Decomposition Of Hydroxylammonium Nitrate Research Articles

Laser-induced fluorescence detection of nitroxyl (HNO) formed from the thermal decomposition of hydroxylammonium nitrate vapor

The decomposition of the ionic liquid hydroxylammonium nitrate (HAN) produces gas phase products which have utility in spacecraft propulsion systems. Among the various gas phase species generated from HAN decomposition is the nitroxyl (HNO) radical, a highly reactive molecule with implications in both chemical and electric propulsion applications. The work described here used a laser-induced fluorescence platform to directly detect the relative density of the HNO radical formed by passing HAN vapor through heated porous disks of varying composition. The use of heated porous 316-stainless steel and aluminum disks showed significant HNO density production and is attributed to a surface hydrogen abstraction mechanism. There was also evidence of surface modification to the metal disks which resulted in a shift in the HNO density temperature profiles. The results reported demonstrate that use of a heated porous material can easily generate a molecular vapor at moderate temperatures for combustion and electric propulsion applications.

On the formation of ammonia from the thermal decomposition of hydroxylammonium nitrate vapor

The ionic liquid hydroxylammonium nitrate (HAN) is a promising propellant for various types of spacecraft propulsion systems. With respect to combustion and plasma-based electric propulsion, the thermal decomposition of HAN into gas phase species provides a convenient feed gas supply. While the decomposition of HAN in the liquid phase has been extensively studied, little is known about the decomposition chemistry of HAN vapor interacting with heated surfaces. The ability to decompose HAN vapor on a reactive surface could provide a means to control the feed gas composition and enhance the performance of spacecraft propulsion systems.In this initial qualitative study, HAN was vaporized and thermally decomposed using porous 316-stainless-steel and quartz disks under vacuum conditions. Decomposition products with low vapor pressures would condense on an in-line quartz tube which was subsequently collected and analyzed with Raman spectroscopy, NMR spectroscopy, and FT-IR spectroscopy. At temperatures above 440 K the 316-stainless-steel system produced significant quantities of ammonia which reacted with vaporized nitric acid to form ammonium nitrate. Temperatures below 440 K yielded partial HAN decomposition which resulted in a binary mixture of HAN and ammonium nitrate. The degree to which HAN was consumed was determined by analysis of the 1008 cm−1N-OH asymmetric Raman band of HAN and the 1049 cm−1 symmetric stretching Raman band of the nitrate ion, NO3−. The quartz system yielded significantly different results with no ammonium nitrate detected at temperatures above 440 K. Reformed HAN was the primary product detected at lower temperatures. The difference in reported measurements and visual observations highlights the distinct differences in HAN vapor decomposition chemistry from the two materials examined.

Effect of Metal Sequestrants on the Decomposition of Hydroxylammonium Nitrate

Hydroxylammonium nitrate (HAN) is an energetic salt used in flight-proven green monopropellants such as ASCENT (formerly AF-M315E), flown in NASA’s 2019 Green Propellant Infusion Mission, and SHP163, flown in JAXA’s Rapid Innovative Satellite Technology Demonstration-1. The decomposition of HAN is catalyzed by metals commonly found in storage tanks, a factor limiting its use. This work investigates the ability of metal-sequestering chelating agents to inhibit the decomposition of HAN. Isothermal and dynamic thermogravimetric analysis (TGA) were used to find isothermal decomposition rates, decomposition onset temperatures, and first-order Arrhenius reaction rate parameters. In the present research, 2,2′-bipyridine (Bipy), triethanolamine (TEA), and ethylenediaminetetraacetic acid (EDTA) were studied as 0.05, 0.1, 0.5, 1, and 5% by weight additives in 90% aqueous HAN. An isothermal decomposition rate of 0.137%/h at 348 K was observed for HAN. The addition of 1% Bipy and 1% TEA reduced the isothermal decomposition rate by 20.4% to 0.109%/h, and by 3.65% to 0.132%/h, respectively, showing that Bipy can inhibit decomposition. The addition of 1% EDTA increased the isothermal decomposition rate by 12.4% to 0.154%/h. Bipy was found to increase the decomposition onset temperature from 454.8 K to 461.8 K, while the results for TEA and EDTA were inconclusive. First order reaction rates calculated by the Ozawa-Flynn-Wall method were found to be insufficient to capture the effects of the tested additives. Bipy was found to inhibit the decomposition of HAN, while TEA and EDTA produced little or negative effect, a result believed to be due to poor metal complex stability at low pH and high acidity, respectively. Spectrophotometry, used for colorimetric analysis of Bipy+iron complexes, showed that Bipy forms chelate complexes with trace iron impurities when added to HAN solutions.

