Hydroxylammonium Nitrate Solution Research Articles

Experimental studies on effects of electrode material and voltage on electrolytic decomposition of Hydroxylammonium nitrate solution

Hydroxylammonium nitrate (HAN)-based propellants have been attracting attention as future low-toxicity liquid propellants owing to their ionic properties. HAN-based propellants are primarily decomposed via catalytic reactions. However, this method has several drawbacks, such as catalyst preheating and deactivation. Therefore, in this study, the electrical characteristics of the electrolysis process of a HAN solution, as well as the by-product gases and reaction residues were analyzed considering the electrode material and applied voltage as the controlling variables. SUS (a designation of stainless steel) electrodes have higher durability than Cu electrodes; however, their decomposition proceeds more slowly because of the suppression of the initial reaction at low voltages. This study confirmed that this suppression could be significantly addressed at a high voltage of 400 V. The investigated electrolytic decomposition mechanism of the HAN solution was validated by analyzing the gases generated during the electrolysis and residue after the reaction, using Fourier-transform infrared spectroscopy. This study has important implications for the development of volume-limited propulsion systems, such as micro-thrusters.

Experimental Studies on Parametric Effects and Reaction Mechanisms in Electrolytic Decomposition and Ignition of HAN Solutions.

The green propellant hydroxylammonium nitrate (HAN) is a good alternative to the conventional propellants in space propulsion applications because of its low toxicity and high energy density. Electrolytic decomposition and ignition of HAN solution, an ionic liquid, is a promising approach. In this work, comprehensive experimental studies were conducted to examine effects of different electrolytic voltages, electrode surface areas, and HAN concentrations on the decomposition process. In the test cases, an optimum electrolytic voltage appears to exist, which leads to the fastest decomposition process. As the voltage increases, a larger electrode surface area on the anode side should be used to overcome an anodic inhibition phenomenon and accelerate the electrolytic process. A high concentration of HAN solution is preferred for its decomposition and ignition. Results also reveal that the electrolytic process of a HAN solution could eventually trigger thermal decomposition reactions, raising the maximum temperature to around 550 K at the final stage. A detailed chemical reaction mechanism was proposed, based on the experimental data and FTIR spectra analyses. Results obtained herein would provide fundamental understandings on the complex electrochemical and physical processes and should be helpful for future applications of the electrolytic decomposition and ignition technology.

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.

Impact of HAN Ternary Propellant System Decomposition on Catalytic Sustainability

AbstractAqueous solution of Hydroxylammonium nitrate (HAN) in combination with a suitable fuel has been explored as a promising high performing green monopropellant in recent times. The current study primarily explores the effect of the addition of a fuel component into HAN solution on the sustainability of a recently developed catalyst which was examined for the only binary system consisting of HAN and water. The HAN ternary system examined was HAN: methanol: water in 70 : 15 : 15 (w/w) composition. The endurance of an ‘iridium over alumina’ catalyst and an indigenously developed cobalt doped ceria‐based catalyst was analysed using a batch reactor wherein a pressure rise during decomposition of propellant whilst a pulse mode operation was monitored. Catalysts were also characterized via SEM/EDS, XRD, and XPS to identify changes over the period of sequential injection in the batch reactor. Doped ceria catalyst was found to be far robust and resistant to any poisoning when compared to iridium catalyst at run time of the operation involving nearly 45 sequential injections of propellant over the catalyst.

Decomposition of Energetic Ionic Liquid Over IrCu/Honeycomb Catalysts.

The objective of this study is to elucidate the influence of a loading procedure of iridium and copper oxides over cordierite honeycomb support on catalytic performance during the decomposition of a hydroxylammonium nitrate (HAN) solution. Iridium and copper composite oxides were successfully supported on the cordierite honeycomb at the same time by repeating the wash coating process more than 2 times. Through the wash coating process, Cu and Ir were supported up to 43.4% and 4.9%, respectively. The cordierite honeycomb without active metal plays little role as a catalyst to lower the decomposition temperature. It was found that IrCu/honeycomb-2 catalyst, which was prepared by repeating the wash coating procedure twice, is an optimal catalyst for the decomposition of HAN solution. The IrCu/honeycomb-2 catalyst had the effect of lowering the decomposition onset temperature by 27.1°C compared to thermal decomposition.

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.

Calorimetric study on electrolytic decomposition of hydroxylammonium nitrate (HAN) ternary mixtures

Electrolytic decomposition of hydroxylammonium nitrate (HAN) is appealing for development of chemical micropropulsion system due to its effectiveness in thermal management. In this paper we present the decomposition characteristics and behaviour of various HAN ternary mixtures prepared according to 0 Oxygen Balance (0 OB). There are multiple stages of decomposition depending on the type of fuels added into the HAN solution. While concentrated HAN solution (73 wt%) has only single stage of decomposition, the saccharides-based HAN ternary mixtures has three stages reaction with increased energy release. The addition of nitrogen-rich compounds has sustained the electrolytic decomposition process into the second stage of reaction, which produced the highest decomposition temperature. The study also reveals a linear relationship between the electrical resistivity of HAN ternary mixture and reaction rate in the first stage of reaction, indicating the presence of Joule heating in the process. The influence of electrical resistivity of the ternary mixture became negligible in the second stage of reaction. This work concludes the importance of combined electrical and thermal energy in the first stage decomposition of HAN ternary mixtures.

