1. Categories of Materials
Principles of EngineeringTM
Lesson 6.1 – Categories of Materials
So, what is stuff made of ?
Section 4.6
Project Lead The Way, Inc.
Copyright 2007

2. Categories of Materials
Organics
Metals and Alloys
Polymers
Ceramics
Composites

3. Organics Organics are or were living organisms
Composed of mostly Carbon and Hydrogen
Structure depends on the way cells developed not by human manipulation
Renewable, sustainable
Infinite variety
Genetically alterable

4. Metals and Alloys
Metals are pure elements which comprise about three-fourths of the periodic table
Few are used in their pure form because of:
Hardness; too hard or too soft
Cost; scarcity of element
Engineers 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

5. Metals Possess material properties, including: Examples
high strength and toughness
high electrical conductance
high thermal conductance
luster
Examples
aluminum - copper - gold - zinc - iron - lead - nickel
silver - thorium - chromium - tin - beryllium

6. Alloys
Consist 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
Examples
Steel- iron, carbon and impurity elements such as boron copper or silicon
Brass - copper, zinc
Stainless Steel - nickel,iron
Monel - nickel,copper

7. Polymers
Polymers
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.

8. Plastics Plastics Human-made polymers
Plastics 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)

9. 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

10. Composites
Laminar 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)

11. 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.

12. 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.

13. 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.

14. Question 2 on page 119
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.