# Zirconium (IV) oxide

Crystal structure
__ Zr 4+      __ O 2−
General
Surname Zirconium (IV) oxide
other names
• Zirconia
• Zirconium oxide
• Zirconia
• CI Pigment White 12
• CI 77990
Ratio formula ZrO 2
Brief description

colorless, odorless solid

External identifiers / databases
 CAS number 1314-23-4 EC number 215-227-2 ECHA InfoCard 100,013,844 PubChem 62395 Wikidata Q36200
properties
Molar mass 123.22 g mol −1
Physical state

firmly

density

monoclinic: 5.7 g cm −3
tetragonal: 6.1 g cm −3
Y 2 O 3 - stabilized: approx. 6 g cm −3

Melting point

2680  ° C

boiling point

approx. 4300 ° C

solubility

1 mg / l (20 ° C)

safety instructions
GHS labeling of hazardous substances

Caution

H and P phrases H: 315-319-335
P: 261-305 + 351 + 338
MAK

1 mg m −3

As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

ZrO 2 ceramic balls for use in roller bearings

Zirconium (IV) oxide (ZrO 2 ), zirconium dioxide , also known colloquially as zirconium oxide (older names are zirconic acid or zirconium earth), is the most common compound of the element zirconium in nature after zirconium .

Technical zirconium dioxide ZrO 2 is an inorganic material from the group of oxides . It is used as a powder u. a. Used for the production of high-performance ceramics ( oxide ceramics ) and as a single-crystalline artificial gemstone as jewelry and in optics.

## Occurrence

The modification in the monoclinic crystal lattice is also called baddeleyite , this also occurs as a mineral in nature.

## Extraction and presentation

Zirconium silicate ZrSiO 4 ( zirconium ) is used as the starting product for the production of zirconium dioxide . This silicate sand is separated from impurities by washing, cleaning and calcining processes and converted into zirconium dioxide. A 99 percent pure zirconium dioxide powder is obtained in this way.

It is also formed during the dehydration and subsequent annealing of zirconium oxide hydrates or salts of zirconium such as nitrates, oxalates, acetates etc. with volatile, oxygen-containing acids.

## properties

Zirconium dioxide is diamagnetic , very resistant to acids and alkaline solutions and has a high resistance to chemical, thermal and mechanical influences. The chemical behavior is strongly dependent on the thermal pretreatment. When heated slightly, it dissolves in mineral acids fairly easily. After intense heating, it is soluble in concentrated sulfuric acid in addition to hydrofluoric acid and after melting it is only attacked by hydrofluoric acid. It is easily digested in melts of alkali hydroxide or carbonate, with which it forms zirconates which are soluble in acid.

Zirconia comes in three modifications :

• at room temperature it crystallizes in the monoclinic space group P 2 1 / c (space group no. 14) with a concentration number ( coordination number ) of zirconium with respect to oxygen of 7 (baddeleyite) and the lattice constants a = 5.138  Å , b = 5.204 Å, c = 5.313 Å, β = 99.2 °.
• Above 1170 ° C, it crystallizes in the tetragonal space group P 4 2 / nmc (No. 137) with a KZ of 8 (tetragonally distorted fluorite type)
• Above 2370 ° C it crystallizes in the cubic space group Fm 3 m (No. 225) with a KZ of 8 ( fluorite type)

monoclinic (1173 ° C) tetragonal (2370 ° C) cubic (2690 ° C) melt ${\ displaystyle \ leftrightarrow}$ ${\ displaystyle \ leftrightarrow}$ ${\ displaystyle \ leftrightarrow}$

The coefficient of thermal expansion depends on the modification of the zirconium dioxide:

• monoclinic: 7 · 10 −6 / K
• tetragonal: 12 · 10 −6 / K
• Y 2 O 3 -stabilized: 10.5 · 10 −6 / K

## stabilization

The addition of other metal oxides stabilizes the high-temperature modification at low temperatures. Properties such as B. The strength and translucency of these high-temperature modifications can thus be stabilized at room temperature. A proportion of at least 16  mol% calcium oxide (CaO) or 16 mol% magnesium oxide (MgO) is sufficient for crystallization in the cubic phase at room temperature. For a long time it was assumed that 8–8.5 mol% yttrium oxide (Y 2 O 3 ) (“8YSZ”) would be sufficient to stabilize the cubic phase at temperatures of up to 1000 ° C. It has been found in recent years that this is not the case (see paragraph on ionic conductivity). At least 9–9.5 mol% at 1000 ° C are necessary. At lower Y concentrations, metastable phases and mixed crystals form from the cubic and monoclinic phase. They generate internal prestress in the structure and ensure good thermal resistance to changes.

