CO、CO2和O2对铀氢初始反应的影响

利用静态容量法测定了288 K下CO、CO2和O2在UO2表面的吸附等温线,利用压降法结合原位显微观测研究了CO、CO2和O2对铀氢初始反应的影响.结果表明,3种气体在U02表面的吸附强弱关系为O2＞CO2 ＞CO,Langmuir和Freundlich方程分别较好描述了CO、CO2的等温吸附行为.含氧气体对孕育期的影响与其吸附特性密切相关,3种气体阻抑效应的强弱关系为CO2＞CO＞O2.CO和O2对孕育期的影响近呈线性关系,CO2对孕育期的影响则与CO2含量有关.CO和CO2的阻抑机制主要是气体分子对铀表面活性位的优先占据,而O2的阻抑机制相对复杂,可能涉及水分子前驱态的形成和吸附O粒子扩散两种表面化学过程.根据阻抑机制和吸附特性导出的数学模型较好描述了CO和CO2对孕育期的影响规律.

Effects of CO, CO2 and O2 on the Induction Time for Uranium-hydrogen Reaction

The adsorption isotherms of CO, CO2 and O2 on UO2 powder at 288 K were measured using static volumetric method, and their effects on the induction time for uranium-hydrogen reaction were investigated by measuring pressure drop combined with in-situ micrographic observation. The Langmuir and Freundlich equations were found to describe well the adsorption behavior of CO and CO2 on UO2, respectively, with the adsorption strength following the ordering of O2>CO2>CO. The effects of oxygen-containing gases on the induction time are closely related to their adsorption properties, and their inhibition efficiency follows the ordering of CO2>CO>O2. The induction time is almost direct proportion to CO or O2 concentration, whereas it varies differently as CO2 concentration depends on its concentration region. The inhibition mechanism of CO or CO2 is mainly attributed to their preferred occupation of active adsorption sites on the uranium surface, whereas that of O2 is relatively complex, which may be related to two surface chemical processes: the formation of water precursor state and the diffusion of adsorbed O particles. The derived model based on the inhibition mechanism and gas adsorption property describes well the influence behavior of CO and CO2 on the induction time.