Influences of aging on thermal decomposition mechanism of high performance oxidizer ammonium dinitramide

Ammonium dinitramide (ADN) is one of the several promising new solid propellant oxidizers. ADN is of interest because its oxygen balance and energy content are high, and it also halogen-free. One of the most important characteristics of a propellant oxidizer, however, is stability and ADN is known to degrade to ammonium nitrate (AN) during storage, which will affect its performance. This study focused on the effects of aging on the thermal decomposition mechanism of ADN. The thermal behaviors of ADN and ADN/AN mixtures were studied, as were the gases evolved during their decomposition, using differential scanning calorimetry (DSC), thermogravimetry–differential thermal analysis-infrared spectrometry (TG–DTA-IR), and thermogravimetry–differential thermal analysis-mass spectrometry (TG–DTA-MS). The results of these analyses demonstrated that the decomposition of ADN occurs via a series of distinct stages in the condensed phase. The gases evolved from ADN decomposition were N₂O, NO₂, N₂, and H₂O. In contrast, ADN mixed with AN (to simulate aging) did not exhibit the same initial reaction. We conclude that aging inhibits early stage, low temperature decomposition reactions of ADN. Two possible reasons were proposed, these being either a decrease in the acidity of the material due to the presence of AN, or inhibition of the acidic dissociation of dinitramic acid by NO ₃ ^? .     

Thermal decomposition of the high-performance oxidizer ammonium dinitramide under pressure

Ammonium dinitramide (ADN) is a promising new oxidizer for solid propellants because it possesses both high oxygen balance and high energy content, and does not contain halogen atoms. A necessary characteristic of solid propellants is chemical stability under various conditions. This study focused on the thermal decomposition mechanism of ADN under pressurized conditions. The pressure was adjusted from 0.1 to 6 MPa, while ADN was heated at a constant rate. The exothermal behavior and the decomposition products in the condensed phase during heating were measured simultaneously using pressure differential scanning calorimetry (PDSC) and Raman spectrometry. PDSC analyses showed the multiple stages of exotherms after melting. The exothermal behavior at low temperatures varied with pressure. Analysis of the decomposition products indicated that ammonium nitrate (AN) was generated during decomposition of ADN at all pressures. At normal pressure, AN was produced at the same time as start of exotherm. However, the temperature at which the ratio of ADN in chemical species in the condensed phase began to decrease under high pressure was higher than that at atmospheric pressure despite the existence of significant exotherm. At initial stage, thermal decomposition of ADN that does not generate AN was thought to be promoted by increased pressure.     

没食子酸铋锆的制备、表征及其燃烧催化作用

以没食子酸、硝酸铋和硝酸氧锆为原料, 首次合成出了双金属有机盐——没食子酸铋锆, 采用有机元素分析、X射线荧光(XRF)光谱和傅里叶变换红外(FTIR)光谱对其进行了表征. 在程序升温条件下, 利用热重(TG)分析、差示扫描量热法(DSC)、固相原位反应池/FTIR 联用技术, 研究了没食子酸铋锆的热行为和热分解机理,描述了没食子酸铋锆的热分解过程, 分析得出其最终分解产物为Bi₂O₃、ZrO₂和C. 利用螺压工艺制备了含没食子酸铋锆的推进剂样品, 研究了没食子酸铋锆对双基(DB)推进剂燃烧性能的影响, 分析了其燃烧催化作用. 结果表明, 没食子酸铋锆对双基推进剂的燃烧具有良好的催化作用, 是一种高效的燃烧催化剂; 没食子酸铋锆热分解的最终产物是催化燃烧的主要物质, 锆和碳则起辅助催化的作用.     

