Chapter 18 Chemistry and Materials

1. Chapter 18 Chemistry and Materials Diamond Paper, plastic, metals, glass, ceramics

2. 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.

3. The use of wood to produce paper was started in USA. • Additives such as rosin (松香) and alum (明矾) were added 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 230 kilograms or six trees.

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

5. Charles Goodyear discovered the rubber vulcanization in 1837. Polymer strands 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 Stretched with little tendency to snap back to original form (a) Original form Polymer strands (b) Original form with disulfide cross-links Stretched with great tendency to snap back because of cross-links

6. Nitrocellulose and celluloid Nitrate group Fig 18.7 nitrocellulose, also known as cellulose nitrate, is highly combustible because of its many nitrate groups, which facilitate oxidation Nitrocellulose (cellulose nitrate)

7. Formaldehyde polymerization phenol Phenol-formaldehyde resin (Bakelite) Bakelite and phenolic resin (酚醛树脂) 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 Polymers win in World War IISynthetic rubber, radar, tank and tentPolymer and environment

8. 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

9. 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

10. Metal-containing compounds can be converted to metals Transforming the metal-containing compound to a metal is less energy intensive Transforming the metal-containing compound to a metal is more energy intensive Sheets of impure copper Sheets of pure copper Solution containing CuSO4 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

11. 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

12. Steel Manufacturing via the Oxygen Process (oxidation process)

13. External pressure Pure iron is fairly soft and malleable because of voids between atoms Fe void Fig 18.24 steel is stronger than iron because of the small amounts of carbon it contains External pressure 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 C Metal resources are not unlimited

14. 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

15. 18.6 Composites (复合材料) combine fibers and a thermoset medium wood Rocket cone Fiberglass Graphite fiber composite Fig 18.34 a few examples of composite materials

16. Fig 18.35 the all-composite voyager airplane

17. 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!

18. Type Metals Ceramics Polymers Chemical structure Metal bond Covalent bond Covalent bond Change of atom position easy difficulty easy Hardness medium high low Toughness tough brittle tough Thermal stability medium high low Chemical stability low high medium Moldability high low high Processing cost medium high low Ability to form film medium hard easy Conductivity high low low Cost medium high low Recycleability high low medium

19. 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?

20. Composites • To combine the advantages of different materials • Expansive! • Difficulty to recycle! • So any new type of composites?