Engineering Chemistry S Datta

326 ENGINEERING CHEMISTRY
The ores are found in the USA, Brazil and Australia. Zirconium also occurs in alluvial
sands of Kerala and Sri Lanka.
Extraction
(i) Zirconium is produced commercially by Kroll process. (See extraction of Titanium.)
(ii) Van Arkel-de Boer process. In this process, crude zirconium is heated with a little
iodine under vacuum at 200 °C when ZrI 4
volatilizes. A tungsten or Zirconium filament
is heated to 1300 °C in the same vessel. This filament decomposes ZrI 4
to pure
Zr which is deposited on the filament.
ZrI 4
= Zr + 2I 2
Properties
Zirconium is a lustrous, silvery metal with m.p. 1857 °C. Zirconium is a good conductor of
heat and electricity. The traces of impurities like O, N and C make the metal brittle.
Chemical: If heated to high temperatures, zirconium reacts directly with most non-metals
viz., O 2
, H 2
; when finely divided, the metal is pyrophoric. So, care should be taken during
machining and the production waste chips should be avoided. Despite this inherent reactivity,
the metal has got outstanding resistance to corrosion, which is due to the formation of a dense,
self-heating oxide film over the metal surface. With the exception of HF, other mineral acids
react at elevated temperatures with the metal. The most important oxidation state of the metal
is +4.
Uses
(i) Zirconium has a high corrosion resistance and it is sometimes preferable to stainless
steel in certain chemical plants.
(ii) It is used in a variety of alloy steels; a notable superconducting alloy is with niobium
which retains its superconductivity even in strong magnetic fields.
(iii) The small percentage of hafnium (Hf), which is almost always present with zirconium,
is not detrimental at all and may even improve the property of Zr. Zirconium’s major
use is as a cladding for uranium dioxide fuel rods in water-cooled nuclear reactors for
its low absorption of ‘Thermal’ neutrons. Here the presence of Hf is disadvantageous,
as Hf is a powerful absorber of ‘Thermal neutrons’. So Hf content of Zr is reduced to
less than 100 ppm.
EXERCISES
1. Define metal and mention some of its characteristics.
2. What do you mean by metallic bonds? Explain electrical conductivity of metal in the light of
metallic bonds.
3. What do you mean by minerals and gangue? Give relations between them.
4. Distinguish between ores and minerals.