Structural and surface characterizations of nanocrystalline Pt–Ru alloys prepared by high-energy ball-milling

Abstract

Abstract The bulk and surface characteristics of Pt–Ru alloys prepared by high-energy ball-milling were studied over the whole compositional range. These materials were prepared in their as-milled and Mg-dispersed forms. The latter form is obtained by milling Mg with nanocrystalline Pt–Ru alloy prepared in a first step and then leaching out Mg in an acidic solution. The structure of the various alloys was determined by X-ray diffraction. Quantitative structural information was extracted from the X-ray histograms through Rietveld refinement analysis. In the as-milled form, a nanocrystalline fcc or a hcp structure is obtained after milling (40 h) of an initial powder mixture whose composition falls into the Pt- or Ru-rich side of the compositional range, respectively. For mixtures whose composition falls into the immiscibility gap, a metastable amorphous phase is formed, which co-exists with a fcc or a hcp structure, depending on which side of the immiscibility gap the composition is. The structure of Mg-dispersed Pt–Ru alloys is identical to that of the as-milled materials. The chemical composition and structure of the alloy surface was determined by X-ray photoelectron spectroscopy. From measurements of the Ru 3p and Pt 4f core level peaks, it is shown that the surface composition of both as-milled and Mg-dispersed alloys closely follow their bulk composition, with only a slight enrichment in Pt. There is also no change in the surface composition resulting from the extra milling step with Mg and its subsequent leaching. The separation between the maximum of the Ru 3d5/2 and Pt 4f7/2 core level peaks varies with the composition of the alloy, indicating that a true surface alloy is formed between Pt and Ru.