Zinc, also known by the symbol Zn, is a lustrous bluish-white metal and the first member of group 12 in the periodic table. Zinc is a naturally abundant metal and stands at 24th place in the list of most abundant elements in the Earth’s crust. This element has an atomic number of 30 and an atomic mass of 65.39 g/mol. Zinc, in its metallic state, has a diamond-type face-centred cubic structure, or α-Zn, at low temperatures that transforms to β-Zn with hexagonal close-packed structure at 13oC. This metal is quite brittle at room temperature; however, it becomes malleable when heated up to ~110 to 150 oC.
The melting and boiling points of zinc are remarkably low, 419 and 907 oC respectively. Such low boiling point is the basis of zinc production via pyrometallurgical processes.
In terms of electrochemical properties, zinc is more negative than iron. This metal has an excellent resistance towards corrosion at different media and this is the main reason for its extensive use in the iron and steel production industries as a protective coating layer. Zinc has a long history of application as a protective coating and the hot-dip galvanizing of steel products by zinc has been used as a common technique for more than 150 years. Upon contact with iron, zinc forms several passivating layers of basic zinc carbonates in atmospheric conditions, which can protect the steel surface from harsh corrosive environments for decades.
Some of the physical and mechanical properties of metallic zinc are listed below:
|Transformation temperature of α-Zn ↔ β-Zn||10 oC|
|Heat of transformation||1966 J.mol-1|
|Density at room temperature||7.14 g.cm-3|
|Thermal conductivity at 0 oC||0.63 W.cm-1.K-1|
|Thermal conductivity at room temperature||116 W.m-1.K-1|
|Electrical resistivity at room temperature||59.0×10-9 Ω.m|
|Melting point||419.53 oC|
|Boiling point||907 oC|
|Density of liquid at melting point||6.57 g.cm-3|
|Vapour pressure at 477 oC||100 Pa|
|Heat of fusion||4.32 kJ.mol-1|
|Oxidation state||+1, +2|
|Atomic radius||134 pm|
|Temperature of superconductivity||3.70 K|
|Young’s modulus||108 GPa|
|Brinell hardness||327- 412 MPa|