Isothermal measurements of the dehydroxylation of kaolinite at temperatures from 400-540°C and with controlled water vapor pressures from <10-3 mm Hg to 175 mm Hg are shown to conform with a single curve of α (fraction reacted) versus t/t50, where hn is the time for t50 percent reaction. The curve agrees well with the supposition that the reaction is diffusion controlled rather than obeys first-order kinetics. The reaction rate constant depends on both the temperature and the ambient water vapor pressure. The activation energy, 51 kcal/mole at <10-3 mm Hg, increases with vapor pressure, becoming 112 kcal/mole at 47 mm Hg. The rate constant diminishes with vapor pressure according to an equation of the type log (1 – kp/ko) = m+n logP, where m and n are temperature-dependent parameters, which is interpreted in terms of a partial coverage of the dehydroxy la ting surface by chemisorbed water molecules. The criteria for distinguishing first order kinetics from diffusion controlled reactions are reviewed critically.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not currently have access to this article.