Physical Properties of Gas Hydrates: A Review

Table 1

Geometrical parameters of the main hydrate crystal structures (data taken from [2, 3, 12]).

	Structure I		Structure II		Structure H
Cavity	small	large	small	large	small	medium	large
Description	$5^{12}$	$5^{12}{6}^2$	$5^{12}$	$5^{12}{6}^4$	$5^{12}$	$4^3{5}^6{6}^3$	$5^{12}$$6^8$
Cavities/unit cell	2	6	16	8	3	2	1
Average cavity radius, nm	0.395	0.433	0.391	0.473	0.391	0.406	0.571
Coordination number	20	24	20	28	20	20	36
Water moleculesper unit cell	46		136		34
Lattice type	Cubic		Face-centered cubic		Hexagonal
Unit cell parameters, nm	$a=1.2$		$a=1.7$		$a=1.21\text{,}$$c=1.01$
Density, kg m^-3	$912$		$940$		$1952$