Rare earths are used in a variety of chemical forms, and in a wide variety of applications, some more complex than others. These applications can be divided into two broad categories:
- Uses that enable the processing of engineered or other materials, and
- Uses within components, which are themselves used as “building blocks” within engineered products.
A broad group of rare-earth element (REE) applications can be categorized as process enablers. They are used in the manufacturing process of other materials and components, yet are not consumed directly by the end product. Examples include:
- Fluid cracking catalysts (FCCs): these are materials used in the petroleum-refining industry, to convert heavy crude oil into gasoline and other valuable products. Lanthanum (La) and cerium (Ce) are added to the catalytic compounds, to take advantage of their ability to interact with the hydrogen (H) atoms found in the long-chain hydrocarbon molecules in the starting raw material. This interaction aids in the transformation of the crude oil into useful petroleum products.
- Automotive catalytic convertors: modern vehicles use catalytic convertors to reduce the emission of pollutants that result from the internal combustion process. CeO2 is the primary rare-earth compound used in this process (with some La2O3 and Nd2O3), usually in conjunction with platinum-group metals.
- Polishing media: significant amounts of CeO2 (with some La2O3 and Nd2O3) are utilized in the polishing of glass, mirrors, TV screens, computer displays and the wafers used to produce silicon chips. When used in a fine-powder form, the REOs react with the surface of the glass to form a softer layer (the so-called ‘mechano-chemical’ effect), thus making it easier to polish the surface to a high-quality finish.
The second group of end uses for rare earths consists of incorporating various REEs into sometimes-complex alloys and compounds, which are then used in engineered components. These components might then be utilized in sub-assemblies, which in turn might be used to produce a complex engineered product or device. In some cases, relatively small amounts of REEs are used in the overall product, but their presence is critical for the functionality of the ultimate end application.
There are many specific “building-block” applications of REEs; significant examples include:
- Permanent magnets: the use of REEs in certain magnetic alloys has made it possible to produce permanent-magnet materials that generate very strong magnetic fields. At the same time, these magnets are able to strongly resist being demagnetized when exposed to other magnetic fields, or to increases in temperature. The REEs present in these alloys, such as neodymium (Nd), praseodymium (Pr), samarium (Sm), dysprosium (Dy) and on occasion terbium (Tb), effectively help to ‘channel’ the inherent ferromagnetism of transition metals such as iron (Fe) and cobalt (Co).These characteristics have revolutionized magnetics design in recent years, most notably in the production of high-performance electric motors, which convert electricity into mechanical motion, and electric generators, which, operating in reverse, convert mechanical motion into electricity. rare-earth permanent-magnet materials have made it possible to miniaturize motors, loudspeakers, hard-disk drives, cordless power tools and other applications that use permanent magnets to operate, while maintaining the same or better output characteristics as other technologies.
- Energy storage: compounds of La and nickel (Ni) are used to produce battery cells for energy storage. The presence of La enables the absorption of H in the cell, and the ease of reversal of this electrochemical process leads to La-Ni-H compounds being particularly suitable for rechargeable-battery applications. Although recent developments in batteries that utilize lithium (Li) ion technology are gaining ground, batteries based on La-Ni-H are still a cost-effective and reliable method of storing electricity.
- Phosphors: phosphor materials emit light after being exposed to electrons or ultraviolet (UV) radiation. Liquid crystal displays (LCDs) and plasma screen displays, light-emitting diodes (LEDs) and compact fluorescent lamps (CFLs) all utilize such materials. Compounds containing europium (Eu), yttrium (Y) and Tb are frequently used to produce phosphors, and are fined-tuned for particular color outputs. Since much more of the electrical energy is converted into light than with conventional light sources, phosphor materials are significantly more energy-efficient that older technologies, requiring a lot less electricity to produce the same outputs.
- Glass additives: CeO2 and La2O3 are used as additives in the glass industry. They are used to remove undesirable coloration in commercial glass by reducing the effects of the presence of Fe within the material. They are also used to reduce UV light penetration, thus protecting the interiors of vehicles and other materials from degradation over time. They can also be used to increase the refractive index of glass lenses.