The difference between Yttrium stabilized Zirconia and magnesium stabilized Zirconia
Rare earth or alkaline earth oxides are common stabilizers of zirconia, and only oxides with a difference between ion radius and Zr4+ radius of no more than 40% can be used as stabilizers of zirconia, among which yttrium oxide, calcium oxide, magnesium oxide and cerium oxide are commonly used. The properties of zirconia stabilized by different stabilizers are different, but the properties of stabilized zirconia obtained with different amount of the same stabilizer are also different. In the application, a reasonable and appropriate amount of stabilizer is often selected according to the actual use requirements.
Stable zirconia doped with yttrium has good comprehensive properties and is the most widely used solid electrolyte at present. Stable zirconia doped with magnesium oxide has general conductivity and low price, but its long-term performance is poor and is generally used as consumables.
Yttria stabilized zirconia is the addition of yttrium oxide into zirconia crystals to form zirconia composed of completely stable cubic crystals and unstable monoclinic crystals, which is called "partially stable zirconia". By controlling the ratio of stable phase to unstable phase, the zirconia coating with low average thermal expansion coefficient, excellent thermal shock resistance and long service life can be obtained. Only after spraying, zirconia is stabilized by yttrium oxide and has good high temperature resistance, thermal shock resistance and insulation properties. it is a kind of thermal barrier coating which is widely used in jet engine combustion chamber and flame nozzle, rocket flame nozzle, turbine combustion chamber and wing assembly. the working temperature is less than 1250 ℃.
Product applications:
Make crucibles for vacuum induction melting, high-purity zirconium sizing nozzles or zirconium composite long nozzle bricks for steelmaking, and bricks for lining of furnace and gas reaction furnace with ultra-high temperature higher than 1800 ℃.
Magnesium oxide is used as a stabilizer. This cubic phase material is loaded into tiny tetragonal precipitates, so the transformation toughness is very high. It has excellent mechanical properties, including high strength, fracture toughness, wear resistance, good thermal shock resistance and low thermal conductivity. Because of its high wear and corrosion, magnesia stabilized zirconia is used in valves, pumps and gaskets. It is also a material for chemical processing and petrochemical industries.
Product applications:
It is widely used in diesel engine plunger, valve cylinder head, mold coating and so on.
Compared with yttria stabilized zirconia, magnesia stabilized zirconia has excellent mechanical properties and creep resistance at relatively high temperature. however, the research and development of magnesium stabilized zirconia is restricted by two unfavorable factors: first, the solution temperature of magnesium oxide in the cubic zone of zirconia is very high, which makes it difficult to sintering magnesium stabilized zirconia completely. Second, magnesium oxide is easy to produce crystal phase separation and a large number of tetragonal phase instability when zirconia is higher than 1000 ℃, which leads to the decline of material properties and seriously restricts its application in high temperature region. Therefore, the future research focus of magnesia to stabilize zirconia is to reduce the sintering temperature and achieve low-temperature sintering, improve its high-temperature mechanical properties and expand the scope of application.
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