Propellant Synthesis Research Articles

The potential of catalysis for closing the loop in human space exploration

This mini-review provides a perspective on how catalysis can contribute to the challenge of human space exploration, i.e. to the establishment of a space habitat on the Moon in the near future and the realization of a journey to Mars in the far future. The role of catalysis for space exploration is reviewed along elemental resource provisions for human life that are based on catalytic chemical processes. As a secondary effect, learning about catalysis under the high constraints of the sustainability requirements inherent to long-term space missions can be beneficial for the advancement of currently developed catalytic processes for a green, circular economy on Earth. In-depth research into catalysis for space applications could therefore also provide answers to urgent industrial, environmental and social sustainability challenges on our planet e.g., as expressed by the United Nations Sustainability Development Goals. Even for today’s short-term space missions, catalysis already plays a key role in the Environmental Control and Life Support System (ECLSS) on the International Space Station (ISS) and moreover, in fuel and propellant synthesis as well as the recycling of combustion products such as CO2.

Green Hypergolic Ionic Liquids: Future Rocket Propellants

Hydrazine and its derivatives have been used as standard propellants for spacecraft propulsion systems since the 1960s, despite being highly toxic and carcinogenic. The propellant synthesis community has constantly been looking for green alternatives for the same. Hypergolic ionic liquids (HILs) with several attractive properties, such as high energy content, high bulk density, low vapor pressure, and low toxicity, have been proposed as an alternative to hydrazine and its derivatives. In the present study, the theoretical performance of sixty-eight HILs was studied at a combustion chamber pressure of 3 MPa and a nozzle expansion ratio of 40. The specific impulse and density specific impulse of the HILs were calculated with white fuming nitric acid (WFNA), inhibited red fuming nitric acid (IRFNA), and nitrogen tetroxide (NTO) as oxidizers. The specific impulse of 2,2-dimethyltriazanium nitrate (HIL-1) was found to be 23 s higher than monomethylhydrazine (MMH), whereas its density-specific impulse was found to be 123 g-s/cm3 higher than MMH. The gains in the specific impulse and density specific impulse coupled with other desirable “green” properties for several HILs are expected to establish them as potential replacements for hydrazine and its derivatives.

Energetic ionic liquid hydroxyethylhydrazinium nitrate as an alternative monopropellant

The propellant synthesis community is constantly looking for green alternative monopropellants. Energetic ionic liquids have several attractive properties such as high energy content, high bulk density, low vapor pressure, high thermal stability, wide liquidus range, low corrosiveness, low toxicity, and ease of handling. The combustion characteristics of an energetic ionic liquid hydroxyethylhydrazinium nitrate (HEHN) was conducted in a pressurized chamber. The performance of HEHN was compared to that of the monopropellant Otto fuel II (OF-II) typically used for torpedo-propulsion. A liquid strand combustion study was performed in an atmosphere of air and nitrogen with chamber pressures varying from 10 to 90 bar. Regressing surface profiles and subsequent burning rates were obtained at different chamber pressures. A B-type thermocouple of 46 µm wire diameter was used to measure the monopropellant flame temperature of HEHN. Thermogravimetric analysis was performed to study the thermal decomposition of HEHN to understand its thermal stability and Fourier transform infrared spectroscopy (FTIR) was utilized to determine the possible reasons behind the high burning rates of HEHN. The gains in the specific impulse and density specific impulse coupled with enhanced burning rates and reasonable thermal stability are expected to establish HEHN as a frontrunner for propulsion and power-generation in oxygen-deficient scenarios.

Upconversion in Er 3+-doped Gd 2O 3 nanocrystals prepared by propellant synthesis and flame spray pyrolysis

In this study, monoclinic luminescent Gd 2O 3 nanocrystals doped with different concentrations of Er 3+ (0.1, 1, and 10 mol%) were produced by propellant synthesis and flame spray pyrolysis (FSP). A comparison of their optical and morphological properties is reported. Following 980 nm excitation, an increase of the emission intensity from the 2H 11/2, 4S 3/2 → 4I 15/2 and 4F 9/2 → 4I 15/2 transitions was observed with increasing Er 3+ concentration in the Gd 2O 3 nanocrystalline samples prepared via both techniques. However, the overall upconversion emission intensity was greater for the samples obtained by FSP. Furthermore, as the Er 3+ concentration was increased, the intensity of the red ( 4F 9/2 → 4I 15/2) emission was observed to increase more rapidly in comparison to the green ( 2H 11/2, 4S 3/2 → 4I 15/2) emission resulting in an overall enhancement of the red component in the upconversion emission. Although both synthetic routes yield average crystallite sizes in the nanoscale, the TEM and SEM images confirm a more homogeneous morphology and lower particle aggregation for the nanocrystals produced by FSP.

