Hydrodynamics of the initial phase of explosion

Physical and hydrodynamic processes accompanying explosions of condensed explosives and fuel–air mixtures have been considered. Wide-range equations of the state of explosion products and air have been derived. A physical model and a program code based on the equations of gas dynamics in Lagrangian representation have been developed for modeling one-dimensional hydrodynamic processes in the near zone of explosion. The described model has shown its working efficiency within a wide range of explosion energies and environmental conditions.     

水的相变过程中辐射机理研究

水的相变过程会出现异常辐射现象,在短波范围内其辐射强度比普朗克辐射强度强4倍左右,这与常规的热辐射不同,称为相变辐射。针对水在凝结过程中所释放的异常辐射现象做了机理性研究,并将热力学、分子理论与所发现的实验数据相结合,提出一个新的机理来解释这一现象。研究结果表明,相变辐射的产生可能与水分子氢键的形成过程相关,辐射的波长...     

Nanogap plasmonic field enhancement on hydrogen-absorbing transition metals

The electromagnetic field enhancement factors by gap plasmons between two spherical metal particles are calculated for hydrogen-absorbing transition metals Pd, Ti, and Ni, and reference noble metals Au, Ag, and Cu, in air, H₂, or vacuum, and H₂O. The dependence of the field enhancement factors on the metal species, the field wavelength, the electric field polarization, the separation of the two metal particles, and the observing location is systematically investigated. Field enhancement is observed significantly large in the gap of two metal particles and sensitive to the particle separation, but insensitive to the position in the gap, indicating a geometric flexibility for applications. The spectral peak field enhancement factors for Pd, Ti, and Ni do not compete with those for Au, Ag, and Cu, but do in the microwave regime. For the electric field parallel to the bipartite alignment, the field enhancement factors in the gap for Pd, Ti, and Ni are observed as large as several hundred and ten thousand for the separation-to-radius ratios of 0.1 and 0.01, respectively, for a wide wavelength region spanning from the visible to the infrared. The large field enhancements in the nanogaps of hydrogen-absorbing transition metals observed in this study can potentially be utilized for various energy applications, such as hydrogen storage, sensing, and nuclear fusion. In practical metallic material systems, it is important to account for such a gap-plasmon effect because nanoscale gaps commonly exist, for instance, on rough metal surfaces and in metal particle aggregates.     

The maximum solid solubility of the transition metals in palladium

The maximum solid solubility limit (C_max) of transition metals dissolved in palladium can be described as an equation in semi-empirical theories with parameters such as electronegativity difference, atomic diameter and covalent electrons. It has been found that the electronegativity difference and the covalent electron number mainly affected the C_max of transition metals in palladium. The atomic size parameter had the smallest effect on the C_max.     

Effect of compact structure on the phase transition in the oxides derived Cu2ZnSnSe4 thin films

Cu₂ZnSnSe₄ (CZTSe) films were prepared by selenization of oxides nanoparticles. A novel densification method was performed to improve the grain size and morphology of the CZTSe films. From absorption spectroscopy measurement, it was also found that the compressed CZTSe films showed Kesterite structure with a band gap of 0.92 eV, while the untreated CZTSe films showed partially disordered Kesterite structure with a band gap of 0.86 eV. The phase transition during the selenization of oxides nanoparticles is affected significantly by the compact density. The nucleation and growth of Kesterite phase is considered to be facilitated by the mass transfer around the particle contacts. The different characterization techniques show that the dense CZTSe layer with very large grain size can be achieved by using compression method.     

The role of transition metal oxides in the decomposition and explosion of arylammonium perchlorates

The influence of MnO₂, CuO, and NiO on the thermal decomposition and explosivity of arylammonium perchlorates has been studied by differential thermal analysis (DTA) and explosive sensitivity measurements. The metal oxides considerably sensitize both decomposition and explosion and the sensitizing effect is in the order NiO < CuO < MnO₂. The accelerated decomposition or explosion seems to occur via the formation of an intermediate, metal perchlorate arylamine complex. The experimental evidence for the mechanism put forward has been included.     

