So, what is stuff made of ?

Section 4.6

• Organics• Metals and Alloys• Polymers• Ceramics• Composites

Organics

Organics are or were living organismsComposed of mostly Carbon and HydrogenStructure depends on the way cells

developed not by human manipulationRenewable, sustainable Infinite varietyGenetically alterable

Metals and AlloysMetals are pure elements which comprise

about three-fourths of the periodic tableFew are used in their pure form because of:

Hardness; too hard or too softCost; scarcity of elementEngineers need certain characteristics that can

only be accomplished by a blending of basic elements

Metallic materials include alloys, which are combinations of metals and other elements

MetalsPossess material properties, including:

high strength and toughnesshigh electrical conductancehigh thermal conductanceluster

Examplesaluminum - copper - gold - zinc - iron - lead -

nickelsilver - thorium - chromium - tin - beryllium

AlloysConsist of materials composed of two or

more elements, at least one being a metal

This combination of elements gives the material a combination of properties from each element

ExamplesSteel- iron, carbon and impurity elements

such as boron copper or silicon Brass - copper, zincStainless Steel - nickel,ironMonel - nickel,copper

PolymersPolymers

Chain-like molecule made of many (poly) smaller molecular units (mono”mers”)

Chaining (polymerization) is responsible for the formation of natural fibers, wood, rubber, skin, bone and the tissues of animals, humans and insects

Polymers- use mostly H, C, N, O, F, SI, S and Cl.

PlasticsPlastics

Human-made polymersPlastics are workable or moldable

Thermosetting plastics are formable once (e.g. epoxy, phonelic (Bakelite), polyurethane)

Thermoplastics can be heated repeatedly and formed into new shapes (e.g. polyethylene, nylon,

Plexiglas)

Ceramics

Crystalline compounds combining metallic and non metallic elements

Mostly use silicon, carbon and oxygen.The absence of free electrons make ceramics

poor electrical conductors. Because of the strength of the bonding,

ceramics have high melting temperatures

CompositesLaminar or Layer Composites - alternate

layers of materials bonded together. (e.g. plywood, safety glass, Formica, bimetallic strips)

Particulate Composites - discrete particles of one material surrounded by a matrix of another material. (e.g. concrete, asphalt, powdered metals and ceramics)

Fiber-Reinforced Composites - composed of continuous or discontinuous fibers embedded in a matrix of another material. (e.g. Kevlar, rayon, steel reinforced tires, fiberglass, graphite-epoxy)

Answers to 4.6 Case Study

a) Perhaps cotton clothing and wood furniture.b) Materials scientists use most of the

elements in the periodic table.c) Perhaps products such as toys, clothing and

automobiles.d) Metals used in 5000 B.C. would have

included gold, silver and copper.e) Metals such as iron, aluminum nickel,

titanium, and tungsten were in use.

f) Metals can be mixed in different combinations to yield alloys with specific properties such as hardness, flexibility, or resistance to corrosion.

g) Natural elastomers could include vines as a substitute for rope.

h) Indestructible polymers can be a waste-disposal problem.

i) Plastics are recycled.j) Carbon fibre is used in sporting equipment

such as tennis racquets.

k) Paper contains plant fibres and wood pulp.

l) Metal canoes are durable and inexpensive but heavy and noisy. Kevlar canoes are light but fragile and expensive. Wood canoes are attractive but heavy. Plastic (ABS) canoes are very tough but heavy.

m) ABS canoes are ideal for rapids, Kevlar for tripping involving portages, and wood canoes fro lade tripping. Fibreglass canoes are a good compromise.

2. a) Polymers could include nylon, polyester, rubber, wool, and leather.

b) Ceramics could include pottery, stoneware, enamels, and carbon fibre.

c) Metals could include iron, aluminum, copper, gold and nickel.

d) Composites could include fiberglass, paper, and reinforced concrete.

Question 2 on page 119