Reaction kinetics of H2, O2, and H2O with rare earths (Y, La, Ce, Pr, Nd, Gd, Tb, Dy, and Er) at 298 K

High reactivity of rare earths (RE) with H-2, O-2 and H2O is well known even at room temperature. The formation of stable surface oxides/hydroxides on the surface is the one of serious problems in the production and use of materials containing RE. We have investigated the quantitative reactivities of H-2, O-2, and H2O with the surface of?, La, Ce, Pr, Nd, Gd, Tb, Dy, and Er under ultra high vacuum condition. The H-2, O-2 and H2O gases exhibited the highest reactivity on the clean surface of the RE at 298 K. This means that all gas molecules impinging the surface dissociate and chemisorbed. The O atoms dissociated from O-2 adsorb to for oxides layers of the metals. The H atoms dissociated from H-2 diffuse into the metals to form hydrides which were found to decrease the H-2 reactivity. The H atoms dissociated form H2O diffuse into the metals or form hydroxides of the metals. With increasing coverage of each gas molecules, the reactivity of each gas was decreased by several orders of magnitude. (C) 2013 Elsevier B.V. All rights reserved.