Lamellar Compounds of Graphite with Nitrogen Pentoxide as Possible Reactor Hazards

Two different reactions have been found to occur simultaneously when graphite is exposed to air which has been ozonized by a high-voltage silent discharge. One is the formation of a lamellar compound with nitrogen pentoxide which is always present in ozonized air. The second reaction is a rapid volatilization because of oxidation, which has also been traced to nitrogen pentoxide rather than to the much less reactive ozone. The lamellar compound has been characterized as an acceptor-type compound in which every two molecules of pentoxide constitute one electron acceptor. Equilibrium concentrations which are established in a few hours in ozonized air amount to about 10wt% of pentoxide at 25°C, and 0.1wt% at 150°C. The oxidation reaction has been studied both in ozonized air and in N₂O₅. A much slower oxidation occurs in ozonized oxygen which can, however, be considerably accelerated if the graphite is first converted to a lamellar N₂O₅ compound. Pre-irradiation of the graphite causes only minor changes in the rates of compound formation and oxidation. The reactions may constitute hazards to reactors operating at low temperatures.