| Abstract
| - The kinetics of the reaction of batches of powdered quartz and sodium carbonate was studied by in situ 23Nanuclear magnetic resonance (NMR) spectroscopy using a laser-heated probe. We show for the first time thatthe technique allows one to study solid-state reactions at high temperatures with good time resolution andwithout the risk of quenching artifacts. The reaction is controlled by solid-state Na+ diffusion across thegrain interface. Independent of the batch composition, the first reaction product is crystalline sodiummetasilicate, Na2SiO3, even if the temperature is high enough for much of the composition space betweensilica and metasilicate to be above the equilibrium liquidus. Fast Na+ diffusion allows the reaction front tocross the grain interface and form the solid product before liquid intermediate equilibrium products can beformed. This purely solid-state reaction slows down as the thickness of the interface increases; the reactionis more deceleratory than published models suggest. If excess quartz is present, it reacts in a second stepinvolving a liquid film wetting the excess grains. Once this reaction has started, it pulls the reaction into thethermodynamic regime, which leads to an increase even in the rate of the first step leading to intermediatesolid metasilicate.
|
