C h a pt e r
21
Metals and Solid-State Materials
Chemistry 4th Edition
McMurry/Fay
Dr. Paul Charlesworth
Michigan Technological University
Occurrence of Metals
Prentice Hall ©2004
Chapter21
Occurrence of Metals
Prentice Hall ©2004
Chapter21
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Metallurgical Processes
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Metallurgy: the science and technology of
separating metals from their ores and of
compounding alloys.
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Gangue: Economically worthless material
including sand, clay, and other impurities.
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Alloys: Metallic solutions composed of two or
more elements.
Prentice Hall ©2004
Chapter21
Metallurgical Processes
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01
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Five principal steps in the process are:
1. Mining.
2. Preparation of the ore.
3. Production of the metal.
4. Purification of the metal.
5. Modification of metal’s properties.
Prentice Hall ©2004
Chapter21
Metallurgical Processes
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Preparation of the Ore: Ores are concentrated by
separating from the gangue. The most common
physical method
is flotation.
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Chapter21
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Metallurgical Processes
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A common chemical method of separation is the
Bayer Process: Al2O3 in bauxite is separated from
Fe2O3 impurities by treatment of the ore with hot
aqueous NaOH, which dissolves Al2O3.
Al2O3 (s) + 2 OH –(aq) + 3 H2O(l) → 2 Al(OH)4–( aq)
•
Al2O3 is recovered by filtration and treatment with a
weak acid (CO2 in air) to precipitate Al(OH) 3 and
heating to give Al2O3.
Prentice Hall ©2004
Chapter21
Metallurgical Processes
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•
After separation, the minerals are converted to a
form that is more easily reduced to metal. Usually,
these are metal oxides.
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Calcination: Elimination of volatile product.
PbCO3(s) → PbO(s) + CO2(g)
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Roasting: The heating of minerals in air.
2 ZnS(s) + 3 O2(g) → 2 ZnO(s) + 2 SO2(g)
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Chapter21
Metallurgical Processes
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Reduction: Chemical or electrolytic methods are
used, depending on the metal.
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Chapter21
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Metallurgical Processes
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Refining: Metals obtained from processing and
reducing ores usually require purification.
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Distillation, chemical purification, and
electrorefining are common methods.
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Mond Process is a chemical method for
purification of nickel using carbon monoxide.
Ni(s) + 4 CO(g) → Ni(CO)4(g)
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?H°= –160.8 kJ
Chapter21
Pyrometallurgy
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Iron and Steel Production:
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Iron is produced by carbon
monoxide reduction of iron
ore, in a blast furnace.
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Iron ore, coke, and
limestone are introduced in
the top.
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Molten iron is removed from
the bottom.
Prentice Hall ©2004
Chapter21
Pyrometallurgy
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?H = –221 kJ
Iron oxides are reduced by CO:
Fe2O3(s) + 4 CO(g) → 3 Fe(l) + 4 CO(g)
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01
Blast Furnace Reactions:
Oxygen reacts with carbon:
2 C(s) + O2(g) → 2 CO(g)
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Slide 10
?H = –15 kJ
Lime (CaO) reacts with acidic oxides to form slag:
CaO(s) + SiO2(s) → 2 CaSiO3(l)
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Chapter21
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Pyrometallurgy
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Iron from a blast furnace
is a brittle material called
cast iron.
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The most important
purification method is the
basic oxygen process.
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CaO, MnO, and O2 are
used to remove impurities.
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03
Chapter21
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Metallic Bonding
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Electron Sea Model:
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Metal crystal is viewed as a
three-dimensional array of
01
cations immersed in a sea
of delocalized electrons.
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This model explains
conductivity, ductility, and
malleability of metals.
Prentice Hall ©2004
Chapter21
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Metallic Bonding
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Band Theory: states that delocalized electrons
move freely through “bands” formed by overlapping
molecular orbitals.
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The band develops as a result of two atomic
orbitals leading to the formation of a bonding and
antibonding
orbital.
