The most significant property of transparent zinc oxide is again the absorption of UV radiation. The main application of zinc oxide is in sunscreens. The usual industrial manufacturing process is either direct combustion of high-purity zinc metal in a plasma with oxygen [5.196] according to the reaction:
2 Zn + O2 ^ 2 ZnO
resulting in zinc oxide powder with a primary particle size distribution of ca. 20 to 30 nm, or hydrolysis of very dilute organozinc compounds [5.197] according to the reaction:
Zn(OR)2 + H2O ^ ZnO + 2 ROH
This process produces primary particles of ca. 15 nm, but it is time-consuming and expensive.
5.5