钚表面钝化层抗氢蚀机理的微观动力学模拟  

Microdynamics Simulations of the Hydrogen-Corrosion Resistance of Passivation Layers on Pu Surface

作　　者：孙博[1] 刘海风[1] 宋海峰[1] 郑晖[1] 

机构地区：[1]北京应用物理与计算数学研究所,北京100094

出　　处：《物理化学学报》2015年第B05期81-89,共9页Acta Physico-Chimica Sinica

基　　金：中国工程物理研究院科学技术发展专项基金（9090707）资助项目

摘　　要：采用基于范德华密度泛函的vdW-DF（＋U）方法，通过系统的第一性原理电子结构计算和分子动力学模拟，研究了两种钚钝化层（PuO2和PuN）的表面电子结构性质，以及表面与H2分子相互作用的微观动力学行为．结果显示：（1）H2很难靠近PuO2表面，与表面发生“碰撞-解离”的几率很小，自钝化层PuO2具有抗氢蚀作用：但是，一方面H2解离后H原子在PuO2表面的吸附放热稳定，另一方面在缺氧条件下PuO2薄层会转化成a-Pu2O3，而H2能穿过a-PuzOs到达钚层，所以PuO2的抗氢蚀性能并不可靠．（2）H2在PuN表面的微观动力学行为与在PuO2表面类似，H2极难解离且H原子的吸附热力学上不稳定：相对于PuO2，PuN的成分单一、稳定而且结构致密，PuN具有比PuO2更好的抗氢蚀性能．我们希望本工作能为钚表面钝化防护技术的发展提供理论基础和依据．Based on the non-local van der Waals density functional （vdW-DF）＋U scheme, we have performed a first-principles molecular dynamics （FPMD） study of the interaction dynamics for H2 impingement against the Pu oxide （PuO2） and Pu nitride （PUN） passivation layers on Pu metal surface. Results show that, except for weak physisorption, both the PuO2 and PuN surfaces are so difficult to access that almost all of the H2 molecules will bounce back to the vacuum when their initial kinetic energies are not sufficient. Although dissociative adsorption of H2 on PuO2 surfaces is found to be very exothermic, the collision-induced dissociation barriers of H2 are calculated to be very high. Unfortunately, PuO2 can be reduced to a-Pu203 under oxygen-lean conditions. Molecular H2 can easily penetrate and diffuse in a-Pu203, and, as a result, a-Pu203 can promote the hydrogenation of Pu metal. Unlike PuO2, PuN is found to be a stable and uniform passivation layer against hydrogen-corrosion of Pu, and the interacting system of PuN and H is shown to be thermodynamically unstable. Overall, the current study reveals the different hydrogen-corrosion resistances of PuO2 and PuN passivation layers, which have implications for the interpretation of experimental observations and will be helpful to understand the surface corrosion and passivation of Pu metal.

关 键 词：表面钝化 钚氧化物 钚氮化物 表面氢蚀 第一性原理分子动力学 

分 类 号：O647[理学—物理化学]