Particle size process measurement

Figure 2 indicates Mn/Fe to be somewhat above the crustal ratio through 19 March, and thereafter a marked Increase is seen. The aerosol ratio Zn/Fe averages about 20 times greater than in the earth crust (somewhat greater on 20-21 March), showing "anomalous" atmospheric enrichment of Zn first recognized by Rahn (7). Since particle size distribution measurements, discussed below, show substantial fine particle concentrations of both Zn and Mn, the processes for their transfer to the atmosphere must be different from those for the other six elements of Figure 2. However, their concentration variations in time still resemble those of Fe shown in Figure 1 and therefore these elements may also be relatively large scale characteristics of air masses, in contrast to S where regional pollution sources and aerosol formation processes must be Important.

Holve DJ, Harvill TL. 1996. Particle size distribution measurements for in-process monitoring and control. Adv. Powder Metal. Part. Mat. 1(4) 81-93. 

Harvill TL, Hoog JH, Holve DJ. 1995. In-process particle size distribution measurements and control. Part. Syst. Charact. 12(6) 309-313. 

Several areas in which chemical measurement technologies have become available and/or refined for airborne applications have been reviewed in this paper. It is a selective review and many important meteorological and cloud physics measurement capabilities of relevance to atmospheric chemistry and acid deposition (e.g., measurement of cloud liquid water content) have been ignored. In particular, we have not discussed particle size spectra measurements for various atmospheric condensed phases (aerosols, cloud droplets and precipitation). Further improvements in chemical measurement technologies can be anticipated especially in the areas of free radicals, oxidants, organics, and S02 and N02 at very low levels. Nevertheless, major incremental improvements in the understanding of acid deposition processes can be anticipated from the continuing airborne application of the techniques described in this review. 

Fig, 6.4 Mean cell size of adenovirus-infected cells resulting from different processing methodologies. Particle size was measured using the Coulter Multisizer II to determine cell sizes within the... 

Use of Particle Size Distribution Measurements for Selection and Control of Solid/Liquid Separation Processes... 

In addition to providing a basis for process selection, particle size distribution measurements are also useful for evaluating predesign pilot plant studies. Turbidity or suspended solids measurements are traditionally used to assess process performance in such studies. However, for low-turbidity waters (< 5 turbidity units) particle counters may provide a more sensitive measure of particulate removal efficiency as well as data on the crucial question of removal efficiency as a function of size. 

Particle counters also show promise for process control and performance evaluation, particularly in low-turbidity waters. Applications include more accurate evaluation of pilot plant studies and more sensitive control of particulate separation processes. However, when the power-law coefficient, p, is greater than 3, submicron particles, which escape detection with available counters, may control the magnitude of the total surface area concentration and the light-scattering properties of the particulate. It is likely that accurate process control and monitoring of solids/liquid separation processes will require both turbidimetric and particle size distribution measurements. Particle counting appears most promising as a feedback control sensor. 

These tests were performed using a universal Zwick tester, model 1435, coimected to a computer with appropriate software. Particle size was measured in paraffin oil using Zetasizemano S90 (Malvern Instmments) analyzer. Zeta potential of filler dispersion in water was studied by the means of Zetasizer 2000 (Malvern Instruments) apparams. Rheological properties of filler suspensions in paraffin oil were determined by viscometer RM500 (Rheometric Scientific). Dibutylphtalate (DBP) absorption was measured by means of an Absorptometer C (Brabender). The modification process was carried out in Brabender Measuring Mixer N50 at following parameters temperature 125°C rotor speed 40 RPM duration 0,5 h. 

Harvill, T. L., Hoog, J. H., Holve, D. J., In-process Particle Size Distribution Measurements and Control, Par/. Part. Syst Charact, 1995, 12, 309-313. 

A fundamental requirement in powder processing is characterization of the as-received powders (10—12). Many powder suppHers provide information on tap and pour densities, particle size distributions, specific surface areas, and chemical analyses. Characterization data provided by suppHers should be checked and further augmented where possible with in-house characterization. Uniaxial characterization compaction behavior, in particular, is easily measured and provides data on the nature of the agglomerates in a powder (13,14). 

Size reduction (qv) or comminution is the first and very important step in the processing of most minerals (2,6,10,20—24). It also involves large expenditures for heavy equipment, energy, operation, and maintenance. Size reduction is necessary because the value minerals are intimately associated with gangue and need to be Hberated, and/or because most minerals processing/separation methods require the ore mass to be of certain size and/or shape. Size reduction is also required in the case of quarry products to produce material of controlled particle size (see Size measurement of particles). In some instances, hberation of valuables or impurities from the ore matrix is achieved without any apparent size reduction. Scmbbers and attritors used in the industrial minerals plants, eg, phosphate, mtile, glass sands, or clay, ate examples. 

Sedimentation (qv) techniques, whether based on gravitational forces or centrifugation, derive the particle size from the measured travel rates of particles in a Hquid. Before the particle analysis is carried out, the sample is usually dispersed in a medium to break down granules, agglomerates, and aggregates. The dispersion process might involve a simple stirring of the powder into a Hquid, but the use of an ultrasonic dispersion is preferred. 

A wide variety of particle size measurement methods have evolved to meet the almost endless variabiUty of iadustrial needs. For iastance, distinct technologies are requited if in situ analysis is requited, as opposed to sampling and performing the measurement at a later time and/or in a different location. In certain cases, it is necessary to perform the measurement in real time, such as in an on-line appHcation when size information is used for process control (qv), and in other cases, analysis following the completion of the finished product is satisfactory. Some methods rapidly count and measure particles individually other methods measure numerous particles simultaneously. Some methods have been developed or adapted to measure the size distribution of dry or airborne particles, or particles dispersed inhquids. 

Continuous emulsion copolymerization processes for vinyl acetate and vinyl acetate—ethylene copolymer have been reported (59—64). CycHc variations in the number of particles, conversion, and particle-size distribution have been studied. Control of these variations based on on-line measurements and the use of preformed latex seed particles has been discussed (61,62). 

Minimum Fluidizing Velocity U,nj, the minimum fluidizing velocity, is frequently used in fluid-bed calculations and in quantifying one of the particle properties. This parameter is best measured in small-scale equipment at ambient conditions. The correlation by Wen audYu [A.l.Ch.E.j., 610-612 (1966)] given below can then be used to back calculate d. This gives a particle size that takes into account effects of size distribution and sphericity. The correlation can then be used to estimate U, at process conditions, if U,nj cannot be determined experimentally, use the expression below directly. 

If PVC polymer particles are mixed, at room temperature, with plasticisers the immediate product may take one of two forms. If there is insufficient plasticiser to fill all the gaps between the particle a mush will be produced. If all the voids are filled then the particles will become suspended in the plasticiser and a paste will be formed. In the case of conventional granular polymer, or with emulsion polymer cenospheres, the particles are too large to remain in suspension and will settle out. Therefore compounds used in paste-processes must use polymers with a small particle size. On the other hand there is a lower limit to this, since small particles will have a very high surface/volume ratio and measurable plasticiser absorption will occur at room temperature to give a paste whose viscosity will increase unduly with time. As a consequence paste polymers have an average particle size of about 0.2-1.5 ptm. 

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