Structural and luminescence investigation on gadolinium gallium garnet nanocrystallinepowders prepared by solution combustion synthesis

Nanocrystalline powders of undoped and lanthanide(Pr3+,Tm3+)-doped gadoliniumgallium garnet, Gd3Ga5O12 (GGG), were prepared by propellant synthesis and studied by x-ray powder diffraction(XRD), electron diffraction (ED), high-resolution electron microscopy (HREM) andluminescence spectroscopy. The x-ray diffraction patterns of the GGG samples wereanalysed using the Rietveld method. The Rietveld refinement reveals the existence of twogarnet-type phases: both are cubic (space group ) with a slightly different lattice parameter and probably a slightly different composition. Electrondiffraction and electron microscopy measurements confirm the x-ray diffraction results. EDXmeasurements for lanthanide-doped samples show that stable solid solutions with compositionGd3−xLnxGa5O12,x≈0.3 (Ln = Pr; Tm) have been obtained. The luminescence properties of theTm3+-doped nanocrystalline GGG samples were measured and analysed.

Structural characterization and luminescence properties of nanostructured lanthanide-dopedSc2O3 prepared by propellant synthesis

Nanocrystalline powders of undoped and lanthanide-doped scandium oxide were preparedby propellant synthesis and characterized by x-ray powder diffraction, electron microscopy,EDX spectroscopy and luminescence spectroscopy. The obtained material has theSc2O3 cubic structure (space group ) with unit cell parameter increasing with the size of the dopant. Thecrystallite size is in the range 20–40 nm. The lanthanide-doped samples formSc2−xLnxO3 solidsolutions with x≈0.2 (Ln = Eu orEr). No inhomogeneity was found by microanalysis on the micron scale. The emission spectrum ofthe Eu3+ doped Sc2O3 sample shows strong bands in the visible region assigned to 4f–4f transitions of thelanthanide ions.

Characterization of Nanoporous Lanthanide-Doped Gadolinium Gallium Garnet Powders Obtained by Propellant Synthesis

In the present work we study the nanocrystalline powders of lanthanide-doped Gd3Ga5O12 (GGG, gadolinium gallium garnet) prepared using propellant synthesis. A series of GGG samples containing a number of different trivalent lanthanide ions (Tm, Er, Ho, Eu, Sm, Nd, and Pr) in different quantities (1%, 5%, 10%) were produced. Samples were characterized by X-ray diffraction (pre- and post calcination) for phase identification and line-broadening analysis, and by electron microscopy (SEM and TEM) for morphological and nanostructural investigation. Thermal behavior of the powder was investigated by thermal gravimetric analysis (TGA) and differential thermal analysis (DTA). The samples have a polycrystalline porous structure. Elemental microanalysis made by energy dispersive X-ray spectroscopy (EDX) detector attached to TEM and XRD unit-cell determinations confirmed that the lanthanides ions entered the structure of GGG. Crystallites have a high degree of disorder.

Characterization of Nanoporous Lanthanide-Doped YAG Powders Obtained by Propellant Synthesis

Characterization of Nanoporous Lanthanide-Doped YAG Powders Obtained by Propellant Synthesis

Nanostructured Lanthanide-Doped Lu2O3 Obtained by Propellant Synthesis

Lu1.98Ln0.02O3 (Ln = Nd, Eu, and Er) powders obtained by propellant synthesis were characterized using XRD, SAXS, TEM, and SEM. Samples have a very porous, open morphology with fractal scaling properties. The building blocks of the fractal aggregates are 60−90 nm lanthanide-doped cubic Lu2O3 crystalline particles, which exhibit changes in the lattice parameter proportional to the lanthanide ionic radius. The NIR luminescence spectrum of nanocrystalline Lu2O3:Nd3+ was measured and emission was observed from the 4F3/2 excited state to the 4IJ (9/2, 11/2, 13/2, 15/2) state. The spectral features are very similar to those of a bulk material of identical composition prepared for comparison, though with a noticeable difference in the relative intensity of the 4F3/2 → 4I9/2 and 4F3/2 → 4I11/2 transitions. The spectroscopic-quality parameter (X) for nanocrystalline samples was calculated and was found to be higher than for the bulk.