Common names and product names:

• partially stabilized ZrO 2 :
• PSZ, partly stabilized zirconia
• TZP, English: tetragonal zirconia polycrystal
• 4YSZ: ZrO 2 partially stabilized with 4 mol% Y 2 O 3 , English: yttria stabilized zirconia
• fully stabilized ZrO 2 :
• FSZ, English: fully stabilized zirconia
• CSZ, cubic stabilized zirconia
• 8YSZ: ZrO 2 fully stabilized with 8 mol% Y 2 O 3
• 8YDZ: 8–9 mol% Y 2 O 3 -doped ZrO 2 (same material as 8YSZ, naming due to the fact that 8YSZ is not completely cubically stabilized and chemically and microstructurally decomposes at temperatures up to 1200 ° C)

Translucent mixed crystals are called zirconia (also diamond imitation ) in the jewelry industry .

## Oxygen ion conductivity and its degradation

Zirconium ions generally have a valence of +4 in the YSZ. Doping with oxides of metals of lower valency creates oxygen defects through the maintenance of the charge neutrality in the crystal, for example when adding Y 2 O 3 . The Y 3+ ions replace Zr 4+ on the cation lattice as follows:

${\ displaystyle {\ text {Y}} _ {2} {\ text {O}} _ {3} \ rightarrow 2 {\ text {Y}} _ {\ text {Zr}} ^ {'} + 3 { \ text {O}} _ {\ text {O}} ^ {\ text {x}} + {\ text {V}} _ {\ text {O}} ^ {\ bullet \ bullet}}$ With ${\ displaystyle [{\ text {V}} _ {\ text {O}} ^ {\ bullet \ bullet}] = {\ frac {1} {2}} [{\ text {Y}} _ {\ text {Zr}} ^ {'}]}$

This means that one oxygen vacancy is created for every two Y 3+ ions. The hopping of oxygen ions onto these vacancies in the electrical field enables high oxygen conductivity with a high electrical resistance for electron transport at the same time (8YSZ> 1 S / m, ref. And publications cited there). Due to these optimal transport properties, YSZ is used as a solid electrolyte e.g. B. used in high temperature fuel cells. It has been observed that, although not completely cubic stabilized, 8YSZ / 8YDZ has the highest conductance value for oxygen ions in the Y 2 O 3 -ZrO 2 system almost independently of the temperature in the range between 800 and 1200 ° C (Ref. And mentioned therein Publications). Unfortunately, it has been found in recent years that 8-9 mol% YSZ is operated at temperatures up to above 1200 ° C. in a miscibility gap of the Y 2 O 3 -ZrO 2 system and is therefore on the nm scale segregated into Y-depleted and enriched areas within a few 1000 hours. This chemical and microstructural segregation is directly linked to the drastic decrease in oxygen conductivity (degradation of 8YDZ) of around 40% at 950 ° C within 2500 hours.

It has also been found that traces of impurities or undesirable transition metals, e.g. B. Ni (from fuel cell production) can drastically increase the rate of segregation, so that segregation and degradation can play a decisive role even at lower operating temperatures of around 500–700 ° C. Therefore, multiply doped zirconium oxides are increasingly being used as electrolytes (e.g. scandium-yttrium codoping).

## use

### powder

Zirconium oxide powder is added to paints to improve the properties (especially scratch resistance), e.g. B. automotive varnishes (topcoats), parquet varnishes, furniture varnishes, varnishes for electronic devices, nail varnishes. Inks for inkjet printers also contain zirconia.

### Ceramics

Ceramic is produced from zirconium oxide powder by sintering and / or hot isostatic pressing . (Partially) stabilized zirconium dioxide is used as a refractory ceramic , as a technical ceramic in mechanical engineering and as a prosthetic material in medical technology due to its good thermal resistance and good mechanical properties .

Due to its ability to conduct oxygen ions electrolytically at higher temperatures (from approx. 600 ° C, oxygen ions can easily diffuse through vacancies in the crystal lattice ), zirconium dioxide is used as a solid electrolyte e.g. B. used in fuel cells (see section on oxygen ion conductivity ). An early application therefore found zirconia ceramic as a material for the filament (Nernst glower) of the Nernst lamp , one of Walther Nernst invented in 1897 incandescent type transmission. The oxygen ion conduction is also used to different oxygen partial pressures z. B. to measure between exhaust gases and air to determine the combustion coefficient ( lambda probe ). The property is also used in sensors or analyzers for measuring the oxygen content of gases. Yttrium-stabilized zirconium (IV) oxide (YSZ) is used for fuel cells and lambda sensors.

Zirconium (IV) oxide ceramic is used in medicine and the like. a. Used for the production of hip joint implants and in dentistry as a material for the production of crown and bridge frameworks, tooth-colored monolithic crowns and bridges, root posts and dental implants that do not contain any elemental metals or metal alloys. Zirconia ceramic is also used in orthodontic treatments to make brackets for fixed appliances. A primary telescope can be produced from zirconium dioxide ceramic for telescope prostheses.

