Materials of Technology 13.1 Natural Sources of the Metallic Elements 13.2 Metallurgy 13.3 Bonding in Metals 13.4 Diamond, Graphite, the Fullerenes, and

Materials of Technology

13.1 Natural Sources of the Metallic Elements

13.2 Metallurgy

13.3 Bonding in Metals

13.4 Diamond, Graphite, the Fullerenes, and Nanotechnology

13.5Semiconductors

13.6 Silicon, Silica, and Silicates

13.7 Ceramics

13.8 Composites

Copyright © by Houghton Mifflin Company. All rights reserved. Copyright © Houghton Mifflin Company.All rights reserved. Presentation of Lecture Outlines, 13–2


• New technologies require new materials.

– Nanotechnology and telecommunications are just two examples of developments in material science.



• New technologies require new materials.

– In this chapter we will look at materials with a view toward the development of useful applications.



• New technologies require new materials.– These materials include:

1. Metals

2. Nonmetallic materials

3. Ceramics

4. Composites


Metals and Metallurgy

• We define a metal as a material that is lustrous (shiny), has high electrical and heat conductivities, and is malleable and ductile.

– Metals may be pure elements or they may be alloys, which can be either compounds or mixtures.

– Most commercial metals are alloys consisting of one metal with small quantities of some other metals.


Natural Sources of Metals

• Metallic elements and their compounds are obtained principally from the earth’s crust, most of which is composed of metal silicates.

– Table 13.1 lists the ten most abundant elements in the earth’s crust.



• Metallic elements and their compounds are obtained principally from the earth’s crust, most of which is composed of metal silicates.

– The two most abundant elements are oxygen and silicon.

– These two elements are the main ingredients of silicates, which are the chief substances of rock and clay. (see Figure 13.4)



• The chief sources of metals, however, are not silicates but oxide, carbonate, and sulfide minerals.

– A mineral is a naturally occurring inorganic solid or solid solution with a definite crystal structure.

– These compounds exist in ore deposits widely scattered over the earth.



• The chief sources of metals, however, are not silicates but oxide, carbonate, and sulfide minerals.

– An ore is a rock or mineral from which a metal can be economically produced

– Table 13.2 lists some of the ores of important metals, along with their country of origin.


Metallurgy

• Metallurgy is the scientific study of the production of metals from their ores and the making of alloys.

• The production of metals from their ores involves three principal steps:– Preliminary treatment– Reduction– Refining


Metallurgy

• In preliminary treatment, the ore is concentrated in its metal-containing mineral.

– The worthless portion of an ore is called gangue (pronounced “gang”).

– To separate the useful mineral from the gangue, both physical and chemical methods may be used.


– Flotation is a physical method of separating the mineral from the gangue by using the differences in their wettabilities in a liquid solution.

(see Figure 13.7)

Metallurgy


– Sulfide ores, such as those of copper, lead, and zinc, are concentrated using flotation.


– The Bayer process is a chemical procedure in which purified aluminum oxide, Al2O3, is separated from the aluminum ore bauxite.

Metallurgy


– The aluminum ore is treated with hot aqueous sodium hydroxide to extract the aluminum as Al(OH)4

-, which is heated to produce Al2O3.


– Once an ore is concentrated, it may be necessary to convert the mineral to a compound more suitable for reduction.

Metallurgy


– Roasting is the process of heating a mineral in air to obtain the oxide.


– Sulfide minerals, such as zinc ore (containing the mineral sphalerite, ZnS), are usually roasted before reduction to the metal.

Metallurgy


kJ 844H );g(SO2)s(ZnO2)g(O3)s(ZnS2 22


Metallurgy

• In reduction, the metal-containing compound is reduced to the metal.– This can be accomplished by electrolysis

or chemical reduction.


Metallurgy

• In reduction, the metal-containing compound is reduced to the metal.– Electrolysis uses an electric current to

reduce the metal compound to the metal.

– Lithium, for example, is obtained commercially by the electrolysis of molten lithium chloride, LiCl (see Figure 13.10).


Metallurgy

• In reduction, the metal-containing compound is reduced to the metal.– Magnesium is obtained by using the Dow

process, where magnesium is precipitated from sea water, converted to MgCl2 , and the molten salt electrolyzed.

)s()OH(Mg)aq(OH2)aq(Mg 22


Metallurgy


process, where magnesium is precipitated from sea water, converted to MgCl2, and the molten salt electrolyzed.

)l(OH2)aq(MgCl)aq(HCl2)s()OH(Mg 222


Metallurgy


process, where magnesium is precipitated from sea water, converted to MgCl2, and the molten salt electrolyzed.

)g(Cl)l(Mg)l(MgCl 221 iselectrolys

2


Metallurgy

• In reduction, the metal-containing compound is reduced to the metal.

– The Hall-Héroult process is another electrolytic method for producing aluminum by the electrolysis of a molten mixture of aluminum oxide in cryolite, Na3AlF6.

– See Figure 13.12.

)g(CO3)l(Al4)s(C3)s(OAl2 2 iselectrolys

32


Metallurgy


– The cheapest chemical reducing agent is in the form of carbon, such as hard coal or coke.

– Some important metals, such as iron and zinc, are obtained by chemical reduction using carbon.


Metallurgy


– Zinc ore, for example, is first roasted to obtain zinc oxide, ZnO.

)g(CO)g(Zn)s(C)s(ZnO

– When the oxide is heated strongly with carbon in a blast furnace, it is reduced to the metal.


Metallurgy


– Iron is also produced by reduction in a blast furnace.

– The coke is burned to carbon monoxide, which reacts with iron oxides to reduce them to iron and carbon dioxide (see Figure 13.14).

)g(CO3)l(Fe2)g(CO3)s(OFe 232


Metallurgy


– Hydrogen and active metals, such as sodium, magnesium, and aluminum, are used as reducing agents when carbon is unsuitable.


Metallurgy


– Tungsten metal, for example, is prepared from tungsten(VI) oxide by reduction in a stream of hydrogen gas.

)g(OH3)s(W)g(H3)s(WO 223

– One of the most important uses of tungsten is the production of filaments for incandescent bulbs. (see Figure 13.15)


Metallurgy

• In refining, the metal is purified, or freed of contaminants.

– For metals with low boiling points, such as zinc, this can be accomplished by distillation.

– Other metals, such as copper, are purified by electrolysis.

– Often the metal obtained from reduction contains impurities and must be refined.


Bonding in Metals

• The electron-sea model is a simple depiction of a metal as an array of positive ions surrounded by delocalized valence electrons.– Metals are good conductors of electricity because

of the mobility of these delocalized valence electrons.

– A metal also conducts heat well because the mobile electrons can carry additional kinetic energy.


Bonding in Metals

• Molecular orbital theory gives a more detailed picture of the bonding in metals.

– Because the energy levels in a metal crowd together into bands, this picture of metal bonding is called band theory.


Bonding in Metals

• Molecular orbital theory gives a more detailed picture of the bonding in metals.– According to band theory, the electrons in a

crystal become free to move when they are excited to the unoccupied orbitals of a band.


Bonding in Metals

• Molecular orbital theory gives a more detailed picture of the bonding in metals.

– In a metal, this requires little energy since the unoccupied orbitals lie just above the occupied orbitals of highest energy. (see Figure 13.16)


Nonmetallic Materials

• In the following sections we will look at several nonmetallic materials with applications in modern technology.– These include:

1. Allotropes of carbon (diamond, graphite, and fullerenes)

2. Silicon, silica, and silicates

3. Ceramics

4. Composites


Nonmetallic Materials

• Carbon is an important nonmetallic material.

– It has several allotropes, including diamond, graphite, and the fullerenes.


Diamond

• Diamond has a three-dimensional network structure in which each carbon is bonded to four others with sp3 orbitals.

– Scientists first synthesized diamond from graphite in 1955 using high temperature and pressure.

– The process produces diamond grit, which is used for drill bits and cutting wheels (see Figure 13.19).


Diamond

– More recently, researchers have made diamond films from graphite using chemical vapor deposition.

– An obvious application of diamond films is as a coating on cutting tools, which depend on the hardness of diamond.



Diamond

– Diamond films are also marketed as a base for microelectronic parts that generate heat.

– In principle, diamond could supplant silicon as the base material for microelectronics devices, which would work much faster than their silicon counterparts.



Graphite

• Graphite has a layered structure, in which the carbon atoms in each layer bond to three other carbons with sp2 orbitals.

– Most commercial graphite is produced by heating coke in an electric furnace.

– Its primary use is in the manufacture of electrodes.– Graphite is used as one of the electrodes in the

new lithium-ion battery (see Figure 13.21).


Graphite

• Graphite has a layered structure, in which the carbon atoms in each layer bond to three other carbons with sp2 orbitals.

– Pyrolytic carbon, produced by high-temperature decomposition of hydrocarbons, has a disordered graphite structure.

– Artificial heart valves use disks coated with pyrolytic carbon, as it gives a sturdy smooth surface that impedes clot formation

(see Figure 13.22).


Fullerenes

• The fullerenes are a family of molecules with a closed cage of carbon atoms arranged in pentagons and hexagons.

– The most symmetrical member is buckminsterfullerene, C60.

– Buckminsterfullerenes show potential for applications in superconductivity and catalytic activity.


Fullerenes

• The fullerenes are a family of molecules with a closed cage of carbon atoms arranged in pentagons and hexagons.– Some of the fullerenes consist of tubes of carbon

atoms, with each end of the tube being capped by half of a buckminsterfullerene molecule.

– These fullerene tube molecules are referred to as carbon nanotubes.


Fullerenes

• The fullerenes are a family of molecules with a closed cage of carbon atoms arranged in pentagons and hexagons.

– These tubes show promise in terms of potential applications in nanotechnology. (see Figure 13.26)


Semiconductors

• Semiconducting elements form the basis of solid state electronic devices.

– A striking property of these elements is that their conductivities increase markedly when they are doped with small quantities of other elements.

– Metalloids (such as silicon or germanium) are semiconducting elements whose electrical conductivity increases as temperature increases.


Semiconductors


– When silicon is doped with phosphorus, it becomes an n-type semiconductor, in which electric current is carried by electrons.


Semiconductors


– When silicon is doped with boron, it becomes a p-type semiconductor, in which an electrical current is carried by positively charged holes

(see Figure 13.29).


Semiconductors


– Joining a p-type semiconductor to an n-type semiconductor produces a p-n junction, which can function as a rectifier.

– A rectifier is a device that allows current to flow in one direction, but not the other.

(see Figure 13.30)


Silicon

• Silicon is prominent in the materials of technology.

– Silicon has a diamond-like structure.– It is a hard, lustrous gray solid.

– Elemental silicon is obtained by reducing quartz sand (SiO2) with coke (C) in an electric furnace.

)g(CO2)l(Si)s(C2)l(SiO2


Silicon

• Silicon is prominent in the materials of technology.– Silicon is the basic material used in the production

of semiconductor devices.

– These devices require silicon of extreme purity.– The impure element is converted to silicon

tetrachloride, which is purified by distillation, after which it is reduced to pure silicon.


Silica

• Silica is chemically known as silicon dioxide; quartz is a common form of silica.

– SiO2 is a covalent network solid in which each silicon atom is covalently bonded in tetrahedral directions to four oxygen atoms.

(see Figure 13.33)– Quartz is the most important crystal form of silica

and is the major component of most sands.


Silica

• Silica is chemically known as silicon dioxide; quartz is a common form of silica.

– Silica quartz exhibits the piezoelectric effect, which is used to control radio, television, and clock frequencies.

– Quartz crystals are now produced synthetically to satisfy commercial demand.


Silicates

• A Silicate is a compound of silicon and oxygen with one or more metals.

– An enormous variety of silicate minerals exist, but all of their structures have SiO4 tetrahedra as basic units.

(see Figure 13.34)


Silicates

• A silicate is a compound of silicon and oxygen with one or more metals.

– Other examples of silicate minerals include asbestos and mica. (see Figure 13.35)

– The aluminosilicate minerals are silicates in which some of the SiO4 tetrahedra are replaced by AlO4 tetrahedra.


Ceramics

• Ceramics are nonmetallic, inorganic solids that are hard and brittle and usually produced at elevated temperatures.

– This definition includes glass.

– In this section we will look at traditional ceramics and glass, then describe some recent developments in ceramic materials.


Traditional Ceramics

• The word ceramics comes from the Greek word for pottery.– Traditional ceramics begin by forming wet clay,

then firing it to make a ceramic object such as a pot or sculpture.

– Clay is a natural earthy mixture of very small crystals of certain silicate sheet minerals.

– Clay minerals easily absorb water, and wet clay is moldable.


Traditional Ceramics

• The word ceramics comes from the Greek word for pottery.

– Most pottery is glazed.

– After firing, the ceramic object is coated with a water suspension of silica and other oxides, and then fired again.

– The oxides melt to form a glassy coating (see Figure 13.39).


Glass

• Glass is an amorphous, or noncrystalline, solid.

– The term glass refers to any supercooled liquid whose viscosity is so high that it has the properties of a solid.

– Ordinary glass is a silicate produced by fusing silica (SiO2) with other oxides such as sodium and calcium oxides.


Recent Ceramic Materials

• Research in glass-ceramics has yielded many new kinds of materials with diverse applications.

– The glass-ceramic stovetop pots shown in Figure 13.40 were made from a lithium aluminosilicate glass to which titanium and zirconium oxides were added.



• Research in glass-ceramics has yielded many new kinds of materials with diverse applications.

– The resulting glass-ceramic has a very low thermal expansion and doesn’t break easily when subjected to large temperature changes.



• Silicon carbide, SiC, is a ceramic material widely used in abrasives and cutting tools.– Silicon nitride, Si3N4, is a newer ceramic

that exhibits even greater hardness– Silicon nitride is used in special cutting

tools and shows promise as a material for high-temperature engine components.



• Ceramics have recently been used to make medical implants and bone replacement materials.

– High-purity alumina, Al2O3, is nearly inert in the human body, and its strength and wear resistance make it useful for hip replacement devices (see Figure 13.41).



• Ceramic superconductors are extreme examples of electrical conductors. (see essay at the end of Section 13.3)

– At low enough temperatures, these ceramic materials lose all electrical resistance.


Composites

• A composite is a material constructed of two or more different kinds of materials.

– An example of a commercial composite is epoxy plastic reinforced with carbon fibers.

– The embedded fibers impede the spread of fractures that might start (see Figure 13.42).

– These composites are used in aircraft parts, golf clubs, fishing poles, and so forth.


Figure 13.4: Pictured rocks along Lake Superior. Photo courtesy of National Park Service.


Figure 13.7: Flotation process for concentrating certain ores.


Figure 13.10: Electrolysis of molten lithium chloride.


Figure 13.12: Hall-Héroult cell for the production of aluminum.


Figure 13.13: Zinc oxide in medicines.

Photo courtesy of American Color.


Figure 13.14: Blast furnace for the reduction of iron ore to iron metal.


Figure 13.15: Tungsten filament of an incandescent lightbulb.

Photo courtesy of American Color.


Figure 13.16: Formation of an energy band in sodium metal.


Figure 13.19: Synthetic diamonds.Photo courtesy of James Scherer.


Figure 13.21: Discharge of a lithium-ion battery.


Figure 13.22: Artificial heart valve.St. Jude Medical, Inc. 2001.

This image is provided courtesy of St. Jude Medical, Inc. All Rights Reserved.


Figure 13.26: Conceptual drawing of a carbon-nanotube electronic device.

Et al., Science, Vol. 289, No. 94 (200). ©2000 American Association for the Advancement of Science.


Figure 13.29: Effect of doping silicon.


Figure 13.30: A p-n junction as a rectifier.


Figure 13.33: Structure of silica (SiO2).


Figure 13.34: Linking of two SiO4 tetrahedra.


Figure 13.35: Structures of some silicate minerals.


Figure 13.39: A vase with a crystalline glaze.


Figure 13.41: A hip replacement device.


Figure 13.42: Carbon fibers.



Figure 13.11: Dow Process for Producing Magnesium from Seawater

Documents

Materials of Technology 13.1 Natural Sources of the Metallic Elements 13.2 Metallurgy 13.3 Bonding in Metals 13.4 Diamond, Graphite, the Fullerenes, and