Effect of vent size on vented hydrogen-air explosion

In this paper, the effect of vent size on vented hydrogen-air explosion in the room was studied by numerical simulation. Analysis of the explosion temperature, overpressure, dynamic pressure and wind velocity under different vent sizes indicate that these explosion parameters have different change rules inside and outside the room. Inside the room, the vent size has little effect on the explosion temperature, dynamic pressure and wind velocity, but it has a significant impact on the explosion overpressure. As the scaled vent size $K_v$ ($A_v/V^{2/3}$) increases from 0.1 to 0.3, the difference between the maximum internal peak overpressure is 87.8%. Outside the room, as the vent size increases, the high-temperature range (above 800 K) first decreases and then increases, while the explosion dynamic pressure and hurricane zone caused by explosion wind gradually decrease. The maximum high-temperature range (32.5 m for $K_v$ = 0.1) and hurricane zone (41.1 m for $K_v$ = 0.1) can reach 7.0 times and 8.9 times the length of the room, respectively. The explosion dynamic pressure can reach the same order of magnitude as the explosion overpressure under the same vent size. Therefore, these damage effects outside the room cannot be ignored. During the change of vent sizes, for $K_v$ ≤ 0.3, the explosion parameters change drastically and the disaster effect is significant. For example, external explosion that affect the discharge of internal explosion overpressure occur; explosion that occurs in masonry structures can destroy the structural integrity of the brick walls. Therefore, $K_v$ = 0.3 can be used as a reference for hydrogen-air venting safety design.     

汽液相变过程的不可逆性分析

要：应用热力学理论对工程上常见的汽液相变过程机理进行不可逆性分析，首次采用化学势-压力(μ-p)图来描述汽液相变过程，研究实施过程的必要热力学条件、过程进行的规律及影响因素。研究结果表明，在相变过程中两相间的化学势差△μ是过程的一个重要的广义热力学驱动力，相变换热过程是在化学势差△μ和温差△T共同作用下并结合流体的对流运动来实现的。另外，从化学势的角度导出汽液相变过程中汽泡临界半径的计算式。     

Progress of graphene and loaded transition metals on Mg-based hydrogen storage alloys

Mg-based hydrogen storage alloys have become a research hotspot in recent years owing to their high hydrogen storage capacity, good reversibility of hydrogen absorption/desorption, low cost, and abundant resources. However, its high thermodynamic stability and slow kinetics limit its application, so the modification of Mg-based hydrogen storage alloys has become the development direction of Mg-based alloys. Transition metals can be used as catalysts for the dehydrogenation of hydrogen storage alloys due to their excellent structural, electrical, and magnetic properties. Graphene, because of its unique sp² hybrid structure, excellent chemical stability, and a specific surface area of up to 2600 m²/g, can be used as a support for transition metal catalysts. In this paper, the internal mechanism of graphene as a catalyst for the catalysis of Mg-based hydrogen storage alloys was analyzed, and the hydrogen storage properties of graphene-catalyzed Mg-based hydrogen storage alloys were reviewed. The effects of graphene-supported different catalysts (transition metal, transition metal oxides, and transition metal compounds) on the hydrogen storage properties of Mg-based hydrogen storage alloys were also reviewed. The results showed that graphene played the roles of catalysis, co-catalysis, and inhibition of grain aggregation and growth in Mg-based hydrogen storage materials.     

Molecular dynamics studies of ultrafast laser-induced phase and structural change in crystalline silicon

In this work, thermodynamic phenomena in crystalline silicon irradiated by an ultrafast laser pulse were studied using the method of molecular dynamics simulations. The Stillinger–Weber potential was used to model the crystalline silicon. The temperature development in silicon when heated by an ultrafast laser pulse was tracked. Melting and resolidification processes and the resulting structural change were investigated. Radial Distribution Functions were used to track the liquid-amorphous interface during resolidification. It was found that the temperature at the solid–liquid interface could deviate from the equilibrium melting temperature by several hundred degrees. After the melted layer was solidified, some melted material became crystalline and the rest of the material remained in an amorphous state. The difference in the final state was associated with the rate of resolidification and both of the qualitative and quantitative analyses of the relationship between the final atom structure and resolidification rate were made.     

