Zirconium dioxide, whose chemical formula is ZrO2, is the primary oxide of zirconium. Under normal conditions, it is a white, odorless and tasteless crystal, and it is insoluble in water, hydrochloric acid and dilute sulfuric acid. The chemical properties are inactive. It has the properties of high melting point, high resistivity, high refractive index and low thermal expansion coefficient, making it an actual high-temperature resistant material, ceramic insulating material and ceramic sunscreen. It is also the primary raw material for artificial drills.
1. Chemical method (alkali metal method)
The zircon concentrate powder is added to high-heat caustic soda to react to produce sodium zirconate. The sodium zirconate is washed with concentrated hydrochloric acid to produce zirconium oxide (ZH) Cl2. SH2OX zirconium oxide can be dissolved in water, and ammonia water is added to make it precipitate Zr(OH)1. Zr(OH)1S can be burnt to obtain zirconia.
It is also possible to melt zircon with caustic soda or pure to obtain sodium zirconate, add water to leaching to remove the solution, and then add hydrochloric acid or sulfuric acid to the precipitate (Zr(OH)4, Na2ZrO3, Na2SiO3 and undecomposed products, etc.) Carry out acid leaching, remove precipitation, and add ammonia water to prepare Zr(OH)4. Besides, zircon is added with alkaline earth metal oxides or carbonates, calcined to generate calcium zirconate, and then boiled with hydrochloric acid to remove impurities to obtain zirconia.
2. Preparation of Zirconia by Electrofusion Method
The reduction and melting of zircon in an electric arc furnace reduce desalinization and enrichment of zirconium. In an electric arc furnace at 2700℃, zircon is wholly decomposed into liquid ZrO2 and SiO2; simultaneously, SiO2 can be decomposed into gaseous SiO2 and O2, which is a reversible reaction.
There are two methods for preparing stable zirconia by the electric melting method: primary electric melting and secondary electric melting. The primary electric fusion method is to mix and grind zircon sand, graphite powder and stabilizer (usually calcite CaCO3) and then add them to the electric arc furnace for melting. After the fused ZrO2 is quenched (to promote crystal development), then Calcined at 1700°C, stable zirconia is obtained. In the secondary electric melting method, the zircon sand is mixed with graphite powder, then melted in an electric arc furnace, quenched and then lightly burned (about 1400°C) to obtain m-ZrO2. The m-ZrO2 is mixed with a stabilizer according to the proportion and mixed uniformly, then added to the electric arc furnace for secondary electric melting, and quenched to obtain stable zirconia.
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