Unusual PT dependence of thermal conductivity for a clathrate hydrate

• Molecular clathrate solids1 are crystals with peculiar and interesting properties. Their characteristic feature2 is that one chemical species, the ‘host’, forms a strongly bonded structure, which encages individual molecules of a second ‘guest’ species. There is virtually no chemical bonding between host and guest molecules. The guests are, nevertheless, firmly constrained by high energy barriers. X-ray and neutron diffraction experiments have shown that clathrates have a periodic structure typical of crystalline solids. A clathrate hydrate2 is a host substance consisting of H2O molecules which form an ice-like, hydrogen-bonded structure. Huge geological deposits of clathrate hydrates containing natural gas are known to exist2,3—these deposits may be exploitable, and in searching for clathrate hydrates knowledge of the thermal conductivity, λ, will be important. We present here a preliminary account of the first measurements of λ versus pressure (P) and temperature (T) for a clathrate hydrate. We studied a clathrate hydrate encaging molecules of tetrahydrofuran. Thermal conductivity was measured using the transient hot-wire method4. The accuracy of the measurements was 3% and the precision 1%. The temperature dependence was found to be unusual in that λ(T) has a positive slope (Fig. 1), a feature never before observed with crystalline organic materials. Furthermore, when λ was measured versus P, it was found unexpectedly that λ (P) was constant—behaviour never before reported for a non-metallic material.

Ämnesord

NATURVETENSKAP  -- Fysik -- Den kondenserade materiens fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Condensed Matter Physics (hsv//eng)

Nyckelord

Thermal conductivity

clathrate hydrate

high pressure

tetrahydrofuran clathrate

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