Yellow or brown powder aid. Density 7.13g / cm3. Melting point 2397 ℃. Insoluble in water and alkali-soluble acid. Use oxidant. The catalyst for organic reactions. Steel analysis for rare earth metal standard. Redox titration analysis. Bleaching glass. Glass enamel sunscreens. Heat-resistant alloys. Additives for glass industry, plate glass for abrasive materials, but also play the role of UV is used in cosmetics. It has now expanded to the optical glass, optical lenses, grinding kinescope of bleaching, clarification, absorbing ultraviolet and electron beam such as the role of the glass.