Burning of Nano-Aluminized Composite Rocket Propellants

Several aluminum nanopowders were examined and compared with the final goal to evaluate their application in solid rocket propulsion. A detailed investigation of pre-burning properties by the Brunauer-Emmet-Teller method, electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy was carried out. Ballistic properties and the combustion mechanism of several aluminized propellant formulations were investigated. In particular, aggregation and agglomeration of metal particles at and near the burning surface were analyzed by high-speed high-resolution color digital video recordings. All tested nano-powders are of Russian production; their physical characterization was carried out at the Istituto Donegani (Novara, Italy); ballistic studies were performed at the Solid Propulsion Laboratory (Milano, Italy) using laboratory and, for comparison, industrial composite propellants based on ammonium perchlorate as an oxidizer. Results obtained under a fair variety of operating conditions typical of rocket propulsion indicate, for increasing nano-Al mass fraction or decreasing nano-Al size, larger steady burning rates with essentially the same pressure sensitivity. While aggregation and agglomeration phenomena still occur, their significance may be reduced by using nano-Al instead of micro-Al. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 6, pp. 80–94, November–December, 2005.     

Aging of ADN Rocket Propellant Formulations with Desmophen®‐Based Elastomer Binder

Desmophen® binder‐based rocket propellant formulations containing ammonium dinitramide (ADN) and different fuel filler types (Al, HMX) were manufactured and investigated. Desmophen® D2220 is a polyesterpolyol. Polyesters are seen as a binder possibility, because of the relatively low temperature of the glass transition region compared to polyether‐based prepolymers such as GAP. The analogous formulations with AP instead of ADN were also included for comparison. The aging was followed by SEM, DSC, and DMA measurements. The accelerated aging program was developed on the principle of thermal equivalent load and the generalized van’t Hoff rule with a scaling factor equal to F=2.9. The aging was performed in air (RH<10 %) at temperature values between 65 and 85 °C and aging times adjusted to a thermal equivalent load of 15 years at 25 °C. DMA measurements of the aged ADN/Desmophen®‐based propellants identified changes in the loss factor curve. In contrast to HTPB‐Al‐AP rocket propellant formulations, the loss factor curve of the ADN formulations with Desmophen®‐based elastomer binder shows only one main apparent peak. The loss factor curves were modeled with exponentially modified Gaussian functions, which have revealed the presence of a second hidden peak. It was found that the aging could be characterized by the time‐temperature dependence of the areas of the hidden peak. The area increased with aging, which is explained by scissioning of the polymer in the shell around the ADN particles. By this process the strength is reduced, which was recognized by the decrease in storage shear modulus.     

Characterization of Gun Propellants by Long‐Term Mass Loss Measurements

Three different gun propellants (A5020, JA‐2 or L5460, NK1074) have been investigated up to 35 years by mass loss at isothermal temperatures between 30 °C and 90 °C. From these data, activation energies for the different reactions of zero order (mass loss increase up to stabilizer consumption) and first order (solvent evaporation at begin) are derived. The mass loss data are described very well by a combination of these two reactions. Stabilizer consumption has been determined by HPLC. In case of diphenylamine (DPA), several consecutive products (mononitro‐DPA up to tetranitro‐DPA) have been regarded also. Activation energies are in the range of energies obtained by other methods: 84 kJ/mol [A5020], 150 kJ/mol [JA‐2], 100 kJ/mol [NK 1074]). Long term measurements show seasonal influence in the mass loss data. Respective graphs are shown in this work. At least four years of measurement are recommended to compensate for the signal drift caused by seasonal changes.     

Effect of Pre‐strain Aging on the Damage Properties of Composite Solid Propellants based on a Constitutive Equation

Accelerated aging tests under pre‐strain were conducted on HTPB‐based composite solid propellant with the goal of investigating the effect of pre‐strain aging on its damage properties. A statistical damage constitutive model based on continuum damage theory and statistical strength theory was established. The aging damage coefficient, making aging process of propellant equivalent to a form of damage, was introduced to correct the damage variable. Experimental results show that theoretical model has good agreement with experimental results and can accurately describe the mechanical behavior of propellant during pre‐strain aging. Further analysis indicated that the damage effects caused by pre‐strain can be identified from the equation of the aging damage coefficient. Aging time influences both tensile strength and shape characteristics of the stress‐strain curve of propellant in the damage stage, while pre‐strain only decreased the tensile strength. The strain damage threshold value decreased linearly over the aging period and with increasing pre‐strain level during the aging process.     

