Accession Number : AD0779044

Title :   Mechanism of Chemical Instability for Periodic Precipitation Phenomena.

Descriptive Note : Technical rept.,

Corporate Author : PURDUE UNIV LAFAYETTE IND PROJECT SQUID HEADQUARTERS

Personal Author(s) : Flicker,Michele ; Ross,John

Report Date : MAR 1974

Pagination or Media Count : 35

Abstract : A mechanism of chemical instability of autocatalytic reactions coupled with diffusion is proposed for spatially periodic precipitation phenomena (such as Liesegang rings or bands). It is postulated that precipitation is preceeded by colloid formation; electric double layers surround the colloid particles, and at sufficient concentration of colloid, autocatalytic growth of particles and formation of new particles occurs due to increased product of ion concentrations within the double layer with increased colloid concentration. A linear stability analysis of the reaction-diffusion equations for this mechanism yields several predictions. The authors conclude with a critique of the Ostwald theory of Liesegang rings, which does not predict revert spacing nor secondary structure.

Descriptors :   *Chemical precipitation, Instability, Phase studies, Theory, Colloids, Diffusion, Periodic variations, Ions, Concentration(Chemistry)

Subject Categories : Physical Chemistry

Distribution Statement : APPROVED FOR PUBLIC RELEASE