Combustion of Gelled HAN/Methanol/Water Propellants

AbstractMonopropellants based on hydroxylammonium nitrate (HAN) are a low‐toxic, high‐performance alternative to hydrazine in space propulsion systems. Gelling such propellants may offer additional advantages such as the long‐term stability of compositions with added energetic and catalytic particles in suspension. However, the effect of gelling on the combustion characteristics and mechanisms of HAN‐based propellants is not well understood. In the present work, an aqueous HAN/methanol solution (70.1 wt% HAN and 14.9 wt% methanol) was gelled with 1 wt% polyacrylamide in an acoustic mixer. Combustion of the obtained gel was studied in a strand burner at nitrogen pressures up to 30 MPa. Thermogravimetric analysis, differential scanning calorimetry, and mass spectrometry were used to investigate the reaction mechanisms in the HAN/methanol/water solutions with and without polyacrylamide. The strand burner tests have shown that gelling suppressed the multiple pressure regimes observed in previous studies of the HAN‐based propellants, with a consistent pressure exponent of 1.15±0.05 over the tested pressure range 4–30 MPa. Thermoanalytical testing of the gelled mixture indicates there is no chemical interaction between the gellant and the HAN decomposition, and the effect of gelling on the combustion of HAN/methanol/water propellants is hydrodynamic in nature.

Kinetics and Mechanism of Thermal and Catalytic Decomposition of Hydroxylammonium Nitrate (HAN) Monopropellant

AbstractHydroxylammonium nitrate (HAN) monopropellant with its low sensitivity, volatility and toxicity, not only promises a safer substitute to hydrazine but also offers a higher specific impulse and a positive oxygen balance. This study primarily explores the decomposition mechanism and underlying kinetics for a newly developed cerium oxide‐based catalyst. The chemical kinetics involved in the thermal and catalytic decomposition was examined through an isoconversional method using thermogravimetric analysis (TG) data. The activation energy (Ea) was evaluated using differential isoconversional method (Friedman's method) and advanced integral isoconversional method (Popescu‐Ortega's method). To find frequency factor, compensation effect method (ACE) and intercept method (A0) were used. Advanced integral method could not provide realistic kinetic parameters while differential method predicted values similar to reported values for thermal decomposition. The values obtained for thermal decomposition were found matching with reported values obtained by other techniques which validated the methodology adopted. The reaction mechanism for both thermal and catalytic decomposition were proposed based on evolved gas analysis. The mechanism proposed was able to describe the variable kinetic parameters extracted from isoconversional method. Overall Ea of thermal decomposition of HAN was ∼95 kJ/mol. The decomposition over ceria‐based catalyst was distributed over three stages namely inception, peak and decay with Ea of ∼33 kJ/mol, ∼170 kJ/mol and ∼130 kJ/mol, respectively. Under identical conditions, iridium‐based catalyst show two decomposition stages with Ea of ∼65 kJ/mol and ∼120 kJ/mol while final stage being evaporation of HNO3. The ceria catalyst favoured N2 formation, increased decomposition of HNO3 and enhanced decomposition enthalpy.

Experimental Study on Thermal and Catalytic Decomposition of a Dual-Mode Ionic Liquid Propellant

With the increasing of space activities and people’s awareness of environmental protection, it is necessary to develop a new non-toxic space propulsion system with high performance. Hydroxylammonium nitrate (HAN)/1-ethyl-3-methyl-imidazolium ethylsulfate([Emim][EtSO4]) blend ionic liquid propellant is a potential replacement with non-toxic and high-performance characteristics for hydrazine type liquid propellants, which can be used in both chemical and electrical propulsion system. This paper introduced the thermogravimetric experimental analysis (TGA-DSC) results of HAN/[Emim][EtSO4] ionic liquid propellant with the thermal decomposition and catalytic decomposition process. Its mass-loss process and exothermic process under different reaction conditions at a heating rate of 5K/min~15K/min were studied. Generally, the mass-loss results showed that there were four characteristic stages during the decomposition process of the HAN/[Emim][EtSO4] ionic liquids, which were the evaporation of the water solvent, decomposition of the HAN component, further decomposition of the [Emim][EtSO4], and slow loss of the residual substances. At the same time, two exothermic peaks were observed, which respectively corresponded to the decomposition of HAN and the further decomposition of [Emim][EtSO4]. Using catalyst can significantly reduce the decomposition temperature of the propellant and the residual mass. The contents in this paper proved that this propellant had a good application prospect within the catalytic ignition aerospace thruster.

