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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on LiAlH4 by Materials Project

LiAlH4 crystallizes in the monoclinic C2/c space group. The structure is two-dimensional and consists of two LiAlH4 sheets oriented in the (0, 1, 0) direction. Li1+ is bonded in a 6-coordinate geometry to six H1- atoms. There are a spread of Li–H bond distances ranging from 2.02–2.10 Å. Al3+ is bonded in a tetrahedral geometry to four H1- atoms. All Al–H bond lengths are 1.65 Å. There are two inequivalent H1- sites. In the first H1- site, H1- is bonded in a trigonal planar geometry to two equivalent Li1+ and one Al3+ atom. In the second H1- site, H1- is bonded in a bent 120 degrees geometry to one Li1+ and one Al3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiAlH4 by Materials Project

LiAlH4 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Li1+ is bonded to five H1- atoms to form LiH5 trigonal bipyramids that share corners with five equivalent AlH4 tetrahedra and an edgeedge with one LiH5 trigonal bipyramid. There are a spread of Li–H bond distances ranging from 1.87–2.01 Å. Al3+ is bonded to four H1- atoms to form AlH4 tetrahedra that share corners with five equivalent LiH5 trigonal bipyramids. There are a spread of Al–H bond distances ranging from 1.62–1.64 Å. There are four inequivalent H1- sites. In the first H1- site, H1- is bonded in a bent 150 degrees geometry to one Li1+ and one Al3+ atom. In the second H1- site, H1- is bonded in a trigonal planar geometry to two equivalent Li1+ and one Al3+ atom. In the third H1- site, H1- is bonded in a bent 150 degrees geometry to one Li1+ and one Al3+ atom. In the fourth H1- site, H1- is bonded in a bent 150 degrees geometry to one Li1+ and one Al3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiAlH4 by Materials Project

LiAlH4 is Zircon-like structured and crystallizes in the tetragonal I4_1/a space group. The structure is three-dimensional. Li1+ is bonded in a 8-coordinate geometry to eight equivalent H1- atoms. There are four shorter (2.06 Å) and four longer (2.19 Å) Li–H bond lengths. Al3+ is bonded in a tetrahedral geometry to four equivalent H1- atoms. All Al–H bond lengths are 1.65 Å. H1- is bonded in a distorted trigonal planar geometry to two equivalent Li1+ and one Al3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LiAlH4 by Materials Project

LiAlH4 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Li1+ is bonded to six H1- atoms to form LiH6 octahedra that share corners with six equivalent AlH4 tetrahedra and edges with two equivalent LiH6 octahedra. There are a spread of Li–H bond distances ranging from 1.96–2.11 Å. Al3+ is bonded to four H1- atoms to form AlH4 tetrahedra that share corners with six equivalent LiH6 octahedra. The corner-sharing octahedra tilt angles range from 45–63°. There is one shorter (1.63 Å) and three longer (1.64 Å) Al–H bond length. There are three inequivalent H1- sites. In the first H1- site, H1- is bonded in a distorted bent 150 degrees geometry to one Li1+ and one Al3+ atom. In the second H1- site, H1- is bonded in a bent 120 degrees geometry to one Li1+ and one Al3+ atom. In the third H1- site, H1- is bonded in a trigonal non-coplanar geometry to two equivalent Li1+ and one Al3+ atom.

