Zirconium oxide
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| Names | |
|---|---|
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IUPAC names
Zirconium dioxide
Zirconium(IV) oxide |
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| Other names
Zirconia
Baddeleyite |
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| Identifiers | |
| ECHA InfoCard | 100.013.844 |
| Properties | |
| ZrO 2 |
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| Molar mass | 123.218 g/mol |
| Appearance | white powder |
| Density | 5.68 g/cm3 |
| Melting point | 2,715 °C (4,919 °F; 2,988 K) |
| Boiling point | 4,300 °C (7,770 °F; 4,570 K) |
| negligible | |
| Solubility | soluble in HF, and hot H2SO4 |
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Refractive index (nD)
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2.13 |
| Thermochemistry | |
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Std molar
entropy (S |
50.3 J K−1 mol−1 |
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Std enthalpy of
formation (ΔfH |
–1080 kJ/mol |
| Hazards | |
| Safety data sheet | MSDS |
| Flash point | Non-flammable |
| Lethal dose or concentration (LD, LC): | |
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LD50 (median dose)
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> 8.8 g/kg (oral, rat) |
| Related compounds | |
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Other anions
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Zirconium disulfide |
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Other cations
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Titanium dioxide Hafnium dioxide |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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 (what is   ?) |
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| Infobox references | |
Zirconium dioxide (ZrO
2), sometimes known as zirconia (not to be confused with zircon), is a white crystalline oxide of zirconium. Its most naturally occurring form, with a monoclinic crystalline structure, is the mineral baddeleyite. A dopant stabilized cubic structured zirconia, cubic zirconia, is synthesized in various colours for use as a gemstone and a diamond simulant.
Zirconia is produced by calcining zirconium compounds, exploiting its high thermal stability.
Three phases are known: monoclinic <1,170 °C, tetragonal 1,170–2,370 °C, and cubic >2,370 °C. The trend is for higher symmetry at higher temperatures, as is usually the case. A few percentage of the oxides of calcium or yttrium stabilize the cubic phase. The very rare mineral tazheranite (Zr,Ti,Ca)O2 is cubic. Unlike TiO2, which features six-coordinate Ti in all phases, monoclinic zirconia consists of seven-coordinate zirconium centres. This difference is attributed to the larger size of Zr atom relative to the Ti atom.
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. This conversion is the basis for the purification of zirconium metal and is analogous to the Kroll process.
Zirconium dioxide is one of the most studied ceramic materials. ZrO2 adopts a monoclinic crystal structure at room temperature and transitions to tetragonal and cubic at higher temperatures. The change of volume caused by the structure transitions from to tetragonal to monoclinic to cubic induces large stresses, causing it to crack upon cooling from high temperatures. When the zirconia is blended with some other oxides, the tetragonal and/or cubic phases are stabilized. Effective dopants include magnesium oxide (MgO), yttrium oxide (Y2O3, yttria), calcium oxide (CaO), and cerium(III) oxide (Ce2O3).
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