Combustion of aqueous HAN/methanol propellants at high pressures

“Green” monopropellants based on hydroxylammonium nitrate (HAN) are of interest for replacing highly toxic hydrazine in space propulsion systems and for other applications. However, their combustion mechanisms at high pressures are not well understood. In the present paper, decomposition of HAN at pressures up to 15 MPa was studied with differential scanning calorimetry, while combustion of an aqueous HAN/methanol solution (70.1 wt% HAN and 14.9 wt% methanol) was studied in a strand burner at pressures up to 30 MPa. The experiments in both setups were conducted in a nitrogen environment. It has been shown that the decomposition temperature of HAN significantly decreases with increasing pressure from atmospheric to 2 MPa and remains virtually constant with further increasing pressure to 15 MPa. The decrease with pressure is explained by suppressing evaporation of HNO3 and H2O formed during the decomposition process. The strand burner experiments have revealed an increase in the linear burning rate by over 50% at 12−14 MPa, explained by reaching the critical pressure of the liquid. Other observed pressure dependencies of the burning rate include a decrease at 9–12 MPa, a plateau at 14–19 MPa, a decrease at 20 MPa, and an increase at 22–30 MPa.

Co-Electrolysis-Assisted Decomposition of Hydroxylammonium Nitrate-Fuel Mixtures Using Stainless Steel-Platinum Electrodes.

Hydroxylammonium nitrate (HAN) is a promising green propellant because of its low toxicity, high volumetric specific impulse, and reduced development cost. Electrolytic decomposition of HAN is an efficient approach to prepare it for further ignition and combustion. This paper describes the investigation of a co-electrolysis effect on electrolytic decomposition of HAN–fuel mixtures using stainless steel–platinum (SS–Pt) electrodes. For the first time, different materials were utilized as electrodes to alter the cathodic reaction, which eliminated the inhibition effect and achieved a repeatable and consistent electrolytic decomposition of HAN solution. Urea and methanol were added as fuel components in the HAN–fuel mixtures. When the mass ratio of added urea ≥20%, the electrolytic decomposition of a HAN–urea ternary mixture achieved 67% increment in maximum gas temperature (Tgmax) and 185% increment in overall temperature increasing rate over the benchmark case of HAN solution. The co-electrolysis of urea released additional electrons into the mixtures and enhanced the overall electrolytic decomposition of HAN. In contrast, the addition of methanol did not improve the Tgmax but only increased the overall temperature increasing rate. This work has important implications in the development of an efficient and reliable electrolytic decomposition system of HAN and its mixtures for propulsion applications.

Performance of Pt and Ir Supported on Mesoporous Materials for Decomposition of Hydroxylammonium Nitrate Solution.

The catalytic decomposition of hydroxylammonium nitrate (HAN) was investigated using a series of platinum and iridium supported on mesoporous materials. In this study, MMZY, KIT-6, and SBA-15 were used as supports. The effects of the active metal and the pore structure of the catalysts on decomposition of HAN solution were studied. The activity of the platinum catalysts supported on mesoporous material is much superior to that of the iridium catalysts on the same support. The Pt(10)/SBA-15 catalyst showed excellent decomposition activity and was the best among the catalysts tested here, which seemed to be because of the pore structure of Pt(10)/SBA-15. Because the pore size of Pt(10)/SBA-15 is larger than that of Pt(10)/MMZY and Pt(10)/KIT-6, it is more advantageous for diffusion of reactant and product gas. The activity of the catalyst increased as the amount of Pt loaded on the SBA-15 support increased.

