环境氧含量对含铝炸药爆热的影响

利用恒温式量热计测定了3种含铝炸药在不同环境中的爆热,研究了其能量释放规律。结果表明,含铝炸药在真空、空气和纯氧环境中的爆热逐渐增高,固体爆轰产物存在一定差异。3种含铝炸药在纯氧中的爆热基本相当,说明发生了完全燃烧反应。在真空和空气环境中,含细铝粉(中位径12.43μm)的含铝炸药爆热均低于含粗铝粉(中位径74.14μm)的炸药。两种粒度铝粉级配后的含铝炸药,在真空和空气环境中的爆热处于铝粉未级配的炸药爆热之间,原因是没有达到细铝粉先反应、粗铝粉后反应的理想状态。     

炸药爆轰时的能量释放

炸药的一个重要特征就是在一定的外界作用下能发生爆轰化学反应,在极短的时间内放出巨大的能量,使爆轰产物达到极高的温度和压力而完成破坏或抛掷作用。单位质量炸药在爆轰时放出的能量叫爆轰能(E_d),这一能量如用热量的单位表示就叫作爆轰热(Q_d)。目前已经能够用实验的方法,测定炸药爆轰后产物在一定条件下冷却到室温时放出的热     

炸药爆轰时的能量释放

炸药的一个重要特征就是在一定的外界作用下能发生爆轰化学反应,在极短的时间内放出巨大的能量,使爆轰产物达到极高的温度和压力而完成破坏或抛掷作用。单位质量炸药在爆轰时放出的能量叫爆轰能(E_d),这一能量如用热量的单位表示就叫作爆轰热(Q_d)。目前已经能够用实验的方法,测定炸药爆轰后产物在一定条件下冷却到室温时放出的热量。为了和前面所讲的爆轰热相区别,习惯上把这一实验测定的热值称之为爆热(或爆炸热、爆破热)(Q_e)。     

爆轰化学:非理想炸药中的扩散控制

炸药的性能既是爆轰波阵面附近所释放的峰值能量的函数,又是泰勒(Taylor)波期间释放的余能的函数。爆轰波阵面和膨胀之间能量的相对分配以及膨胀中能量释放的速率可能受化学动力学过程或扩散过程的支配。爆轰量热法已是研究这些过程所用的主要实验方法。对硝铵(AN)和梯恩梯(TNT)的一些配方,确定了总的能量释放;也确定了膨胀等熵线上一点或一个区域爆轰产物的定量分析。在这些配方中,组份和AN的颗粒大小都是变化的。为进一步洞察反应区中或其附近发生的反应,对选用的炸药也应用了同位素示踪法。在一种理想均质炸药中,做了类似的实验。     

爆轰化学:非理想炸药中的扩散控制

炸药的性能既是爆轰波阵面附近所释放的峰值能量的函数,又是泰勒(Taylor)波期间释放的余能的函数。爆轰波阵面和膨胀之间能量的相对分配以及膨胀中能量释放的速率可能受化学动力学过程或扩散过程的支配。爆轰量热法已是研究这些过程所用的主要实验方法。对硝铵(AN)和梯恩梯(TNT)的一些配方,确定了总的能量释放;也确定了膨胀等熵线上一点或一个区域爆轰产物的定量分析。在这些配方中,组份和AN的颗粒大小都是变化的。为进一步洞察反应区中或其附近发生的反应,对选用的炸药也应用了同位素示踪法。在一种理想均质炸药中,做了类似的实验。     

含纳米级铝粉的复合炸药研究

铝粉的颗粒尺寸对含铝炸药的爆轰性能有显著影响，在以RDX为主体的粘结炸药中，加入20％粒径为50nm的超细铝粉，得到的新型复合炸药，其爆轰性能及作功能力明显高于含20％粒径为5μm和50μm的复合炸药。     

