Lecture 8
Other significant alloys
Subjects of interest
• Objectives / Introduction
• Lead and its alloys
• Tin and its alloys
• Chromium and its alloys
• Cadmium and its alloys
• Antimony and its alloys
• Bismuth and its alloys
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Objectives
• This chapter provides basic information of other
significant non-ferrous alloys such as alloys of lead,
tin, chromium, cadmium, antimony, bismuth.
• This includes its source, nature, properties which
are related to its applications.
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Introduction
• Apart from alloys of Al, Mg, Cu, Zn, Ti,
Ni, there are a variety of other alloys,
which have been used for other
applications with however in a smaller
extent but still important.
• There are for example: Pb, Sn, Bi, Sb, Cd
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Lead and its alloys - Applications
• Lead sheets are used in x-ray and gamma-ray
protection, building construction of roofing and
flashing, shower pan, flooring, vibration damping
and soundproofing.
Lead sheet
• Lead pipes are made from pure lead
metal (99.97% min.) or lead alloys
- Readily fabricated by extrusion.
- Excellent corrosion resistance applications in chemical industry.
Lead pipe
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Lead- Resources
• Lead (Pb) is found in many countries but mainly produced from
USA, Australia, Mexico, Canada and Germany.
• In Thailand, found in Kanchanaburi (cerussite).
• Normally found in the forms below (or the combination of both)
1) Lead sulphide (PbS) or called Galena or Galenite.
2) Lead carbonate (PbCO3) called Cerussite.
• Also found in the form of anglesite (PbSO4) and pyromorphite
(2Pb3P2O5.PbCl2) but not commercially significant.
• Normally contain Ag, Zn, Ni, Co as impurities.
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Pyromorphite
Galenite
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Cerussite
Anglesite
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Lead – Extraction of lead
Pyrometallurgical process
Ore (PbS)
• Concentrated Pb ore is produced
through flotation process and it is then
roasted at T ~450-700oC with air blow
to reduce sulphur.
Concentration
2 PbS + 72 O2 → PbO + PbSO4 + SO2
Flotation
• Other reactions also occur due to the
existence of Zn.
Reduce
sulphur
Roasting
At T ~ 450-700oC
with air blowing
Blast furnace or
reverberatory
Lead
Mixed with coke
T ~ 900oC
2 ZnS + 72 O2 → ZnO + ZnSO4 + SO2
FeS + 32 O2 → FeO + SO2
• The obtained Pb ore (with decreased amount of
sulphur) is then reduced in the blast furnace or
reverberatory by mixing with coke or iron.
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Lead – Reduction of lead in blast furnace
• Reduction of lead is carried out in
a blast furnace at T ~ 900oC.
• The obtained ore is mixed with flux
(limestone) and coke (~10%) which
will reduce PbO or PbS into lead.
PbO + C → Pb + CO
PbO + CO → Pb + CO2
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Charge hopper
Exhaust off-take to
afterburne
Charge
Cool water
Average level
of charge
Charge hole
Shalf
PbS + Fe → Pb + FeS
• During reduction, matte or speiss
(mixtures of sulphide of Fe and Cu)
form on top of the molten lead.
• The molten lead forms at the bottom
of the furnace is then drained out.
Water jacket
Hot water
Cold water
Diameter at Tuyeres
68 – 120 cm
Tuyere
Hot water
Slag layer
Lead spout
Dam
Crucible
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Working height of
charge 2.4-3.0 m
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Lead blast furnace
Slag spout
Load layer
Drain tap
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Lead – Refining of lead
• As, Bi, Sb, Sn, Cu are typical impurities in lead high
hardness but low toughness.
• Removal of Sn, Sb, As is called softening by heating at
500oC. They will form oxides (Dross) which float on the top of
lead due to their lower densities. easily remove.
• Cu is removed by mixing molten lead with PbS to give Cu2S
and Pb.
PbS + 2Cu → Cu 2 S + Pb
• Bi is removed via electrolysis process using PbSiF6 and H2SiF6 acid as
electrolyte, giving pure lead at cathode and the remained Bi at anode.
• Desilvering is carried out using two methods : Pattinson and Parkes.
Pattinson: High purity lead is extracted at the eutectic temperature (304oC).
