共查询到20条相似文献,搜索用时 15 毫秒
1.
Nico Eigen Mirko Kunowsky Thomas Klassen Rüdiger Bormann 《Journal of Alloys and Compounds》2007,430(1-2):350-355
The present study highlights the advantages of milling NaH/Al under moderate hydrogen pressure as a favourable production step for NaAlH4-based hydrogen storage materials. Firstly, it is demonstrated that NaAlH4 can be obtained by applying a moderate hydrogen pressure (6–12 bar) during milling of NaH and Al with and without the presence of an inexpensive catalyst (TiCl4). The yield of NaAlH4 depends critically on process parameters, such as hydrogen pressure and milling time. A fully converted product is capable of reversible hydrogen storage without any activation procedure. Under optimized conditions, a capacity of 4.2 wt.% was achieved and kinetics in the first desorption are comparable to NaAlH4 doped with TiCl3. Secondly, the synthesis has been optimized towards shorter milling times. By applying a few absorption/desorption cycles to material that was partially converted during milling, almost full reversible storage capacity can be reached. In addition, kinetics is extremely enhanced. For example, such material exhibits an optimum capacity already after two sorption cycles at 100 bar and 125 °C and allows to absorb 80% of the reversible hydrogen content within a few minutes. 相似文献
2.
B. Bogdanovi M. Felderhoff M. Germann M. Hrtel A. Pommerin F. Schüth C. Weidenthaler B. Zibrowius 《Journal of Alloys and Compounds》2003,350(1-2):246-255
The processes occurring in the course of two sequential hydrogen discharging and recharging cycles of Ti-doped sodium alanate were investigated in parallel using XRD analysis and solid-state NMR spectroscopy. Both methods demonstrate that in hydrogen storage cycles (Eq. (1)) the majority phases involved are NaAlH4, Na3AlH6, Al and NaH. Only traces of other, as yet unidentified phases are observed, one of which has been tentatively assigned to an Al–Ti alloy on the basis of XRD analysis. The unsatisfactory hydrogen storage capacities heretofore observed in cycle tests are shown to be due entirely to the reaction of Na3AlH6 with Al and hydrogen to NaAlH4 (Eq. (1), 2nd hydrogenation step) being incomplete. Using XRD and NMR methods it has been shown that a higher level of rehydrogenation can be achieved by adding an excess of Al powder. 相似文献
3.
Tao Wang Jun Wang Armin D. Ebner James A. Ritter 《Journal of Alloys and Compounds》2008,450(1-2):293-300
A systematic study was carried out to compare the reversible hydrogen storage properties of Sc-doped NaAlH4 with Ti-doped NaAlH4. Uncycled and cycled (five times) samples of 1, 2 and 4 mol% Sc-doped NaAlH4 and 4 mol% Ti-doped NaAlH4 were examined. Temperature programmed desorption, constant temperature desorption, and constant temperature cycling results revealed the following: Sc-doped NaAlH4 realized very fast hydrogenation kinetics, reasonably fast dehydrogenation kinetics and minimal hydrogen capacity losses during cycling over a broad range of temperatures without any additives or co-dopants. Sc-doped NaAlH4 also exhibited comparable kinetics and a higher hydrogen storage capacity compared to Ti-doped NaAlH4, depending on the temperature, metal dopant level, and cycling. Sc exhibited this superior performance over Ti perhaps because Sc is an earlier transition metal than Ti. 相似文献
4.
