metallurgy : types,blah,blah,blah,blah,blah

metallaurgy

2. . Metallurgy (i) Occurrence of metals in nature.
• Mineral and ore - meaning only.
• Common ores of aluminium.
(ii) Extraction of Aluminium. (a) Chemical method for
purifying bauxite by using NaOH – Baeyer’s Process.
(b) Electrolytic extraction – Hall Heroult’s process:
Structure of electrolytic cell - the various components
as part of the electrolyte, electrodes and electrode
reactions.
Description of the changes occurring, purpose of the
substances used and the main reactions with their
equations

10. EXTRACTION OF METALS
DRESSING OF THE
ORE OR
CONCENTRATION
OF THE ORE
CONVERSION OF
CONCENTRATED
ORE TO ITS OXIDE
REDUCTION OF
METALLIC OXIDE
TO ITS METALS
ELECTROREFINING

17. HALL HEROULT’S PROCESS
1
st
step :- Dissociation of ions :-
Alumina :- 2Al
20
3 4Al
3+
+ 6O
2-
Cryolite :- Na
3AlF
6 3Na
1+
+ Al
3+
+ 6F
1-
Fluorspar :- CaF
6 Ca
2+
+ 6F
1-
2
nd
step :- cathode reaction :- 4Al
3+
+ 12e- 4Al
Anode reaction :- 6O
2-
- 12e- 6[O] 3O
2
3
rd
step :- product at cathode :- Pure Aluminium metal
product at anode :- oxygen gas (O2) [ CO & CO2]

18. REDUCTION OF METALLIC OXIDE TO ITS METAL HALL HEROULT’S
PROCESS

19. ❖FUSED ALUMINA - reduced to aluminium its highly stable oxide and aluminium has strong affinity for oxygen
so fused alumina can be reduced to aluminium electrolytically and not by reducing agent.
❖Difficulties faced during reduction of alumina.
❖Fused alumina is non –electrolyte and has high melting point of 2050
o
C.
I.At high temperatures . – a large amount of electrical energy is required to liberate Al.the liberated Al with
m.p 660
o
C may tend to volatize out.so the fusion temp of electrolyte mixture has to be lowered.
III
. Fused cryolite Na
3Al F
6and Fluorspar CaF
2are added to the electrolytic mixture.
a)addition of cryolite in higher ratio and fluorspar – lowers the fusion point of the mixture from 2050
o
C
to 950
o
C.
b)Enhances the mobility of the fused mixture by acting as solvent for electrolyte mixture.
c)Only cryolite –enhances the conductivity of the mixture as pure alumina is non conductor of
electricity .
iv. A layer of powered coke is sprinkled over the electrolytic mixture – to prevent the burning of carbon
electrodes in air and also minimizes or prevents –heat loss by radiation.
v. Graphite rods or carbon rods are continuously replaced during electrolysis--- as oxygen is evolved at
the anode and gets oxidized to carbon monoxide. So it is consumed and renewed periodically after
certain period of usage.
vi. Electrolytic reduction is a continuous process. As by the process of reduction Al obtained is 99.5% and
can be further purified to obtain 99.9%of Al by Hoope’s process.
❖IMPORTANT FACTORS TO BE REMEMBERED IN THE HALL HEROULT’S PROCESS

24. ▪ALLOY – It’s substance prepared by adding other
metals. Or non-metals to a baser metal in appropriate
proportions to obtain certain desirable properties . Its
usually made by –melting the component together and
solidifying the mixture.
▪Its components must be miscible in liquid state and
not on solidification.
▪It has properties intermediate between the metals.
▪Ex . Amalgam – an alloy in which baser metal is
mercury
▪Na/Hg , Zn/Hg, Ag/Hg , Au /Hg .

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