| Abstract: |
Enthalpies of adsorption, -Δ/H/_a ^0 , are reported for several light hydrocarbons on normal construction concrete. -Δ/H/_a ^0 , which describes the adhesion strength of a molecule on a surface, was determined by gas-solid chromatography with a packed column of 60-80 mesh concrete particles. With this approach the specific retention volume for a compound is measured as a function of temperature, and these data are used to calculate -Δ/H/_a ^0 . For the hydrocarbons studied, we found that -Δ/H/_a ^0 depended only weakly on branching. However, -Δ/H/_a ^0 was found to be relatively large for unsaturated compounds. The extent of dehydration affected the chromatographic behavior of the concrete column, which changed irreversibly above ~473 K. These are the first determinations of -Δ/H/_a ^0 of hydrocarbons on concrete, but useful comparisons with other ionic solids like clays can be made. Our work with concrete is part of a larger project to study the surface energetics of a variety of chemicals on construction materials. |