Nanosized Sodium-Doped Lanthanum Manganites: Role of the Synthetic Route on Their Physical Properties

In this paper we present the results of the synthesis and characterization of nanocrystalline La1-xNaxMnO3+δ samples. Two synthetic routes were employed: polyacrylamide-based sol−gel and propellant synthesis. Pure, single-phase materials were obtained with grain size around 35 nm for the sol−gel samples and around 55 nm for the propellant samples, which moreover present a broader grain size distribution. For both series a superparamagnetic behavior was evidenced by means of magnetization and EPR measurements with peculiar features ascribable to the different grain sizes and morphology. Preliminary magnetoresistivity measurements show enhanced low-field (<1 T) magnetoresistance values which suggest an interesting applicative use of these manganites.

A spectroscopic investigation of trivalent lanthanide dopedY2O3 nanocrystals

Nanocrystalline yttrium oxide doped with the lanthanide ionsSm3+,Dy3+ orTm3+ with a particle diameter of approximately 10 nm was prepared by propellant synthesis. TheY2O3:Sm3+ nanocrystals showed a visually dominant red emission from the transition and a strong concentration dependence of both theemission spectra and decay was observed. The decay time of the4G5/2 excited state in the 1 mol% nanocrystallineY2O3:Sm3+ sample was determined to be longer than in the identically doped bulk (microcrystalline)sample. We have shown that the lifetime of this state in the nanocrystalline material isstrongly dependent on the index of refraction of the medium surrounding the nanoparticlesand a 0.75 filling factor was obtained. Yellow emission was observed from theY2O3:Dy3+ nanocrystals from the transition. The decay curves of the4F9/2 state deviated from exponentiality and were fitted with the Inokuti–Hirayama model inorder to probe the energy transfer processes. The model revealed that a dipole–dipolemechanism was responsible for the interactions and a critical transfer distance(R0) of 6.05 Å wasobtained. Tm3+ doped Y2O3 nanocrystals showed predominantly blue emission from the and transitions. Red-to-blue up-conversion was detected following excitation with 656 nm into the3F2 state which occurred via a two-photon ESA/ETU process.

Effect of Yb3+ Codoping on the Upconversion Emission in Nanocrystalline Y2O3:Er3+

The Stokes emission of nanocrystalline and bulk Y2O3:Er3+, Yb3+ following 488 nm were reported. Two nanocrystalline samples were studied, one produced via propellant synthesis and the other via wet synthesis. Green, red, and NIR emission from the Er3+ ion was observed in both bulk and nanocrystalline samples. Emission from the 2F5/2 → 2F7/2 Yb3+ transition was also observed in the bulk and nanocrystalline samples following 488 nm excitation, thereby signifying the presence of an energy transfer process from Er3+ to Yb3+. The peaks attributed to Yb3+ emission were much less intense in the nanocrystalline material, indicating that the energy transfer process occurs less readily in this material because of the inherent high phonon energies from the adsorbed CO2 and H2O on their surface. Following excitation with 978 nm, green and red anti-Stokes luminescence was evidenced in the samples under investigation. An enhancement of the red emission is observed in both bulk and nanocrystalline samples, although to a...

Fractal aggregates of lanthanide-doped Y2O3 nanoparticles obtained by propellant synthesis

Y2-xLnxO3 (Ln 4 Ce, Pr, Nd, Eu, Gd, Ho, and Er) powders obtained by propellant synthesis have been characterized using small-angle x-ray scattering, wide-angle x-ray scattering, and transmission and scanning electron microscopy. All the samples showed a very porous, open microstructure with fractal scaling properties. The building blocks of the fractal aggregates are nanocrystallites of lanthanide-doped Y2O3, with variations in the cubic lattice constant proportional to the composition of the solid solution and to the lanthanide ionic radius. The particles had a narrow distribution of sizes with an average value in the 20–50 nm range. They are made of a core of 10–20 nm, consisting of almost perfectly ordered crystals and a “fuzzy” layer, characterized by either a growing lattice disorder or by a compositional gradient. From this dimension, up to at least 200 nm, the particle aggregate is a mass fractal with a fractal dimension, DMf, in the 1.6–2.0 range.