Production of Particles and Fibers

The existence of vacancies has been also reported by Kwei et al. [41], w ho observed that in the C-B-C chain, the central boron atom w as relatively loosely held and that these locations could form vacancies. The increasing concentration of atomic defects has been attributed to w eakly bound electrons, w hich explains the increasing electrical conductivity w ith increasing boron content [w ith a break at 13.3 mol% 

The central position in the linear chain is considered to be occupied by larger atoms such as Si or Al, w hich form solid solutions w ith boron carbide [42-46]. 

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There is an extensive literature that reports on the production of tubes and fibers using different routes, synthetic conditions, carbon sources, and catalysts. Tibbetts and Gorkiewicz [20a] appear to have been the first researchers to use an organometallic complex, FcH, to produce CNFs and CNTs. Thermal decomposition of FcH alone resulted in the formation of SWCNTs [20]. Also, Barreiro et al. [20] used FcH as the sole source of both catalytic Fe particles and C feedstock which nucleated from the C species to form SWCNTs. As highlighted earUer, most tubular nanocarbons made in the gas phase are produced... 

Wood particle and fiber driers are used to dry the raw material for particleboard and similar products (20). Just as with the veneer for plywood, the parhcles must be dried before being mixed with the resins and formed into board. Drying is accomplished in a gas-fired drier, a direct wood-fired drier, or steam coil driers. Many different types of driers are used in the industry. Emissions are fine particles and condensible hydrocarbons, which produce... 

It is known that the toxic effects of some solid particles and fibers (latex, zeolite, asbestos fibers, etc.) depend on the stimulation of free radical production. Therefore, the inhibitory effects of flavonoids on particle-mediated damaging processes might be expected. Thus, rutin... 

Production of phenol and acetone is based on liquid-phase oxidation of isopropylbenzene. Synthetic fatty acids and fatty alcohols for producing surfactants, terephthalic, adipic, and acetic acids used in producing synthetic and artificial fibers, a variety of solvents for the petroleum and coatings industries—these and other important products are obtained by liquid-phase oxidation of organic compounds. Oxidation processes comprise many parallel and sequential macroscopic and unit (or very simple) stages. The active centers in oxidative chain reactions are various free radicals, differing in structure and in reactivity, so that the nomenclature of these labile particles is constantly changing as oxidation processes are clarified by the appearance in the reaction zone of products which are also involved in the complex mechanism of these chemical conversions. 

In GAS, a compressed gas acting as antisolvent is dissolved in the solution of a nonvolatile component with gas contents in the order of equimolar mixtures. This causes a volumetric expansion and hence a remarkable reduction in solvent power. Consequently, precipitation or crystallisation of the solute occurs, leading to ultrafine particles and fibers in the micrometer range. Furthermore, the precipitates e g. pharmaceutical products are purified while impurities remain in solution. 

The single largest use for the phenol-formaldehyde resins is in adhesive applications for the production of plywood, chipboard, and particle board. The resin can comprise as much as one-third of the weight of the board, particularly of particle boards, which contributes to a total demand for phenolics in the U.S.A. of over half a million metric tonnes per year. They are also used as the matrix adhesives for the production of several types of grindstones. In combination with paper, woven cotton, glass fiber, etc., components, phenolics contribute to the production of engineering and decorative laminates in the form of rods, tubes, and sheets. The sheet products Arborite and Formica are familiar as the finished surfaces of furniture, bathroom, and kitchen counter tops and other areas where attractive patterns and water resistance are important characteristics. Molded products from phenolics are also important where heat or electrical resistance is required, such as saucepan and toaster handles, switches, and the printed circuit boards used in computers. Recent phenolics production in the U.S.A. has totaled over 500,000 metric tonnes per year, not including fillers [38]. 

Antimony pentoxide is an alternative to antimony trioxide. It finds applications in semi-transparent materials and dark colors because of its low tinting strength. As with antimony trioxide, antimony pentoxide must be used together with halogen-containing compounds to function as a flame retardant (sec discussion under antimony trioxide). The other advantages of antimony pentoxide include its refractive index which is closer to most materials, its very small particle size, its high specific surface area, and its substantially lower density. Because of its small particle size, its is frequently used in the textile industry since its addition has only a small effect on color or on mechanical properties. Production of fine-denier fibers requires a stable dispersion and a small particle size filler. The flame retardancy of laminates is also improved with antimony pentoxide because small particles are easier to incorporate in the interfiber spaces. 

However, carbon black has been used with success as a filler in rotationally molded products. At concentrations of up to 2.5 wt% it improves the weathering resistance of the product. Since dimensional stability and the shape of articles would benefit Ifom the use of fillers and fibers, it is probable that they will start to be used in the future. When this happens, fillers will be introduced in a premixed form to assure homogeneous distribution (forces normal to the surface of product cannot cause the movement of particles towards the mold surface when particles are premixed with polymer). 

Tables 21 and 22 summarize the usual press strategies for the production of particleboards and MDF. The warming up of the mat is performed by the so-called steam shock effect [442-447]. The precondition for this is the high permeability to steam and gases of the particle or fiber mat [442,443,448,449]. High moisture contents of the face layers and spraying of water on the surface layers sustain this effect. The press temperature influences the possible press time and by this the capacity of the production line. The minimum press time has to guarantee that the bond strength of the still hot board can withstand the internal steam pressure as well as the elastic springback in board thickness at press opening.

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