Whiskers metal

Most whiskers up to 1 micrometer in diameter obey Hooke s law to the point of fracture, regardless of their composition (Evans, 1972). Whiskers of brittle and ductile materials with larger diameters respond to stress differently. Metallic whiskers fail under tension by shear, whereas other compounds fail through fracture. 

A number of these polymers exhibit a phenomenon called anomalous fiber formation, reminiscent of metallic whiskers. ... 

The whiskers that are commonly added to silicon nitride to form composites are Si3N4 and SiC (common nomenclature is to add the suffix (w) to denote whiskers and this will be used where appropriate). Although other ceramic and metallic whiskers are available (e.g. BN, TaC, TiC, B4C and Fe), Si3N4 and SiC each have properties that make them prime candidates as reinforcements, not least of which is that they can sustain the high temperatures and reactivity of the sintering process without being degraded. 

The detector used to convert incident microwave power into an output voltage is often a crystal detector consisting of a fine metal whisker in point contact with a semiconductor. The contact resistance is greater in one direction than in the other, and the small contact capacitance means that the crystal acts as a fast rectifier which is sensitive to microwave radiation. Incident microwave power on the crystal causes a voltage drop so that a current flows. At very low incident microwave power levels the rectified current is proportional to the power and, since this is proportional to the square of the voltage drop across the crystal, the detector is known as a square-law detector. At higher incident powers the rectified current is proportional to the first power of the voltage and the detector is then a linear detector. 

Types of reinforcements include fibers of glass, carbon, graphite, boron, nylon, polyethylene, polypropylene, cotton, sisal, asbestos, metals, whiskers, etc. Other types and forms of reinforcements include whiskers, bamboo fibers, burlap fibers, carbon blacks, platelet forms (includes mica, glass, and aluminum), and hemp fibers (Chapter 2). 

The most obvious area of application are as fibers for composites. There are a number of metallic whiskers that are employed as high-strength fibers in composites. These composites are among the strongest known. The mechanical and electrical properties of the fibers also need to be studied. It is possible that the... 

A problem initially experienced with rechargeable Li batteries was that during a recharge cycle, the Li metal tended to form dendrites (metal whiskers) that shorted the electrodes and limited the number of charge/recharge cycles. It also had an incipient fire risk [53]. 

D nanomaterial composites - Two dimensions of the nanomaterials are oti the nanometer scale. Fillers include materials such as carbon nanotubes, cellulose whiskers, metal whiskers, and rod-like clay fillers. 

In August 2006, additional exemptions were allowed for the RoHS legislation. As will be discussed in subsequent chapters, lead has been used to reduce or eliminate the occurrence of tin whiskers (metallic dendrites of tin that grow from pure tin surfaces). Metallic whiskers, such as from tin or zinc, are known to pose a reliability risk in terms of electrical shorting between oppositely charged conductors. Therefore, the RoHS legislation has been amended to allow lead in surface finishes of components with pitch <0.65 mm for tin whisker repression. This applies to NiFe (Alloy 42, also known as Kovar) lead-frames as well as to components with copper lead-frames. Curiously, the exemption does not cover connectors. 

ImSn This finish is similar to immersion silver in most characteristics. However, because tin tends to form metallic whiskers that can cause electrical shorts, it is not widely used. 

There are organic and inorganic whiskers. Organic whiskers include fibrin whiskers, polyCbutyl acrylate-phenylethylene) whiskers, and so forth, and are usually used in polymers. Inorganic whiskers include metal whiskers and nonmetal whiskers. Metal whiskers are mainly applied in metal matrix composite material. Ceramic whiskers, a kind of nonmetal... 

The generalized BE approach also finds application in the P/M processing of composite materials for high-temperature service— i.e., the term could be applied to the introduction of oxide particles or unconstitutional precipitates (e.g., refractory intermetallic compounds) as dispersion strengtheners, or of suitably coated SiC or refractory metallic whiskers for fiber reinforcement. 

When this value for steel (12 x 10 /4 = 3x10 psi = 20.7 GPa) is compared with actual values of maximum strength for ordinary samples (10 psi), a discrepancy of 30 is observed. However, very small metal whiskers have been specially grown which do have a strength approaching 3 X 106 psi = 20.7 GPa. 

Metal particles, principally Ni, Cu, Ag, A1 and Fe, have been used. These, particularly in the form of metal flakes, offer a higher conductivity (up to 10 Scm" ) than carbon black. Even lower percolation-thresholds can be achieved with conductive fibres. These can be either metal whiskers or metal-coated graphite or glass fibres. The use of lower loading-levels leads to improved mechanical properties, which are influenced by both filler loading and shape. 

Herley, P.J. and Jones, W. (1989) Metal hydrides as precursors for the generation of supported metal particles and alkali metal whiskers. Zeitschrifi fuer Physikalische Chemie, 164,1151-5. 

Hawkins, D.T. Metal Whiskers, 1945-1975. Bell Labs internal document, a comprehensive collection... 

Arnold, S.M. The growth and properties of metal whiskers. Proc. Am. Electroplaters Soc. 1956, 43,... 

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