Temperature Programmed Desorption Characterization of Oxidized Uranium Surfaces: Relation to Some Gas−Uranium Reactions†
Temperature Programmed Desorption Characterization of Oxidized Uranium Surfaces: Relation to Some Gas−Uranium Reactions†
复制标题
氧化铀表面的程序升温解吸表征：与某些气体-铀反应的关系†
作者：
A. Danon;J. Koresh;M. Mintz
当暴露于氧化气氛时，在金属上形成的氧化覆盖层的化学吸附特性和表面组成对于确定这些层对某些气相反应（例如，腐蚀和腐蚀）。在本研究中，一个特殊的设置超声分子束程序升温脱附被用来确定不同的化学吸附物种存在于氧化铀表面。主要确定的物种包括水（以不同的结合形式）和氢。后一种氢来源于水-铀氧化反应，该反应产生二氧化铀和两种类型的氢：近表面氢化物和在比氢化物低的温度下解吸的表面化学吸附形式。提出了不同的水解吸峰对应于不同的结合位点。在一般情况下，四个水解吸特征被确定（标记为W 0，W 1，W 2，和W 3，分别按照解吸温度增加的顺序）。这些特征对应于可逆化学吸附的分子形式（W 0）、更紧密结合的水（化学吸附在不同类型的氧化物位点上）或羟基簇（W 1）以及强烈结合的（可能是孤立的）羟基（W 2）。最高温度峰（W 3）与复杂的水-碳氧化合物的形成有关，并且仅存在于氧化覆盖层上，该氧化覆盖层包含适当的化学吸附的碳氧物种。讨论了水和氢的热释放行为与氢铀反应和水铀反应中某些效应的关系。对于后者，提出了一个微观机制。
The chemisorption characteristics and surface composition of oxidation overlayers developing on metals when exposed to oxidizing atmospheres are important in determining the protective ability ofthese layers against certain gas-phase reactions (e.g., corrosion and hydriding). In the present study, a special setup of supersonic molecular beam-temperature-programmed desorption was utilized to determine the different chemisorbed species present on oxidized uranium surfaces. The main identified species included water (in different binding forms) and hydrogen. The latter hydrogen originates from the water-uranium oxidation reaction, which produces uranium dioxide and two types of hydrogen: a near surface hydride and a surface-chemisorbed form that desorbs at a lower temperature than that of the hydride. Assignments of the different water desorption peaks to different binding sites were proposed. In general, four water desorption features were identified (labeled W 0 , W 1 , W 2 , and W 3 , respectively, in the order of increasing desorption temperatures). These features correspond to a reversibly chemisorbed molecular form (W 0 ), a more tightly bound water (chemisorbed on different type of oxide sites) or hydroxyl clusters (W 1 ), and strongly bounded (possibly isolated) hydroxyl groups (W 2 ). The highest temperature peak (W 3 ) is related to the formation of complex water-carbo-oxy compounds and is present only on oxidation overlayers, which contain proper chemisorbed carbo-oxy species. The relation of the water and hydrogen thermal release behavior to some problems addressed to certain effects observed in hydrogen-uranium and water-uranium reactions is discussed. For the latter, a microscopic mechanism is proposed.