Fiber measurements

Several methods exist for the determination of respirable fibers. In the case of asbestos fibers, unspecific light microscopic techniques [6-110] as well as highly sensitive X-ray methods can be employed [6-111]. Differentiation from inert fibers, e.g., fibers of gypsum, is only possible with the latter method, although light microscopic analyses are more cost effective. All these procedures are suitable for the determination of total respirable fibers, especially for determining the concentration of man-made mineral fibers. 

For a thorough assessment of different types of fibers, special analytical methods have to be used. The scanning electron microscope (SEM) is usually the equipment of choice for the characterization of asbestos fibers. Energy disperse X-ray analysis (EDX) enables asbestos fibers to detected even at very low concentrations. This procedure requires very expensive technology and can be performed only by highly skilled technicians. 

For scanning electron microscopic analysis a special type of monitor has to be used. The appropriate filter materials, usually condensed with gold, can be used for personal as well as stationary sampling. In the case of stationary air sampling using selected pumps, fiber concentrations below 200 fibers per m can be de- 

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Stress—Strain Curve. Other than the necessity for adequate tensile strength to allow processibiUty and adequate finished fabric strength, the performance characteristics of many textile items are governed by properties of fibers measured at relatively low strains (up to 5% extension) and by the change ia these properties as a function of varyiag environmental conditions (48). Thus, the whole stress—strain behavior of fibers from 2ero to ultimate extension should be studied, and various parameters should be selected to identify characteristics that can be related to performance. 

Optical fiber measurement of local solids concentrations of FCC catalyst fluidized in a 9-cm-i.d. column gave the results shown typically in Fig. 26. Analysis of these data showed that the radial voidage profile could be described solely by the cross-section-average voidage e, calculated as shown in Sec. 5.1, and the reduced radial coordinate r/R ... 

Gulino, R. and Phoenix, L. (1991). Weibull strength statistics for graphite fibers measured from the break progression in a model graphite/glass/cpoxy microcomposites. J. Mater. Sci. 26, 3107-3118. 

Although fibers can be classified in numerous ways, in terms of present-day technology, they are fundamentally classified as(l) natural libers, and (2) synthetic libers. The principal natural fibers are cotton, wool. and. to a much lesser extent, silk. liax. and mohair. Synthetic tihers have made inroads into the use of all natural fibers, bul the greatest impact has occurred in connection with the latter three libers. Cotton continues to be a major textile fiber, measured in terms of billions of pounds used per year. Colton is one of the most versalile of all libers and blends well with synthetics. This is also true of wool, bul lo a somewhat lesser extent. Synthetic Fibers. Introduced in 1910 as a substitute for silk, rayon was the first artificial or synthetic fiber. Rayon, of course, differs completely in chemical constitution from silk. Rayon typifies most reconstituted or synthetic fibers, which perform almost as well and. in a number of respects, far better than their natural counterparts Some of the more recently developed synthetic libers have lilile if any resemblance to naturally available fibers and thus enlirely new types of end-producls with previously unobtainable end-qualities are available,... 

Figure 5. The zeta potential of crushed, untreated fibers measured using a Pen Kem 3000 Analyzer.

Fig. 2.2. FSB spectra of Ge02-doped fused silica (a), low-OH fused silica (b), and normal fused silica (c) fibers measured with 785nm excitation (modified from [8])...

Fig. 13. Gamma-ray spectra on neutron-irradiated E-glass fiber measured after 30 days of cooling...

Since the fiber is heavier than the liquid, it would sink when placed on the liquid if it were not sustained by an upward force caused by the surface tension of the liquid. This force is exerted at the three-phase air-liquid-fiber boundary lines. If the contact angle 0 and the surface tension y are high enough, this upward force can become sufficient to balance the sinking force, and the fiber will come to rest when the two forces become equal, at an equilibrium depth corresponding to a definite value of < . In this situation, as shown in Figure 1, the force exerted vertically upward on a unit length (1 cm.) of fiber, measured in dynes, will be ... 

