It is also known as yttria. It is an air-stable, white solid substance. Yttrium oxide is a common starting material for both materials science and inorganic compounds. It can also be used as a precursor material for high-temperature superconductors, in the production of yttrium and other yttrium compounds One of its uses is it is considered as candidate materials for insulator coating. Particularly due to its extremely high temperature stability up to approximately 2,200°C and its outstanding resistance to alkaline melts with high oxygen affinity. Yttrium oxide is used in many special applications such as in insulators, glass, electrical conducting ceramics, refractories, and stains. 1.2 Zirconium dioxide (ZrO2 ) It is also known as zirconia, a white crystalline oxide of zirconium, which is a thermal insulator with high thermodynamic and chemical stability. Mineral baddeleyite is its most naturally occurring form, with a monoclinic crystalline structure. A dopant stabilized cubic structured zirconia, cubic zirconia, is synthesized in various colours for use as a gemstone and a diamond simulant. Zirconia is chemically unreactive. It is slowly attacked by concentrated hydrofluoric acid and sulfuric acid. When heated with carbon, it converts to zirconium carbide, when heated with carbon in the presence of chlorine, it converts to zirconium tetrachloride. Zirconium dioxide is one of the most researched ceramic materials. It is more useful when it is being ‘stabilized’ . Upon heating, zirconia undergoes disruptive phase changes.ZrO2 adopts a monoclinic crystal structure at room temperature and transitions to tetragonal and cubic at higher temperatures. Figure XX Ranges of Stability for the Crystallographic Phases of Zirconia Phase transformation of Zirconia is start from monoclinic which is stable at room temperature to tetragonal at about 1173 °C then to cubic at about 2370 °C. The phase transitions of zirconia from tetragonal to monoclinic to cubic caused volume change and induces large stresses which causing it to crack when cooling from high temperatures. When the zirconia is blended with some other oxides, the tetragonal and cubic phases are stabilized. Effective dopants include magnesium oxide (MgO) and yttrium oxide (Y2O3, yttria).
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