1 research outputs found
Water Adsorption Isotherms on Fly Ash from Several Sources
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 (3Al<sub>2</sub>O<sub>3</sub>·2SiO<sub>2</sub>), 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