『Abstract
Dissolution behavior of muscovite under alkaline conditions at
25-50℃ was investigated using in situ atomic force microscopy
(AFM) with an air/fluid heater system to derive reliable dissolution
rates and determine the dissolution mechanism and the effect of
temperature on the dissolution rates. The muscovite dissolution
took place only at the edge surfaces that are less than a few
percent of the total surface area (TSA), while the basal surfaces
were completely unreactive. During the initial stage of the experiments,
some rough edge surfaces of muscovite dissolved much faster at
the reactive site and appeared to straighten. The straightened
edge surfaces seemed to retreat with a lower constant rate, which
may correspond to the actual dissolution rate of muscovite, in
the late stage. The edge surface area (ESA)-normalized dissolution
rate at a certain pH and temperature condition, therefore, has
a constant value independent of the size of etch pit or island
(particle). The ESA-normalized dissolution rates derived from
this AFM study were consistent with the dissolution rates renormalized
to the estimated ESA of the earlier studies. In contrast, the
TSA-normalized dissolution rates varied with the size of etch
pit or island.
The activation energy for muscovite dissolution under alkaline
conditions was very close to that for montmorillonite and illite
dissolution. A model dissolution rate equation, which simultaneously
includes the effect of pH and temperature, was deduced from the
effect of pH on the activation energy, the rate equation of muscovite
dissolution at 25℃, and the Arrhenius equation. The dissolution
rates estimated from the model were in good agreement with the
experimental rates from 25 to 70℃. The dissolution reaction order
with respect to hydroxyl activity (or pH) increases with temperature.
Keywords: Muscovite; AFM; dissolution kinetics; dissolution mechanism;
surface studies; hot-stage AFM』
Introduction
Experimental methods
Materials
Dissolution experiments and AFM imaging
Results and discussion
Dissolution behavior and kinetics of muscovite
Effect of temperature on dissolution rate
Acknowledgments
References cited