What is ZnO2 in chemistry

zinc oxide ZnO
      





White dust

Occurrence  
Zincite (red zinc ore)
molar mass 81.408 g / mol
   
  


AGW 2 mg / m3 A (TRGS 900)
density 5.6 g / cm3   
Melting point + 1974 ° C
Water solubility 
insoluble
Pictograms    
GHS 09
Danger
Hazard classes + category  
   
Hazardous to the aquatic environment chronic / acute 1
HP rates (see note)   
H 410 P 273,391
disposal G 4
print a labelGerman nameEnglish name
CAS 1314-13-2zinc oxideZinc oxide
   
  
properties 
  
The white, loose powder sublimates at around 1800 ° C, and under pressure it melts at 1974 ° C. The zinc oxide turns yellow when heated, and turns white again after cooling. This phenomenon is called thermochromism. The production of zinc oxide by burning zinc vapor produces an intense, green luminescence that has a brief afterglow effect after cooling down in the dark. The red color in red zinc ore is due to traces of iron or manganese atoms. Zinc oxide only dissolves in traces in water, but acids and alkalis break it down. When welding zinc sheets, zinc oxide smoke is formed, which irritates the airways and causes a fever. An increased concentration of this smoke can also occur in foundries.
   

 

Thermochromism when heating zinc oxide
   
  
Manufacturing 
  
When zinc was strongly heated in a crucible, the alchemists obtained a white wool. This so-called "Lana philosophica" arises on the edge of the crucible when you poke around and the zinc burns. In the laboratory, zinc oxide can be produced by precipitation from zinc salt solutions. The resulting zinc carbonate or zinc hydroxide can be converted into zinc oxide by annealing. In the industrial production according to the American process, the zinc ores are roasted, reduced to zinc with coal and then oxidized again immediately. This gives a relatively impure zinc oxide. In the French process, pure zinc vapor is burned with air. This creates the zinc white known as a painter's pigment:
   
2 Zn + O2  2 ZnO
   
If pure zinc is not used, then the zinc white is contaminated with toxic lead compounds. There are “lead-free” types on the market, which are preferable if you want to use it as a pigment.
   
  
use 
  
In contrast to the poisonous white lead, the zinc white as a painter's pigment is far from being as poisonous, but its water-polluting effect must be taken into account. It is very lightfast and does not decompose with hydrogen sulfide. In paints, it absorbs UV light, so it significantly prevents the aging process in paintwork. As a white pigment, it is now largely replaced by the even better opaque titanium white. In the rubber industry it is used as an activator for vulcanization, for example with rubber. As an additive in glass production, it increases chemical stability. It is used to make zinc soaps. These are used, for example, to dry paints and varnishes or to stabilize PVC. Zinc oxide is used in medicinal zinc ointments or plasters because of its drying and antiseptic properties.