Interaction of Rare Earth Oxide with Alumina Refractories

To understand the refractory and rare earth oxide interactions, a series of different refractory grades were taken for phase equilibrium experiments. Refractories with 50%, 70% and 90% alumina were tested with CeO2 and La2O3. Steel pins of 1018 and 304 were placed inside the refractory bricks along with rare earth oxide powder. A resistance furnace then heated up to 1590C (2894F), held there for two hours. After the experiment, Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) analyses was conducted to observe the rare earth oxide interaction with these refractory grades. It was observed that the 50% refractory had a significant reaction with rare earth oxides forming rare earth silicates. Whereas, the 70% refractory had very little reaction with the rare earth oxides. However, the 90% alumina refractory did not react with the rare earth oxides due to the small amount of silica. There was no real reaction between the rare earth oxides and the 1018 steel, while, the chromium from the 304 stainless reacted with the 50% alumina refractory and was absorbed into the rare earth silicates that formed. Whereas, in the 90% alumina refractory only chromium had reacted from 304 steel but not with the rare earth oxides. Therefore, pure alumina refractories are beneficial for industrial castings for grain refining experiments for low carbon steels.