Mg(BH 4) 2 is one of the few complex hydrides which have the potential to meet the requirements for hydrogen storage materials, because it contains 14.9 mass% H and has suitable thermodynamic properties. It has not been investigated for hydrogen storage applications yet. In this study, several ways to synthesize solvated and desolvated magnesium tetrahydroborate by wet-chemical and mechanochemical methods were tested and compared. A direct synthesis by a reaction of MgH 2 with aminoboranes yields magnesium tetrahydroborate quantitatively and in pure form. The method is also applicable to the synthesis of other tetrahydroborates. The products were characterised by elemental analysis, in-situ X-ray diffraction (XRD), infrared spectroscopy (FTIR), and thermal analysis methods, such as thermogravimetric analysis (TGA-DSC) and high-pressure calorimetry under hydrogen atmosphere (HP-DSC).

lated and exfoliated PMMA and PS±clay nanocomposites foams were prepared using supercritical CO 2 as the foaming agent. Presence of a small amount of clay nanoparticles greatly reduces foam cell size and increases the cell density. Exfoliated nanocomposites yield foams with the smallest cell size and the highest cell density. Cell morphology can be furthered manipulated by adjustment of polymer±clay surface±CO 2 interaction and foaming conditions to achieve microcellular and submicrocellular foams. The high nucleation efficiency can produce microcellular nanocomposite foams at less stringent processing conditions, leading to cost savings and processing flexibility. ExperimentalMaterials: Methylmethacrylate (MMA), Styrene (St) and 2,2¢-azobisisobutyronitrile (AIBN) were purchased from Aldrich. PS (CX 5197) is from AtoFina Petrochemicals, while PMMA (PL25) is from Plaskolite. Two types of organically modified MMT clays were used. Cloisite 20A (20A) is an MMT modified by dimethyl dihydrogenated tallowalkylammoniumonium cations (Southern Clay Products). Na + ±MMT (cation exchange capacity 92.4 milliequivalent/100 g, from Southern Clay Products) was modified using a reactive cationic surfactant 2-methacryloyloxyethylhexadecyldimethylammonium bromide (MHAB) via ion-exchange reaction [16]. The resulting organoclay is denoted as MHABS. Polymer±20A nanocomposites were prepared using a Leistritz ZSE-27 intermesh twin-screw extruder (L/D = 40, d = 27 mm) in co-rotating mode between 200±220 C and 200 rpm (revolutions per minute) screw speed. In-situ polymerization was carried out to prepare PMMA and PS±MHABS nanocomposites. The monomer, MHABS, and AIBN (0.5 wt.-%) were mixed using a high shear mixer. The mixture was reacted isothermally (60 C for styrene, 50 C for MMA) for 20 h, after which the temperature was raised to 105 C for another 30 min. A two-stage method was also used to prepare PS±MHABS nanocomposites. First a 20 wt.-% nanocomposite masterbatch was prepared by in-situ polymerization. It was then blended with neat PS to prepare nanocomposites with desired clay concentration using a DACA microcompounder at 200 C and 250 rpm. Soxhlet extraction was used to extract non-bonded PMMA from PMMA±MHABS nanocomposites, using dichloromethane as the solvent. The unextractable portion consists of MHABS and a substantial amount of PMMA (64 % of the total weight of the unextractable nanocomposite). The resulting material was blended with neat PS to produce PS±(MHABS±PMMA). (PS±MHABS)±PMMA was prepared via blending a PS±MHABS nanocomposite with PMMA. These two materials have the same weight composition (PS/ PMMA/MHABS = 86:9:5).Foaming of Nanocomposites: The foaming agent, bone-dry grade carbon dioxide, was provided by Praxair. Samples were placed in a stainless steel vessel and CO 2 was delivered via a syringe pump. The system was allowed to equilibrate at the foaming temperature and pressure for sufficient time to ensure equilibrium. The pressure was then rapidly released and the foam cells were fixed by cooling with an ice and ...

