Ultrasmall-angle X-ray scattering (USAXS) studies of morphological trends in high energy milled NaAlH4 powders

Dobbins, Tabbetha; Bruster, Edward L.; Oteri, Ejiroghene U.; Ilavský, Ján

doi:10.1016/j.jallcom.2007.02.161

Cited by 8 publications

(7 citation statements)

References 11 publications

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“…Ball milling for a longer time, such as 15 min, may break this subsurface porosity, resulting in smoother surfaces. A similar decrease in particle surface roughness with longer milling times at RT has been found previously …”

Section: Resultssupporting

confidence: 86%

“…Understanding the mechanism of the enhanced kinetics with the addition of transition metals such as Ti is a potential key to destabilizing more stable compounds such as LiBH 4 and Mg(BH 4 ) 2 . A wide variety of techniques have been employed to study the effect of Ti additives on NaAlH 4 , − such as Raman spectroscopy, nuclear magnetic resonance, X-ray absorption, and X-ray photoelectron spectroscopy, among others. Nevertheless, despite years of intense research, the role of the additives remains uncertain.…”

Section: Introductionmentioning

confidence: 99%

“…The effect of several additives on the morphology of NaAlH 4 has been measured at room temperature with ultrasmall-angle X-ray scattering. 35 In their study, Dobbins et al 35 concluded that among TiCl 2 , TiCl 3 (which give the best kinetic enhancement of NaAlH 4 ), and VCl 3 and ZrCl 4 (which do not perform as well) the one which provides the highest powder particle surface area at room temperature is TiCl 3 . These data suggest a correlation between the kinetic activity and the morphological changes on sodium alanate induced by additives.…”

Section: Introductionmentioning

confidence: 99%

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New Aspects on the Decomposition of Sodium Alanate Revealed by Small-Angle X-ray Scattering

2012

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Transition metals added to sodium aluminum hydride by high-energy ball milling have been shown to significantly enhance its absorption and desorption properties. In the present study, we have used small-angle X-ray scattering to elucidate how TiCl 3 affects the nanostructure of NaAlH 4 particles. Scattering data from as-purchased and ball milled NaAlH 4 for 6 and 15 min are compared with NaAlH 4 ball milled for the same time with 4 mol % TiCl 3 . Drastic differences were noticed in the two systems which cast a new light on the decomposition of NaAlH 4 , in particular on the effect of ball milling and of TiCl 3 on the morphology, grain size, and distribution of the phases. The particle morphology of pure NaAlH 4 showed significant evolution/changes during heating from room temperature to 290 °C, as evidenced by the variations in the power-low scattering parameter, α. Drastic changes were noticed in the particle surface structure during the phase transformation from NaAlH 4 to Na 3 AlH 6 + Al, when the system becomes less compact and the particle surface rougher. The addition of TiCl 3 induces a different effect on both surface and mass structure, at least in the nanometer length scale considered in this study: the particles retain their surface morphology at all temperatures. Furthermore, even after short ball milling times the addition of TiCl 3 increases the system compactness with reduction of internal voids.

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Section: Resultssupporting

confidence: 86%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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New Aspects on the Decomposition of Sodium Alanate Revealed by Small-Angle X-ray Scattering

2012

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“…From all these studies, the presence of one or more phases of Ti-Al compounds is expected to tune the thermodynamics and kinetics of Ti-doped sodium alanates. Moreover, the surface morphology of the doped particles may also affect the kinetics of hydrogen desorption [20,21]. In spite of all experimental and theoretical investigations on this topic, the basic role of titanium dopant in the formation of key intermetallics for improved hydrogen kinetics by sodium alanates is still unknown.…”

