steps Put the coverslip in the groove of the settler. The dusty air is placed in the cylinder of the settler. After resting horizontally for 3 hours, the coverslips were removed to prepare dust samples. When measuring the dispersion degree of dust particles, the dispersion degree counting method of the natural sedimentation method and the filter membrane dissolution smear method is the same.
According to various types of experiments, it can be seen that the types of microscopes that may be used for dust research include biological microscopes, metallographic microscopes, phase contrast microscopes, dark field microscopes, and stereo microscopes. Different microscopes can analyze and magnify dust differently.
