z i n c 鋅

Zinc 鋅

Basic info.◆Symbol: Zn◇Atomic no.: 30◆Has 5 stable isotopes

(64, 66, 67, 68, 70 Zn)◇24th most abundant element in Earth’s crust◆ Large deposits in Australia, Canada, the US

(with largest reserve in Iran)◇ The Earth has been estimated to have 46

years supply of Zn

Discovery◆ Who: Andreas Marggraf◇ Nationality: German◆ When to discover: 1764◇ How: heat a mixture of calamine and carbon in a closed vessel isolate zinc

Physical property◆ Lustrous solid at room temp.◇ Hard/Brittle at most temp.◆ Malleable between 100-150oC◇ Density: 7.14g/cm3

◆ Boiling point: 907oC◇ Melting point: 419.53oC◆ Crystal structure: hexagonal◇ Fair conductor of electricity

Production◆ ~70% Zn comes from mining

(most from sphalerite, ZnS deposits)◇ ~30% Zn comes from recycling of secondary Zn◆ Production process:1) Ore grinding2) Froth flotation3) Roasting4) a) pyrometallurgy

b) electrowinning5) Electrolysis of molten ore

Application: anti-corrosion

Cathodic Cathodic protectionprotection

◆ Zn: an efficient sacrificial anode in cathodic protection◇ Cathode of a car battery is always connected to the car body, supplying electrons to iron body

Sacrificial Sacrificial protectionprotection

◆ Galvanization: Zn coating on Fe ◇ Zn is more reactive than Fe◆ Zn releases electron to Fe◇ Zn is corroded first to save Fe evenwhen the Zn coating is scratched

Application: alloy

BrassBrass

◆ Cu + Zn◇ low melting point: 900-940oC◆ more ductile / stronger than Cu alone◇ has superior corrosion resistance

Cadmium Cadmium zinc zinc

telluridetelluride

◆ Cadmium telluride + zinc telluride◇ Direct bandgap semiconductor

Application: use of other compounds

Zinc oxideZinc oxide ◆ used as a white pigment in paints◇ protect its polymers from UV, thus often used in photocopying products

Zinc chlorideZinc chloride◆ deodorant ◇ often added to lumber as a fire retardant as a wood preservative

Zinc sulphideZinc sulphide◆ used in luminescent pigments (eg in X-ray / television screens)

Zinc lactateZinc lactate◇ used in toothpaste in order to prevent halitosis

Biological importance

◆ Zn: essential trace element for human

◇ Red meat : rich in Zn in general

◆ Some plants (eg nuts) contain Zn

◇ Highest conc. of Zn in body: in part of the eye / prostate

◆ Zn: flexible coordinate geometry proteins use Zn to shift conformations perform biological reactions

◇ Zn deficiency growth retardation / diarrhea, etc.

◆ Zn overdose suppress Cu / Fe absorption ataxia / lethargy

The endThe end

Biological importance