INDEX Aerogels

Density, BET-surface area and surface capacitance of two non-activated aerogels with different densities and their activated derivatives. The index (0) corresponds to the reference, ( ) to the electrochemically, ( ) to the thermally activated samples, respectively. 5-10% error must be assumed for the evaluated data. 

Agent Index A061 Mixed with Silica Aerogel Agent Index A062 Mixed with Trioctylphosphite Evacuation Distances None established IP —... 

The index 0 indicates properties of the evacuated aerogel, k is an effective adiabatic exponent for the system gas-skeleton. For most aerogels it is very close to unity. Only at extremely low aerogel densities does it become both larger and pressure dependent [65]. In Fig. 6, the variation in Ci with gas pressure is depicted for air and SFe for p = 5 kg/m3 aerogel. 

Because of their low density, aerogels have a refractive index very close to 1. Experimentally one finds that... 

As a result of the small refractive index, light enters and leaves a piece of aerogel almost without reflective losses and refractive effects. The dependence... 

All applications of aerogels make use of their high porosity, which is responsible for the low index of refraction, the small Young s modulus, the low acoustic impedance, the low thermal conductivity, and the excellent accessibility of the inner surface. In addition, in some applications the high optical transparency is of importance. 

The refractive index of silica aerogels increases with their density p (kg m ) accord-... 

The techniques presented here allow to produce ultralight materials with anisotropic properties. Optical absorption and emission, hydrophobicity mechanical strength and index of refraction can be tuned within the same monolith. Conceivable applications of our technique include fabrication of photonic devices, membranes, radiation collimators, fuel cell electrodes as well as hierarchically structured materials that combine mechanical strength with the acoustic and thermal insulation properties of conventional aerogels. 

Figure 28.7 shows a typical model of a threshold-type Cherenkov counter. Silica aerogel is filled in a box to which photomultiplier tubes (PMTs) are attached. The refractive index of aerogel is set so that the Cherenkov light is emitted for pions but not for kaons [8,9]. In this way, it is known that kaon/pion/proton separation in the momentum region of 1.0-3.5 GeV/c is possible using aerogel with low refractive index such as 1.01-1.03. 

MacKenzie J D (1988) Applications of the sol-gel process. J Non-Cryst Solids 100 162—168 Adachi I, Sumiyoshi T, Hayashi K, lida N, Enomoto R, T sukada K, Suda R, Matsumoto S, Natori K, Y okoyama M, Yokogawa H (1995) Study of a threshold Cherenkov counter based on silica aerogels with low refractive index. Nucl Instr Meth Phys Res A, 335 390-398... 

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