Surface area sieve analysis

Various techniques and equipment are available for the measurement of particle size, shape, and volume. These include for microscopy, sieve analysis, sedimentation methods, photon correlation spectroscopy, and the Coulter counter or other electrical sensing devices. The specific surface area of original drug powders can also be assessed using gas adsorption or gas permeability techniques. It should be noted that most particle size measurements are not truly direct. Because the type of equipment used yields different equivalent spherical diameter, which are based on totally different principles, the particle size obtained from one method may or may not be compared with those obtained from other methods. 

The sieve analysis only gives an approximation of the particle distribution. The geometric shape of the particles is a factor in its moving to the proper-size sieve. For many process operations, more detail about the shape and surface area of the particles is important for the proper design and operation of equipment. 

Triplicate aliquots were taken for particle size analysis and two of those aliquots were mixed for BET surface area analysis results are in Table III. The nine samples were individually sieved for size distribution. A chi-squared test was performed on each triplicate set in order to check the apparent efficiency of composite mixing. For all three composite samples, there was a 90 percent probability that each of the three replicates from each composite sample came from the same population. The A and C samples were combined and evaluated for surface area by nitrogen adsorption (BET). The B samples were then subjected to scanning electron microscopy (SEM) analysis. 

Brunauer-Emmett-Teller (BET) analysis was carried out on the ceramic aggregate with both nitrogen and krypton as adsorbates. The sample was crushed and dry sieved, and the fraction between 74 and 589 micrometer was retained for analysis. Results were repeatable, and consistent for the two gases. Over the range of firing and proportioning conditions studied, specific surface area of the ceramic aggregate was between 0.3 and 6 m Vg, which can be compared, for example, to a non-porous... 

British Standard Specifications BS 410 [13] adopts a primary size of 75 pm (200-mesh) with a fourth root of two progression in size and suggest that alternate sieves should normally be used for an analysis (i.e. a root two progression of sizes). Thus, the specific surface area of particles on consecutive sieves is in a 2 1 progression. BS 1796 describes the methods to be used in sieving with woven wire and perforated plate sieves [14],... 

Figure 4 represents the evolution of the EoWo/EorcfWo ref ratio for the different carbon molecular sieves of the two series, as a function of the molecular size of the immersion liquid, and using CH2CI2 as a reference. A decrease of this ratio as the size of the immersion liquid increases indicates that the accessibility of the porosity is limited. It can be seen that the pore size distributions obtained by this method are comparable to those shown in Figure 3, corresponding to the surface area accessible to the different immersion liquids. In conclusion of this pore-size analysis, a variety of CMS with different pore size distribution, but always smaller than 0.7 nm, have been obtained. CMS with the narrowest pore diameter are prepared from the acid-washed precursors, i.e., without ashes able to catalyse the gasification reaction. 

In materials containing micropores (and mesopores), such as molecular sieves and activated carbons, the boundary conditions (multilayer adsorption) are not fulfilled and the BET analysis is not applicable here. When (traditionally) reported in the literature, the BET surface area should be understood as a niunber proportional to the pore volume rather than the specific surface area. Note also that conceptually the term specific surface area is inapplicable once the solid material surroimds sorbed molecules. 

Sieve analysis 0.1-20% retained on 325 (44 pm) sieve Specific surface area, m /g 5-35... 

Sieve analysis 325 mesh residue - trace to 17.6% Specific surface area, m /g 0.7-180 ... 

Experiments were conducted on an ACE-R fixed fluidised bed microreactor, using a typical vacuum gas-oil. The study considers three sets of catalyst micro-spheres, after being steamed (hydrotermically deactivated) for 8 h at 788 °C. After steaming catalyst particles were dryed at 150 °C for 2h, then sieved to particle sizes in the range F3=44-74, F2=74-150, and Fl=150-250 pm. Texture analysis, as shown in table 1, was performed by N2 adsorption (ASAP-2000) following ASTM-D-3663 and ASTM-4222 (t-plot) methods, which allowed to estimate the total BET surface area and the micropore (zeolite) area, respectively. 

CMS are amorphous materials. Their pore structure below 5 A can not be studied by X-ray diffraction, in contrast to most mineral molecular sieves. Transmission electron microscopy has also not been found suitable for determining such small pore dimensions. The most effective method for characterization is the analysis of adsorption isotherms of small probe molecules with different critical dimensions, viz. O2, N2, CO2, CH4. These adsorption isotherms are useful in determining the pore size distribution, surface area, pore volumes and separation capacity of CMS. In addition, these isotherms give information on the potential industrial applications of these materials, e.g. for the separation of nitrogen from air or of carbon dioxide and methane from flue gases. 

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