Deformation of Porous Carbons upon Adsorption

Abstract

N2 and CO2 sorption measurements with in situ dilatometry implemented in a commercial volumetric sorption instrument were performed at 77 and 273 K, respectively. The resolution of the linear deformation was about ±0.2 μm. To separate effects due to microporosity, external surface area and mesopores synthetic porous carbons (xerogels) with different external surface areas and microporosities were applied as a model system. The experimental data show that the relative length change of the monolithic carbon xerogels investigated passes different stages during ad- and desorption, which are connected to micropore-, multilayer- and mesopore-sorption. The length change observed in the range of micropore and surface adsorption was found to be nonmonotonic and to take negative as well as positive values, with the maximum swelling observed being on the order of 4‰. With respect to the length change, the micropore structure seems to have the most significant impact on the overall length change, while the external surface is only of minor importance. Quantiative analysis of the deformation according to the models of Bangham and Scherer for the length change in the range of multilayer- and mesopore-adsorption allows extracting the macrosopic as well as the skeletal Young's modulus.

Relationship Between Pore Structure and Sorption-Induced Deformation in Hierarchical Silica-Based Monoliths

“…In contrast to previous studies [30,32] The combined measurement of n-pentane sorption and dilatometry was performed with a commercial volumetric sorption unit (ASAP Micromeritics, Norcross GA, USA) re-equipped with a dilatometric setup, which replaced the standard sample holder of the instrument. The dilatometric setup consisted of a custom designed sample holder, a linear variable differential transducer (LVDT, Macro Sensors, Pennsauken, NJ, USA) and a temperature controlled shield for the LVDT [22]. The setup allows simultaneous determination of the amount of gas adsorbed by the sample and the corresponding linear length change, .…”

“…Theoretical modelling of n-pentane adsorption in cylindrical mesopores predicts the expansive Bangham effect to be dominant [29], whichas stated above -fits both experimental data sets. Using the procedure summarized in [22] we calculate the surface energy reduction solid from the n-pentane sorption isotherm and plot solid versus the corresponding strains as seen by insitu dilatometry and in-situ SAXS. The results presented in Figure 6 show a linear relation between surface energy reduction and dilatometric strain in region 3.…”

“…Similar to Reichenauer and Scherer, these investigations focused on high relative vapor pressures, where the deformation of filled pores can be attributed to capillary pressure. In contrast, dilatometry and ellipsometric porosimetry were recently applied to investigate sorption-induced deformation especially in materials with highly disordered pore structures [21][22][23], addressing to some extent the pressure regime related to monoand multilayer formation as well as micropore filling.…”

Adsorption-induced deformation of nanoporous materials—A review

“…The simplicity of macroscopic measurements of adsorption-induced strains and the sensitivity of these measurements to the pore sizes suggest that in situ dilatometry can be used as a tool for the characterization of porous materials. 37 Experimental strain isotherms can be treated similarly to an adsorption isotherm to derive the pore size distribution using a kernel of theoretical adsorption/strain isotherms. 49 Such a method could be especially efficient for the characterization of microporous samples, since the pressures and thus the strains are extremely sensitive to the pore sizes in this pore size range; 50 see the discussion in Section IV B.…”

“…At the low strains typically observed in experiments, of order 10 -3 , the deformation cannot affect the adsorption isotherm to that extent. In particular, there are a number of systems where adsorption-induced deformation is observed but the isotherms do not show any hysteresis, for example, carbons 37,127 and mesoporous silica with small pore sizes. 30,70 Another work which predicted adsorption-desorption hysteresis due to the flexibility of the adsorbent was a Monte Carlo model by Shen and Siderius.…”