36 MATERIALS SCIENCE↗
NASA NTRS2012

Formulation and Testing of Paraffin-Based Solid Fuels Containing Energetic Additives for Hybrid Rockets

Many approaches have been considered in an effort to improve the regression rate of solid fuels for hybrid rocket applications. One promising method is to use a fuel with a fast burning rate such as paraffin wax; however, additional performance increases to the fuel regression rate are necessary to make the fuel a viable candidate to replace current launch propulsion systems. The addition of energetic and/or nano-sized particles is one way to increase mass-burning rates of the solid fuels and increase the overall performance of the hybrid rocket motor.1,2 Several paraffin-based fuel grains with various energetic additives (e.g., lithium aluminum hydride (LiAlH4) have been cast in an attempt to improve regression rates. There are two major advantages to introducing LiAlH4 additive into the solid fuel matrix: 1) the increased characteristic velocity, 2) decreased dependency of Isp on oxidizer-to-fuel ratio. The testing and characterization of these solid-fuel grains have shown that continued work is necessary to eliminate unburned/unreacted fuel in downstream sections of the test apparatus.3 Changes to the fuel matrix include higher melting point wax and smaller energetic additive particles. The reduction in particle size through various methods can result in more homogeneous grain structure. The higher melting point wax can serve to reduce the melt-layer thickness, allowing the LiAlH4 particles to react closer to the burning surface, thus increasing the heat feedback rate and fuel regression rate. In addition to the formulation of LiAlH4 and paraffin wax solid-fuel grains, liquid additives of triethylaluminum and diisobutylaluminum hydride will be included in this study. Another promising fuel formulation consideration is to incorporate a small percentage of RDX as an additive to paraffin. A novel casting technique will be used by dissolving RDX in a solvent to crystallize the energetic additive. After dissolving the RDX in a solvent chosen for its compatibility with both paraffin and RDX, the mixture will be combined with the melted paraffin. With the melting point of the paraffin far below the decomposition temperature of the RDX, the solvent will be boiled off, leaving the crystallized RDX embedded in the paraffin. At low percentages of RDX additive and with crystallized RDX surrounded by paraffin, the fuel grains will remain inert, maintaining a key benefit of hybrids in the safety of the solid fuel.

Larson, Daniel B.↗
NASA NTRS2012

Formulation, Casting, and Evaluation of Paraffin-Based Solid Fuels Containing Energetic and Novel Additives for Hybrid Rockets

This investigation studied the inclusion of various additives to paraffin wax for use in a hybrid rocket motor. Some of the paraffin-based fuels were doped with various percentages of LiAlH4 (up to 10%). Addition of LiAlH4 at 10% was found to increase regression rates between 7 - 10% over baseline paraffin through tests in a gaseous oxygen hybrid rocket motor. Mass burn rates for paraffin grains with 10% LiAlH4 were also higher than those of the baseline paraffin. RDX was also cast into a paraffin sample via a novel casting process which involved dissolving RDX into dimethylformamide (DMF) solvent and then drawing a vacuum on the mixture of paraffin and RDX/DMF in order to evaporate out the DMF. It was found that although all DMF was removed, the process was not conducive to generating small RDX particles. The slow boiling generated an inhomogeneous mixture of paraffin and RDX. It is likely that superheating the DMF to cause rapid boiling would likely reduce RDX particle sizes. In addition to paraffin/LiAlH4 grains, multi-walled carbon nanotubes (MWNT) were cast in paraffin for testing in a hybrid rocket motor, and assorted samples containing a range of MWNT percentages in paraffin were imaged using SEM. The fuel samples showed good distribution of MWNT in the paraffin matrix, but the MWNT were often agglomerated, indicating that a change to the sonication and mixing processes were required to achieve better uniformity and debundled MWNT. Fuel grains with MWNT fuel grains had slightly lower regression rate, likely due to the increased thermal conductivity to the fuel subsurface, reducing the burning surface temperature.

