1. OCCURRENCE OF METALS 1) Elemental Form e.g. Ag, Au, Pt – noble metals.
2) Aluminosilicates and Silicates
Metal + Al, Si, O
e.g. Beryl = Be3Al2Si6O18
Hard to extract metals.
3) Nonsilicate Minerals
Oxides – Al2O3, TiO2, Fe2O3
Sulfides – PbS, ZnS, CuFeS2
Carbonates – CaCO3

2. Metallurgy the process of obtaining a metal from its ores
Preliminary treatment to concentrate ore:
Floatation.
Hindered settling
Magnetic separation
2) Further purification and reduction to obtain the metal in its elementary state:
Hydrometallurgy – leaching.
Pyrometallurgy – roasting, smelting.
Electrometallurgy.
3) Final purification and refining of the metal.

3. Hydrometallurgy Metal is refined from ore using aqueous reactions
Example: Dissolve Au by forming complex ion with CN
4Au(s) + 8CN(aq) + O2(g) + 2H2O(l)  [Au(CN)4](aq) + 4OH(aq)
Kf[Au(CN)4] = 2x1038
Pure gold is then obtained by reduction:
2Au(CN)4(aq) + 3Zn(s)  3Zn2+(aq) + 8CN-(aq) + 2Au(s)
Similar process for silver (dissolves as [Ag(CN)2])

4. SILVER Found as pure metal (Ag) or sulfide (Ag2S)
[Ag(CN)2] Kf = 1 x 1021
4Ag + 8CN(aq) + O2 + 2H2O  4[Ag(CN)2](aq) + 4OH(aq)
Ag2S + 4CN(aq)  2[Ag(CN)2](aq) + S2(aq)
Practice problem: Use Kf, with E0 and Ksp values (from tables) to calculate Keq for these reactions.

5. COPPER Electrolyzed to Cu
Copper containing ore (CuFeS2) is stirred with aqueous H2SO4 + O2
2CuFeS2(s)+2H+(aq)+SO42(aq) + 4O2(g) 
2Cu2+(aq) + 2SO42-(aq) + Fe2O3(s) + 3S(s) + H2O
\ /
2CuSO4(aq) 
Electrolyzed to Cu

6. Electrometallurgy Electrorefining of Copper
Slabs of impure Cu are used as anodes, thin sheets of pure Cu are the cathodes.
Acidic copper sulfate is used as the electrolyte.
The voltage across the electrodes is designed to produce copper at the cathode.
The metallic impurities do not plate out on the cathode.
Metal ions are collected in the sludge at the bottom of the cell.

7. Electrometallurgy

8. Hydrometallurgy of Aluminum
Aluminum is the second most useful metal.
Bauxite: Al2O3.xH2O.
primary ore for Al
impurities: SiO2
Fe2O3
Bayer Process
Bayer process: bauxite (~ 50 % Al2O3) is concentrated to produce aluminum oxide.
Dissolve bauxite in strong base (NaOH) at high T, P
Al2O3 dissolves [Al(H2O)2(OH)4]
hydrated metal complex
Filter out solids
Fe2O3, SiO2 do not dissolve
Lower the pH so that Al(OH)3(s) precipitates
Takes advantage of the amphoteric nature of Al oxide.

9. Electrometallurgy of Aluminum
Hall process is used to obtain aluminum metal.
Problem: Al2O3 melts at 2000C and it is impractical to perform electrolysis on the molten salt.
Hall: use purified Al2O3 in molten cryolite (Na3AlF6, melting point 1012C).
Anode: C(s) + 2O2(l)  CO2(g) + 4e
Cathode: 3e + Al3+(l)  Al(l)
The graphite rods are consumed in the reaction.

10. Electrometallurgy of Al
The Hall Process
Anode: C(s) + 2O2-(l)  CO2(g) + 4e-
Cathode: Al3+(l) + 3e-  Al(l)

11. Electrometallurgy of Sodium
Sodium is produced by electrolysis of molten NaCl.
CaCl2 is used to lower the melting point of NaCl from 804C to 600C.
At the cathode (iron): 2Na+(aq) + 2e  2Na(l)
At the anode (carbon): 2Cl-(aq)  Cl2(g) + 2e
All metals in Groups I and II are obtained by molten salt electrolysis

12. Pyrometallurgy
Pyrometallurgy: using high temperatures to obtain the free metal.
Calcination is heating of ore to eliminate a volatile product:
PbCO3(s)  PbO(s) + CO2(g)
Roasting is oxidation of the ore:
Burns off organic matter.
Converts carbonates and sulfides to oxides:
2 ZnS(s)+ 3O2(g) 2ZnO(s) + SO2(g)
3. Less active metals are often reduced
HgS(s) + O2(g)  Hg(l) + SO2(g)

13. The Pyrometallurgy of Iron
sources of iron:
hematite Fe2O3 and magnetite Fe3O4.
Iron Ore: Iron oxides and SiO2
Add limestone and coke
Coke is coal that has been heated to drive off the volatile components.

14. Blast Furnace

15. Pyrometallurgy of Fe Reactions 2C(s) + O2(g)  2CO(g) + heat
heat + C(s) + H2O(g)  CO(g) + H2(g)
Fe3O4(s) + 4CO(g)  3Fe(l) + 4CO2(g)
Fe3O4(s) + 4H2(g)  3Fe(l) + 4H2O(g)
Coke: 1) heats furnace
2) reduces iron
Why is limestone (CaCO3) added?

