Segregation of hydrogen at internal Ag/MgO (metal/oxide)-interfaces as observed by small angle neutron scattering

Abstract

The chemical composition of metal/oxide (M/O)-interfaces was studied for an internally oxidized Ag-lat.%Mg-alloy with small MgO nanoprecipitates in a dilute Ag matrix. This composition was varied by exposing the sample to oxygen (p(O-2) = 2 x 10(4) Pa), hydrogen (p(H-2) = 10(5) Pa) or vacuum (p < 10(-4) Pa). By means of small angle neutron scattering (SANS) we were able to show that hydrogen segregates at the internal Ag/MgO-interfaces. The average hydrogen occupancy at the Ag/MgO-phase boundary can be determined to be Theta(H) = (7.1 +/- 0.5) x 10(14) H/cm(2). In addition it could be shown that for each segregated hydrogen atom one Ag atom is displaced from the M/O-interface. The amount of hydrogen at the interfaces is in agreement with a model of structural vacancies at densely packed interface planes. To the best of our knowledge these are the first SANS-measurements that provide information about the segregation of hydrogen and deuterium at internal interfaces. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved