Chapter_23_Metals_and_Metallurgy.ppt

1、Prentice Hall 2003Chapter 23Chapter 23Metals and MetallurgyPrentice Hall 2003Chapter 23Early history is divided into the Stone Age,Bronze Age,and the Iron Age.If we consider a jet engine,there are 7 metals present.Fe is not.A modern jet engine consists mostly of Ti and Ni with decreasing amounts of

2、Cr,Co,Al,Nb and Ta.The solid portion of the earth is called the lithosphere.Concentrated metal deposits are found beneath the earths surface.Occurrence and Distribution of MetalsPrentice Hall 2003Chapter 23MineralsOre:deposit that contains enough metal that we can extract economically.Most metals ar

3、e found in minerals.Names of minerals are usually based on the location of their discovery.Other minerals are named after their colors:malachite comes from the Greek malache(the name of the tree with very green leaves).Most important ores are oxide,sulfide and carbonates.Prentice Hall 2003Chapter 23

4、Prentice Hall 2003Chapter 23MetallurgyMetallurgy is the science and technology of extracting metals from minerals.There are five important steps:Mining(getting the ore out of the ground);Concentrating(preparing it for further treatment);Reduction(to obtain the free metal in the zero oxidation state)

5、;Refining(to obtain the pure metal);andMixing with other metals(to form an alloy).Prentice Hall 2003Chapter 23Pyrometallurgy:using high temperatures to obtain the free metal.Several steps are employed:Calcination is heating of ore to cause decomposition and elimination of a volatile product:PbCO3(s)

6、PbO(s)+CO2(g)Roasting is heating which causes chemical reactions between the ore and the furnace atmosphere:PyrometallurgyPyrometallurgyPrentice Hall 2003Chapter 232ZnS(s)+3O2(g)2ZnO(s)+2SO2(g)2MoS2(s)+7O2(g)2MoO3(s)+4SO2(g)Smelting is a melting process that causes materials to separate into two or

7、more layers.Slag consists mostly of molten silicates in addition to aluminates,phosphates,fluorides,and other inorganic materials.Refining is the process during which a crude,impure metal is converted into a pure metal.Prentice Hall 2003Chapter 23The Pyrometallurgy of IronMost important sources of i

8、ron are hematite Fe2O3 and magnetite Fe3O4.Reduction occurs in a blast furnace due to carbon.The ore,limestone and coke are added to the top of the blast furnace.Coke is coal that has been heated to drive off the volatile components.Prentice Hall 2003Chapter 23Prentice Hall 2003Chapter 23Coke reacts

9、 with oxygen to form CO(the reducing agent):2C(s)+O2(g)2CO(g),H=-221 kJCO is also produced by the reaction of water vapor in the air with C:C(s)+H2O(g)CO(g)+H2(g),H=+131 kJSince this reaction is endothermic,if the blast furnace gets too hot,water vapor is added to cool it down without interrupting t

10、he chemistry.Prentice Hall 2003Chapter 23At around 250C limestone is calcinated(heated to decomposition and elimination of volatiles).Also around 250C iron oxides are reduced by CO:Fe3O4(s)+4CO(g)3Fe(s)+4CO2(g),H=-15 kJFe3O4(s)+4H2(g)3Fe(s)+4H2O(g),H=+150 kJMolten iron is produced lower down the fur

11、nace and removed at the bottom.Slag(molten silicate materials)is removed from above the molten iron.Prentice Hall 2003Chapter 23If iron is going to be made into steel it is poured directly into a basic oxygen furnace.The molten iron is converted to steel,an alloy of iron.To remove impurities,O2 is b

12、lown through the molten mixture.The oxygen oxidizes the impurities.Prentice Hall 2003Chapter 23Formation of SteelSteel is an alloy of Fe.From the blast furnace,the iron is poured into a converter.A converter consists of a steel shell encasing a refractory brick liner.After treatment in the blast fur

13、nace,there are impurities in the iron,which must be removed by oxidation.Air cannot be present in the converter because the nitrogen will form iron nitride(causes the steel to be brittle).Formation of SteelOxygen diluted with Ar is used as the oxidizing agent.When oxygen emerges from the converter,t

14、hen all the impurities have been oxidized and the iron is poured into a ladle.Prentice Hall 2003Chapter 23Hydrometallurgy is the extraction of metals from ores using water.Leaching is the selective dissolution of the desired mineral.Typical leaching agents are dilute acids,bases,salts,and sometimes

15、water.Gold can be extracted from low-grade ore by cyanidation:HydrometallurgyPrentice Hall 2003Chapter 23NaCN is sprayed over the crushed ore and the gold is oxidized:4Au(s)+8CN-(aq)+O2(g)+2H2O(l)4Au(CN)2-(aq)+4OH-(aq)The gold is then obtained by reduction:2Au(CN)2-(aq)+Zn(s)Zn(CN)42-(aq)+2Au(s)Pren

16、tice Hall 2003Chapter 23Electrorefining of CopperBecause of its good conductivity,Cu is used to make electrical wiring.Impurities reduce conductivity,therefore pure copper is required in the electronics industry.ElectrometallurgyPrentice Hall 2003Chapter 23Electrorefining of CopperSlabs of impure Cu

17、 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

18、the cell.Prentice Hall 2003Chapter 23ElectrometallurgyPrentice Hall 2003Chapter 23Alloys have more than one element with characteristics of metals.Pure metals and alloys have different physical properties.In jewelry an alloy of gold and copper is used(the alloy is harder than soft gold).Solution all

19、oys are homogeneous mixtures.Heterogeneous alloys:components are not dispersed uniformly(e.g.pearlite steel has two phases:almost pure Fe and cementite,Fe3C).AlloysPrentice Hall 2003Chapter 23There are two types of solution alloy:substitutional alloys(the solute atoms take the positions of the solve

20、nt);interstitial alloys(the solute occupies interstitial sites in the metallic lattice).Substitutional alloys:atoms must have similar atomic radii,elements must have similar bonding characteristics.Prentice Hall 2003Chapter 23Interstitial alloys:one element must have a significantly smaller radius than the other(in order to fit into the interstitial site),e.g.a nonmetal.The alloy is much stronger than the pure metal(increased bonding between nonmetal and metal).Example steel(contains up to 3%carbon).Prentice Hall 2003Chapter 23