The kinetics of heterogeneous reactions, involving one reactant in the solid phase, usually follow the lawα=K∞ exp(−E/kT)f(1−α), where α is the degree of conversion of the solid, andK∞ andE are the kinetic constants. A critical examination is given of the various methods which are currently used to analyse dynamic experimental data. The limitations of these methods and their insensitivity to the form off(1-α) are pointed out. An alternative approach free from these limitations is suggested. In this,f(1−α) is determined from isothermal experiments, and then the dynamic data are accurately analyzed to obtain the values of the kinetic constants. A case study is given to elucidate the applicability of the approach.

Analysis of dynamic kinetic data from solid-state reactions

The decompositions of urea nitrate (UN) and guanidine nitrate (GN) are determined with isothermal heating followed by quantification of both remaining nitrate and remaining base. Activation energies determined for UN were 158 and 131 kJ/mol with the preexponential factors being 1.39 × 1012 s−1 and 2.66 × 109 s−1 for nitrate and urea, respectively. These pairs of Arrhenius constants predict decomposition rates less than a factor of two apart. For GN the activation energies were 199 and 191 kJ/mol with the preexponential factors being 1.94 × 1015 s−1 and 3.20 × 1014 s−1 for nitrate and guanidine, respectively. These pairs of Arrhenius constants predict identical decomposition rates. Literature values for ammonium nitrate decomposition indicate that it should decompose somewhat slower than UN and faster than GN. DSC also indicates this ordering but suggested that UN is substantially less stable than was observed in the isothermal experiments. Decomposition products, both gaseous and condensed, are reported f...

Decompositions of Urea and Guanidine Nitrates

B.M. Borham

Papers

Estimation of activation energies from differential thermal analysis curves

Isothermal decomposition of urea nitrate