Particle size distribution refers to the use of specific instruments and methods to reflect the difference betweenParticle sizePercentage of particles in total particlespercentage。There are two forms of interval distribution and cumulative distribution.Interval distribution is also calleddifferentialDistribution orfrequency distribution, which represents the percentage content of particles in a series of particle size ranges.The cumulative distribution is also called the integral distribution, which represents the percentage content of particles smaller or larger than a certain size.
Chinese name
Particle size distribution
Foreign name
particle size distribution
Definition
Percentage of samples with different particle sizes in total particles
There are two key indicators for granularity characteristics, which are introduced as follows：
① D50: cumulative particle size distribution of one samplepercentageThe corresponding particle size when reaching 50%.itsPhysical meaningThe particles larger than it account for 50%, and the particles smaller than it also account for 50%,D50Also called median diameter or median particle size.D50 is commonly used to represent theAverage particle size。
② D97: The corresponding particle size when the cumulative particle size distribution of a sample reaches 97%.Its physical meaning is that 97% of the particles are smaller than it.D97 is often used to indicate the particle size index of the coarse end of the powder.The definitions and physical meanings of other parameters such as D16 and D90 are similar to D97.
Data representation
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Table 2.2
It is usually impossible to measure each particle separately, so the particles are divided into several appropriately narrow particle size ranges during particle size analysis.The data is generally listed in table form (Table 2.2), but the graphical representation (such as the relationship between quantity and granularity) is clearer (Figure 2.2).[1]
Mathematical equations can also be used to describe particle size distribution.Although some people have tried to connect these mathematical formulas with actual fracture mechanics, most of them are empirical formulas that are only convenient for expressing data.When data must be processed, the mathematical formula may be useful;But this often requires the use of computers, and under such conditions, the matrix representation of actual data is also convenient and more reliable.[1]
Figure 2.2
The graphical representation of particle size data usually lists the particle size in the abscissa (x-axis) and the measured reference quantity in the ordinate (y-axis).There are two ways to express quantity: one is to list the quantity (absolute quantity, fraction, or percentage) in each particle size; the other is to list the cumulative quantity (fraction or percentage) higher or lower than a certain particle size.[1]
Measurement principle
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Dust settles in order of particle size in liquid or gas phase medium.The dust concentration of different particle sizes in the light column is measured at a certain sedimentation height h by light transmission method, and the particle size distribution of the dust is calculated.[2]
Determination steps
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1. Switch onParticle size analyzer(hereinafter referred to as the instrument) power supply, preheating for 15min.
2. Input the true density of dust, liquid level height, density and viscosity of butyl acetate at the measured temperature according to the instrument use procedure.
3. After the instrument prints the input valueButyl acetatePour into a clean instrument measuring cell, and the pouring amount is about 2/3 of the liquid level height.Put the measuring cell with butyl acetate into the measuring position of the instrument, and adjust the zero adjustment knob to make the instrument display the optical density value of 0.0.
4. Put the dusty filter membrane into a clean porcelain crucible or beaker, drop 5~10mL butyl acetate and stir it fully with a glass rod.During mixing, use a pipette to drop the dusty liquid into the measuring cell filled with butyl acetate to make the liquid level reach the input liquid level scale.
5. For coal mine dust not normally taken on the filter membraneAnhydrous ethanolInstead of butyl acetate.The method is to take 3~5g of dust and fully mix it on white paper. Use a horn spoon to take about 10mg of dust and put it into a clean crucible or beaker. Operate according to the method described in Article 4.
6. Put on the cover of the measuring cell, hold the measuring cell tightly with your thumb and shake it fully, so that the dust in the measuring cell is evenly dispersed, and at the same time, wipe the liquid on the surface of the measuring cell with absorbent cotton gauze.Quickly put the measuring cell into the measuring position of the instrument, so that the optical density value displayed by the instrument is within the range of 90~100, and quickly press the measurement key to start measuring the dust distribution.If the optical density value initially displayed by the instrument is not within the range of 90~100, it means that the concentration of the suspension is too high or too low, and the dust concentration in the liquid needs to be readjusted.
7. After pressing the measurement key, the instrument starts to display the measurement time and the optical density value of the corresponding time at 0.5s intervals.Calculate the time t required for the dust particle size to be measured according to the following formula.When the time displayed by the instrument is greater than t, press the Halfway Stop key, and the instrument will automatically print the required dust particle size distribution of all levels of particle size that is not less than the dust particle size.[2]