酒石酸铅锆的制备、表征及其燃烧催化作用

以酒石酸、硝酸氧锆和硝酸铅为原料,合成出了双金属盐酒石酸铅锆,采用有机元素分析、X射线荧光光谱和FTIR对其进行了表征。在程序升温条件下,利用TG/DTG、DSC、固相原位反应池/FTIR联用技术,研究了酒石酸铅锆的热行为和热分解机理,描述了酒石酸铅锆的热分解过程,分析得出其最终分解产物为ZrO2、PbO和C。利用螺压工艺制备了含酒石酸铅锆的推进剂样品,研究了酒石酸铅锆对双基系推进剂燃烧性能的影响,分析了其燃烧催化作用。结果表明,酒石酸铅锆对双基系推进剂的燃烧具有良好的催化作用,是一种高效的燃烧催化剂;酒石酸铅锆热分解的最终产物PbO是催化燃烧的主要活性物质,推进剂燃烧过程中形成了氧化铅-铅循环催化体系,而锆和碳则起辅助催化的作用。     

Thermophysical studies on uranyl nitrate hexahydrate–Iron (III) nitrate nonahydrate system

Individual nitrates, UO₂(NO₃)₂·6H₂O and Fe(NO₃)₃·9H₂O as well as their binary mixtures in various mol ratios have been studied using simultaneous thermal techniques and X-ray powder diffraction measurements. Nature and stoichiometry of hydroxynitrates of iron and uranium were altered by changing the heating rates for the equal mass of binary nitrate mixtures under identical gas flow conditions. Evolved gas analysis and thermogravimetric measurements indicated the absence of direct interaction between two nitrates in the binary nitrate mixtures. Both the nitrates decomposed independently in the mixtures to their respective oxides. These results have been supported by X-ray powder diffraction measurements. Phase diagram of UO₂(NO₃)₂·6H₂O–Fe(NO₃)₃·9H₂O system containing 0–100 mol% of UO₂(NO₃)₂·6H₂O was constructed using differential thermal analysis technique. The formation of the eutectic at 33 °C for 50 mol% uranyl nitrate hexahydrate–50 mol% iron (III) nitrate nonahydrate mixture has been observed for the first time.     

Synthesis of nanosized bismuth ferrite (BiFeO3) by a combustion method starting from Fe(NO3)3·9H2O-Bi(NO3)3·9H2O-glycine or urea systems

Two bismuth ferrite potential precursors systems, namely Fe(NO₃)₃·9H₂O-Bi(NO₃)₃·9H₂O-glycine/urea with different metal nitrate/organic compound molar ratios have been investigated in order to evaluate their suitability as BiFeO₃ precursors. The presence into the precursor of both reducing (glycine and urea) and oxidizing (NO₃⁻) components, modifies dramatically their thermal behaviour comparative with the raw materials, both from the decomposition stoichiometries and temperature occurrence intervals points of view. Also, the thermal behaviour is dependent on the fuel nature but practically independent with the fuel content. The fuel nature influences also some characteristics of the resulted oxides (phase composition, morphologies). In the case of the oxides prepared using urea as fuel, a faster evolution toward a single phase composition with the temperature rise is evidenced, the formation of the BiFeO₃ perovskite phase being completed in the temperature range of 500–550°C.     

Thermal properties of 1,2,4-triazole-3-one and copper nitrate mixtures

1,2,4-Triazole-3-one (TO) is anticipated to have applications as a high performance alternative gas generating agent, while basic copper nitrate (BCN) is typically used as the oxidizing agent in air bag systems. In order to obtain a better understanding of the thermal properties of TO/BCN mixtures, thermal behavior was investigated using the differential scanning calorimetry. Mixtures of TO with copper, copper oxide, and trihydrated copper nitrate (Cu(NO₃)₂·3H₂O) were also examined for comparison purposes. Samples were prepared at TO/BCN ratios (on a per mass basis) of 10/0, 7/3, 5/5, 3/7, 2/8, 1.6/8.4, 1/9, and 0/10. The endothermic onset temperatures for TO/BCN mixtures were lower than those for either pure TO or pure BCN. TO/BCN mixtures exhibited an initial exothermic peak immediately after an endothermic peak, in the range of 219–234 °C. TO/BCN mixtures with ratios of 3/7, 2/8, 1.6/8.4, and 1/9 displayed a second series of exothermic peaks in the range of 260–300 °C, which appear to result from the oxidation–reduction reaction of previously formed intermediate species with NO₂ and NO generated by unreacted BCN. The TO/CuO mixtures are believed to undergo reaction between molten TO and CuO at approximately 230 °C. In general, the presence of copper was shown to be effective at promoting the decomposition of TO. The reaction between TO and Cu(NO₃)₂·3H₂O seems to be initiated by the melting of Cu(NO₃)₂·3H₂O, following which TO reacts with nitric acid resulting from the dissociation of Cu(NO₃)₂·3H₂O. Overall, the triggering event for the reaction between TO and each of the copper nitrate species is a phase change of one of the two mixture components.     

