Destabilization of LiBH4 for reversible hydrogen storage has been studied using MgH2 as a destabilizing additive. Mechanically milled mixtures of LiBH4 + (1/2)MgH2 or LiH + (1/2)MgB2 including 2-3 mol % TiCl3 are shown to reversibly store 8-10 wt % hydrogen. Variation of the equilibrium pressure obtained from isotherms measured at 315-400 degrees C indicate that addition of MgH2 lowers the hydrogenation/dehydrogenation enthalpy by 25 kJ/(mol of H2) compared with pure LiBH4. Formation of MgB2 upon dehydrogenation stabilizes the dehydrogenated state and, thereby, destabilizes the LiBH4. Extrapolation of the isotherm data yields a predicted equilibrium pressure of 1 bar at approximately 225 degrees C. However, the kinetics were too slow for direct measurements at these temperatures.

Alloying with Si is shown to destabilize the strongly bound hydrides LiH and MgH 2 . For the LiH/Si system, a Li 2.35 Si alloy forms upon dehydrogenation, causing the equilibrium hydrogen pressure at 490°C to increase from approximately 5 × 10 -5 to 1 bar. For the MgH 2 /Si system, Mg 2 Si forms upon dehydrogenation, causing the equilibrium pressure at 300°C to increase from 1.8 to >7.5 bar. Thermodynamic calculations indicate equilibrium pressures of 1 bar at approximately 20°C and 100 bar at approximately 150°C. These conditions indicate that the MgH 2 /Si system, which has a hydrogen capacity of 5.0 wt %, could be practical for hydrogen storage at reduced temperatures. The LiH/Si system is reversible and can be cycled without degradation. Absorption/desorption isotherms, obtained at 400-500°C, exhibited two distinct flat plateaus with little hysteresis. The plateaus correspond to formation and decomposition of various Li silicides. The MgH 2 /Si system was not readily reversible. Hydrogenation of Mg 2 Si appears to be kinetically limited because of the relatively low temperature, <150°C, required for hydrogenation at 100 bar. These two alloy systems show how hydride destabilization through alloy formation upon dehydrogenation can be used to design and control equilibrium pressures of strongly bound hydrides.

Sorption G 6000Reversible Storage of Hydrogen in Destabilized LiBH 4 . -The addition of 0.5 equiv. MgH2 to LiBH4 yields a destabilized, reversible hydrogen storage material system with a capacity of approximately 8-10 wt% H2. MgH2 reduces the hydrogenation/dehydrogenation enthalpy by 25 kJ/(mol of H2) compared with pure LiBH4, and the temperature for an equilibrium pressure of 1 bar is estimated to be 225°C. -(VAJO*, J. J.; SKEITH, S. L.; MERTENS, F.; J. Phys. Chem. B 109 (2005) 9, 3719-3722; Hughes Res. Lab., Malibu, CA 90265, USA; Eng.) -W. Pewestorf 21-016

The contributions of terephthalic acid and Zn(2+)-coordinated water in N,N-diethylformamide (DEF) to the overall proton activity in the synthesis of MOF-5 (Zn4O(BDC)3, BDC = 1,4-benzenedicarboxylate) were quantitatively determined by combined electrochemical and UV-vis spectroscopic measurements. Structural transformations of zinc carboxylate-based metal organic frameworks due to their exposure to environments with variable water concentrations and the chemical means necessary to revert these transitions have been investigated. It was found that the water-induced structural transition of MOF-5 to the hydroxide structure Zn3(OH)2(BDC)2 x 2 DEF (MOF-69c) can be reverted by a thermal treatment of the obtained compound and its subsequent exposure to anhydrous DEF. MOF-5 syntheses from simple carboxylates as well as a water-free synthesis based on nitrate decomposition are presented. The latter demonstrates that nitrate can serve as the sole source for the oxide ion in MOF-5.

Plants of 43 families, encompassing 100 species and selected on the basis of literature data and medicinal folklore reports are being studied in a broad screening programme. A total of 428 extracts are being evaluated for antimicrobial, antiviral, antiparasitic and pharmacological actiyities. In this communication, the biological test methods for screening plants for antibacterial and antifungal activities in vitro are described. The results of the testing showed ;hat 84O/o and 75O/0 of the plants respectively exhibited some level of antibacterial and antifungal action; 17O/o of the latter were found to be inhibitory towards the yeast Candida albicans and 83 010 inhibited filamentous fungi to varying degrees.