Zirconium dioxide
- Zirconia
- Zirconia
- Zirconia
- C. I. Pigment White 12
- C. I. 77990
Colorless, odorless solid
Fixed
Monoclinic: 5.7 g · cm -3 tetragonal: 6.1 g · cm -3 Y2O3 - stabilized: about 6 g · cm -3
2680 ° C
About 5000 ° C
1 mg / l (20 ° C)
Attention
1 mg · m-3
Template: Infobox chemical / molecular formula search available
Zirconium ( IV ) oxide ( ZrO2), zirconia or zirconium oxide with the common name referred to (older names are zirconic or zirconia ), according to zircon, the most common in nature compound of the element zirconium. Zirconia ZrO2 is a high-performance ceramics, ie a non-metallic, inorganic material, and belongs to the group of oxide ceramics and is used accordingly. The modification in the monoclinic crystal lattice is also known as baddeleyite, this comes as a mineral in nature.
Production and representation
As a starting material for the preparation of zirconia zirconium silicate ZrSiO4 (zircon ) will be used. Silicatsand this is separated by washing, cleaning and Calcinierungsprozesse impurities and converted into zirconia. There is thus obtained a 99 - percent pure zirconia.
It is also produced during dewatering and subsequent annealing of Zirkonoxidhydraten or salts of zirconium such as nitrates, oxalates, acetates, etc. with volatile oxygen-containing acids.
Properties
Zirconia is diamagnetic, to acids and alkali solutions very stable and has a high resistance to chemical, thermal and mechanical influences. The chemical behavior is strongly dependent on the thermal pretreatment. Weak heated it dissolves fairly easily in mineral acids. After strong heating, it is out in hydrofluoric acid more soluble in concentrated sulfuric acid, and after melting it is attacked only by hydrofluoric acid. It is easily digestible in melts of alkali metal hydroxide or carbonate, with which it forms soluble Zirconates in acid.
Zirconia comes in three modifications:
- At room temperature it crystallizes in the monoclinic space group P21 / c with a KZ ( coordination number ) of zirconium with respect to the oxygen of 7 ( baddeleyite ) and the lattice constants a = 5.138 Å, b = 5.204 Å, c = 5.313 Å, β = 99.2 degrees.
- Above 1170 ° C, it crystallizes in the tetragonal space group P42/nmc with a concentration camp of 8 (tetragonal distorted fluorite - type)
- Above 2370 ° C, it crystallizes in the cubic space group Fm3m with a concentration camp of 8 ( fluorite - type)
Monoclinic ( 1173 ° C), tetragonal ( 2370 ° C) cubic ( 2690 ° C) melt
The thermal expansion coefficient is dependent upon the modification of the zirconia:
- Monoclinic: 7 · 10-6 / K
- Tetragonal: 12 · 10-6 / K
- Y2O3 - stabilized: 10.5 · 10-6 / K
Stabilization
The addition of other metal oxides stabilizes the high-temperature modification at low temperatures. A proportion of at least 16 mol % of calcium oxide (CaO ), 16 mol% of magnesium oxide (MgO ), or 8 mole % of yttrium oxide ( Y2O3 ) ( " 8YSZ " ) is sufficient for the crystallization in the cubic phase at room temperature. In smaller proportions mixed crystals form from the cubic and monoclinic phase. You create an internal bias in the structure and good thermal shock resistance.
Designations:
- Partially stabilized ZrO2: PSZ, English: partly stabilized zirconia
- TZP, English: tetragonal zirconia polycrystal
- 4YSZ: teilstablilisiertes with 4 mol% Y2O3 ZrO2, English: yttria stabilized zirconia
- FSZ, English: fully stabilized zirconia
- CSZ, English: cubic zirconia stabilized
- 8YSZ: fully stabilized with 8 mol% Y2O3 ZrO2
Translucent mixed crystals are used in jewelry cubic zirconia (also called diamond imitation).
Zirconium has a 4 valence. By doping with lower valence oxides of metals caused oxygen vacancies. The high oxygen mobility in combination with low electrical Leitfähgigkeit achieved, for example at an ionic conductivity of YSZ of 10 S / m.
Use
Indications: refractory ceramics, technical ceramics, Prosthetics
Is used (partially) stabilized zirconia due to the good thermal stability of refractory ceramics, technical ceramics in mechanical engineering as well as prosthetic material in medical technology.
It is added to paints to improve the properties ( insbesonderes scratch resistance). eg automotive coatings ( topcoats ), floor coatings, furniture coatings, coatings for electronic equipment, nail polishes. Also, colors for inkjet printers contain zirconia.
An early application was zirconia as material for the filament ( Nernststift ) of the Nernst lamp, a Walther Nernst in 1897 invented the design of the electric light bulb. As with the lambda probe here the electrolytic conductivity was exploited.
Zirconia has the ability to conduct oxygen ions at elevated temperature electrolytically. This property is exploited to measure different oxygen partial pressures, eg, between exhaust gases and air ( oxygen sensor ).
Zirconium ( IV) oxide is furthermore in medicine including among hip implants and in dentistry as the basis for the fabrication of crowns and bridge frameworks with the help of CAD / CAM method in endodontic posts and metal-free dental implants are used. For telescopic dentures is possible through new software, a metal-free primary telescope. Zirconia is also used in the context of orthodontic treatments for the manufacture of brackets for fixed appliances. As a household item, it is now included in the so-called blade ceramic knife. After alumina zirconia oxide ceramic is the most commonly used.
Yttria stabilized zirconium ( IV) oxide is used in fuel cells and in particular in oxygen sensors as an ion conductor. From about 600 ° C oxygen ions can easily diffuse through vacancies in the crystal lattice. YSZ is also used as the ceramic material in the medical field and in the turbine art. Zirconia is also used in storage technology for hybrid bearings ( rolling elements made of zirconia ) and full ceramic bearings ( rolling elements and raceways zirconia ).