In this study, horizontal attenuated total reflection (HATR) Fourier-transform infrared (FT-IR) spectroscopy was combined with quartz crystal microbalance (QCM) gravimetry to investigate the adsorption isotherms of water on fly ash, a byproduct of coal combustion in power plants. Because of composition variability with the source region, water uptake was studied at room temperature as a function of relative humidity (RH) on fly ash from several regions: United States, India, The Netherlands, and Germany. The FT-IR spectra show water features growth as a function of RH, with water absorbing on the particle surface in both an ordered (ice-like) and a disordered (liquid-like) structure. The QCM data was modeled using the Brunauer, Emmett, and Teller (BET) adsorption isotherm model. The BET model was found to describe the data well over the entire range of RH, showing that water uptake on fly ash takes place mostly on the surface of the particle, even for poorly combusted samples. In addition, the source region and power-plant efficiency play important roles in the water uptake and ice nucleation (IN) ability of fly ash. The difference in the observed water uptake and IN behavior between the four samples and mullite (3Al₂O₃·2SiO₂), the aluminosilicate main component of fly ash, is attributed to differences in composition and the density of OH binding sites on the surface of each sample. A discussion is presented on the RH required to reach monolayer coverage on each sample as well as a comparison between surface sites of fly ash samples and enthalpies of adsorption of water between the samples and mullite.

中文翻译：

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不同来源的粉煤灰对水的吸附等温线

在这项研究中，将水平衰减全反射（HATR）傅里叶变换红外（FT-IR）光谱与石英晶体微量天平（QCM）重量分析法相结合，研究了水在飞灰中的吸附等温线，飞灰是电厂燃煤的副产物。由于来源地区的成分差异，研究了美国，印度，荷兰和德国几个地区在室温下吸水量与粉煤灰相对湿度（RH）的关系。FT-IR光谱显示水的特征是RH的函数，水分以有序的（冰状）和无序的（液体状）结构在颗粒表面吸收。使用Brunauer，Emmett和Teller（BET）吸附等温线模型对QCM数据进行建模。发现BET模型很好地描述了整个RH范围内的数据，表明粉煤灰的吸水率大部分发生在颗粒表面，即使是燃烧不良的样品也是如此。此外，源区和电厂效率在粉煤灰的吸水和冰核（IN）能力中也起着重要作用。四个样品与莫来石（3Al₂ O ₃ ·2SiO ₂），粉煤灰中的铝硅酸盐主要成分，归因于每个样品表面的OH结合部位的组成和密度的差异。讨论了达到每个样品的单层覆盖率所需的相对湿度，以及粉煤灰样品的表面位置与样品与莫来石之间的水吸附焓的比较。