Zirconium dioxide ( ZrO
2 ), sometimes known as zirconia (not to be confused with zircon), is a white crystalline oxide of zirconium. The most natural form, with a monoclinic crystal structure, is the mineral baddeleyite. A stable cubic stabilized cubic zirconia, cubic zirconia, is synthesized in a variety of colors for use as gemstones and diamond simulants.
Video Zirconium dioxide
Production, chemical properties, events
Zirconia is produced by calcining a zirconium compound, exploiting its high thermal stability.
Structure
Three phases are known: monoclinic & lt; 1,170 Â ° C, tetragonal 1,170-2,370 Â ° C, and cubic & gt; 2,370 ° C. This trend is for higher symmetry at higher temperatures, as is usually the case. A small percentage of calcium or yttrium oxide is stable in the cubic phase. Very rare tazheranite minerals (Zr, Ti, Ca) O 2 are cubic. Unlike TiO 2 , which has six Ti coordinates in all phases, monoclinic zirconia consists of seven zirconium coordinates. This difference is associated with a larger size of Zr atoms relative to Ti atoms.
Chemical reactions
Zirconia is chemically not reactive. It is slowly attacked by concentrated hydrofluoric acid and sulfuric acid. When heated with carbon, it is converted into zirconium carbide. When heated with carbon in the presence of chlorine, it turns into zirconium tetrachloride. This conversion is the basis for zirconium metal refining and analogous to the Kroll process.
Maps Zirconium dioxide
Engineering properties
Zirconium dioxide is one of the most studied ceramic materials. ZrO 2 adopts a monoclinic crystal structure at room temperature and transitions to tetragonal and cubic at higher temperatures. Volume changes caused by structural transitions from tetragonal to monoclinic to cubic induce large voltages, causing them to crack on cooling from high temperatures. When zirconia is mixed with some other oxides, the tetragonal and/or cubic phase becomes stable. Effective dopants include magnesium oxide (MgO), yttrium oxide (Y 2 O 3 , yttria), calcium oxide (CaO), and cerium (III) oxide (Ce < sub> 2 O 3 ).
Zirconia is often more useful in the 'stable' state phase. During warming, zirconia undergoes a disturbing phase change. By adding a small percentage of yttria, this phase change is removed, and the resulting material has superior thermal, mechanical, and electrical properties. In some cases, the tetragonal phase may metastasize. If sufficient quantities of the metastable tetragonal phase are present, then the applied stress, magnified by the stress concentration at the crack tip, may cause the tetragonal phase to convert to monoclinic, with an associated volume expansion. This phase transformation can then place cracks into compression, slow the growth, and increase fracture toughness. This mechanism is known as the toughness of the transformation, and significantly extends the reliability and lifetime of products made with stable zirconia.
The band gap ZrO 2 depends on the phase (cubic, tetragonal, monoclinic, or amorphous) and preparation method, with typical estimates of 5-7 eV (0.80-1.12 aj).
The special case of zirconia is tetragonal polycrystalline zirconia, or TZP, which indicates polycrystalline zirconia consisting only of the metastable tetragonal phase.
Usage
The main use of zirconia is in the production of hard ceramics, as in dentistry (see below), with other uses included as a protective coating on titanium dioxide pigment particles, as a refractory material, in insulation, abrasive and enamel materials. Stable Zirconia is used in oxygen sensors and fuel cell membranes because it has the ability to allow oxygen ions to move freely through the crystalline structure at high temperatures. This high ionic conductivity (and low electronic conductivity) makes it one of the most useful electro-ceramics. Zirconium dioxide is also used as a solid electrolyte in electrochromic devices.
Zirconia is a precursor for lead zirconate titanate ( PZT ), which is a high dielectric K, which is found in many components.
Niche uses
The very low thermal conductivity of the cubic phase of zirconia has also led to its use as a thermal barrier layer, or tuberculosis, in jets and diesel engines to enable operation at higher temperatures. Thermodynamics, the higher the engine operating temperature, the greater the efficiency. Other low thermal conductivity uses are ceramic fiber insulation for crystal growth furnaces, stack fuel cell isolation and infrared heating systems.
This material is also used in dentistry in the manufacture of 1) subframes for the construction of dental restorations such as crowns and bridges, which are then coated with conventional feldspathic porcelain for aesthetic reasons, or 2) strong and durable dental prosthesis made. entirely from monolithic zirconia, with a limited but increasing aesthetic. Stable zirconia with yttria (yttrium oxide) can be used as a strong base in some full ceramic crown restorations. The zirconia used in dentistry is stabilized zirconium oxide with the addition of yttrium oxide. The full names of zirconia used in dentistry are zirconia yttria-stable or YSZ.
Zirconia-hardened transformation is used to make ceramic knives. Because of its hardness, the spoon of ceramics remained sharper longer than the steel-edged products.
Because of its infusibility and brilliant luminosity when incandescent, it is used as a stick material for the center of attention.
Zirconia has been proposed for electrolysis of carbon monoxide and oxygen from the Martian atmosphere to provide both fuel and oxidizers that can be used as chemical energy storage for use with surface transport on Mars. Carbon monoxide/oxygen engine has been advised for the use of initial surface transport as both carbon monoxide and oxygen can be directly produced by zirconia electrolysis without requiring the use of any of Martian water resources to obtain hydrogen, which would be required for the production of methane or any hydrogen-based fuel.
Zirconia is also potential as a high dielectric material with potential applications as an insulator in transistors.
Zirconia is also used in the deposition of optical coatings; it is a high index material that can be used from near-UV to central IR, due to its low absorption in this spectral region. In such applications, it is usually stored by PVD.
In the manufacture of jewelry, some watch boxes are advertised as "zirconium oxide black". In 2015 Omega released a full hour ZrO 2 named "Dark Side of the Moon" with ceramic boxes, bezels, anesthesia and buckles, advertises it four times harder than stainless steel and therefore much more resistant to scratches during daily use.
Diamond simulant
Single-phase cubic crystals of zirconia are commonly used as diamond simulants in jewelry. Like diamonds, cubic zirconia has a cubic crystal structure and a high refraction index. Visually distinguishing cubic zirconia gems of good quality from hard diamonds, and most jewelers will have thermal conductivity gauges to identify cubic zirconia with low thermal conductivity (diamond is an excellent thermal conductor). This zirconia state is commonly called cubic zirconia , CZ , or zircon by jewelry, but the last name is not chemically accurate. Zircon is actually a mineral name for natural zirconium silicate (ZrSiO 4 ).
See also
- Quell
- Sintering
- The S-type star emits zirconium spectrum lines
- Yttria-stabilizes zirconia
References
Further reading
-
Green, D. J.; Hannink, R.; Swain, M. V. (1989). Transforming Strengthening Ceramics . Boca Raton: CRC Press. ISBNÃ, 0-8493-6594-5. - Heuer, A.H.; Hobbs, L.W., eds. (1981). Zirconia Science and Technology . Down payment in Ceramics. 3 . Columbus, OH: American Ceramic Society. p.Ã, 475.
- Claussen, N.; RÃÆ'¼hle, M.; Heuer, A.H., eds. (1984). Proc. Int'l Conf 2nd. about Zirconia Science and Technology . Down payment in Ceramics. 11 . Columbus, OH: American Ceramic Society.
External links
- The NIOSH Pocket Guide for Chemical Hazards
Source of the article : Wikipedia
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