The properties of ammonium dinitramide (ADN): Part 1, basic properties and spectroscopic data

Abstract

Basic properties and spectroscopic data for the energetic oxidizer ADN (Ammonium dinitramide (NH₄N(NO₂)₂)) are presented. The ADN used for this work was synthesized by a new efficient and environmentally friendly method. The method is based on a direct nitration of salts of sulfamic acid by ordinary mixed acid, followed by neutralization and separation of the ADN by the use of an adsorption column. The heat of formation was measured by burning in hydrogen atmosphere in an adiabatic bomb calorimeter and was found to be 148 kJ/mole ±10 kJ/mole. The melting point was determined using DSC technique and is 93.5°C. This paper reports drop weight, friction and bullet impact sensitivity data. The friction sensitivity of ADN is much lower than that of RDX. The impact sensitivity of ADN is of the same magnitude as that of RDX but varies a great deal with the morphology of the particles, e. g. prilled ADN is nearly twice as insensitive as RDX. The bulk density measured by powder X-ray diffraction and was found to be 1.82 gcm^?3. ADN does not show any sign of phase transitions in the -150°C to +80°C temperature interval (measured by single crystal X-ray diffraction). FTIR and FT-Raman spectra are also presented. In the UV-VIS region, ADN is characterized by two absorption peaks at 214 and 284 nm. UV-VIS spectroscopy was also found to be the most useful method for quantitative routine analysis of ADN.     

Symmetry,Conjugated System,and N-oxides in 2,4,6-Trinitro-1,3,5-triazine-1,3,5-trioxides: A New Design Concept for Energetic Oxidizers

A new strategy for an energetic oxidizer, 2,4,6-trinitro-1,3,5-triazine-1,3,5-trioxides (TNTATO), was designed by keeping symmetry and conjugation and introducing N-oxides into 1,3,5-triazine. Molecular mechanics (MM) and density functional theory (DFT) were employed to study the crystal structure, infrared (IR) spectrum, electronic structure, thermodynamic properties, gas-phase and condensed-phase heats of formation, detonation performance, and burning rate of TNTATO. The pyrolysis mechanism and thermal stability were predicted by evaluating the bond dissociation energy (BDE) and activation energy. The calculated results indicate that TNTATO has a symmetric hyperconjugation structure, which contributes to its stability. The BDE (210.64 kJ/mol^?1) and activation energy (27.74 kJ/mol^?1) of the weakest bond C3–N8 show that the C–NO₂ bond is the trigger bond during thermolysis. The detonation velocity (8.51 km/s^?1) and detonation pressure (32.69 GPa) are larger than those of 2,4,6-trinitro-1,3,5-triazine (TNTA). TNTATO exhibits better burning properties than ammonium dinitramide (ADN), indicating that TNTATO may be a potential candidate for a highly energetic oxidizer.     

Small-scale cook-off experiments and models of ammonium nitrate

We have completed a series of small-scale cook-off experiments of ammonium nitrate (AN) prills in our Sandia Instrumented Thermal Ignition test at nominal packing densities of about 0.8 g/cm³. We increased the boundary temperature of our aluminum confinement cylinder from room temperature to a prescribed set-point temperature in 10 min. Our set-point temperature ranged from 508 to 538 K. The external temperature of the confining cylinder was held at the set-point temperature until ignition. We used type K thermocouples to measure temperatures associated with several polymorphic phase changes as well as melting and boiling. As the AN boiled, our thermocouples were destroyed by corrosion, which may have been caused by reaction of hot nitric acid (HNO₃) with nickel to form nickel nitrate, Ni(NO₃)₂. Videos of the corroding thermocouples showed a green solution that was similar to the color of Ni(NO₃)₂. We found that ignition was imminent as the AN boiling point was exceeded. Ignition of the AN prills was modeled by solving the energy equation with an energy source due to desorption of moisture and decomposition of AN to form equilibrium products. A Boussinesq approximation was used in conjunction with the momentum equation to model flow of the liquid AN. We found that the prediction of ignition was not sensitive to small perturbations in the latent enthalpies.     

