Download Metals & Metallurgy

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Metals like bronze (an alloy of Cu and Zn) and
Iron have played a big role in civilization hence the Bronze Age and Iron Age.
The abundance of the metals in the Earth's
surface varies greatly.
Only metals that occur in concentrated
deposits - called ores - are economically
valuable.
About 23,000 kg of materials are extracted
from the surface and processed per person in
our country each year.
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Vanadium is a rare element that is a
contaminant in crude oil.
Oil was produced from the decomposition of
once living life forms.
Since crude oil is not found near any
naturally occurring deposits of vanadium,
then how did it find its way into this
important resource?
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Most metals are found in solid inorganic
compounds known as minerals.
Although 75% on the elements are metals,
they make up only 25% of the Earth’s crust.
Distribution of elements in the Earth’s crust.
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Most minerals are oxides, sulfides, or
carbonates.
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Metallurgy is the
science and
technology of
extracting metals
from their ores for
usage.
It usually involves up to five steps:
1. Mining of the ore.
2. Concentrating the ore to remove the gangue.
3. Reducing the ore to obtain the free metal.
4. Refining or purifying the metal.
5. Mixing the metal with other elements to modify
properties.
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In many mining
applications, the ore is
crushed and then put
into an industrial
cyclone.
A stream of air moves
upward through the
crushed ore to remove
the lighter particles of
the gangue.
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In some cases, a
detergent solution
that attaches to the
mineral is added to
achieve separation.
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This is a process that utilizes high
temperatures. Some examples are:
Calcination - heating of a carbonate to
eliminate carbon dioxide.
 PbCO3  PbO + CO2
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Roasting is a thermal treatment that leads to
reduction of the free metal.
 2 ZnS + 3 O2  2 ZnO + 2 SO2
 ZnO + C Zn + CO
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Reduction using H2 or CO often produces the
free metal.
 PbO + CO  Pb + CO2
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Uses an aqueous solution to extract the
metal from the ore.
Gold was once extracted by dissolving the
metal in sodium cyanide.
4Au(s)+8CN-(aq)+O2(g)+2H2O(l) 4Au(CN)2-(aq)+4OH-(aq)
2 Au(CN)2-(aq) + Zn(s)  Zn(CN)4-(aq) + 2Au(s)
Streams and rivers were often contaminated
by cyanide.
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This uses the electrolysis
discussed in the
electrochemistry chapter.
Metals high on the activity
series (most reactive) can
only be produced
commercially via molten
salt electrolysis.
Metals lower on the
activity series like Cu can
be purified using aqueous
electrolysis.
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4th most abundant metal in Earth’s crust.
Mineral sources are rutile (TiO2) and ilmenite
(FeTiO3).
Ore is first converted to TiCl4 before
reduction to pure metal.
FeTiO3(s) + 3Cl2(g) + 3C(s) → 3CO(g) + FeCl2(s) + TiCl4(g)
TiCl4(g) + 2Mg(s) → 2MgCl2(l) + Ti(s)
Titanium metal is used in many parts found
on planes due to its lighter weight and
superior strength.
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The main ore source is
chromite (FeCr2O4) and none
is found in the US.
Metal is produced by
reduction using Al metal.
3FeCr2O4(s) + 8Al(s) →
4Al2O3(s) + 6Cr(s) + 3Fe(s)
Chromium metal is an
additive used in making
different types of steel –
mainly known as stainless
steel.
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Ore sources include
pyrolusite (MnO2) and
hausmannite (Mn3O4).
Produced by reaction of ore
with Al metal like Chromium.
Manganese is added to steel
alloys to make it deform
easier at high temperatures.
Steel alloys containing 12%
Mn are used for military
armor and bulldozer blades.
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Only ore sources found in
Africa.
An important additive to
make high-strength steel
alloys.
Cobalt is also found in
Vitamin B12, so it is an
important trace element in
the human body.
Cobalt is also added to glass
to produce a blue color.
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Most nickel metal comes
from meteorite impact in
Ontario, Canada
Nickel is fairly unreactive
and used where resistance
to corrosion is critical.
Monel alloy contains 72%
Ni, 25% Cu, and 3% Fe.
Monel is used in marine
applications, musical
instruments, and by the
chemical industry.
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High abundance and
concentration = useful
industrially
Easy to recycle
Second best electrical
conductor – used in
electrical wiring and
devices
High heat conductivity –
used in heat exchangers
Used in water piping
because of its resistance
to corrosion
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Copper is a high strength metal so it is often
used as an alloy with another metal.
Bronze = Cu + Sn
Brass = Cu + Zn
Amounts of each metal can vary to produce
different features.
