ZINC OXIDE

Pure ZnO is a white powder, but in nature it occurs as the rare mineral zincite, which usually contains manganese and other impurities that confer a yellow to red color.[8] Crystalline zinc oxide is thermochromic, changing from white to yellow when heated in air and reverting to white on cooling.[9] This color change is caused by a small loss of oxygen to the environment at high temperatures to form the non-stoichiometric Zn1+xO, where at 800 °C, x = 0.00007.[9] Zinc oxide is an amphoteric oxide. It is nearly insoluble in water, but it will dissolve in most acids, such as hydrochloric acid:[10] ZnO + 2 HCl → ZnCl2 + H2O Solid zinc oxide will also dissolve in alkalis to give soluble zincates: ZnO + 2 NaOH + H2O → Na2[Zn(OH)4] ZnO reacts slowly with fatty acids in oils to produce the corresponding carboxylates, such as oleate or stearate. ZnO forms cement-like products when mixed with a strong aqueous solution of zinc chloride and these are best described as zinc hydroxy chlorides.[11] This cement was used in dentistry.[12] Hopeite ZnO also forms cement-like material when treated with phosphoric acid; related materials are used in dentistry.[12] A major component of zinc phosphate cement produced by this reaction is hopeite, Zn3(PO4)2·4H2O.[13] ZnO decomposes into zinc vapor and oxygen at around 1975 °C with a standard oxygen pressure. In a carbothermic reaction, heating with carbon converts the oxide into zinc vapor at a much lower temperature (around 950 °C).[14] ZnO + C → Zn(Vapor) + CO Zinc oxide can react violently with aluminium and magnesium powders, with chlorinated rubber and linseed oil on heating causing fire and explosion hazard.[15][16] It reacts with hydrogen sulfide to give zinc sulfide. This reaction is used commercially.[citation needed] ZnO + H2S → ZnS + H2O
Rubber/ Ceramic/ Medicine/ Feed additive/ Pigment/ Coating