Adsorption-desorption isotherms and x-ray diffraction of Ar condensed into a porous glass matrix

Abstract

Ar condensed into a porous glass matrix has been investigated by simultaneous measurements of adsorptiondesorption isotherms and x-ray diffraction patterns as function of the pore filling above and below the melting point. The chemical-potential-temperature phase diagram has been established. It is consistent with a firstorder phase transition between the adsorbate state and the capillary condensed state, above and below the melting temperature. The adsorbate and the capillary condensed state can also be distinguished in the diffraction patterns. A consistent picture of the structure and the thermodynamics is obtained.

Evidence for high saturation of porous amorphous carbon films by noble gases

“…However, our results evince that solid Kr and Xe condensates formed in pores closely to their sublimation points are stable in a wide temperature range, which correlates with the observation of a capillary condensation of solid Ar studied by means of x-ray diffraction [27].…”

“…The concept of adsorption, wetting and capillary condensation was well established for van der Waals liquids in porous matrices [25][26][27], and below the triple point we could expect the reduced wetting for substances which were studied in this work, because of substrate roughness [26] or elastic compression [25]. However, our results evince that solid Kr and Xe condensates formed in pores closely to their sublimation points are stable in a wide temperature range, which correlates with the observation of a capillary condensation of solid Ar studied by means of x-ray diffraction [27].…”

Monolayer sorption of neon in mesoporous silica glass as monitored by wide-angle x-ray scattering

“…Initially, we assume the monolayer sorption takes place on a triangular lattice, similar to the (111) plane of a bulk fcc lattice (coordination number, t = 6) [25]. The total scattering function for a partial monolayer is then given by:…”

“…For example, Huber and Knorr report diffraction patterns for adsorption of Argon in 75 Å pores at 65 K, which is below the confined freezing point [15]. They find that below bilayer coverage, the diffraction pattern suggests that the layers form a triangular lattice with coherence length of the order of 16 Å.…”

“…In addition, wide angle X-ray scattering experiments have measured the atomic structure of a condensate within a mesoporous structure. These have focused mostly on phase transitions within pores, see for example Ref [5]; although some have monitored the full diffraction pattern as adsorption and then capillary condensation occurs [15,16].…”