Aerogel thermal characterization

To reveal the thermal properties of aerogels, stationary hot-plate measurements are usually employed [45]. In such a measurement two equal aerogel specimens are sandwiched between a hot plate and two cold plates. If the electrical power fed into the hot plate and the temperature difference between the hot and the cold plates, as well as the thickness of the specimens, are known, the thermal conductivity can be derived. For the thermal characterization of opacified aerogels, the faster nonstationary hot-wire method can also be used. In this case a thin platinum wire is embedded into the aerogel specimen and a constant power is delivered into the wire, which also serves as a temperature sensor. From the temperature increase in the wire as a function of time, the thermal conductivity of the aerogel specimen can be determined [49]. 

Lee D, Stevens PC, Zeng SQ, Hunt AJ (1995) Thermal characterization of carbon-opacified silica aerogels. 

Figure 16.6. Photocatalytic characterization of pure silica and Si02-Sn02 composite aerogels thermally treated at 500°C (reproduced from [23] by permission of Elsevier).

NaY zeolite at 60.1 ppm. The image was obtained for a 3mm slice with full chemical shift imaging (note that for thermally polarised Xe this type of imaging experiment would be far more demanding in terms of experimental time even than chemical shift resolved imaging, as practiced for the Aerogel samples[30]), and was obtained in 30 min. Thus, the improvement in imaging with HP xenon over thermally polarized xenon is impressive, and indicates that there are real prospects for applications in the characterization of materials. 

Zirconia is a very interesting material in ceramic industry, with exceptional electrical, thermal (Chap. 23), and mechanical properties (Chap. 22 Mechanical characterization of aerogels) allowing its use in fuel cells, thermal barrier coatings, oxygen sensors, and many other high-temperature applications. In all these applications, this material is doped with other oxides to stabilize the tetragonal or cubic phase at low temperatures. 

Rettelbach T, Sauberlich J, Korder S, Fricke J (1995) Thermal conductivity of silica aerogel powders at temperatures from 10 to 275K. J Non-Cryst Solids 186 278-284 Shen Q, Toyoda T (2003) Dependence of thermal conductivity of porous silicon on porosity characterized by photoacoustic technique. Rev Sci Instr 74 601-603 Shinoda H, Nakajima T, Ueno K, Koshida N (1999) Thermally induced ultrasonic emission from porous silicon. Nature 400 853-855... 

Rigacci A., Achard P., Ehrburger-Dolle F., Pirard R. Structural investigations in monolithic silica aerogels and thermal properties. J. Non-Cryst. Solids 1998 225 260 Rouquerol J., Avnir D., Fairbridge C.W., Everett D.H., Haynes J.H., Pernicone N., Ramsay J.D. F., Sing K.S.W., Unger K.K. Recommendations for the characterization of porous solids. Pure Appl. Chem. 1994 66 1739... 

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