Charge transfer and thermal decomposition of NH 4ClO 4 crystals

Abstract

On the basis of previous work on the determination of transport numbers the following mechanism has been proposed for the formation and migration of the conduction proton in the NH 4ClO 4 (AP) lattice. 1. Transfer of the proton from cation to anion NH 4 + +ClO 4 − →NH 3 +HClO 4. 2. Reorientation of the protonated anion HClO 4 →ClO 4H. 3. Proton jump to a neighboring anion ClO 4H+ClO 4 − →ClO 4 − +HClO 4 The conductivity of AP crystals is increased proportionally to the concentration of added proton donor impurity HSO 4 − ion. analysis of the impurity conductivity allows one to write for the mobility of protons in the AP lattice the expression μ = 20exp (−0.81 eV/ kT) cm 2/V sec. The dielectric relaxation of AP crystals has been investigated. Agreement has been shown of the time of dielectric relaxation with the correlation time of the diffusion process as determined by the Nernst-Einstein relation from the magnitude of the mobility. Values of the activation energy for the mobility and for the time of dielectric relaxation are also close to each other. These data are considered in the nature of experimental evidence for use of the proposed mechanism of conductivity in AP. The influence of the indicated impurity on formation rate V n and growth rate V g of nuclei on thermal decomposition of AP has been investigated and corresponding activation energies E n and E g calculated. For pure AP, E n = 70 ± 4kcal/mole; whereas for doped AP, 50 ± 4 kcal/mole. Significant differences between pure and doped AP with respect to corresponding values of V g and E g were not detected. Attention is directed to the closeness of the values of the activation energy for the overall rate of low temperature decomposition E 1 t = 33.9 ± 1.6kcal/mole and E g = 35 ± 5kcal/mole. Consequently, just the processes of nuclear growth determine the total rate of thermal decomposition of AP. Arguments are presented in favor of a proton-donating character for the effect of adding HSO 4 − on the thermal decomposition of AP. It is predicted that addition of proton acceptors, among them (NH 4) 2HPO 4, will significantly decrease the value of V n in AP.