Particle size overview

Apart from manifold structures, carbons can have various shapes, forms, and textures, including powders with different particle size distributions, foams, whiskers, foils, felts, papers, fibers [76, 77], spherical particles [76] such as mesocarbon microbeads (MCMB s) [78], etc. Comprehensive overviews are given, for example in [67, 71, 72], Further information on the synthesis and structures of carbonaceous materials can be found in [67, 70, 72, 75, 79]. Details of the surface composition and surface chemistry of carbons are reviewed in Chapter II, Sec. 8, and in Chapter III, Sec. 6, of this handbook. Some aspects of surface chemistry of lithiated carbons will also be discussed in Sec. 5.2.2.3. 

Both LC modules and columns must withstand higher generated backpressures. Table 3.3 presents an overview of commercially available columns for use with particle sizes below 2.0 /.an. Wu17 cites additional manufacturers and the numbers increase continuously. According to Kofmann et al.,18... 

This chapter provides an overview of essential concepts in HPLC including retention, selectivity, efficiency, and resolution as well as their relationships with key column and mobile phase parameters such as particle size, column length and diameter, mobile phase strength, pH, and flow rate. The significance of several concepts important in pharmaceutical analysis such as peak capacity, gradient time, void volume, and limit of quantitation are discussed. 

The submicron particle number size distribution controls many of the main climate effects of submicron aerosol populations. The data from harmonized particle number size distribution measurements from European field monitoring stations are presented and discussed. The results give a comprehensive overview of the European near surface aerosol particle number concentrations and number size distributions between 30 and 500 nm of dry particle diameter. Spatial and temporal distributions of aerosols in the particle sizes most important for climate applications are presented. Annual, weekly, and diurnal cycles of the aerosol number concentrations are shown and discussed. Emphasis is placed on the usability of results within the aerosol modeling community and several key points of model-measurement comparison of submicron aerosol particles are discussed along with typical concentration levels around European background. 

The activity in the field of particle size analysis has produced an explosion of papers. A useful review of recent literature is provided by H. G. Barth and S.-T. Sun in Analytical Chemistry4. This survey covers papers, books, and reviews from late 1981 to late 1984. A monograph published in 1984 and edited by H. G. Barth5 gives excellent overviews of most new... 

There are several different ways of producing these fillers resulting in various forms differing in particle size, surface area, purity, and morphology, which can have a profound influence on their performance as fire retardants. An overview of their principal methods of production is considered in the following text. 

Table 5.1. Overview of light-scattering measurements on toluene and chlorobenzene solutions of MDMO-PPV. Particle sizes [nm] are shown for different concentrations (0.25%, 0.125% and 0.0625%) 90% of the number or volume are below the given value. More details are given in the text...

Table 1 Overview of the Three Efficiency-Enhancing Pore Flow Effects and Their Relations to Pore Flow and Particle Size...

The dimensionless retention parameter X of all FFF techniques, if operated on an absolute basis, is a function of the molecular characteristics of the compounds separated. These include the size of macromolecules and particles, molar mass, diffusion coefficient, thermal diffusion coefficient, electrophoretic mobility, electrical charge, and density (see Table 1, Sect. 1.4.1.) reflecting the wide variablity of the applicable forces [77]. For detailed theoretical descriptions see Sects. 1.4.1. and 2. For the majority of operation modes, X is influenced by the size of the retained macromolecules or particles, and FFF can be used to determine absolute particle sizes and their distributions. For an overview, the accessible quantities for the three main FFF techniques are given (for the analytical expressions see Table l,Sect. 1.4.1) ... 

Barman BN, Giddings JC (1991) Overview of colloidal aggregation by sedimentation field-flow fractionation. In Provder T (ed) Particle size distribution II Assessment and characterization. American Chemical Society, Washington, DC, pp 217-228... 

Dispersion polymerization has also been applied to the ring opening polymerization of e-caprolactone and lactide in heptane-dioxane (4/1 v/v) with poly(dodecyl methacrylate)-g-poly(e-caprolactone) as stabilizer [97]. Diethyl-aluminium ethoxide and tin(II) 2-ethylhexanoate were used as initiators in these two systems, respectively, to obtain functional microspheres with a narrow particle size distribution and a narrow molecular weight distribution [98]. Table 2 provides an overview of microspheres obtained by living dispersion polymerization. 

In an aqueous latex that has been cleaned to remove various materials such as suifece active agents one is dealing in many cases with a dispersion of charged spherical particles. Frequently, the distribution of particle sizes is veiy narrow and the term monodisperse is used to describe latices of this type. In an attempt to obtain a concise overview of the properties of aqueous latices in electrolyte solutions some of the essential features are summarized schematically in Fig. 4. 

FIGURE 20.1 Overview of particle sizes and separation processes. The shaded blocks mark the typical range of sizes of some ingredients of beer. 1000 pm= 1 mm. (Courtesy of GE Infrastructure, Water and Process Technologies. With permission.)... 

While the focus of this overview has to this point been on API physical properties that are directly affected by milling (particle size and, hence, surface area), it is important to note that other API properties may be affected by milling. For example, milling is known to induce loss of crystallinity, through compressive or impact force and/or exposure to elevated temperatures. This is typically undesirable, as amorphous solids are usually less chemically and physically stable than crystalline solids. It is expected that much of the amorphous content is localized at the particles surfaces, so while the overall amorphous content may be low, its impact on particle-particle interactions in formulation can be significant. ° Milled compounds that are partially amorphous or that have different surface energies can have different wettability or different flow properties compared with unmilled API. In some cases, these differences are caused by recrystallization of amorphous material upon storage.P ... 

Fig. 35 Spray-dried extracts and pantothenate solution. Spray-dried calcium pantothenate overview (A) and detail (B), showing mainly particles that were damaged during preparation of the SEM sample either by the high vacuum of the SEM or by the heat created during the sputter coating process. Spray-dried Tussilago farfara extract prepared by a system using atomizing air to form droplets and leading to small particle sizes (C) and a magnification thereof (D).

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