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    Surface characteristics of selected carbon materials exposed to supercritical water

    Year: 2013

    Journal: Journal of Supercritical Fluids, 76, pp. 32-40, 20130926

    Authors: Ali Ashraf, Seyed A. Dastgheib, Glennys Mensing, Mark A. Shannon,

    Organizations: Department of Mechanical Science and Engineering, University of Illinois, 1206 W. Green Street, Urbana, IL 61801, USA, Illinois State Geological Survey, Prairie Research Institute, University of Illinois, 615 E. Peabody Drive, Champaign, IL 61820, USA

    Interactions of supercritical water (SCW) with several carbon (including polycrystalline graphite, highlyordered pyrolytic graphite (HOPG), pyrolytic carbon, and diamond) and selected ceramic materials underoxic or anoxic conditions are investigated. Wettability and surface/material properties of samples, beforeand after the SCW exposure, are characterized with sessile drop contact angle measurement, profilometry,XPS, XRD, and ToF-SIMS. All tested ceramic materials became more hydrophilic during the SCW exposure,mainly due to hydrolysis reactions. Carbon samples exposed to oxic SCW became more hydrophilic asa result of surface oxidation. Carbon materials, except HOPG and diamond, became more hydrophobicwhen exposed to anoxic SCW because of degradation of hydrophilic oxygen functionalities. HOPG anddiamond became more hydrophilic after anoxic SCW exposure mainly due to the removal of hydrophobichydrocarbon contaminants. Hydrophobicity of different carbon samples exposed to SCW are explainedbased on the abundance of surface hydrophilic sites (i.e., oxygen functionalities, reactive carbon danglingbonds or defects), hydrocarbon impurities, and surface roughness.