Particle size distribution measurements

Figure 6. Pt particle size distributions measured from TEM images.

Parameters of Particle Size Distributions Measured by Light Scattering... 

It was found that the requirements were satisfied for application of the linear regression technique to species mass concentrations in a multicomponent aerosol. The results of 254 particle size distributions measured at China Lake in 1979 indicate that the normalized fine aerosol volume distribution remained approximately constant. The agreement between the calculated and measrued fine particle scattering coefficients was excellent. The measured aerosol sulfur mass distribution usually followed the total distribution for particles less than 1 ym. It was assumed that organic aerosol also followed the total submicron distribution. 

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.

FIGURE 9.23 (a) Aerosol particle size distribution measured at Pomona during the 1972 State of California Air Resources Board ACHEX program, (b) Calculated optical scattering by particles, bsp, for measured size distribution (adapted from Waggoner and Charl-son, 1976). 

To reconstruct an initial particle size distribution from observations at a later time, one must either have particle size distribution measurements at many different space-time points or make some assumption about the initial spatial distribution. The simplest assumption is that the initial spatial and particle size distributions are independent. 

Particle Number Concentration and Size Distribution. The development of aerosol science to its present state has been directly tied to the available instrumentation. The introduction of the Aitken condensation nuclei counter in the late 1800s marks the beginning of aerosol science by the ability to measure number concentrations (4). Theoretical descriptions of the change in the number concentration by coagulation quickly followed. Particle size distribution measurements became possible when the cascade impactor was developed, and its development allowed the validation of predictions that could not previously be tested. The cascade impactor was originally introduced by May (5, 6), and a wide variety of impactors have since been used. Operated at atmospheric pressure and with jets fabricated by conventional machining, most impactors can only classify particles larger... 

Figure 6. Particle size distributions measured (A) at the beginning and (B) after initial particle growth in a seeded methylcyclohexane-NOx photooxidation experiment conducted in the Caltech outdoor smog chamber. (Reproduced from reference 49. Copyright 1991 American Chemical Society.)...

Particle Size Analysis. Particle size distribution measurements of the dry resin were made using a Micromeritics Sedigraph 5000D particle size analyzer. This instrument employs a gravity settling technique and uses Stokes law to determine the particle size. The PSD was run over the size range of 0.36 to 100 micrometers. All measurements were made in dibutyl sebacate as the suspending medium. 

Figure 9. Particle size distribution measured in wind tunnel.

One study (18) showed that aerially applied pigmented mexacarbate particles observed on western spruce budworm larvae and Douglas-fir needles were minute (Table VII). Eighty-seven percent of the particles found on western spruce budworm larvae were less than 16 pm in diameter while 87 percent of the particles found on Douglas-fir needles were less than 11 ym in diameter. It is noteworthy that 76 percent of the particles observed on the larvae were 6 to 15 ym in diameter. We assune that the particle size distribution in the field was similar to the particle size distribution measured in the laboratory. 

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. 

In summary, particle size distributions measured at similar conditions using optical and sampling probe-impactor methods are vastly different. No conclusions can be drawn concerning the relative accuracy of these two techniques because of experimental differences. All indications are that the optical counter is operating properly and is applicable and advantageous for in situ measurements. Further experiments comparing the two techniques directly on a common engine will be performed soon to substantiate the particulate formation hypotheses. 

Many commercially available particle size distribution measuring instruments may be considered to be sub-standard in that they need to be calibrated at regular intervals using standards powders of known size... 

Figure 3 shows the particle size distributions measured with the optical instrument. 

The use of transmission electron microscopy in heterogeneous catalysis centers around particle size distribution measurement, particle morphology and structural changes in the support. Consideration is given to the limitations of conventional electron microscopy and how modifications to the instrument enable one to conduct in-situ experiments and be in a position to directly observe many of the features of a catalyst as it participates in a reaction. In order to demonstrate the power of the in-situ electron microscopy technique examples are drawn from areas which impact on aspects of catalyst deactivation. In most cases this information could not have been readily obtained by any other means. Included in this paper is a synopsis of the methods available for preparing specimens of model and real catalyst systems which are suitable for examination by transmission electron microscopy. 

Particle shape can also influence particle size analysis. The particle size distribution measured by sieve analysis can be influenced by particle shape, because irregularly shaped panicles take longer to reach their final sieve. Biased results will be reported if the test is stopped before the particles reach their final sieve. 

Brock CA, Schroder F, Ka rcher B, Petzold A, Busen R, Fiebig M (2000) Ultrafme particle size distributions measured in aircraft exhaust plumes. J Geophys Res 105 26555-26567 Brunekreef B (2000) SESSION 2 What properties of particulate matter are responsible for health effects Inhal Toxicol 12 (Suppl 1) 15-18... 

Particle size distribution measurements should also be made from lab milled samples only. The particle size distribution influences the compacting behavior and green density as well as the sintering properties. 

Leung K, Louca E, Gray M, et al. Use of the next generation pharmaceutical impactor for particle size distribution measurements of live viral aerosol vaccines. J Aerosol Med 2005 18 414-426. 

Larger scale Fischer-Tropsch synthesis runs were performed in a pilot plant slug-flow slurry reactor using 3-8kg catalyst as well as in a slurry phase bubble column demonstration unit using 500-1500kg catalyst. The reaction conditions were similar to those in the laboratory CSTR runs. The reactor wax production varied between 5 and 30kg per day for the pilot plant runs and up to 60 bbl/day for the demonstration unit. On-line catalyst samples were taken for particle size distribution measurements and Scanning Electron Microscope analyses. 

Particle size distribution measurements were performed by means of a Leeds Northrop Microtrac Particle Size Analyser, equipped with a laser beam to determine the particle sizes. A water suspension was prepared by addii ca 2g of the sample and a few drops of a suitable detergent. The sample was uhrasonically treated for 1 minute before the analysis was performed. An average of three runs was used to calculate the final particle size distribution. 

As a result of the complex aerodynamics of the particle beam and associated skimmers, the size distribution of the particles that reach the ion source differs significantly from that in the gas samples from outside the system. To relate the measured chemical compositions to the outside aerosol, it is necessary to correct for this effect. This can be accomplished in principle by determining the elficiency of transmission of particles from the exterior into the chamber. It is also possible to use data for particle size distributions measured outside the spectrometer to characterize the external aerosol. Because the particle size distribution measured with an optical particle counter does not correspond to the aerodynamic diameter, there will be some difficulties of interpretation. 

The above measurements should be supplemented by particle size distribution measurements of the diluted dispersion (ensuring that no floes are present after dilution) to assess the extent of Ostwald ripening. Another compHcation may arise from the nature of the flocculation which, if it occurs in an irregular fashion (producing strong and tight floes), may cause i (0) to be increased while cr may show some decrease, and this wiU complicate the analysis of the results. Yet, in spite of these complications, constant stress measurements may provide valuable information on the state of the dispersion on storage. 

DHTDMAC vesicles have been characterized by Okumura et al. [92], The width of the bimolecular layer is 50 A, and the interlamellar spacing is between 100 and 400 A. Each DHTDMAC molecule is hydrated with 7 water molecules. The particle size distribution, measured by dynamic light scattering and optical microscopy, is very broad, ranging from 0.1 to 10 p,m. This may be assigned to the presence of both unilamellar and multilamellar vesicles in the dispersion. 

Apart from the basic definitions above, there are other shape factors which are defined as ratios of two different types of equivalent particle size. These are obtained by comparing particle size distribution measured by two different methods the shape factor is the multiplier which would bring the results into coinci-... 

---