The effects of ball milling and molar ratio of LiH on the hydrogen storage properties of nanocrystalline lithium amide and lithium hydride (LiNH2 + LiH) system
The effects of ball milling and molar ratio of LiH on the hydrogen storage properties of nanocrystalline lithium amide and lithium hydride (LiNH2 + LiH) system
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DOI：
10.1016/j.jallcom.2009.11.035
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发表时间：
2010-02
影响因子：
6.2
通讯作者：
R. Varin;M. Jang;M. Polański
中科院分区：
文献类型：
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作者：
R. Varin;M. Jang;M. Polański
采用高能球磨法对物质比分别为1:1、1:1.2和1:1. 14 LiH的linh2h和LiH的混合物进行研磨。在1:1摩尔比的高能球磨过程中，随着球磨时间的增加，linh2和LiH组分的晶粒（晶体）尺寸单调减小，而粉末的比表面积（SSA）在球磨25h前呈增大趋势，但在球磨100h后由于粉末颗粒过度结块而减小。单相的linh2o2通过熔化和氨（NH3）的释放而分解。刚混合的LiNH2+LiH混合物仍然主要通过LiNH2的熔化和NH3的释放来分解。为了使氢从（LiNH2+LiH）混合物中有效地释放出来，必须进行高能球磨，使两种成分之间紧密接触。（LiNH2+LiH）球磨混合物解吸氢的活化能随着粉末SSA的增加而降低，当SSA达到~ 26m2/g时，活化能趋于稳定。对于LiNH2:LiH球磨混合物，当LiH摩尔比为1:1.2时，活化能最低。混合物中LiH部分水解/氧化为LiOH，使得LiH部分在NH3+LiH→LiNH2+ h2中间反应中失活，成为LiNH2+LiH球磨混合物解吸氢的主要障碍。当LiNH2:LiH的摩尔比为1:1.2时，活性LiH的质量最大，解吸氢量最大（约5wt.%）。从5到100h，随着磨矿时间的增加，LiNH2+LiH的解吸氢量略有减少，这是由于LiH的晶粒（晶）尺寸减小，使其对水解和LiOH的形成更加敏感。
High-energy ball milling was applied to the mixtures of LiNH2and LiH having the molar ratio 1:1, 1:1.2 and 1:1.4LiH. During a high-energy ball milling of the 1:1 molar ratio mixture the grain (crystallite) size of LiNH2and LiH constituent decreases monotonically with increasing milling time while the specific surface area (SSA) of powder increases up to 25h of milling duration and then decreases after milling for 100h due to the excessive agglomeration of powder particles into lumps. A single-phase LiNH2decomposes through melting and the release of ammonia (NH3). A just mixed LiNH2+LiH mixture still mostly decomposes through the melting of LiNH2and release of NH3. For the hydrogen to be effectively released from the mixture of (LiNH2+LiH) a high-energy ball milling is necessary which makes an intimate contact between both constituents. The activation energy for hydrogen desorption from the ball milled mixture of (LiNH2+LiH) decreases with increasing SSA of powders up to ∼26m2/g and then levels off with further increase of SSA. For the ball milled mixture of LiNH2:LiH the lowest activation energy is observed for the molar ratio of 1:1.2LiH. The hydrolysis/oxidation of the fraction of LiH into LiOH in the mixture makes a fraction of LiH inactive in the intermediate reaction NH3+LiH→LiNH2+H2and creates the major obstacle to the hydrogen desorption from the ball milled mixture of LiNH2+LiH. At the molar ratio 1:1.2 of LiNH2:LiH the mass of the active LiH is the largest one which leads to the largest quantity of desorbed hydrogen (∼5wt.%). The amount of hydrogen desorbed from LiNH2+LiH slightly decreases with increasing milling time from 5 to 100h due to the reduction in grain (crystallite) size of LiH which renders it more sensitive to hydrolysis and the formation of LiOH.