Evaluation of hydroxylammonium nitrate (HAN) decomposition using bifunctional catalyst for thruster application

Monopropellant thruster technology is at the cusp of revival with new age ionic liquids which are safe, less toxic and high performing emerging as substitutes for traditionally used hydrazine. One such promising candidate is Hydroxylammonium nitrate (HAN). Current study explores an iridium metal impregnated bifunctional variant of an earlier developed doped cerium oxide catalyst for HAN decomposition. The performance of bifunctional catalyst was compared against unsupported cerium oxide catalyst and conventional iridium over gamma alumina catalyst. Thermal analysis was the primary test used for performance evaluation and was subsequently followed up in a batch reactor to evaluate the durability of the catalyst to extreme high temperature exposure. Characterization of catalyst before and after decomposition reaction was comprehensively conducted using surface area analysis, SEM/EDS, XRD and XPS. Results did suggest promotional effect of iridium over doped ceria support as demonstrated through increased pressure build-up and rate of pressure-rise.

Experimental and analytical study on electrolytic decomposition of HAN-water solution using graphite electrodes

This paper describes the investigation of electrolytic decomposition of hydroxylammonium nitrate (HAN)-water solution using graphite electrodes. The decomposition reaction consists of two stages. Electrical energy was consumed for 5 s before the stage 1 reaction ceased. An interesting phenomenon was observed in the stage 2 reaction where the decomposition of HAN resumed after the power supply was switched off. A series of spectroscopy and microscopy analyses confirmed that the production of nitric oxide (NO) in the stage 1 reaction causes the formation of nitrous acid (HNO2), which leads to a further autocatalytic reaction. The reaction mechanisms were proposed and compared with the case of using copper electrodes. Graphite electrodes were demonstrated as more energy efficient in initiating the electrolytic decomposition of HAN-water solution as lower energy consumption (342 J) was achieved in comparison to copper electrodes (1926 J).

Influence of Activated Carbon on the Thermal Decomposition of Hydroxylammonium Nitrate

This paper presents experimental results for the thermal decomposition of hydroxylammonium nitrate (HAN) in the presence of activated carbon with a high specific surface (up to 3000 m2/g) obtained by activation of rice husk with potassium hydroxide at a temperature of 700°C in a rotating spherical furnace. The addition of activated carbon reduces the temperature of the onset of decomposition of HAN from 185 to 86 ± 0.5°C. The burning rate of HAN doped with activated carbon increases to 400 mm/s at an overpressure of 6 MPa. It has been shown that the addition of activated carbon reduces the amount of NO x gases produced by decomposition to 30%.

Decomposition of hydroxylammonium nitrate in a low pressure flowing thermal capillary system

Hydroxylammonium nitrate (HAN) is a potential monopropellant for plasma-based electric propulsion thrusters. However, little is known about the thermal decomposition of HAN at pressures typically encountered in aerospace applications. In this study, using residual gas analysis (RGA) we examine the production of nitrous oxide (N2O), nitrosamide (H2N2O), and nitroxyl (HNO) by thermally decomposing HAN exposed to pressures between 2 and 50 mTorr. Initial expectation was that NO and NO2 would be the primary species producing signal at 30 and 46 m/z respectively. Kinetic modeling studies of HAN solution, however, attributed these signals to HNO and H2N2O, respectively. Thermal decomposition was achieved by passively injecting an aqueous HAN solution into a flowing thermal capillary and detecting the gas products with mass spectrometry. N2O and H2N2O produced relatively small signal with a minor pressure dependence at low temperatures and no pressure dependence above ~460 K. HNO produced a much larger signal relative to N2O and H2N2O and exhibited a high level of pressure dependence as temperature increased above the onset of thermal decomposition, ~393 K. These results indicate that the formation of N2O, H2N2O, and HNO is occurring not only in the bulk solution but possibly on the surface of the aqueous HAN solution and in the vapor phase immediately above the solution surface. The kinetics and mechanism of possible decomposition pathways to form these species are discussed.

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.

