Synthetic Metals, 7 (1983) 107 - 115 107 INTERCALATE DISPLACEMENT AND EXCHANGE IN GRAPHITE* S. H. ANDERSON and D. D. L. CHUNG Department of Metallurgical Engineering and Materials Science, Carnegie-Mellon Uni- versity, Pittsburgh, PA 15213 (U.S.A.) Summary The mechanism of intercalate transport in graphite was studied by sequential intercalation of bromine and iodine monochloride. It was found that the transport involved solid-state intercalate displacement such that the first intercalate molecule to enter an interlayer space is the first to reach the center of the graphite sample. Upon exposure of stage-2 graphite-bromine to IC1, the in-plane superlattice diffraction pattern was observed to change from that of graphite-bromine to that of graphite-IC1, while the IC1 intercalate distributed itself uniformly at a concentration level above that of the bromine intercalate. This is interpreted as the expulsion of bromine by the in-coming IC1, which dissolved the remaining bromine to form a solid solution with the ICl in-plane structure. 1. Introduction The question of intercalate transport is important from a technological viewpoint. In batteries, for example, intercalate transport would have a direct bearing on the cell current. Intercalate transport also must be considered in replacement or exchange reactions where the first intercalation compound to be formed is an intermediate to the final compound. Examples of replace- ment reactions include the formation of transition metal intercalation com- pounds from alkali metal intercalation compounds [1], and the reaction of aluminum bromide with residue graphite-bromine compounds [ 2]. The keynote of work pertaining to the mechanism of intercalate trans- port is Hooley's [3, 4] observation that intercalation begins at the basal edges adjacent to basal surfaces, and that the intercalating species migrate between *Research sponsored by the Air Force Office of Scientific Research, Air Force Systems Command, USAF, under Grant No. AFOSR-78-3536. The United States Govern- ment is authorized to reproduce and distribute reprints for governmental purposes not- withstanding any copyright notation hereon. 0379-6779/83]$3.00 ©Elsevier Sequoia/Printed in The Netherlands