Plastics, metallization vapor phase

Designing of OrganometalHcs for Vapor Phase Metallization of Plastics... 

Fracture of massive brittle and ductile pieces are rather well understood. By taking proper account of the microstructure as well as the micro- and macro-defects, most catastrophic and fatigue failures find a satisfactory explanation within the scope of the linear elastic fracture mechanics or the elasto-plastic fracture mechanics. Metallic filaments are particular and in many respects deserve a treatment of their own. Particular fabrication methods, such as drawing, melt spinning or crystallization from the vapor phase for whiskers are needed to obtain their small lateral dimensions. These processes may give rise to particular textures, intrinsic and extrinsic defects. Thermal treatments may modify or eliminate such defects but in many cases fracture is initiated by defects that stem from the fabrication process. Moreover, the small lateral dimensions, especially in micro-wires, make metallic filaments prone to external influences. Corrosive attacks may rapidly affect an important fraction of their cross-section. Hydrogen, for instance, which usually results in a severe embrittlement, may diffuse up to the core in a rather short time. 

Conventional carbon fibers are currently based either on the polymer PAN (polyacri-lonitrile) or petroleum pitch (see Chapter 7). Although they have many properties that would make them useful in many matrices like plastics, metal, and cement, their expense has limited their use. In contrast, the GMR method is an inexpensive way to produce carbon fibers (called Pyrograf, because the method uses pyrolysis to form graphitic carbon). The testing of the vapor phase process has been so promising that GM s Inland Division has built a pilot plant in Dayton to produce Pyrograf. 

The top-down approach starts with a bulk material and attempts to break it down into nanoscaled materials through physical methods. Hence, most of these techniques are really forms of fabrication rather than synthesis. For nanostructured bulk phases, including powders, the common methods are milling, devitrification of metallic glass, and severe plastic deformation. For nanocrystalline thin films (films with nanosized crystallites), methods include thermal vaporization (under high vacuum), laser ablation, and sputtering (thermal plasma), all of which were... 

In aqueous media where hydrochloric and hypochlorous acid and halogens are present in either vapor or liquid phase, the utility of the above materials of construction is severely lin ited and can best be determined by rates of corrosion study during pilot laboratory operation. Tantalum, zirconium, and titanium are usually resistant but expensive. The plastics are of variable resistance and are severely limited by temperature and solvent attack. Stoneware, Karbate, glass, glazed tile, carbon brick, and enameled steel all have utility within rigid limits. The other metals and alloys are usually questionable but may be desirable for replaceable piarts i... 

One example (out of many) to illustrate the complexity of adsorption from solution (as compared with gas-phase adsorptions), is the removal of mercury, an unacceptable toxic pollutant in aqueous systems. It is found in wastewaters (before treatment) from such manufacturing industries as chloroalkali, paper and pulp, oil refining, plastic and batteries, and can exist as free metal, as Hg(I) and Hg(II). Mercury adsorption capacity, on AC, increases as the pH of the aqueous systems decreases. Carbons with different activation methods have widely different capacities. Sulfurization of the carbon, loading the carbon with zirconium, as well as the dispersion of FeOOH species over the carbon, enhanced Hg(II) uptake. Mercury vapor can be taken up using AC which have been pre-treated with sulfur, the effect of chemisorbed oxygen being to retard (not prevent) the uptake of mercury, Lopez-Gonzalez et al. (1982). 

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