MECHANISM OF SOLID-VERTICAL-BAR-LIQUID INTERFACIAL REACTIONS - THE REACTIVE DISSOLUTION OF P-CHLORANIL IN AQUEOUS-SOLUTION AS STUDIED BY THE CHANNEL FLOW CELL WITH ELECTROCHEMICAL DETECTION AND ATOMIC-FORCE MICROSCOPY

A quantitative study of the hydrolytic dissolution of solid p-chlorani l at alkaline pH using a combination of the channel flow cell and in s itu atomic force microscopy measurements shows that the dissolution is driven by reaction of the substrate with hydroxide ions at, or very c lose to, the dissolving surface. The dissolution rate equation, deduce d from the channel flow cell for single crystals of p-chloranil, is ra te/mol cm(-2) s(-1) = 3.8 X 10(-7)[OH-](0) where [OH-](0)/M is the hyd roxide ion concentration adjacent to the solid surface. An analogous r ate law is derived for pressed pellet substrates. The novel applicatio n of the atomic force microscope to make absolute measurements of surf ace averaged dissolution rates is described. Comparison with the indep endent channel flow cell data reveals good mechanistic agreement and c onsistency of rate constants provided it is recognised that a thick st agnant diffusion layer can be present under the usual conditions emplo yed for AFM. (C) 1997 Elsevier Science S.A.