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Minerals are roasted in air to form
oxides, then reduced with carbon
Used in alloys with Cu (brass) and
Cu and Ni (German brass)
Resists corrosion because it forms
an adhering oxide coat
Galvanizing is plating Zn onto
other metals to protect them from
corrosion
◦ both coating and sacrificial anode
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Zinc compounds used in paints
for metals
◦ if scratched, becomes sacrificial anode
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Zinc phosphate used to coat steel
so that it may be painted
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One of the most widely produced metals is Fe.
Fe is produced from both hematite and
magnetite ore deposits.
Reduction is achieved via pyrometallurgical
techniques in a blast furnace.
The main ingredients are the iron ore, coke,
and limestone.
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Coke is essentially Carbon and serves as BOTH
the fuel and the source of the reducing gases
CO and H2.
 2 C + O2  2 CO
 C + H2O  CO + H2
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Limestone (CaCO3) produces CaO, which
reacts with silicates (sand) to produce the
waste product called "slag".
 CaO + SiO2  CaSiO3
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In the upper part of the furnace, the iron
oxides are reduced by the CO and H2 gases.
 Fe3O4 + 4 CO  3 Fe + 4 CO2
 Fe3O4 + 4 H2  3 Fe + 4 H2O
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Molten iron collects at the base of the furnace
with a layer of slag on top.
The slag and the molten iron are tapped to
drain off. The iron is then transported to
convert into steel.
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The molten iron
contains many
impurities like Mn, P,
S, and C.
This makes it
unusable in present
form.
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The raw iron is hit with
a “blast” of O2 to
remove the impurities.
Then, the purified raw
iron is converted to
steel, an alloy of iron.
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There are 1000's of different types of steel
that are produced. Each varies in
composition to produce the desired
properties.
Carbon steel contains up to 1.5% C.
Alloy steel contains C plus other elements
like Cr, Co, Mn, Mo, S, B, and other trace
elements.
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Production of small quantities of iron can be
achieved by reacting iron oxide with
aluminum powder.
This is called the thermite reaction.
Fe2O3 + 2 Al  2 Fe + Al2O3
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Aluminum production involves the use of
hydrometallurgy – a process that involves
selectively dissolving the metal ion in water
– and electrometallurgy – a process that
involves using electrical current to reduce
the metal ores.
In the Bayer process, bauxite is first
dissolved in NaOH producing Al(OH)4-.
Other metal hydroxides present in bauxite
are not soluble.
Al2O3 + 2 OH- + 2 H2O  2 Al(OH)4-
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The Al(OH)4- is then converted to Al2O3 via
calcination.
H2CO3 + 2 Al(OH)4-  Al2O3 + CO3-2 + 5
H2O
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The Al2O3 precipitates from the solution,
whereas any silicates remain in solution.
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Melting point of Al2O3 is 2054oC.
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The Al2O3 is then dissolved in molten
cryolite, Na3AlF6, which has a lower melting
point , 1012o C.
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To the molten salt are inserted graphite
electrodes, which serve as the anodes. These are
consumed in the electrolytic cell.
The voltage applied is about 4.5V and the current
used is quite large. This electrolytic cell is called
the Hall process. Al+3(l) + 3e-  Al(l)
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The rare earth metals are composed of
seventeen elements – Sc, Y, and the
lanthanides (#57 - #71)
Despite their name, they are relatively
plentiful in the Earth’s crust.
The lanthanides can have larger numbers of
unpaired electrons giving them powerful
magnetic properties.
Used in lasers, electronics, and hightemperature superconductors
Element
Uses
Sc
Light Al-Sc alloy for aerospace parts, additive in Hg vapor lamps
Y
Y-Ba-Cu-O superconductors
Ce
Oxidizing agent, yellow color in glass and ceramics
Nd
Strongest magnets known to man
Gd
MRI contrast agent
Er
Alloy with vanadium steel, dental lasers, fiber optic applications
Tm
Portable x-ray machines
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Bonding in metals is very unique.
The valence electrons in metals are held
loosely and are free to move about - this is
often referred to as the "sea of electrons".
The conductivity of metals is due to this
concept of loosely held electrons.
This model does not explain all properties of
metals - for example, the highest melting
points are found for group 6B.
•Most of the time, the electrons move past the atoms freely.
•Occasionally, though, the electrons will bump into a nuclei
causing friction, which generates heat.
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When atomic orbitals on each metal atom
overlap, they produce a band of Molecular
Orbitals.
The energy separations of these M.O.'s are so
close that they form a band of M.O.'s.
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Because the bands are so close, it is easy to
promote electrons to a higher energy level.
With M.O.'s, half of the orbitals are bonding
and half are antibonding. Thus, with halffilled d subshells, the bonding M.O.'s are filled.
After that, the electrons begin to fill
antibonding orbitals which weaken the
bonding and hence a lower melting point.
Silicon and other semi-conductors have an
energy gap between the occupied M.O.'s and
the unoccupied M.O's.