One-Pot Synthesis,Crystal Structure,and Thermal Decomposition Behavior of 1,1ʹ-Diamino-4,4ʹ,5,5ʹ-Tetranitro-2,2ʹ-Biimidazole

1,1?-Diamino-4,4?,5,5?-tetranitro-2,2?-biimidazole (DATNBI) was synthesized, by employing one-pot facile method, from 4,4?,5,5?-tetranitro-2,2?-biimidazole. The crystal structure was determined by X-ray diffraction for the first time. DATNBI crystallized in monoclinic system P2₁/c, with a crystal density of 1.934 g cm^?3 at 293(2) K and 2.019 g cm^?3 at 130(2) K, respectively. Its crystal parameters at 293 K are a = 4.8833(15) Å, b = 6.960(2) Å, c = 6.928(4) Å, α = γ = 90°, β = 93.418(6)°, V = 591.1(3) ?³, Z = 2, μ = 0.178 mm^?1, and F(000) = 348. The thermal stability and non-isothermal kinetics of DATNBI were studied by differential scanning calorimeter (DSC) with heating rates of 5, 10, 15, and 20 K min^?1. The apparent activation energy (E_a) at the first decomposition peak calculated by Kissinger, Ozawa, and Starink equations were 85.50, 89.67, and 86.10 kJ mol^?1, respectively. For the second peak, these were 116.49, 119.82, and 117.45 kJ mol^?1, respectively, with individual pre-exponential factors lnA = 18.40 s^?1 and lnA = 25.11 s^?1. The thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR) analysis of thermal decomposition products reveals that the main decomposition gas products are H₂O, N₂O, CO₂, and NO₂. Based on the new crystalline densities, the detonation velocity and pressure predicted by EXPLO5 are 9062 m s^?1 and 36.4 GPa, respectively.     

Kinetics and mechanism of the thermal decomposition of dimethylnitramine at low temperatures

Abstract

Dimethylnitramine (DMNA) was pyrolyzed between 466 and 524 K at about 475 Torr pure DMNA pressure in static cells. A radical mechanism was proposed and computer-modeled to account for the disappearance of DMNA and the production of (CH₃)₂NNO and CH₃NO₂. The rate constant for DMNA decomposition into (CH₃)₂N and NO₂, based on these low-temperature results and other high-temperature shock tube data, covering 460–960 K, can be given by k₁ = 10^15.9±0.2 exp(?22,000±200/T) sec^?1. This result leads to values for the N-N bond energy of 43.3±0.5 kcal/mole and the heat of formation of the (CH₃)₂N radical, 35±2 kcal/mole at 298 K. Kinetic modeling of the CH₃NO₂ and (CH₃)₂NNO production profiles has been carried out.     

Ammonium perchlorate-based molecular perovskite energetic materials: preparation,characterization, and thermal catalysis performance with MoS2

ABSTRACT

In this study, ammonium perchlorate (AP)-based molecular perovskite structural high-energetic materials (H₂dabco)[NH₄(ClO₄)₃] (DAP) were fabricated and their catalytic performance upon the addition of MoS₂ nanosheets was investigated. The DAP samples were succesfully prepared via a self-assembly reaction and their morphology and structure were characterized via scanning electron microscopy, X-ray diffractometry, and Fourier transform infrared spectroscopy. The thermal decomposition performance of a pure DAP sample and of a mixture of DAP with MoS₂ nanosheets were analyzed via differential scanning calorimetry. The results show that DAP has a high thermal stability at its initial decomposition temperature of 319.8°C, and that its apparent decomposition heat measures 4199 J/g. This value is higher than for AP (829.7 J/g). Furthermore, the thermal decomposition peak temperature of DAP upon the addition of 1 wt% and 3 wt% MoS₂ nanosheets decreases from 394.4°C to 343.3°C and 328.8°C, respectively. The investigation of the catalysis thermal performance of DAP may foster its practical application in composite propellant.     