Thermal behavior of new oxidizer ammonium dinitramide

Ammonium dinitramide (ADN) is a promising new oxidizer for solid propellants because of its high oxygen balance and high energy content, and halogen-free combustion products. One of the characteristics needed for solid propellants is stability. Heat, light, and moisture are factors affecting stability during storage, manufacture, and use. For practical use of ADN as a solid propellant, clarification of the mechanism of decomposition by these factors is needed to be able to predict lifetime. This study focused on thermal decomposition of ADN. Exothermal behavior of ADN decomposition was measured by isothermal tests using high-sensitive calorimetry (TAM) and non-isothermal tests using differential scanning calorimetry (DSC). Based on these results, analysis of the decomposition kinetics was conducted. The activation energy determined by TAM tests was lower than that from DSC tests. Thus, the decomposition path in TAM tests was different from that in DSC tests. The amount of ADN decomposition predicted from TAM tests was closer to that found under real storage conditions than the amount of decomposition predicted from DSC tests. Non-isothermal tests may not be able to precisely predict the lifetime of materials with a decomposition mechanism that changes with temperature, such as ADN. The lifetime predicted from DSC results was much longer than that from TAM tests especially at low temperature. It is necessary to use isothermal tests to predict the long-term stability at low temperature.     

The thermal decomposition of the new energetic material ammoniumdinitramide (NH4N(NO2)2) in relation to Nitramide (NH2NO2) and NH4NO3

This qualitative study examines the response of the novel energetic material ammonium dinitramide (ADN), NH₄N(NO₂)₂, to thermal stress under low heating rate conditions in a new experimental apparatus. It involved a combination of residual gas mass spectrometry and FTIR absorption spectroscopy of a thin cryogenic condensate film resulting from deposition of ADN pyrolysis products on a KCl window. The results of ADN pyrolysis were compared under similar conditions with the behavior of NH₄NO₃ and NH₂NO₂ (nitramide), which served as reference materials. NH₄NO₃ decomposes into HNO₃ and NH₃ at 182°C and is regenerated on the cold cryostat surface. HNO₃ undergoes presumably heterogeneous loss to a minor extent such that the condensed film of NH₄NO₃ contains occluded NH₃. Nitramide undergoes efficient heterogeneous decomposition to N₂O and H₂O even at ambient temperature so that pyrolysis experiments at higher temperatures were not possible. However, the presence of nitramide can be monitored by mass spectrometry at its molecular ion (m/? 62). ADN pyrolysis is dominated by decomposition into NH₃ and HN(NO₂)₂ (HDN) in analogy to NH₄NO₃, with a maximum rate of decomposition under our conditions at approximately 155°C. The two vapor phase components regenerate ADN on the cold cryostat surface in addition to deposition of the pure acid HDN and H₂O. Condensed phase HDN is found to be stable for indefinite periods of time at ambient temperature and vacuum conditions, whereas fast heterogeneous decomposition of HDN at higher temperature leads to N₂O and HNO₃. The HNO₃ then undergoes fast (heterogeneous) decomposition in some experiments. Gas phase HDN also undergoes fast heterogeneous decomposition to NO and other products, probably on the internal surface (ca. 60°C) of the vacuum chamber before mass spectrometric detection. © 1993 John Wiley & Sons, Inc.     

A theoretical study on the structure and hygroscopicity of ammonium dinitramide

Density functional theory (DFT) and the dispersion corrected DFT have been used to investigate the hygroscopicity of ammonium dinitramide (ADN). Calculation results show that the gaseous ADN has a strong hydrogen bond. But the ionic pair structure NH₄ ⁺ · N(NO₂)^? is stabilized upon the addition of water molecules. Natural bond orbital calculations suggest that the intra- and intermolecular orbital interactions LP(O) → σ*(N–H) or LP(O) → σ*(O–H) make the system stabilized as a whole. En energy decomposition analysis reveals that the interactions between ADN and H₂O are dominated by the electrostatic and orbital interactions. The formation reactions become more spontaneous with the increasing number of water molecules but can be weakened by the growing temperature from 200 to 400 K. Moreover, the molecular dynamic method is applied to explore a more realistic cluster model to study the interactions between ADN and H₂O.     

