Aerogels physical

Tsujimi, Y., Courtens, E., Pelous, J. and Vacher, R., Raman-Scattering Measurements of Acoustic Superlocalization in Silica Aerogels. Physical Review Letters, 1988. 60(26) p. 2757-2760. 

Sleator, T., Bemasconi, A., Posselt, D., Kjems, J.K. and Ott, H.R., Low-Temperature Specific Heat and Thermal Conductivity of Silica Aerogels. Physical Review Letters, 1991. 66(8) p. 1070 1073. 

Fig. 4. Comparison of physical properties of silica xerogels and aerogels. Note the similar properties of the aerogels prepared with and without supercritical...

A detailed discussion of the properties of aerogels can be found ia several recent review articles (51—55) and the references thereia. This section provides a physical basis for these properties by focusiag on the microstmcture of an aerogel. The latent is to provide a bridge between the two previous sections, which discuss the preparative and dryiag parameters that affect microstmcture, and the next one, which oudines the potential appHcations made possible by unique stmctural features. The emphasis is on siUca aerogels because they have been the most extensively characteri2ed. 

Table 2 summari2es the key physical properties of siUca aerogels. A range of values is given for each property because the exact value is dependent... 

Table 2. Typical Values of Physical Properties of Silica Aerogels ...

Agents have also been micropulverized, encapsulated, or treated with flowing agents such as silica aerogel to facilitate their dispersal and increase their persistency. Color and other physical properties of the agent may be affected by these additives. 

Silica aerogels, 1 753 applications, 1 760-767 physical properties of, 1 758, 761t versus xerogels, 1 758 Silica-alumina, 72.190-191 coke formation on, 5 268 poisons in representative reactions,... 

Mg. 1. Comparison of physical properties of silica xerogels and aerogels. Note the similar properties of the aerogels prepared with and without supercritical drying. Reproduced from C. J Brinkei and co-workeis, Mat. Res. Soe S mp. Proc. 271. 567 (1992). Courtesy of the Materials Research Society... 

TABLE 2 TYPICAL VALUES OF PHYSICAL PROPERTIES OF SILICA AEROGELS... 

We now proceed to describe in more detail the ACAR-aerogel work of Hyodo and coworkers, and the TRDBS measurements of Skalsey et al. (1998). It is worth noting, following Hyodo (1992), the physical processes which contribute to the two-gamma events registered by the ACAR technique in this type of experiment ... 

Fig. 7.18. Derived momentum distributions for the perturbed m = 0 state of ortho-positronium, for various gases (Nagashima et al., 1995) in an applied static magnetic field of 0.29 T. Reprinted from Physical Review A52, Nagashima et al., Thermalization of free positronium atoms by collisions with silica-powder grains, aerogel grains and gas molecules, 258-265, copyright 1995 by the American Physical Society.

Fig. 7.19. The time dependence of the mean ortho-positronium kinetic energy measured in silica aerogel under vacuum (o) and with 0.92 amagat of helium gas added ( ). The two curves were simultaneously fitted to the data by Nagashima et al. (1998), to obtain estimates of the Ps-He momentum transfer cross section. Reprinted from Journal of Physics B31, Nagashima et al, Momentum transfer cross section for slow positronium-He scattering, 329-339, copyright 1998, with permission from IOP Publishing.

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