Solid + liquid phase equilibria in the hydroxylammonium nitrate + water system

Abstract

The binary solid + liquid phase diagram has been measured for the water + hydroxylammonium nitrate (HAN) system. The phase diagram is a simple eutectic type with the eutectic at 231.5 K (41.7°C) and a mole fraction HAN of 0.281 (wt fraction HAN - 0.676).

The enthalpy of fusion of the HAN was determined from the solid + liquid results to be 11 ± 2 kJ·mol^?1. The HAN was obtained from Southwestern Analytical Chemicals, Inc. as an approximately 2.8 molar solution. The water was removed by vacuum drying over a three month time period, but the sample still contained some impurity. The impurity level calculated from the change in melting temperature with fraction melted is 0.040 mole fraction. Chemical analysis indicates the sample contains 0.005 mole fraction HNO₃ and 0.007 mole fraction NH₄NO₃, with N₂H₅NO₃ absent. The remainder of the impurity could be water, but this is not known for sure.

We obtained a melting temperature for the impure sample of HAN of 315.9 K (42.7°C). The melting point corrected to zero impurity is 317.7 ± 1 K (44.5°C).     

Crystal structures and EPR spectra of nitroguanidine chloride and nitroguanidine nitrate

Abstract

Crystal structures of nitroguanidine chloride and nitroguanidine nitrate were solved by x-ray diffraction. The nitroguanidine chloride crystal is triclinic, space group P1, with unit cell parameters: a = 6·656(8)A, b = 6·719(9) A, c = 6·816(8)A, α = 66·8(2)°, β = 75·4(2)°, γ = 84·5(2)°, D_C = 1·7g cm^?3, Z = 2. The nitroguanidine nitrate crystal is monoclinic, space group P2₁/c with unit cell parameters: a = 4·587(4)A, b = 6·377(6)A, c = 21·167(15)A, β = 94·7(1)°, D_C = 1·8g cm^?3, Z = 4. EPR spectra were detected from crystals of both compounds which had been exposed to gamma or x-radiation. The EPR spectra are assigned to NO₂ and (NH₂)₂CN.     

Structural Effect of Potassium Sulfamate on Synthesis of Ammonium Dinitramide

Potassium sulfamate (PS) is an efficient starting material for the nitration reaction used in the synthesis of ammonium dinitramide (ADN), which is an environmentally friendly high-energy oxidizer for propellants that does not release chlorine-based compounds. PS is a core structure to form dinitramide, -N(NO₂)₂, by taking NO₂^? from nitric acid. In this work, five test batches of PS were prepared using a few solvents including ethanol, methanol, acetone, isopropanol, and their mixtures. The lab-made PSs matched well with the commercial PS in terms of the chemical structure. The use of acetone led to a high recovery of PS up to 97 w/w% and ultimately contributed to the formation of high-purity and (99.2%) and a high yield (57.3%) that are greater than those for commercial PS (87.3% purity and 31.3% yield). Therefore, we proved that the crystallinity and homogeneity of PS influenced the properties of ADN and the synthesis efficiency.     

Kinetics and mechanism of thermolysis of hexammine metal perchlorates

Abstract

The thermal decomposition studies on four transition metal hexammine perchlorates, viz. [Cu(NH₃)₆](CIO₄)2, [Co(NH₃)₆](CIO₄)₂, [Ni(NH₃)₆](CIO₄)₂ and [Zn(NH₃)₆](CIO₄)₂. have been carried out using Thermogravimetry (TG), derivative thermogravimetry (DTG) and explosion delay (D_E) measurements. Although, the kinetics of thermolysis of these complexes were evaluated by fitting isothermal TG data in nine mechanism-based kinetic models but the contracting area (n=2) and contracting cube (n=3) give the best fits. It has been observed that deammination takes place at lower temperatures and ammine metal perchlorates and/or metal perchlorates are formed as intermediates which decompose to metal oxides at higher temperatures. The decomposition pathways for hexammine metal perchlorates have also been suggested.     