Parkes: Stirring Zn rod in molten lead to dissolve Ag on its surface. Let it
cool down to form crust and then remove.
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Lead - Physical properties and
application
Crystal structure
Atomic number
Atomic weight
Density (g.cm-3)
Melting point (oC)
Boiling point (oC)
Cubic closed packed
82
63.546
11.34
327.35
1740.0
• Lead ingots of 99-98 % purity can be
produced with Sb, Sn, As, Fe, Bi, Cu
as impurities.
CCP
82
Pb
Lead
207.2
• High density.
• Good corrosion resistance
• Low strength but high ductility.
• Lubricating properties.
• Used in batteries, chemical
applications.
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Lead screws
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Lead alloys - Classification
Lead alloys can be classified as follows:
1) Calcium-lead alloys
2) Antimony-selenium lead alloys
3) Antimony-lead alloys
4) Copper lead alloys
5) Tin-lead alloys
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Classification - Antimony lead alloys
• Antimony Sb is partially soluble in lead and give a eutectic
reaction at 250oC at 11.2% Sb.
L ↔α +β
• Hypo-eutectic structure
(<11.2%Sb) consists of α phase and
eutectic phase of α+β.
Sb-Pb phase diagram
6.5% Sb (Hypo)
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• Hyper-eutectic structure
(>11.2%Sb) consists of β and eutectic
phases.
• Sb addition gives higher eutectic
structure more strength / hardness.
• Used in batteries and cable wire coating.
11.5% Sb (eutectic)
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12.25% Sb (Hyper)
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Classification - Tin-lead alloys
• Tin Sn can form solid solution (α phase upto 19.2% Sn) with
lead and give a eutectic reaction at 183oC at 61.9% Sn.
• Hypo-eutectic structure
(<61.9%Sn) consists of α phase and
eutectic phase of α+β.
• Hyper-eutectic structure
(>61.9%Sn) consists of β and eutectic
phases.
• Sn addition also gives strength and
hardness and lower Tm , fluidity .
Sn-Pb phase diagram
70% Sn
• Used as soldering materials.
Eutectic
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60% Sn
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50% Sn
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Tin alloys - Introduction
• Tin is found in the form of oxide (SnO2) as vein tin or
stream tin. Its colour is in white and grey.
• Found in Malaysia, Indonesia, (Thailand), Myanmar, China,
Australia. Note: Most resources are almost used up.
• Easily extracted because it is already in its oxide form.
• Used for applications such as in soldering metals.
Tin oxide
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Tin alloys - Extraction
Ore(SnO2)
Concentration
Mixing with
coke and flux
• The ore is first concentrated and then mix with
coke and flux (CaCO3) in the blast furnace
(reverberatory) at T~1350oC.
C + O2 → CO2
CO2 + C → 2CO
SnO2 + 2CO → Sn + 2CO2
SnO2 + C → Sn + CO2
o
Blast furnace or T ~ 1350 C
oC to give CaO,
•
CaCO
will
decompose
at
1350
3
reverberatory
Tin
which will catch high melting point oxides (SiO2 ,
FeO) to form slag (low Tm).
• Molten tin at the bottom of the furnace is
drained out for further refining while slag on its
top surface is skimmed out Sn will be
separated again.
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Tin alloys - Refining
Fire refining
• For tin with Fe <1%, fire refining
is carried out at tin’s melting point
232oC to give pure tin at the
bottom of the furnace.
• Fe will from FeSn2 compound
and can be separated from
molten tin (<0.01%Fe).
Electrolytic refining
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• For a higher purity, poling
process (using fresh lump of
wood stirring in boiling tin)
allows impurities to float to the
surface and form oxides (slag).
• If the impurity is Pb, flux
(SnCl2) is added at T~245oC to
form PbCl2 (dross), which also
floats to the surface. Dross will
be skimmed out later.
Give high purity of tin but expensive.
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Tin - Physical properties
Crystal structure
Atomic number
Atomic weight
Density (g.cm-3)
Melting point (oC)
FC Tetragonal (white tin)
Cubic (grey tin)
50
118.7
7.298 (white tin)
5.765 (grey tin)
231.9oC
50
Sn
Tin
118.7
• High corrosion resistance.