In addition to aluminum oxide ceramic, zirconium oxide ceramic is also used for the blades of so-called ceramic knives.

Yttrium-stabilized zirconium (IV) oxide (YSZ) is also used as a ceramic material in medicine and in turbine technology.

Zirconium dioxide ceramic is used to manufacture rolling elements for hybrid bearings and all-ceramic bearings.

Due to its good abrasion resistance and chemical resistance, zirconium oxide is used in mills, e.g. B. as grinding balls

### Single crystal

Man-made zirconium oxide single crystals are used as gemstones and as a material for optical components. Its high refractive index (2.15 at 643 nm wavelength) and its transparency in the 0.37–7 µm wavelength range are decisive for this.

## Individual evidence

1. Entry on zirconium dioxide in the GESTIS substance database of the IFA , accessed on November 25, 2012 (JavaScript required)
2. a b c d
3. D. N. Argiou, C. J. Howard: Re-investigation of Yttria-Tetragonal Zirconia Polycrystal (Y-TZP) by Neutron Powder Diffraction - a Cautionary Tale . In: Journal of Applied Crystallography , 1995 , 28 (2) , pp. 206-208 ( doi : 10.1107 / S0021889894011015 ).
4. D. G. Lamas, N. E. Walsöe de Reca: X-ray diffraction study of compositionally homogeneous, nanocrystalline yttria-doped zirconia powders . In: Journal of Materials Science , 2000 , 35 , pp. 5563-5567.
5. a b Data sheet zirconium (IV) oxide from Sigma-Aldrich , accessed on November 25, 2012 ( PDF ).
6. Hermann Salmang , Horst Scholze (Ed.): Ceramics . 7th edition. Springer Science & Business Media, 2006, ISBN 978-3-540-63273-3 ( Google Books ).
7. a b c Georg Brauer (Ed.): Handbook of Preparative Inorganic Chemistry . 3., reworked. Edition. tape II . Enke, Stuttgart 1978, ISBN 3-432-87813-3 , p. 1370 .
8. a b c Benjamin Butz: Yttria-doped zirconia as solid electrolyte for fuel-cell applications: Fundamental aspects . Ed .: Südwestdt. Verl. For Hochschulschr. 2011, ISBN 978-3-8381-1775-1 ( kit.edu ).
9. F. Hund: Anomalous mixed crystals in the system ZrO2 – Y2O3. Crystal construction of the Nernst pins. In: Journal for Electrochemistry and Applied Physical Chemistry . tape 55 , no. 5 , 1951, pp. 363-366 , doi : 10.1002 / bbpc.19510550505 .
10. Ekbert Hering: Sensors in Science and Technology. Vieweg + Teubner Verlag, 2012, ISBN 978-3-834-88635-4 ( limited preview in Google book search), p. 107.
11. B. Butz, R. Schneider, D. Gerthsen, M. Schowalter, A. Rosenauer: Decomposition of 8.5 mol.% Y2O3-doped zirconia and its contribution to the degradation of ionic conductivity . In: Acta Materialia . tape 57 , no. 18 , October 1, 2009, p. 5480–5490 , doi : 10.1016 / j.actamat.2009.07.045 ( sciencedirect.com [accessed November 17, 2016]).
12. B. Butz, A. Lefarth, H. Störmer, A. Utz, E. Ivers-Tiffée: Accelerated degradation of 8.5 mol% Y2O3-doped zirconia by dissolved Ni . In: Solid State Ionics . tape 214 , April 25, 2012, p. 37-44 , doi : 10.1016 / j.ssi.2012.02.023 ( sciencedirect.com [accessed November 17, 2016]).
13. Oxygen sensor A15-N. metrotec.eu, accessed on May 30, 2017 .
14. Zirconium Dioxide Analyzers | APM Technik GmbH. (No longer available online.) Archived from the original on July 2, 2017 ; accessed on May 30, 2017 .
15. Patent EP0386006 : Sensor element for limit sensors in determining the lambda value of gas mixtures.
16. ↑ Dental implants made of zirconium oxide on the advance? , NZZ , April 15, 2009.
17. Milling center CADSPEED: zircon
18. zwp-online.info: Zahntechnik - Werkstoffe - Zirkondioxid , April 1st, 2009.
19. ^ New thermal insulation layers (WDS) ( Memento from January 19, 2012 in the Internet Archive )
20. U. Weber and D. Langlois: The effect of grinding media performance on milling and operational behavior . Ed .: The Southern African Institute of Mining and Metallurgy. tape 110 , 2010, doi : 10.1007 / bf03402910 ( org.za [PDF; accessed October 31, 2019]).
21. http://www.korth.de/index.php/material-detailansicht/items/42.html Zirconium dioxide from Korth Kristalle GmbH, accessed on March 20, 2018