Cerium oxide (CeO2), the largest fraction of rare earth element ores, is often discarded as a low-value byproduct of rare earth mining for materials used in green-energy transition technologies. Converting this byproduct to a value-added co-product, such as aluminum–cerium alloy, could support the volatile rare earth market.
In the last decade, high-performance aluminum (Al) alloys with up to 10% cerium (Ce) have been developed that exhibit superior temperature stability, in addition to being lightweight and strong.
However, the current Al–Ce alloy production method, which uses Al melts and metallic Ce, is costly and consumes large amounts of energy, particularly because the process first requires CeO2 reduction to metallic Ce.
A recent study co-authored by Alfred Amon, a staff scientist at Lawrence Livermore National Laboratory, proposed an energy- and cost-efficient route for Al–Ce alloy production without requiring the production of metallic Ce. The key reaction in the proposed process involves the combination of CeO2 with liquid Al to form Ce and Al2O3 (aluminothermic reduction).
Researchers investigated the mechanism of this multi-step reduction reaction and applied differential scanning calorimetry, metallography, time-resolved synchrotron diffraction at Advanced Light Source (ALS) Beamline 12.2.2, and thermodynamic calculations to determine the rate-limiting step.
Because aluminothermic reduction occurs at high temperatures and is generally very rapid and exothermic, investigating its reaction mechanisms is difficult. The high data-acquisition rate and temperature tolerance of the time-resolved diffraction experiments enabled the researchers to observe short-lived intermediate phases, gaining crucial mechanistic insight. Amon noted that almost all theoretically predicted intermediate products were also observed experimentally. The data obtained at the ALS revealed that the reaction mechanism was highly dependent on temperature, particularly the intermediate reaction of Ce2O3 with Al to form CeAlO3, highlighting the importance of temperature control to maximize the reaction yield while minimizing heating costs.
“If we can apply this method on an industrial scale,” said Amon, “we can reduce the price and environmental impacts of Al–Ce alloy production and stabilize the rare earth supply chain.” The insights uncovered in this study will support industrial partners in the scaling up of this method to reduce several hundred kilograms of CeO2.
A. Amon, E.E. Moore, H.B. Henderson, J. Shittu, M. Kunz, S. Kastamo, N. Huotari, A. Loukus, R. Ott, D. Weiss, and S.K. McCall, “Aluminothermic reduction of CeO2: mechanism of an economical route to aluminum-cerium alloys,” Mater. Horiz. 11, 2382 (2024), doi:10.1039/D4MH00087K.