Particle analysis

Early in the environmental sampling program of the IAEA it was recognized that the analysis of individual micrometer-sized particles was a source of unique information about nuclear materials and activities. O Table 63.17 shows the calculated composition of 1 pm diameter particles coming from various nuclear processes. Thus, it can be seen that a pure particle of natural U oxide ( NU ) contains about 10 U atoms in total and that when this particle is irradiated in a reactor, approximately 5 million atoms of Pu would be created. Furthermore, a particle of high-enriched uranium ( HEU ) would produce only small numbers of Pa and Th daughter atoms in 10 years of decay. To be able to age-date such a particle would involve measurement of these small components, something which is currently not possible with the most sensitive techniques. 

Composition of typical 1 pm diameter particles found in nuclear facilities 

Note GWD/T = gigawatt-days per ton MWD/T = megawatt days per ton LEU 4% = low-enriched uranium with 4% abundance of 

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Recommended Equipment. A list of analy2ers (stand-alone or in a mobile cart) and level of detection for specific gas and particle analysis... 

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 recent trend in particle analysis has been the introduction of personal computer-based automation (3). Sophisticated software packages can be used to automate and speed up the analysis. In some cases these computers can even carry out continuous process control (qv) (see Computer technology). The latest machines also allow the measurements of smaller particles and can detect a wider range of sizes. Machines based on light-scattering principles are being more widely accepted by the industry because of speed. An average analysis takes from 1—2 min, whereas those based on sedimentation principles require from 10—120 min. 

NOTE This table was compiled with the assistance of T. Allen, DuPont Particle Science and Technology, and is not intended to he comprehensive. Many other fine suppliers of particle analysis equipment are available. 

Mathai (21) summarized the specialty conference on atmospheric visibility. With the exception of water content of particles and the measurement of organic species, analytical laboratory techniques are readily available for particle analysis. Regulatory approaches to mitigate existing visibility impairment and to prevent further impairment are being formulated. A... 

Large data base, amenable to chemical analysis coarse particle analysis... 

Particle count tests are important to anticipating potential system or machine problems. This is especially true in hydraulic systems. The particle count analysis made a part of a normal lube oil analysis is quite different from wear particle analysis. In this test, high particle counts indicate that machinery may be wearing abnormally or that failures may occur because of temporarily or permanently blocked orifices. No attempt is made to determine the wear patterns, size and other factors that would identify the failure mode within the machine. 

Wear particle analysis is related to oil analysis only in that the particles to be studied are collected through drawing a sample of lubricating oil. Where lubricating oil analysis determines the actual condition... 

The first method used for wear particle analysis is routine monitoring and trending of the solids content of machine lubricant. In simple terms the quantity, composition and size of particulate matter in the lubricating oil is indicative of the mechanical condition of the machine. A normal machine will contain low levels of solids with a size less than 10 microns. As the machine s condition degrades, the number and size of particulate matter will increase. 

At present only low resolution (>30A) structures, all derived from single particle analysis of images from electron microscopy, are available for the entire DP3R. These structures differ in their details, but all show a roughly square structure with fourfold symmetry and lateral dimensions of about 20 nm (Fig. 2). 

Figure 5. Height of the silver nanoparticles plotted as a function of their lateral diameter, determined by extended particle analysis for the AFM image (silver deposition time was 180 s). The broken line is for perfect spheres (height/diameter = 1).

In a transmission mode instrument, the Nd YAG laser beam is focussed on the back side surface of thin samples (<1 pm thick). A spot diameter of 0.5 pm is possible, and commercial instruments of this configuration have been used primarily for biomedical and particle analysis applications. 

Single particle analysis offers improved resolution of species in mixtures. 

Molecular and particle analysis using well-established optical methods such as fluorescence and Raman scattering is but one of the possibilities that LC-ARROWs offer. A whole new research area based on the study and exploitation... 

Fig. 18.15 Advanced methods for single particle analysis in LC ARROW chips, (a) Nanopore added to reservoir for single particle entry into LC ARROW (b) Optical dual beam particle trap based on balancing the scattering force due to counter propagating beams...

Analytical electron microscopy has been shown to be an effective technique for the chemical analysis of catalyst particles. In some cases AEM may be the only technique to provide chemical profiles across small particles. Analysis of thin sections of... 

Figure 4.12 Histogram from automated SEM-EDS particle analysis of 362 zeolite precursor particles. Particles were reacted from silica and alumina sources slowly combined and aged at (a) room temperature and (b) 75°C.

Recently, a miniaturized thermal apparatus, [t-ThFFF, was developed and applied to characterize the molar mass distribution of synthetic polymers in organic solvent as well to determine the particle size distribution of nanoparticles (PSs latex) in aqueous carrier. This 4-ThFFF proved to performed well in both macromolecule and particle analysis [48]. 

Particle analysis Particle analyser Size distribution... 

It should be noted that there are likely to be some aerosol particle components that are not readily detectable by the techniques in use now. For example, Kao and Friedlander (1995) have suggested that compounds such as H202 and free radicals that may be important toxicologically would have reacted prior to particle analysis and that species formed from such reactions, e.g., sulfate, may be used as markers of their presence. 

Figure 9.55a shows the results of single-particle analysis (see Chapter ll.B.4a) of a typical particle in the upper troposphere (Murphy et al., 1998). In the negative ion spectra, a variety of fragments due to organics are observed, along with sulfates and some halogens. In other particles, soot and minerals were also common constituents. For comparison, Fig. 9.55b shows that a typical particle in the stratosphere is primarily sulfate (see Chapter 12.C.5). 

In short, care must be taken in sampling and analysis of airborne particles, as well as in the data interpretation, to minimize or at least recognize potential artifact problems. Such problems, along with a need to understand not only the bulk composition of a collection of airborne particles but also that of individual particles, have contributed to the development of realtime and single-particle analysis techniques discussed in the following section. 

Cox, X. B., and R. W. Linton, Particle Analysis by X-Ray Photoelectron Spectroscopy, in Physical and Chemical Characterization of Individual Airborne Particles (K. R. Spurny, Ed.), Chap. 18, pp. 341-357, Ellis Horwood, Chichester, 1986. 

Fung, K. H., and I. N. Tang, Aerosol Particle Analysis by Resonance Raman Spectroscopy, J. Aerosol Sci., 23, 301-307 (1992b). 

McKeown, P. J., M. V. Johnston, and D. M. Murphy, On-Line Single-Particle Analysis by Laser Desorption Mass Spectrometry, Anal. Chem., 63, 2069-2073 (1991). 

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