Promoting thermal stability and acid resistance of rare earth sulfide powders by coating ZnO and SiO₂ double shells

As an environment-friendly powder with good coloring performance, rare earth sulfide is one kind of the important choices to replace cadmium and lead colorants. In particular, gamma-Ce2S3 belongs to rare earth sesquisulfide, which has a bright red color. However, the uncoated gamma-Ce2S3 is easy to decompose and release H2S in a humid or acidic environment, and its air thermal stability is limited to 350 degrees C. In this work, gamma-Ce2S3 powders coated with zinc oxide were prepared by heterogeneous precipitation method, and a dense protective layer was formed by ZnO to improve chemical and thermal stability. Moreover, silicon dioxide was deposited on the surface of the zinc oxide coating using the microemulsion process to strengthen the powder's acid resistance. The double shells structure greatly promoted thermal stability and acid resistance of gamma-Ce2S3 powders. The results showed that rare earth sulfide powders with double shells have good stability for coloring applications.