Zinc oxide
- Zinc (II ) oxide
- Zinci oxidum
- Zinc white
- Chinese White
- C. I. Pigment White 4
- C. I. 77947
- Lana philosophica
D02AB
Colorless, hexagonal crystals or a white, fluffy powder
Fixed
5.61 g · cm -3
1975 ° C ( under pressure)
- Practically insoluble in water: 1.6 mg · l-1
- Soluble in dilute acids
Attention
1 mg · m-3
Template: Infobox chemical / molecular formula search is not possible
Zinc oxide (ZnO) is a chemical compound of zinc and oxygen on the one hand forms colorless crystals of hexagonal or otherwise, due to the refraction of light at very small crystals, as a fluffy white powder.
The traditional name of zinc white ( Chinese White, Eternal White, Snow White ) comes from the use of a white colorant in painting color.
Medical preparations for skin and wound treatment often contain zinc oxide because of its antiseptic properties. It is often used in dentistry (eg, root canal treatments) and is considered as a biomaterial.
Occurrence
Mineral deposits of zinc oxide can be found in the form of coarse-grained Rotzinkerz ( zincite ).
Production and representation
Depending on the manufacturing method you win or zinc white zinc oxide. Zinc white is prepared by the so-called French process zinc vapor and oxygen.
Zinc oxide on the other hand you win either of the implementation of the production by the so-called American process zinc ores or scrap by roasting, by reduction with coal and direct subsequent reoxidation or wet chemically by precipitation as hydroxide or carbonate of zinc salt solutions and subsequent calcination.
Zinc oxide produced by the combustion of zinc. In this case, the oxide in feinfilziger, wool -like form ( Lana philosophia ) may form.
It can also be obtained by annealing (pyrolysis ) of zinc hydroxide, zinc carbonate or zinc nitrate:
During roasting of zinc sulfide is also produced zinc oxide:
Depending on the application can be prepared by varying the reaction conditions in different zinc oxide grades. Industrially produced zinc oxide pigments are frequently contains lead and thus to characterize additionally assigned the symbol Xn (harmful).
Thin films of zinc oxide is manufactures by physical deposition ( PVD) such as sputtering and chemical vapor deposition ( CVD). CVD allows the formation of rough surfaces, which are characterized to scatter incident light and to give a higher efficiency solar cells, for example.
Properties
Zinc oxide evaporates from about 1300 ° C, the sublimation point at atmospheric pressure is about 1800 ° C. Melting of zinc oxide is to be observed only under elevated pressure at 1975 ° C. When heated it turns lemon yellow, after cooling it is white again (see thermochromism ). In the dark you can then observe a faint afterglow. The color change is due to a low, caused by release of oxygen when heated zinc excess ( about 0.03 %). This zinc surplus or the concentration of oxygen defects is strongly dependent on the synthesis method, temperature and impurities of the zinc oxide.
Zinc oxide is a semiconductor with a direct band gap of 3.2 to 3.4 electron volts. Accordingly, it absorbed UV - light and is transparent to visible light. Due to the non-centrosymmetric unit cell is zinc oxide piezoelectric.
The electric conductivity of zinc oxide can be increased by doping with suitable elements. Often this aluminum ( aluminum -doped zinc oxide AZO) or boron used. Other elements for an N -type dopant such as indium or gallium are not currently used. P- doped zinc oxide is more difficult to produce and a range of current research.
Zinc oxide is insoluble in water, dilute acids during solve it with salt formation. With alkali, such as caustic soda, freshly precipitated hydrated zinc oxide dissolves in an excess of base again. This produces a soluble zincate.
If the connection with cobalt (II ) oxide ( CoO ) is heated, the result is a green solid solution of cobalt in zinc oxide ( Rinmans Green).
Use
Pigment
Zinc oxide is used under the name of zinc white as a pigment. In addition, you can also find names such as Chinese white, Everlasting White or Snow White. In contrast to white lead paints, it is hydrogen sulphide and light resistant, but less opaque. Therefore, mixtures of lead and zinc white were used as a painter color often. Zinc white is compatible with all pigments. Alkaline binder should also be avoided because of the risk of a Zinkatbildung there. Add oil to form zinc soaps may be limited. Zinc White has been widely used in aqueous techniques, such as in glue, watercolor and gouache paints. It was known in ancient times already Cadmea and Porerpholyx. The alchemists called it Nix alba (white snow) or Nihilum album (white thing). 1782 replaced Bernard Courtois in Dijon lead by zinc white, 1840 it was commercially processed into oil paints. Since 1834 there is zinc white as a water color. Zinc white was only slowly adopted by the artists as a substitute for white lead. There were regular arguments about its use. Because zinc white just looks colder, it was eventually used mainly for mixing with cool tones, while white lead was mixed with the warmer colors. The use of zinc white as the top color is today more and more back in favor of those of titanium white.
Photography
With zinc oxide coated paper was previously the direct method of electrophotography ( electrostatic copying process ) use. The so-called zinc - paper of the zinc - printing technology, however, contains no zinc.
Energy Storage
Researchers at the Swiss Paul Scherrer Institute in Villigen try to implement the solar energy into chemical energy. They focus to sun rays on a crucible. The light is incident at about 1200 ° C in zinc oxide then evaporates and is converted to metallic zinc, if it is ensured that the resulting zinc reoxidized immediately. Since this can be stored and transported, the energy of the sun can be so save and later use eg in zinc -air batteries directly as electrical energy or for the production of hydrogen. This is shown in simplified form, because of the zinc -air batteries discharged the Zn - ZnO is taken together with KOH.
Semiconductor
Zinc oxide as a semiconductor is used as a transparent conductive layer in the manufacture of blue light emitting diodes ( LED), liquid crystal displays (TFT), varistors (VDR) and thin-film solar cells. For this purpose, it is usually with aluminum doped ZnO: Al (AZO = aluminum zinc oxides). The doping increases the conductivity by several orders of magnitude. As semiconducting nanowires is zinc oxide in the measurement technology for its piezoelectric properties and UV light transparency application.
Medicine
As part of pharmaceutical zinc ointments, pastes, plasters ( bandaids ) and associations leads to a zinc oxide dehydration of the skin surface. This one uses for example in intertrigo, diaper rash and other weeping wounds. In Fußpilzen and other dermatomycoses zinc oxide supports healing.
Other Applications
Is also used in sunscreens and an additive in the vulcanization of rubber zinc oxide use. ( The tire wear is then released into the environment ). In addition, it comes as a phosphor in fluorescent lamps are used.
Self -activated zinc oxide ( ZnO: Zn) is used as Kathodolumineszenzleuchtstoff in magic eye-use and there shows blue-green luminescence.
Zinc oxide is added as Depleted Zinc Oxide ( DZO ) the cooling water of nuclear reactors ( BWRs ) in order to improve the corrosion behavior of coming into contact with the cooling water components.
Since 1888, zinc oxide is also used in deodorants, as it is easy is antibacterial.