CL-20基含铝炸药组分微结构对其爆炸释能特性的影响

为了改善铝粉在CL-20基含铝炸药中的反应动力学特性,利用溶剂-非溶剂法制备了CL-20/Al复合颗粒,实现了CL-20与Al在微结构上的紧密结合,通过直接法制备了由CL-20/Al复合颗粒构成的组分质量分数为85%CL-20/10%Al/5%黏结剂的含铝炸药,并与常规法制备的相同组成的CL-20基含铝炸药进行了机械感度、爆热、爆炸罐试验和圆筒试验等结果的对比。结果表明,CL-20/Al复合颗粒会使含铝炸药的撞击感度略有提高,而摩擦感度不变,但总体上对机械感度影响不大;通过CL-20/Al在微结构上的复合,缩短了Al粉与爆轰产物之间的扩散距离,可以显著改善Al粉的反应动力学性能,提高Al粉在含铝炸药爆炸过程中的反应完全性,促使部分Al粉在爆轰区内参与反应,相比于常规法制备的相同组成的含铝炸药,可使含铝炸药的爆热从6787J/g提高至6930J/g,爆炸罐内爆炸场最高温度从544.3℃提高至661.2℃,格尼系数由2.88mm/μs提高至3.10mm/μs。     

固体炸药爆轰产物的状态

多方方程连同爆轰波关系式一起,提供了表征固体高能炸药爆轰产物除温度以外的所有参数的实用值。但是,多方方程的应用被限于描述处在绝对零度的材料,即被限于纯粹具有位能的各种固体。因此,虽然多方爆轰产物的聚集状态是气体,但是它们具有固体的特性。事实上,多方方程可以通过假定固体在内部膨胀压力足够破坏所有的原子键的条件下推导出来。根据德拜(Debye)理论,多方方程是近似的,在不考虑原子振动的热能贡献时是正确的。密度足够高的固体炸药的爆轰产物满足这个要求,因为炸药的爆轰热被完全吸收来破坏所有的原子键或使原子晶格升华。在反应期间,由升华过程中两相之间的平衡,可以确定爆轰产物的C-J温度。另外,断裂理论提供的材料数据,表明爆轰产物具有金属的特性,并指出它们形成一种导电等离子体。     

固体炸药爆轰产物的状态

多方方程连同爆轰波关系式一起,提供了表征固体高能炸药爆轰产物除温度以外的所有参数的实用值。但是,多方方程的应用被限于描述处在绝对零度的材料,即被限于纯粹具有位能的各种固体。因此,虽然多方爆轰产物的聚集状态是气体,但是它们具有固体的特性。事实上,多方方程可以通过假定固体在内部膨胀压力足够破坏所有的原子键的条件下推导出来。根据德拜(Debye)理论,多方方程是近似的,在不考虑原子振动的热能贡献时是正确的。密度足够高的固体炸药的爆轰产物满足这个要求,因为炸药的爆轰热被完全吸收来破坏所有的原子键或使原子晶格升华。在反应期间,由升华过程中两相之间的平衡,可以确定爆轰产物的c-J温度。另外,断裂理论提供的材料数据,表明爆轰产物具有金属的特性,并指出它们形成一种导电等离子体。     

微/纳米粒度级配对炸药爆轰波阵面D_n(κ)关系的影响

为了研究微/纳米铝粉/RDX粒度级配对含铝炸药爆轰波阵面曲率效应的影响,采用光学波形扫描及电探针测速法测量了不同微/纳米铝粉/RDX粒度级配的含铝炸药在常温环境下的拟定态爆轰波形及爆速,并基于实验结果分析了炸药爆轰波阵面法向速度D_n与当地曲率κ之间的函数关系。结果表明,采用微/纳米铝粉/RDX粒度级配时,波阵面弯曲程度明显变小,且法向爆速受曲率效应的影响减弱,其中,微/纳米RDX颗粒质量比为50∶25或微/纳米铝粉颗粒质量比为15∶5时波形较为平坦,其最大曲率分别约为0.013和0.014mm~(-1),法向爆速较拟定态爆速的最大降幅分别约为0.03和0.04mm/μs,相当于常规微米试样的56%和61%,反映出波阵面能量因侧向流动而发生的损耗较小。     

Effect of Nano‐Aluminum and Fumed Silica Particles on Deflagration and Detonation of Nitromethane

