SPEEDING-UP OF HETEROGENEOUS REACTIONS IN NEAR-CRITICAL PHASES

In the last decade, it has been shown that an interface reaction takin g place in a gaseous mother-phase could be affected by the existence o f thermo-acoustic convection in the fluid, due to its compressibility. In particular, crystal growers involved in space experiments have bee n concerned by such kinds of problems, as the absence of gravitational convection can make thermo-acoustic convection predominent above othe r transport phenomena. It was consequently natural to investigate the effect of compressibility on interface reactions taking place in super critical mother phases, which are known to exhibit a diverging compres sibility. In the present study, matched asymptotic expansions methods are applied to the 1-D Navier-Stokes equations written for a near-crit ical van der Waals gas, in order to investigate the response of an int erface reaction to a thermal disturbance. It is shown that the high co mpressibility of the fluid may provoke in some cases a strong increase of the flux of matter at the interface. A mechanism is put in evidenc e, which could, among others, contribute to the strong corrosion effec ts witnessed in supercritical fluid containers. Copyright (C) 1996 Els evier Science Ltd