Larson, Daniel B.↗
DOE OSTI2020

Electrolyte-Assisted Hydrogen Cycling in Lithium and Sodium Alanates at Low Pressures and Temperatures

An investigation of electrolyte-assisted hydrogen storage reactions in complex aluminum hydrides (LiAlH4 and NaAlH4) reveals significantly reduced reaction times for hydrogen desorption and uptake in the presence of an electrolyte. LiAlH4 evolves ~7.8 wt% H2 over ~3 h in the presence of a Li-KBH4 eutectic at 130 °C compared to ~25 h for the same material without the electrolyte. Similarly, NaAlH4 exhibits 4.8 wt% H2 evolution over ~4 h in the presence of a diglyme electrolyte at 150 °C compared to 4.4 wt% in ~15 h for the same material without the electrolyte. These reduced reaction times are composed of two effects, an increase in reaction rates and a change in the reaction kinetics. While typical solid state dehydrogenation reactions exhibit kinetics with rates that continuously decrease with the extent of reaction, we find that the addition of an electrolyte results in rates that are relatively constant over the full desorption window. Fitting the kinetics to an Avrami-Erofe’ev model supports these observations. The desorption rate coefficients increase in the presence of an electrolyte, suggesting an increase in the velocities of the reactant-product interfaces. In addition, including an electrolyte increases the growth parameters, primarily for the second desorption steps, resulting in the observed relatively constant reaction rates. Similar effects occur upon hydrogen uptake in NaH/Al where the presence of an electrolyte enables hydrogenation under more practical low temperature (75 °C) and pressure (50 bar H2) conditions.

25 ENERGY STORAGE↗
DOE OSTI2021

Reversing the Irreversible: Thermodynamic Stabilization of LiAlH 4 Nanoconfined Within a Nitrogen-Doped Carbon Host

A general problem when designing functional nanomaterials for energy storage is the lack of control over the stability and reactivity of metastable phases. Using the high-capacity hydrogen storage candidate LiAlH4 as an exemplar, we demonstrate an alternative approach to the thermodynamic stabilization of metastable metal hydrides by coordination to nitrogen binding sites within the nanopores of N-doped CMK-3 carbon (NCMK-3). The resulting LiAlH 4 @NCMK-3 material releases H 2 at temperatures as low as 126 °C with full decomposition below 240 °C, bypassing the usual Li 3 AlH 6 intermediate observed in bulk. Moreover, >80% of LiAlH 4 can be regenerated under 100 MPa H 2 , a feat previously thought to be impossible. Nitrogen sites are critical to these improvements, as no reversibility is observed with undoped CMK-3. Density functional theory predicts a drastically reduced Al–H bond dissociation energy and supports the observed change in the reaction pathway. Finally, the calculations also provide a rationale for the solid-state reversibility, which derives from the combined effects of nanoconfinement, Li adatom formation, and charge redistribution between the metal hydride and the host.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1971

Hydrocarbon polymeric binder for advanced solid propellant

The results of curing vinyl alcohol terpolymers of ethylene, propylene and vinyl acetate are reported for an average functionality of 1.24 when reacted with an equivalent amount of diisocynate, and saturated polyisoprene derivative is described having terminal methyl ester functionality. The development is reported of two hydroxy-telechelic polyisoprenes prepared by DEAB initiated free radical polymerization followed by LiAlH4 reduction of the end groups.

Potts, J. E.↗
NASA NTRS1989

Iptycene synthesis: A new method for attaching a 2,3-anthracene moiety to the 9,10-positions of another anthracene moiety - Exceptional conditions for a Lewis acid catalyzed Diels-Alder reaction

An efficient three-step method for appending a 2,3-anthracene moiety to the 9,10-positions of an existing anthracene moiety is described. The first step uses excess 1,4-anthraquinone (3 equiv) and aluminum chloride (6 equiv) to obtain the anthracene-quinone cycloadduct (omission of the AlCl3 resulted in no adduct). The resulting diketone was reduced to the corresponding diol (excess LiAlH4), which was dehydrated to the arene with phosphorus oxychloride and pyridine. Specific examples include the preparation of heptipycene 8 from pentiptycene 6 (66 percent overall yield) and a similar conversion of 8 to the noniptycene 13 (75 percent overall yield). The methodology led to a markedly improved synthesis of tritriptycene 9 and the first synthesis of undecaiptycene 14.

Chen, Yong-Shing↗