Ultraviolet Laser-induced ignition of RDX single crystal
The RDX single crystals are ignited by ultraviolet laser (355 nm, 6.4 ns) pulses. The laser-induced damage morphology consisted of two distinct regions: a core region of layered fracture and a peripheral region of stripped material surrounding the core. As laser fluence increases, the area of the whole crack region increases all the way, while both the area and depth of the core region increase firstly, and then stay stable over the laser fluence of 12 J/cm2. The experimental details indicate the dynamics during laser ignition process. Plasma fireball of high temperature and pressure occurs firstly, followed by the micro-explosions on the (210) surface, and finally shock waves propagate through the materials to further strip materials outside and yield in-depth cracks in larger surrounding region. The plasma fireball evolves from isotropic to anisotropic under higher laser fluence resulting in the damage expansion only in lateral direction while maintaining the fixed depth. The primary insights into the interaction dynamics between laser and energetic materials can help developing the superior laser ignition technique.
Critical conditions of reaction initiation in the PETN during laser heating of light-absorbing nanoparticles
This paper describes the micro-hotspot model of laser initiation of energy materials. The relationship of the critical energy density and the temperature of the reaction hotspot in PETN with the nanoparticle radii of 12 metals at a pulse duration at half-height of 14 ns is determined. It is established that, as the nanoparticle radius is about 10 nm, the critical energy density tends to a certain value independent of heat capacity of metal. This is due to the reduction of the ratio of the nanoparticle volume to the volume of the heated PETN layer, which leads to the fact that most of the energy is spent on heating the matrix. It is shown that the critical hotspot temperature depends on both pulse duration and nanoparticle radius. The analytical expressions for the relationships of the critical parameters of reaction initiation with the radius and heat capacity of metal nanoparticles and for the relationship of the critical hotspot temperature with pulse duration are obtained. The invariant binding the critical energy density and the characteristic development time of the reaction is discovered. The results of this paper are necessary for the optimization of the composition of the optical detonator cell.
EFFECT OF SAMPLE PREPARATION ON WATER TREE RESISTANCE OF XLPE/SEBS BLENDS
The effects of an aromatic polymer, such as poly[styrene-b-(ethylene-co-butylene)b-styrene] (SEBS), and its preparation processes on water tree resistance, morphology, crystallinity, dielectric constant and dielectric loss tangent of crosslinked polyethylene (XLPE)/SEBS and XLPE/SEBS/ethylene vinyl acetate (EVA) blends were investigated. The XLPE/SEBS samples were characterized by means of differential scanning calorimetry, scanning electron microscopy, dielectric spectral analysis and the accelerated water treeing experiment. The results clearly showed that although SEBS was partially compatible with LDPE and it was dispersed evenly in XLPE matrix, the blends demonstrated excellent dielectric performances, such as dielectric constant and dissipation factor. The crystallinity of XLPE/SEBS blends was decreased with increase in SEBS content and it was further decreased with the addition of EVA. SEBS could effectively improve the water-tree resistance of XLPE and both SEBS and EVA were found to improve the water tree resistance of XLPE synergistically as expected. The differences in sample preparation processes could change the phase morphology and dielectric performance of the blends, and could also influence the dispersion of SEBS in XLPE matrix as well as the crystallinity of the blends. Different preparation processes led to different water tree resistance behaviours of the samples. The improvement of SEBS dispersion in XLPE matrix helped to improve the water tree resistance of XLPE.