Effect of sulfate additives on the 60Co gamma ray induced decomposition of lanthanum,europium and terbium nitrates in solid state

Gamma radiolysis of binary mixtures of La(NO₃)₃·6H₂O, Eu(NO₃)₃·6H₂O and Tb(NO₃)₃·6H₂O along with their respective sulfates have been studied over a wide range of absorbed doses up to 500 kGy. Radiolytic decomposition of the nitrate salts is affected by the concentration of the sulfate in the binary mixture as well as on the absorbed dose. G(NO₂⁻) values calculated on the basis of electron fraction of the nitrate salt in the binary mixture are enhanced by 10²–10³ times at >90 mol% of the sulfate additive. A study of binary mixtures of lanthanum nitrate with other mono-, bi-, tri- and tetra-valent sulfate additives shows that G(NO₂⁻) values are also affected by the nature and oxidation state of the cation including electron configuration. ESR and TL measurements suggest the formation of radical species, which may interact with the radical species of nitrate (NO₃²⁻, NO₂ etc.) causing enhanced decomposition by energy transfer. A possible mechanism of decomposition has been suggested. Anomalous behavior of Eu(NO₃)₃·6H₂O has been correlated with the electronic configuration and +2 oxidation state of Eu.     

Physico-chemical characterization of thermal decomposition course in zinc nitrate-copper nitrate hexahydrates

This study reports experimental investigations by non-isothermal TG/DSC analysis of Zn(NO₃)₂·4H₂O, Cu(NO₃)₂·4H₂O and their mixtures of known compositions in the temperature range 30–1200°C. Solid/liquid transitions in the sealed samples of the hexahydrate salts and their mixtures were also studied by DSC in the temperature range 0–60°C. The mixture with composition 0.85Zn(NO₃)₂·6H₂O+0.15Cu(NO₃)₂·6H₂O showed single melting peak at 29°C. This mixture was chosen for detailed studies. Melting temperature and heat of fusion of single salt hexahydrates and of the mixture were calculated from DSC endotherms. The different stages in the thermal decomposition processes have been established. The intermediate and the final solid products of the thermal decomposition were analyzed by XRD. The scheme and the decomposition temperature depended on the composition of the starting material. The final decomposition products were CuO (monoclinic), Cu₂O (cubic), ZnO (hexagonal) and their mixtures with the defined crystalline structures. Possible influence of the addition of CuCl₂·2H₂O into the mixture 0.85Zn(NO₃)₂·6H₂O+0.15Cu(NO₃)₂·6H₂O and a gel combustion technique of the precursor preparation, on the composition and morphology of the solid decomposition products, were also studied. The gel combustion technique, using citric acid added to a mixture of 0.85Zn(NO₃)₂·6H₂O+0.15Cu(NO₃)₂·6H₂O, was applied in an attempt to obtain mixed Zn/Cu oxides of a particular mole ratio. The morphology of the solid decomposition products was examined by SEM.     

Thermoanalytical investigation of relative reactivity of some nitrate oxidants in tin-fueled pyrotechnic systems

In order to investigate relative reactivity of different oxidants in solid-state reactions of pyrotechnic mixtures, thermal properties of Sn + Sr(NO₃)₂, Sn + Ba(NO₃)₂, and Sn + KNO₃ pyrotechnic systems have been studied by means of TG, DTA, and DSC methods and the results compared with those of pure oxidants. The apparent activation energy (E), ΔG ^#, ΔH ^#, and ΔS ^# of the combustion processes were obtained from the DSC experiments. The results showed that the nature of oxidant has a significant effect on ignition temperature, and the kinetic of the pyrotechnic mixtures’ reactions, and the relative reactivity of these mixtures was found to obey in the following order: Sn + Sr(NO₃)₂ > Sn + Ba(NO₃)₂ > Sn + KNO₃.     

