Arnold Thomas, Cook Richard E, Larese J Z
Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831, USA.
J Phys Chem B. 2005 May 12;109(18):8799-805. doi: 10.1021/jp046065w.
The layering properties of ethane on MgO(100) were measured between 91 and 144 K using high-resolution adsorption isotherms. In contrast to previous studies, the results demonstrate that only three layers are formed. The thermodynamic functions derived from the data (isosteric heat, differential enthalpy, and entropy of adsorption) compare well with literature values and show a steady trend toward the bulk properties as the number of layers increased. Phase transitions for two of the layers were identified by monitoring the changes in the two-dimensional isothermal compressibility as a function of chemical potential. Both of these phase transitions occur at approximately 127 K and within 1 K of each other. Through the use of neutron diffraction, it is possible to identify at least one solid surface phase that melts at approximately 75 K. The transition at 127 K is therefore a transition between a liquidlike phase and a hyper-critical fluid. A comparison is made between the present data and our recent study of methane on MgO.
利用高分辨率吸附等温线在91至144 K之间测量了乙烷在MgO(100)上的分层特性。与之前的研究不同，结果表明只形成了三层。从数据中得出的热力学函数（等量吸附热、微分焓和吸附熵）与文献值比较吻合，并且随着层数增加呈现出向体相性质稳定变化的趋势。通过监测二维等温压缩率随化学势的变化，确定了其中两层的相变。这两个相变都发生在大约127 K，且彼此相差在1 K以内。通过中子衍射，可以识别出至少一种在大约75 K熔化的固体表面相。因此，127 K处的转变是类液相和超临界流体之间的转变。对本研究数据与我们最近关于甲烷在MgO上的研究进行了比较。
