Interactions Of Oxygen, Hydrogen And Water With Zr(0001) And Zr(1010)

The interaction of oxygen, hydrogen and water with Zr(0001) and Zr(1010) has been studied by surface science techniques. A hopping model of the diffusion of adsorbed species from a surface into the bulk has been formulated and solved mathematically. Applying this model to our AES results on oxygen dissolution, we obtained the Arrhenius expressions for diffusion as: 0.115exp({dollar}-{dollar}44.45 kcal/RT) cm{dollar}\rm\sp2s\sp{lcub}-1{rcub}{dollar} along {dollar}\langle0001\rangle,{dollar} and 1.07exp({dollar}-{dollar}46.18 kcal/RT) cm{dollar}\rm\sp2s\sp{lcub}-1{rcub}{dollar} along {dollar}\langle10\=10\rangle.{dollar};Oxide dissolution was studied by measuring the change of the oxide thickness at a series of temperatures for a constant initial coverage prepared at a fixed and low temperature. The rate-controlling step in oxide dissolution is O diffusion into bulk Zr.;The bond between H(D) and Zr on a Zr surface is energetically similar to those in zirconium hydride. There are two types of adsorption sites for H adsorption, one above the surface and another in the subsurface region. Hydrogen has a very strong tendency to segregate to a Zr surface. Measured by the kinetics of the surface segregation, the diffusion coefficients of hydrogen can be determined as {dollar}3.40\times 10\sp{lcub}-4{rcub}{dollar}exp({dollar}-{dollar}9565/RT) cm{dollar}\rm\sp2s\sp{lcub}-1{rcub}{dollar} along {dollar}\langle0001\rangle,{dollar} and {dollar}1.73\times 10\sp{lcub}-3{rcub}{dollar}exp({dollar}-{dollar}8887/RT) cm{dollar}\rm\sp2s\sp{lcub}-1{rcub}{dollar} along {dollar}\langle10\=10\rangle.{dollar};The adsorption of D{dollar}\sb2{dollar}O at 80 K can be divided into three stages: a chemisorbed layer (coverages between 0 and {dollar}\sim{dollar}0.25 ML), second adsorbed layer, (up to a total coverage of {dollar}\sim{dollar}0.65 ML) and an ice layer. The D{dollar}\sb2{dollar}O in the chemisorbed layer is probably all dissociated into {dollar}\rm OD\sb{lcub}ad{rcub}{dollar} and {dollar}\rm D\sb{lcub}ad{rcub},{dollar} or {dollar}\rm O\sb{lcub}ad{rcub}{dollar} and {dollar}\rm D\sb{lcub}ad{rcub}.{dollar} The second adsorbed layer is molecular water and begins to form before the chemisorbed layer is fully saturated. Molecular water can desorb from this layer at 173 K. The ice layer begins to form before the second adsorbed layer is fully covered, and desorbs with zero order kinetics at 163 K