The heterogeneous interaction between nitromethane (NM), particles of nanoscale aluminum (38 and 80 nm diameter), and fumed silica is examined in terms of the deflagration and detonation characteristics. Burning rates are quantified as functions of pressure using an optical pressure vessel up to 14.2 MPa, while detonation structure is characterized in terms of failure diameter. Nitromethane is gelled using fumed silica (CAB‐O‐SIL^®), as well as by the nanoaluminum particles themselves. Use of nanoaluminum particles with fumed silica slightly increases burning rates compared to the use of larger diameter Al particles; however distinct increases in burning rates are found when CAB‐O‐SIL is removed and replaced with more energetic aluminum nanoparticles, whose high surface area allows them to also act as the gellant. Mixtures including fumed silica yield a reduced burning rate pressure exponent compared to neat NM, while mixtures of aluminum particles alone show a significant increase. Failure diameters of mixture detonations are found to vary significantly as a function of 38 nm aluminum particle loading, reducing more than 50% from that of neat nitromethane with 12.5% (by mass) aluminum loading. Failure diameter results indicate a relative minimum with respect to particle separation (% loading) which is not observed in other heterogeneous mixtures.     

Exit of a Heterogeneous Detonation Wave into a Channel with Linear Expansion. II. Critical Propagation Condition

Propagation of a detonation wave in monodisperse suspensions of reacting particles (based on the model of the suspension of aluminum particles in oxygen) in channels with linear expansion is studied within the framework of mechanics of heterogeneous reacting media. Reduced kinetics is described with allowance for the transitional (from diffusion to kinetic) regime of combustion of micron-sized and submicron-sized spherical aluminum particles. The effects of the channel width, particle diameter, and expansion angle on propagation conditions and detonation regimes are determined. The critical channel width is found to be a nonmonotonic function of the expansion angle, which is associated with qualitatively different wave patterns behind an oblique step. Flow charts are constructed, and the results are compared with solutions of problems of heterogeneous detonation wave propagation in channels with a backward-facing step and with sudden expansion.     

Characteristics and criteria of ignition of suspensions of aluminum particles in detonation processes

A physicomathematical model of ignition of suspensions of aluminum particles under dynamic conditions including melting, low-temperature oxidation of aluminum, and polymorphic transformation of the oxide film is presented. Model verification is based on experimental data on the limit temperatures and delays of ignition of suspensions of aluminum particles in shock and detonation waves. Applicability of reduced models (without melting and pre-frame oxidation) at an adequate temperature criterion that ensures identical ignition delays is demonstrated, based on the analysis of thermal dynamics of the mixture. Dependences of the ignition temperature on the shock wave parameters, particle size and concentration, and oxidizer concentration are obtained. Formulas for an invariant (with respect to concentrations) criterion are derived, which express the dependence of the ignition temperature on the current temperature of the gas. The governing constants are found for suspensions of particles in air and oxygen.     

Exit of a heterogeneous detonation wave into a channel with linear expansion. I. Propagation regimes

Propagation of a plane detonation wave in a stoichiometric mixture of a gas and aluminum particles in a plane channel with a linear expansion section is studied by methods of numerical simulation. The slope of the wall is varied from 15 to 60°. The basic regimes of detonation propagation are analyzed: supercritical (without detonation failure), critical (with partial failure and re-initiation), and subcritical (with complete separation of the shock front and combustion front and with detonation failure). The detonation configuration formed in the expanding section can be a cellular structure with large differences in cell sizes at large angles of expansion or a close-to-uniform structure at the wall angle of 15°.     

Axisymmetric expanding heterogeneous detonation in gas suspensions of aluminum particles

A problem of expansion of heterogeneous detonation in a suspension of aluminum particles in gaseous oxygen from a circular tube and its propagation in a semi-bounded or unbounded space is studied by numerical methods. The effects of the particle diameter in monodisperse suspensions and of the composition of bidisperse suspensions on detonation propagation regimes are studied. The calculated results are compared with data on heterogeneous detonation of gas suspensions in a plane channel and on gas detonation. The critical values of the channel width and the tube diameter are found to differ by a factor of 2–2.5, as it is also observed in gas detonation. However, the ratio of the critical diameter to the detonation cell size in the case of heterogeneous detonation can be smaller than that in gas mixtures by an order of magnitude.     

Modeling of Plane Detonation Waves in a Gas Suspension of Aluminum Nanoparticles

A physicomathematical model of detonation of a gas suspension of aluminum nanoparticles with allowance for the transition from the continuum to free-molecular flow regime and heat transfer between the particles is proposed. A formula for logarithmic interpolation for the thermal relaxation time in the transitional regime is derived. A semi-empirical model of Arrheniustype reduced kinetics of combustion is developed, which ensures good agreement with available experimental data. Steady (Chapman–Jouguet and overdriven) structures and also attenuating detonation waves in suspensions of nanoparticles are analyzed. Typical features of detonation in nanoparticle suspensions are found: the normal detonation regimes correspond to the solution in the Chapman–Jouguet plane with a sonic final state in terms of the equilibrium velocity of sound; combustion occurs in an almost equilibrium mixture in terms of velocities and temperatures; a strong dependence of the combustion region length on the amplitude of the leading shock wave is observed.     

