Whisker characterization

Ceramic composites, which use ceramic fiber or whisker reinforcement in a ceramic matrix, are less susceptible to brittle failure since the reinforcement intercepts, deflects and slows crack propagation. At the same time, the load is transferred from the matrix to the fibers to be distributed more uniformly. These ceramic composites are characterized by low density, generally good thermal stability, and corrosion resistance. 

Whiskers are sometimes formed in solutions with high concentrations of surface-active substances. These are long single crystals, growing in only one direction, while growth in the remaining directions is retarded by adsorption of surface-active substances. Whiskers are characterized by quite... 

Similar to the 3M whisker support discussed earlier, electronic conducting ceramic columnar supports have also been proposed. Bonakdarpour et al. [48] characterized colunmar titanium structures on smooth glassy... 

All of the various methods of producing whiskers may be characterized as one-dimensional growth. The term refers to conditions that are constrained in such a way as to promote growth in one crystallographic direction. If the basic units, or crystal structure, of the phase to be made as a whisker are anisotropic, the direction of growth is influenced and possibly enhanced along certain directions by chemical affinities that lower the nu-cleation energy. A well-known example is polymerization. 

More, K.L., Koester, D.A. and Davis, R.F., (1991), Microstructural characterization of a creep-deformed SiC whisker-reinforced Si3N4 Ultramicroscopy, 31, 263-278. 

R. Ruh, K. S. Mazdiyasni, and M. G. Mendiratta, Mechanical and Microstructure Characterization of Mullite and Mullite-SiC-Whisker and Zr02-Toughened-Mullite-SiC-Whisker Composites, J. Am. Ceram. Soc., 71[6], 503-512 (1988). 

Li, Y.Y., Bae, S.D., Sakoda, A. and Suzuki, M., 2000, Fabrication and characterization of carbon whisker. The 2nd Pacific Basin Conference on Adsorption Science and Technology, May 14-18, Queensland, Australia, p376-380. 

Whiskers are single crystalline fibers with a diameter of several tenths of a im and lengths of 10 to 200 pm. They are characterized by maximum achievable mechanical properties. Thus, for example, tensile strengths of over 10 GPa have been measured with SiC-whiskers. 

More than 100 different materials have to date been produced as whiskers and characterized. However, only SiC- (50 to 100 t, 1996) and potassium titanate whiskers (ca. 5000 t) have achieved commercial importance. Important properties of whiskers are summarized in Table 5.2-18. 

This review focuses on the characterization of the whisker-matrix chemical interactions and on the relationships between the chemistry of the ceramic components, their grain morphologies, and their fracture... 

The authors wish to thank Dan Beaman and Dave Susnitzky for SEM and TEM characterization colleagues from Dow Chemical Central Research and Development Advanced Ceramics Laboratory and Ceramics and Advanced Materials Laboratory for helpful discussions Terry Tiegs from Oak Ridge National Laboratory for help in obtaining some whiskers and Laura Riester from Oak Ridge National Laboratory for photographs of CVD SiC. 

NanoDMA has been successfully used in characterizing viscoelastic properties for a range of polymeric materials, including polyethylene [62], bis-maleimide and thermoplastics [63], There have also been recent reports of nanoDMA being used to examine biological materials such as hairs and whiskers [64], However, the data presented in this section are amongst the first ever obtained for a biofilm. 

Crystallographic characterization has revealed that nearly all Si whiskers produced by Au-seeded VLS by CVD are oriented with their long axes in the (111) direction. Some whiskers are observed to be oriented with their long axes extended in the (211) or (110) axis. This observation is somewhat unexpected, as the rate of epitaxial Si deposition on monolithic substrates by CVD occurs much faster on 211 and 110 surfaces than on 111 surfaces. The preferential (111) growth direction of Au-seeded Si whiskers is believed to relate to the formation of an energetically favorable flat 111 interface with the liquid alloy seed droplet. 

A battery of complementary techniques is often necessary (and always desirable) to provide reliable, applications-oriented characterization of the bulk properties of (catalytic) carbon materials. Arguably the most useful ones are transmission electron microscopy (TEM), thermoelectric power (TEP) measurements, electron spin resonance (ESR) spectroscopy coupled with a superconducting quantum interference device (SQUID), and Raman spectroscopy. For example, among the recently reported virtues of Raman spectroscopy is the identification of graphite whiskers [152,153] in three carbonaceous chondrite meteorites (M. Fries and A. Steele, Science Online, Feb. 28, 2008), which contain some of the oldest matter in the solar system and has thus generated tremendous interest among astrophysicists. 

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