F.E. Pinkerton 《Journal of Alloys and Compounds》2011,509(36):8958-8964
This work compares the initial desorption and hydrogen cycling kinetics of NaAlH4 melt infused into carbon aerogel with NaAlH4-carbon aerogel composite synthesized by ball milling. Samples having comparable carbon content (47.4 wt%) prepared by either method yield virtually identical desorption and cycling behavior. Furthermore, the ball milled material can be made with lower carbon content and still maintain only slightly reduced kinetic improvements. Surprisingly, there is no evidence for mixed infused-like and bulk-like behavior even for carbon content as low as 9.1 wt%. Unlike melt infused NaAlH4, where co-infusion of TiCl3 catalyst has proven difficult, the ball milled material can easily accommodate co-doping with both carbon and TiCl3. The inclusion of carbon with TiCl3 results in a modest but significant improvement in kinetics compared to NaAlH4 doped with TiCl3 alone, especially for rehydrogenation. Ball milling with activated carbon produces an improvement very similar to that of carbon aerogel, whereas graphene and graphite have smaller effects, in that order. During cycling of the second stage NaAlH4 reaction, i.e., Na3AlH6 ↔ 3NaH + Al + (3/2)H2, addition of either activated carbon or carbon aerogel at 23.1 wt%, but without TiCl3, results in kinetic performance as good as or better than NaAlH4 doped with TiCl3. 相似文献
5.
Possibilities and limitations in using transmission electron microscopy to characterize pure NaAlH4 and transition metal enhanced NaAlH4 have been investigated in detail. NaAlH4 is extremely sensitive to O2 and H2O and must be handled under inert atmosphere at all times. Furthermore, it is highly unstable under the electron beam and only basic techniques such as diffraction contrast imaging and selected area diffraction that can be performed with a low flux electron beam can be used without the NaAlH4 decomposing. By comparison, phases containing transition metal additive are very stable under the electron beam. The latter are investigated by a combination of high resolution imaging, electron diffraction and spectroscopy to determine distribution, composition, crystal structure and defect content in ball milled and hydrogen cycled, TiCl3 and FeCl3 enhanced NaAlH4. It is demonstrated that a large amount of the added Ti or Fe is located at the surface of the NaAlH4 grains as a combination of crystalline and amorphous Al1−xTMx (TM = Ti, Fe) nanoparticles. 相似文献
6.
The formation of ErNbO4 powder, prepared by calcining an Er2O3 (50 mol%) and Nb2O5 (50 mol%) powder mixture at 1100 and 1600 °C for different durations, was investigated by using X-ray diffraction. The experimental results have displayed that although the solid-state reaction had started to some extent when the mixture was pre-calcined at 1100 °C for a duration of 13 h, the two original phases Er2O3 and Nb2O5 still dominated the mixture. When the duration of the calcination reaction was increased to 120 h at the same temperature, the resultant mixture experienced a nearly complete phase transformation. Accordingly, the ErNbO4 phase was dominant phase in the mixture. Nevertheless, a small portion of the raw powder still existed in the mixture. When the calcining temperature was elevated to 1600 °C, ErNbO4 powder with higher purity could be obtained for a relatively much shorter duration (only up to several tens of hours). A simple formation mechanism of ErNbO4, an elevated-temperature-assisted solid-state chemical reaction: Er2O3+Nb2O52ErNbO4, is suggested. In addition, the present experimental results offer important evidence for the formation of the additional phase ErNbO4 induced in Er:LiNbO3 crystals by vapour transport equilibration (VTE) treatment. 相似文献
7.
R. Gupta F. Agresti S. Lo Russo A. Maddalena P. Palade G. Principi 《Journal of Alloys and Compounds》2008,450(1-2):310-313
The catalytic effect of the addition of lanthanum oxide (La2O3), in the range 0.5–2.0 mol%, on the hydrogen storage properties of MgH2 prepared by ball milling has been studied. The addition of La2O3 reduces the formation during milling of the metastable orthorhombic γ-MgH2 phase. The desorption rate of samples with 1 and 2 mol% La2O3 comes out to be about 0.010 wt% per second at 573 K under an hydrogen pressure of 0.3 bar, better than for sample with 0.5 mol% La2O3. The presence of LaH3 after hydrogenation/dehydrogenation cycles has been observed in all samples. The sample with 1 mol% of La2O3 gives a lower hysteresis factor compared with sample with 2 mol%. 相似文献
8.
