BY THE COMPACTION OF GRAPHITE-CrO 3 INTERCALATION COMPOUNDS

The changes resulting from the compression of graphite-CrO a intercalation compounds are demonstrated in the TG curves. In comparison with the samples examined in the form of a flake bed, the compacted compounds begin to decompose at lower temperatures and their weight loss is higher, particularly above 220 ~ To explain the obtained results, the pressure-induced changes in the structures and the activities of the compounds are considered in relation to the method of intercalation, the concentration of the intercalant and the extent of exfoliation, Intercalation compounds of graphite (GIC) are formed in reactions between graphite and certain elements or molecules. The alternating sequence of n hexagonal graphite layers and a monolayer of foreign species, called the stage number, is a characteristic feature of their structure. The insertion of the guest species between the host graphite interspaces results in the creation of new, interesting properties. The structural, electrical and thermal changes effected by intercalation have been the most intensivelY explored [1, 2]. The thermal studies have often related to the exfoliation phenomenon caused by the thermal decomposition of GIC [3-9], Above a critical temperature, the intercalant escapes from the graphite interspaces, as demonstrated by a large expansion of the sample along the c-direction and consequently a very swollen product is formed. The process ofdeintercalation can be observed in the TG curves if the released intercalant itself undergoes thermal decomposition and/or participates in a secondary reaction with the graphite carbons. The occurrence of both processes has been reported for graphite-CrO 3 intercalation compounds (GIC-CrO3's) [10-12]. When flakes of GIC-CrO3's are heated above 220 ~ lower oxides of chromium are formed, not only due to the thermal decomposition of the intercalated CrO3, but also as a result of the reduction of CrO 3 by the graphite carbons. Consequently, a two-phase mixture of these oxides and the depleted