Section: Introductionmentioning

confidence: 99%

Structure and dynamics of Ti–Al–H compounds in Ti-doped NaAlH₄

Dathara

Mainardi

2008

Molecular Simulation

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Structure and stability of pristine and modified NaAlH 4 are first investigated using density functional theory (DFT) with plane-wave basis and PW91 functional. Vacancy and Ti-dopant effects in the sodium alanate bulk, (0 0 1) surface, and on-top (0 0 1) surface are then studied considering Na and interstitial lattice sites. Calculated substitution energies of Ti-doped (0 0 1) NaAlH 4 surfaces have shown almost equal probability of substitution at both lattice and interstitial sites. Ti-Al -H complexes are formed depending on the accessible AlH 4 groups around the Ti dopant. TiAl 2 H 7 and TiAl 2 H 2 complexes are found after geometry optimising doped-NaAlH 4 surface models. Their stability and dynamics over time at 423 and 448 K are investigated using periodic density functional molecular dynamics (DFT-MD) simulations. Results have shown increased association of Al and H with the complexes as time evolves. DFT-MD simulations show evolution from TiAl 2 H 7 to TiAl 5 H 7 as time and temperature increase in case of Ti dopant at Na surface site (Ti !

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“…Examining phase distributions of two phases, i.e ., LiBH 4 and MgH 2 , using 3D imaging will provide the opportunity to understand diffusion and desorption kinetic limitations in the destabilized hydride systems. Likewise, the addition of catalysts, which have been shown to enhance diffusion in the single phase regions [ 6 ], is expected to improve overall kinetics and address reversibility issues.…”

Section: Introductionmentioning

confidence: 99%

Study of Morphological Changes in MgH2 Destabilized LiBH4 Systems Using Computed X-ray Microtomography

2012

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The objective of this study was to apply three-dimensional x-ray microtomographic imaging to understanding morphologies in the diphasic destabilized hydride system: MgH2 and LiBH4. Each of the single phase hydrides as well as two-phase mixtures at LiBH4:MgH2 ratios of 1:3, 1:1, and 2:1 were prepared by high energy ball milling for 5 minutes (with and without 4 mol % TiCl3 catalyst additions). Samples were imaged using computed microtomography in order to (i) establish measurement conditions leading to maximum absorption contrast between the two phases and (ii) determine interfacial volume. The optimal energy for measurement was determined to be 15 keV (having 18% transmission for the MgH2 phase and above 90% transmission for the LiBH4 phase). This work also focused on the determination of interfacial volume. Results showed that interfacial volume for each of the single phase systems, LiBH4 and MgH2, did not change much with catalysis using 4 mol % TiCl3. However, for the mixed composite system, interphase boundary volume was always higher in the catalyzed system; increasing from 15% to 33% in the 1:3 system, from 11% to 20% in the 1:1 system, and 2% to 14% in the 2:1 system. The parameters studied are expected to govern mass transport (i.e., diffusion) and ultimately lead to microstructure-based improvements on H2 desorption and uptake rates.

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Ultrasmall-angle X-ray scattering (USAXS) studies of morphological trends in high energy milled NaAlH4 powders

Cited by 8 publications

References 11 publications

New Aspects on the Decomposition of Sodium Alanate Revealed by Small-Angle X-ray Scattering

New Aspects on the Decomposition of Sodium Alanate Revealed by Small-Angle X-ray Scattering

Structure and dynamics of Ti–Al–H compounds in Ti-doped NaAlH₄

Study of Morphological Changes in MgH2 Destabilized LiBH4 Systems Using Computed X-ray Microtomography

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Ultrasmall-angle X-ray scattering (USAXS) studies of morphological trends in high energy milled NaAlH4 powders

Cited by 8 publications

References 11 publications

New Aspects on the Decomposition of Sodium Alanate Revealed by Small-Angle X-ray Scattering

New Aspects on the Decomposition of Sodium Alanate Revealed by Small-Angle X-ray Scattering

Structure and dynamics of Ti–Al–H compounds in Ti-doped NaAlH4

Study of Morphological Changes in MgH2 Destabilized LiBH4 Systems Using Computed X-ray Microtomography

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Structure and dynamics of Ti–Al–H compounds in Ti-doped NaAlH₄