Processes and kinetics of mass gain in archeological brick following drying and reheating
The mass gain behavior of archeological bricks was examined following drying (130°C)/reheating (500°C) and aging at a range of temperatures (25°C, 35°C, 45°C). For drying or reheating, samples exhibit a two‐stage mass gain behavior, the second stage, Stage 2, continuing indefinitely and better described by a t 1/n model (1/n=1/6‐1/2); a correlation between the 1/n value and the specific surface area/pore volume demonstrates diffusion mechanisms with some pore geometry/morphology dependence. Stage 2 is shown to have an Arrhenius temperature dependence with activation energies of similar orders of magnitude following both drying and reheating. Supported by thermogravimetric‐mass spectrometry (TG‐MS), Stage 2 is demonstrated as likely due to the recombination of chemisorbed water, previously removed, whereas following reheating due to two components, a chemisorbed component associated with drying and a component associated with rehydroxyls removed at higher temperatures during reheating. Differences between activation energies of chemisorption and rehydroxylation components support this. Evidence for a fundamental compositional relationship between these processes is presented by a strong linear relationship between the drying and reheating mass gain rates. Stage 1, following drying or reheating, is shown to be likely associated with physisorption processes alone.
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