The effect of transition metals on hydrogen migration and catalysis in cast Mg-Ni alloys

The inexpensive fabrication technique of casting is applied to develop new Mg-Ni based hydrogen storage alloys with improved hydrogen sorption properties. A nanostructured eutectic Mg-Mg₂Ni is formed upon solidification which introduces a large area of interfaces along which hydrogen diffusion can occur with high diffusivity. After a few cycles of hydrogenation and dehydrogenation, an ultrafine porous structure formed in the eutectic Mg-Mg₂Ni and some cracks developed along the interface between the eutectic and the α-Mg matrix. This indicates that hydrogen atoms introduced into the alloys preferentially migrate along the interfaces in the nanostructured eutectic which enables effective short-range diffusion of hydrogen. Furthermore, transition metals (TMs) such as Nb, Ti and V in the range 240-560 ppm are added directly to molten Mg-10 wt% Ni alloys and are found to form intermetallic compounds with Ni during solidification. The alloys can store 5.6-6.3 wt% hydrogen at 350 °C and 2 MPa. TM-rich intermetallics distributed homogeneously in the cast alloys appear to play a key role in accelerating the nucleation of Mg from MgH₂ upon dehydrogenation. This leads to a significant improvement in the hydrogen desorption kinetics.     

Effects of attapulgite-supported transition metals catalysts on glycerol steam reforming for hydrogen production

The attapulgite supported transition metals (Ni, Cu, Co or Fe) catalysts were prepared by precipitation method at constant loading (10 wt%) and investigated in the glycerol steam reforming reaction for H₂ production under 400–750 °C, water/glycerol (W/G) = 3, N₂ flow ratio = 0.16 L/min and WHSV = 6.46 h^?1. The as-prepared catalysts were characterized by N₂ adsorption-desorption, XRD, H₂-TPR and TEM-EDS. The results shown different active metals presented various crystalline sizes and reduction properties. The experimental results revealed Ni/ATP and Co/ATP catalysts had more active for glycerol steam reforming than Cu/ATP and Fe/ATP catalysts, due to the fact that active metal Ni and Co have superior capacity to promote the necessary CC rupture and facilitate the water gas shift reaction. In addition, the results revealed that CH₄ production was favored at low temperatures while CO production was presented at high temperatures, which were induced by the different reaction networks over catalysts. In addition, the stability test shown all catalysts had different various degrees of inactivation, resulting from the sintering of active metals and carbon deposition. The characterizations of XRD, TEM and TG-DTG for spent catalysts revealed the smallest amount of carbon deposited for Cu/ATP, which was attributed to the lowest Cu particle size. Additionally, two different types of carbon was found, namely filamentous carbon for Ni and Co/ATP and encapsulating carbon for Cu and Fe/ATP.     

Effect of hydrogen on explosion characteristics of liquefied petroleum gas-air mixtures

The effects of hydrogen addition on the explosion characteristics of liquefied petroleum gas (LPG)-air mixtures were experimentally investigated under initial conditions of 1 atm and 298 K. Furthermore, with reference to the detailed USC-Mech II mechanism, sensitivity and the rate of production (ROP) analyses were conducted. When the hydrogen proportion is constant, the maximum explosion pressure and the maximum rate of pressure rise first increase and then decrease, reaching peaks at an equivalence ratio of 1.3. The experimentally measured maximum explosion pressure is lower than the numerically calculated adiabatic pressure. The calculated adiabatic pressure decreases slightly with an increase in the hydrogen proportion. However, under the experimental conditions, owing to the high reactivity of hydrogen, the LPG-H₂-air mixtures experience a small heat loss in the early stage of the explosion, and the maximum explosion pressure and maximum rate of pressure increase considerably, with the arrival time of the pressure peak is advanced. The addition of hydrogen promotes the sensitivity coefficient of reactants C₃H₈ and C₄H₁₀ and increases the maximum ROP of free radicals H, O, and OH. Meanwhile, the addition of hydrogen significantly influences the maximum ROP of the elementary reaction R2.     

