Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases p. 2831 - 2842 (1988)
Update date:2022-08-11
Topics:
Takriti, Salaheddin
Duplatre, Gilles
The thermal decomposition of KIO4 and NaIO4 has been studied.The decomposition product, KIO3 or NaIO3, suffers a very efficient exodiffusion during heating in such a way that the partly decomposed crystals consists of two parts: the outer part is a fragile layer of almost pure iodate, while the inner part is a solid crystalline lattice of almost pure periodate.The dimensions of the latter are not affected by the decomposition, so that its density decreases in proportion to the decomposed fraction.The decomposition isotherms present a saturation at long heating times which is not due to atmospheric effects, but is supressed when heating is performed with continuous removal of the outer layer.Kinetic analysis of the data shows a remarkable continuity between the exchange process, occurring at lower temperatures, and the decomposition.In paticular, the dimensionality of the reaction, n, from the Erofeev equation, ranges in KIO4 roughly from 1 to 2 with increasing temperature in the former case, then from 2 to 3 in the latter.These values are systematically higher by one unit in NaIO4, indicating that the nucleation process, which creates the driving defect, cannot be neglected as it can for KIO4.Both exchange and decomposition are dominated by the exodiffusion of some combined vacancy type defect, promoting the exodiffusion of the iodate and eventually triggering the decomposition; at sufficiently high temperature, the latter process becomes autocatalytic and develops three-dimensionally (n= 3 or 4).
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