Aluminothermic reduction of CeO2: mechanism of an economical route to aluminum-cerium alloys.

Cerium oxide is a low-value byproduct of rare-earth mining yet constitutes the largest fraction of the rare earth elements. The reduction of cerium oxide by liquid aluminum is proposed as an energy- and cost-efficient route to produce high-strength Al-Ce alloys. This work investigated the mechanism of a multi-step reduction reaction to facilitate the industrial adaptation of the process. Differential scanning calorimetry in combination with time-resolved synchrotron diffraction data uncovered the rate-limiting reaction step as the origin of the reported temperature dependence of reduction efficiency. This is the first in situ study of a metallothermic reaction mechanism and will serve as guidance for cost- and energy efficient industrial process control.

Biocompatible High Entropy Alloys with Excellent Degradation Resistance in a Simulated Physiological Environment.

Bioimplants are susceptible to simultaneous wear and corrosion degradation in the aggressive physiological environment. High entropy alloys with equimolar proportion of constituent elements represent a unique alloy design strategy for developing bioimplants due to their attractive mechanical properties, superior wear, and corrosion resistance. In this study, the tribo-corrosion behavior of an equiatomic MoNbTaTiZr high entropy alloy consisting of all biocompatible elements was evaluated and compared with 304 stainless steel as a benchmark. The high entropy alloy showed a low wear rate and a friction coefficient as well as quick and stable passivation in simulated body fluid. An increase from room temperature to body temperature showed excellent temperature assisted passivity and nobler surface layer of the high entropy alloy, resulting in four times better wear resistance compared to stainless steel. Stem cells and osteoblast cells displayed proliferation and migratory behavior, indicating in vitro biocompatibility. Several filopodia extensions on the cell periphery indicated early osteogenic commitment, and cell adhesion on the high entropy alloy. These results pave the way for utilizing the unique combination of tribo-corrosion resistance, excellent mechanical properties, and biocompatibility of MoNbTaTiZr high entropy alloy to develop bioimplants with improved service life and lower risk of implant induced cytotoxicity in the host body.