Sieve fractionation

In industrial practice, the size-distribution cui ve usually is not actually construc ted. Instead, a mean value of the population density for any sieve fraction of interest (in essence, the population density of the particle of average dimension in that fraction) is determined directly as AN/AL, AN being the number of particles retained on the sieve and AL being the difference between the mesh sizes of the retaining sieve and its immediate predecessor. It is common to employ the units of (mm-L)" for n. 

MgS04 or NaOH and distd under vacuum. Further dried by reaction with sodium under nitrogen, refluxed for several hours and distd. The distillate was then passed through a column of Linde type 4A molecular sieves and finally distd under nitrogen, from more molecular sieves. Fractionally distd. 

Data in Table I reveal that sieved fractions of different particle size distribution lose varying amounts of moisture dining the same drying period at 70° C. The last column in the table shows that the apparent percentage of moisture in the different frac-... 

Bisdom EBA, Dekker LW, Schoute JFT. Water repellency of sieve fractions from sandy soils with organic material and soil structure. Geoderma 1993 56 105-118. 

For these experiments, a binary mixture of sieved fractions of 150-250 pm (nominally 200 pm) and 710-840 pm (nominally 775 pm) glass beads was used. A symmetrical initial condition (top-to-bottom loading) is implemented. The blender is run at constant rotation rate a segregation pattern was assumed to be stable when it did not discernibly change for 100 revolutions. In many pharmaceutical operations, the mixing time is on the order of 100 500 revolutions, and experiments are run with regard to this timeframe. 

Figure 21 Change in the value of one plane critical stability with the number of revolutions of the spheronizer plate for granules from within the largest sieve fraction for batches spheronized on varying diameter plates A, 22.9 cm A, 38.1 cm , 65.6 cm.

In considering the correlation results, it is well to keep in mind the range of fractionation, as indicated by the values of the r89,95 ratio, shown by the samples in question. For the Small Boy event most of the gross samples from the collecting stations in the local fallout field yielded values of 189,95 in the range between 0.1 and 0.2. However, when cloud samples, sieve fraction samples, and samples from the peripheral stations are also considered, the range of the ratio runs from about 0.01 to about 7.0. 

Figure 2. Onset of softening of a coal of 23.0% volatile matter daf at 390°C. Pore formation in the coarse sieve fraction. Magnification 110 X, oil immersion...

Figure 7 shows carbonized coal particles of the sieve fraction 5 to 3 mm. It can be seen that for all types of coals practically all particles display devolatilization pores. This result, obtained by counting, is particularly interesting for the low volatile bituminous coal (No. 6 in Figure 7) because in high temperature cokes produced under normal conditions from another coal of the same rank, the particles of carbonized coal show no pores and will be found as so-called unmelted particles in the coke. 

The strong increase in mean particle diameter of the sieve fraction 1.0-0.5 mm. for the coal with 32.2% volatile matter cannot be explained on the basis of the relationships discussed. The unusually high swelling ability in this case is caused by a very high proportion of exinite (21%) in the sample and the correspondingly very small proportion of inertinite (9). 

Standing-Crop Particles. Standing-crop, noncolloidal, particulate matter was sampled by using two techniques 1, niskin casts followed by filtration onto track-etched filters and 2, serial sieve fractionation in-line with continuous-flow centrifugation, which enabled the collection of gram quantities of suspended particles. 

The catalysts were all calcined and prereduced. For the calcination/reduction, a sieve fraction (225 < dp < 450 im) was placed in a downflow fixed-bed reactor. The prereduced catalysts were stored in air. The Pt particle size was determined by H2 chemisorption, high resolution transmission electron microscopy and EXAFS analysis. Details of H2 chemisorption25, HRTEM26 and EXAFS25 are given elsewhere. 

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