Carbon deposition on MxCo1 –xFe2O4(M = Mn, Fe, Ni) spinels

Abstract

The deposition of carbon on power reactor steels results in a reduction in heat-transfer efficiency. Methane and carbon monoxide are added to the gaseous coolant to reduce the radiolytic oxidation of the graphite moderator and this is known to increase the rate of carbon deposition. However, the composition of oxides formed on steel surfaces within the reactor may also influence deposition. Previous studies have indicated that carbon is deposited on spinel-type oxides containing manganese, iron, nickel and chromium. Such deposits are often associated with particles containing iron, nickel or manganese. In this investigation carefully characterised cobalt-containing spinel-type oxides of varying composition have been subjected to γ-irradiation under conditions of temperature, pressure and atmosphere similar to those experienced in a reactor with the aim of furthering our understanding of the catalytic processes involved in deposit initiation and growth. It has been shown that the availability of rapid electron exchange (between octahedrally coordinated metal ions of mixed valency) greatly enhances the role of carbon deposition in these systems.