Study on flame propagation of premixed N2O–NH3/N2O–NH3–C3H8 in cylindrical vessels

The flame propagation behavior of premixed N₂O–NH₃/N₂O–NH₃–C₃H₈ was experimentally investigated in elongated vented cylindrical vessels with central ignition. The effect of vessel diameter and propane concentration ([C₃H₈] = 1.96–7.41 wt.%) on the process of flame acceleration was studied and discussed. The results revealed that the maximum value of flame acceleration rate was found in the cylindrical vessel with an inner diameter of 7 mm, followed by 5 mm, 10 mm, and 15 mm. At a constant vessel diameter, the rate of flame acceleration was noticeably improved by adding propane ([C₃H₈] = 1.96–3.85 wt.%) to the premixed N₂O–NH₃. However, a further increase in the propane fraction up to 5.66%, caused a decline in the flame acceleration rate, probably as a consequence of a combined effect between the reduction of oxygen and greater dilution of the ammonia in the total concentration.     

A Theoretical Study of Polynitropyridines and their N-oxides

ABSTRACT

The geometries of polynitropyridines and their N-oxides have been optimized using the B3LYP density functional method and the 6-311++G** basis set. The accurate gas phase enthalpy of formation (at p = 1.013 × 10⁵ Pa and T = 298.15 K) for pyridine and its N-oxide has been calculated employing the G3(MP2) method and the atomization scheme, and for polynitropyridines and their N-oxides at the B3LYP/6-311++G** level by designing the isodesmic reactions in which the pyridine ring maintains integral. Based on B3LYP/6-311++G** optimized geometries and calculated natural charges, this paper has calculated the crystal structures by the Karfunkel-Gdanitz method, and based on estimated solid enthalpies of formation and crystal densities has predicted the Chapman-Jouguet detonation velocities (D_CJ) by the Stine method. Calculated results show that for polynitropyridines and their N-oxides the introduction of ─NH₂ groups increases the strength of C─NO₂ bonds but reduces the gas phase enthalpy of formation. The least C─NO₂ bond order indicates that compounds 3,5-diamino-2,4,6-trinitropyridine and its N-oxide, whose D_CJ values are predicted to be approximately 8.2 and 8.6 km/s, respectively, are most possibly low-sensitive or insensitive energetic materials. The largest D_CJ value obtained in polynitropyridines and their N-oxides is about 9.5 km/s.     

The Effect of Pd Precursors on the Catalytic Activity of a Pd/Al2O3 Catalyst for Cumene Hydroperoxide Hydrogenation

Abstract

Abstract Pd/Al₂O₃ catalysts were prepared by wet impregnation using K₂PdCl₄, (NH₄)₂PdCl₄, and Pd(NO₃)₂ as precursors. All catalysts were characterized by means of inductively coupled plasma-atomic emission spectroscopy (ICP-AES), temperature-programmed reduction (TPR), X-ray diffraction (XRD), and CO chemisorption. The results obtained in the hydrogenation of cumene hydroperoxide (CHP) to α-cumyl alcohol (CA) showed that Pd/Al₂O₃ catalyst prepared from Pd(NO₃)₂ exhibited the highest turnover frequency (TOF) value and the greatest deactivation extent, whereas Pd/Al₂O₃ catalyst prepared from (NH₄)₂PdCl₄ displayed the lowest TOF value but the best stability.     

Optimization,kinetics, physicochemical and ecotoxicity studies of Fenton oxidative remediation of hydrocarbons contaminated groundwater

