Addressing Rare-Earth Element Criticality: An Example from the Aviation Industry

Abstract

Rare-earth (RE) elements are enablers for a wide range of technologies, including high-strength permanent magnets, energy-efficient lighting, hightemperature thermal barrier coatings, and catalysts. While direct material substitution is difficult in many of these applications because of the specific electronic, optical, or electrochemical properties imparted by the individual rare-earth elements, we describe an example from the aviation industry where supply chain optimization may be an option. Ceramic matrix composite engine components require environmental barrier coatings (EBCs) to protect them from extreme temperatures and adverse reactions with water vapor in the hot gas path. EBC systems based on rare-earth silicates offer a unique combination of environmental resistance, thermal expansion matching, thermal conductivity, and thermal stability across the service temperature window. Several pure rare-earth silicates and solid solutions have been demonstrated in EBC applications. However, all rely on heavy rare-earth elements (HREEs) for phase stability. This article considers the possibility of using separation tailings containing a mixture of HREEs as a source material in lieu of using the high-purity HREE oxides. This option arises because the desired properties of RE-silicate EBCs derive from the average cation size rather than the electronic properties of the individual rare-earth cations. Because separation tailings have not incurred the costs associated with the final stages of separation, they offer an economical alternative to high-purity oxides for this emerging application.

Apatite and garnet stability in the Al–Ca–Mg–Si–(Gd/Y/Yb)–O systems and implications for T/EBC: CMAS reactions

“…There is a growing interest in understanding the performance of multi‐cation coating materials developed either using a “high entropy” approach, or designed to take advantage of more economical partially‐refined RE oxide feedstock 60–62 . Results from this study demonstrate the significant influence of rare earth cation size on the identity, compositions, and relative phase fractions of the reaction products formed during coating‐deposit interactions.…”

The Sustainable and Efficient Ionic Liquid-Type Saponification Strategy for Rare Earth Separation Processing

“…The mass percentage of Y accounts for 30–60% in the ion-adsorption deposits. Because the cation radius of Y (0.89 Å) is similar to those of Ho (0.90 Å), Er (0.89 Å), Tm (0.88 Å), Yb (0.868 Å), and Lu (0.861 Å), the efficient separation of Y from Ho–Lu is an industrial challenge. As can be seen in Figure (a), the distribution ratios of HREEs extracted by [P 6,6,6,14 ]­[SOPAA] are bigger than those extracted by HSOPAA.…”

Synergistic Effect of Acid–Base Coupling Bifunctional Ionic Liquids in Impregnated Resin for Rare Earth Adsorption

“…The sequence can be attributed to the coordination abilities of functional groups in the combined ABC-BILs with REEs. The sequence of cation radii of REEs are Ho (0.90 Å), Y (0.89 Å), Er (0.89 Å), Tm (0.88 Å), Yb (0.868 Å), Lu (0.861 Å) . Accordingly, the electrostatic interaction abilities between ABC-BILs and REEs increase as the ionic radii of REEs decrease.…”