• Low strength but high ductility not suitable for
structural materials.
• Lubricating properties.
• Transformation from white to
grey tin occurs at T = 13.2oC,
giving a change in density from
7.3 to 5.76 g/cm-3. tin pest.
Tin pest
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Tin - Applications
Electrical
applications
Soldering
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Tin as jewellery
Steel can coated with tin.
Tin foils for capacitors
• Tin is used as coating for structural steels for corrosion protection.
• Used as an alloying element.
• Soldering materials and in electrical applications.
• Tin or tin foil for food containers and wrapping.
• Tin alloys are also used as vases, candle stands, jewellery.
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Tin alloys – Classification
• Tin alloys are used as soldering materials.
- 30-50% Pb – Sn alloy
- 5% Sb – Sn alloy
- 5% Ag – Sn alloy
• Tin alloys (pewter) are used as vases, candle stands, etc.
- 7% Sb – 2% Cu alloys (40% ductility, 9.5 HBN).
• Tin alloys are used as bearing called ‘Babbit’
- 10-15% Sb – 3-4% Cu – 60-90% Sn alloys.
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Cadmium
Crystal structure
Atomic weight
Density (g.cm-3)
Melting point (oC)
Boiling point (oC)
HCP
48
HCP
112.41
8.65
320oC
769oC
Cd
Cadmium
112.41
• Cadmium has a bluish white colour and appears
in a form of CdS.
• Normally obtained from zinc extraction process.
• Hardness Sn<Cd<Zn. Good toughness, readily
rolled into plates or wires at RT.
• Used in automatic fire extinguishers, electrical
fuses, safety plugs.
• Alloyed with Sn to produce soldering materials,
bearing.
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Batteries
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Antimony – Physical properties and
applications
Crystal structure
Atomic number
Atomic weight
Density (g.cm-3)
Melting point (oC)
Boiling point (oC)
Trigonal
51
121.76
6.62
630oC
1140oC
51
Sb
Antimony
121.76
• Antimony has a silvery white colour and found as stibnite Sb2S3.
• Hard and brittle and cannot be deformed at RT.
• React with oxygen at high temperature, giving Sb2O3 (white powder).
• Used as alloying element in Sn and Pb alloys, providing better
fluidity and hardness.
• Applications: storage battery plates, soldering materials, shrapnel
bullets and bearing or babbit.
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Antimony - Extraction
Ore(Sb2S3)
Liquation
Roasting
Blast furnace
T ~ 500-600oC
T ~ 500oC
Charcoal
Sb
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• Antimony ore is concentrated by
liquation process (heating at 500-600oC)
to give low Tm antimony (85-90%)
separating from the ore.
• Roasting at 500oC to convert to oxide
Sb2O4, which is then reduced to Sb metal
by using charcoal with flux (Na2CO3) in
the blast furnace.
• S, Pb and Fe appear as impurities in the
obtained Sn metal. good enough for
alloying.
• Higher purity is achieved by electrolytic
process.
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Bismuth – Physical properties and
applications
Crystal structure
Atomic number
Atomic weight
Density (g.cm-3)
Melting point (oC)
Boiling point (oC)
Monoclinic
83
209
9.80
271oC
1436oC
83
Bi
Bismuth
209
• Bismuth is found as native Bismuth in nature or
Bismuth ocher or Bismite (Bi2O3).
• Low melting point used as alloying elements to
lower Tm, soldering materials and thermoelectric
applications -fuses.
• Provide thermal expansion during solidification.
• Hard and brittle similar to Sb.
Fuses
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Bismuth - Extraction
Ore(Bi2O3)
Reduction
Liquation
Bi
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• Bismuth ore (Bi2O3) is reduced using
charcoal and CaCO3 with fluoride and
Na2CO3 as flux.
• Roasting should be applied if the ore is a
sulphur type.
• Higher purity Bi is produced by liquation
to give molten Bi at the bottom of the
furnace.
• For higher purity, bismuth is dissolved in
nitric acid to give Bi(NO3)3 and then
precipitate as Bi(OH)2NO3. washed and
heated to give pure Bi oxide. reduced to
give Bi metal.
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References
• , กกก, 2536, ก
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", ISBN
974-582-155-1.
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