Fuel‐Rich Explosive Energy Release: Oxidizer Concentration Dependence

Small‐scale detonation experiments were conducted in a controlled atmosphere chamber to investigate the post‐detonation reactivity of a fuel‐rich, plastic bonded explosive. The atmosphere surrounding these 20 g explosive charges was varied in oxygen content from 0.2 to 100% with the total pressure held constant at 101 kPa. The performance of this small‐scale explosive charge is sensitive to the changing atmospheric conditions, perhaps more so than a larger charge size, due to burning inefficiencies corresponding to a scaling effect (increased surface area to volume ratio). Time‐resolved optical emission spectroscopy was used to contrast the dependence of the post‐detonation combustion properties on external oxygen content. The dominant near‐ultraviolet and visible emission features evolve from aluminum (Al) and aluminum monoxide (AlO) when oxygen is present. The time evolution of AlO emission was used to estimate the aluminum particle burning times, which lengthen from 6 to 31 μs as the oxygen content is reduced from 100 to 1%. The absence of AlO spectral features below 1% oxygen levels imply that the emission spectroscopy applied to this detonation environment is most sensitive to the aerobic component of the post‐detonation combustion. Pressure and optical pyrometry measurements recorded during the same experiments exhibit the strong dependence of the early time energy release on the oxygen content in the surrounding atmosphere. Numerical simulations of the detonation and subsequent multiphase flow expansion predict the position of the fuel particles to extend beyond the detonation products and, in some cases, beyond the shock front during the timescales covered in these experiments, stressing the importance of mixing with ambient oxygen for early combustion to occur.     

Thermal and dielectric properties of the aluminum particle/epoxy resin composites

Microsized aluminum/epoxy resin composites were prepared, and the thermal and dielectric properties of the composites were investigated in terms of composition, aluminum particle sizes, frequency, and temperature. The results showed that the introduction of aluminum particles to the composites hardly influenced the thermal stability behavior, and decreased T_g of the epoxy resin; moreover, the size, concentration, and surface modification of aluminum particles had an effect on their thermal conductivity and dielectric properties. The dielectric permittivity increased smoothly with a rise of aluminum particle content, as well as with a decrease in frequency at high loading with aluminum particles. While the dissipation factor value increased slightly with an increase in frequency, it still remained at a low level. The dielectric permittivity and loss increased with temperature, owing to the segmental mobility of the polymer molecules. We found that the aluminum/epoxy composite containing 48 vol % aluminum‐particle content possessed a high thermal conductivity and a high dielectric permittivity, but a low loss factor, a low electric conductivity, and a higher breakdown voltage. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of powdered aluminum additives on the detonation parameters of high explosives

The effect of additives of various brands of aluminum on the detonation parameters of high explosives is investigated. It is shown that the detonation velocity of aluminized mixtures depends not only on the size of the additive particles used but also on their form.Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 2, pp. 115–117, March–April, 1993.     

Performance Properties of Commercial Explosives

The aquarium test is a proven means of obtaining nonidial performance property data for commercial blasting agents. Optical data on the detonation velocity, shock wave in water, and expansion rate of the pipe enclosing the detonation products (in combination with the equilibrium thermodynamic chemistry code BKW) give the C-J state and degree of chemical reaction at the detonation front, as well as information on additional chemical reaction that occurs as the detonation products expand. Specific explosive systems that are studied are ammonium nitrate-fuel oil mixture (ANFO), aluminized ANFO, flaked trinitrotoluene (TNT), and several other commercial products in 10-cm-diam and 20-cm-diam pipes of Plexiglas and clay. Experimental shock pressure data are obtained with lithium niobate transducers placed in the water surrounding the explosive charge. These data show that the addition of ∼ 100-μm aluminum particles to ANFO significantly increases the initial peak shock pressure delivered to the surrounding medium. Peak shock pressures in the water, calculated from the shock-wave orientation, are also useful in comparing performance properties of various commercial explosives.