Zirconium Of The Stabilization
Zirconia in the crust is about 0.026%, because the distribution is very scattered, so feel scarce. There are two zirconium-containing ores in nature: oblique zircon and zircon. Oblique zircon contains ZrO280% -90%, the highest taste of up to 90% -99%, but very rare. ZrO2 in zircon is about 67%, Zirconium the main impurity is silica. In the zirconium ore, often accompanied by 0.5% -3% with radioactive hafnium oxide and other ingredients in the process of refining zirconia is difficult to separate it clean. The pure zirconia powder is yellow and gray, and the high purity zirconia powder is white.
Zirconia has two main homogeneous crystals: low temperature type monoclinic crystal, the density of 5.56g / cm3; high temperature of the tetragonal crystal, Zirconium the density of 6.10g / cm3. Monoclinic and tetragonal two crystal can be transformed into each other , The reversible conversion temperature is about 1000 ℃. With the crystallization of about 9% of the volume mutation, heating from monoclinic crystal into tetragonal crystallization, volume shrinkage; cooling from tetragonal crystallization into monoclinic crystal, volume expansion.
The bulk expansion curve and differential thermal analysis curve of ZrO2 show that this shrinkage and expansion do not occur at the same temperature, Zirconium the former occurs at about 1200 ℃, the latter occurs near 1000 ℃.
Due to the crystalline transition and volumetric properties of zirconia, it is difficult to produce sintered and non-cracked products with pure zirconia alone. (CaO), magnesium oxide (MgO), yttrium oxide (Y2O3), cerium oxide (CeO2), and the like are added to the zirconia in an amount equal to or less than 12% of the radius of the Zr4 + ion, After the high temperature treatment can be obtained from room temperature until 2000 ℃ above are stable cubic crystal zirconia solid solution, thus eliminating the heating or cooling process in the volume mutation. This cubic solid solution of zirconium oxide is called stable zirconia. The process of preparing stable zirconia is called zirconia stabilization. The above-mentioned added oxide is called a stabilizer. The stabilizing range of the stabilizer is: the mole fraction of magnesium oxide is 16% -26%; the mole fraction of calcium oxide is 15% -29%; Zirconium the mole fraction of yttrium oxide 7 % -40%; the mole fraction of cerium oxide is greater than 13%. Stabilizers depending on the specific requirements, can be used alone or at the same time with several.
Zirconia stabilization, the general content of more than 96% monoclinic zirconia raw materials and stabilizer with the ball in the ball mill grinding and mixing 8-24h, and then add a small amount of binder, pressure in the 60-100MPa pressure into the billet. The purpose of the briquettes is to bring the particles into close contact and promote the solid phase reaction, which is conducive to uniform stability. Zirconium According to the specific process requirements, the briquettes can be stabilized in the temperature range of 1450-1800 ° C. Finally, the stability of the material crushed to a variety of particle size of the powder. Stabilized briquettes at 1800 ° C are not easily finely ground and are therefore generally used as aggregates for molding or plasma pellets for plasma spraying.