Papers by Keyword: NaAlH₄

Abstract: Orthogonal experiment design and variance analysis were adopted to investigate the hydrogen desorption properties of NaAlH₄ and LiAlH₄, which consisted of three stages, ball-milled under argon. Optimum milling condition was very important for the performance of NaAlH₄ and LiAlH₄, which was obtained from the orthogonal experiments. The orthogonal experiment design considered three experimental factors, i.e. weight ratio of ball to power, weight ratio of ɸ8 ball to ɸ4 ball and milling time, which varied on three different levels, respectively. According to the range analysis and variance analysis from the orthogonal experiments, the weight ratio of ball to powder and ɸ8 ball to ɸ4 ball had more impacts on the hydrogen desorption time of NaAlH₄,while the most sensitive influencing factor of LiAlH₄ was milling time. NaAlH₄ had the optimum performance when the weight ratio of ball to power was 30:1, the weight ratio of ɸ8 ball to ɸ4 ball was 0.5:1 and milling time was 0.5h. LiAlH₄ had the optimum performance when the weight ratio of ball to power was 40:1, the weight ratio of ɸ8 ball to ɸ4 ball was 0.5:1 and milling time was 2h.

Abstract: Interest in hydrogen as a future energy carrier in mobile applications has led to a strong increase in research on the structural properties of complex alkali metal and alkaline earth hydrides, with the aim to find structural phases with higher hydrogen densities. This contribution reviews recent work on the structural properties and phase diagrams of these complex hydrides under elevated pressures, an area where rapid progress has been made over the last few years. The materials discussed in greatest detail are LiAlH4, NaAlH4, Li3AlH6, Na3AlH6, LiBH4, NaBH4, and KBH4. All of these have been studied under high pressure by various methods such as X-ray or neutron scattering, Raman spectroscopy, differential thermal analysis or thermal conductivity measurements in order to find information on their structural phase diagrams. Based mainly on experimental studies, preliminary or partial phase diagrams are also given for six of these materials. In addition to this information, data are provided also on experimental results for a number of other complex hydrides, and theoretical predictions of new phases and structures under high pressures are reviewed for several materials not yet studied experimentally under high pressure.

Abstract: NaAlH4 has a theoretical hydrogen capacity of 5.6 wt. % with two-step reaction, and the control of the reaction temperature and reversibility is a critical issue for onboard application. To clarify nano-structural details of decomposition of NaAlH4, the in-situ annealing experiment was carried out in a high resolution microscope. It was confirmed that NaAlH4 decomposed at between 200 and 300°C, resulted in formation of many gas bubbles at interface between the particle and oxide film. A reactive intermediate, Na3AlH6, may decompose in this temperature range. Sodium alanate particle was originally agglomeration of small nano-sized crystal with the size of 10 – 20 nm, and the crystal grain grew to 110 nm in diameter after completing decomposition at around 400°C. This is the first step for examination of the microstructural response of catalysts on hydrogen storage materials.