Chapter 3: Metal Synthesis and Processing

3.1 Introduction3.2 Ellingham diagrams3.3 Pyrometallurgy of iron and steel3.4 Primary copper production3.5 Primary aluminum production3.6 Other synthesis routes

Relative importance of different materials

7000 years ago, prehistoric people discovered methods of heating minerals to extract tin, lead and other metals.Human passed from Stone age to Bronze age. Then they found the use of iron and created Iron Age.

Metal ores

Cinnabar, HgS; Rutile TiO2 in a quartz matrix, and Gold embedded in quartz.

盐

Cinnabar (朱砂) and rutile (金红石)

chirality

Synthesis methods for metals

1) Metallurgy (冶金，冶金学): ores metals• Powder metallurgy (粉末冶金) (mostly processsing)• Pyrometallurgy (热冶金，火法冶金)• Hydrometallurgy (湿法冶金)

2) Electrowinning (电解冶金)and electrorefinning (电解精炼)

3) Electroplating (Electrodeposition) (of metal films)

4) Electroless plating (Electroless deposition)(化学镀，无电镀)

5) Mechanical alloying

6) Plasma spraying

7) CVD/PVD

Electrochemistry basics

• The amount of electricity that flows through the cell depends on the amount of species being oxidized or reduced according to the Faraday law:

AMnFitm =

n- number of electrons in a redox reaction, N-number of moles,MA- molecular weight, F- Faraday constant (96485C/mole)

I = dQ/dt Q = ∫Idt• Electricity:

ΔG0 = -nFE0 ΔG = -nFE E=E0 – (RT/nF)lnQΔrS = nF(∂E/∂T)P ΔrH = -nFE + nFT(∂E/∂T)P

• In an electrochemical reaction: aA + bB == gG + hH

ΔGocell = -nFEo

cell

Eocell= Eo

cathode – Eoanode

If Eocell> 0, then the

process is spontaneous (galvanic cell)

If Eocell< 0, then the

process is nonspontaneous(electrolytic cell)

Pyrometallurgy of metals

Ellingham diagram

Ellingham diagram

Construction of an Ellingham diagram

An Ellingham diagram is a plot of ΔG0 versus temp. Since ΔH and ΔS are essentially constant with temp. Unless a phase change occurs, and ΔG = ΔH-TΔS, the ΔG0~T plot can be drawn as a series of straight lines, where ΔS is the slope and ΔH is the y-intercept.

The Ellingham diagram is for metals reacting to form oxides (similar diagrams can also be drawn for metals reacting with sulfur, chlorine, etc., but the oxide form of the diagram is most common). The oxygen partial pressure is taken as 1 atmosphere, and all of the reactions are normalized to consume one mole of O2.

Features of Ellingham diagram

1) The majority of the lines slope upwards with an approximately same slope.

2) The slope of a line changes when there is a phase change.

3) Under standard states, all metals with negative value of ΔG may be oxidized spontaneously. The oxides with positive ΔG is not stable and are easily decomposed to elemental metals.

4) A given metal can reduce the oxides of other metals whose lines lie above theirs on the diagram.

Richardson-Ellingham diagram

Closer look at Ellingham diagram

Ellingham diagram

HC

0K

ΔG0 =

RTl

nPO

2

0

0 400 800 1200 1600

1

10-4

10-8

10-12

10-16

10-20

10-24

10-28

C + O2 = CO2

2M + O2 = 2MO

PO2 (atm)T (K)

Three main uses of the Ellingham diagram

1) Determine the relative ease of reducing a given metallic oxide to metal;

2) Determine the partial pressure of oxygen (PO2) that is in equilibrium with a metal oxide at a given temperature;

3) Determine the ratio of carbon monoxide to carbon dioxide (PCO/PCO2) that will be able to reduce the oxide to metal at a given temperature.

