Discrepancy between thermodynamic and kinetic stabilities of the tert-butanol hydrates and its implication for obtaining pharmaceutical powders by freeze-drying.

The tert-butanol (TBA)-water system is studied in relation to increasing the efficiency of obtaining pharmaceutical powders by freeze-drying. Trehalose was used as a model target product. We report the X-ray diffraction and thermal analysis data which add surprising new information to the phase diagram of this previously repeatedly studied system. The freezing protocol has a strong impact on the specific surface area of the trehalose freeze-dried cakes and on the primary drying time. This is related to a discrepancy between the kinetic and thermodynamic stabilities of several TBA hydrates: di-hydrate (H1), heptahydrate (H2), and decahydrate (H3).

Creation of nanosized holes in graphene planes for improvement of rate capability of lithium-ion batteries.

Holes with an average size of 2-5 nm have been created in graphene layers by heating of graphite oxide (GO) in concentrated sulfuric acid followed by annealing in an argon flow. The hot mineral acid acts simultaneously as a defunctionalizing and etching agent, removing a part of oxygen-containing groups and lattice carbon atoms from the layers. Annealing of the holey reduced GO at 800 °C-1000 °C causes a decrease of the content of residual oxygen and the interlayer spacing thus producing thin compact stacks from holey graphene layers. Electrochemical tests of the obtained materials in half-cells showed that the removal of oxygen and creation of basal holes lowers the capacity loss in the first cycle and facilitates intercalation-deintercalation of lithium ions. This was attributed to minimization of electrolyte decomposition reactions, easier desolvation of lithium ions near the hole boundaries and appearance of multiple entrances for the naked ions into graphene stacks.

Formation and decomposition of ethane, propane, and carbon dioxide hydrates in silica gel mesopores under high pressure.

The experimental data on decomposition temperatures for the gas hydrates of ethane, propane, and carbon dioxide dispersed in silica gel mesopores are reported. The studies were performed at pressures up to 1 GPa. It is shown that the experimental dependence of hydrate decomposition temperature on the size of pores that limit the size of hydrate particles can be described on the basis of the Gibbs-Thomson equation only if one takes into account changes in the shape coefficient that is present in the equation; in turn, the value of this coefficient depends on a method of mesopore size determination. A mechanism of hydrate formation in mesoporous medium is proposed. Experimental data providing evidence of the possibility of the formation of hydrate compounds in hydrophobic matrixes under high pressure are reported. Decomposition temperature of those hydrate compounds is higher than that for the bulk hydrates of the corresponding gases.