Comparison of Sieve analyses, laser diffraction, image analyses and FBRM for the determination of particle size distributions part 3

Comparison of Sieve analyses, laser diffraction, image analyses and FBRM for the determination of particle size distributions part 3

Material and Methods

Sample Selection and Sieving

Two particulate products with different mophologies were selected: Sodium Chloride and Glass Beads. Figure 2 shows the shape of each material observed by microscopy. It can be seen that the Sodium Chloride appears to be in square shape (non-spherical) and
Glass Beads are very regular with spherical shape.

Ten fractions of each material differing by their particle size distributions were obtained by sieving (106-125µm, 125-150 µm, 150-180 µm, 180-212 µm, 212-250 µm, 250-300 µm, 300-355 µm, 355-420 µm, 420-500 µm and 106-500 µm). One more sample was prepared
by mixing the same material smaller size particles with the larger size, by the ratio of 1:1 w/w (125-150 µm and 420-500 µm).

The whole sample collection therefore included twenty two samples in range between 106-500 µm (two wide range samples, eighteen narrow fractions and two mixing range materials).

In theory, each sphere should just pass through a square mesh aperture which has internal side length dimensions equivalent to the diameter of the sphere, and therefore sieving should provide an accurate physical description of the size distribution of a
population of spheres (glass beads)

Instruments

Laser Diffraction (LD). The Beckman Coulter LS-130 was used to measure the PSD of the proposed samples. The instrument measures the forward scattering (diffraction) of light from a single laser which has a wavelength of 750 nm and
it uses the new PIDS i.e. Polarization Intensity Differential Scattering method (Beckman Coulter LS-130 user manual).

The instrument has 126 photodiode detectors and can measure particles in the size range of 0.4 to 900 µm. In all the experiments, the measurements were carried out in suspensions which were prepared in Silicon Oil. The refractive index of 1.49 was used for
Silicon Oil. The obscuration of all samples in the LD experiments was maintained in the range 9%—18%.

Image Analyses (IA). Ernst Leitz, Wetzlar microscope was used for IA.
 There is an automated camera and a television camera- port fitted with the instrument for digital imaging. Images were captured using Aver-TV software. The processing, analysis, and measurements were carried out using Photoshop and Image-J software.

In the IA experiments, the particles were distributed on the slides and were measured in from at random orientations. More care was required to make sure the particles are separated completely.
 Roughly 600—800 particles of each material in the specified range were analyzed (125-150 µm, 420-500 µm and 106-500 µm) in this study.

Image Processing

The basic procedure followed during the experiment for image processing is explained in the Figure 3. The aim of the image processing was to obtain binary images of the individual particles. To achieve this, initial processing was carried in Photoshop, which
included image filtering (sharpening), border killing and debris removing.

The images were then processed in Image-J to produce number based PSD of the particles. The number based PSD was converted to the equivalent spherical volume based PSDs to facilitate comparison with the other techniques.

Continued in part 4

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Posted by Ahmed Tariq on Jan 10 2012. Filed under Sci-Tech. You can follow any responses to this entry through the RSS 2.0. You can leave a response or trackback to this entry