Particle size and properties

The book is arranged in two parts Part I deals with basic relationships and phenomena, including particle size and properties, collision mechanics of solids, momentum transfer and charge transfer, heat and mass transfer, basic equations, and intrinsic phenomena in gas-solid flows. Part II discusses the characteristics of selected gas-solid flow systems such as gas-solid separators, hopper and standpipe flows, dense-phase fluidized beds, circulating fluidized beds, pneumatic conveying systems, and heat and mass transfer in fluidization systems. 

Fig. 5.13 Particle size and properties of iron oxide pigments based on a a-Fe203 [5.101].

Colored mixed-metal oxide pigments result from the incorporation of color-giving transition metal ions into an oxide host-lattice (see Table 5.9-13). Depending upon the particle size and properties of the chosen host, pigments (0.2 to 2 pm) or ceramic colorants (stains) (up to ca. 10 pm) result, which in many cases are characterized by high thermal and chemical stability and thus are suitable for the coloring of enamels and ceramics. 

The basic steps are identical to those of catalytic gas-solid reactions. However, as indicated above, the process is transient (non-steady-state) due to change in particle size and properties as the reaction progresses. 

A combination of heat and shear has been used to create whey protein particles with controlled particle size and properties. A well-known example of the use of microparticulation of thermally denatured whey protein is for the production of Simplesse 100, a whey-based fat replacer (Lieske and Konrad, 1993). Shear can be used to modulate gel properties of whey protein isolate gels. 

Grimm, S. Schultz, M. Barth, S. Muller, R. Flame pyrolysis - A preparation route for ultrafine pure y-Fe203 powders and the control of their particle size and properties. Journal of Materials Science 1997, 32, 1083-1092. 

This chapter discusses the role of various nanoparticles in inuniscible polymer blends for control of the size of the dispersed polymer phase particles, phase inversitMi and rheological behavior, impact strength, and mechanical performance. Various issues such as the effect of nanoparticle dimensions on the polymer particle size and properties, blending sequence, location of nanoparticles in the blend components, mechanism behind improvement in... 

Physical properties of blends consisting of a continnons matrix and one or more dispersed (discrete) components can be predicted by nsing adapted models proposed for particulate composite systems (216-220). Most of these models do not consider effects of the particle size, but only of volnme fractions of components in the system. Thus, the increase in particle size dne to particle coalescence is not presumed to perceptibly affect mechanical properties, except for fractnre resistance, which is controlled by particle size and properties of dispersed rnbbers. As polymer blends with three-dimensional continuity of two or more components are isotropic materials, simple parallel or series models or models for orthotropic or quasi-isotropic materials are not applicable. Physical properties of blends with partially co-continuous constituents can be calculated by means of a predictive... 

The relationship between particle size and properties has been known since the nineteenth century, when Faraday showed that the color of colloidal solution of An particles can be modified depending on their size. However, despite the long history of his discovery, the interest in nanoparticles has only increased significantly in the last 15 years. The research activities related to this area were driven by the ability to control material properties by controlling the size of the particles. 

Initial experiments involve separations at analytical scale, to determine the chromatographic parameters of the separation such as the effect of flow rate on column efficiency, so that the parameters of the Knox equation may be estimated, the effects of retention and solvent on the selectivity (note that in general the solvent system which gives the maximum selectivity is used, unless there are strong cost factors involved), the effects of packing material on selectivity, etc. In the ideal case, a few packings of different particle sizes and properties will be identified to give reasonable... 

Another important area of analytical chemistry, which receives some attention in this text, is the development of new methods for characterizing physical and chemical properties. Determinations of chemical structure, equilibrium constants, particle size, and surface structure are examples of a characterization analysis. 

Specific gravity is the most critical of the characteristics in Table 3. It is governed by ash content of the material, is the primary deterrninant of bulk density, along with particle size and shape, and is related to specific heat and other thermal properties. Specific gravity governs the porosity or fractional void volume of the waste material, ie. 

Aluminum hydroxide gel may be prepared by a number of methods. The products vary widely in viscosity, particle size, and rate of solution. Such factors as degree of supersaturation, pH during precipitation, temperature, and nature and concentration of by-products present affect the physical properties of the gel. 

Precipitation Hardening. With the exception of ferritic steels, which can be hardened either by the martensitic transformation or by eutectoid decomposition, most heat-treatable alloys are of the precipitation-hardening type. During heat treatment of these alloys, a controlled dispersion of submicroscopic particles is formed in the microstmeture. The final properties depend on the manner in which particles are dispersed, and on particle size and stabiUty. Because precipitation-hardening alloys can retain strength at temperatures above those at which martensitic steels become unstable, these alloys become an important, in fact pre-eminent, class of high temperature materials. 

Black Pigments. The only black pigment used to an appreciable extent in inks is carbon black It is used in newsprinting, pubHcation, commercial and packaging printing therefore, in large quantities. Black pigments ate offered in fluffy or beaded forms and in a variety of particle sizes and physical properties. 

Some studies (6) have been carried out to measure distribution of soHds in mixing tanks. Local soHds concentrations at various heights are measured at different impeller speeds. Typical data (Fig. 16) demonstrate that very high mixer speeds are needed to raise the soHds to high levels. At low levels, soHds concentration can exceed the average concentration at low mixer speeds. These soHds distributions depend on the impeller diameter, particle size, and physical properties. 

Pigments and Extenders. Pigments are selected for use in house paints based on thek appearance and performance quaUties. Appearance includes color and opacifying abiUty. Performance quaUties include ultraviolet light resistance, fade resistance, exterior weatherabiUty, chemical resistance, as well as particle size and shape. Toxicity profiles and safety and health related properties are also important criteria in pigment selection. 

Bioavailability, Bioequivalence, and Pharmacokinetics. Bioavailabihty can be defined as the amount and rate of absorption of a dmg into the body from an adrninistered dmg product. It is affected by the excipient ingredients in the product, the manufacturing technologies employed, and physical and chemical properties of the dmg itself, eg, particle size and polymorphic form. Two dmg products of the same type, eg, compressed tablets, that contain the same amount of the same dmg are pharmaceutical equivalents, but may have different degrees of bioavailabihty. These are chemical equivalents but are not necessarily bioequivalents. For two pharmaceutically equivalent dmg products to be bioequivalent, they must achieve the same plasma concentration in the same amount of time, ie, have equivalent bioavadabihties. 

The value of pigments results from their physical—optical properties. These ate primarily deterrniaed by the pigments physical characteristics (crystal stmcture, particle size and distribution, particle shape, agglomeration, etc) and chemical properties (chemical composition, purity, stabiUty, etc). The two most important physical—optical assets of pigments are the abiUty to color the environment in which they ate dispersed and to make it opaque. 

The most commonly measured pigment properties ate elemental analysis, impurity content, crystal stmcture, particle size and shape, particle size distribution, density, and surface area. These parameters are measured so that pigments producers can better control production, and set up meaningful physical and chemical pigments specifications. Measurements of these properties ate not specific only to pigments. The techniques appHed are commonly used to characterize powders and soHd materials and the measutiag methods have been standardized ia various iadustries. 

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