Optical Particle Sizing: Theory and Practice
Is so, this is the course you need to gain a solid understanding of particle sizing using light scattering, the fastest growing particle sizing method. The course consists of two parts which can be attended separately, the first lecture being a prerequisite for the second lab. Lecture: Introduction to Particle Sizing by Light Scattering 2 days Introduction to particle science and technology Comparison of different methods of particle sizing in use today. Theory and practice of light scattering. Fraunhofer versus Mie Theory. Strengths and limitations of sizing using light scattering.
Sampling, sample preparations, and sample dispersion techniques. Data analysis and interpretation of results. Optical models - when are they necessary and how to create them. One-on-one consultation to resolve particle characterization problems. In , Wallace Coulter invented the Coulter Principle, a revolutionary way to count and size cells and particles.
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The Coulter Principle changed the science of particle sizing and counting forever. Another point of interest, however, is that particles possessing the same volume but different shape and structure de- liver more or less different spectra and hence different ultrasonic U values. An absolutely unique relationship will only atomizer, exist between the mean value U and the equivalent diameter x for particles possessing an identical shape and structure. This is, for example, the case for nonspherical but regular homogeneous and isotro- pic particles such as cubes, cylinders, and cones.
In a strict sense, this no longer holds for completely irregular particles. Nevertheless, it has been observed that specific materials yield characteristic shape and structure elements, so that equally characteristic spectra emerge, from which the possibility of an accurate correlation between U and x arises see Section III. The aim of this paper is to present the experimental procedure and discuss the results from exhaustive measurements using particles of various materials.
Moreover, further measures and considerations exist that can, only be briefly mentioned here. The results of such measurements as exemplarily presented may be used as a basis for numeric simulations and for the elimination of the influence of shape and screen structure on the results of concrete measurements. With the elimi- Fig. Schematic illustration of the measuring setup for scattered- nation of the shape and structure influence, the high light measurements with individual particles suspended in an inhomogeneous electrical field electrodynamic balance.
The laser resolution of a single-particle size analysis is also is an auxiliary instrument. With the aid of the diffraction pattern guaranteed for measurements involving irregular below the measuring cell, one can ascertain whether only one particles. The complete concept and its results are particle oscillates within the measuring volume i.
The scattered light is received at beneath the electrodynamic balance. The large free- micrographs, the projected areas can be determined working distance of approximately 70 mm proved to from three orthogonal directions. From the average be an advantage for the given task, since it allows the projected area, the equivalent diameter of the sphere measuring cell with the electrodes schematically possessing the same projected area can be derived, illustrated in Fig.
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A further possibility is to apply this light-scattering size analyzer are shown in Fig. Weichert and Huller's three-dimensional 3-D shape If the single-particle pulse height spectrum is to be determination and analysis concept.simpateashka.com/11.php
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High-speed filming clearly verified that a particle suspended in such an simulation of the particle's shape. Their motion may be observed to be of a the equivalent diameter x. A survey of the principal tumbling nature. The angular velocity with which approach is schematically illustrated in Fig.
Results and Discussion measuring volume 40 jim their orientation re- mains practically constant.
Theory and Practice
Consequently, a suffi- Measurements were conducted with individual parti- ciently large number of signals need only be recorded cles of latex, glass, limestone, quartz, and coal. The to obtain spectra containing every possible orienta- following examples are confined to the results derived tion.
It has not, however, been verified whether an from the measurements with glass spheres and with equal probability exists for all orientations. After one completes the scattered-light measure- The results of the measurements conducted with ments, the particle is recovered. To accomplish this, two spherical glass particles are compared in Figs. Both objects are equal in size and free of electrodes is reduced, and ultimately disconnected, inclusions and superficial imperfections.
While the together with the dc potential of the other electrodes. I'-UIlAdI-- d. Schematic illustration of the principal features of the single-particle light-scattering size analyzer with an optically defined measuring volume.
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By means of micrometer adjustment, the measuring cell can be shifted to allow the particle to oscillate exactly through the center of the measuring volume. Measurement and calculation of the various parameters to be derived from individual particles. A survey of the fundamental technique. Con- used, even minute deviations from the pure spherical trary to the true spherical particle, which, as antici- shape will deliver a wide range of scattering intensi- pated, yields a narrow pulse height spectrum, the ties, depending on the orientation of the particle.
These pronounced intensity variations are viewed as Indeed, the standard deviation between the two dif- being chiefly caused by interferences resulting from fers by a factor of It is known e. As the above results display, however, compara- 1Nolt tively large scattering-intensity differences appar- 10 ently also exist when white light is used and especially e when an average scattering angle of is applied.
Different results derived from two different glass beads. As Fig. Both spheres are number density distribution.
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One can observe a well-defined maximum at 0. In addition, however, unusually large signal values can be seen to exist. The reason for these high 2- signal values is not altogether clear, as the smaller 5. It may, however, be quartz. As such, strongly divergent scattering inten-. The characteristic results of measurements derived Fig. Results of the measurements conducted on a quartz from a limestone and a quartz particle, extracted particle, including the 2-D simulation of the particle shape, the projected area from three orthogonal directions, and the single- from the total range of approximately 50 investigated particle pulse height spectrum with an arithmetic mean value U.
These include the three the three projected areas. The single-scattered light signal with the orthogonal projected areas, the 2-D reconstruction of peak value U pulse height possesses the same principal trend as each particle shape, the temporal pulse trend U t of a that for the limestone particles and is hence not included. Altogether, approximately particles of each material were investigated. When comparing the pulse height spectra deter- mined from the limestone and quartz particles, at least two significant differences become apparent.
The quartz particle spectra are much wider Fig. The limestone 8. In contrast, however, the quarter particle spectra are 0. Standard deviation udepending on the mean scattered- light signal with the peak value U pulse height , and the single- light pulse height U of the spectrum. The individual values particle pulse height spectrum with arithmetic mean value U. The quadratic symbols depict the trend of the quartz particles. For xpvalue is the equivalent diameter derived from the mean of the comparison, the corresponding regressive curve for limestone has three projected areas.
Limestone Fig. This corresponds to the theoretical dependence on the particle size are clearly demon- value to be derived for adequately large spherical strated in Fig. One can observe that the standard tained from quartz is significantly flatter, at approxi- deviation within the investigated particle size range mately 1. The reason for this cannot now be defi- increases linearly with U. The differences between the slopes of mately constant. Apparently, the effect of the shape- the calibration function may not be adequately ex- and -structure defining elements is directly related to plained by Fig.
It is indeed quite possible, in the total particle size despite the fact that the lateral addition to the effect demonstrated in this graph, that sizes of the shape and structure elements are still a systematic correlation also exists between the light larger than the wavelength of the light used, which absorbed and the particle size.
Nevertheless, the ratio u! U of the quartz size parameters, obtained in each case from the same particles is nearly seven times larger than for the single particles, may be observed to be both reliable limestone. While this significant difference may to and informative, since the scattering of the individual some extent be caused by the different particle shapes, value pairs warrants a certain insight into the funda- the effect of the different superficial structures is mentally attainable correlation quality. Scanning electron micro- graphs verify that the limestone particles possess uniformly structured surface elements, which are IV.
Conclusions relatively small compared with the size of the whole The experimentally determined single-particle pulse particle. This generates a diffusive scattering in which height spectra h U quantify the influence that the the mean spectrum value U is proportional to the shape and structure of irregularly shaped and tex- average cross-sectional area of the particle.
In con- tured particles exert on single-particle light-scatter- trast, the quartz particles possess a distinctly inconsis- ing size analyses. These spectra are material depen- tent surface structure with flat, strongly reflecting dent and may be regarded as characteristic of the regions. Depending on the particle's orientation within substance in question.
The spectrum width standard the measuring volume, these superficial regions can deviation becomes narrower with a decreasing significantly contribute to the strong scattered-light particle size, which means that the ratio between signals flashes that emerge but with a lower proba- and U remains constant within the investigated size bility than the smaller, diffusive scattering regions.
The This explains the share of the larger pulse height effect of the shape and structure elements of the values in the quartz spectra. Such behavior is even particles in the investigated size range is apparently more dominant in the case of coal dust, which gener- directly related to the total size of the particles ally yields even wider single-particle pulse height concerned. The results of these measurements are not The spectra allow the loss of resolution of common included here.
The reader may, however, refer to the light-scattering size analyses to be assessed.