A Multi-Scale Study of Solid Phase Reactions: Unraveling Mechanical-Chemical Interactions

摘要：机构：内布拉斯加州大学林肯分校提案号：0096381某些非经典爆炸物类别的固体材料，在流体静力压缩下会发生极其剧烈的反应。固体晶格中的弹性势能以雪崩般的方式“解锁”，如果这种能量释放与化学反应同步，则可以在固体结构中形成异常强度的冲击波。固相爆轰的存在成为可能。可以设想这样一个激波锋的条件：压力超过100万大气压，激波速度为5-10公里/秒。虽然这样的压力和速度在内爆实验和常规爆炸中通常都能达到，但固相爆炸的能量密度比常规过程高出好几个数量级。这种高能波构成了材料的非平衡状态，但同时它在原子、介观和宏观尺度上发现了谐波相互作用。这个项目的目标是研究这三个尺度上的能量转移事件。计划采用分层方法。由几千个原子组成的单个元素/化合物的小簇将通过分子动力学模拟进行研究。能量分布和平衡的特征时间计算了各种动态和静水载荷。不同化合物的团簇作为一种附加形式的势能引入系统。当预压缩团簇接触并在一个面引发晶格坍塌时，化学和弹性势能释放之间的共生相互作用将得到阐明。介观模型用于研究粒子水平上的能量传递。虽然时间尺度仍然小到足以研究非平衡态，但原子-原子相互作用仅限于最近的邻居，以扩大长度尺度。波开始在几个原子层之间形成。当在积累过程中提供足够的能量时，就会产生一个孤子。这种特殊的波能捕获弹性势能。在非均质状态下，部分能量转化为热能，但也会发生局部剥落和晶格坍塌。逆散射理论将用于分析孤子的形成。连续介质模型需要改进，因为动力学不是取决于反应物的浓度，而是取决于它们的表面积。组合学提供了共同表面积的期望值，以及由于孤子作用、熔融和凝聚相产物的抑制而对表面积的依赖。必须包括对物种状态的描述：粒度和表面积。这将宏观模型与介观模型联系起来。此外，计划进行一系列实验来测试所提出的机制。反应性混合物装入布里奇曼铁砧中。系统中加载的势能是变化的，超过临界负荷时，预期会出现弹性势能积极参与反应过程的快速反应。将探索具有不同物理性质的金属/氧化物和金属/非氧化物体系。电热爆炸法将与Bridgman铁砧相结合，研究压力下的动力学。

ABSTRACTPI: H. J. Viljoen Institution: University of Nebraska at LincolnProposal Number: 0096381Certain solid materials, outside the class of classic explosives, can react in an extremely violent manner if they are hydrostatically compressed. The elastic potential energy in the solid's lattice is "unlocked" in an avalanche-like manner and if this energy release is synchronized with a chemical reaction, a shock wave of extraordinary intensity could form in the solid structure. The existence of solid phase detonation becomes a real possibility. The conditions in such a shock front could be contemplated: presses in excess of one million atmospheres and shock wave velocities of 5-10 km/s. Although such pressures and velocities are routinely reached in implosion experiments and conventional explosive, energy density in a solid phase detonation exceeds conventional processes by several orders of magnitude. This high-energy wave constitutes a non-equilibrium state of the material, but simultaneously it finds a harmonic interaction across atomic, mesoscopic and macroscopic scales. It is the goal of this project to investigate events of energy transfer on these three scales. A hierarchical approach is planned.Small clusters of single element/compound of a few thousand atoms will be studies by molecular dynamics simulation. Energy distributions and characteristic times to equilibrate are calculated for a variety of dynamic and hydrostatic loadings. Clusters of different compounds introduce chemistry as an additional form of potential energy to the system. When pre-compressed clusters are brought in contact and lattice collapse is initiated at one face, the symbiotic interaction between chemistry and elastic potential energy release will be elucidated. The mesoscopic models are used to study energy transfer on a particle level. Although time scales are still small enough to study non-equilibrium states, atom-atom interaction is limited to nearest neighbors to expand the length scale. Waves begin to build up across several atomic layers. When sufficient energy is supplied during build-up, a soliton is created. This particular wave type traps elastic potential energy. At heterogeneities some energy is transferred to thermal energy, but local spalling also occurs and lattice collapse is initiated. The inverse scattering theory will be employed to analyze formation of solitons. Contiuum models need refinement, because kinetics depends not on the concentration of reactants, but on their surface area. Combinatorics provides expectation values of common surface area and dependency on surface area due to soliton action, melting and inhibition by condensed phase products. Descriptions of the state of species must be included: particle size and surface area. This links the macroscopic model with mesoscopic models.In addition, a series of experiments are planned to test the proposed mechanisms. Reactive mixtures are loaded in a Bridgman anvil. The amount of potential energy loaded in the system is varied and beyond critical load a fast reaction with active participation of the elastic potential energy in the reaction process is anticipated. Metal/oxide and metal/non-oxide systems with different physical properties will be explored. The electrothermal explosion method will be combined with the Bridgman anvil to study kinetics under pressure.