Abstract
The kinetics of spinodal decomposition of glasses with a composition of (in mol%) 8 Na2O, 26 B2O3, and 66 SiO2, are investigated as a function of time (up to 64 d) and temperature (between 630 and 750 °C) of heat after leaching in diluted HCl and NaOH solution to generate porosity. The glasses as well as porous materials are analyzed by dilatometry, mercury intrusion porosimetry, nitrogen sorption, X‐ray diffraction, X‐ray fluorescence spectroscopy, helium pycnometry, and scanning electron microscopy (SEM). The development of microstructure parameters like pore sizes are evaluated to characterize the kinetics of microstructure formation. Two different growth stages are identified via their size growth kinetics and the analysis of the obtained microstructures. In both stages the pore sizes follow size time laws dp ∝ tβ with an exponent β of 0.33 or 0.5. Both processes are running parallel in the second stage. This lead to the conclusion that the dominating mechanism of microstructure formation in the first identified stage is Ostwald ripening. This process is followed by a new stage which is concluded to be diffusion limited with a calculated activation energy of 220 ± 10 kJ mol−1. The observed size time laws do not limit the pore sizes.
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