Online tutorials on Ellingham diagramshttp://www.engr.sjsu.edu/ellingham/tutorial.html (San Jose State Univ)http://www.doitpoms.ac.uk/tlplib/ellingham_diagrams/index.php (Cambridge)

Similar diagram with CO2 reactions

100 100

0 0

-100 -100

-200 -200500 5001000 10001500 1500

T / K T / K

ΔrG

0 / kJ⋅m

ol-1

ΔrG

0 / kJ⋅m

ol-1

SrTiO3

SrZrO3

SrCeO3

SrO

BaTiO

BaZrO3

BaCeOBaO

SrTiO3,SrZrO3等钙钛矿在高温下能在CO2气氛中稳定存在。

ABO3(s) + CO2(g) = ACO3(s) + BO2 (s)

Abundance of elements in Earth's crust

Compound Composition

SiO2 59.71%

Al2O3 15.41%

CaO 4.90%

MgO 4.36%

Na2O 3.55%

FeO 3.52%

K2O 2.80%

Fe2O3 2.63%

H2O 1.52%

TiO2 0.60%

P2O5 0.22%

Total 99.22%

Fe: 5.63% Al: 8.23% Cu: 0.006%

http://www.jfe-21st-cf.or.jp

Pyrometallurgy of iron and steel

Heat treatment procedure for iron production

• Drying: @~100°C, to remove mechanically bounded

H2O

• Calcination: @>900°C, to drive off CO2 from limestone.

CaCO3(s) CaO(s) + CO2(g)

• Roasting: to convert sulfides to oxides

2ZnS(s) + 3O2(g) 2ZnO(s) + 2SO2(g) (ΔH=-211kcal)

4FeS2(s) + 11O2 2Fe2O3(s) + 8SO2(g) (ΔH=-796kcal)

• Smelting: to let the material melts and produce a

molten melt and a slag. The impurities are either carried

off by the slag, or are burned off as a gas.

Iron ore and its pretreatment

Coal and coking

Indirect heating at 1,473-1,573K (1,200-1,300oC ) for 14-18h

Blast furnace (BF)

BF operation

Iron blast furnace

Iron blast furnace

Slag: SiO2+Si+CaS

Hot metal pretreatment

Basic Oxygen Furnace (BOF)

BOF operation

Direct reduction process

Electric Arc Furnace (EAF)

Secondary refining

Continuous casting

Continuous casting

Continuous caster operation

Pyrometallurgical equipment

Shaft furnace (竖炉 )

Muffle furnace

Hearth furnacesA. Reverberatory(反射炉 );

B. B. Rotary(回转炉 )

Electric furnace

Roasters

Flash/suspension roaster(悬浮焙烧炉 )

Fluid bed roaster

(流化床焙烧炉 )

Hearth Roaster(床式焙烧炉 )

Steel productionIntegrated steel mill and electric-arc furnace minimill

Comparison between pig iron and steel

<0.04%0.025-2.5%Phosphorus

0.02-0.04%Up to 0.2%Sulfur

Trace0.5-4%Silicon

0.3-0.9%0.15-2.5%Manganese

0.04-1.7%3-4%Carbon

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(a) The eutectoid portion of the Fe-Fe3C phase diagram. (b) An expanded version of the Fe-C diagram, adapted from several sources.

T-T-T diagram

Electron micrographs of (a) pearlite, (b) bainite, and (c) tempered martensite, illustrating the differences in cementite size and shape among these three microconstituents (× 7500).

Flame surface hardening

• Heat the surface of a steel part rapidly to a temperature above the critical point of the steel → form austenitic grain structure (austenitized) → quickly quench (water or force air) to transform austenite to martensite → form a hard case (the core of the part in its original state: ferrite and pearlite);

• Requirements: hardenable carbon steels (wrought or cast, 0.37-0.55%C) and cast irons (0.35-0.80%C), martensitic stainless steels, tool steels, steels with adequate carbon and other alloy elementaddition.

Relationship of carbon content to minimum surface hardness attainable by flame heating and water quenching

Flame surface hardening

Spinning methods of flame hardening. In methods shown at left and at center, the part rotates. In method at right, the flame head rotates.

Combination progressive-spinning flame hardening.

Primary copper production

Copper Pyrometallurgical Reactions(Assuming a feed contains no sulfides other than chalcopyrite CuFeS2)

• Roasting: (500-700°C)CuFeS2 + 4O2 ==> CuSO4 + FeSO4

2CuFeS2 + 13/2O2 ==> 2CuO + Fe2O3 + 4SO2

• Smelting: (1200°C)FeS + 6CuO ==> 3Cu2O + FeO + SO2

FeS + Cu2O ==> FeO + Cu2S

Cu2S + FeS ==> Cu2S•FeS (matte)

• Coverting reactions: to convert matte to copper.

