Preparation and characterization of superhydrophobic surfaces based on hexamethyldisilazane-modified nanoporous alumina

Superhydrophobic nanoporous anodic aluminum oxide (alumina) surfaces were prepared using treatment with vapor-phase hexamethyldisilazane (HMDS). Nanoporous alumina substrates were first made using a two-step anodization process. Subsequently, a repeated modification procedure was employed for efficient incorporation of the terminal methyl groups of HMDS to the alumina surface. Morphology of the surfaces was characterized by scanning electron microscopy, showing hexagonally ordered circular nanopores with approximately 250 nm in diameter and 300 nm of interpore distances. Fourier transform infrared spectroscopy-attenuated total reflectance analysis showed the presence of chemically bound methyl groups on the HMDS-modified nanoporous alumina surfaces. Wetting properties of these surfaces were characterized by measurements of the water contact angle which was found to reach 153.2 ± 2°. The contact angle values on HMDS-modified nanoporous alumina surfaces were found to be significantly larger than the average water contact angle of 82.9 ± 3° on smooth thin film alumina surfaces that underwent the same HMDS modification steps. The difference between the two cases was explained by the Cassie-Baxter theory of rough surface wetting

Hydrogen tracer diffusion in LiBH(4) measured by spatially resolved Raman spectroscopy

The hydrogen tracer diffusion in LiBH4 has been determined by spatially resolved Raman spectroscopy. The measurements give direct evidence of a macroscopic diffusion of BH-4 ions as well as atomic exchange of hydrogen between the anions. An effective tracer diffusion coefficient of deuterium in LiBH4 of D ≃ 7 × 10-14m2 s -1 at 473 K is derived. The direct exchange rate of hydrogen between BH4 units is 10 orders of magnitude slower, i.e. the relatively fast effective hydrogen diffusion has its origin in the fast diffusion of BH 4 units. © 2010 The Owner Societies

Synthesis and thermal decomposition of potassium tetraamidoboranealuminate, K[Al(NH2BH3)4]

© 2017 Hydrogen Energy Publications LLC A new potassium tetraamidoboranealuminate, K[Al(NH2BH3)4], has been synthesized by a mechanochemical reaction between KAlH4and NH3BH3. The compound, K[Al(NH2BH3)4], crystallizes in a triclinic unit cell with space group symmetry P-1. The crystal structure consists of [K(NH2BH3)6]5-octahedra which facilitate the bridging between K+in 1D chains, while also bridging K+to Al3+to connect the 1D chains in a 3D network. Thermal analysis reveals that K[Al(NH2BH3)4] decomposes in two exothermic steps at T ~ 94 and 138 °C and releases primarily hydrogen. The total gas release amounts to ~6.0 wt% H2. The decomposition products are investigated ex situ by powder X-ray diffraction, infrared spectroscopy, and11B and27Al NMR and identified as KBH4and amorphous phases, possibly BN3, N2BH, and/or NBH2whereas aluminum is found in four-, five-, and six-fold coordination. Unfortunately, the decomposed sample shows no hydrogen absorption at T = 260 °C and p(H2) = 110 bar