21 research outputs found
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Catalytic Decomposition of Hydroxylammonium Nitrate Ionic Liquid: Enhancement of NO Formation.
Hydroxylammonium nitrate (HAN) is a promising candidate to replace highly toxic hydrazine in monopropellant thruster space applications. The reactivity of HAN aerosols on heated copper and iridium targets was investigated using tunable vacuum ultraviolet photoionization time-of-flight aerosol mass spectrometry. The reaction products were identified by their mass-to-charge ratios and their ionization energies. Products include NH3, H2O, NO, hydroxylamine (HA), HNO3, and a small amount of NO2 at high temperature. No N2O was detected under these experimental conditions, despite the fact that N2O is one of the expected products according to the generally accepted thermal decomposition mechanism of HAN. Upon introduction of iridium catalyst, a significant enhancement of the NO/HA ratio was observed. This observation indicates that the formation of NO via decomposition of HA is an important pathway in the catalytic decomposition of HAN
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Catalytic Decomposition of Hydroxylammonium Nitrate Ionic Liquid: Enhancement of NO Formation
Hydroxylammonium
nitrate (HAN) is a promising candidate to replace
highly toxic hydrazine in monopropellant thruster space applications.
The reactivity of HAN aerosols on heated copper and iridium targets
was investigated using tunable vacuum ultraviolet photoionization
time-of-flight aerosol mass spectrometry. The reaction products were
identified by their mass-to-charge ratios and their ionization energies.
Products include NH<sub>3</sub>, H<sub>2</sub>O, NO, hydroxylamine
(HA), HNO<sub>3</sub>, and a small amount of NO<sub>2</sub> at high
temperature. No N<sub>2</sub>O was detected under these experimental
conditions, despite the fact that N<sub>2</sub>O is one of the expected
products according to the generally accepted thermal decomposition
mechanism of HAN. Upon introduction of iridium catalyst, a significant
enhancement of the NO/HA ratio was observed. This observation indicates
that the formation of NO via decomposition of HA is an important pathway
in the catalytic decomposition of HAN
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Flow-Tube Investigations of Hypergolic Reactions of a Dicyanamide Ionic Liquid Via Tunable Vacuum Ultraviolet Aerosol Mass Spectrometry.
The unusually high heats of vaporization of room-temperature ionic liquids (RTILs) complicate the utilization of thermal evaporation to study ionic liquid reactivity. Although effusion of RTILs into a reaction flow-tube or mass spectrometer is possible, competition between vaporization and thermal decomposition of the RTIL can greatly increase the complexity of the observed reaction products. In order to investigate the reaction kinetics of a hypergolic RTIL, 1-butyl-3-methylimidazolium dicyanamide (BMIM+DCA-) was aerosolized and reacted with gaseous nitric acid, and the products were monitored via tunable vacuum ultraviolet photoionization time-of-flight mass spectrometry at the Chemical Dynamics Beamline 9.0.2 at the Advanced Light Source. Reaction product formation at m/z 42, 43, 44, 67, 85, 126, and higher masses was observed as a function of HNO3 exposure. The identities of the product species were assigned to the masses on the basis of their ionization energies. The observed exposure profile of the m/z 67 signal suggests that the excess gaseous HNO3 initiates rapid reactions near the surface of the RTIL aerosol. Nonreactive molecular dynamics simulations support this observation, suggesting that diffusion within the particle may be a limiting step. The mechanism is consistent with previous reports that nitric acid forms protonated dicyanamide species in the first step of the reaction
Flow-Tube Investigations of Hypergolic Reactions of a Dicyanamide Ionic Liquid Via Tunable Vacuum Ultraviolet Aerosol Mass Spectrometry
The
unusually high heats of vaporization of room-temperature ionic
liquids (RTILs) complicate the utilization of thermal evaporation
to study ionic liquid reactivity. Although effusion of RTILs into
a reaction flow-tube or mass spectrometer is possible, competition
between vaporization and thermal decomposition of the RTIL can greatly
increase the complexity of the observed reaction products. In order
to investigate the reaction kinetics of a hypergolic RTIL, 1-butyl-3-methylimidazolium
dicyanamide (BMIM<sup>+</sup>DCA<sup>–</sup>) was aerosolized
and reacted with gaseous nitric acid, and the products were monitored
via tunable vacuum ultraviolet photoionization time-of-flight mass
spectrometry at the Chemical Dynamics Beamline 9.0.2 at the Advanced
Light Source. Reaction product formation at <i>m</i>/<i>z</i> 42, 43, 44, 67, 85, 126, and higher masses was observed
as a function of HNO<sub>3</sub> exposure. The identities of the product
species were assigned to the masses on the basis of their ionization
energies. The observed exposure profile of the <i>m</i>/<i>z</i> 67 signal suggests that the excess gaseous HNO<sub>3</sub> initiates rapid reactions near the surface of the RTIL aerosol.
Nonreactive molecular dynamics simulations support this observation,
suggesting that diffusion within the particle may be a limiting step.
The mechanism is consistent with previous reports that nitric acid
forms protonated dicyanamide species in the first step of the reaction
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Thermal and Catalytic Decomposition of 2-Hydroxyethylhydrazine and 2-Hydroxyethylhydrazinium Nitrate Ionic Liquid.
To develop chemical kinetics models for the combustion of ionic liquid-based monopropellants, identification of the elementary steps in the thermal and catalytic decomposition of components such as 2-hydroxyethylhydrazinium nitrate (HEHN) is needed but is currently not well understood. The first decomposition step in protic ionic liquids such as HEHN is typically the proton transfer from the cation to the anion, resulting in the formation of 2-hydroxyethylhydrazine (HEH) and HNO3. In the first part of this investigation, the high-temperature thermal decomposition of HEH is probed with flash pyrolysis (<1400 K) and vacuum ultraviolet (10.45 eV) photoionization time-of-flight mass spectrometry (VUV-PI-TOFMS). Next, the investigation into the thermal and catalytic decomposition of HEHN includes two mass spectrometric techniques: (1) tunable VUV-PI-TOFMS (7.4-15 eV) and (2) ambient ionization mass spectrometry utilizing both plasma and laser ionization techniques whereby HEHN is introduced onto a heated inert or iridium catalytic surface and the products are probed. The products can be identified by their masses, their ionization energies, and their collision-induced fragmentation patterns. Formation of product species indicates that catalytic surface recombination is an important reaction process in the decomposition mechanism of HEHN. The products and their possible elementary reaction mechanisms are discussed