Thermal decomposition of silver squarate

Abstract

The kinetics of the thermal decomposition (473–510 K) of crystalline silver(I) squarate, Ag₂C₄O₄, under reduced pressure in an accumulatory gas apparatus, have been studied for comparison with results obtained for the decompositions of the nickel(II) and copper(II) salts. No melting was observed and the overall products of decomposition were solid silver particles in a carbonaceous residue, pseudomorphic with the original reactant crystallites, and gaseous CO and CO₂. The isothermal αvs. time curves were mainly deceleratory and approximated, for α < 0.5, to either the contracting-area or the contracting-volume rate equations, with an apparent activation energy of 190 ± 8 kJ mol^–1. Silver oxide powder was found to catalyse the decomposition and this, together with the presence of CO₂ in the gaseous products, led us to suggest that Ag₂O is a reaction intermediate, which reacts further with product CO gas. This sequence of reactions in a solid-state decomposition and our failure to detect any recognisable reactant/product interface in electron microscopic studies of partially decomposed material are the central features of this study. The relationship between these results and those for silver oxalate and for nickel and copper squarates is discussed.