Thermal decomposition of ozone at high temperature leading to ozone zero phenomena

Abstract

A gradual decrease in the concentration of ozone produced by the continuous operation of a large-scale dielectric barrier discharge-type ozone generator (OG) was observed under the supply of a constant discharge power and high-purity oxygen as the feed gas. This finding was named the ‘ozone zero phenomena’ on the basis of our experiments demonstrating that the ozone molecules disappeared at the surface of the electrodes in the OG, in which both the formation and decomposition of ozone occur simultaneously. To clarify the cause of the phenomena, we performed new experiments with an OG separated functionally into two parts to avoid the effects of the discharge, which also oxidizes stainless-steel and increases the temperature in the generator, although the discharge is indispensable for ozone generation. The first part was an OG supplying ozone to the following part. The second part was an ozone destructor that simulated an OG in which only the ozone zero phenomena occurred. The ozone destructor was an incubator with pipes made of stainless-steel or borosilicate glass in them and maintained at a constant temperature of up to 473 K. The generator and destructor were connected serially with a gas flow line. Ozone–oxygen mixtures with constant ozone concentrations produced by the first part were introduced into the ozone destructor, and the ozone concentrations at the inlet and outlet of the pipes were monitored simultaneously. Using the two ozone concentrations, the decomposition rate of ozone was evaluated as functions of time, the pipe material, the pipe temperature, and the concentration of ozone introduced into the pipe. We concluded that in this model experiment the ozone zero phenomena are induced by the thermal decomposition of ozone in the pipes which is installed in the heated incubator to provide ambient temperature conditions for the conversion of ozone molecules.