Preparation and Characteristics of Foamed NC‐Based Propellants

Foaming properties of the three NC‐based (nitrocellulose‐based) propellants, namely, single‐base propellant, NG (nitroglycerine) propellant and TEGDN (triethylene glycol dinitrate) propellant were investigated in the batch foaming process by using supercritical CO₂ as the physical foaming agent. Burning characteristics of the foamed NC‐based propellants were also investigated in this work. For this study, the CO₂ desorption of the three NC‐based propellants were plotted by the gravimetric method. The morphology and burning characteristics of these foamed NC‐based propellants were characterized by scanning electron microscope (SEM) and closed vessel experiment. The test data revealed that the energetic plasticizer has a considerable effect on the pore formation in the NC matrix although it has little effect on the CO₂ solubility in the NC‐based propellants. Moreover, the SEM images showed the foaming temperature also plays an important role in the pore parameters of foamed propellants. Furthermore, the data of closed vessel experiment indicated that the burning characteristics of foamed NC‐based propellants largely depend on the pore parameters, and the porous structure of foamed propellants would considerably increase the mass conversion rate.     

Measurement and Analysis of the Burning Rate of HAN‐Based Liquid Propellants

A new device for measuring the linear burning rate of liquid propellants at high pressures is reported. High‐pressure environments were generated by the combustion of solid propellants. The coated propellants, which burn progressively, were introduced to maintain the approximate constant‐pressure environments. By use of ion probe transducers, measurements were made of the spread velocity of the flame surface, i.e. the apparent linear burning rate of the HAN‐based liquid propellant LP1846 (HAN =hydroxylammonium nitrate) was measured quantitatively at pressures from 6 to 28 MPa. The results show that it follows the exponential burning rate law. The burning rate coefficient and exponent were fitted by least‐squares methods. Based on the experiment, a simplified model of the linear burning rate of HAN‐based liquid propellants at high pressures was developed. The numerical simulation is found to be in good agreement with the experimental data.     

Burning Characteristics of Ammonium Nitrate‐Based Composite Propellants Supplemented with Fe2O3

Ammonium nitrate (AN)‐based composite propellants have attracted a considerable amount of attention because of the clean burning nature of AN as an oxidizer. However, such propellants have several disadvantages such as poor ignition and a low burning rate. In this study, the burning characteristics of AN‐based propellants supplemented with Fe₂O₃ as a burning catalyst were investigated. The addition of Fe₂O₃ is known to improve the ignitability at low pressure. Fe₂O₃ addition also increases the burning rate, while the pressure exponent generally decreases. The increasing ratio (R) of the burning rate of the AN/Fe₂O₃ propellant to that of the corresponding AN propellant vs. the amount of Fe₂O₃ added (ξ) depends on the burning pressure and AN content. R decreases at threshold value of ξ. The most effective value of ξ for increasing the burning rate was found to be 4 % for the propellant at 80 % AN, and the value generally decreased with decreasing AN content. According to thermal decomposition kinetics, Fe₂O₃ accelerates the reactions of AN and binder decomposition gases in the condensed‐ and/or gas‐phase reaction zones. The burning characteristics of the AN‐based propellant were improved by combining catalysts with differing catalytic mechanisms instead of supplementing the propellant with a single catalyst owing to the multiplicative effect of the former.     

GS-1改性双基推进剂老化的动态力学表征

用动态热机械分析仪表征了65C下老化不同天数的GS-1改性双基固体推进剂的老化性能。在低温段（-50～10℃）,tanδ值随老化时间延长有明显下降,β松弛峰也越来越明显。老化15d前,GS-1α松弛的tanδ峰温随老化时间延长而上升,在较高温度下的动态柔量J′和J″的值则随老化时间延长而下降。以未老化试样主曲线的高温段为参比线,获得动态模量E′和E″的垂直位移因子随老化时间延长而上升,而由J′和J″获得的垂直位移因子则下降。TG-DTG试验发现,试样的质量损失随老化时间延长逐渐减小,说明了增塑剂（硝化甘油）含量随老化时间延长而减小。因此,除了因结构松弛造成的“物理老化”外,这是造成上述各力学损耗量随老化时间延长而下降的又一主要原因。老化21d后,上述各力学损耗量有一定上升,是由于试样出现了气泡的原因。     

Aging of HTPB/AP‐based composite solid propellants,depending on the NCO/OH and triol/diol ratios

Aging behavior of hydroxyl‐terminated polybutadiene/ammonium perchlorate (HTPB/AP)‐based composite solid propellants was studied as a function of crosslink density, which is predominantly determined by the molar ratio of diisocyanate to total hydroxyl (NCO/OH ratio) and the molar ratio of triol to diol (triol/diol ratio). For this purpose, 16 propellant samples with different compositions were prepared by changing the NCO/OH ratio as 0.81, 0.82, 0.83, and 0.85 for each triol/diol ratio of 0.07, 0.09, 0.11, and 0.13, and subjected to an accelerated aging at 65°C. The changes in the mechanical properties were monitored throughout the aging period. In the initial part of the aging period, a sharp increase in stress, modulus, and hardness values and a sharp decrease in strain values were observed for all the propellants. At further stages of aging, only slight changes were observed in the mechanical properties. Concerning the aging criterion as reduction in the strain capability more than the half of the initial value, the propellants with respective NCO/OH‐triol/diol ratios of 0.81–0.09, 0.85–0.09, 0.81–0.13, 0.83–0.13, and 0.85–0.13 can be considered to be aged with time. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 959–964, 2001     