Interference of nitrite and nitrogen dioxide on mercury and selenium determination by chemical vapor generation atomic absorption spectrometry

In this study, a systematic investigation was performed concerning the interference of nitrogen oxides on the determination of selenium and mercury by hydride generation atomic absorption spectrometry (HG AAS) and cold vapor atomic absorption spectrometry (CV AAS). The effect of nitrate, nitrite and NO₂ dissolved in the condensed phase was evaluated. No effect of NO₃⁻ on Se and Hg determination was observed up to 100 mg of sodium nitrate added to the reaction vessel. The Se signal was reduced by about 80% upon the addition of 6.8 mg NO₂⁻. For Hg, no interference of nitrite was observed up to 20 mg of NO₂⁻. A complete suppression of the Se signal was observed when gaseous NO₂ was introduced into analytical solutions. For Hg, a signal decrease between 8 and 13% occurred. For Se, bubbling argon or heating the solution was not able to recover the original absorbance values, whereas Hg signals were recovered with these procedures. When gaseous NO₂ was passed directly into the atomizer, Se signals decreased similarly to when NO₂ was bubbled in analytical solutions. The addition of urea, hydroxylamine hydrochloride and sulfamic acid (SA) was investigated to reduce the NO₂ effect in sample digests containing residual NO₂, but only SA was effective in reducing the interference. Based on the results, it is possible to propose the use of SA to prevent interferences in Se and Hg determinations by HG AAS and CV AAS, respectively.     

Thermal decomposition studies of catalysed double base propellants

To understand the rote of lead salts of organic acids in the combustion of double base rocket propellants, thermal decomposition behaviour of propellants was studied bydta andtg methods. Catalysed propellants decomposed at lower temperatures than the control. Percent thermal decomposition of propellants containing lead salts was also higher. Rate constants were higher and energy of activation was lower for catalysed propellants. Results obtained suggest that condensed phase reactions may be the site for the action of lead salts in the combustion of double base propellants     

Sputtered ammonium dinitramide: Tandem mass spectrometry of a new ionic nitramine

The recently synthesized ammonium dinitramide (ADN) is an ionic compound containing the ammonium ion and a new oxide of nitrogen, the dinitramide anion (O₂N? N? NO₂^?). ADN has been investigated using high-energy xenon atoms to sputter ions directly from the surface of the neat crystalline solid. Tandem mass spectrometric techniques were used to study dissociation pathways and products of the sputtered ions. Among the sputtered ionic products were NH₄⁺, NO⁺, NO₂^?, N₂O₂^?, N₂O, N₃O₄^? and an unexpected high abundance of NO₃^?. Tandem mass spectra of the dinitramide anion reveal the uncommon situation where a product ion (NO₃^?) is formed in high relative abundance from metastable parent ions but is formed in very low relative abundance from collisionally activated parent ions. It is proposed that the nitrate anion is formed in the gas phase by a rate-determining isomerization of the dinitramide anion that proceeds through a four-centered transition state. The formation of the strong gas-phase acid, dinitraminic acid (HN₃O₄), the conjugate acid of the dinitramide anion, was observed to occur by dissociation of protonated ADN and by dissociation of ADN aggregate ions with the general formula [NH₄(N(NO₂)₂)_n] NH₄⁺, where n = 1–30.     

硝酸钕水合物热分解机理及脱水过程动力学的研究

本文采用TG-DTG法研究了Nd(NO)·nHO(n=6,5,4)的热分解行为,并通过IR对反应物、中间产物和最终产物进行了鉴别。发现中间产物有低水合物、无水盐和碱式盐,最终产物是氧化钕。另外,还进行了上述样品某些脱水过程的动力学研究,借助不同升温速率下的TG-DTG曲线,应用Kissinger法计算了它们脱水的表观活化能值,并利用DSC求出了它们的脱水焓值。     

