铝/有机氟化物复合物对含铝HTPB推进剂燃烧性能的影响

为研究有机氟化物(OF)对含铝HTPB固体推进剂燃烧性能的影响,采用球磨法制备了纳米和微米铝/有机氟化物复合物(nmAl/OF和μmAl/OF),将其作为复合添加剂替代微米铝粉加入HTPB推进剂中,并考察其对推进剂燃烧性能的影响。采用SEM、TEM、粒度分析等对nmAl/OF和μmAl/OF复合物及推进剂凝聚相燃烧产物进行了表征。结果表明,nmAl/OF和μmAl/OF复合物有不同的结合状态;添加OF、nmAl/OF和μmAl/OF后,推进剂的爆热值下降约2%;添加nmAl/OF的推进剂配方燃速最低,在3MPa时仅为6.28mm/s,添加OF和μmAl/OF体系的推进剂燃速压强指数相比于原配方降低约20%;添加nmAl/OF的推进剂配方凝聚相燃烧产物粒度(D_(50))比原配方降低约47%。     

Application of Cerimetric Methods for Determining the Metallic Aluminum Content in Ultrafine Aluminum Powders

Ultrafine (nano‐sized) aluminum is a promising component for solid propellants, gel propellants, explosives, etc. The work is focused upon a problem of determining active (metallic) aluminum content in nanoAl powders as one of the characteristics of their reactivity. It is shown that the high reactivity, the presence of either the gases adsorbed or coating matter on the particle surface restricts the traditionally used permanganatometric and volumetric analytic methods. A new technique determining the active aluminum content is presented. This is the adaptation of known cerimetric method based on the analytical reaction Ce⁴⁺+e⁻=Ce³⁺. The method can be applied for analysis of metallic aluminum in the probes of nanoAl (including ones with organic coating), as well as micron sized aluminum, and their condensed combustion products.     

Products of Combustion of Aluminum Hydride in Air

The paper reports results of studying the process and products of combustion of aluminum hydride in air. It is shown that the final combustion products of aluminum hydride contain 50% aluminum nitride (by weight) for large sample weights of 1000 g. The formation mechanism of the final combustion products of aluminum hydride is similar to that of ultradisperse aluminum powder.     

Experimental Study on Dynamic Combustion Characteristics of Aluminum Particles

Studying the combustion characteristics and properties of the condensed phase products of aluminum particles is significant for the application of aluminum‐based propellants. The microstructure, particle size distribution, specific surface area and metallic Al contents of three different samples were analyzed by scanning electron microscopy, laser particle size analyzer, nitrogen adsorption and inductively coupled plasma atomic emission spectroscopy. The thermal oxidation characteristics of the samples were also studied by a thermal analyzer. A dynamic combustion test system was used to study the combustion process in motion and the properties of the products. The results show that as the activation energy of the sample decreases, the initial reaction temperature decreases during the thermal analysis. Moreover, the thermal oxidation degree increases with the decrease in particle size. In the dynamic combustion process, the combustion efficiency of the sample was calculated by using the temperature distribution in the combustion process, and the calculated results were in good agreement with the results of ICP measurements. With the increase in the particle size of the samples, the heat release was reduced, and the agglomerationand oxidation degree of the condensed phase products were also decreased. By increasing the feeding amount, the combustion temperature and the combustion efficiency would increase. The reaction mechanism in the dynamic furnace involves not only the diffusion reaction, but also the melt‐dispersion reaction. The initial reaction temperature of sample A was between 500∼600 °C, the combustion temperature was between 900∼1000 °C, the ignition delay time was around 270 ms, and the reaction time was about 0.6s.     

Combustion of Agglomerated Ultrafine Aluminum Powders in Air

It is shown experimentally that agglomeration of ultrafine aluminum powders decreases their reactivity during nonisothermal oxidation in air. Under normal and low pressures, the concentration of bound nitrogen in combustion products is lower for agglomerated powders than for unagglomerated powders, and under high pressures (>120 kPa), it is higher for agglomerated powders. Key words: ultrafine powder, aluminum, agglomeration, combustion, reactivity, aluminum nitride.     

