Electrostatic Discharge Ignition of Energetic Materials

Electrostatic discharge(ESD) ignition of explosives, pyrotechnics, or propellants is often considered to be mainly dependent upon various physical characteristics of the energetic material. This work shows that ESD ignition of secondary explosives tested in powdered form is primarily dependent upon the chemical characteristics of the energetic material(i.e., the decomposition rate kinetics of the materials). We propose that ignition occurs when a spark raises the temperature of the explosive particles to the point where thermal runaway occurs. ESD sensitivities of a diverse series of explosives were measured using a traveling needle test apparatus with the powders slightly confined by Mylar tape to prevent formation and ignition of a dust cloud. Using global thermal decomposition rate coefficient expressions, two parameters were calculated for each explosive:(1) the critical temperatures according to the Frank-Kamenetskii formula for 20 μm particles of each explosive and(2) the temperatures at which the rate coefficient equaled 10³ s⁻¹. These two sets of data were correlated with the observed ESD sensitivities for 50 percent probability of ignition, E₅₀. Excellent correlations resulted, indicating that for ESD ignition under these conditions the spark discharge is primarily a thermal source.     

含能材料冲击波引发判据的分析

分析含能材料的五种典型冲击波引发的判据和有关数据,认为目前的判据局限于没有考虑装药微结构的影响。据此,提出了用局部化因子修正原判据的新思想。     

Influence of Particle Size Distribution on Ductile-Phase Toughening in Brittle Materials

In ductile-phase-toughened brittle materials the size distribution of the ductile phase sometimes has a remarkable effect on toughening. An equation for predicting the toughness increment due to crack bridging, taking into account a ductile-phase particle size distribution, has been deduced. Comparison between the toughness value predicted by the equation and that obtained from a double cantilever beam (DCB) method on a Al2O3–20 vol% Ni composite material has shown that the equation gives a more reasonable estimate of the toughness than previous equations.     

Metal Particle Size Determination of Supported Metal Catalysts

The variety of supported metal catalysts utilized in the operations of the petroleum and chemical industries emphasizes the importance of metal-catalyzed reactions. As a result, many scientific investigators have attempted to characterize and follow closely the changes in the crystallite size and shape of supported metal particles in commercial and simulated environments. From these efforts a massive production of experimental facts has emerged.     

Metal Particle Size Determination of Supported Metal Catalysts

The variety of supported metal catalysts utilized in the operations of the petroleum and chemical industries emphasizes the importance of metal-catalyzed reactions. As a result, many scientific investigators have attempted to characterize and follow closely the changes in the crystallite size and shape of supported metal particles in commercial and simulated environments. From these efforts a massive production of experimental facts has emerged.     

Influence of the Metal Particle Size on the Crack Growth Resistance in Mullite–Molybdenum Composites

The R -curve for mullite–molybdenum (32 vol%) composites, which were obtained at 1650°C under reducing conditions with three different Mo average grain sizes (1.5, 3, and 9 μm), was estimated by the indentation-strength method and compared with that monolithic mullite obtained under similar conditions. The composites material exhibited rising R -curve behavior. The composite with larger grain size, however, displayed better damage tolerance and higher resistance to crack growth. Microscopic observation of the crack path revealed, in the composites, the systematic presence of dispersoids acting as bridging sites in the crack wake. Therefore, the increased fracture toughness of these ceramic-matrix composites with adherent ductile phase can be attributed to clamping forces applied by metal ligaments that bridge the crack faces behind the crack front. These clamping forces retard the crack from opening as an external stress is applied. It was inferred that this superior performance of the larger Mo particle size composite can be attributed mainly to more effective bridging of the metal grains. Because of this, a higher applied stress intensity will be required to propagate the crack tip. These results suggest that the rising R -curve should be proportional to the metal grain size, since the grain bridging area is proportional to the metal grain size.     

Particle Size, Particle Size Distribution, and Related Measurements of Supported Metal Catalysts

It should be apparent from the contents of this review that no single method provides a full characterization of particle size and/or particle size distribution in supported metal catalysts without some inherent theoretical shortcoming, experimental difficulty, or ambiguities in interpretation of results. The message is clearly to use more than one technique whenever possible in order to obtain intercomparisons both of size/size distribution number themselves and internal consistency of the data. However, to be avoided are incorrect comparisons, such as sizes obtained from the Scherrer formula and chemisorption experiments, for example, which measure different things. We believe that high-resolution TEM has a bright future in catalyst characterization, but perhaps the most accessible and convenient combination at present is that of Fourier line profile x-ray analysis and chemisorption, albeit at the expense of some analysis in the former case.     