Adsorption and decomposition of monopropellant molecule HAN on Pd(100) and Ir(100) surfaces: A DFT study

We have performed density functional theory calculations with the generalized gradient approximation to investigate the catalytic decomposition reactions of one of the most promising monopropellants, hydroxylammonium nitrate (HAN), on two catalytically active single crystal Pd(100) and Ir(100) surfaces, aiming at exploring different reaction pathways and reactivities of these two surfaces towards the catalytic decomposition of HAN. We find that the HAN molecule binds both the Pd(100) and Ir(100) surfaces molecularly in different orientations with respect to the surface. The HONO elimination is found to possess the lowest activation energy on the Pd(100) surface; whereas, NO2 elimination is predicted to show the lowest activation energy on the Ir(100) surface. Exothermicities associated with different reaction steps are also discussed. This is the first theoretical report on the catalytic decomposition reactions of the HAN molecule on the single crystal Pd(100) and the Ir(100) surfaces using the periodic DFT calculations.

Resonant Laser Ignition Study of HAN-HEHN Propellant Mixture

Resonant laser ignition at wavelengths in the UV and IR was demonstrated for hydroxyl ammonium nitrate (HAN)–hydroxyethylhydrazinium nitrate (HEHN) mixtures. This prototypical ionic liquid propellant was successfully and reliably ignited under confinement with single laser pulses in the mid IR at 2.94 and 10.6 µm. UV wavelengths at 193 and 248 nm were also resonant with sample absorption, but they did not lead to ignition with the available excimer laser pulse energies. The results are consistent with absorption of the IR laser pulse within a short path length, efficient V→T relaxation, and thermal decomposition of HAN that leads to additional chemical reaction and ignition of milligram samples within tens of microseconds.

Catalytic Decomposition of Hydroxyl Ammonium Nitrate at Room Temperature

A series of alumina- or silica-supported precious metal catalysts have been screened for catalytic decomposition of hydroxyl ammonium nitrate by a thermal analysis method. Ir/SiO2 exhibits the highest catalytic activity, on which 80% hydroxyl ammonium nitrate can be completely decomposed even at 20.7°C, manifesting its great potential as an environmentally benign monopropellant. H2 chemisorption on Ir/SiO2 and Ir/Al2O3 suggests that a large particle size seems to be favorable for this reaction.

A model for the deflagration of aqueous solutions of hydroxylammonium nitrate

Deflagration theory of the type that has achieved success for describing burning rates of ammonium perchlorate and nitramine propellants is applied to aqueous solutions of hydroxyl-ammonium nitrate (HAN). The theory considers the chemical kinetics, energetics and fluid dynamics of the combustion zone, making use of asymptotic analysis to decide what combustion mechanisms are consistent with available data. The model is used in conjunction with experimental results to obtain frequency factors and overall activation energies for HAN decomposition. Results suggest that deflagration rates are controlled by condensed-phase combustion with production of water dominating the heat release and that phase and chemical equilibrium are not approached in the condensed-phase combustion zone. The results also support the postulate that the rate of HAN decomposition is controlled by the rate of proton transfer from NH 3 OH + to NO 3 − . Theoretical predictions of deflagration rates compare favorably with experimental data.

The burning rate of hydroxylammonium nitrate-based liquid propellants

To improve the understanding of the physical processes which occur during the combustion of liquid propellants (LP), a strand burner was used to study hydroxylammonium nitrate-based LP flames. From observations of the combustion of LP in such an arrangement, much has been deduced of the physical processes that occur during LP ignition and combustion. Combustion experiments were performed in which mixtures of the salts hydroxylammonium nitrate (HAN) and triethanolammonium nitrate (TEAN) in water were ignited by an electric discharge in a vessel at pressures of up to 30 MPa. The mixtures were contained in a strand burner that permitted visual observation of LP combustion at nearly constant pressure. Images of the combustion were obtained through windows, in the pressure vessel by backlit photography, at a framing rate of 60 frames per second, with an exposure time of 100 microseconds. These images clearly showed the movement of a liquid-gas interface and a bright flame during LP combustion. Results of experiments conducted during turbulent combustion are: (1) the combustion of HAN-based LP occurs in two stages in which the liquid phase decomposition of HAN is followed by the decomposition of TEAN, (2) the turbulent combustion rate of LP 1846 decreases with increasing pressure. This variation of apparent burning rate with pressure, a result which is not seen in single component propellant combustion, is attributed to changes in the stability of the liquid-gas interface with pressure, and (3) a model of the combustion of HAN-based liquid propellants as it occurs in bulk has been presented, showing the reaction sequence of the components of HAN-based liquid propellants.