Metallic fibers processing

The depressed prices of most metals in world markets in the 1980s and early 1990s have slowed the development of new metal extraction processes, although the search for improved extractants continues. There is a growing interest in the use of extraction for recovery of metals from effluent streams, for example the wastes from pickling plants and electroplating (qv) plants (276). Recovery of metals from Hquid effluent has been reviewed (277), and an AM-MAR concept for metal waste recovery has recentiy been reported (278). Possible appHcations exist in this area for Hquid membrane extraction (88) as weU as conventional extraction. Other schemes proposed for effluent treatment are a wetted fiber extraction process (279) and the use of two-phase aqueous extraction (280). 

Alternatively, tows of fibers can be passed through a Hquid metal bath, where the individual fibers are wet by the molten metal, wiped of excess metal, and a composite wine is produced. A bundle of such wines can be consoHdated by extmsion to make a composite. Another pressureless Hquid metal infiltration process of making MMCs is the Prim ex process (Lanxide), which can be used with certain reactive metal alloys such as Al—Mg to iafiltrate ceramic preforms. For an Al—Mg alloy, the process takes place between 750—1000°C ia a nitrogen-rich atmosphere (2). Typical infiltration rates are less than 25 cm/h. 

But carbon and glass fibers are notable for their fragility and are inconvenient for processing and, therefore metal fibers of brass (Aron Kasei Co.), copper (Toshiba Chemical Corp.) [14], stainless steel (Brunswick Corp., Bekaert) [16], aluminium (MB ASSOCIATES, TRANSMET) [15] have been introduced. 

Reactive fibers, 9 486-489 Reactive flame retardants, 11 474-479 brominated, ll 475-477t Reactive gases, 13 456 Reactive groups, types of, 9 178 Reactive hot melt butyl sealants, 22 44 Reactive hot melt polyurethanes, 22 37-38 Reactive hot melt silicones, 22 35 Reactive ion-beam etching (RIBE), 22 184 Reactive ion etching (RIE), 20 278 22 183 of lotus effect surfaces, 22 120 Reactive lead alloys, 14 779 Reactive liquid metal infiltration process, 16 168... 

Other than in polymer matrix composites, the chemical reaction between elements of constituents takes place in different ways. Reaction occurs to form a new compound(s) at the interface region in MMCs, particularly those manufactured by a molten metal infiltration process. Reaction involves transfer of atoms from one or both of the constituents to the reaction site near the interface and these transfer processes are diffusion controlled. Depending on the composite constituents, the atoms of the fiber surface diffuse through the reaction site, (for example, in the boron fiber-titanium matrix system, this causes a significant volume contraction due to void formation in the center of the fiber or at the fiber-compound interface (Blackburn et al., 1966)), or the matrix atoms diffuse through the reaction product. Continued reaction to form a new compound at the interface region is generally harmful to the mechanical properties of composites. 

This is a process in which ink is pushed through a screen comprising a fine mesh of plastic or metal fibers (Fig. 12.IE). The pattern is defined by filling certain openings of the mesh with a stencil material. The screen is coated with the ink, and us-... 

Filament winding (FW) is a fabrication technique for forming reinforced plastic parts of high strength/modulus and lightweight. It is made possible by exploiting the remarkable strength properties of their continuous fibers or filaments encased in a matrix of a resinous material. For this process, the reinforcement consists of filamentous non-metallic or metallic materials processed either in fibrous or tape forms.488 489... 

Silicon-containing preceramic polymers are useful precursors for the preparation of ceramic powders and fibers and for ceramic binder applications (i). Ceramic fibers are increasingly important for the reinforcement of ceramic, plastic, and metal matrix composites (2, 3). This chapter will emphasize those polymer systems that have been used to prepare ceramic fibers. An overview of polymer and fiber processing, as well as polymer and fiber characterization, will be described to illustrate the current status of this field. Finally, some key issues will be presented that must be addressed if this area is to continue to advance. 

Metal fibers of steel, nickel, tungsten and various alloys constitute, based on their diameters, the transition between fibers and wires. They are generally polycrystalline and are mainly produced by physical working processes. 

Metal fibers can be produced by metal-cutting processes, by foil cutting processes, powder metallurgically by the sintering of metal powders which can be extruded with the help of organic binders to fibers, by metallization of non-metalic fibers and also by the controlled chemical dissolution of wires to the required fiber thickness. Thin metal wires and thick metal fibers can in principle be produced by the same methods. 

In addition to these process, special processes are known, particularly for the manufacture of thin metal fibers the continuous filament process, melt spinning processes and the Taylor process. 

Much thinner metal fibers are manufactured by the so-called bundle pulling process, in which wires are embedded in a ductile matrix (e.g. copper) and are jointly subjected to a continuous filament process. The fibers remaining, after removal of the matrix, have diameters down to 12 pm, but diameters down to 0.5 pm can be obtained with this process. 

Fibers that retain their high strength to temperatures in the range 1200-1500°C are needed for use as the reinforcement in ceramic and metal matrix composites. This portion of this chapter deals with the fabrication of SiC fibers using CVD. It is divided into sections on current status, hot- and cold-wall reactor designs, stresses in coated fibers, processing results, and economics. 

Filtration The process of removing particles or large molecules from a fluid phase by passing the fluid through some medium that will not permit passage of the particles or large molecules. The filtration medium may comprise woven fabric or metal fibers, porous media, or other ma-... 

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