Zirconium Oxide ZrO₂ ייצור חלקי זירקוניה לפי שרטוט
In fine ceramics, zirconium oxide has a good mechanical strength at room temperature. Its coefficient of thermal expansion is similar to metals, so it is especially suitable for combination with metals. Owing to its low thermal conductivity and high toughness, it is a product that can overcome frangibility of ceramics.
Zirconium oxide was found by Hussak in 1892. It exists in natural ore zircon sand or baddeleyite.
Pure zirconium oxide exists in the form of monoclinic crystal, cubic crystal and cubic lattice.
Zirconium oxide is characterized by high strength, high toughness, high hardness as well as excellent chemical corrosion and abrasive resistance.
The world's 80% zircon sand producing areas are concentrated in Australia, South Africa and the United States. The methods of refining zirconia from zircon sand include chlorination method and pyrolysis method. It can be used in fireproofing materials, dewaxing casting and high quality powders.
Major baddeleyite producing areas are concentrated in South Africa, Brazil and Soviet Union, and baddeleyite is mainly used in abrasive material and ceramic dye.
Zirconium oxide exists in monoclinic crystal at room temperature, and will be converted into square crystal phase as temperature rises to 1170°C and then converted into cubic crystal phase as temperature rises to 2,370°C, while cubic crystal phase will be dissolved into liquid phase at 2,680°C, the conversion from square crystal into monoclinic crystal is a martensitic transformation, and such phase conversion may produce 3 - 5% volume change, resulting micro cracks. Later, magnesium oxide, calcium oxide and other phase stabilizing agents are added to make sure that zirconium oxide can maintain the high-temperature stable phase, that is cubic crystal phase, which is called the stabilized zirconium oxide; if yttrium oxide phase stabilizer is added to keep partial square crystal phase, it can be called partially stabilized zirconium oxide.
Zirconium oxide thermal conductive ceramic ZrO₂ is pure white while yellow or gray containing impurities, and generally contains HfO₂, not easy to separate. The production of zirconia ceramics requires the preparation of narrow powder characterized by high purity, good dispersion performance, ultrafine particle and narrow particle size distribution. There are many methods to prepare superfine powder of zirconium oxide, and the purification methods of zirconium oxide mainly include chlorination and thermal decomposition method, alkali metal oxidation decomposition method, lime melting method, plasma arc method, precipitation method, colloid method, hydrolysis method and spray pyrolysis method.
Advantages of Zirconia ceramics are as follows:
1. It has high hardness, toughness and bending strength, and the density is between 5.95 - 6.05g/cm³. There are three kinds of ceramics produced by Touch-down, including aluminium oxide Al₂O₃, silicon carbide Sic and zirconium oxide ZrO₂, among which zirconium oxide has the highest toughness which is above 8MPa • m1/2.
2. It has high-wearing feature and low friction coefficient, whose abrasive resistance is 15 times of aluminum oxide ceramics while friction coefficient is only 1/2 of aluminum oxide ceramics. After abrasive machining, its surface smoothness becomes even higher and can reach above ▽ 9. It is in mirror shape and extremely smooth, and the friction coefficient is lower.
3. It has good insulation and strong corrosion resistance, is static-free, heat resisting and has excellent heat-shielding performance, whose coefficient of thermal expansion is close to steel.
4. It is self-lubricating and can solve the problem of pollution caused by lubricating medium and inconveniences added.
Processing form of Zirconia Ceramics:
1. Processing by Opening the Mould: Dry-type forming machine, CIM injection forming. CIP equalizing processing and plate cutting processing.
2. Shape Processing Product: Plane grinding shall be adopted according to customer interface requirements, as well as inner / outer diameter grinding, NC program processing and grinding and polishing.