Thermoanalytical studies on the thermal and catalytic decomposition of aqueous hydroxylammonium nitrate solution

Green monopropellants based on hydroxylammonium nitrate (HAN) are a promising alternative to hydrazine in space propulsion systems. In the present paper, thermal and catalytic decomposition of aqueous HAN solution was studied using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and mass spectrometry. The tests were conducted at heating rates of 1, 2.5, 5, and 10 K/min. The values of the apparent activation energy obtained for thermal decomposition using TGA and DSC are 62.2 ± 3.7 kJ/mol and 57.5 ± 3.5 kJ/mol, respectively, and they are in agreement with the literature data for solid HAN and solutions with high concentrations of HAN. The obtained values of the pre-exponential factor, 2.24 × 104 s−1 for TGA and 3.55 × 103 s−1 for DSC, are lower by six to seven orders of magnitude than those reported in the literature for aqueous HAN solutions, apparently because of full vaporization of water from the HAN solution at the beginning of the TGA and DSC tests. The use of an iridium/rhodium foam catalyst decreased the temperature of full decomposition by over 60 °C. The value of the apparent activation energy obtained for the catalytic decomposition using TGA is 63.9 ± 2.5 kJ/mol, while the obtained value of the pre-exponential factor is 3.31 × 105 s−1.

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.

Thermal stability of hydroxylammonium nitrate (HAN)

Among the various non-toxic chemicals being explored as a replacement for hydrazine, hydroxylammonium nitrate (HAN) appears to be most promising and most extensively explored monopropellant for space thrusters. The paper discusses some of the thermal stability issues related to highly concentrated HAN, ensuing from the route adopted for its preparation. It was observed that discharge of metal ions like barium and calcium ions from the reactants and the by-products into HAN solution during preparation could influence the thermal and catalytic decomposition behavior of HAN which is critical for its use in space thrusters. Influence of traces of nitric acid on the thermal decomposition behavior of HAN was also examined.

Role of electrodes in ambient electrolytic decomposition of hydroxylammonium nitrate (HAN) solutions

Decomposition of hydroxylammonium nitrate (HAN) solution with electrolytic decomposition method has attracted much attention in recent years due to its efficiencies and practicability. However, the phenomenon has not been well-studied till now. By utilizing mathematical model currently available, the effect of water content and power used for decomposition was studied. Experiment data shows that sacrificial material such as copper or aluminum outperforms inert electrodes in the decomposition of HAN solution. In the case of using copper wire to electrolyse HAN solutions, approximately 10seconds is required to reach 100°C regardless of concentration of HAN. In term of power consumption, 100W–300W was found to be the range in which decomposition could be triggered effectively using copper wire as electrodes.

Thermodynamic properties of aqueous solutions of ammonium Nitrate salts

We present Differential Scanning Calorimetry (DSC) results on Hydroxyl Ammonium Nitrate (HAN) solutions and Triethanol Ammonium Nitrate (TEAN) solutions with varying concentrations. These results are used to generate phase diagrams of these solutions. The results of the melting points of these liquids are compared with the theoretical calculations of the depression of melting points. The melting temperatures of the HAN solutions at some specified concentration range are predicted rather well using the two electrolyte assumption. The phase diagram of the TEAN solutions explains an instability with respect to phase separation of this liquid.

Thermal decomposition of energetic materials. 8. Evidence of an oscillating process during the high-rate thermolysis of hydroxylammonium nitrate, and comments on the interionic interactions

Relatively dry, solid hydroxylammonium nitrate (HAN), (NH/sub 3/OH)NO/sub 3/, was examined by IR spectroscopy from 170 K to well above its decomposition point. The modes in the 2600-2950-cn/sup -1/ range are assigned to -NH/sub 3//sup +/ combination tones, rather than to nu(OH) as was recently proposed for aqueous HAN solutions. Frequency-to-distance correlations for solid HAN cast doubt on the viability of using nu(NH/OH) fundamentals to determine accurate interionic distances in HAN. Several of the thermolysis products of HAN (HNO/sub 3/, N/sub 2/O, and NO/sub 2/) were quantified in real time by rapid-scan FTIR and were found to oscillate when solid HAN and aqueous HAN solutions were pyrolyzed at a high rate (130 K s/sup -1/) with pressures greater than or equal to 100 psi of Ar. The onset of the oscillation is delayed by increasing the initial H/sub 2/O content. The period of oscillation at constant pressure increases with the heating rate. Some comments on the reactions that may lead to the decomposition products of HAN are made based on these findings. 28 references, 5 figures, 1 table.