16. Pyrometallurgy of Fe At high T CaCO3  CaO + CO2
CaO SiO2  CaSiO3(l)
Metal + nonmetal  slag
oxide oxide
basic acidic
Limestone (CaCO3)
removes SiO2 (and other) impurities
slag floats on Fe(l); protects it from oxidation by O2
Slag: cement
cinder block
building materials

17. Physical Properties of Metals
Metals and Alloys
Physical Properties of Metals
Important physical properties of pure metals: malleable, ductile, good conductors of heat and electricity.
Metals are crystals in which every atom has 8 or 12 neighbors.
There are not enough electrons for the metal atoms to make electron pair bonds to each neighbor.
Alloys: Mixtures of metals - often have improved physical properties

18. ALLOYS Homogeneous (solution) alloys:
Mixed at the atomic level - one solid phase
2) Heterogeneous alloy:
Non-homogeneous solid (e.g. pearlite steel has two phases: almost pure Fe and cementite, Fe3C).
3) Intermetallic alloys – compounds of two different metals having definite proportions:
e.g. Cr3Pt – razor blades.
Ni3Al – jet engines, lightweight and strong.
Co5Sm – permanent magnets in headsets.
Au3Bi, Nb3Sn – superconductors

19. Homogeneous (solution) alloys
substitutional
interstitial
Cr in Fe
C in low-carbon steel

20. SOLUTION ALLOYS Two kinds:
Substitutional alloy – when one metal substitutes for another in the structure.
metals must have similar atomic radii,
metals must have similar bonding characteristics.
Interstitial alloy – when a non-metal is present in the “holes” in a metal crystal lattice.
Interstitial atoms are smaller
The alloy is much stronger than the pure metal (increased bonding between nonmetal and metal).
Example steel (contains up to 3 % carbon).

21. Mechanical Properties of Metals and Alloys
Hypothetical situation:
Upon graduation, you go to work for Boeing.
Your job – select a high-strength Al alloy for jet airplanes.
50 tons cargo
Airplane: 500 tons } tons plane structure
300 tons fuel
If you can triple the alloy strength, you can triple cargo load (to 150 tons).
Material Tensile Yield Stress (psi)
pure (99.45%) annealed Al 4 x 103
pure (99.45%) cold drawn Al 24 x 103
Al alloy - precipitated, hardened 50 x big improvement
But, “perfect” single crystal Al as a yield stress of ca. 106 psi!

22. Defects in Metallic Crystals
Defects are responsible for important mechanical properties of metals: malleability, yield stress, etc.
Non-directional bonding, large number of nearest neighbor atoms  metallic structures readily tolerate “mistakes”
vacancy dislocation
(missing atom) (extra plane of atoms)
point defect line defect
Not important Very important

23. Dislocations Move Under Stress
shear force
Key point:
Moving a dislocation breaks/makes a line of metal-metal bonds (easy)
Shearing a perfect crystal means we have to break a plane of bonds (requires much more force)

24. Hardening of Alloys
Structural alloys - e.g., girders, knife blades, airplane wings
Need to minimize movement of dislocations. How?
Use annealed single crystals (expensive)
Some specialty applications – e.g. jet turbine blade
Impossible for large items (airplane wings, bridges…)
Work hardening - moves dislocations to grain boundaries
planar defect
(stronger under stress)
“Cold working” or “drawing” of a metal increases strength and brittleness (e.g., iron beams, knives, horseshoes)

25. Hardening of Alloys (contd.)
Work Hardening and Annealing have opposite effects
Annealing: crystal grains grow, dislocations move (metal becomes more malleable)
Alloying – homogeneous or heterogeneous
Impurity atoms or phases “pin” dislocations.

26. Metal Crystal Structures
Body-centered cubic (bcc)
8 nearest neighbors
Not close packed
Close packed
(hexagonal or cubic)
hcp ccp

27. Malleability of Metals and Alloys
Some metals are soft and ductile (Au, Ag, Cu, Al, etc.)
Others are hard (Fe, W, Cr, etc.) Why?
Crystal structure is important.
Two types: body centered cubic (bcc) coordinate - hard
close packed (fcc and hcp) - 12-coordinate - soft
Close-packed planes slip easily Non-close packed - “speed bumps”
Cu (fcc) CuZn alloy (brass)
Zn (hcp)

28. Amorphous (Glassy) Alloys
Metals are typically polycrystalline
Amorphous alloys have superior mechanical properties because dislocations cannot move.

29. Iron and Steels Below 900oC, iron has bcc structure - “hard as nails”
Above 900oC, iron is close packed (fcc) - soft
Can be worked into various shapes when hot
Steelmaking:
Carbon steel contains ~ 1% C by weight (dissolves well in fcc iron but not in bcc)
Slow cooling (tempering):
fcc Fe/1%C  mixture of bcc Fe and Fe3C (pearlite)
Fe3C (cementite) grains stop movement of dislocation in high carbon steel - very hard material

30. STEELS Steel: Fe (pig iron) + small amounts of C
Mild Steel: <0.2% C – malleable and ductile
used in cables, nails, and chains.
Medium Steel: % C – tough
used in girders and rails.
High Carbon Steel: % C – very tough
used in knives, tools, and springs.
Stainless Steel:
73% Fe, 18% Cr, 8% Ni, 1% C.