Splith Tobias, Fröhlich Dominik, Henninger Stefan K, Stallmach Frank
University of Leipzig, Faculty of Physics and Earth Sciences, Linnéstr. 5, 04103 Leipzig, Germany.
Fraunhofer Institute for Solar Energy Systems ISE, Heidenhofstr. 2, 79110 Freiburg, Germany.
J Magn Reson. 2018 Jun;291:40-46. doi: 10.1016/j.jmr.2018.04.009. Epub 2018 Apr 17.
Diffusion of water in aluminum fumarate was studied by means of pulsed field gradient (PFG) nuclear magnetic resonance (NMR). Due to water molecules exchanging between the intracrystalline anisotropic pore space and the isotropic intercrystalline void space the model of intracrystalline anisotropic diffusion fails to describe the experimental PFG NMR data at high observation times. Therefore, the two-site exchange model developed by Kärger is extended to the case of exchange between an anisotropic and an isotropic site. This extended exchange model is solved by numerical integration. It describes the experimental data very well and yields values for the intracrystalline diffusion coefficient and the mean residence times of the respective sites. Further PFG NMR studies were performed with coatings consisting of small aluminum fumarate crystals, which are used in adsorptive heat transformation applications. The diffusion coefficients of water in the small crystal coating are compared to the values expected from the extended two-site exchange model and from the model of long-range diffusion.
通过脉冲场梯度（PFG）核磁共振（NMR）研究了富马酸铝中水的扩散。由于水分子在晶体内各向异性孔隙空间和各向同性晶间空隙空间之间交换，晶体内各向异性扩散模型无法描述高观测时间下的实验PFG NMR数据。因此，将卡尔格开发的双位点交换模型扩展到各向异性位点和各向同性位点之间交换的情况。通过数值积分求解该扩展交换模型。它能很好地描述实验数据，并得出晶体内扩散系数和各个位点的平均停留时间值。还对由小富马酸铝晶体组成的涂层进行了进一步的PFG NMR研究，这些涂层用于吸附式热转换应用。将小晶体涂层中水的扩散系数与扩展双位点交换模型和长程扩散模型预期的值进行了比较。
