Ratio aspect

Aspect ratio is the length of a particle divided by its diameter. Table 5.7 provides information on aspect ratios of some fillers. 

Aspect ratio range Filler (actual aspect ratios are given in parentheses) 

3-10 milled carbon fiber (6-30), milled glass fiber (3-25), talc (5-20), wollastonite (4-68) 

10-20 silver-coated nickel flakes (15), nickel flakes (15-50) 

Particle size range Aspect ratio Hardwoods Softwoods 

The figures for aspect ratio are rounded up in a more realistic manner than in the original publication [129] (in which aspect ratios were given with a precision to a second decimal). 

More specifically, some WPCs were made using wood flour derived from pine, with an average aspect ratio of 4.0 from salt cedar, with an average aspect ratio of 3.2 and from juniper, with an average aspect ratio of 4.4 [130]. Wood fiber typically has higher aspect ratio, such as 10 1-25 1. For example, many wood fibers have a length of 3 mm and width of 0.2 mm (aspect ratio of 15) or a length of 10 mm and width of 0.4 mm (aspect ratio of 25). 

Commercial wood fiber from aspen, birch, maple, and spruce typically has a length of 0.4-3.5 mm, that is, 400-3500 pm (spruce is the longest one), and width 50-27 pm. Average aspect ratio values for fiber from these species are 35 (maple), 60 (aspen), 100 (birch), and 130 (spruce). 

Commercially available levers arc supplied with typical average specifications the aspect ratio is one of these (e.g., 0.7 for routine pyramidal tips or 3.0 for conical etched tips). It is a crucial parameter in terms of interpretation of an image (see 

Fiber properties ean be classified into primary and secondary properties. Primary properties are those that fibers must possess so they can be converted into usefitl products. Examples of primary properties are aspect ratio, strength, flexibility, cohesiveness, and rmiformity. Secondary properties are those that are desirable and can improve consitmer satisfaction with the end-products made from the fibers. Secondary properties include, but are not limited to physical shape, density, modulus, elongation, elastic recovery, resilience, thermal properties, electrical properties, color and optical properties, moisture regairt, resistance to chemical and environmental conditions, resistance to biological organisms, and resistance to insects. This chapter provides a brief introduction on these primary and secondary properties. Chapters 15-20 give more detailed discussion on some of the important properties. 

Primary properties are essential for converting the fibers into useful products. The requirement for primary properties varies from application to application. The following is a brief discussion on five primary properties that often are required in many fiber-based products. 

One important stractural characteristic of fibers is their lengths are cottsiderable greater than diameters. Fibers with relatively short lengths, measured in terms of centimeters or inches, ate called staple fibers. Long fibers, measured in kilometers or miles, are called filament fibers. The diameters of most fibers range from 

Due to the long lengths and small diameters, fibers typically have large aspect ratios, i.e., length-to-diameter ratios. All natural polymer fibers except silk are staple fibers, and the aspect ratios range from 1000 to 5000. Synthetic polymer fibers are produced as filaments, bnt they can be cut into staple fibers with desired aspect ratios. Inorganic fibers and nanofibers often are produced in continuous filament form. But they also can be made into staple fibers for certain applications. 

Aspect ratio has an important effect on the stractnre and properties of the products made from fibers. For example, in the textile indnstiy, staple fibers are twisted or otherwise assembled together to make continnons yams. Yams made from staple fibers often have dnll appearance since there are many fiber ends on the yam surface. On the other hand, filaments can be made into yams with httle or no twisting, and the resnltantyams look smooth and Instrons. In the composite application, filaments can be assembled into preforms, and the introduction of resins leads to the formation of composites with excellent mechanical properties. Staple fibers also can be used to make composites by directly mixing with resins. Composites made from very short staple fibers are often weaker than those made from filaments. However, when the aspect ratio is beyond 100, staple fiber composites could have comparable properties as filament composites. 

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Kent A D, Shaw T M, Moinar S V and Awschaiom D D 1993 Growth of high aspect ratio nanometer-scaie magnets with chemicai vapor deposition and scanning tunneiiing microscopy Science 262 1249... 

Figure C2.17.2. Transmission electron micrograph of a gold nanoneedle. Inverse micelle environments allow for a great deal of control not only over particle size, but also particle shape. In this example, gold nanocrystals were prepared using a photolytic method in surfactant-rich solutions the surfactant interacts strongly with areas of low curvature, thus continued growth can occur only at the sharjD tips of nanocrystals, leading to the fonnation of high-aspect-ratio nanostmctures [52].

Another important use of dielectrics is as intermetal dielectrics (IMDs), where the dielectrics insulate metal lines from each other. The dielectric material must fill small gaps with high aspect ratios (depth to width) while maintaining all other dielectric properties. It is essential that the IMDs are void-free at submicrometer dimensions for both performance and rehabiUty. 

Aspect ratio (long side/short side)... 

It generally is accepted that the mechanism of coercivity in the Alnicos is incoherent rotation of single-domain particles of the a -phase based on shape anisotropy. As coercivity increases, the larger the aspect ratio of the tods and the smoother thek surface becomes the difference between the saturation polarizations of the two phases also increases. It is thought that Ti increases the coercivity of Alnico because of an increased aspect ratio of the rods and a smoother surface. 

Aspect Ratio. The aspect ratio of mica is determined with electromicroscopic image analysis techniques. 

Wet Ground Mica. Wet ground mica is used because of its unique properties, ie, luster, sHp and sheen, and high aspect ratio (1,1 )-... 

Fig. 26. Bagley plot of pressure,, drop along a capidary versus capidary aspect ratio, E/R, at A, 7 = 590 s, and B, 7 = 295 s N To convert MPa to psi,...

As with any other fabrication process, masks are needed to define the features to be etched. It is common that the etch used for the semiconductor also etches the masking material. For this reason many different masks are used in etching, including photoresist, dielectric films, and metals. Masking can be a complex issue, especially when very deep etches (>5 fim) are performed with high aspect ratios (148). 

Immiscible Blends. When two polymers are blended, the most common result is a two-phase composite. The most interesting blends have good adhesion between the phases, either naturally or with the help of an additive. The barrier properties of an immiscible blend depend on the permeabihties of the polymers, the volume fraction of each, phase continuity, and the aspect ratio of the discontinuous phase. Phase continuity refers to which phase is continuous in the composite. Continuous for barrier appHcations means that a phase connects the two surfaces of the composite. Typically, only one of the two polymer phases is continuous, with the other polymer phase existing as islands. It is possible to have both polymers be continuous. 

The aspect ratio E/IE refers to the shape of the particles in the discontinuous phase. It is the average dimension of this phase parallel to the plane of the film E divided by the average dimension perpendicular to the film W. Plates in the plane of the film would have a high aspect ratio. Spheres or cubes would have an aspect ratio equal to 1. 

Pig. 11. Calculated permeabihties for a two-phase blend using Maxwell s result. Discontinuous phase has aspect ratio of 1.0. See Table 1 for unit... 

Steel, copper, and brass fiber may have a variety of aspect ratios, shape, ie, straight versus curved fibers and cross-sectional geometry, surface roughness, and chemical compositions. Fibers having tight specifications in terms of cleanliness, chemical composition, and aspect ratio ate necessary. The fibers are usually machined from larger metallic forms. 

Particle shape also affects the sintering of a powder compact. Jagged or irregular shaped particles, which have a high surface area to volume ratio, have a higher driving force for densification and sinter faster than equiaxed particles. High aspect ratio platey particles, whiskers, and fibers, which pack poorly, sinter poorly. 

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