The formation of CO2 clathrate hydrate was investigated by using time-of-flight neutron powder diffraction at temperatures ranging from 230 to 290 K with a CO2 gas pressure of 900 psi. CO2 clathrate hydrate was prepared in situ from deuterated ice crystals at 230, 243, 253, and 263 K by pressurizing the system with CO2 gas to produce the hydrate in approximately 70% yield. Nearly complete conversion from the hexagonal ice to the sI type CO2 hydrate was observed as the temperature of the sample was slowly increased through the melting point of D2O ice. The conversion of ice into hydrate is believed to be a two-stage process in which an initial fast conversion rate is followed by a slower, diffusion-limited rate. On the basis of a shrinking core diffusion model, an activation energy of 6.5 kcal/mol was obtained from the temperature dependence of the reaction. Our findings suggest that the formation of the hydrate is through a reaction between CO2 and water molecules in the quasi-liquid layer (QLL). The CO2 hydrate remained stable following removal of excess liquid CO2 and subsequent pressurization with helium, allowing for a low-temperature (14 K) structure analysis from powder diffraction data without the presence of solid CO2.

The kinetics of methane hydrate formation was investigated by in-situ time-of-flight neutron powder diffraction. Samples were prepared from deuterated ice particles (< 0.25 mm) and transformed to clathrate hydrate by pressurizing the system with methane gas. The rates of sI methane hydrate formation were measured in-situ under isothermal conditions with a methane pressure of 1000 psi (6.9 MPa). Kinetic data were analyzed in terms of a shrinking core model, including possible contributions of nucleation, methane diffusion, and interface reaction. The data support the hypothesis that methane hydrate formation reaction from ice particles is diffusioncontrolled. The reaction starts quickly at the nucleation stage, which propagates to form a hydrate layer that covers the ice particle. Further reaction is limited by the growth of the hydrate layer and inward diffusion of methane molecules through the hydrate layer to the unreacted ice core. The reaction rate at the interface between hydrate and unreacted ice particle is fast compared to that of methane diffusion. The conversion of ice particle to methane hydrate follows Arrhenius behavior, from which an activation energy of 14.7(5) kcal/ mol was derived. Complete transformation of ice to methane hydrate was achieved through temperature rampingsa nonisothermal procedure that involves slowly increasing the sample temperature through the ice melting point.

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A new triterpenoid sapogenin was isolated and found to be 30,2O£-dihydroxy-23£-acetoxylanost-9( 11 )-ene-18c arboxylic acid lactone (18 -*• 20) (5). The functionality at C-23 is unprecedented in sapogenins from the sea cucumber.Sapogenins from sea cucumbers have been very actively investigated in recent years. Structure proof of many of these compounds has been carried out.1,5-12

Two novel Intumescent fire retardants have been prepared which are thermally stable enough for processing in thermoplastics. They were synthesized from pentaerythritol, melamine, and phosphorus oxychloride and were found to be effective in fire-retarding polypropylene at levels of 20% or higher. Compared to the standard halogenantimony fire retardants for polypropylene, each of the Intumescent fire retardants was found to be more efficient and to have less adverse effect on the physical properties.