Thermal reactions of lead(IV) chloride complexes in the solid state. Part V. Thermolysis of mono-n-alkylammonium hexachloroplumbates

Abstract

Ammonium and mono-n-alkylammonium hexachloroplumbates of general formula (Cn H2n+1 NH3)2PbCl6, with n = 0–8, undergo thermal decomposition on heating to 650 K. The thermal processes were studied by differential thermal analysis and thermogravimetry with a derivatograph. Isothermal experiments were performed in an apparatus permitting a quantitative determination of amounts of evolved chlorine. For most compounds (n > 2) thermal processes proceed in two steps: 1.liberation of chlorine (CnH2n+1NH3)2 PbCl6(s) → PbCl2(s) +2(CnH2n+1 NH3)Cl(s) + Cl2(g)2.thermal processes which occur on heating the solid products of step (I) PbCl2(s) + 2(CnH2n+1NH3)Cl(s) → PbCl2(s) +2 CnH2n+1NH2(g) + 2 HCl(g)The experimental TG and DTG curves were used to examine the thermodynamics and kinetics of the first decomposition step. In the kinetic treatment of the data, sixteen f(α) and corresponding g(α) functions which describe the primary mechanism of thermal decomposition of solid substances, i.e. nucleation, growth of nuclei, phase boundary reactions and diffusion processes, were applied in the least-squares error analysis. Seven of the most adequate forms of kinetic equations, five of them based on integral kinetic equations and two of them based on differential kinetic equations, were used to evaluate kinetic constants. This approach also gave us an opportunity to compare different forms of mathematical equations used in non-isothermal kinetics.