Nitride Formation during Combustion of Ultrafine Aluminum Powders in Air. I. Effect of Additives

This paper summarizes the results from studies of the effect of 17 additives on the process and products of ultrafine aluminum combustion in air. It is shown that the additives influence the temperature and duration of the combustion process and the structure of the end products, including the yield of aluminum nitride. The major factor determining the yield of aluminum nitride is the maximum temperature reached in combustion of mixtures of ultrafine aluminum powder with definite additives.__________Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 3, pp. 74–85, May–June, 2005.     

Agglomeration of the condensed phase of energetic condensed systems containing modified aluminum

Thermodynamic analysis of aluminum-containing energetic condensed systems was performed. It was shown that the replacement of aluminum by aluminum carbide led to a decrease in the amount of the condensed phase in the combustion products and a reduction in the specific impulse. The particle size distribution of the condensed phase of samples of energetic condensed systems containing different amounts of aluminum particles coated with aluminum carbide was studied experimentally. It was found that replacing aluminum with a particle size of 18–20 μm nanosized aluminum halved the maximum size of condensed-phase agglomerates of the combustion products.     

铝含量和含氟有机化合物对丁羟推进剂燃烧性能的影响

为进一步提高HTPB推进剂的能量并抑制铝粉在燃烧过程中的团聚,制备了铝粉质量分数为16%~22%的端羟基聚丁二烯(HTPB)推进剂,并分别加入含氟有机化合物(OF)作为铝燃烧促进剂,研究了铝含量和OF对HTPB推进剂燃烧性能的影响;使用氧弹量热仪测定了推进剂在氩气氛围下(3 MPa)的爆热;收集在3 MPa下推进剂燃烧的凝聚相产物,采用激光粒度仪、X射线光电子能谱仪(XPS)及X射线衍射仪(XRD)等分别对其进行粒度分布、元素和物相分析;通过线扫描摄像机和高压燃烧室系统测定推进剂的燃速;利用高速摄影系统观察推进剂燃面上熔铝粒子的团聚过程。结果表明,HTPB推进剂在铝粉质量分数为20%时实测爆热最大,含氟有机物OF的引入使得爆热有所下降;随着HTPB推进剂中铝含量的提高,燃面上熔铝粒子的团聚愈加严重,凝聚相燃烧产物的尺寸和残留铝含量均逐渐增加;加入含氟有机物OF能够促使-Al2O3和AlF3的生成,有效抑制铝颗粒在燃烧过程中的团聚,使凝聚相燃烧产物的尺寸和残留铝含量显著降低,当铝粉质量分数为20%时,OF的加入使得残留铝的生成率降低了50%;较低的铝含量和OF的添加有利于HTPB推进剂燃速的提高。     

纳米氮化铝的制备方法及其应用研究

纳米氮化铝是一种用途广泛的纳米材料．它的制备方法主要有气相法,液相法和固相法。本文对这三种方法分别进行叙述,并介绍了各种方法的国内外研究进展．同时对纳米氮化铝的应用领域和发展现状作了阐述。     

Effect of an External Electric Field on the Disperse Composition of Condensed Products of Aluminum Particle Combustion in Air

Investigation was performed of the effect of an external electric field on the completeness of combustion of ASD-1 aluminum powder in an airflow and on the disperse composition of condensed combustion products. It is established that for an oxidizer-to-fuel ratio of 0.8 and a combustor inlet flow rate of 10 m/sec, the application of an electric field increases the completeness of aluminum combustion from 43 to 75%. In this case, the sizes of submicron particles of aluminum oxide practically do not change, and the mass average sizes and the mass concentration of the 4 – 50 m fraction decrease, due to the activating effect of the electric field on the vapor-phase combustion of aluminum particles. A decrease of the mass concentration of the size fraction larger than 50 m from 12 to 3% under the action of the electric field suppress markedly the agglomeration of aluminum particles during combustion in air. Key words: aluminum, turbulent combustion, electric field, disperse composition of condensed products of combustion.     