K. Itoh T. Watanabe T. Otomo M. Sugiyama K. Mori T. Fukunaga 《Journal of Alloys and Compounds》2009,483(1-2):213
Neutron and X-ray diffraction and reverse Monte Carlo (RMC) simulation were performed on Zr0.39Ni0.61 and (Zr0.39Ni0.61)D0.59 amorphous alloys to investigate the rearrangement of metal atoms due to the deuterium absorption. The RMC models showed that the Zr–Zr distances slightly increase but the Zr–Ni and Ni–Ni distances remain virtually unchanged after the deuterium absorption. Additionally, the Voronoi polyhedral analysis of the RMC configurations showed that there is not much difference in the local structure around Zr and Ni between Zr0.39Ni0.61 and (Zr0.39Ni0.61)D0.59 amorphous alloys. 相似文献
9.
The reactions for LiNH2 under a H2 and an Ar flow were investigated, respectively. The results showed that LiNH2 can be converted into LiH and NH3 by reacting with H2 under a H2 flow condition, whereas LiNH2 is converted into Li2NH and NH3 by decomposition under an Ar flow. Moreover, the reaction between LiNH2 and H2 can be accelerated by mixing LiNH2 with LiH as well as doping LiNH2 with TiCl3. The confirmation of reaction between LiNH2 and H2 is helpful for the deeper insight in the systems of Li–N–H and Li–Mg–N–H for hydrogen storage materials. 相似文献
10.
High-energy dry ball-mill and post-anneal processing were applied to synthesize MgTiO3 and Mg2TiO4 single crystalline phases from the predetermined compositions of MgO–TiO2 powder mixtures. Also, the experiments were performed to show that it is possible to prepare MgAl2O4 single crystalline phase from the predetermined composition of MgO–Al2O3 powder mixture only by employing high-energy dry ball milling, i.e. without post-annealing the milled samples. In contrast, fully developed single crystalline powders of MgTiO3 and Mg2TiO4 were obtained after post-annealing the milled samples for 1 h at 900 and 1200 °C, respectively. 相似文献
11.
Y. Filinchuk V.V. Lisnyak D.A. Stratiichuk N.V. Stus 《Journal of Alloys and Compounds》2008,463(1-2):124-128
The crystal structure of sodium pentamolybdyl tetradiphosphate Nax(MoO)5(P2O7)4 has been determined from synchrotron diffraction data collected at 293 K on two microcrystals. The compound crystallizes in a monoclinic space group I 1 1 2/a (no. 15, setting 11), with unit cell parameters a = 22.905(3), b = 23.069(2), c = 4.8537(2) Å, γ = 90.641(9)° and a = 22.898(3), b = 23.056(2), c = 4.8551(2) Å, γ = 90.82(1)°, for crystals I and II, respectively. The structure is pseudo-tetragonal, and the crystals are pseudo-merohedrally twinned by 90° rotation around the c-axis. The structure closely resembles the previously reported Li-deintercalated Mo1.3OP2O7 [V.V. Lisnyak, N.V. Stus, P. Popovich, D.A. Stratiychuk, Ya. Filinchuk, V.M. Davydov, J. Alloys Compd. 360 (2003) 81–84]. Comparison of the two structures led us to conclude that the Mo2 and Mo3 clusters were erroneously identified in Mo1.3OP2O7. A revised structure of Mo1.3OP2O7 contains a fully occupied oxygen site instead of the 16% occupied Mo(2) site, thus the revised formulae for the Li-deintercalated compound is (MoO)5(P2O7)4. In both structures, the (MoO)5(P2O7)4 framework strongly resembles the one in the earlier reported Ag(MoO)5(P2O7)4, while the location of Na and Ag atoms differ. 相似文献
12.
A. Kawasuso H. Arashima M. Maekawa H. Itoh T. Kabutomori 《Journal of Alloys and Compounds》2009,486(1-2):278-283
We have studied the structural changes of Ti24Cr36V40 alloy prepared by arc-melting using positron annihilation spectroscopy and X-ray diffraction (XRD) as functions of the number of hydrogen pressure swing cycles and degassing temperature. As the hydrogen storage capacity decreased with the number of pressure swing cycles, both positron lifetime and XRD peak width increased. Upon hydriding, the crystal structure changed from bcc to bct with increased lattice constants. The increase in positron lifetime is due to the volume expansion caused by hydride formation. After degassing at 500 °C, the hydrogen storage capacity recovered to 95% of the initial level, and the XRD peak width and the lattice constants nearly completely returned to their initial values. However, the positron lifetime was still longer than the initial level suggesting the survival of dislocations. The degradation of hydrogen storage capacity is probably caused by both hydride formation and the generation of dislocations. 相似文献
13.
