Rare earth elements, owing to their unique electron shell structures and exceptional magnetic, optical, and electrical properties, have become strategic resources contested globally. As a new round of technological revolution and industrial transformation accelerates, risks to global supply chain security have become prominent, and the focus of major powers' resource security has shifted from bulk minerals to critical minerals. Against this backdrop, the strategic value of rare earths has risen sharply, and their strategic position has become further pronounced, making them a key focus of resource competition and industrial rivalry among major powers.
Cerium oxide (CeO₂) offers the advantages of relatively abundant reserves and low cost, coupled with particularly outstanding physicochemical properties, making it one of the most widely studied and representative rare earth oxides.
From March 31 to April 10, 2025, within just ten days, three research papers on cerium oxide were successively published in JACS, Science, and Nature, sparking a wave of "crazy cerium oxide."
In practical production applications, rare earth polishing powders enjoy a stellar reputation for their exceptional performance in precision polishing, earning the title of "king of polishing materials." The main component of these rare earth polishing powders is CeO₂, hence they are also known as cerium-based rare earth polishing powders, or simply cerium-based polishing powders, and can also be referred to as CeO₂ polishing powders.
It has earned the title of "king" mainly for the following four reasons:
(1) CeO₂ crystals have a fluorite-type face-centered cubic lattice structure, with the space group Fm-3m. In the fluorite structure, cerium ions are located at the corners of the cube and the geometric centers of the faces, while oxygen ions fill the tetrahedral and octahedral interstices formed by the cerium ions in a close-packed manner.
(2) Compared with other types of polishing powders, CeO₂ polishing offers faster polishing speeds, higher surface finish of the polished products, and greater flatness. In addition, products polished with CeO₂ have a longer service life.
(3) CeO₂ has a Mohs hardness of about 7, which means that during mechanical action, it has sufficient hardness to cut and polish softer materials, yet does not cause excessive physical damage to the workpiece being polished.
(4) CeO₂ exhibits high chemical reactivity toward silicate glass, meaning it can react with the glass surface to create a chemical mechanical polishing (CMP) effect. This process involves both physical abrasion and chemical reaction, which is why it is widely used in glass polishing.
Four "synthesis methods" for rare earth cerium oxide
Currently, there are four main methods for preparing rare earth cerium oxide:
(1) Hydrothermal synthesis. This method is typically carried out in a sealed high-pressure autoclave, using an aqueous solution as the medium. By heating to subcritical or supercritical conditions, the cerium salt precursor directly crystallizes in the presence of a mineralizer or surfactant, yielding CeO₂ particles.
(2) Chemical precipitation. Precipitation is the most fundamental and most widely used method in industrial applications. By adding a precipitant (such as sodium hydroxide, ammonium bicarbonate, ammonia water, etc.) to a cerium salt solution, a hydroxide or carbonate precursor is obtained, which is then calcined to produce CeO₂.
(3) Sol-gel method. This method uses metal organic compounds or soluble inorganic salts as precursors, which are dissolved and then undergo hydrolysis and condensation reactions to form a transparent sol, which further transforms into a three-dimensional network gel, and is finally calcined to obtain CeO₂.
(4) Microemulsion method. This method utilizes a microemulsion system composed of surfactants, an oil phase, and an aqueous phase as a "nanoreactor," where nucleation, coalescence, and heat treatment take place to yield CeO₂.