氮化铝粉体工程的研究进展

电子技术微型化、轻型化、高集成和大功率的发展,对基板和封装材料提出更高要求。氮化铝陶瓷具有高导热性、绝缘性、热膨胀系数与半导体硅相近、机械强度高、化学稳定性好、无毒无害等优良特性,是理想的基板材料之一,具有很好的发展前景。高质量氮化铝粉体是制备高性能氮化铝陶瓷的关键。本文分别归纳介绍了微米/纳米氮化铝合成的新技术、新方法及其研究进展,并展望了氮化铝粉体合成的发展趋势。     

Enhancement of Aluminum Reactivity to Achieve High Burn Rate for an End Burning Rocket Motor

Aluminum is used in solid propellants to increase the specific impulse (I _sp). It is desirable to have high propellant loading in any stage as it reduces the structural coefficient and an end burning grain is known to be the one with the highest propellant loading. As aluminum combustion is a slow process, the time available for aluminum combustion in an end burning configuration will be very small at the start of the combustion process. This demands an increase in the reactivity of the aluminum. This study is built on the fact that mechanical activation of aluminum powder with PTFE (poly‐tetra‐flouro‐ethylene) enhances the reactivity of aluminum powder. This study also deals with the use of this activated aluminum powder in conjunction with various other methods to enhance the burn rates of the solid propellant. The temperature sensitivity was also measured. Based on these results, new designs with end burning grains for the third stage of Polar Satellite Launch Vehicle (PSLV) and for the second and third stage of Pegasus launch vehicle have been proposed to increase the payload capacity. With this new design, it is seen that the payload can be increased by 12.7 % and 17.6 % for PSLV and Pegasus, respectively. The novelty of this design is that with no changes to any other hardware of the above two systems the increase in payload can be achieved.     

Combustion of Ultrafine Aluminum in Air

The paper reports results of studying the combustion of ultrafine aluminum (surface average diameter of particles is 0.1 m) in a sealed bomb at an initial air pressure of 1 atm. The combustion proceeds in two stages, similarly to combustion in air. It is shown that during the twostage combustion of ultrafine aluminum powder in the bomb, the mass concentration of chemically bound nitrogen in the final products increases by 20% in terms of aluminum nitride. An increase in nitrogen content in confined combustion validates the previously proposed mechanism of binding air nitrogen with participation of the gas phase during aluminum combustion.     

Study of self-propagating high-temperature synthesis in the Ti–TiO<Subscript>2</Subscript>–Al–Air system and preparation of ceramic materials based on titanium nitride and corundum

Mechanisms for titanium nitride formation during burning in air of a mixture of coarse titanium powder and its dioxide with addition of aluminum powder, and formation of the phase composition of ceramic materials prepared by sintering combustion products in a hydrogen atmosphere, are considered. Material of the composition titanium nitride – corundum is prepared.     

Influence of aluminum particle size on ignition and nonstationary combustion of heterogeneous condensed systems

The results of studies of the effect of particle size of aluminum powder in condensed systems on the ignition, nonstationary combustion, and acoustic conductivity of the burning surface are presented. Analysis of the experimental data shows that the ignition delay and the temperature of burning surface of the heterogeneous condensed systems under study decrease with increasing particle size of aluminum powder, and the nature of the dependence of the nonstationary burning rate on the time of depressurization of the combustion chamber for compositions containing micron or ultrafine aluminum powders is in qualitative agreement with the phenomenological theory of nonstationary combustion. Replacement of micron aluminum powder by ultrafine powder in a heterogeneous condensed system increases acoustic conductivity.     

DENSIFICATION OF ALUMINUM NITRIDE-BASED CERAMIC MATERIALS SYNTHESIZED BY COMBUSTION OF ALUMINUM IN AIR

Aluminum nitride based materials were synthesized by combustion of aluminum powder in air. When aluminum nitride powder is used as a diluent, mostly aluminum nitride product with small amount of alumina was obtained. For reactant mixtures consisting of 33 wt% of aluminum and 67 w% of alumina, materials with a high content of aluminum oxynitride (AION) were formed. Synthesized aluminum nitride based powders with and without in-situ added sintering aids were characterized and tested for their sintering ability. Densification characteristics of combustion synthesized powders by pressureless sintering in nitrogen atmosphere are also reported.     