(silica is added as a flux)2Cu2S•FeS + 3O2 + SiO2 ==> 2FeO•SiO2 + 2SO2 + Cu2S

Cu2S + O2 ==> 2Cu + SO2

• Fire-refinning reactions:4CuO + CH4 ==> Cu + CO2 + 2H2O

Pierce-Smith copper converter

During the converting process, air is injected

through the tuyeres（风口 ）, and off-gases are collected by a removablehood that covers the charging port. The tuyeresare equipped with pneumatic“punchers” to break throughany slag or other solids that may solidify over thetuyere opening.

Outokumpu flash smelting process

Sulfide concentrate is injected through a burner along with preheated air, and partially burned as it falls through a flash-roasting zone. The heat produced by roasting the sulfide helps to melt the concentrate, with supplemental fuel injected into the flash-roasting area to provide the remaining heat.

Integrated flash smelting/flash converting copper production facility.

Hydrometallurgy

Hydrometallurgy of copper

Advantages:

• Producing little pollution

• Saving energy

• Treatment is carried out at a low temperature

• Liquid effluent consists of chemical compounds that are easy to reprocess and recover.

• Well suited to extracting metal from low-grade ores.

Hydrometallurgy of copper: leaching

A. Dump leaching

B. Heap leaching

Leaching reagents = acids, complexing agents, oxidizers, etc.

Leaching reactions

• Non-oxidative reactions:

CuSO4(s) + H2O(l) ===> Cu+2(aq) + SO4-2(aq)

Cu2(OH)2•CO3(s) + 2H2SO4(aq) ===> 2CuSO4(aq) + CO2 + 3H2O

• Oxidative leaching:CuS(s) + 2O2(g) ===> CuSO4(aq)

4H2O + CuS(s) + 4Fe2(SO4)3(aq) ===> CuSO4(aq) + 8FeSO4 (aq) + 4H2SO4

• Bacterial leaching:

Thiobacillus ferrooxidans (硫杆菌）:

to oxidize pyrite (FeS2) to leaching reagents.

Bacteria

4FeS2(s) + 15O2 + 2H2O ======> 2Fe2(SO4)3(aq) + 2H2SO4(aq)

Solution purification

• Ion-exchange reagent:

Metal recovery

• Cementation (置换沉淀法):Dissolved copper will plate out on an iron surface due to:

Cu+2(aq) + Fe(s) ===> Fe+2(aq) + Cu(s)

A. Electrowinning B. Electrorefinning

• Electrowinning: electrochemically precipitate metals from solution.

Cu+2(aq) + 2e- ===> Cu(s)

• Electrorefinning: from impure copper (generally from the fire-refiningstage in a pyrometallurgical operation) is cast into copper anodes.

Complete layout of the hydrometallurgy of copper

Hydrometallurgy of zinc (Zn), gold (Au) and silver (Ag)

Hydrometallurgy of zinc (Zn), gold (Au) and silver (Ag)

Hydrometallurgy of titanium (Ti)

Primary aluminum production

The primary ore of aluminum: bauxite (铝矾土）

a mixture of hydrated aluminum oxides:

• Gibbsite - Al(OH)3 (most extractable form)

水铝矿

• Boehmite – γ-AlO•OH (less extractable than Gibbsite)

水软铝石，勃姆石

• Diaspore – α-AlO•OH (difficult to extract)

水铝石

Bayer process for alumina production

• Dissolution: (in autoclave)Al(OH)3 + NaOH ==> NaAlO2 + 2H2O (Gibbsite dissolution)

(150-255 g/L Na2CO3 , 100-150°C, 3.8-5 atm)

AlO•OH + NaOH ==> NaAlO2 + H2O (Boehmite dissolution)

(205-445 g/L Na2CO3 , 200-315°C, 19-100 atm)

• Precipitation: (room temp., with Al(OH)3 seed)

NaAlO2 + 2H2O ==> Al(OH)3 + 2NaOH

• Calcination: (1300-1500°C)

2Al(OH)3 ==> Al2O3 + 3H2O

Bayer process flowsheet-The "Bayer Process" used at Sherwin

Hall-Heroult process for aluminum production (1886)

• Dissolution: (935-975°C)

Dissolving Al2O3 in molten cryolite (Na3AlF6, 冰晶石)

• Electrolysis: (4-5V vs. 1.15V Etheo)

