Thermal Decomposition of Hydroxylammonium Nitrate: ReaxFF Training Set Development for Molecular Dynamics Simulations

Depew, Daniel D.; Wang, Joseph J.; Parmar, Shehan M.; Chambreau, Steven D.; Bedrov, Dmitry; Duin, Adri van; Vaghjiani, Ghanshyam L.

doi:10.2514/6.2019-4367

Cited by 5 publications

(7 citation statements)

References 27 publications

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“…Ionic liquids (ILs) are versatile materials , with applications ranging from tailored solvents for chemical synthesis − to spacecraft propellants. − Here, we are concerned with the protic IL 2-hydroxyethylhydrazinium nitrate (HEHN), , which is comprised of the ionic constituents with the structures displayed in Scheme a,c. Dubbed as a “green propellant,” this high-performance IL displays low toxicity (compared to hydrazine, N 2 H 4 ) and low vapor pressure, both highly desirable properties for the manufacture and performance of satellite thrusters .…”

Section: Introductionmentioning

confidence: 99%

Ionic Liquid Clusters Generated from Electrospray Thrusters: Cold Ion Spectroscopic Signatures of Size-Dependent Acid–Base Interactions

et al. 2020

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We determine the intramolecular distortions at play in the 2-hydroxyethylhydrazinium nitrate (HEHN) ionic liquid (IL) propellant, which presents the interesting case that the HEH + cation has multiple sites (i.e., hydroxy, primary amine, and secondary ammonium groups) available for H-bonding with the nitrate anion. These interactions are quantified by analyzing the vibrational band patterns displayed by cold cationic clusters, (HEH + ) n (NO 3 − ) n−1 , n = 2−6, which are obtained using IR photodissociation of the cryogenically cooled, mass-selected ions. The strong interaction involving partial proton transfer of the acidic N−H proton in HEH + cation to the nitrate anion is strongly enhanced in the ternary n = 2 cluster but is suppressed with increasing cluster size. The cluster spectra recover the bands displayed by the bulk liquid by n = 5, thus establishing the minimum domain required to capture this aspect of macroscopic behavior.

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Section: Introductionmentioning

confidence: 99%

Ionic Liquid Clusters Generated from Electrospray Thrusters: Cold Ion Spectroscopic Signatures of Size-Dependent Acid–Base Interactions

et al. 2020

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“…It is somewhat surprising that the cation’s hydrogens do not exhibit a similar geometry around the nitrate as the water. Previous DFT studies of HAN which employed an implicit solvent model reported optimized ion pair geometries with noticeably nonlinear N n –O n ···H a and N n –O n ···H h angles, , though such isolated calculations cannot be reliably used to infer the bulk H-bonding structure of the explicit cosolvents. Perhaps more tellingly, a CPMD simulation of neat MAN generated SDFs where the H a hydrogens strongly preferred an off-axis coordination with the nitrate N–O bond .…”

Section: Resultsmentioning

confidence: 99%

Liquid Structure and Hydrogen Bonding in Aqueous Hydroxylammonium Nitrate

Depew,

Vaghjiani,

Parmar

et al. 2024

J. Phys. Chem. B

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Hydroxylammonium nitrate (HAN) has emerged as a promising component in ionic liquid-based spacecraft propellants. However, the physicochemical and structural properties of aqueous HAN have been largely overlooked. The purpose of this study is to investigate the hydrogen bonding in aqueous HAN and understand its implications on these properties and the proton transfer mechanism as a function of concentration. Classical polarizable molecular dynamics simulations have been employed with the APPLE&P force field to analyze the geometry of individual hydrogen bonds and the overall hydrogen-bonding network in various concentrations of aqueous HAN. Radial distribution functions (RDFs) and spatial distribution functions (SDFs) indicate the structural arrangement of the species and their hydrogen bonds. Projections of water density and the orientation of its electric dipole moment near the ions provide insight into the hydrogen-bonding network. The incorporation of water into the hydrogen-bonding network at high ion concentrations occurs via interstitial accommodation around the ions immediately outside the first solvation shell. While ion pairs are observed at all concentrations considered, the frequency of Ha···On hydrogen bonds increases substantially with the ion concentration. The findings contribute to a better fundamental understanding of HAN and the precursors of reactivity, crucial to the development of “green” spacecraft propellants.

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“…113−115 All condensed-phased MD simulations were performed using the original APPLE&P force field 113 with reparameterized repulsion−dispersion terms using a HEHN/HAN/ H 2 O dataset of quantum chemical (QC) calculations. 20 As previously mentioned, a companion paper explores HAN− H 2 O systems at varied mole fractions, whereas in this work, the same force field was used to explore HAN−HEHN systems. The functional form used to define the interatomic potential energy is provided in eq S1.…”

Section: ■ Theory and Methodsmentioning

confidence: 99%

“…However, realizing desirable thruster performance remains a challenge and heavily depends on propellant properties. Many competing propellant breakdown mechanisms, including thermal, − catalytic, ,− or electrochemical decomposition, evaporation, , or Coulombic fission, , may occur during thruster operation and produce undesirable byproducts that hinder thruster performance and lifetime during spacecraft mission operations . Thus, a better understanding of fundamental IL properties is crucial for improved design and propellant selection.…”

Section: Introductionmentioning

confidence: 99%

Structural Properties of HEHN- and HAN-Based Ionic Liquid Mixtures: A Polarizable Molecular Dynamics Study

Parmar,

Depew,

Wirz

et al. 2023

J. Phys. Chem. B

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Molecular dynamics simulations of binary mixtures comprising 2-hydroxyethylhydrazinium nitrate (HEHN) and hydroxylammonium nitrate (HAN) were conducted using the polarizable APPLE&P force field to investigate fundamental properties of multimode propulsion (MMP) propellants. Calculated densities as a function of temperature were in good agreement with experiments and similar simulations. The structural properties of neat HEHN and HAN–HEHN provided insights into their inherent, protic nature. Radial distribution functions (RDFs) identified key hydrogen bonding sites located at N–H···O and O–H···O within a first solvation shell of approximately 2 Å. Angular distribution functions further affirmed the relatively strong nature of the hydrogen bonds with nearly linear directionality. The increased hydroxylammonium cation (HA+) mole fraction shows the influence of competitively strong hydrogen bonds on the overall hydrogen bond network. Dominant spatial motifs via three-dimensional distribution functions along with nearly nanosecond-long hydrogen bond lifetimes highlight the local bonding environment that may precede proton transfer reactions.

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Thermal Decomposition of Hydroxylammonium Nitrate: ReaxFF Training Set Development for Molecular Dynamics Simulations

Cited by 5 publications

References 27 publications

Ionic Liquid Clusters Generated from Electrospray Thrusters: Cold Ion Spectroscopic Signatures of Size-Dependent Acid–Base Interactions

Ionic Liquid Clusters Generated from Electrospray Thrusters: Cold Ion Spectroscopic Signatures of Size-Dependent Acid–Base Interactions

Liquid Structure and Hydrogen Bonding in Aqueous Hydroxylammonium Nitrate

Structural Properties of HEHN- and HAN-Based Ionic Liquid Mixtures: A Polarizable Molecular Dynamics Study

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