Kinetics and mechanism of thermal decomposition of mercuric oxide

The dissociative evaporation scheme has been used for interpretation of the kinetics and mechanism of thermal decomposition of HgO. A comprehensive analysis of literature data provided explanation for the main features of the process, in particular, the comparatively low decomposition rate above 400 degrees C, which is at odds with the high equilibrium pressure of the gaseous products, and the existence of an additional low-temperature decomposition region within the 160-220 degrees C interval. It has been shown that decomposition in the high-temperature region follows the HgO(s) --> Hg(g) + O scheme, and in the low-temperature domain it proceeds by the Hg2O(s) --> 2Hg(g) + O reaction. The formation of Hg2O(s) on the HgO surface at low temperatures is in accord with the previously developed theoretical concepts of the mechanism of autocatalysis in the presence of a film of a solid product. (C) 1999 Elsevier Science B.V. All rights reserved.