Fenton oxidation remediation of hydrocarbons contaminated groundwater was investigated for efficiency and effectiveness. 10% pollution was simulated in the laboratory by contaminating groundwater samples with diesel and domestic purpose kerosene (DPK) in two different experimental set ups. Optimum conditions of concentrations of the treatment solutions and pH were established: 300 mg/L (FeSO₄), 150,000 mg/L (H₂O₂) and pH = 3 for the kerosene contaminant; 100 mg/L (FeSO₄), 300,000 mg/L (H₂O₂) and pH = 3 for the diesel contaminant. The results from kinetics study show that the remediation process is pseudo-first order reaction with a rate constant of 8.07 × 10⁴ mgL^?1hr^?1 and 3.13 × 10⁴ mgL^?1hr^?1 for the diesel and kerosene contaminants in that order with 95.32% and 79.25% reduction in chemical oxygen demand (COD) for diesel and kerosene contaminated samples at the end of the remediation process respectively indicated that remediation have occurred significantly. Percent reduction in Total Petroleum Hydrocarbon (TPH) as kerosene was 89.84% and that of the diesel contaminant as 91.87% after 6 hours of remediation. The general pollution index (GPI) for the hydrocarbons contaminated samples was in the range of 6.70–7.52 against the background value of 4.39 for the control groundwater sample. After treatment the GPI had dropped to 4.13–4.43 which depicts remarkable remediation although the samples remained impaired. Therefore there is the need of post-treatments to make the groundwater fit for domestic and agricultural uses. The application of the Fenton oxidative process is found to be very efficient, effective and rapid in reducing total petroleum hydrocarbon as kerosene and diesel as target contaminants.     

Thermal decomposition of RDX: Evidence of a nitronylnitroxyl free radical intermediate

Abstract

The thermal decomposition of RDX produces free radical intermediates which are detected by using ESR (electron spin resonance) spectroscopy. The assignment of certain ESR signals from thermally decomposed RDX and HMX to a nitroxyl radical (RNO·) has been discussed in earlier publications. Spectral data from isotopically labelled RDX (RDX-d₆ and RDX-¹⁵NO₂) supports a nitronylnitroxyl radical (R(N⁺?O^?)NO·) assignment to the ESR signals detected during liquefaction of RDX at 200°C.     

Relative rates of CH3NO2, CH3ONO,and CH3ONO2 formation in the thermal reaction of NO2 with acetaldehyde and DI-T-butyl peroxide at low temperatures

Abstract

The relative yields of CH₃NO₂, CH₃ONO, and CH₃ONO₂ have been measured at five temperatures between 323 and 455 K above 300 torr of pressure. Kinetic modelling of the observed CH₃NO₂/(CH₃ONO + CH₃ONO₂) and CH₃ONO/CH₃ONO₂ ratios from this study and that of Phillips and Shaw (Ref. 5), with and without added NO, led to the rate constant for CH₃ + NO₂ → CH₃NO₂ (1), k₁ = 6.0x10¹² cc/mol-sec, and for CH₃O + NO₂ → CH₃ONO₂ (4), k₄ = 7.5x10¹² cc/mol-sec. The results of the modelling also indicate that the oxidation of CH₃NO by NO₂ accounts for a large fraction of CH₃NO₂ formed in the NO-added mixtures. The rate constant for this reaction is estimated to be k₂₅ ? 1.3×10⁹e^(-10,000/RT) cc/mol-sec. Combination of k₁ with the equilibrium constant for reaction (1) gives rise to the rate constant for the decomposition of CH₃NO₂, k_?1 = 1.3x10¹⁶e^(-60,050/RT) sec^?1.     

The ignition and combustion characteristics of Al/Ni(IO3)2·4H2O nanothermites

ABSTRACT

Nickel iodate tetrahydrate (Ni(IO₃)₂·4H₂O) particles with different morphology and size were synthesized by precipitation method (PM) and electrospray precipitation method (EPM). The electrospray was used in chemical precipitation to synthesize nanoscale metal iodate particles with a narrow size distribution. The thermal decomposition mechanism of Ni(IO₃)₂·4H₂O at different heating rates, ignition, and combustion of Al/Ni(IO₃)₂·4H₂O nanothermites was studied by thermogravimetry–differential scanning calorimetry–mass spectrometry, T-jump and time-of-flight mass spectrometry, T-jump equipped with high-speed camera, and combustion cell test. The Al/Ni(IO₃)₂·4H₂O prepared by EPM had a lower ignition temperature (587 ± 14°C) and a shorter burn time (159 µs). The ignition processes of Al/Ni(IO₃)₂·4H₂O nanothermites prepared by EPM and PM were solid–solid and gas–liquid reactions, respectively. The rate-determining step of their combustion processes was the burning of aluminum powder and the decomposition of Ni(IO₃)₂· 4H₂O, respectively.     

