AVS 65th International Symposium & Exhibition
    Surface Science Division Wednesday Sessions
       Session SS+HC-WeM

Paper SS+HC-WeM5
Extracting Diffusing Parameters for Cu and S from Surface Segregation Data Recorded with AES on a Ni-Cu(S) Ternary Alloy

Wednesday, October 24, 2018, 9:20 am, Room 203C

Session: Catalytic Alloys: Understanding Heterogeneity
Presenter: Jacobus Terblans, University of the Free State, South Africa
Authors: J.J. Terblans, University of the Free State, South Africa
X.-L. Yan, University of the Free State, China
J.Y. Wand, Shantou University, China
H.C. Swart, University of the Free State, Republic of South Africa
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The catalytic selectivity and activity of Cu-Ni bimetallic catalysts, used for oil hydrogenation, have been investigated extensively over the years. A catalytic surface that is Cu rich have higher selectivity than a Ni rich surface. The Cu-Ni alloy system has a simple phase diagram and forms a solid solution in the entire compositional range. In this study the segregation of Cu and S to the surface of a Cu-Ni alloy with 21.3 at.% Cu and 7 ppm S was measured by using Auger electron spectroscopy (AES) coupled with a linear programmed heater. It was found that first the Cu segregated to the surface and reached a maximum surface coverage of 40 %. Once the Cu reached a maximum surface coverage, it started to desegregate as it was replaced by the S that was also segregating to the surface. The measured segregation data were fitted by Fick’s and Guttmann’s ternary segregation models and the diffusing parameters (namely segregation energy (ΔG), interaction parameter (Ω), pre-exponential factor (D0) and the diffusion activation energy (Q)) for both Cu and S were extracted from the data.