Laser granulometry

Particle Size Distribution. The particle size distribution is determined by conventional sieving or other methods such as laser granulometry (see Section 1.2.1 Particle Size). 

Pye, K. and Blott, S. J. (2004b). Particle size analysis of sediments, soils and related particulate materials for forensic purposes using laser granulometry. Forensic Sci. Int. 144, 19-27. 

Laser granulometry indicated little variation in the particle size with depth in the trench section, the median size being 12-15 pm. On average the bulk sediments were found to contain approximately 20% clay ( < 2 pm), 70% silt (2-63 pm) and < 10% sand ( > 63 pm). Bulk sediment XRF analyses also showed that the major element proportions are also relatively constant with depth (Figure 7.7). X-ray diffraction (XRD) analyses showed some variability in the relative proportions of clay minerals present in the < 2 pm fraction, but all samples were dominated by illite, smectite, kaolinite and chlorite. The calcium carbonate content was low ( < 1%), much of the detrital material apparently having been dissolved. The sediment pH ranged from 6.2 to 6.7. 

The role of settleable matter and supracolloids in the absorbance of suspended solids of wastewater has been studied more precisely. A simple experience has been carried out. Raw wastewater has been introduced into an Imhoff cone over 1 h. Figure 7 presents the settling device used for the separation of four granulometric fractions. These fractions have been analyzed both with laser granulometry (laser diffraction) and with UV spectrophotometry (deconvolution method, see Chapter 2). 

Figure 7. Granulometric size distribution study (left separation device, right laser granulometry results) [20],...

Granulometric analysis of fractions 1, 2, 3 (Fig. 6) clearly shows that particles are mainly supracolloids, between 1 to 100 xm, with a mode value close to 30 xm. The fraction 4 (at the bottom of the Imhoff cone) presents the widest range size with particle larger than 100 im, and a multi-modal distribution. After 1 h of settling, the separation of settleable matter is achieved, as fractions 1 to 3 do not contain particles of size above 100 xm, even if, in the first fraction, some millimetric floating particles are present. One can note that no colloidal population is detected by laser granulometry. 

The normalisation of the set of spectra (Fig. 9) allows comparing the quality of each fraction. The slope break of the UV spectrum of fraction 4, around 240 nm, is softened, confirming the presence of large particles [21], If the discrimination between supracolloids and settleable matter is not possible by UV spectrophotometry, the laser granulometry results confirm the major role of supracolloids in diffuse absorbance. 

Most commercial hydrated limes have median particle sizes, as measured by laser granulometry, of about 5 to 10 pm. Hydrated lime quality may also be assessed by testing either a milk or a lime putty prepared from the hydrate under specified conditions (see section 22.7.2). 

Fig. 1 Particle size distribution of a Pd nanoparticles, b Pd particles on silica support (Pd/Si02), c silica support particles, d Pd micrometer particles. Data obtained by evaluation of different series of TEM images (a, b n = 100 particles were obtained from three independent syntheses) or measured by laser granulometry (c, d)...

Laser granulometry is the method most commonly employed for testing samples in the advanced ceramics industry for determination of the grain size distribution. The particles are set in rotation in a measuring cell and exposed to a defined laser irradiation (Fig. 5). The diffraction pattern of the rotating particles is converted to grain sizes from which the grain size distribution is established. 

Recently, a method has been patented to determine filler dispersibility. It consists of measuring continuously the size of the filler by laser granulometry during an ultrasonic desagglomeration (W09928376 et al., 1997). This characterization can be applied to any filler and is an intrinsic property however, the use of water as a desagglomeration medium can be a problem because of its high polarity compared to elastomers. 

These measures, performed using laser granulometry, show that the spray-drying method allows us to obtain a thinner and more homogenous powder than the powder obtained using an agate mortar. 

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