| Popis: |
An isothermal kinetic and mechanistic study of the thermal decomposition of nickel acetate is reported. Plots of yields of volatile products against time were sigmoid. Calculated activation energies were 150 ± 8 (548–578 K) and 80 ± 8 (578–618 K) kJ mol−1. There were systematic variations in kinetic behaviour with temperature. At the upper end of the temperature interval studied here ( > 580 K) a second rate process became apparent during the final stages of reaction ( > 80%). It is concluded that the autocatalytic reaction is a nucleation and growth process in which anion breakdown is promoted by the predominant solid product, nickel carbide. Towards the end of reaction, and increasingly at higher temperatures, nickel, produced by Ni3C decomposition, more effectively accelerates reaction and this acccounts for the second rate process. These mechanistic proposals are based also on scanning electron micrographs which showed that the salt did not comprehensively melt during pyrolysis. Little information could, however, be obtained concerning the structure of the reaction interface because textural features were below the limits of resolution. Analytical determinations failed to reveal the existence of any anionic reaction intermediate. |