Nearly dual-phase Mg–Ni alloy fabricated by ingot metallurgy (IM) and comprising 30 vol% Mg2Ni and 61 vol% MgNi2 intermetallic compounds (remaining 9 vol% of unreacted Mg) was mechanically (ball) milled under controlled shearing for 10, 30, 70 and 100 h. The majority of the medium- and small-sized powder particles exhibited a relatively homogeneous microstructure of milled Mg2Ni and MgNi2. A fraction of large-sized particles developed the ‘core and mantel’ microstructure after milling for 70 and 100 h. The ‘core’ contains poorly milled MgNi2 particles and the ‘mantel’ is a thoroughly milled mixture of Mg2Ni, MgNi2 and, possibly, residual Mg. X-ray diffraction provides evidence of nanostructurization and eventual amorphization of a fraction of a heavily ball milled Mg2Ni phase. The remnant Mg2Ni developed a nanocrystalline/submicrocrystalline structure. The co-existing MgNi2 phase developed a submicrocrystalline structure within the powder particles. The results are rationalized in terms of enthalpy effects by the application of Miedema’s semi-empirical model to the phase changes in ball milled intermetallics. 相似文献
14.
15.
Mg6Ir2H11 has been synthesised by both hydrogenation of the intermetallic compound Mg3Ir at 20 bar and 300 °C, and sintering of the elements at 500 °C under 50 bar hydrogen pressure. Neutron powder diffraction on the deuteride indicates a monoclinic structure (space group P21/c, Mg6Ir2D11: a=10.226(1), b=19.234(2), c=8.3345(9) Å, β=91.00(1)°, T=20 °C) that is closely related to orthorhombic Mg6Co2H11. It contains a square-pyramidal [IrH5]4− complex and three saddle-like [IrH4]5− complexes of which one is ordered and two are disordered. Five hydride anions H− are exclusively bonded to magnesium. The compound has a red colour, is presumably non-metallic and decomposes under 3 bar argon at 500 °C into Mg3Ir, iridium and a previously unreported intermetallic compound of composition Mg5Ir2. 相似文献
16.
Hiroyuki T. Takeshita Nobuaki Fujiwara Toshio Oishi Dag Nor us Nobuhiko Takeichi Nobuhiro Kuriyama 《Journal of Alloys and Compounds》2003,360(1-2):250-255
Zr7Ni10 has three hydrogen occlusion phases, , β and γ, and the following unusual features are known for the phase transitions in the Zr7Ni10–H2 system: (1) The intermediate hydride phase (β) appears only during dehydrogenation but not during hydrogenation, and (2) The continuous hydrogen solid solution phase () exhibits a much higher hydrogen solubility during hydrogenation than during dehydrogenation. In order to clarify the mechanism about the difference in the hydrogen solubility of the phase, the relation between the pressure-composition isotherms and corresponding structural change has been examined by a conventional volumetric method and X-ray diffraction. Through the examination, we discovered that the crystal structure of the phase, which undergoes hydrogenation followed by dehydrogenation, is different from that of its pure metal phase, where the crystal structure of the dehydrogenated phase changes from an orthorhombic structure to a tetragonal structure. The conditions causing the structural change were then examined, and it has been found that the phase maintains its original orthorhombic structure as long as it is hydrogenated so as not to absorb enough hydrogen to change it to the hydride with a higher hydrogen content (γ). The phenomenon can be understood as one of the hydrogen-assisted phase transitions such as hydrogen-induced amorphization (HIA) in the sense that the phase transition requires hydrogenation under special conditions. 相似文献
17.
