Properties whiskers

Thermal Stresses and Properties. In general, ceramic reinforcements (fibers, whiskers, or particles) have a coefficient of thermal expansion greater than that of most metallic matrices. This means that when the composite is subjected to a temperature change, thermal stresses are generated in both components. 

Whisker and Short Fiber Composites. Whiskers and short fibers tend to align during forming, lea ding to anisotropic properties and large... 

Directed Oxidation of a Molten Metal. Directed oxidation of a molten metal or the Lanxide process (45,68,91) involves the reaction of a molten metal with a gaseous oxidant, eg, A1 with O2 in air, to form a porous three-dimensional oxide that grows outward from the metal/ceramic surface. The process proceeds via capillary action as the molten metal wicks into open pore channels in the oxide scale growth. Reinforced ceramic matrix composites can be formed by positioning inert filler materials, eg, fibers, whiskers, and/or particulates, in the path of the oxide scale growth. The resultant composite is comprised of both interconnected metal and ceramic. Typically 5—30 vol % metal remains after processing. The composite product maintains many of the desirable properties of a ceramic however, the presence of the metal serves to increase the fracture toughness of the composite. 

Fig. 1. Reinforcement aichitectuies foi ceiamic—matrix composites and corresponding composite properties, (a) Spherical particles (b) platelets, whiskers,...

Ceramic matrix composites are candidate materials for high temperature stmctural appHcations. Ceramic matrices with properties of high strength, hardness, and thermal and chemical stabiUty coupled with low density are reinforced with ceramic second phases that impart the high toughness and damage tolerance which is required of such stmctural materials. The varieties of reinforcements include particles, platelets, whiskers and continuous fibers. Placement of reinforcements within the matrix determines the isotropy of the composite properties. 

The term s plastic, polymer, resin, elastomer, and reinforced plastic (RP) are some-what synonymous. However, polymer and resin usually denote the basic material. Whereas plastic pertains to polymers or resins containing additives, fillers, and/or reinforcements. Recognize that practically all materials worldwide contain some type of additive or ingredient. An elastomer is a rubberlike material (natural or synthetic). Reinforced plastics (also called composites although to be more accurate called plastic composites) are plastics with reinforcing additives, such as fibers and whiskers, added principally to increase the product s mechanical properties. 

Fig. 6-14 Properties of different RPs that includes whiskers, aluminum, titanium, and steel.

Glass OTC (GC) drawing 134 etching HCl 140 leaching HCl 140 particle deposition 143 properties 135 whisker formation 142 Glassy carbon (GC) 204 Golay equation GC 21 LC 342 SFC 607... 

The phenomenon of pseudopolymorphism is also observed, i.e., compounds can crystallize with one or more molecules of solvent in the crystal lattice. Conversion from solvated to nonsolvated, or hydrate to anhydrous, and vice versa, can lead to changes in solid-state properties. For example, a moisture-mediated phase transformation of carbamazepine to the dihydrate has been reported to be responsible for whisker growth on the surface of tablets. The effect can be retarded by the inclusion of Polyoxamer 184 in the tablet formulation [61]. 

Aluminate cement, 2 415-416 Aluminate ions, silica sols and, 22 394s Aluminates, 2 273-279 analysis, 2 275-276 chemical reactions, 2 273-274 dispersants, 8 710t economic aspects, 2 275 health and safety factors, 2 276 manufacture, 2 274-275 physical properties of, 2 273-274 uses of, 2 276-277 Alumina trihydrate (ATH), 2 274 in synthetic fillers, 11 314-315 Alumina whisker reinforcement, 5 574t Alumina xerogels, X-ray diffraction of, 23 78... 

Whipple s rules, 20 138 Whisker reinforcement, 5 554, 555, 654 performance in ceramic—matrix composites, 5 572-575 physical properties, 5 557t synthesis, 5 642-643 and toughening, 5 622 Whiskers, silicon carbide, 22 533-534 White... 

R. Bacon, Growth, structure, and properties of graphite whiskers, J. Appl. Phys. 31, 283—290 (1960). 

Whiskers are synthetic crystalline fibers of variable size, but with diameters of usually less than 25 microns. An upper limit in diameter exists because the physical and chemical properties approach those of the bulk material as the diameter of fibrous sample increases. Since the purpose of synthesis is to take advantage of some characteristic property of the material in fibrous form, such as enhanced strength for small volume, the optimum material has a small diameter. For similar reasons the aspect ratio of useful whiskers is often well over 100. Whiskers can be single crystals, but many are polycrystalline aggregates of fibrils with preferred orientations. The compositions and crystal structures of the compounds synthesized as crystalline fibers also have the broadest possible variety (Brenner, 1958). 

Brcck, D. R. (1974). Zeolite Molecular Sieves. Wiley-Interscience, New York. Brenner, S. S. (1958). Growth and properties of whiskers. Science 128 569-575. Brindley, G. W. (1980). Order-disorder in clay mineral structures, pp. 125-195. In Brindley, G. W. and G. Brown, eds. Crystal Structures of Clay Minerals... 

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