Thermal conductivity of Xe clathrate hydrate at low temperatures

Abstract

The effective thermal conductivity of the powder samples of xenon hydrate was measured in the interval 2 -170 K using the steady-state method. The thermal conductivity of the homogeneous Xe clathrate hydrate was estimated from the effective thermal conductivity using an empirical expression. The applicability of the formula was checked by comparing two powder samples with different grain size and porosity. The temperature dependence of the thermal conductivity ͑T͒ϳT n of Xe clathrate hydrate is divided into four distinct temperature regimes ͑I-IV͒ with different n. In the interval 55-97 K ͑III͒ the behavior of ͑T͒ shows an anomaly, where the thermal conductivity decreases by almost 50% as the temperature increases. This observation is attributed to the resonant scattering where the coupling of the lattice with "rattling" motions of Xe atom dominates the thermal resistivity at high temperature. Since the observed vibrational energy of Xe in the small cages is ϳ4 meV ͑or Ϸ46 K͒ the resonant scattering contribution to the thermal resistivity is expected to decrease in an interval of comparable temperature. The thermal conductivity in the low temperature regime ͑regimes I and II͒ is found to follow the prediction of the soft-potential model. The data on thermal conductivities of several gas clathrate hydrates are compared.

A cometary nucleus model taking into account all phase changes of water ice: amorphous, crystalline, and clathrate

“…The temperature dependence of the thermal conductivity of Xe and CH 4 is divided into four (I−IV) distinct temperature regimes. The temperature dependences in the intervals I−II (below 54 K) and IV (greater than 95 K) are similar to what is observed in tetrahydrofuran and dioxolane clathrate hydrates of structure II (Krivchikov et al 2006). The thermal conductivity grows with temperature and the curve has a shape typical for amorphous substances.…”

“…However, at high temperature (170 K), the thermal conductivities of clathrates of CH 4 , Xe and tetrahydrofuran differ by only 20% (Krivchikov et al 2007). The temperature dependences of the thermal conductivity of structure I of Xe and CH 4 are similar (Krivchikov et al 2006) but are different from the ones of structure II of tetrahydrofuran, dioxolane and cyclobutanone. The temperature dependence of the thermal conductivity of Xe and CH 4 is divided into four (I−IV) distinct temperature regimes.…”

“…The thermal conductivity grows with temperature and the curve has a shape typical for amorphous substances. In the intervals I−II (below 54 K), the temperature dependence of clathrate hydrate is only weakly dependent on the type of clathrate structure (Krivchikov et al 2006). In these intervals the thermal conductivity is practically independent on the nature of the guest molecules.…”

“…Moreover, the thermal conductivity of the CH 4 hydrate coincides within the experimental error with the thermal conductivity of the dioxolane clathrate (Krivchikov et al 2005a,b). At present there is no theoretical model permitting a quantitative description and prediction of the thermal conductivity of clathrate hydrates in a wide range of temperatures (Krivchikov et al 2006). Thus, in the absence of more data on the thermal conductivity of single and MG clathrates, we adopt the temperature-dependent thermal conductivity of the methane clathrate given in Table 3 and use it independently of the clathrate composition.…”

“…There are limited data on the conductivity of clathrates at low temperatures. Their thermal conductivity has been measured on gas hydrates of structure I as CH 4 (Krivchikov et al 2005a), Xe (Handa & Cook 1987;Krivchikov et al 2006) and ethylene oxide (Cook & Laubitz 1983), and gas hydrates of structure II as tetrahydrofuran (Ross & Andersson 1982;Tse & White 1988;Andersson & Suga 1996;Krivchikov et al 2005b), dioxolane (Andersson & Ross 1983;Ahmad & Phillips 1987) and cyclobutanone (Andersson & Ross 1983) in a wide range of temperatures. It is very challenging to measure the bulk thermal conductivity of a homogeneous continuous solid (Krivchikov et al 2007).…”