Particle shape fibrous

More than 20 different types of clay can be actually distinguished. Those most appreciated for making ceramics, for example, kaolinite, are built up of combinations of the basic structural units described above. The particles of most consist of platelets (very small, flat sheets) that, when stacked together, form layered arrangements having extensive surface areas, much like the pages of a book. Other common clay particle shapes are fibrous or tubular. 

Dust masks, or particulate filter respirators, protect the respiratory system against any kind of inhaled particles. The simplest type, in the form of a cone-shaped fibrous filter that fits over the nose and mouth, is held in place by an elastic band around the back of the head. It is disposable, relatively comfortable to wear, and is useful when the dust is neither excessive nor toxic. It becomes readily clogged and should be discarded and replaced whenever breathing becomes restricted. Its use should not be carried over from day to day. 

Particle size and shape Finer particles tend to be more cohesive and hence more difficult to handle. Similarly, particle shape also affects flowability. Fibrous and angular particles are usually more cohesive than particles that are rounded. 

Particle shape and orientation Fibrous, Cellular, Crystalline, etc. ... 

Particle shape (an aspect ratio increase in a certain range improves tensile properties see examples for fibrous fillers and mica)... 

Microcrystalline form, Avicel. Prepn and manuf of crystallite cellulosic aggregates Battista, fntf. Eng. Chem. 42, 502 (1950) Battista. Smith, U-S. pats. 2,978,446 and 3.141,-875 (1961 to Am. Viscose and 1964 to FMC). Non-fibrous powder. Particle shape rigid rods. Refractive index 1-55. Bulk density 18-19 lb/cubic foot. Practically insol. but... 

Conventionally produced cellulose powders (microcrystalline cellulose) consist of irregularly shaped fibrous particles of limited use for column chromatography. Beaded cellulose is prepared by dissolution of cellulose powder in a suitable solvent, followed by droplet formation in a suspension medium, and subsequent solvent extraction or crosslinking. Cellulose triacetate and tricarbamate derivatives are useful as low-cost sorbents for the process-scale separation of enantiomers (section 10.4.2). 

These relationships assume that the particle shape factors C2 and C3 are independent of particulate size. For homogeneous suspensions (for example, clays) and for many heterogeneous aqueous particulates, this appears to be a reasonable assumption (10,21). When fibrous or unusually shaped particulates are present in large numbers, appropriate corrections to this assumption must be made. 

FIGURE 9.3 Particle Shapes (a) Spherical - Calcite (b) Acicular - Calcite with Stibnite (c) Fibrous - ActinoUte (d) Dendritic - Gold (e) Hakes - Abhurite (f) Polyhedron - Apophyllite (g) CyUndrical Particles (For color version of this figure, please refer the color plate section at the end of the book.)... 

Industrial carbon adsorbents are complex products difficult to classify on the basis of their behaviour, surface characteristics, properties or utility. However, they are usually categorised according to their particle shapes and size into powdered, granulated, spherical, pelletised or fibrous (in the form of felt or cloth) activated carbons. These categories can be further sub-divided according to their various properties, e.g. porous structural or surface chemical structural characteristics. 

In addition to the shapes already mentioned, there are also particles of fibrous or acicular form ft)risms, needles, fibers, etc.) having one dimension greatly exceeding the others. These include particles of zinc oxide (0.4-1 m), asbestos [(0.3-3) 100 m or (0.5-1.5) 1 m], tobacco virus [(1.0-2.0) (10-30) /x], etc. 

The characteristics which determine the properties filler that will impart to a composite are particle shape, particle size, surface area, and particle-matrix compatibility (Fig. 1). Particle-matrix compatibility relates to the ability of the polymer to coat and adhere to the filler. The shape of most mineral filler particles can be a sphere, cube, block, plate, needle, or fiber whereas some filler also contain a mixture of shapes. Mineral particles resembling plates, needles, and fibers are further characterized by their aspect ratio (http //www.rtvanderbilt.com/ fillersintroweb.pdf). In rubber/polymer composites, applied stress is transferred from the rubber/polymer matrix to the strong and stiff mineral. It seems reasonable that this stress transfer will be better affected if the mineral particles are smaller, because greater surface is thereby exposed for a given mineral concentration. Moreover, if these particles have a high aspect ratio (are needle-like, fibrous or platy in shape), they will better intercept the stress propagation through the matrix (Fig. 2) (http //www.rtvanderbilt.com/fillersintroweb.pdf). 

The addition of small particles to polymers enhances their viscosity in the molten state and their modulus in the solid state. Generally, tensile strength and brittleness are also enhanced. Particles with fibrous or disklike shapes induce anisotropic mechanical and electrical behavior. 

Fillers with particles nearly spherical in shape usually dimish <7n under a fixed shear stress [178,181, 182,202] in comparison with the pure polymer. In contrast, scales tend to step up the first difference of normal stresses [181]. Fibrous fillers have little effect on a, x value [181], except in a few cases where the tendency for... 

The inherent toxicity of the particle will depend on its chemical composition. For example, a particle of CdCl2 can be expected to be more toxic than NaCl because of the known toxicity of Cd+2 (6). In the case of fibrous particles, the toxicity of the material will also depend on the size and shape of the fibers, with long, thin fibers being the most toxic (7.8). 

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