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Aluminum trihydride (alane) is one of the most promising among the prospective solid hydrogen-storage materials, with a high gravimetric and volumetric density of hydrogen. In the present work, the alane, crystallizing in the gamma-AlH3 polymorphic modification, was synthesized and then structurally characterized by means of synchrotron X-ray powder diffraction. This study revealed that gamma-AlH3 crystallizes with an orthorhombic unit cell (space group Pnnm, a = 5.3806(1) A, b = 7.3555(2) A, c = 5.77509(5) A). The crystal structure of gamma-AlH3 contains two types of AlH6 octahedra as the building blocks. The Al-H bond distances in the structure vary in the range of 1.66-1.79 A. A prominent feature of the crystal structure is the formation of the bifurcated double-bridge bonds, Al-2H-Al, in addition to the normal bridge bonds, Al-H-Al. This former feature has not been previously reported for Al-containing hydrides so far. The geometry of the double-bridge bond shows formation of short Al-Al (2.606 A) and Al-H (1.68-1.70 A) bonds compared to the Al-Al distances in Al metal (2.86 A) and Al-H distances for Al atoms involved in the formation of normal bridge bonds (1.769-1.784 A). The crystal structure of gamma-AlH3 contains large cavities between the AlH6 octahedra. As a consequence, the density is 11% less than for alpha-AlH3.

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Nickel and gold meshes having three-dimensional periodicity at optical wavelengths and nanoscale structural fidelity have been prepared by electrodeposition within closepacked silica sphere arrays.There is major current interest in the fabrication of nanoporous metal arrays. [1][2][3][4] Routine access to such materials could impact a variety of areas including photonics, magnetics, catalysis, electrochemical applications and thermoelectrics. Recent reports have described the formation of 3-D metal meshes within colloidal silica or polymer membranes through the use of molten metal infiltration, nanoparticle infiltration and electroless methods. 4-6 Though metal electrodeposition methods have been effectively used for membranes with one-dimensional pore structures, 7 the extension of this technique to threedimensional structures has not been reported. This electrochemical method has the major advantage of readily producing well defined metal meshes of materials melting at such high temperatures that melt infiltration is prohibited by template structural instability. Herein, we describe the use of this approach for the fabrication of nickel and gold arrays having three-dimensional periodicity at optical wavelengths.Silica membranes (opal) were prepared by published methods. 8 Silica spheres with a diameter of ca. 300 nm diameter were initially prepared from tetraethylorthosilicate (TEOS). The spheres were then formed into close-packed lattices through a sedimentation process over several months. This precipitate was then sintered at 120 °C for two days and then 750 °C for 4 h, producing a robust opalescent piece that could be readily cut into smaller sections. Electrodes were formed from the opal (typically 7 3 10 3 1.5 mm) by first depositing ca. 0.5 mm thick copper films on one side of the piece by magnetron sputtering. A length of wire was attached to the copper backing with silver paste (Ted Pella, Inc.) and the copper/wire side of the electrode, as well as the edges, were sealed off with neoprene glue (Elmer's). For metal deposition, the electrodes were immersed into nickel or gold plating solutions (Technic, Inc.) with a platinum wire counter electrode. Electrodeposition was carried out by a constant current method over a 36 h period; a low current density (0.50 mA cm 22 ) was used in an effort to achieve even deposition within the opal membrane. Low current densities such as that used here have been found to be effective in the growth of nanowires. After deposition, the opal was washed thoroughly with distilled water and the neoprene layer peeled off. To remove the silica matrix, the metal-opal pieces were soaked in a 2% HF solution for 24 h. This resulted in a dark opalescent metal membrane (ca. 100 mm thick). Scanning electron micrographs (SEM) were obtained on a JEOL JSM 5410 SEM. Magnetic measurements on the nickel mesh were performed on a Quantum Design MPMS-5S SQUID susceptometer. The mesh was fixed between two pieces of Kapton tape and placed in a commercially available soda straw. No correction for t...