High Chrome Refractory Characterization: Part I. Impact of Melt Reduction/Oxidation on the Corrosion Mechanism

High Cr 2 O 3 containing Monofrax ™ K‐3 is a robust refractory that is used in the fiberglass industry and used in radioactive waste glass melters worldwide. Monofrax ™ K‐3 is tolerant of transition metal oxides but contains highly reduced solid solutions of spinels, that is, (Mg,Fe 2+ )(Al,Cr) 2 O 3 . Conversely, many of the waste feeds being processed are highly oxidizing. The K‐3 refractory corrosion was tested in sealed crucibles starting with slurried melter feed instead of prereacted glass called for by ASTM C621. Testing the refractory coupon during the feed‐to‐glass conversion exposes the refractory to the oxidizing and reducing species being released during vitrification, for example, NO 3 − , NO 2 − , CO 2 , CO , O 2 . Corrosion rates measured in highly oxidizing (high nitrate) feeds were ~1.8–2.8 times higher than those determined using prereacted glass or reduced feeds. Confirmatory corrosion rates were measured on Monofrax ™ K‐3 coupons immersed in oxidizing feed in a 1/100th‐scale HLW pilot‐scale melter. Corrosion is heterogeneous or incongruent as Ni and Fe in the waste glass exchange with Mg and Al in the refractory. An insoluble NiFe 2 O 4 spinel corrosion product is formed that can build up a protective layer along the refractory walls or spall and settle to the melter floor depending on melt pool convection/agitation.