Ceramic dusting corrosion of yttria-stabilized zirconia in ultra high temperature reverse-flow pyrolysis reactors

A reverse-flow reactor enables the pyrolysis of hydrocarbons, at temperatures ranging from 1500°C to 2000°C, to high-value petrochemical products through acetylene intermediate. Materials in the hottest regions of the reactor, exposed to such extreme temperatures, are subject to oxidative cycling over a period of several seconds between a regeneration (heat addition) step that is mildly oxidizing and a pyrolysis (cracking) step that is strongly reducing, accompanied by high carbon activity. Experimental results obtained from single crystal and polycrystalline yttria-stabilized zirconia (YSZ) ceramics of different porosities show that the pyrolysis reaction triggers the carburization of YSZ by diffusion of carbon through the lattice, the grain boundaries, and the pores. Subsequently graphite deposition occurs on the carburized surface. During the regeneration step, some of the graphite and (oxy)carbide are reoxidized. Corrosion advances in subsequent cycles by a repetition of oxide-carbide interconversion, carbon precipitation, and reoxidation steps. Since degradation involves the breakup of the bulk ceramic structure into powder or "dust" and is reminiscent of metal dusting corrosion observed in metallic materials in carbon-supersaturated environments, we name this corrosion "ceramic dusting." Details of the corrosion mechanism and the steps leading to such degradation are discussed.