2Al2O3 + 3C ==> 4Al + 3CO2

Hall-Heroult process for aluminum production (1886)

Electrometallurgy of other metals

Copper

Sodium

Cu2+(aq) + 2e- Cu(s) E°red = +0.34V

Ni2+(aq) + 2e- Ni(s) E°red = -0.28V

2H2O(l) + 2e- H2(g)+ 2OH- E°red = -0.83V2H+(aq) + 2e- H2(g) E°red = -0.00V

Production of Li

LiCl

Li

Method 1. Electrometallurgy

Method 2. Pyrometallurgy

a) 2Li2O + Si = 4Li + SiO2 ∵ΔG0

278 = + 298 kJ，ΔH0298 = + 320kJ) ∴ High temp. + Vacuum: Li(g)

Li2CO3

b)

c)

Production of Li

周园等,《稀有金属》,28(2)(2004)343.

Powder Metallurgy

MN (825 ton) mechanical press

Powder Metallurgy

Distribution of P/M parts in a car

Advantages of P/M:•Metal powders are high-purity materials •Close dimensional tolerances can be maintained •High-volume process with excellent reproducibility •Quality control is inherent in the process •Low labor input •Machining is eliminated or reduced •Scrap losses are eliminated or reduced •Segregation is avoided •Controllable porosity and density can be precisely controlled •Combines immiscible metals •Complex shapes can be produced

Disadvantages of P/M:• costs of powder production• limitations on the shapes and features, e.g. re-reentrant angles by fixed die pressing or radial holes in vertically pressed cylinders• the size will always change on sintering.

Powder Metallurgy

FINISHEDPRODUCTS

P/M ProcessOPTIONAL

OPERATIONSSINTERINGFORMINGMIXINGRAWMATERIALS

Elemental orAlloy Metal

Powders

Additives(graphite, die,

lubricants)

Mixing

IsostaticExtrusion

Die CompactingSpraying

Pressureless-Sintering

Die CompactingIsostaticRolling

Injection MoldingSlip Casting

Cold Compaction

Hot Compaction

AtmosphereVacuum

High Temperature

SinteringRepressing

ConingSizing

RepressingForging

RerollingMetal Infiltration

OptionalManufacuring Steps

MachiningHeat Treating

Steam TreatingPlastic Impregnation

PlatingTumbling

Oil ImpregnationShot Peening

OptionalFinishing Steps

FinishedProducts

粉末冶金生产工艺

Powder production

• Mechanical comminution(top-down)

• Electrolytic deposition(bottom-up)

• Chemical reactions(bottom-up)

• Atomization(top-down)

喷射沉积

Stone mills

挤压

拉拔

轧制

A typical compaction cycle

连铸连轧

连续挤压conform

Mechanical Alloying

C.C. Koch, “Intermetallic matrix composites prepared by mechanical alloying—a review”, Mater. Sci. Eng. A244 (1998) 39-48.

Au-Ag 1970's, International Nickel Co. (INCO)

dispersing nanosized oxide inclusions into Ni-based alloys

Mechanical Alloying equipment: shaker and planetary mills

Planetary ball mill

Shaker mill

Mechanical Alloying equipment: Attritors

100-500rpm

Low energy ball mill

Most ball mills operate most efficiently between 65% ~75% of their critical speed.

Low energy ball mill

Jet mills

Jet mill

Jet mills and other mills

Jet mill, 0.1~1 μm,tight PSD

Air-swept impact mill, ~1 μm, tightest PSD

Centrafugalpin-type impact mill, 50~200 mesh

Air claasifier Hammer millfor friable materials

Roll crusherfor friable materials

Jaw crusherCoarse and intermediate crushing

Rotary crusherRugged rotary action with high reduction ratios and production rates. Soft-to medium hard materials

Sample grinderwith small throughput rates

“x” mesh = 25.4/x mm

Plasma spraying

Spray conversion process

Preparation of metallic glass-Melt spinning

It is possible to rapidly quench a molten metallic alloy, thereby bypassing crystallization, and forming a glassy metal commonly called a metallic glass. The process is called melt spinning.

Preparation of metallic glass-Melt spinning

Cooling 105-106K/s

Metglas: Fe-Si-B, Fe-Ni-P-B, …

Liquidmetal®(Zr41.2Be22.5Ti13.8Cu12.5Ni10.0)