chapter 18 chemistry and materials diamond paper, plastic, metals, glass, ceramics
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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?
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