In addition to specific chemical substances, a variety of other determinations is very important and is often required for environmental studies and protection programs. These include identifications and measurements of bacteria, viruses, protozoa, and minerals such as asbestos fibers. Measurements of meteorological conditions, particulate matter in air by size, water turbidity, biological oxygen demand, chemical oxygen demand, and radioactivity are also very important. These and other similar determinations are beyond the scope of this chapter and the reader should consult other reference books for information about these topics. 

With fibers, measurements are usually in terms of fiber length L and diameter d. Writing the aerodynamic diameter as... 

Fig. 6. Instrumentation for optical-fiber measurement and alternate-layer arrangement of fibers (after Qin and Liu, 1982).

The assumption made when the Coulter counter was first developed was that the variability in speed of the fibers, as they passed through the sensor, was small and could be assumed constant [67]. Analysis showed that this assumption was incorrect and a later instrument included a sensor to measure fiber speed [68]. Since the fibers are aligned with flow, the pulse length is a measure of fiber length and the pulse height is a measure of fiber width. The results showed excellent agreement with Suter-Webb measurements. The AFIS is widely used for cotton fiber measurement in the dry state. 

One paired fiber ( ) measured 107.8 (xm, and one single fiber measured 58.5-68... 

Fig. 8 Excitation geometry for direct illumination of surface bound molecules. Image on the left shows the modified fiber optic cormector with a fluid port and adjacent optical fiber. Measured nearfield intensity distribution of the distal end confirms propagations of leaky modes...

The buffering action of a coating in this situation is determined by the relaxation modulus of the coating material. The relaxation modulus may be measured on a film cast from the material by carrying out tensile-stress relaxation measurements with a suitable apparatus such as a Rheovibron dynamic viscoelastometer operated in a static mode. Figure 13 (inset) displays such measurements for the four coating materials used on the fibers measured in Figure 12. The measurements were carried out at 23 °C at small tensile strains, where the materials exhibit linear viscoelastic behavior. 

FIGURE 4-26 Comparison of particle velocities determined by LDV and cross-correlation of optic fiber measurement (Yang et al., 1992)... 

FIGURE 4-36 Schematic of the logic distribution functions of the five-fiber measuring system. 

Lischer, D.J., and Louge, Optical Fiber Measurements of Particle... 

Passive optodes shown in Figure 17-34 are used for Raman or fluorescence spectrometry. 1 vo types of monofiber optode have been described [166], as shown in Figure 17-34a. They require the use of a pierced mirror and suitable optics to separate the source laser and fluorescence emission beams at the fiber-measuring instrument junction. With a single fiber the observation of fluorescence is divided into four zones in order to calculate the effective optical path (/,). For a fiber with radius rg and numerical aperture A and observation in a medium with refractive index n , this path was evaluated by Deaton [191] as... 

Fig. 8 Fabrication of novel random fibrous chitosan scaffolds, (a) Illustration of the micromolding process, (b-d) SEM images of chitosan scaffolds composed of fibers measuring 22 pm (b), 13 pm (c), and 4 pm (d) in width [106]...

Figure 16.39 TMA curves of textured and untextured fibers measured in tension, showing...

This paper describes pure N2 permeation and CO2-N2 separation characteristics of ILM-s of pure water and aqueous 302 wt/wt K2CO3 solutions Immobilized in Celgard X-10 hollow fibers. Measurements were carried out over a wide range of applied pressure differences. The CO2 partial pressure difference was varied from about 40 cm Hg to 140 cm Hg while the N2 partial pressure difference was Increased from about 125 cm Hg to 425 cm Hg. The total applied pressure difference was varied between 140 to 550 cm Hg. Facilitated transport membranes of aqueous 3UZ wt/wt K2CO3 solution for the separation of CO2 from were utilized and the separation behaviors... 

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