Thermodynamic and kinetic properties of the formation of Mn 2P2O7 by thermal decomposition of Mn(H 2PO2)2·H2O

Abstract

The kinetic properties in terms of activation energies and pre-exponential factors of two decomposition stages of Mn(H2PO2) 2·H2O were calculated through the isoconversional method of Kissinger. The calculated results were further used to calculate some transition-state thermodynamic functions (ΔH‡, ΔS‡, ΔG‡) of the transition-state complex according to the transition-state complex theory of Erying. Kinetic and thermodynamic results are consistent with the indication that the two steps are nonspontaneous before the introduction of heat is involved. The Avrami constant, n, of the two decomposition steps was calculated and interpreted to be responsible for the mechanism of 1D growth decomposition, which is a nucleation controlled mechanism. Vibrational frequencies of breaking bonds in two stages were estimated and assigned by comparison with the observed FTIR spectra. The results exhibit a very close correlation between calculated and observed values. © 2009 American Chemical Society.