Chapter 18 Chemistry and Materials

DiamondPaper, plastic, metals, glass, ceramics

18.1 Paper is made of cellulose fibers

• Paper was first made in China as early as AD 100, of mulberry bark, and then introduced to Western world by Arabs in eighth century. The first paper mills were built in Spain in 11th century.

• The use of wood to produce paper was started in USA.• Additives such as rosin (松香 ) and alum (明矾 ) were a

dded to strengthen paper and make it accept ink well. Chlorine as used to bleaching paper and titanium dioxide （钛白粉） was used to make the paper white.

• Acidic paper, acid-free paper and alkaline paper• Plants alternative to trees: willow (柳 ), kenaf (麻 ). They

usually have high fiber content and grow fast.• 70 million tons of paper are used in USA: one person 23

0 kilograms or six trees.

18.2 The development of plastics involved experimentation and discovery

• The search for a lightweight, nonbreakable, moldable material began with the invention of vulcanized rubber (硫化橡胶 ).

+ + isoprene

polyisoprene

polymerization

Fig18.5 isoprene molecules react with one another to form polyisoprene, the fundamental chemical unit of natural rubber, which comes from rubber trees

Charles Goodyear discovered the rubber vulcanization in 1837.

(a) Original form Stretched with little tendency to snap back to original form

Stretched with great tendency to snap back because of cross-links

(b) Original form with disulfide cross-links

Fig18.6 (a) when stretched, the individual poly-isoprene strands in natural rubber slip past one another and the rubber stays stretched. (b) when vulcanized rubber is stretched, the sulfur cross-links hold the strands together, allowing the rubber to return to its original shape

Polymer strands

Polymer strands

Nitrocellulose and celluloid

Fig 18.7 nitrocellulose, also known as cellulose nitrate, is highly combustible because of its many nitrate groups, which facilitate oxidation

Nitrate group

Nitrocellulose (cellulose nitrate)

Bakelite and phenolic resin (酚醛树脂 )

Polymers win in World War IISynthetic rubber, radar, tank and tentPolymer and environment

Fig 18.9 the molecular network of bakelite shown in two dimensions. The actual structure projects in all three dimensions. The first handset telephones were made of bakelite

OH

CH2

CH2

CH2

OH

OH

CH2

CH2

OH

OH

CH2

CH2 OH

CH2

OH

CH2

OHOH

CH H

O

OH

Formaldehyde

phenol

polymerization

Phenol-formaldehyde resin (Bakelite)

18.3 Metals come from the Earth’s limited supply of oresMetallic bond is responsible for the high conductivity and high gross.

Fig18.14 metal ions are held together by freely flowing electrons. These loose electrons form a kind of “electronic fluid” that flows through the lattice of positively charged ions

The form in which a metal is most likely to be found in nature is a function of its position in periodic table.

Fig 18.19 which compound of a metal is most prevalent in nature is related to the metals position in the periodic table

Metal-containing compounds can be converted to metals

Sheets of impure copper

Sheets of pure

copper

Solution containing CuSO4

Transforming the metal-containing compound to a metal is less energy intensive

Transforming the metal-containing compound to a metal is more energy intensive

Fig 18.21 high-purity copper is recovered by electrolysis. Pure copper metal deposits on the negative electrode as copper ions in solution gain electrons. The source of these copper ions is a positively charged electrode made of impure copper

Some metals are most commonly obtained from metal oxides

Fig 18.22 a mixture of iron

oxide ore, coke, and limestone is dropped into a blast furnace, where the iron

ions in the oxide are reduced to metal atoms

Steel Manufacturing via the Oxygen Process (oxidation process)

Metal resources are not unlimited

Fig 18.24 steel is stronger than iron because of the small amounts of carbon it contains

External pressure

External pressure

Pure iron is fairly soft and malleable because of voids between atoms

When the voids are filled with carbon atoms, the carbon helps hold the iron atoms in their lattice. This is strengthened metal is called steel

Fe

void

C

18.4 Glass is made primarily of silicates18.5 Ceramics are hardened with heat

• brittle, but withstand extremely high temperature

• Ceramic engine and superconductors (超导体 )

Fig 18.32 Engine parts made of Ceramic Silicon Nitride ,which is a High-strength material

18.6 Composites (复合材料 ) combine fibers and a thermoset medium

Fig 18.34 a few examples of composite materials

wood

Rocket cone

Fiberglass

Graphite fiber composite

Fig 18.35 the all-composite voyager airplane

More Important!

• The properties of materials are decided by their chemical structure.

(Structure – Property Relationships)

• Features of each type of material.

(Advantages and shortcomings)

• Selection of materials!

Type Metals Ceramics Polymers

Chemical structure Metal bond Covalent bond Covalent bondChange of atom position easy difficulty easyHardness medium high lowToughness tough brittle toughThermal stability medium high lowChemical stability low high mediumMoldability high low highProcessing cost medium high lowAbility to form film medium hard easyConductivity high low lowCost medium high lowRecycleability high low medium

Property requirement and Selection of materials

Valve: hard, friction resistance, metal

Valve in contact with chemicals?

Plane: metal or alloy

Supersonic planes?

Tennis racket: wood is not strong enough and too heavy, so?

Composites

• To combine the advantages of different materials

• Expansive!

• Difficulty to recycle!

• So any new type of composites?