含不同粒度铝粉的铝/冰燃料的燃烧特性

用微米铝粉逐级取代部分纳米铝粉制备铝/冰燃料,采用表面接触法和高速摄影技术研究了不同粒度铝粉改善铝/冰燃料燃烧特性的效果. 结果表明,随微米铝粉取代量增加,铝/冰燃料燃烧反应速率和剧烈程度均先提高后降低,微米铝粉取代量为30%(w)时,铝/冰燃料最高升温速率达6062.24℃/s,是纯纳米铝/冰燃料的3.8倍. 用微米铝粉取代部分纳米铝粉均不同程度提高铝/冰燃料的燃面传播速率,微米铝粉取代量约为20%(w)时燃烧性能最佳,燃面传播速率较纯纳米铝/冰燃料提高57.8%. 在分析实验结果的基础上,建立了铝/冰燃料的燃烧火焰模型.     

Condensed combustion products of aluminized propellants. IV. Effect of the nature of nitramines on aluminum agglomeration and combustion efficiency

The condensed combustion products of two model propellants consisting of ammonium perchlorate, aluminum, nitramine, and an energetic binder were studied by a sampling method. One of the propellants contained HMX with a particle size D ₁₀ ≈ 490 μm, and the other RDX with a particle size _{D 10} ≈ 380 μm. The particle-size distribution and the content of metallic aluminum in particles of condensed combustion products with a particle size of 1.2 μm to the maximum particle size in the pressure range of 0.1–6.5 MPa were determined with variation in the particle quenching distance from the burning surface to 100 mm. For agglomerates, dependences of the incompleteness of aluminum combustion on the residence time in the propellant flame were obtained. The RDX-based propellant is characterized by more severe agglomeration than the HMX-based propellant — the agglomerate size and mass are larger and the aluminum burnout proceeds more slowly. The ratio of the mass of the oxide accumulated on the agglomerates to the total mass of the oxide formed is determined. The agglomerate size is shown to be the main physical factor that governs the accumulation of the oxide on the burning agglomerate. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 4, pp. 78–92, July–August, 2006.     

Interaction of powdery Al, Zr and Ti with atmospheric nitrogen and subsequent nitride formation under the metal powder combustion in air

The combustion process in air for aluminum nanopowders (nAl), micron-sized powders of aluminum (μAl), titanium (μTi) and zirconium (μZr) was accompanied by the predominant reaction of the metals with N₂ and the subsequent stabilization of the nitride phases (from 38 wt.% of ZrN for μZr combustion to 72 wt.% of AlN for nAl combustion) in the condensed combustion products (CCP). The combustion process, composition and structure of CCP of nAl, μAl, μTi, and μZr were studied. Scanning electronic microscopy (SEM), X-ray diffraction (XRD), energy dispersive (X-ray) spectroscopy (EDX), and chemical analysis were performed on both initial powders and CCP. The combustion mechanism for the studied metal powders was experimentally proved. The formation of a large amount of non-equilibrium products (AlN, ZrN, TiN) instead of oxides in air is the special feature of the above mentioned experimental conditions. Nitride formation in air was defined by high temperatures and high burning rates during combustion of powdery Al, Ti and Zr.     

Kinetics and Mechanisms for Nitridation of Floating Aluminum Powder

Aluminum powder entrained by ammonia-containing nitrogen gas was reacted at various temperatures and time to form aluminum nitride powder. The kinetics of nitride formation were determined by a quantitative X-ray analysis and compared with those determined by a nitrogen analysis of the product. The conversion to aluminum nitride increased with the reaction time following a sigmoidal rate law. The reaction time for full conversion decreased as the temperature increased in the range 1050°–1300°C. The reaction rate constant at a given temperature was evaluated using the Avrami equation. The activation energy for the reaction was 1054 ± 91 kJ/mol in the temperature range of 1050°–1200°C, and decreased to 322 ± 70 kJ/mol above 1200°C. Comparative analysis of powders formed below and above 1200°C suggested strongly that the rate-controlling step changed from chemical reaction to mass transport above 1200°C.