This MedLibrary.org supplementary page on Zirconia is provided directly from the open source Wikipedia as a service to our readers. Please see the note below on authorship of this content, as well as the Wikipedia usage guidelines. To search for other content from our encyclopedia supplement, please use the form below:
Related Sponsors
- Zirconia redirects here. For the Sailor Moon character, see Dead Moon Circus.
| Thermodynamic data | |
|---|---|
 |
|
| IUPAC name | Zirconium dioxide; Zirconium(IV) oxide |
| Other names | Zirconia; Baddeleyite |
| Identifiers | |
| CAS number | 1314-23-4 |
| Properties | |
| Molecular formula | ZrO2 |
| Molar mass | 123.22 g/mol |
| Appearance | white solid |
| Density | 5.89 g/cm³, solid |
| Melting point |
2715 °C |
| Boiling point |
°C |
| Solubility in water | Insoluble |
| Thermochemistry | |
| Std enthalpy of formation ΔfH |
−1080 kJ/mol |
| Standard molar entropy S |
50.3 J.K−1.mol−1 |
| Hazards | |
| EU classification | not listed |
| Related compounds | |
| Other anions | Zirconium disulfide |
| Other cations | Titanium dioxide; Hafnium dioxide |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references |
|
Zirconium dioxide (ZrO2), sometimes known as zirconia, is a white crystalline oxide of zirconium. Its most naturally occurring form, with a monoclinic crystalline structure, is the rare mineral, baddeleyite. The high temperature cubic crystalline form, called 'cubic zirconia', is rarely found in nature as mineral tazheranite (Zr,Ti,Ca)O2 (and a doubtful mineral arkelite), but is synthesized in various colours for use as a gemstone. The cubic crystal structured variety cubic zirconia is the best-known diamond simulant.
Contents |
Ceramic and engineering properties
Zirconium dioxide is one of the most studied ceramic materials. Pure ZrO2 has a monoclinic crystal structure at room temperature and transitions to tetragonal and cubic at increasing temperatures. The volume expansion caused by the cubic to tetragonal to monoclinic transformation induces very large stresses, and will cause pure ZrO2 to crack upon cooling from high temperatures. Several different oxides are added to zirconia to stabilize the tetragonal and/or cubic phases: magnesium oxide (MgO), yttrium oxide, (Y2O3), calcium oxide (CaO), and cerium(III) oxide (Ce2O3), amongst others.
Zirconia is very useful in its 'stabilized' state. In some cases, the tetragonal phase can be metastable. If sufficient quantities of the metastable tetragonal phase is present, then an applied stress, magnified by the stress concentration at a crack tip, can cause the tetragonal phase to convert to monoclinic, with the associated volume expansion. This phase transformation can then put the crack into compression, retarding its growth, and enhancing the fracture toughness. This mechanism is known as transformation toughening, and significantly extends the reliability and lifetime of products made with stabilized zirconia. A special case of zirconia is that of tetragonal zirconia polycrystaline or TZP, which is indicative of polycrystalline zirconia composed of only the metastable tetragonal phase.
The cubic phase of zirconia also has a very low thermal conductivity, which has led to its use as a thermal barrier coating or TBC in jet and diesel engines to allow operation at higher temperatures. Thermodynamically the higher the operation temperature of an engine, the greater the possible efficiency (see Carnot heat engine). As of 2004, a great deal of research is ongoing to improve the quality and durability of these coatings. It is used as a refractory material, in insulation, abrasives, enamels and ceramic glazes. Stabilized zirconia is used in oxygen sensors and fuel cell membranes because it has the ability to allow oxygen ions to move freely through the crystal structure at high temperatures. This high ionic conductivity (and a low electronic conductivity) makes it one of the most useful electroceramics.
The ZrO2 band gap is dependent on the phase (cubic, tetragonal, monoclinic, or amorphous) and preparation methods, with typical estimates from 5-7 eV.1
This material is also used in the manufacture of subframes for the construction of dental restorations such as crowns and bridges, which are then veneered with a conventional feldspathic porcelain.2
Zirconium dioxide can occur as a white powder which possesses both acidic and basic properties. On account of its infusibility and brilliant luminosity when incandescent, it was used as an ingredient of sticks for limelight.
Zirconia is also an important high-k dielectric material that is being investigated for potential applications as an insulator in transistors in future nanoelectronic devices.
Diamond substitute
Single crystals of the cubic phase of zirconia are commonly used as a substitute for diamond (diamond simulant) in jewelery. Like diamond, cubic zirconia has a cubic crystal structure and a high index of refraction. Discerning a good quality cubic zirconia gem from a diamond is difficult, and most jewellers will have a thermal conductivity tester to identify cubic zircona by its low thermal conductivity (diamond is a very good thermal conductor). This state of zirconia is commonly called "cubic zirconia," "CZ," or "zircon" by jewellers, but the last name is not chemically accurate. Zircon is actually the mineral name for naturally occurring zirconium silicate (ZrSiO4). Its transparent form is also used as a gemstone, and its opaque form as a refractory.
Patents
On August 7, 2006, Apple Inc. filed a patent for using zirconia as casing for mobile devices. Future iPods likely will contain radios for Bluetooth and wide area wireless. Using zirconia rather than steel or aluminium for its radio transparency characteristics enables antennae to be hidden internally in the device. Additionally, some iPods with plastic fronts have been known to scratch easily.3
See also
References
- ^ Chang, Jane P; You-Sheng Lin; Karen Chu (September 2001). "Rapid thermal chemical vapor deposition of zirconium oxide for metal-oxide-semiconductor field effect transistor application". Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures (American Vacuum Society) 19 (5 ): 1782-1787.
- ^ Papaspyridakos, Panos; Kunal Lal (September 2008). "Complete arch implant rehabilitation using subtractive rapid prototyping and porcelain fused to zirconia prosthesis: A clinical report". The Journal of Prosthetic Dentistry (Mosby, Inc.) 100 (3): 165-172. doi:.
- ^ "Apple seeks patent on radio-transparent zirconia CE casings", Apple Insider (30 November 2006).
External links
 |
This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (August 2007) |
Wikipedia content modification information:
- This page was last modified on 2 December 2008, at 16:12.
Wikipedia Authorship and Review
Wikipedia content provided here is not reviewed directly by MedLibrary.org. Wikipedia content is authored by an open community of volunteers and is not produced by or in any way affiliated with MedLibrary.org.
Wikipedia Usage Guidelines
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article on "Zirconia".
The URL for this specific entry is:
All Wikipedia text is available under the terms of the GNU Free Documentation License. (See Copyrights for details). Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc.