Abstract
Determining reliable structural parameters for an aerogel by applying suitable characterization techniques is a key factor in terms of understanding the different synthesis steps and their impact on the resulting aerogel. Combining structural parameters with the physical properties of the material allows optimization for specific applications. It is only the profound knowledge of the structure–properties relationships that provides access to the full potential of this type of material. This chapter presents different characterization methods commonly used and discusses their potential and limitations. Furthermore, more recent developments and new approaches are introduced.
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- 1.
Note that the intensity per detector area decreases with the sample-detector distance squared.
- 2.
The volume specific differential cross-section translates into the mass specific differential cross-section by multiplying with one over the bulk density of the sample: \( \frac{{{\text{d}}\Sigma }}{{{\hbox{d}}\Omega }}\frac{1}{\rho } = \frac{{{\text{d}}\sigma }}{{{\hbox{d}}\Omega }}. \)
- 3.
- 4.
Micropores: pores <2 nm, mesopores: pores between 2 and 50 nm, macropores: pores >50 nm (IUPAC definition), see [34].
- 5.
In case of carbon aerogels the pairs are: K, density of the interconnected backbone particles ⇨ particle surface, K′, ρ carbon ⇨ surface of particles and micropores.
- 6.
It has to be emphasized that due to the large uncertainties of the background contribution at high q values, the accuracy is on the order of 10–20% only.
- 7.
STP stands for standard temperature and pressure; cm3 STP gives the equivalent volume of a gas at standard temperature (273.15 K) and pressure (101,325.02 Pa).
- 8.
β = 0.33 for CO2 at 273 K and 0.35 for N2 at 77 K.
- 9.
The relationship was established for pore width d derived from SAXS data.
- 10.
Other equations are provided by Frenkel, Halsey, and Hill (FHH) as well as Broekhoff and de Boer.
- 11.
For example, S N2=0.162 nm2, S CO2=0.170 nm2.
- 12.
BET stands for Brunauer, Emmett, and Teller who developed the method.
- 13.
When the adsorbate is only partially wetting a factor of cos (θ C), with θ C the contact angle, has to be included on the right side of the equation.
- 14.
For liquid nitrogen at 77 K, the values for the surface tension and the molar volume are 0.00885 J/m2 and 34 cm3/mol.
- 15.
For adsorption in cylindrical pores therefore \( d = 2 \cdot (\left| {{r_{\rm{M}}}} \right|/2 + {t_{\rm{L}}}) \) holds.
- 16.
Values for water: γ SL= 40 × 10−3 N/m, γ S/V S = (S L − S S)/V S=334 × 103 J/m3, T m = 0°C. A 10 nm spherical pore radius causes a shift in melting temperature by about 22°C.
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Reichenauer, G. (2011). Structural Characterization of Aerogels. In: Aegerter, M., Leventis, N., Koebel, M. (eds) Aerogels Handbook. Advances in Sol-Gel Derived Materials and Technologies. Springer, New York, NY. https://doi.org/10.1007/978-1-4419-7589-8_21
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