The characteristics and application of zirconia ceramics
Zirconia ceramics are white, yellow or gray when they contain impurities, and generally contain HfO2, which is difficult to separate. Pure zirconia has three crystalline states under normal pressure. The production of zirconia ceramics requires the preparation of powders with high purity, good dispersibility, ultrafine particles and narrow particle size distribution. There are many ways to prepare ultrafine zirconia powder. The purification of zirconia mainly includes chlorination and thermal decomposition, alkali metal oxidative decomposition, lime melting, plasma arc, precipitation, colloid, hydrolysis and spray pyrolysis.
Types and properties of zirconia ceramics;
Zirconia ceramic impurities are white, yellow or gray, and usually contain hydrogen dioxide, which is difficult to separate. The proven zirconium resources in the world are about 19 million tons. Zirconia is usually made from zircon ore. Under normal pressure, pure zirconia has three crystal states: monoclinic zirconia (m-ZrO2), tetragonal zirconia (t-ZrO2) and cubic zirconia (c-ZrO2), which exist in different temperature ranges and can be Mutual conversion:
Zirconia Ceramic Temperature Density
Square zirconia 1200-2370°C, 6.10 g/cm3
Cubic zirconia > 2370°C ± 6.27 g/cm3
The above three crystalline states have different physical and chemical properties. In order to obtain the desired crystallization state and performance in practical applications, different types of zirconia ceramics, such as partially stabilized zirconia (PSZ), are usually added. When the stabilizers are calcium oxide, magnesium oxide and Y2O3, they are respectively expressed as calcium-PSZ, magnesium-PSZ, yttrium-PSZ, etc. Tetragonal zirconia composed of metastable t-zirconia is called tetragonal zirconia polycrystalline (TZP). When Y2O3 and CeO2 are added as stabilizers, Y-TZP, Ce-TZP, etc.
Application of Zirconia Ceramics
Among structural ceramics, zirconia ceramics are widely used in structural ceramics because of their high toughness, high flexural strength, high wear resistance, excellent thermal insulation properties, and a thermal expansion coefficient close to that of steel. Mainly include: Y-TZP grinding balls, dispersed grinding media, nozzles, ball valve seats, zirconia molds, micro fan shafts, fiber optic pins, fiber optic sleeves, drawing dies and cutting tools, wear-resistant knives, clothing buttons, watch cases and watch straps , bracelets and pendants, ball bearings, golf putters and other wear-resistant parts.
In terms of functional ceramics, its excellent high temperature resistance can be used as induction heating tubes, refractory materials and heating elements. Zirconia ceramics have sensitive electrical parameters and are mainly used in oxygen sensors, solid oxide fuel cells (SOFCs) and high-temperature heaters. Zirconia has a high refractive index (n-21 22). By adding certain coloring elements (V2O5, MoO3, Fe2O3, etc.) to make ultrafine zirconia powder, it can be made into colorful translucent polycrystalline zirconia material, shining like a natural gemstone, and can be made into various decorations. In addition, zirconia is also widely used in thermal barrier coatings, catalyst carriers, medical treatment, health care, refractory materials, textiles and other fields.