Ageing mechanisms of nitroethylbenzenes

Simulated ageing of 2,4-dinitro-1-ethylbenzene (DNEB) in DMSO in the presence of O₂ in a closed system at 85–105°C gave benzylic oxidised products 1-(2,4-dinitrophenyl)ethanol (DNPE) and 2,4-dinitroacetophenone (DNAP), with the latter as the major product. Evidence for the formation of 3-methyl-6-nitro-2,1-benzoisoxazole (an ‘anthranil’), suggested in the literature as a likely decomposition product, is scant. A mechanism with initial H-abstraction to yield an electron-rich benzylic radical as the rate-limiting step is suggested, supported by a small kinetic isotope effect k_H/k_D ~2 and a reactivity in the order 2,4,6-trinitro-1-ethylbenzene TNEB > DNEB > 4-nitro-1-ethylbenzene (NEB). The activation energy for DNEB oxidation is 40 kJ mol^?1, a value that translates to 1% oxidative decomposition of DNEB after ~ 14 d under an O₂ atmosphere, or 70 d in air at ambient temperature.     

Optimization of reaction condition on the product selectivity of Fischer–Tropsch synthesis over a Co–SiO2/SiC catalyst using a fixed bed reactor

The Fischer–Tropsch (FT) synthesis is an important method for producing valuable key raw materials such as heavy and light hydrocarbons in various industries. The effects of process conditions (temperature of 503–543 K, pressure of 10–25 bar, and gas hourly space velocity (GHSV) of 1,800–3,600 Nml g _cat^?1 h^?1) on the FT product distribution using Co–SiO₂/SiC catalyst in a fixed bed reactor were studied by the design of experimental procedure and the Taguchi method. The optimization of the reaction conditions for the production selectivity of C₂–C₄ and heavy hydrocarbon (C₅₊) that has not been completely indicated elsewhere was investigated. The effect of operating conditions on the average carbon number distribution, dispersion, and skewness was also studied. Data analysis indicated the highest selectivity for the light hydrocarbons at a pressure of 20 atm, GHSV of 2,400 Nml g _cat^?1 h^?1, and temperature of 543 K resulting in a highest selectivity for heavier hydrocarbons (C₅₊) and the minimum amount of methane in the reaction products that is optimal at the pressure of 10 atm, GHSV of 1,800 Nml g _cat^?1 h^?1, and a temperature of 503 K. Furthermore, based on the surface plot, temperature has more significant effects than the other parameters. In addition, the obtained results indicated that the maximum average number of carbon was obtained in a pressure of 10 atm and a temperature of 503 K.     

金属铁盐辅助稠油多环芳烃对CO水热变换新生氢富存研究

以蒽为稠油多环芳烃模型化合物,考察了不同条件下蒽对CO水热变换新生氢的富存影响,并对CO水热变换和蒽储氢之间的协同效应进行了分析。研究表明,Fe(NO_3)_3·9H_2O和环烷酸铁对蒽富存CO水热变换新生氢均有催化作用,Fe(NO_3)_3·9H_2O的作用效果更好。随着反应温度、CO初始压力和加入的Fe(NO_3)_3·9H_2O中铁含量的增加,CO转化率和蒽储氢效率均呈现逐渐增大的趋势。CO初压2 MPa,Fe(NO_3)_3·9H_2O中铁的质量分数为0.08%时,对蒽储氢反应较为适宜,储氢效率较高。蒽储氢可对CO变换产生的新生氢进行富存,从而消耗新生氢,进而促进CO水热变换反应。因此,蒽储氢与CO水热变换反应之间存在正协同效应,二者相互促进。