σ∗
Energy
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Prentice Hall ©2004
3s
Chapter21
σ
3s
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Metallic Bonding
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03
Orbitals become so closely spaced that they are described
as a band.
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Chapter21
Metallic Bonding
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Filled energy levels are
called the valence band.
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Unfilled energy levels are
the conduction band.
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In the presence of an
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electric potential, the
electrons are accelerated
toward the positive terminal,
creating a net current.
Prentice Hall ©2004
Chapter21
Metallic Bonding
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Conductors are materials that
have partially filled bands.
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Insulators are materials that
have completely filled bands.
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In magnesium the 3s and 3p
orbitals overlap, creating a
partially filled composite band.
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Transition metals have d-bands.
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Chapter21
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Semiconductors
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01
Semiconductors are materials that have an
electrical conductivity intermediate between that of
a metal and that of an insulator.
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Chapter21
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Semiconductors
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•
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Valence Band: is formed from bonding MOs.
Conduction Band: is formed from antibonding MOs.
Band Gap: is the energy separation between the valence
and conduction bands.
•Element
•C (diamond)
•Si
•Ge
•Sn (gray tin)
•Sn (white tin)
•Pb
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•Band Gap (kJ/mol)
•520
•107
•65
•8
•0
•0
•Type of Material
•Insulator
•Semiconductor
•Semiconductor
•Semiconductor
•Metal
•Metal
Chapter21
Semiconductors
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•
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n-type semiconductors: provide conduction by the
incorporation of donor impurities.
p-type semiconductors: provide conduction by the
incorporation of acceptor impurities.
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Chapter21
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Semiconductors
04
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Light Emitting Diodes: are semiconductor light
sources that can be made into lasers.
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The color (λ) of light, energy of light, and voltage
requirement are all related to their chemistry.
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The use of a blue rather than red laser for CD
players would quadruple its storage capacity. How
can we do this?
Prentice Hall ©2004
Chapter21
Semiconductors
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Size of band gap (Eg) = wavelength of light (λ).
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Size of band gap can be adjusted with:
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1. Distance between nuclei.
2. The Boltzmann factor.
3. Electronegativity difference between atoms.
4. Solid solution formation.
Prentice Hall ©2004
Chapter21
Semiconductors
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Solid Solutions:
Two elements with a
general formula A 1– x Zx .
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x varies in a range from
pure A to pure Z.
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x provides a means to
tune band gap
energies.
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Chapter21
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Superconductors
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Superconductors are
materials that lose all electrical
resistance below a
characteristic temperature, the
superconducting transition
temperature.
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More than 6000 are known.
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The current highest value of Tc
is about 133 K.
Prentice Hall ©2004
Chapter21
Superconductors
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YBa2Cu 3O7 has layers of Y
(yellow) and Ba (blue) in
square pyramids of CuO5
(red) and chains of square
planar CuO4 groups (green).
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YBa2Cu 3O7 is a 1-2-3
compound, named for its
structural ratio of
1Y:2Ba:3Cu.
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Chapter21
Superconductors
Prentice Hall ©2004
Chapter21
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Superconductors
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YBa2Cu 3O7 pellet at 77 K and
computer representation of
crystal structure.
Prentice Hall ©2004
Chapter21
Ceramics
01
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Ceramics are inorganic,
nonmetallic crystals such as
quartz, nonmolecular solids,
and amorphous materials
such as glasses.
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Advanced Ceramics are
materials with high-tech
engineering, electronic, and
biomedical applications.
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Chapter21
Ceramics
Prentice Hall ©2004
Slide 28
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Chapter21
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Ceramics
03
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Ceramics are usually formed from fine powders,
which are combined with organic binder, shaped,
compacted, and sintered at 1300–2000°C.
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Sintering is the welding of powder particles just
below the compound’s melting point.
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Sol–gel method is the synthesis of metal oxide
powers from metal alkoxides .
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Chapter21
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