Evaluation of Nano‐Co3O4 in HTPB‐Based Composite Propellant Formulations

Different propellant compositions were prepared by incorporating nano‐sized cobalt oxide from 0.25 % to 1 % in HTPB/AP/Al‐based composite propellant formulations with 86 % solid loading. The effects on viscosity build‐up, thermal, mechanical and ballistic properties were studied. The findings revealed that by increasing the percentage of nano‐Co₃O₄ in the composition, the end of mix viscosity, the modulus and the tensile strength increased, whereas the elongation decreased accordingly. The thermal property data envisaged a reduction in the decomposition temperature of ammonium perchlorate (AP) as well as formulations based on AP. The ballistic property data revealed an enhanced burning rate from 6.11 mm s⁻¹ (reference composition) to 8.99 mm s⁻¹ at 6.86 MPa and a marginal increase in pressure exponent from 0.35 (reference composition) to 0.42 with 1 % nano‐cobalt oxide.     

钛系TPI老化性能和热刺激温度的表征

分析了实验室条件下老化3a的TPI胶料的机械性能,并测试了其老化100℃×2d后的性能;同时表征了材料的热刺激温度。防老剂4010对TPI具有较好的防老化性能。防老剂可能起到了成核剂的作用,促进了TPI的结晶。热刺激温度的变化规律基本上与300%定伸应力变化一致。     

Characterization of ADN/GAP‐Based and ADN/Desmophen®‐Based Propellant Formulations and Comparison with AP Analogues

Several ADN‐based rocket propellant formulations containing different pre‐polymers (GAP diol/triol, Desmophen® 2200), curing agents (BPS, Desmodur® N100, Desmodur® N3400), plasticizers (BDNPA‐F, TMETN), and filler types (Al, HMX) have been manufactured. Propellant formulations were characterized by tensile tests, SEM analyses and DMA measurements. The study has focused on characterizations of the propellants in terms of evaluation of the strength and strain capability, investigation of the presence/absence of dewetting phenomena, compatibility issues and evaluation of the glass transition temperature. Ammonium perchlorate‐based propellant formulations have also been manufactured and analyzed in order to make comparisons. Aging was investigated using mass loss measurements.     

NMMO工艺天然高分子绿色复合膜的制备和表征

以纤维索、木质索和淀粉为原料,以N-甲基吗琳-N-氧化物(NMMO)为洛剂,制备了天然高分子绿色复合膜。利用傅里叶红外光谱和X射线衍射测试了复合薄膜的结钩,采用电子显微镜和轻敲模式原子力显微镜观察了该模型薄膜的表明形貌,并测定了薄膜力学性能。结果表明,通过NMMO工艺技术,3种天然高分子打破了原有的结晶结钩,重组形成了具有一定塑性的均相复合薄膜;该薄膜具有较高的拉伸强度(17. 25 MPa)和断裂伸长率(80.90%),表现出较好的耐水性能。     

Preparation and electrochemical studies of metal–carbon composite catalysts for small-scale electrosynthesis of H2O2

Numerous transition metal–carbon composite catalysts (M = V, Zn, Ni, Sn, Ce, Ba, Fe, Cu) have been synthesized and tested for electroreduction of O₂ to H₂O₂, The activity and selectivity of all synthesized catalysts for electrosynthesis of H₂O₂ were determined by the rotating ring-disk electrode method in acidic and neutral electrolytes. The Co-based catalysts in general showed the highest activity towards H₂O₂ formation. Experiments with different loading contents of Co showed that the activation overpotential losses of oxygen reduction to H₂O₂ reduces as loading increases to about 4 wt% Co. Addition of Co beyond this level did not seem to impact the overpotential losses. The cobalt-based catalysts, were spray-coated onto 120 μm thick Toray^® graphite substrates, and were studied in bulk electrolysis cells for up to 100 h at potentiostatic conditions (0.25 V vs. RHE) in pH 0, 3, and 7 electrolytes. At (25 °C and 1 bar) with a catalysts loading of about and using dissolved O₂ in 0.5 M H₂SO₄, typical H₂O₂ electrosynthesis rates of about were reached with current efficiencies of about 85 ± 5% at 0.25 V (vs. RHE).