Abstract
The kinetics of the isothermal decomposition of K 2VO(O 2) 2F and K 3Nb(O 2) 2F 4 have been investigated in the temperature range 432–463 K using a constant volume apparatus. The α-time plots for both these solids are sigmoidal in nature. The kinetic obedience to the Avrami-Erofe'ev equation ( n = 2) is observed for the initial stage of the decomposition. The contracting volume equation fits well for the deceleratory region. The activation energies are 108 and 53 kJ mole −1 for K 2VO(O 2) 2F, and 163 and 120 kJ mole −1 for K 3Nb(O 2) 2F 4. The effect of grinding on the latter solid shows deceleratory α-time curves. The decomposition of the ground sample is best described by the unimolecular decay and contracting volume equations. The change in reactivity also confirms the topochemical nature of solid state decompositions. In addition to this, the absence of lattice water in these two solids may also be responsible for the appearance of induction and acceleratory regions in pristine solids, in contrast to hydrated fluoroperoxozirconates, wherein the dehydration step precedes peroxide decomposition leading to facile nucleation and the totally deceleratory nature of isothermal decomposition (α-time) curves.
Published Version
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