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

摘要：H.J.维尔京研究所：内布拉斯加大学林肯分校建议编号：0096381某些固体材料，在经典炸药类别之外，如果受到流体静压压缩，会以极其剧烈的方式发生反应。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，就可能在固体结构中形成非常强烈的冲击波。固相爆轰的存在成为一种可能。这种冲击波阵面的条件是：压力超过100万个大气压，冲击波速度为5-10公里/S。虽然这样的压力和速度通常在内爆实验和常规炸药中达到，但固相爆轰中的能量密度比传统工艺高出几个数量级。这种高能波构成了材料的非平衡态，但同时它也发现了跨越原子、介观和宏观尺度的谐和相互作用。这个项目的目标是调查这三个尺度上的能量转移事件。计划了一种层次化的方法，将通过分子动力学模拟来研究由几千个原子组成的单个元素/化合物的小团簇。计算了各种动态和静压载荷下的能量分布和达到平衡的特征时间。不同化合物的簇合物将化学作为势能的另一种形式引入系统。当预压缩团簇接触并在一个面上引发晶格崩塌时，化学与弹性势能释放之间的共生相互作用将被阐明。介观模型被用来研究粒子水平上的能量传递。尽管研究非平衡态的时间尺度仍然很小，但原子与原子的相互作用被限制在最近邻，以扩展长度尺度。波开始在几个原子层上积聚。当在建立过程中提供足够的能量时，就会产生孤子。这种特殊的波动类型捕获了弹性势能。在异质结中，一些能量被转化为热能，但也会发生局部剥落，从而引发晶格崩塌。利用逆散射理论分析孤子的形成。连续模型需要改进，因为动力学不取决于反应物的浓度，而是取决于它们的表面积。组合数学提供了共同表面积的期望值，以及由于孤子作用、熔化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：颗粒大小和表面积。这将宏观模型与介观模型联系起来。此外，还计划进行一系列实验来测试所提出的机制。反应性混合物被装入布里奇曼砧板中。体系中所加载的势能量是变化的，在临界负载之后，弹性势能将积极参与到反应过程中，从而实现快速反应。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。电热爆炸方法将与Bridgman砧板相结合来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.