Whiskers whisker crystals

Whisker, whisker-crystal A modern technical term originating in the field of solid-state physics for highly elongate crystals resembling mineral fibers that are synthesized from a variety of inorganic substances, usually at elevated temperatures or pressures. Whiskers are synthetic fibrous materials (see chapter 2). 

The graph shown in Figure 6.7 plots the strength versus the modulus of some typical fibres. Note the very special performance of the whiskers (single-crystal fibres). 

Gallliumphosphide (GaP) is a light-colored highly pure crystal form used as whiskers and crystals in semiconductor devices. 

Webb, W. W., H. D. Bartha, and T. B. Shaffer (1966). Strength eharacteristics of whisker crystals, macrocrystals and microcrystals, pp. 329-354. In Strengthening Mechanisms, Metals and Ceramics. Burke, J. J., N. L. Reed, and V. Weiss, Eds. Syracuse University Press, New York. 

Fillers can take many forms, including particles, fibers, flakes, and whiskers. Whiskers are individual crystals that act like tiny fibers. In the pleasure boat example, the glass, plastic, carbon, or other fiber constitutes the filler of the composite, and the plastic makes up the matrix. 

The rapid expansion of supercritical solutions (RESS) was explored by several authors as a novel route to the formation of microparticles. Ohgaki [1] produces fine stigmasterin particles by the rapid expansion of a supercritical C02 solution. Amorphus fine particle and whisker-like crystals (0,05 - 3 pm) were obtained with different preexpansion pressures. Johnston [2] obtained submicron particles from different polymers. Loth [3] described the mirconisation of phenacetin with supercritical fluids. 

It is well known that this theoretical strength is seldom, if ever, achieved by solids, although freshly drawn glass fibres and certain whisker crystals do appear to exhibit tensile strengths approaching the theoretical limit. 

Available forms Filament, powder, whiskers, single crystals. 

In Fig. IB, the VLS process is illustrated. At reaction temperatures exceeding the eutectic. Si vapor dissolves in the Au seed to form a liquid alloy droplet. As more gaseous Si dissolves in the alloy, the droplet becomes supersaturated, and Si crystallizes on the droplet surface. The shape of the droplet interface and the surface tension difference between the liquid alloy and the solid semiconductor promote crystallization in one direction. In many cases, the liquid alloy droplet displaces off the surface and rides on the top of the vertically growing whisker—crystallization continues to occur at the liquid-solid interface as the metal seed is continuously fed with Si from the gas phase. 

Measurements of whisker crystallization rates by VLS have revealed that the linear growth rate is proportional to the whisker diameter, with larger fibers growing faster than smaller ones. The observed diameter-dependence has been attributed to differences in seed saturation concentration resulting from the curved interface of the seeds. The Gibbs-Thomson equation provides the relationship between the sphere diameter, d, and the chemical potential difference between the nutrient phase (e.g., molecular Si in the vapor) and the liquid alloy droplet Ap ... 

Figure 138. Arrhenius plot of whisker crystal growth kinetics in ethenzamide tablets. (Reproduced from Ref. 588 with permission.)...

Standard CVD reactors employing the aforementioned precursors have been employed for the formation of Nb Sn films, whiskers/single-crystals, and powders. In addition, two novel reactor designs have been employed for the fabrication of continuous tapes and small diameter particles. Figure 2-12 shows apparatus for the continuous CVD growth of Nb.iSn films on metallic ribbons and wires developed by researchers at RCA [40]. The system consists of niobium and tin chlorinators, a precursor delivery system for the introduction of the metal chlorides plus reactive HCI and H2 gases, and a deposition chamber. The ends of the reaction chamber are fitted with carbon elec-... 

Figure 7.13 SEM images of combustion products of ferrosilicon in nitrogen, (a, b) Whisker crystals of silicon nitride (arrows point to globules at tops of crystal growing by VLC...

Stable aqueous suspensions of polysaccharide nanocrystals can be prepared by the acid hydrolysis of vegetable biomass. Different descriptors of the resulting colloidal suspended particles are used, including whiskers, mono-crystals and nanocrystals. The designation whiskers is used to describe elongated rod-like nanoparticles. These crystallites have also often been referred in the literature as microfibrils, microcrystals or microcrystallites, despite their nanoscale dimensions. Most of the studies reported in the literature refer to cellulose nanocrystals. A recent review described the properties and applications of cellulose whiskers in nanocomposites [31]. 

The s mthesis of aromatic polyketone particles has been carried out [336] by means of precipitation polycondensation and is carried out at very the low concentration of monomer [0, 05 mol/liter]. The polyketones are produced from bisphenoxybenzophenone (0,005 mole) or isophlha-loylchloride (0.005 mole) in 100 milliliters of 1,2-dichloroethane. Some of obtained particles have highly organized the needle-shaped structure (the whisker crystals). The use of isophthaloyl instead of terephthaloyl at the same low concentration of monomer results in formation of additionally globular particles, the binders of strip structures gives rise. The average size of needle-shaped particles is 1-5 mm in width and 150-250 mm in length. 

These structural studies have revealed that crystalline polymers such as PTOX and PTeOX are not so perfect as the socalled single crystal, but rather disordered, on comparing with a whisker-type crystal prepared by a cationic polymerization of TOX in solution... 

The nickel crystal changes shape into a pear-like particle, leaving small fragments of nickel behind in the whisker. Whisker carbon is also observed on cobalt and iron catalysts [278] [498],... 

Whisker-like crystals 153 7.1. Crucihle wetting and melt ... 

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