Characterizing Powders Using Sieves

B. H. Kaye and N. I. Robb, A New Algorithm for Calculating Kinetic Residues for the Characterization of Powders Using Sieves, Powder Technology, 24 (1979) 125-128. 

In this contribution we report on the incorporation of tin into the mesoporous molecular sieves MCM-41 and MCM-48 comparing traditional hydrothermal approach with microwave synthesis of these materials. X-ray powder diffraction, nitrogen adsorption isotherms, scanning electron microscopy and FUR of probe molecules were employed to characterize these molecular sieves. Oxidation of adamantanone with hydrogen peroxide was used as model reaction. 

We also described the different analytical techniques used to characterize powders both in terms of their size and composition. To determine particle size it is necessary to choose a method that has sufficient sensitivity. Sieving is a low-cost method and is reliable when the particle size is greater than about 60 pm. But if the particles are smaller than this, as is often the case, then the use of light scattering or X-ray diffraction should be considered. In determining both particle size and chemical composition it is essential that the specimen we choose for analysis is representative of the entire powder sample. 

Microspheres intended for nasal administration need to be well characterized in terms of particle size distribution, since intranasal deposition of powder delivery systems is mostly determined by their aerodynamic properties and particle sizes. Commonly used methods for particle size determinations described in the literature are sieving methods [108], light microscopy [58], photon correlation spectroscopy [66], and laser diffractometry [25,41,53,93], The morphology of the microparticles (shape and surface) has been evaluated by optical, scanning, and transmission electron microscopy [66, 95],... 

The USP uses descriptive terms to characterize the particle size of a given powder, which are related to the proportion of powder that is capable of passing through the openings of standardized sieves of varying dimensions in a specified time period under the mechanical sieve shaker as follows ... 

Sieving is a widely used method for characterizing the range of grain sizes present in a powder. In this... 

The condition of the SAS can be characterized as a dry powder state, high solids concentration, and little or no dispersion. Laser diffraction with a sedimentation shaft for sample feeding (low shearing) and classical sieving (DIN 66 165) proved to be useful tools to determine the particles sizes properly [7]. 

It is not possible to assess the effect of the substrate surface independently however, the powder can be characterized with respect to effective size by means of a simple sieve analysis that can be used to get a cumulative size distribution. If the total fraction that passes each size sieve is plotted against the sieve opening on normal probability paper, the mean weight-diameter from the 50% point is obtained and the standard deviation from the sizes corresponding to the 13% and/or 83% diameter. The effective (surface mean) particle diameter can then be calculated by means of the equation given by Orr and Dallavalle [66] ... 

Synthesis of mesoporous molecular sieves MCM-41 and MCM-48 was carried out under microwave and hydrothermal conditions. Molecular sieves prepared were characterized using X-ray powder diffraction, scanning electron microscopy, nitrogen adsorption isotherms and infrared spectroscopy to evaluate the properties of these materials. It was observed that mesoporous molecular sieves synthesized under microwave conditions exhibit higher activity in oxidation of adamantanone by hydrogen peroxide to the respective lactone (Baeyer-Villiger oxidation). 

Zeolites are crystalline aluminosiUcates characterized by a structure comprising a three-dimensional pore system and regular framework formed by linked TO4 tetrahedral (T = Si, Al) with different morphological and physico-chemical properties. Due to their impressive selectivity and uniform pore structure, they have very efficient molecular sieving properties, and are able to separate molecules based on size and shape. Zeolite powders, films and membranes are widely used in catalysis, adsorption and separation applications (McLeary et al, 2006 Pina et al., 2011). Zeolites are cheap and widely available due to their abundance in both natural and synthetic forms. The application of zeolites in the membrane field is growing very fast, and has been the subject of increased research focus during the last few decades (McLeary et al., 2006). 

There are several single-particle characteristics that are very important to product properties (Davies, 1984). They include particle size, particle shape, surface, density, hardness, adsorption properties, and so on. From all these mentioned features, particle size is the most essential and important one. The term "size" of a powder or particulate material is very relative. It is often used to classify, categorize, or characterize a powder, but even the term powder is not clearly defined and the common convention considers that for a particulate material to be considered powder, its approximate median size (50% of the material is smaller than the median size and 50% is larger) should be less than 1 mm. It is also common practice to talk about "fine" and "coarse" powders several attempts have been made at standardizing particle nomenclature in certain fields. For example. Table 1.1 shows the terms recommended by the British Pharmacopoeia referred to standard sieves apertures. Also, by convention, particle sizes may be expressed in different units depending on the size range involved. Coarse particles may be measured in centimeters or... 

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