On the nature of elementary reactions from methane to hydrogen over transition metals

Elementary reactions that are relevant to catalytic hydrogen production have been evaluated over a wide range of transition metals. The UBI-QEP formalism was used to estimate heats of chemisorption and activation energies. The reactions were evaluated on a clean surface with the primary purpose of illustrating relative differences of intrinsic properties. The results were supportive of what is typically observed experimentally, in particular with respect to the relative difference between classical combustion catalysts (Pt, Pd) and state-of-art reforming catalysts (Ni, Rh). The likely scrambling of CH_x species was also predicted which is in accordance with isotopic tracer studies in the literature.     

Atomically dispersed low-cost transition metals catalyze efficient hydrogen evolution on two-dimensional SnO nanosheets

Two-dimensional (2D) electrocatalyst plays an important role in hydrogen production via water splitting. In this work, the first-principles calculation was used to investigate the hydrogen evolution reaction (HER) performance of transition metal (TM) single atom catalysts (SACs) on 2D SnO nanosheets. Among the TM considered (TM = V, Cr, Mn, Fe, Co, Ni, Cu and Pt), V, Fe, Co, Ni, Cu and Pt can effectively improve the catalytic activity of SnO. More importantly, the low-cost Co can exhibit promising HER performance with the Gibbs free energy as low as ~0.015 eV, which is competitive with the precious catalyst Pt. The theoretical exchange current densities of Co SACs can reach ~10⁻¹⁶ A/site. The exciting HER activity is mainly facilitated through the d-d hybridization between the TM and Sn atoms on the SnO surface, which introduces new electron states near the Fermi level. Our work highlights the complexity and diversity of the effect of TM SACs on SnO nanosheets and implies their potential applications as efficient HER electrocatalysts.     

Stability of transition metals on Mg(0001) surfaces and their effects on hydrogen adsorption

The interactions of a hydrogen atom with clean, vacancied, and transition metal-doped (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Au, Pt) Mg(0001) surfaces are investigated using first-principles calculations. The H adsorption on Mg(0001) with TMs doped within the second layer is generally more stable than that on clean Mg but clearly weaker than that on Mg surfaces with TM in the first layer. We find, however, that all these TM atoms prefer to substitute for the Mg atoms in the second layer rather than for those in the outermost layer of the Mg surface. To enhance the catalytic effect of the TM dopants, we investigated various co-doping conditions of TMs, and we found that i) Ti is a good “assistant” that stabilizes co-doped Co, Ni, Pd, Ag, Pt, and Au within the first layers and that ii) Ni and Co are more easily incorporated into the first layer of a Mg surface when co-doped with Ti, V, and Nb. These observations may lead to a possible approach to stabilize the TM dopants within the first layer and thus promote the hydrogenation of Mg accordingly.     

基于碟式聚光系统的Al-Si相变储热锅炉试验

基于多碟式太阳能聚光器,设计开发Al-Si合金的相变储热锅炉,并进行了试验。对锅炉储热过程的压力、蒸汽温度及Al-Si合金相变过程的温度变化测试结果表明,在8:00¹4:30,太阳平均直射辐射强度不足550 W/m2的条件下,相变温度为577℃的铝硅合金在高温储热过程中能充分加热锅炉中的水介质,产生250℃的饱和蒸汽及400℃的过热蒸汽,蒸汽压力达到3.5 MPa。     

Influence of ducting on the explosion pressure

In spite of many investigations of pressure generation due to gaseous explosions in a vessel there is no reliable correlation between the experimental data and the theoretical models. It was shown that such factors as the presence of obstacles [1] and the acoustical feedback [2] can lead to a dramatic increase in pressure in the vessel in comparison with the theoretical predictions based on the one-dimensional laminar flame propagation speed [3].In this short communication we report another example of the unusual increase in the explosion parameters due to ducting. It was found that for a relatively short (12 diameters) tube connected to the vent of the combustion vessel there is a strong maximum of the maximal pressure and the maximal pressure rise of explosion. This is a preliminary report and we cannot give an explanation of the observed phenomenon.