Heng WangGuangshe Li Xiangfeng GuanLiping Li 《Journal of Alloys and Compounds》2011,509(10):4160-4166
A series of Gd1−xCaxPO4·nH2O nanorods were prepared using a simple hydrothermal reaction which was optimized by tuning the pH values of the precursor. The resulted nanorods were characterized by X-ray diffraction, transmission electron microscopy, Fourier transformation infrared spectroscopy, and alternative current impedance technique. It is demonstrated that all Gd1−xCaxPO4·nH2O nanorods crystallized in a pure hexagonal structure. For x = 0, the particle dimension decreased with increasing the pH value. For x > 0, the solid solution limit of Ca2+ in GdPO4·nH2O nanorods was about 3 mol%, below which the lattice volume increased with increasing the doping level of Ca2+. The conductivities of nanorods were highly dependent on both the particle size and Ca2+ concentration, as indicated by the increased conductivity as particle size reduces or Ca2+ doping level increases. These observations were understood in terms of the dehydration and the introduction of HPO42− defects by Ca2+ doping. 相似文献
18.
D. Blanchard A.I. Lem S.
vergaard H.W. Brinks B.C. Hauback 《Journal of Alloys and Compounds》2008,458(1-2):467-473
The reduction reaction of VCl3 mixed with LiAlD4 is studied for different ball-mill energies. From low to high ball-milling energies VCl3 is reduced by the formation of Li–V–Cl metastables phases, LiCl and free Al and V or Al–V phases. It is also shown that the enhancement of the kinetics reaches a limit with increased ball-mill energy. From measurements of the released hydrogen with a Sieverts apparatus and X-ray and neutron diffraction, it is shown that even under mild conditions, at or close to room temperature, the two first steps of the decomposition of VCl3-enhanced LiAlD4 occurs during the first weeks after milling at temperatures in the range 20–50 °C. 相似文献
19.
Investigations of phase relations in the Ba-rich part of the In2O3–BaO(CO2)–CuO pseudo-ternary system at 900 °C have revealed the existence of new indium–copper oxycarbonate – Ba4In0.8Cu1.6(CO3)0.6O6.2. Rietveld refinement of the X-ray powder diffraction data combined with infrared studies gives evidence that this phase is a oxycarbonate crystallising in the tetragonal structure (space group I4/mmm) with unit cell parameters: a=4.0349(1) Å and c=29.8408(15) Å. In the binary part of the In2O3–BaO(CO2) system we have identified the occurrence of Ba4In2−x(CO3)1+xO6−2.5x oxycarbonate solid solution showing a crystal structure also described by I4/mmm space group, but with the unit cell parameters: a=4.1669(1) Å and c=29.3841(11) Å for x=1. The existence range of this phase, −0.153<x<0.4, includes chemical compositions of earlier found phases: Ba5In2+xO8+0.5x with 0≤x≤0.45 (known as the -solid solution), as well as the binary Ba4In2O7 phase. The crystal structures of both new oxycarbonates are isomorphic and related to n=3 member of the Ruddlesden–Popper family. 相似文献
20.
采用X射线衍射(XRD)和拉曼光谱2种方法测量了不同硅碳比的CVD掺硅金刚石薄膜的残余应力。采用偏压增强热丝化学气相沉积装置在硬质合金基底上制备了掺硅金刚石薄膜,将正硅酸乙酯以不同的体积比溶解在丙酮中以使得反应气体中的硅碳比从0.1%变化到1.4%,从而控制掺硅金刚石薄膜的掺杂浓度。SEM和XRD的表征结果显示,随着硅掺杂浓度的增加,金刚石薄膜的晶粒尺寸减小,而金刚石(110)的晶面则逐渐占优。XRD法是测量入射角从0°到45°变化时对应的金刚石(220)面XRD衍射峰,并采用sin2ψ方法计算掺硅金刚石薄膜的残余应力。拉曼谱法则是通过检测金刚石特征峰偏移1332cm1位置的偏移量来测量残余应力。2种方法测得的残余应力随着硅掺杂含量的升高显示出良好的一致性,所有的硅掺杂金刚石的残余应力均为压应力,Si/C摩尔比为0.1%的薄膜具有最高的残余应力,为~1.75GPa(拉曼谱法)或~2.3GPa(XRD法)。随着硅掺杂浓度的进一步升高,薄膜的残余应力则稳定在~1.3GPa左右。 相似文献