A mechanism for the photochemical transformation of nitrate in snow

Photochemical reactions of trace compounds in snow have important implications for the composition of the atmospheric boundary layer in snow-covered regions and for the interpretation of concentration profiles in snow and ice regarding the composition of the past atmosphere. One of the prominent reactions is the photolysis of nitrate, which leads to the formation of OH radicals in the snow and to the release of reactive nitrogen compounds, like nitrogen oxides (NO and NO₂) and nitrous acid (HONO) to the atmosphere. We performed photolysis experiments using artificial snow, containing variable initial concentrations of nitrate and nitrite, to investigate the reaction mechanism responsible for the formation of the reactive nitrogen compounds. Increasing the initial nitrite concentrations resulted in the formation of significant amounts of nitrate in the snow. A possible precursor of nitrate is NO₂, which can be transformed into nitrate either by the attack of a hydroxy radical or the hydrolysis of the dimer (N₂O₄). A mechanism for the transformation of the nitrogen-containing compounds in snow was developed, assuming that all reactions took place in a quasi-liquid layer (QLL) at the surface of the ice crystals. The unknown photolysis rates of nitrate and nitrite and the rates of NO and NO₂ transfer from the snow to the gas phase, respectively, were adjusted to give an optimum fit of the calculated time series of nitrate, nitrite, and gas phase NO_x with respect to the experimental data. Best agreement was obtained with a ∼25 times faster photolysis rate of nitrite compared to nitrate. The formation of NO₂ is probably the dominant channel for the nitrate photolysis. We used the reaction mechanism further to investigate the release of NO_x and HONO under natural conditions. We found that NO_x emissions are by far dominated by the release of NO₂. The release of HONO to the gas phase depends on the pH of the snow and the HONO transfer rate to the gas phase. However, due to the small amounts of nitrite produced under natural conditions, the formation of HONO in the QLL is probably negligible. We suggest that observed emissions of HONO from the surface snow are dominated by the heterogeneous formation of HONO in the firn air. The reaction of NO₂ on the surfaces of the ice crystals is the most likely HONO source to the gas phase.     

Differences and similarities among hypoxanthinium nitrate hydrate structures

Crystals of hypoxanthinium (6‐oxo‐1H,7H‐purin‐9‐ium) nitrate hydrates were investigated by means of X‐ray diffraction at different temperatures. The data for hypoxanthinium nitrate monohydrate (C₅H₅N₄O⁺·NO₃^?·H₂O, Hx1 ) were collected at 20, 105 and 285 K. The room‐temperature phase was reported previously [Schmalle et al. (1990). Acta Cryst. C 46 , 340–342] and the low‐temperature phase has not been investigated yet. The structure underwent a phase transition, which resulted in a change of space group from Pmnb to P2₁/n at lower temperature and subsequently in nonmerohedral twinning. The structure of hypoxanthinium dinitrate trihydrate (H₃O⁺·C₅H₅N₄O⁺·2NO₃^?·2H₂O, Hx2 ) was determined at 20 and 100 K, and also has not been reported previously. The Hx2 structure consists of two types of layers: the `hypoxanthinium nitrate monohydrate' layers (HX) observed in Hx1 and layers of Zundel complex H₃O⁺·H₂O interacting with nitrate anions (OX). The crystal can be considered as a solid solution of two salts, i.e. hypoxanthinium nitrate monohydrate, C₅H₅N₄O⁺·NO₃^?·H₂O, and oxonium nitrate monohydrate, H₃O⁺(H₂O)·NO₃^?.     

Hydrogen Promoted Decomposition of Ammonium Dinitramide: an ab initio Molecular Dynamics Study

Thermal decomposition of a famous high oxidizer ammonium dinitramide (ADN) under high temperatures (2000 and 3000 K) was studied by using the ab initio molecular dynamics method.Two different temperature-dependent initial decomposition mechanisms were observed in the unimolecular decomposition of ADN, which were the intramolecular hydrogen transfer and N-NO₂ cleavage in N (NO₂)^-.They were competitive at 2000 K, whereas the former one was predominant at 3000 K.As for the multimolecular decomposition of ADN, four different initial decomposition reactions that were also temperature-dependent were observed.Apart from the aforementioned mechanisms, another two new reactions were the intermolecular hydrogen transfer and direct N-H cleavage in NH₄⁺.At the temperature of 2000 K, the N-NO₂ cleavage competed with the rest three hydrogen-related decomposition reactions, while the direct N-H cleavage in NH₄⁺ was predominant at 3000 K.After the initial decomposition, it was found that the temperature increase could facilitate the decomposition of ADN, and would not change the key decomposition events.ADN decomposed into small molecules by hydrogen-promoted simple, fast and direct chemical bonds cleavage without forming any large intermediates that may impede the decomposition.The main decomposition products at 2000 and 3000 K were the same, which were NH₃, NO₂, NO, N₂O, N₂, H₂O, and HNO₂.