含能液滴着火过程的实验研究

应用光学层析和计算机多媒体技术研究了含能液滴LP1846在大气压下的着火过程。动态显示液滴从受热、分解到着火燃烧的时间序列干涉图,并算出液滴着火温度。该方法为研究含能液滴着火燃烧特性提供了新的实验手段。     

激光粒度分析仪测定特种陶瓷坯料粒度

根据多年实践研究与应用，分析了如何应用激光粒度分析仪提高特种陶瓷产品的质量问题，提出了一组较优化的粒度及其分布情况的控制指标，确定了较为合理的原料研磨时间。     

PETN粒度对其机械感度的影响

用微团化动态结晶方法和溶剂/非溶剂滴加重结晶方法制备出3种粒径的PETN颗粒,采用粒度分析仪和扫描电子显微镜(SEM)对其粒度进行了表征。测定了3种粒度PETN试样的撞击感度(特性落高H50)和摩擦感度(爆炸百分数)值。结果表明,3种粒度PETN撞击感度分别为33.7、28.3和22.9cm,摩擦感度分别为52%、24.8%和40%。撞击感度随粒度的减小逐渐降低,亚微米级PETN最低。摩擦感度随粒度的减小先降低再升高,而且亚微米PETN最敏感。     

金属橡胶过滤材料孔径分布特性研究

孔径分布是金属橡胶过滤材料重要的孔隙特征,它对过滤器的过滤精度和截留效率起着决定性作用,采用压汞法对金属橡胶滤材的孔径分布进行研究,结果表明在孔隙体积构成中,一部分狭窄范围内的孔隙总是占有多数,金属橡胶滤材孔径分布规律为正态分布。     

纳米镁基储氢材料的粒度分布表征

用碱熔、酸洗、碳化处理制得的微晶碳做助磨剂,球磨金属镁3 h,制得储氢材料70Mg30C。用扫描电镜和原子力显微镜观测可见,颗粒的平均粒径约为100 nm,颗粒大小主要分布在50~100 nm之间,而透射电镜观测的颗粒大小主要集中在50 nm左右。扫描电镜图的粒度分布近似为对数正态分布,粒度分布范围为25~260 nm。     

颗粒粒度对Cu基载氧体反应性能的影响

基于化学链燃烧新流程,采用固定床反应器研究了Cu基载氧体粒度、作为活性组分的Cu粉粒度及作为惰性载体的g-Al2O3粒度对载氧体反应性能的影响. 结果表明,载氧体的还原率及氧化率随Cu粉粒度减小而增大,Cu粉平均粒度小于63 mm时,载氧体还原率和氧化率达95%和93%以上. 载氧体还原过程中有少量CH4生成,生成量随Cu粉粒度减小而减少,Cu粉平均粒度小于32 mm时低于1%;当载氧体粒度接近g-Al2O3粒度时,载氧体的性能明显降低,只有g-Al2O3粒度明显小于载氧体粒度时,g-Al2O3才能起到分散活性组分、抑制活性组分烧结的作用.     

Modeling of the Mixing of Disperse Materials Differing in Particle Size

A multistage mechanism is suggested for particle exchange in the preparation of multicomponent mixtures, and the layered model of mixing is adapted to the case of particles differing in size and/or density.     

基于填料粒度对离合器摩擦材料性能影响的研究

本文提出采用丁腈乳胶改性酚醛树脂作粘结剂、采用玻璃纤维和复合包芯纱作为增强纤维、丁腈橡胶复合填料制备离合器摩擦材料的工艺方法。试验表,在相同配方和工艺条件下,复合填料的粒度对离合器摩擦材料的性能有很大影响。当复合填料粒度为20-60目左右时,摩擦材料具有较好的物理机械性能和良好的摩擦磨损性能。     

Influence of Particle Size on the Sintering Kinetics of Ultrapure Sodium Chloride

Sodium chloride particles with size fractions covering the range <38 to 180 μm were sintered in air at T=973 to 1048 K. At any given time and temperature, the degree of densification was found to be a decreasing function of particle size. Calculated activation energies from these densification results showed a corresponding dependence on particle size, i.e. higher energies were associated with the sintering of larger size fractions. Surface-area reduction measurements showed a similar trend with respect to particle size. These results are discussed in terms of simultaneous contributions from densifying (bulk diffusion) and nondensifying (evaporation-condensation) processes in the sintering of sodium chloride.     

粉末涂料粒径对涂装产品质量的影响

介绍了用激光粒度分布仪检测粉末涂料粒径的原理,分析了粉末涂料的粒径对涂料的流平性、上粉率、稳定性、回收率及涂装产品质量外观等的影响,结合实际生产经验,根据涂装产品质量的要求,提出了控制粉末涂料粒径的生产工艺参数。     

亚微米级LiFePO4材料的粒径控制及性能研究

研究了亚微米级的LiFePO4材料的制备与粒径控制,使之同时具有微米级LiFePO4材料的加工性能和纳米级LiFePO4材料的高倍率放电性能,采用添加多糖的方法制备的0.56μm、0.76μm、0.96μm三种粒径的亚微米LiFePO4材料具有优良的大电流放电性能和大电流循环稳定性能。随着LiFePO4材料粒径的减小,大电流下容量保持率不断提高,0.56μm的LiFePO4材料20 C放电的容量保持率达到89.3%,在10 C倍率下放电,100个循环容量保持率在97%以上。