Ce(III) Salt Induced Changes of Superficial Microstructure in Freshwater Pearls

The transition of the superficial microstructure of freshwater pearls induced by Ce was investigated by means of scanning electron microscopy. The pearls were cultured in freshwater containing 0 (control group), 0.5, 1, and 1.5 mg · L−1 of a Ce additive. X-ray photoelectron spectroscopy (XPS) measurement showed that the concentration of Ce absorbed in the superficial microstructure of pearls was positively correlated to the additive Ce. At the same time, the surface microstructure of pearls changed greatly with Ce concentration, the shape of the blocks changed from spindly to perfect regular hexagonal sheets and finally to round discs. The glossiness of the pearls changed correspondingly with the microstructure, pearls possessing the regular hexagonal blocks having the highest glossiness. Therefore, the REE Ce exerted a significant influence on the microstructure and glossiness of freshwater pearls. An appropriate quantity of Ce may improve the glossiness of pearls.